JP3981100B2 - Reflective optical components - Google Patents

Description

  The present invention relates to a reflective optical component such as a reflective optical circulator or a reflective optical isolator used in an optical communication system.

  Optical components used in optical communication systems include optical circulators and optical isolators. Many configurations of optical circulators and optical isolators are known. Reflective optical circulators and optical isolators in which the optical fiber is arranged only on one side and the reflector is arranged on the opposite side can reduce the optical fiber housing space when arranged in the device compared to the transmission type, This is effective for downsizing the entire device.

  FIG. 31 shows a configuration of a conventional reflective optical circulator described in Patent Document 1. As shown in FIGS. 31A and 31B, this reflection type optical circulator includes three sets of optical fiber 100 and lens 102, birefringent plate 104, two half-wave plates 106 and 107, and Faraday rotation. It has a child 108, a birefringent plate 110, a Faraday rotator 112, and a reflecting mirror 114. In the configuration shown in FIGS. 31A and 31B, there are three types of optical elements (two birefringent plates 104 and 110 and two half-wave plates except for the reflecting mirror 114 and the lens 102). 106, 107 and two Faraday rotators 108, 112) are required, and the element configuration of the reflective optical circulator becomes complicated. For this reason, there arises a problem that it is difficult to reduce the size and price of the reflective optical circulator. 31A and 31B, the light that has passed through the birefringent plate 104 as ordinary light passes through the birefringent plate 104 as ordinary light even when reflected by the reflection mirror 114 and returned. On the other hand, the light passing through the birefringent plate 104 as extraordinary light also passes through the birefringent plate 104 as extraordinary light even when reflected by the reflection mirror 114 and returned. Since the optical path length differs between the case of passing as ordinary light and the case of passing as extraordinary light, in this configuration, the polarization mode dispersion (PMD) value does not become 0 (zero) and becomes large.

  FIG. 32 shows a configuration of another conventional reflective optical circulator described in Patent Document 1. In FIG. As shown in FIGS. 32A and 32B, this reflective optical circulator includes three sets of optical fiber 100 and lens 102, birefringent plate 104, Faraday rotator 108, and two birefringent plates 110a and 110b. , A Faraday rotator 112, and a reflection mirror 114. In the configuration shown in FIGS. 32A and 32B, the element configuration is simplified as compared with the configuration shown in FIG. 31, but the PMD value does not become zero for the same reason as described above.

  FIG. 33 shows the configuration of a conventional reflective optical circulator described in Patent Document 2. As shown in FIG. 33, this reflective optical circulator includes three optical fibers 100, a birefringent plate 104, four half-wave plates 106 (only two are shown in FIG. 33), a Faraday rotator. 108, a birefringent plate 110, a lens 102, and a reflecting mirror 114. In the configuration shown in FIG. 33, three types of optical elements (two birefringent plates 104 and 110, four half-wave plates 106, and one Faraday plate) except for the reflecting mirror 114 and the lens 102 are used. The rotor 108) is required, and the element configuration of the reflective optical circulator is complicated. For this reason, there arises a problem that it is difficult to reduce the size and price of the reflective optical circulator. Further, for the same reason as described above, there arises a problem that the PMD value does not become zero.

  FIG. 34 shows the configuration of a conventional reflective optical circulator described in Patent Document 3. As shown in FIGS. 34A and 34B, this reflection type optical circulator includes a birefringent plate 104, a birefringent plate 105, two Faraday rotators 108a and 108b, a birefringent plate 110, and two Faraday plates. Rotors 112a and 112b and a reflecting mirror 114 are provided. In this configuration, the light that has passed through the birefringent plate 104 as ordinary light passes through the birefringent plate 105 as extraordinary light, and further passes through the birefringent plate 105 as extraordinary light when reflected back by the reflecting mirror 114, thereby causing 104 passes through as ordinary light. On the other hand, light that has passed through the birefringent plate 104 as extraordinary light passes through the birefringent plate 105 as ordinary light, and further passes through the birefringent plate 105 as ordinary light when reflected by the reflection mirror 114 and returns to the birefringent plate 104. It passes as light. For this reason, the PMD value becomes zero in the configuration shown in FIGS. Such a combination of two birefringent plates 104 and 105 is known as a Savart plate. The Savart plate is used as an element that gives a lateral shift with no phase difference between two polarization components orthogonal to each other. However, in the configuration shown in FIGS. 34 (a) and 34 (b) using a Savart plate, seven optical elements (three birefringent plates 104 and 105, except for the reflection mirror 114 and the lens (not shown)) are used. 110 and four Faraday rotators 108a, 108b, 112a, 112b) are required, and the element configuration of the reflective optical circulator becomes complicated. For this reason, there arises a problem that it is difficult to reduce the size and price of the reflective optical circulator.

As described above, the conventional reflection type optical circulator has at least one of the problems that the element configuration becomes complicated and it becomes difficult to reduce the size and cost, or the PMD value does not become zero. is doing.
US Pat. No. 5,471,340 US Pat. No. 5,930,422 US Pat. No. 6,111,695

  An object of the present invention is to provide a reflective optical component that can simplify the element configuration and obtain good optical characteristics.

  The above object is achieved by separating the light incident from the first port into the first light of the ordinary light component and the second light of the extraordinary light component, and emitting the first polarization separation and multiplexing unit, A first Faraday rotator that rotates the polarization direction of light by 45 ° and emits it as third light, and a polarization direction of the third light by rotating the polarization direction of the second light in the opposite direction by 45 ° A second Faraday rotator that emits as fourth light having a polarization direction substantially parallel to the light, a polarizer that transmits the third and fourth light, and a reflection that reflects the third and fourth light. And the third light reflected by the reflecting part and passing through the polarizer and the third Faraday rotating part as an extraordinary light, and reflected by the reflecting part and reflected by the polarizer and the fourth Faraday The fourth light that has passed through the rotating part is transmitted as ordinary light, and the third and fourth lights are transmitted. This is achieved by a reflection type optical component having a second polarization separation / multiplexing unit that multiplexes and emits the light from the second port.

  In the reflection-type optical component of the present invention, the first to fourth Faraday rotators are formed of the same magneto-optical element.

  In the reflection-type optical component of the present invention, the first polarization separation / combination unit is configured by a first birefringence plate, and the second polarization separation / combination unit is a second birefringence plate. The first and third Faraday rotators are configured by the same region of the same magneto-optical element, and the second and fourth Faraday rotators are configured by the same region of the same magneto-optical element. It is characterized by being.

  The reflection type optical component according to the invention is characterized in that the first birefringent plate and the second birefringent plate are elements having the same specifications.

  In the reflective optical component according to the present invention, the polarizer is a third birefringent plate, and the reflecting portion is a two-surface reflector.

  The reflective optical component according to the invention is characterized in that the polarizer is a wedge birefringent crystal.

  In the reflection-type optical component of the present invention, the first and second polarization separation / combining units are configured by the same birefringence plate, and the first and fourth Faraday rotation units are configured by the same magnetic field. The second and third Faraday rotators are configured by the same region of the same magneto-optical element.

  The reflection-type optical component according to the invention is characterized in that it includes at least one half-wave plate whose rotation direction is rotated by 90 °, and the reflection part is composed of a lens and a reflection film. .

  The reflection-type optical component of the present invention, wherein the first Faraday rotator and the second Faraday rotator have Faraday rotators having the same material composition and having opposite magnetization directions. It is characterized by having.

  The reflection type optical component of the present invention, wherein the first Faraday rotator has a magnetic domain A in which magnetization is uniformly made in one direction in a region of the Faraday rotator, and the second Faraday rotator Has a magnetic domain B in which magnetization is made uniform in the opposite direction to the magnetic domain A in the other region of the Faraday rotator.

  In the reflection-type optical component of the present invention, the first and second polarization separation / combining sections are formed of the same birefringent plate.

  According to the present invention, it is possible to realize a reflective optical component that can simplify the element configuration and obtain good optical characteristics.

[First Embodiment]
A reflective optical component according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 schematically shows the configuration of a reflective optical circulator according to this embodiment. In FIG. 1, the Z-axis is taken in the light traveling direction, and the direction in which the light from the outside is directed to the two-surface reflector (reflecting portion) 32 provided in the reflective optical circulator is the + Z direction. Further, the X axis and the Y axis are taken in two directions orthogonal to each other in a plane orthogonal to the Z axis. FIG. 1A shows a configuration of the reflective optical circulator viewed in the −Y direction, and FIG. 1B shows a configuration of the reflective optical circulator viewed in the −X direction.

  As shown in FIG. 1, the reflective optical circulator 1 is connected to four optical fibers 41, 42, 43, 44. At the end of each optical fiber 41, 42, 43, 44 on the −Z side, four light incident / exit ports P1, P2, P3, P4 through which light enters or emits light from the outside (in the drawing) (Indicated by the numbers (1) to (4)). In the + Z direction of each of the optical fibers 41, 42, 43, and 44, lenses 51, 52, 53, and 54 that convert the divergent light emitted from the optical fibers 41, 42, 43, and 44 into parallel light are respectively disposed. . In order to reduce the size of the reflection-type optical circulator 1 and the apparatus that accommodates it, it is important to reduce the size of the lenses 51, 52, 53, and 54.

  FIG. 2A shows an example of a lens configuration that can be miniaturized. As shown in FIG. 2A, a gradient index lens (GI (Gradient Index) lens) 50 having a cylindrical shape coaxial with the optical fiber 40 is fused to the tip of the single-mode optical fiber 40. Yes. The GI lens 50 has a diameter (for example, 125 μm) substantially equal to the diameter of the single mode optical fiber 40. The optical fiber 40 and the GI lens 50 are integrated with each other and function as an optical fiber with a lens. The GI lens 50 has an end face 50a perpendicular to its cylindrical axis. The light that has entered the GI lens 50 from the optical fiber 40 is converted into parallel light, and is emitted from the end face 50a in a direction perpendicular to the end face 50a (a direction parallel to the cylindrical axes of the optical fiber 40 and the GI lens 50). The GI lens 50 can be used as the lenses 51, 52, 53, and 54 of the reflective optical circulator 1 of the present embodiment shown in FIG.

  FIG. 2B shows a modification of the lens configuration. As shown in FIG. 2B, an optical fiber with a lens in which a small spherical lens 55 is fixed to the optical fiber 40 instead of the GI lens 50 is also suitable for this embodiment. In addition to these configurations, it is also possible to use a core expansion (TEC; Thermal Expand Core) fiber that has a core expansion region in the vicinity of the tip that has a function similar to that of the lens.

  Returning to FIG. 1, the birefringent plate (polarization separating / combining unit) 11 is disposed in the + Z direction of the lenses 51 and 53, and the birefringent plate 12 is disposed in the + Z direction of the lenses 52 and 54. The two birefringent plates 11 and 12 are disposed adjacent to each other in parallel to the XY plane and have a light incident / exit surface perpendicular to the Z axis. Here, in optics, the “light incident surface” may be defined as a surface including the normal of the incident light ray and the boundary surface, but the “light incident / exit surface” in this specification is not this definition, but a birefringent plate. 11 and 12 (or other optical elements) means surfaces on which light is incident / exited.

FIG. 3 is a diagram for explaining the optical axis of the birefringent plate 11. FIG. 3A shows a configuration of the birefringent plate 11 viewed in the −Z direction, and FIG. 3B shows a configuration of the birefringent plate 11 viewed in the −X direction. As shown in FIGS. 3A and 3B, the optical axis OA of the birefringent plate 11 is arranged parallel to the YZ plane. The angle formed by the optical axis OA and the XZ plane is about 45 ° clockwise with respect to the X axis when viewed in the −X direction. The light incident perpendicularly to the light incident / exit surface (parallel to the XY plane in this example) 11a is separated into ordinary light and abnormal light and emitted onto different optical paths. At this time, the extraordinary light is axially shifted downward (−Y direction), for example, as shown in FIG. Hereinafter, in the view of the birefringent plate 11 in the −Z direction as shown in FIG. 3A, the downward one-side arrow C indicates that the abnormal light of the light incident in the + Z direction is shifted downward. To do. On the other hand, since the birefringent plate 12 is arranged such that the angle formed by the optical axis OA and the XZ plane is 45 ° counterclockwise with respect to the X axis when viewed in the −X direction, the extraordinary light is compared with the ordinary light. The axis is shifted upward in FIG. 3B (not shown). Therefore, when the birefringent plate 12 is viewed in the −Z direction, an upward single arrow C indicates that the extraordinary light of the light incident in the + Z direction is displaced upward. As the crystals constituting the birefringent plates 11 and 12, rutile (TiO ₂ ), yttrium vanadate (YVO ₄ ), or the like is used. The birefringent plates 11 and 12 are, for example, elements of the same specification cut out from the same crystal into the same shape, and are adjacent so that the optical axis OA is parallel to the YZ plane and the direction of the axis deviation of the extraordinary light is reversed. Are arranged. Depending on the optical characteristics of the birefringent crystal, a birefringent plate 11 that is axially displaced upward in the drawing in the arrangement of the optical axis OA shown in FIG. 3B may be used in combination.

  Returning to FIG. 1, a Faraday rotator 20, which is a magneto-optical element having nonreciprocity, is disposed in the + Z direction of the birefringent plates 11 and 12. The Faraday rotator 20 is formed by using, for example, a magnetic garnet single crystal film that is grown by a liquid phase epitaxy (LPE) method and has a perpendicular magnetization property in which an easy axis of magnetization appears in a direction perpendicular to the film growth surface. A permanent magnet 61 is disposed at the + Y direction end of the Faraday rotator 20, and a permanent magnet 62 is disposed at the −Y direction end. The permanent magnets 61 and 62 have magnetic poles opposite to each other. For example, as indicated by an arrow in the figure, the direction of the magnetic pole of the permanent magnet 61 is the + Z direction, and the direction of the magnetic pole of the permanent magnet 62 is the -Z direction. The magnetic field component applied to the region on the + Y side from approximately the center of the Faraday rotator 20 is dominated by the magnetic field component in the −Z direction by the permanent magnet 61. On the other hand, the magnetic field component applied to the region on the −Y side from approximately the center of the Faraday rotator 20 is dominated by the magnetic field component in the + Z direction by the permanent magnet 62. By setting the strength of the magnetic field applied to both regions to be equal to or higher than the saturation magnetic field of the Faraday rotator, a magnetic domain A having a uniform magnetization in one direction is formed in the region where the magnetic field in the -Z direction is applied. In the region to which a magnetic field in the + Z direction is applied, a magnetic domain B having a uniform magnetization in the direction opposite to the magnetic domain A is formed. A domain wall I is formed on the boundary surface between the magnetic domain A and the magnetic domain B. In this example, the Faraday rotation angle of the magnetic domain A is, for example, 45 ° clockwise with respect to the Z axis when viewed in the −Z direction, and the Faraday rotation angle of the magnetic domain B is similarly 45 ° counterclockwise. Since the Faraday rotator 20 has nonreciprocity, the condition of the rotation angle is maintained even if light enters from either of the two light incident / exit surfaces of the Faraday rotator 20. Instead of causing one Faraday rotator 20 to function as two Faraday rotators, a Faraday rotator that functions as one Faraday rotator and another Faraday rotator that functions as the other Faraday rotator You may arrange | position adjacent to a direction. In this case, both Faraday rotators have, for example, the same material composition. Moreover, it is of course possible to use a semi-hard magnet that has a coercive force smaller than that of the permanent magnet and can reverse the magnetization instead of the permanent magnets 61 and 62.

  A birefringent plate 13 is disposed in the + Z direction of the Faraday rotator 20. The birefringent plate 13 is produced using, for example, the same crystal as the birefringent plates 11 and 12. The optical axis of the birefringent plate 13 is parallel to a plane obtained by rotating the YZ plane 45 degrees counterclockwise about the Y axis when viewed in the −Y direction, using the coordinate system shown in FIGS. 1 and 3. , At least not included in a plane parallel to the optical axis of the birefringent plate 11 and the birefringent plate 12. Further, the extraordinary light of the light incident on the birefringent plate 13 in the + Z direction is misaligned in both the −X direction and the −Y direction. On the + Z side of the birefringent plate 13, a two-surface reflector 32 such as a right-angle prism is disposed. The two-surface reflector 32 has a function of changing the optical path by two-surface reflection. The two-surface reflector 32 may have a structure in which two reflecting mirrors (reflecting plates) are combined in addition to the right-angle prism as shown in FIG.

In the present embodiment, the reflective optical circulator 1 can be configured by using four optical elements (three birefringent plates 11, 12, 13 and one Faraday rotator 20). Even when two Faraday rotators are used without using the magnetic domain structure of the Faraday rotator 20, the reflective optical circulator 1 can be configured using five optical elements. Further, as the birefringent plates 11 and 12, for example, elements of the same specification cut out from the same crystal can be used. Therefore, according to the present embodiment, the element configuration of the reflective optical circulator 1 is simplified, and the miniaturization and the cost reduction are facilitated.
In FIG. 1, light is vertically incident on each element. However, in order to prevent the reflected light from each boundary surface from returning to its original state, it is desirable to dispose each element obliquely with respect to the incident light.

  Next, the operation of the reflective optical circulator according to this embodiment will be described with reference to FIGS. 4 to 6 are diagrams in which the polarization state of the light passing through each optical element constituting the reflective optical circulator 1 is viewed in the −Z direction. 4A to 6A show the polarization state of light on the light incident / exit surface Z1 on the −Z side of the birefringent plates 11 and 12, as shown in FIG. 4B to 6B show the polarization state of the light on the light incident / exit surface Z2 on the + Z side of the birefringent plates 11 and 12. FIG. FIGS. 4C to 6C show the polarization state of the light on the light incident / exit surface Z3 on the −Z side of the birefringent plate 13. FIG. 4 to FIG. 6D show the polarization state of the light on the light incident / exit surface Z4 on the + Z side of the birefringent plate 13.

  4 to 6, for easy understanding, the birefringent plates 11 and 12, the Faraday rotator 20, and the birefringent plate 13 are viewed in the −Z direction, and the two-surface reflector 32 is −Y. The state seen in the direction is schematically shown together.

  FIG. 4 shows light that enters from the light incident / exit port P1 and exits to the outside from the light incident / exit port P2, as indicated by the solid line in FIG. As shown on the left side of FIG. 4A, the light L1 incident from the light incident / exit port P1 enters the birefringent plate (first birefringent plate) 11 and is shown on the left side of FIG. 4B. As described above, the light is separated into the ordinary light L2a and the extraordinary light L2b shifted in the -Y direction, and is emitted from the birefringent plate 11. Next, the ordinary light component light L2a enters the magnetic domain A (first Faraday rotator) of the Faraday rotator 20, and the extraordinary light component light L2b enters the magnetic domain B (second Faraday rotator) of the Faraday rotator 20. Incident. For example, the Faraday rotation angle of the magnetic domain A of the Faraday rotator 20 is + 45 ° with respect to the Z axis when viewed in the −Z direction, and the Faraday rotation angle of the magnetic domain B is −45 ° with respect to the Z axis when viewed in the −Z direction. As shown on the left side of FIG. 4C, the light L2a is emitted from the Faraday rotator 20 as light L3a whose polarization direction is rotated 45 ° clockwise about the Z axis when viewed in the −Z direction, and the light L2b is polarized direction. Is emitted from the Faraday rotator 20 as light L3b rotated by 45 ° counterclockwise. Thereby, the polarization azimuth | direction of light L3a and L3b is parallel to the plane formed by the straight line parallel to the advancing direction of light L3a and L3b, and the straight line parallel to the optical axis of the birefringent plate (polarizer) 13 crossing. become. Next, as shown on the left side of FIG. 4 (d), the lights L3a and L3b are incident on one surface of the birefringent plate 13 and are transmitted as extraordinary light. Are emitted as light L4a and L4b. The lights L4a and L4b are reflected by the two-surface reflector 32 and enter the other surface of the birefringent plate 13 as lights L5a and L5b whose optical paths are changed as shown on the right side of FIG.

  As shown on the right side of FIG. 4C, the light beams L5a and L5b are emitted as light beams L6a and L6b from one surface of the birefringent plate 13 with their axes shifted from each other. The light L6a is incident on the magnetic domain A of the Faraday rotator 20 (the same region as the region where the light L2a is incident), and the light L6b is incident on the magnetic domain B of the Faraday rotator 20 (the same region as the region where the light L2b is incident). To do. As shown on the right side of FIG. 4B, the light L6a is emitted from the Faraday rotator 20 as light L7a whose polarization direction is rotated 45 ° clockwise about the Z axis when viewed in the −Z direction, and the light L6b is polarized direction. Is emitted from the Faraday rotator 20 as light L7b rotated 45 ° counterclockwise. The light L7a enters the birefringent plate (second birefringent plate) 12 and becomes extraordinary light, and the light L7b enters the birefringent plate 12 and becomes ordinary light. As shown on the right side of FIG. 4A, the light L7a is off-axis and combined with the light L7b, and is emitted from the birefringent plate 12 as light L8. The light L8 enters the light incident / exit port P2 and exits to the outside.

  FIG. 5 shows light that enters from the light incident / exit port P2 and exits to the outside from the light incident / exit port P3, like a light beam indicated by a broken line in FIG. As shown on the right side of FIG. 5A, the light L11 incident from the light incident / exit port P2 enters the birefringent plate (first birefringent plate) 12 and is shown on the right side of FIG. 5B. As described above, the light is separated into the ordinary light L12a and the extraordinary light L12b whose axis is shifted in the + Y direction, and is emitted from the birefringent plate 12. Next, the ordinary light component light L12a enters the magnetic domain B (first Faraday rotator) of the Faraday rotator 20, and the extraordinary light component light L12b enters the magnetic domain A (second Faraday rotator) of the Faraday rotator 20. Incident. As shown on the right side of FIG. 5C, the light L12a is emitted from the Faraday rotator 20 as light L13a rotated 45 ° counterclockwise with respect to the Z axis when viewed in the −Z direction, and the light L12b is polarized. The light is emitted from the Faraday rotator 20 as light L13b whose azimuth is rotated 45 ° clockwise. Thereby, the polarization directions of the lights L13a and L13b are perpendicular to a plane formed by intersecting a straight line parallel to the traveling direction of the lights L13a and L13b and a straight line parallel to the optical axis of the birefringent plate (polarizer) 13. become. Therefore, the lights L13a and L13b are incident on one surface of the birefringent plate 13 and become ordinary light, and the light L14a is transmitted from the other surface of the birefringent plate 13 without being misaligned as shown on the right side of FIG. , L14b. The lights L14a and L14b are reflected by the two-surface reflector 32 and enter the other surface of the birefringent plate 13 as lights L15a and L15b whose optical paths are changed as shown on the left side of FIG.

  Lights L15a and L15b are incident on the other surface of the birefringent plate 13 and become ordinary light. As shown on the left side of FIG. 5C, light L16a, The light is emitted as L16b. The light L16a is incident on the magnetic domain B of the Faraday rotator 20, and the light L16b is incident on the magnetic domain A. As shown on the left side of FIG. 5B, the light L16a is emitted from the Faraday rotator 20 as light L17a whose polarization direction is rotated 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and the light L16b is polarized. The light is emitted from the Faraday rotator 20 as light L17b whose azimuth is rotated 45 ° clockwise. The light L17a enters the birefringent plate (second birefringent plate) 11 and becomes extraordinary light, and the light L17b enters the birefringent plate 11 and becomes ordinary light. As shown on the left side of FIG. 5A, the light L17a is off-axis and combined with the light L17b, and is emitted from the birefringent plate 11 as light L18. The light L18 is incident on the light incident / exit port P3 disposed next to the light incident / exit port P1 and is emitted to the outside.

  FIG. 6 shows light that enters from the light incident / exit port P3 and exits to the outside from the light incident / exit port P4, like a light beam indicated by a one-dot chain line in FIG. As shown on the left side of FIG. 6A, the light L21 incident from the light incident / exit port P3 enters the birefringent plate (first birefringent plate) 11 and is shown on the left side of FIG. 6B. As described above, the light is separated into the ordinary light L22a and the extraordinary light L22b whose axis is shifted in the -Y direction, and is emitted from the birefringent plate 11. Next, the ordinary light component light L22a enters the magnetic domain A (first Faraday rotator) of the Faraday rotator 20, and the extraordinary light component light L22b enters the magnetic domain B (second Faraday rotator) of the Faraday rotator 20. Incident. As shown on the left side of FIG. 6C, the light L22a is emitted from the Faraday rotator 20 as light L23a whose polarization direction is rotated 45 ° clockwise about the Z axis when viewed in the −Z direction, and the light L22b is polarized direction. Is emitted from the Faraday rotator 20 as light L23b rotated by 45 ° counterclockwise. Thereby, the polarization azimuth | direction of light L23a and L23b is parallel to the plane formed by the straight line parallel to the advancing direction of light L23a and L23b, and the straight line parallel to the optical axis of the birefringent plate (polarizer) 13 crossing. become. Next, as shown on the left side of FIG. 6 (d), the lights L23a and L23b are incident on one surface of the birefringent plate 13 and become extraordinary light. Are emitted as light L24a and L24b. The lights L24a and L24b are reflected by the two-surface reflector 32 and enter the other surface of the birefringent plate 13 as lights L25a and L25b whose optical paths are changed as shown on the right side of FIG. 6 (d).

  As shown on the right side of FIG. 6C, the light beams L25a and L25b are emitted as light beams L26a and L26b from one surface of the birefringent plate 13 with their axes shifted from each other. The light L26a enters the magnetic domain A of the Faraday rotator 20, and the light L26b enters the magnetic domain B. As shown on the right side of FIG. 6B, the light L26a is emitted from the Faraday rotator 20 as light L27a whose polarization direction is rotated 45 ° clockwise about the Z axis when viewed in the −Z direction, and the light L26b is polarized direction. Is emitted from the Faraday rotator 20 as light L27b rotated 45 ° counterclockwise. The light L27a enters the birefringent plate (second birefringent plate) 12 and becomes extraordinary light, and the light L27b enters the birefringent plate 12 and becomes ordinary light. As shown on the right side of FIG. 6A, the light L27a is off-axis and combined with the light L27b, and is emitted from the birefringent plate 12 as light L28. The light L28 enters the light incident / exit port P4 disposed next to the light incident / exit port P2, and exits to the outside.

  Thus, in the reflection type optical circulator 1 according to the present embodiment, the input light from the light incident / exit port P1 is output from the light incident / exit port P2, and the input light from the light incident / exit port P2 is the light incident / exit port P3. The input light from the light incident / exit port P3 is output from the light incident / exit port P4.

  In the present embodiment, light that has passed through one of the birefringent plates 11 and 12 having the same optical characteristics as ordinary light passes through the other as abnormal light when reflected by the two-surface reflector 32 and returned. Conversely, light that has passed through one of the birefringent plates 11 and 12 as extraordinary light passes through the other as ordinary light when reflected by the two-surface reflector 32 and returned. In addition, after passing through the Faraday rotator 20 and before being reflected by the two-surface reflector 32 and entering the Faraday rotator 20 again, the polarization directions of the two separated lights are the same. Therefore, according to the reflective optical circulator 1 according to the present embodiment, the PMD value can be made zero.

[Second Embodiment]
Next, a reflective optical component according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 7 schematically shows the configuration of the reflective optical circulator according to the present embodiment. In FIG. 7, the coordinate system is taken as in FIG. FIG. 7A shows a configuration of the reflective optical circulator viewed in the −Y direction, and FIG. 7B shows a configuration of the reflective optical circulator viewed in the −X direction. As shown in FIGS. 7A and 7B, the reflective optical circulator 1 ′ according to this embodiment is connected to optical fibers 41, 42, 43, and 44 arranged in a line. The ends of the optical fibers 41, 42, 43, and 44 on the −Z side are indicated by four light input / output ports P1, P2, P3, and P4 (in the drawing, numbers (1) to (4), respectively). )It has become. The optical fibers 41, 42, 43, 44 and the GI lenses 71, 72, 73, 74 fused to the + Z side ends of the optical fibers 41, 42, 43, 44 are integrated with a lens, respectively. It functions as an optical fiber. One birefringent plate 14 is disposed in the + Z direction of the GI lenses 71, 72, 73, 74. The optical axis of the birefringent plate 14 is parallel to a plane obtained by rotating the YZ plane 45 degrees clockwise about the Y axis when viewed in the -Y direction, using the coordinate system shown in FIG. The extraordinary light of the light incident on the birefringent plate 14 in the + Z direction is misaligned in both the + X direction and the −Y direction.

  A half-wave plate 22 that rotates the polarization direction of light by 90 ° is disposed at a position corresponding to the light incident / exit ports P2 and P4 in the + Z direction of the birefringent plate. A Faraday rotator 20 is disposed in the + Z direction of the half-wave plate 22. A permanent magnet 61 is disposed at the + Y direction end of the Faraday rotator 20, and a permanent magnet 62 is disposed at the −Y direction end. The permanent magnets 61 and 62 have magnetic poles opposite to each other. For example, as indicated by an arrow in the figure, the direction of the magnetic pole of the permanent magnet 61 is the + Z direction, and the direction of the magnetic pole of the permanent magnet 62 is the -Z direction. A magnetic domain A having a uniform magnetization in one direction is formed in a region where a magnetic field in the -Z direction of the Faraday rotator 20 is applied. The magnetic domain B made uniform in the opposite direction is formed. A domain wall I is formed on the boundary surface between the magnetic domain A and the magnetic domain B. In this example, the Faraday rotation angle of the magnetic domain A is, for example, 45 ° clockwise with respect to the Z axis when viewed in the −Z direction, and the Faraday rotation angle of the magnetic domain B is similarly 45 ° counterclockwise. A birefringent plate 15 is disposed in the + Z direction of the Faraday rotator 20. The optical axis of the birefringent plate 15 is parallel to the XZ plane when shown using the coordinate system shown in FIG. The extraordinary light that is incident on the birefringent plate 15 in the + Z direction is off-axis in the −X direction. In the + Z direction of the birefringent plate 15, a lens 34 and a reflecting mirror 36 are disposed as a reflecting portion. As the lens 34, a gradient index rod lens, a spherical lens, an aspherical lens, or the like is used. The reflecting mirror 36 is manufactured by forming a total reflection film on a glass plate, and is disposed in the + Z direction of the lens 34. The reflecting mirror 36 includes a focal point when parallel light is incident on the lens 34 and is disposed in a plane perpendicular to the traveling direction of the parallel light. As a result, when parallel light passing through a certain optical path is incident on the lens 34 and the reflecting mirror 36, the optical path of the reflected light is converted to a symmetrical position with respect to a straight line including the focal point and parallel to the traveling direction of the parallel light. The Instead of the reflecting mirror 36, a total reflection film may be directly formed on the lens 34.

In the present embodiment, the reflection type optical circulator 1 ′ using four optical elements (two birefringent plates 14 and 15, one half-wave plate 22 and one Faraday rotator 20). Can be configured. Even when two Faraday rotators are used without using the magnetic domain structure of the Faraday rotator 20, the reflective optical circulator 1 ′ can be configured using five optical elements. Therefore, according to the present embodiment, the element configuration of the reflective optical circulator 1 ′ is simplified, and miniaturization and cost reduction are facilitated.
Moreover, in this Embodiment, since four light incident / exit ports P1-P4 (optical fiber 41-44) can be arrange | positioned in a row, there exists an advantage that an assembly becomes easy.

  Next, the operation of the reflective optical circulator according to this embodiment will be described. 8 to 10 are views of the polarization state of the light passing through the optical elements constituting the reflective optical circulator 1 ′ as seen in the −Z direction. (A) of FIG. 8 thru | or FIG. 10 has shown the polarization state of the light in the light entrance / exit surface Z1 of the -Z side of the birefringent plate 14 shown in FIG. FIGS. 8B to 10B show the polarization state of light on the light incident / exit surface Z2 on the + Z side of the birefringent plate. FIGS. 8C to 10C show the polarization state of light on the light incident / exit surface Z3 on the −Z side of the birefringent plate 15. FIGS. 8D to 10D show the polarization state of light on the light incident / exit surface Z4 on the + Z side of the birefringent plate 15. FIG. 8 to 10, in order to facilitate understanding, the birefringent plate 14, the half-wave plate 22, the Faraday rotator 20, the birefringent plate 15, and the reflecting portion (the lens 34 and the reflecting mirror 36) are − The state seen in the Z direction is also schematically illustrated.

  FIG. 8 shows light that enters from the light incident / exit port P1 and exits to the outside from the light incident / exit port P2, as indicated by the solid line in FIG. 7A. As shown on the left side of FIG. 8 (a), the light L51 incident from the light incident / exit port P1 enters the birefringent plate 14, and as shown on the left side of FIG. Separated into extraordinary light L52b that is axially misaligned in both directions in the −Y direction, is emitted from the birefringent plate. Next, the ordinary light component light L52a is incident on the magnetic domain A (first Faraday rotator) of the Faraday rotator 20, and the abnormal light component light L52b is incident on the magnetic domain B (second Faraday rotator) of the Faraday rotator 20. Incident. Here, neither the light L52a nor L52b passes through the half-wave plate 22. For example, the Faraday rotation angle of the magnetic domain A of the Faraday rotator 20 is + 45 ° with respect to the Z axis when viewed in the −Z direction, and the Faraday rotation angle of the magnetic domain B is −45 ° with respect to the Z axis when viewed in the −Z direction. As shown on the left side of FIG. 8C, the light L52a is emitted from the Faraday rotator 20 as light L53a whose polarization direction is rotated 45 ° clockwise about the Z axis when viewed in the −Z direction, and the light L52b is polarized direction. Is emitted from the Faraday rotator 20 as light L53b rotated 45 ° counterclockwise. Thereby, the polarization azimuth | direction of light L53a, L53b becomes perpendicular | vertical to the plane formed by the straight line parallel to the advancing direction of light L53a, L53b, and the straight line parallel to the optical axis of the birefringent plate 15 crossing. Therefore, the lights L53a and L53b are incident on one surface of the birefringent plate 15 and become ordinary light, and the light L54a is transmitted from the other surface of the birefringent plate 15 without being misaligned as shown on the left side of FIG. , L54b. The lights L54a and L54b pass through the lens 34, are reflected by the reflecting mirror 36, and enter the other surface of the birefringent plate 15 as light L55a and L55b whose optical paths are changed as shown on the right side of FIG. .

  The lights L55a and L55b are incident on the other surface of the birefringent plate 15 and become ordinary light. As shown on the right side of FIG. 8C, the lights L56a and L55b are transmitted from one surface of the birefringent plate 15 without being misaligned. The light is emitted as L56b. The light L56a enters the magnetic domain B of the Faraday rotator 20 (the same region as the region where the light L52b is incident), and the light L56b enters the magnetic domain A of the Faraday rotator 20 (the same region as the region where the light L52a is incident). To do. The light L56a is emitted from the Faraday rotator 20 as light whose polarization direction is rotated by 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and is incident on the half-wave plate 22 as shown in FIG. As shown on the right side of (), the light is emitted as the light L57a whose polarization orientation is rotated by 90 ° about the Z-axis. The light L56b is emitted from the Faraday rotator 20 as light whose polarization azimuth is rotated 45 ° clockwise, is further incident on the half-wave plate 22, and is emitted as light L57b whose polarization azimuth is rotated 90 ° about the Z axis. To do. The light L57a enters the birefringent plate 14 and becomes extraordinary light, and the light L57b enters the birefringent plate 14 and becomes ordinary light. As shown on the right side of FIG. 8A, the light L57a is off-axis and combined with the light L57b, and is emitted from the birefringent plate 14 as light L58. The light L58 enters the light incident / exit port P2 and exits to the outside.

  FIG. 9 shows light that enters from the light incident / exit port P2 and exits to the outside from the light incident / exit port P3, like a light beam indicated by a broken line in FIG. As shown on the right side of FIG. 9A, the light L61 incident from the light incident / exit port P2 enters the birefringent plate 14, and as shown on the right side of FIG. Separated into extraordinary light L62b shifted in both directions in the −Y direction, and emitted from the birefringent plate 14. Next, the ordinary light component L 62 a is incident on the half-wave plate 22, is emitted from the half-wave plate 22 as light whose polarization orientation is rotated by 90 ° with respect to the Z axis, and is further magnetic domain A of the Faraday rotator 20. Incident to (first Faraday rotator). The extraordinary light component L62b is incident on the half-wave plate 22, is emitted from the half-wave plate 22 as light whose polarization orientation is rotated by 90 ° with respect to the Z axis, and is further magnetic domain B of the Faraday rotator 20 ( Incident to the second Faraday rotating part). The Faraday rotation angle of the magnetic domain A of the Faraday rotator 20 is + 45 ° with respect to the Z axis when viewed in the −Z direction, and the Faraday rotation angle of the magnetic domain B is −45 ° with respect to the Z axis when viewed in the −Z direction. As shown on the right side of FIG. 9C, the light incident on the magnetic domain A of the Faraday rotator 20 is the light L63a whose polarization direction is rotated 45 ° clockwise about the Z axis when viewed in the −Z direction. From the Faraday rotator 20 is emitted as light L63b whose polarization direction is rotated by 45 ° counterclockwise. Thereby, the polarization azimuths of the lights L63a and L63b are parallel to a plane formed by intersecting a straight line parallel to the traveling direction of the light L63a and L63b and a straight line parallel to the optical axis of the birefringent plate 15. Therefore, the lights L63a and L63b are incident on one surface of the birefringent plate 15 and become extraordinary light. As shown on the right side of FIG. The light is emitted as L64a and L64b. The lights L64a and L64b pass through the lens 34, are reflected by the reflecting mirror 36, and enter the other surface of the birefringent plate 15 as light L65a and L65b whose optical paths are changed as shown on the left side of FIG. .

  Lights L65a and L65b are incident on the other surface of the birefringent plate 15 and become extraordinary light. As shown on the left side of FIG. , L66b. The light L66a is incident on the magnetic domain B of the Faraday rotator 20, and the light L66b is incident on the magnetic domain A. As shown on the left side of FIG. 9B, the light L66a is emitted from the Faraday rotator 20 as light L67a whose polarization direction is rotated 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and the light L66b is The light is emitted from the Faraday rotator 20 as light L67b whose polarization direction is rotated 45 ° clockwise. Here, neither the light L67a nor L67b passes through the half-wave plate 22. The light L67a enters the birefringent plate 14 and becomes extraordinary light, and the light L67b enters the birefringent plate 14 and becomes ordinary light. As shown on the left side of FIG. 9A, the light L67a is off-axis and combined with the light L67b, and is emitted from the birefringent plate 14 as light L68. The light L68 enters the light incident / exit port P3 disposed next to the light incident / exit port P1 and is emitted to the outside.

  FIG. 10 shows light that enters from the light incident / exit port P3 and exits to the outside from the light incident / exit port P4, like a light beam indicated by a one-dot chain line in FIG. As shown on the left side of FIG. 10 (a), the light L71 incident from the light incident / exit port P3 enters the birefringent plate 14, and as shown on the left side of FIG. 10 (b), the normal light L72a and the + X direction and Separated into extraordinary light L72b that is axially misaligned in both directions in the -Y direction and emitted from the birefringent plate 14. Then, the ordinary light component light L72a is incident on the magnetic domain A (first Faraday rotator) of the Faraday rotator 20, and the extraordinary light component light L72b is incident on the magnetic domain B (second Faraday rotator) of the Faraday rotator 20. Incident. Here, neither the light L72a nor L72b passes through the half-wave plate 22. The Faraday rotation angle of the magnetic domain A of the Faraday rotator 20 is + 45 ° with respect to the Z axis when viewed in the −Z direction, and the Faraday rotation angle of the magnetic domain B is −45 ° with respect to the Z axis when viewed in the −Z direction. As shown on the left side of FIG. 10C, the light L72a is emitted from the Faraday rotator 20 as the light L73a whose polarization direction is rotated 45 ° clockwise about the Z axis when viewed in the −Z direction, and the light L72b is the polarization direction. Is emitted from the Faraday rotator 20 as light L73b rotated 45 ° counterclockwise. Thereby, the polarization azimuth | direction of light L73a, L73b becomes perpendicular | vertical to the plane formed by the straight line parallel to the advancing direction of light L73a, L73b, and the straight line parallel to the optical axis of the birefringent plate 15 crossing. Therefore, the lights L73a and L73b are incident on one surface of the birefringent plate 15 and become ordinary light, and light L74a is transmitted from the other surface of the birefringent plate 15 without being misaligned as shown on the left side of FIG. , L74b. The lights L74a and L74b pass through the lens 34, are reflected by the reflecting mirror 36, and enter the other surface of the birefringent plate 15 as light L75a and L75b whose optical paths are changed as shown on the right side of FIG. .

  The lights L75a and L75b are incident on the other surface of the birefringent plate 15 and become ordinary light. As shown on the right side of FIG. 10C, the lights L76a, L75a, The light is emitted as L76b. The light L76a is incident on the magnetic domain B of the Faraday rotator 20, and the light L76b is incident on the magnetic domain A of the Faraday rotator 20. The light L76a is emitted from the Faraday rotator 20 as light whose polarization orientation is rotated by 45 ° counterclockwise with respect to the Z axis when viewed in the −Z direction, and is incident on the half-wave plate 22 as shown in FIG. As shown on the right side of (), the light is emitted as light L77a whose polarization orientation is rotated by 90 ° about the Z axis. The light L76b is emitted from the Faraday rotator 20 as light whose polarization azimuth is rotated 45 ° clockwise, is further incident on the half-wave plate 22, and is emitted as light L77b whose polarization azimuth is rotated 90 ° about the Z axis. To do. The light L77a enters the birefringent plate 14 and becomes extraordinary light, and the light L77b enters the birefringent plate 14 and becomes ordinary light. As shown on the right side of FIG. 10A, the light L77a is off-axis and combined with the light L77b, and is emitted from the birefringent plate 14 as light L78. The light L78 enters the light incident / exit port P4 disposed next to the light incident / exit port P2, and exits to the outside.

  Thus, in the reflection type optical circulator 1 ′ according to the present embodiment, the input light from the light incident / exit port P1 is output from the light incident / exit port P2, and the input light from the light incident / exit port P2 is output to the light incident / exit port. The light input from the light incident / exit port P3 is output from the light incident / exit port P4.

  In the present embodiment, incident light that has passed through one of the two Faraday rotators (the magnetic domains A and B of the Faraday rotator 20) is reflected by the reflecting mirror 36 by the optical path conversion by the lens 34 and the reflecting mirror 36. Pass through the other when returning as reflected light. Since the Faraday rotation angles of both Faraday rotation sections are the same in magnitude and different from each other, the polarization direction of light eventually returns to the original. Since the half-wave plate 22 is disposed on either the incident optical path or the reflected optical path between the birefringent plate 14 and the Faraday rotator 20, the light L52a, L62a emitted from the birefringent plate 14, The polarization azimuth of L72a (or light L52b, L62b, L72b) and the polarization azimuth of light L57a, L67a, L77a (or light L57b, L67b, L77b) incident on the birefringent plate 14 are orthogonal to each other. Therefore, the light that has passed through the birefringent plate 14 as ordinary light passes as abnormal light when reflected back by the reflecting mirror 36, and conversely, the light that has passed through the birefringent plate 14 as extraordinary light is reflected by the reflecting mirror 36. And pass as ordinary light when returning. In addition, after passing through the Faraday rotator 20 and before being reflected by the reflecting mirror 36 and entering the Faraday rotator 20 again, the polarization directions of the two separated lights are the same. Therefore, according to the reflective optical circulator 1 ′ according to the present embodiment, the PMD value can be made zero. The half-wave plate 22 may be disposed not between the birefringent plate 14 and the Faraday rotator 20 but between the Faraday rotator 20 and the birefringent plate 15. The half-wave plate 22 is disposed on the reflection optical path of light incident from the light incident / exit ports P1 and P3 (on the incident optical path of light incident from the light incident / exit port P2). You may arrange | position on the incident optical path of the light which injects from P1 and P3 (on the reflection optical path of the light which injects from the light incident / exit port P2).

  In the present embodiment, an optical fiber with a lens in which GI lenses 71 to 74 are fused to the tips of the optical fibers 41 to 44 is used. When the optical fibers 41 to 44 to which the GI lenses 71 to 74 are not fused are used, the spread angle of the light emitted from the end portions of the optical fibers 41 to 44 is increased, and the light from the light incident / exit ports P1 to P4 is transmitted. There is a risk of overlapping. For this reason, it is desirable to add a lens function to the optical fibers 41 to 44 to suppress the light spreading angle. Instead of fusing the GI lenses 71 to 74, the cores at the tips of the optical fibers 41 to 44 may be enlarged. Of course, lenses 51 to 54 may be provided separately as shown in FIG.

In this embodiment, the amount of axial deviation of the birefringent plate 14 is set to 2√2 times the amount of axial deviation of the birefringent plate 15, but the present invention is not limited to this, and the birefringent plates 14, 15 are not limited thereto. Can be set independently of each other.
When the configuration according to the present embodiment functions as an optical isolator, polarizing glass can be used as a polarizer instead of the birefringent plate 15.

  11 and 12 show modifications of the reflective optical circulator according to the present embodiment, and correspond to FIGS. 8 and 9, respectively. As shown in FIGS. 11 and 12, the reflective optical circulator according to the present modification includes a birefringent plate 14 ′ having a different optical axis direction from the birefringent plate 14. The extraordinary light that is incident on the birefringent plate 14 ′ in the + Z direction is off-axis in the −Y direction. Two half-wave plates 23 and 24 are disposed in the + Z direction of the birefringent plate 14 ′. The half-wave plate 23 is disposed at a position corresponding to the light incident / exit ports P1 and P3, and rotates the polarization direction of the light incident in the + Z direction by 45 ° clockwise as viewed in the −Z direction. Yes. The half-wave plate 24 is disposed at a position corresponding to the light incident / exit ports P2 and P4, and rotates the polarization direction of the light incident in the + Z direction by 45 ° in the reverse direction.

  FIG. 11 shows light that enters from the light incident / exit port P1 and exits to the outside from the light incident / exit port P2. As shown on the left side of FIG. 11 (a), the light L81 incident from the light incident / exit port P1 enters the birefringent plate 14 ′ and, as shown on the left side of FIG. 11 (b), normal light L82a and −Y. It is separated into extraordinary light L82b whose axis is shifted in the direction and emitted from the birefringent plate 14 ′. The ordinary light component L82a is incident on the half-wave plate 23 and is emitted from the half-wave plate 23 as light whose polarization direction is rotated by 45 ° clockwise about the Z axis when viewed in the −Z direction. The light enters the magnetic domain A of the rotor 20. As shown on the left side of FIG. 11C, the light incident on the magnetic domain A is emitted from the Faraday rotator 20 as light L83a whose polarization direction is further rotated by 45 ° in the clockwise direction. The extraordinary light component light L82b is incident on the half-wave plate 23 and is emitted from the half-wave plate 23 as light whose polarization direction is rotated by 45 ° clockwise about the Z axis when viewed in the −Z direction. The light enters the magnetic domain B of the Faraday rotator 20. The light incident on the magnetic domain B is emitted from the Faraday rotator 20 as light L83b whose polarization direction is rotated by 45 ° counterclockwise. Thereby, the polarization azimuth | direction of light L83a and L83b becomes perpendicular | vertical to the plane formed by the straight line parallel to the advancing direction of light L83a and L83b, and the straight line parallel to the optical axis of the birefringent plate 15 crossing. Accordingly, the lights L83a and L83b are incident on one surface of the birefringent plate 15 and become ordinary light, and the light L84a from the other surface of the birefringent plate 15 is not displaced as shown in the left side of FIG. , L84b. The lights L84a and L84b pass through the lens 34, are reflected by the reflecting mirror 36, and enter the other surface of the birefringent plate 15 as light L85a and L85b whose optical paths are changed as shown on the right side of FIG. .

  The lights L85a and L85b are incident on the other surface of the birefringent plate 15 and become ordinary light. As shown on the right side of FIG. 11 (c), the lights L86a, L86a, The light is emitted as L86b. The light L86a is incident on the magnetic domain B of the Faraday rotator 20, and the light L86b is incident on the magnetic domain A of the Faraday rotator 20. The light L86a is emitted from the Faraday rotator 20 as light whose polarization direction is rotated by 45 ° counterclockwise with respect to the Z-axis when viewed in the −Z direction, and is incident on the half-wave plate 24 as shown in FIG. As shown on the right side of (), the light is emitted as light L87a whose polarization direction is rotated by 45 ° clockwise. The light L86b is emitted from the Faraday rotator 20 as light whose polarization orientation is rotated by 45 ° clockwise with respect to the Z axis when viewed in the −Z direction, and is incident on the half-wave plate 22 so that the polarization orientation is Z axis. Is emitted as light L87b rotated clockwise by 45 °. The light L87a enters the birefringent plate 14 'and becomes extraordinary light, and the light L87b enters the birefringent plate 14' and becomes ordinary light. As shown on the right side of FIG. 11A, the light L87a is off-axis and combined with the light L87b, and is emitted from the birefringent plate 14 'as light L88. The light L88 enters the light incident / exit port P2 and exits to the outside.

  FIG. 12 shows light that enters from the light incident / exit port P2 and exits to the outside from the light incident / exit port P3. As shown on the right side of FIG. 12 (a), the light L91 incident from the light incident / exit port P2 enters the birefringent plate 14 ′ and, as shown on the right side of FIG. 12 (b), the ordinary light L92a and −Y. It is separated into extraordinary light L92b whose axis is displaced in the direction, and is emitted from the birefringent plate 14 ′. The ordinary light component L92a is incident on the half-wave plate 24, and is emitted from the half-wave plate 24 as light whose polarization direction is rotated by 45 ° counterclockwise about the Z axis when viewed in the −Z direction. The light enters the magnetic domain A of the Faraday rotator 20. As shown on the right side of FIG. 12C, the light incident on the magnetic domain A is emitted from the Faraday rotator 20 as light L93a whose polarization direction is rotated by 45 ° clockwise. The extraordinary light component light L92b is incident on the half-wave plate 24, and is emitted from the half-wave plate 24 as light whose polarization orientation is rotated by 45 ° counterclockwise about the Z axis when viewed in the -Z direction. , And enters the magnetic domain B of the Faraday rotator 20. The light incident on the magnetic domain B is emitted from the Faraday rotator 20 as light L93b whose polarization direction is further rotated 45 ° counterclockwise. Thereby, the polarization azimuths of the lights L93a and L93b are parallel to a plane formed by intersecting a straight line parallel to the traveling direction of the lights L93a and L93b and a straight line parallel to the optical axis of the birefringent plate 15. Therefore, the lights L93a and L93b are incident on one surface of the birefringent plate 15 to become abnormal light, and are shifted in the -X direction as shown on the right side of FIG. Are emitted as light L94a and L94b. The lights L94a and L94b pass through the lens 34, are reflected by the reflecting mirror 36, and enter the other surface of the birefringent plate 15 as light L95a and L95b whose optical paths are changed as shown on the left side of FIG. .

  The lights L95a and L95b are incident on the other surface of the birefringent plate 15 and become extraordinary light. As shown on the left side of FIG. Are emitted as light L96a and L96b. The light L 96 a is incident on the magnetic domain B of the Faraday rotator 20, and the light L 96 b is incident on the magnetic domain A of the Faraday rotator 20. The light L96a is emitted from the Faraday rotator 20 as light whose polarization direction is rotated by 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and is incident on the half-wave plate 23 as shown in FIG. As shown on the left side of), the light is emitted as light L97a whose polarization direction is further rotated by 45 ° counterclockwise. The light L96b is emitted from the Faraday rotator 20 as light whose polarization orientation is rotated by 45 ° clockwise with respect to the Z-axis when viewed in the −Z direction, and further enters the half-wave plate 23, and the polarization orientation is counterclockwise. The light is emitted as light L97b rotated around 45 °. The light L97a enters the birefringent plate 14 'and becomes extraordinary light, and the light L97b enters the birefringent plate 14' and becomes ordinary light. As shown on the left side of FIG. 12A, the light L97a is off-axis and combined with the light L97b, and is emitted from the birefringent plate 14 'as light L98. The light L98 enters the light incident / exit port P3 and exits to the outside.

  Thus, in the reflection type optical circulator according to this modification, the input light from the light incident / exit port P1 is output from the light incident / exit port P2, and the input light from the light incident / exit port P2 is output from the light incident / exit port P3. It is supposed to be. Although not shown and described, input light from the light incident / exit port P3 is output from the light incident / exit port P4.

In the reflection-type optical circulator according to this modification, the light incident / exit ports can be arranged in a line at equal intervals, as in the reflection-type optical circulator shown in FIGS. This facilitates assembly of the reflective optical circulator.
Further, in this modification, the two light beams separated by polarization have almost the same optical path length in the lens 34, and therefore, the polarization dependent loss (PDL) is compared with the reflection type optical circulator shown in FIGS. ) Can be further reduced.

[Third Embodiment]
Next, a reflective optical component according to a third embodiment of the present invention will be described with reference to FIGS. FIG. 13 schematically shows the configuration of a reflective optical isolator according to this embodiment. In FIG. 13, the Z-axis is taken in the direction orthogonal to the surface of the reflection film (reflection part) 30 provided in the reflection type optical isolator, and the direction in which light from the outside is directed to the reflection film 30 is the + Z direction. Further, the X axis and the Y axis are taken in two directions orthogonal to each other in a plane orthogonal to the Z axis. FIG. 13A shows a configuration when the reflective optical isolator is viewed in the −Y direction, and FIG. 13B shows a configuration when the reflective optical isolator is viewed in the −X direction.

  As shown in FIG. 13, the reflective optical isolator 2 is connected to two optical fibers 41 and 42. The end of the optical fiber 41 on the −Z side is a light incident port P1 (indicated by the numeral (1) in the drawing) through which light enters from the outside. An end portion on the −Z side of the optical fiber 42 is a light emission port P2 (indicated by a numeral (2) in the drawing) that emits light to the outside. A lens 51 is disposed in the + Z direction of the optical fiber 41 to convert the divergent light emitted from the optical fiber 41 into parallel light. In the + Z direction of the optical fiber 42, the parallel light is converted into convergent light and incident on the optical fiber 42. A lens 52 is disposed.

  The birefringent plate 11 is disposed in the + Z direction of the lens 51, and the birefringent plate 12 is disposed in the + Z direction of the lens 52. A Faraday rotator 20 is disposed in the + Z direction of the birefringent plates 11 and 12. A permanent magnet 61 is disposed at the + Y direction end of the Faraday rotator 20, and a permanent magnet 62 is disposed at the −Y direction end. The permanent magnets 61 and 62 have magnetic poles opposite to each other. For example, as indicated by an arrow in the figure, the direction of the magnetic pole of the permanent magnet 61 is the + Z direction, and the direction of the magnetic pole of the permanent magnet 62 is the -Z direction. A magnetic domain A having a uniform magnetization in one direction is formed in a region where a magnetic field in the -Z direction of the Faraday rotator 20 is applied. The magnetic domain B made uniform in the opposite direction is formed. A domain wall I is formed on the boundary surface between the magnetic domain A and the magnetic domain B. In this example, the Faraday rotation angle of the magnetic domain A is, for example, 45 ° clockwise with respect to the Z axis when viewed in the −Z direction, and the Faraday rotation angle of the magnetic domain B is similarly 45 ° counterclockwise. Since the Faraday rotator 20 has nonreciprocity, the condition of the rotation angle is maintained even if light enters from either of the two light incident / exit surfaces of the Faraday rotator 20.

  A polarizing glass (polarizer) 16 is arranged in the + Z direction of the Faraday rotator 20. The polarizing glass 16 transmits predetermined linearly polarized light and absorbs linearly polarized light orthogonal thereto. The transmission axis of the polarizing glass 16 is parallel to a direction tilted 45 ° clockwise with respect to the Z axis with respect to the Z axis when viewed in the −Z direction. A reflective portion is disposed in the + Z direction of the polarizing glass 16. In this example, since the function of changing the optical path is not necessary, for example, a reflection mirror in which a dielectric multilayer film or a metal thin film such as aluminum is deposited on the glass substrate surface as the reflection film 30 can be used as the reflection portion. Instead of the reflection mirror, the reflection film 30 may be formed on the surface of the polarizing glass 16 on the + Z side.

  In the present embodiment, the reflective optical isolator 2 can be configured by using four optical elements (two birefringent plates 11, 12, one polarizing glass 16, and one Faraday rotator 20). Even when two Faraday rotators are used without using the magnetic domain structure of the Faraday rotator 20, the reflective optical isolator 2 can be configured using five optical elements. Further, as the birefringent plates 11 and 12, for example, elements of the same specification cut out from the same crystal can be used. Therefore, according to the present embodiment, the element configuration of the reflective optical isolator 2 is simplified, and miniaturization and cost reduction are facilitated.

  Next, the operation of the reflective optical isolator according to this embodiment will be described with reference to FIGS. 14 and 15 are views of the polarization state of light passing through each optical element constituting the reflective optical isolator 2 as viewed in the -Z direction. 14A and 15A show the polarization state of light on the light incident / exit surface Z1 on the −Z side of the birefringent plates 11 and 12, as shown in FIG. FIG. 14 and FIG. 15B show the polarization state of light on the light incident / exit surface Z2 on the + Z side of the birefringent plates 11 and 12. FIG. FIG. 14 and FIG. 15C show the polarization state of the light on the light incident / exit surface Z <b> 3 on the −Z side of the polarizing glass 16. 14 and 15 schematically show the states of the birefringent plates 11 and 12, the Faraday rotator 20, the polarizing glass 16, and the reflective film 30 viewed in the -Z direction for easy understanding. Show.

  FIG. 14 shows light that enters from the light incident port P1 and exits to the outside from the light exit port P2. As shown on the left side of FIG. 14A, the light L31 incident from the light incident port P1 enters the birefringent plate (first birefringent plate) 11 and is shown on the left side of FIG. 14B. Are separated into the ordinary light L32a and the extraordinary light L32b whose axis is shifted in the -Y direction. Next, the ordinary light component light L32a is incident on the magnetic domain A (first Faraday rotator) of the Faraday rotator 20, and the abnormal light component light L32b is incident on the magnetic domain B (second Faraday rotator) of the Faraday rotator 20. Incident. For example, the Faraday rotation angle of the magnetic domain A of the Faraday rotator 20 is + 45 ° with respect to the Z axis when viewed in the −Z direction, and the Faraday rotation angle of the magnetic domain B is −45 ° with respect to the Z axis when viewed in the −Z direction. As shown on the left side of FIG. 14C, the light L32a is emitted from the Faraday rotator 20 as light L33a whose polarization direction is rotated 45 ° clockwise about the Z axis when viewed in the −Z direction, and the light L32b is polarized direction. Is emitted from the Faraday rotator 20 as light L33b rotated 45 ° counterclockwise. Thereby, the polarization azimuth | direction of light L33a and L33b becomes parallel to the transmission axis (it shows by the double arrow in a figure) of polarizing glass (polarizer) 16. FIG. Therefore, the lights L33a and L33b are transmitted through the polarizing glass 16, reflected by the reflecting film 30, and again transmitted through the polarizing glass 16 and emitted as lights L34a and L34b shown on the right side of FIG.

  The light L34a is incident on the magnetic domain A of the Faraday rotator 20, and the light L34b is incident on the magnetic domain B of the Faraday rotator 20. As shown on the right side of FIG. 14B, the light L34a is emitted from the Faraday rotator 20 as light L35a whose polarization direction is rotated 45 ° clockwise about the Z axis when viewed in the −Z direction, and the light L34b is polarized direction. Is emitted from the Faraday rotator 20 as light L35b rotated by 45 ° counterclockwise. The light L35a enters the birefringent plate (second birefringent plate) 12 and becomes extraordinary light, and the light L35b enters the birefringent plate 12 and becomes ordinary light. As shown on the right side of FIG. 14A, the light L35a is off-axis and combined with the light L35b, and is emitted from the birefringent plate 12 as light L36. The light L36 enters the light exit port P2 and exits to the outside.

  FIG. 15 shows light incident from the light output port P2. As shown on the right side of FIG. 15 (a), the light L41 incident from the light exit port P2 enters the birefringent plate (first birefringent plate) 12, and as shown on the right side of FIG. 15 (b). Then, the light is separated into the ordinary light L42a and the extraordinary light L42b shifted in the + Y direction and emitted from the birefringent plate 12. Next, the ordinary light component light L42a enters the magnetic domain B (first Faraday rotator) of the Faraday rotator 20, and the abnormal light component light L42b enters the magnetic domain A (second Faraday rotator) of the Faraday rotator 20. Incident. As shown on the right side of FIG. 15C, the light L42a is emitted from the Faraday rotator 20 as light L43a whose polarization direction is rotated 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and the light L42b is polarized. The light is emitted from the Faraday rotator 20 as light L43b whose azimuth is rotated 45 ° clockwise. As a result, the polarization directions of the lights L43a and L43b are perpendicular to the transmission axis of the polarizing glass (polarizer) 16. Accordingly, the light L43a and L43b are both absorbed by the polarizing glass 16 and do not pass through the polarizing glass 16.

  Here, the polarization directions of the light L43a and L43b are transmitted through the polarizing glass 16 due to a manufacturing error of the Faraday rotator 20, an angular shift of the Faraday rotation angle accompanying a change in temperature wavelength, or an optical axis shift of the birefringent plate 12. It may not be perpendicular to the axis and some light may pass through the polarizing glass 16. As shown on the left side of FIG. 15C, the light L44a that has been transmitted through the polarizing glass 16, reflected by the reflective film 30, and transmitted through the polarizing glass 16 again enters the magnetic domain B of the Faraday rotator 20, and again again. The light L44b transmitted through the polarizing glass 16 enters the magnetic domain A of the Faraday rotator 20. As shown on the left side of FIG. 15B, the light L44a is emitted from the Faraday rotator 20 as light L45a whose polarization direction is rotated 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and the light L44b is polarized. The light is emitted from the Faraday rotator 20 as light L45b whose azimuth is rotated 45 ° clockwise. The light L45a enters the birefringent plate (second birefringent plate) 11 and becomes ordinary light, and the light L45b enters the birefringent plate 11 and becomes extraordinary light. As shown on the left side of FIG. 15A, the light L45a is emitted from the birefringent plate 11 as light L46a without being off-axis, and the light L45b is off-axis and emitted from the birefringent plate 11 as light L46b. Neither the light L46a nor L46b is incident on the light incident port P1. Therefore, even if a part of the light passes through the polarizing glass 16, the transmitted light does not enter the light incident port P1. Thus, it can be seen that the reflective optical isolator 2 of the present embodiment functions as a two-stage optical isolator.

  In the present embodiment, light that has passed through one of the birefringent plates 11 and 12 having the same optical characteristics as ordinary light passes through the other as abnormal light when reflected by the reflective film 30 and is reversed. The light that has passed through one of the birefringent plates 11 and 12 as extraordinary light passes through the other as ordinary light when reflected by the reflecting film 30 and returned. Further, after passing through the Faraday rotator 20 and before being reflected by the reflection film 30 and entering the Faraday rotator 20 again, the polarization directions of the two separated lights are the same. Therefore, according to the reflection type optical isolator 2 according to the present embodiment, the PMD value can be made zero, and it has a two-stage configuration and high isolation characteristics can be obtained.

  In FIG. 13, the polarizing glass 16 and the reflective film 30 are shown to be parallel to each other, but actually, the polarizing glass 16 and the reflective film 30 are arranged non-parallel to each other. FIG. 16 shows a reflective optical isolator 2 ′ in which the polarizing glass 16 and the reflective film 30 are arranged in parallel to each other. As shown in FIG. 16, when the polarizing glass 16 and the reflective film 30 are arranged in parallel to each other, the light from the light exit port P <b> 2 is scattered by the reflected light reflected by the light incident / exit surface of the polarizing glass 16 or the polarizing glass 16. Is incident on the light incident port P1 as scattered light (lights L201 and L202 in FIG. 16). For this reason, the reflective optical isolator 2 ′ has a problem that high isolation characteristics cannot be obtained.

  Further, in the reflection type optical isolator 2 ′, interference occurs between the reflected light reflected by the light incident / exit surface of the polarizing glass 16 or the scattered light scattered by the polarizing glass 16, and the reflected light reflected by the reflective film 30, There is also a problem that wavelength characteristics become unstable. FIG. 17 is a graph showing the wavelength characteristics of the reverse loss of the reflective optical isolators 2 and 2 ′. The horizontal axis in FIG. 17 represents the wavelength (nm), and the vertical axis represents the reverse loss (dB). A line a in the graph represents a reflective optical isolator 2 in which the distance between the + Z side surface of the polarizing glass 16 and the light reflecting surface of the reflecting film 30 is 0 mm, and the polarizing glass 16 and the reflecting film 30 are arranged in parallel. The wavelength characteristics of the reverse loss are shown. The line b is such that the distance between the + Z side surface of the polarizing glass 16 and the light reflecting surface of the reflecting film 30 is 0.16 mm, and the angle between the polarizing glass 16 and the reflecting film 30 is 5 °. The wavelength characteristic of the reverse loss of the reflection type optical isolator 2 arranged in FIG. As shown in FIG. 17, in the reflective optical isolator 2, the reverse loss is generally higher than the reverse loss of the reflective optical isolator 2 '. The waveform indicated by line a has ripples, and the wavelength characteristic of the reverse loss of the reflective optical isolator 2 ′ is unstable, whereas the wavelength of the reverse loss of the reflective optical isolator 2 is unstable. The characteristics are relatively stable.

  Thus, in order to obtain high isolation characteristics, it is necessary to dispose the polarizing glass 16 and the reflective film 30 non-parallel to each other and make the distance between them as wide as possible.

  Next, a modified example of the configuration of the reflective optical isolator according to the present embodiment will be described. FIG. 18 shows a reflective optical isolator 2 '' according to this modification. As shown in FIG. 18, in this modification, a wedge birefringent crystal 18 having a wedge shape is used as a polarizer instead of the polarizing glass 16. The surface on the −Z side of the wedge birefringent crystal 18 is disposed substantially parallel to the light incident / exit surfaces of the birefringent plates 11 and 12 and the Faraday rotator 20. A reflective film 30 is disposed on the surface of the wedge birefringent crystal 18 on the + Z side, and the reflective film 30 is directly formed on the surface of the wedge birefringent crystal 18 on the + Z side, for example. Since the surface on the + Z side and the surface on the −Z side of the wedge birefringent crystal 18 are not parallel, the light reflecting surface of the reflecting film 30 and the light incident / exiting surfaces of the birefringent plates 11 and 12 and the Faraday rotator 20 are different. It is non-parallel. The light incident on the −Z side surface of the wedge birefringent crystal 18 is separated into ordinary light and extraordinary light. Ordinary light and extraordinary light are reflected by the reflective film 30 and are emitted in different directions from the −Z side surface of the wedge birefringent crystal 18. Thereby, since only one polarization component can be taken out, the wedge birefringent crystal 18 functions as a polarizer.

  In this modification, even if the light incident / exit surfaces of the birefringent plates 11, 12, the light incident / exit surface of the Faraday rotator, and the −Z side surface of the wedge birefringent crystal 18 are arranged in parallel to each other, the reflective film 30. The light-reflecting surface is non-parallel to these. Therefore, the reflected light L211 reflected by the reflecting film 30 from the light exit port P2, the reflected light L212 reflected by the light entrance / exit surface on the −Z side of the birefringent plate 12, and the −Z side of the Faraday rotator 20 are reflected. The traveling direction of the reflected light L213 reflected by the light incident / exit surface and the reflected light L214 reflected by the surface of the wedge birefringent crystal 18 on the −Z side are different from each other. Therefore, problems such as interference do not occur, and a reflective optical isolator 2 '' having high isolation characteristics can be obtained. In this modification, the reflective film 30 can be formed directly on the + Z side surface of the wedge birefringent crystal 18. For this reason, this modification is also effective in reducing the number of members and reducing the size of the reflective optical isolator 2 ''.

[Fourth Embodiment]
Next, a reflective optical component according to a fourth embodiment of the present invention will be described with reference to FIGS. FIG. 19 schematically shows the configuration of a reflective optical isolator according to this embodiment. In FIG. 19, the Z-axis is set in the traveling direction of light, and the direction in which the light from the outside is directed to the reflecting plates (reflecting portions) 36a and 36b provided in the reflective optical isolator is the + Z direction. Further, the X axis and the Y axis are taken in two directions orthogonal to each other in a plane orthogonal to the Z axis.

  As shown in FIG. 19, the reflective optical isolator 4 is connected to two optical fibers 41 and 42. The −Z side end of the optical fiber 41 is a light incident port P1 (1) through which light enters from the outside. The −Z side end of the optical fiber 42 is a light emission port P2 (2) that emits light to the outside. A lens 51 is disposed in the + Z direction of the optical fiber 41 to convert the divergent light emitted from the optical fiber 41 into parallel light. In the + Z direction of the optical fiber 42, the parallel light is converted into convergent light and incident on the optical fiber 42. A lens 52 is disposed.

  A birefringent plate 17 is disposed in the + Z direction of the lenses 51 and 52. The birefringent plate 17 has an optical axis OA that is parallel to a direction tilted 45 ° counterclockwise with respect to the Y axis when viewed in the + Y direction. A Faraday rotator 20 is disposed in the + Z direction of the birefringent plate 17. For example, a permanent magnet that applies a predetermined magnetic field to the Faraday rotator 20 is disposed in proximity to the Faraday rotator 20.

  FIG. 20 shows the arrangement of the Faraday rotator and the permanent magnet. FIG. 20A shows an arrangement of the Faraday rotator and permanent magnet viewed in the + Y direction, and FIG. 20B shows an arrangement of the Faraday rotator and permanent magnet viewed in the + Z direction. 20A and 20B also show the magnetization direction of the permanent magnet. As shown in FIGS. 20A and 20B, three permanent magnets 63, 64, and 65 are arranged in proximity to the + Y direction of the Faraday rotator 20. The permanent magnets 63, 64, 65 are arranged in this order from the + X side. The magnetization direction of the permanent magnets 63 and 65 is the + Z direction, and the magnetization direction of the permanent magnet 64 is the -Z direction. As a result, as shown in FIG. 19, the magnetic domain A having the magnetization uniformly in the −Z direction is formed on the + X side and the −X side of the Faraday rotator 20. Then, a magnetic domain B is formed in which the magnetization is uniformly in the + Z direction (the arrow in FIG. 19 indicates the direction of magnetization). That is, the Faraday rotator 20 has a three-domain structure in which the magnetic domains A are formed on both sides of the magnetic domain B. Light that has entered from the light incident port P1 and passed through the birefringent plate 17 as ordinary light is incident on the magnetic domain B of the Faraday rotator 20, and light that has passed through the birefringent plate 17 as abnormal light enters the magnetic domain A of the Faraday rotator 20. Incident. In addition, light that has entered from the light exit port P2 and passed through the birefringent plate 17 as ordinary light is incident on the magnetic domain A of the Faraday rotator 20, and light that has passed through the birefringent plate 17 as abnormal light is in the magnetic domain of the Faraday rotator 20. It is incident on B.

  A polarizing glass (polarizer) 16 is arranged in the + Z direction of the Faraday rotator 20. The polarizing glass 16 transmits predetermined linearly polarized light and absorbs linearly polarized light orthogonal thereto. The transmission axis of the polarizing glass 16 is substantially parallel to the direction tilted 45 ° clockwise with respect to the Z axis when viewed in the −Z direction. A reflective portion is disposed in the + Z direction of the polarizing glass 16. The reflection unit includes two reflection plates 36a and 36b in which the respective light reflection surfaces are arranged substantially perpendicular to each other so that the optical path of the incident light is changed by two-surface reflection. The light reflecting surface of the reflecting plate 36a is disposed substantially parallel to a surface inclined 45 ° counterclockwise about the YZ plane when viewed in the + Y direction, and the light reflecting surface of the reflecting plate 36b is viewed in the + Y direction. The YZ plane is disposed substantially parallel to a plane inclined 45 ° clockwise about the Y axis.

  Next, the operation of the reflective optical isolator according to this embodiment will be described with reference to FIGS. 21 and 22 are diagrams in which the polarization state of light passing through each optical element constituting the reflective optical isolator 4 is viewed in the −Z direction. FIG. 21 and FIG. 22A show the polarization state of light on the light incident / exit surface Z1 on the −Z side of the birefringent plate 17 shown in FIG. FIG. 21 and FIG. 22B show the polarization state of light on the light incident / exit surface Z2 on the + Z side of the birefringent plate 17. FIG. 21 and FIG. 22C show the polarization state of light on the light incident / exit surface Z <b> 3 on the −Z side of the polarizing glass 16. In FIG. 21 and FIG. 22, for easy understanding, the birefringent plate 17, the Faraday rotator 20, and the polarizing glass 16 are viewed in the −Z direction, and the reflecting plates 36a and 36b are viewed in the + Y direction. The state is also schematically shown together.

  FIG. 21 shows light that enters from the light incident port P1 and exits to the outside from the light exit port P2, as indicated by the solid line in FIG. As shown in the lower side of FIG. 21A, the light L101 incident from the light incident port P1 enters the birefringent plate 17. The light L101 is separated into the ordinary light L102a and the extraordinary light L102b shifted in the + X direction as shown in the lower side of FIG. The ordinary light component light L102a is incident on the magnetic domain B (first Faraday rotator) of the Faraday rotator 20, and the extraordinary light component light L102b is incident on the magnetic domain A (second Faraday rotator) of the Faraday rotator 20. . For example, the Faraday rotation angle of the magnetic domain A of the Faraday rotator 20 is + 45 ° with respect to the Z axis when viewed in the −Z direction, and the Faraday rotation angle of the magnetic domain B is −45 ° with respect to the Z axis when viewed in the −Z direction. As shown in the lower side of FIG. 21C, the light L102a is emitted from the Faraday rotator 20 as light L103a whose polarization direction is rotated 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and the light L102b is The light is emitted from the Faraday rotator 20 as light L103b whose polarization direction is rotated 45 ° clockwise. As a result, the polarization directions of the lights L103a and L103b are parallel to the transmission axis of the polarizing glass 16 (indicated by double arrows in the figure). Therefore, the lights L103a and L103b are transmitted through the polarizing glass 16, reflected by the reflecting plates 36a and 36b in order, and then transmitted again through the polarizing glass 16 and emitted as the lights L104a and L104b shown on the upper side of FIG. .

  The light L104a is incident on the magnetic domain B (third Faraday rotator) of the Faraday rotator 20, and the light L104b is incident on the magnetic domain A (fourth Faraday rotator) of the Faraday rotator 20. Here, the magnetic domain B where the light L104a is incident is formed in the same region as the magnetic domain B where the light L102a is incident, and the magnetic domain A where the light L104b is incident is formed in a region different from the magnetic domain A where the light L102b is incident. Has been. As shown in the upper side of FIG. 21B, the light L104a is emitted from the Faraday rotator 20 as light L105a whose polarization orientation is rotated 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and the light L104b is polarized. The light is emitted from the Faraday rotator 20 as light L105b whose azimuth is rotated 45 ° clockwise. The lights L105a and L105b are incident on the birefringent plate 17, the light L105a passes through the birefringent plate 17 as extraordinary light, and the light L105b passes through the birefringent plate 17 as ordinary light. As shown in the upper side of FIG. 21A, the light L105a is offset in the −X direction and combined with the light L105b, and is emitted from the birefringent plate 17 as light L106. The light L106 enters the light exit port P2 and exits to the outside.

FIG. 22 shows light incident from the light exit port P2 like a light beam indicated by a broken line in FIG. As shown in the upper side of FIG. 22A, the light L111 incident from the light exit port P2 enters the birefringent plate 17. The light L111 is separated into the ordinary light L112a and the extraordinary light L112b shifted in the + X direction as shown in the upper side of FIG. The ordinary light component light L 112 a is incident on the magnetic domain A of the Faraday rotator 20, and the extraordinary light component light L 112 b is incident on the magnetic domain B of the Faraday rotator 20. As shown in the upper side of FIG. 22 (c), the light L112a is emitted from the Faraday rotator 20 as light L113a whose polarization direction is rotated 45 ° clockwise about the Z axis when viewed in the −Z direction, and the light L112b is polarized direction. Is emitted from the Faraday rotator 20 as light L113b rotated 45 ° counterclockwise. As a result, the polarization directions of the lights L113a and L113b are perpendicular to the transmission axis of the polarizing glass 16. Therefore, both the light L113a and L113b are absorbed by the polarizing glass 16 and do not pass through the polarizing glass 16.

  Here, the polarization directions of the light L113a and L113b are transmitted through the polarizing glass 16 due to a manufacturing error of the Faraday rotator 20, an angular shift of the Faraday rotation angle accompanying a change in temperature wavelength, or an optical axis shift of the birefringent plate 17. It is possible that some of the light does not pass through the axis and passes through the polarizing glass 16. As shown in the lower side of FIG. 22 (c), the light L114a that has been transmitted through the polarizing glass 16, reflected by the reflecting plates 36b and 36a, and again transmitted through the polarizing glass 16 is incident on the magnetic domain A of the Faraday rotator 20, Similarly, the light L <b> 114 b again transmitted through the polarizing glass 16 enters the magnetic domain B of the Faraday rotator 20. As shown in the lower side of FIG. 22B, the light L114a is emitted from the Faraday rotator 20 as light L115a whose polarization direction is rotated 45 ° clockwise about the Z axis when viewed in the −Z direction, and the light L114b is polarized. The light is emitted from the Faraday rotator 20 as light L115b whose azimuth is rotated 45 ° counterclockwise. The lights L115a and L115b are respectively incident on the birefringent plate 17, the light L115a passes through the birefringent plate 17 as ordinary light, and the light L115b passes through the birefringent plate 17 as extraordinary light. As shown in the lower side of FIG. 22A, the light L115a is emitted from the birefringent plate 17 as the light L116a without being misaligned, and the light L115b is misaligned in the −X direction as the light L116b. Emanates from. Neither the light L116a nor L116b is incident on the light incident port P1. Therefore, even if a part of the light passes through the polarizing glass 16, the transmitted light does not enter the light incident port P1. Thus, it can be seen that the reflective optical isolator 4 of the present embodiment functions as a two-stage optical isolator.

  In the present embodiment, the reflective optical isolator 4 can be configured using three optical elements (one birefringent plate 17, one Faraday rotator 20, and one polarizing glass 16). Therefore, according to the present embodiment, the element configuration of the reflective optical isolator 4 is simplified, and miniaturization and cost reduction are facilitated. Compared with the reflection type optical isolator 2 according to the third embodiment, two reflection plates 36a and 36b for performing two-surface reflection are required, but the number of birefringence plates is one. Further, since the incident / exit angles of the light incident / exited from the ports P1, P2 with respect to the birefringent plate 17 are substantially equal, the optical fibers 41, 42 can be disposed substantially parallel to each other. Therefore, the reflective optical isolator 4 can be further reduced in size. Further, the reflection type optical isolator 4 according to the present embodiment has a two-stage configuration although the element configuration is simple. For this reason, the reflection type optical isolator 4 having high isolation characteristics can be realized.

  In the present embodiment, the light that has passed through the birefringent plate 17 as ordinary light passes through the birefringent plate 17 as extraordinary light when reflected by the reflecting plates 36a and 36b and returns to the birefringent plate 17 as anomalous. The light that has passed as light passes through the birefringent plate 17 as ordinary light when returning by being reflected by the reflecting plates 36a and 36b. Further, after passing through the Faraday rotator 20 and before being reflected by the reflectors 36a and 36b and entering the Faraday rotator 20 again, the polarization directions of the two separated lights are the same. Therefore, according to this embodiment, the PMD value can be made extremely small, and the polarization-independent reflection type optical isolator 4 can be realized.

[Fifth Embodiment]
Next, a reflective optical component according to a fifth embodiment of the present invention will be described with reference to FIGS. FIG. 23 schematically shows the configuration of a reflective optical circulator according to this embodiment. As shown in FIG. 23, the reflective optical circulator 5 is connected to four optical fibers 41, 42, 43, 44. Each optical fiber 41, 42, 43, 44 is disposed in a plane parallel to the XZ plane, and is disposed substantially parallel to each other. The optical fiber 43 is arranged on the most + X side, and the optical fibers 41, 42, 44 are arranged in this order at equal intervals, for example, on the −X side of the optical fiber 43. The ends of the optical fibers 41, 42, 43, and 44 on the −Z side are indicated by four light input / output ports P1, P2, P3, and P4 (in the drawing, numbers (1) to (4), respectively). )It has become. Lenses 51, 52, 53, and 54 are fused to the + Z side ends of the optical fibers 41, 42, 43, and 44, respectively. The optical fiber 41 and the lens 51 are integrated with each other and function as an optical fiber with a lens. Similarly, the optical fibers 42, 43, 44 and the lenses 52, 53, 54 are integrated with each other to function as an optical fiber with a lens.

  A birefringent plate 17 is disposed in the + Z direction of the lenses 51, 52, 53, and 54. The birefringent plate 17 has an optical axis OA that is parallel to a direction inclined 45 ° counterclockwise with respect to the Y axis when viewed in the −Y direction.

  A Faraday rotator 20 is disposed in the + Z direction of the birefringent plate 17. Although not shown, a permanent magnet that applies a magnetic field having a predetermined distribution to the Faraday rotator 20 is disposed, for example, adjacent to the Faraday rotator 20. A seven-domain structure is formed in the Faraday rotator 20 by a magnetic field applied by a permanent magnet. Light that has entered through the light incident / exit port P1 and passed through the birefringent plate 17 as ordinary light enters the magnetic domain B of the Faraday rotator 20, and light that has passed through the birefringent plate 17 as extraordinary light passes through the magnetic domain of the Faraday rotator 20. It is incident on A. Light that has entered through the light incident / exit port P2 and passed through the birefringent plate 17 as ordinary light enters the magnetic domain A of the Faraday rotator 20, and light that has passed through the birefringent plate 17 as abnormal light passes through the magnetic domain of the Faraday rotator 20. It is incident on B. Light that has entered through the light incident / exit port P3 and passed through the birefringent plate 17 as ordinary light is incident on the magnetic domain B of the Faraday rotator 20, and light that has passed through the birefringent plate 17 as extraordinary light is in the magnetic domain of the Faraday rotator 20. It is incident on A. Light that has entered through the light incident / exit port P4 and passed through the birefringent plate 17 as ordinary light enters the magnetic domain A of the Faraday rotator 20, and light that has passed through the birefringent plate 17 as abnormal light passes through the magnetic domain of the Faraday rotator 20. It is incident on B.

  A birefringent plate 19 is disposed in the + Z direction of the Faraday rotator 20. The optical axis OA of the birefringent plate 19 is parallel to a plane inclined by 45 ° counterclockwise about the Z axis when viewed in the −Z direction. In the + Z direction of the birefringent plate 19, reflecting plates 36a and 36b that change the optical path by two-surface reflection are arranged.

  Next, the operation of the reflective optical circulator according to this embodiment will be described. 24 to 26 are diagrams in which the polarization state of the light passing through each optical element constituting the reflective optical circulator 5 is viewed in the −Z direction. FIG. 24A to FIG. 26A show the polarization state of light on the light incident / exit surface Z1 on the −Z side of the birefringent plate 17 as shown in FIG. FIG. 24 to FIG. 26B show the polarization state of the light on the light incident / exit surface Z2 on the + Z side of the birefringent plate 17. FIG. 24 to FIG. 26C show the polarization state of light on the light incident / exit surface Z <b> 3 on the −Z side of the birefringent plate 19. FIG. 24 to FIG. 26 (d) show the polarization state of light on the light incident / exit surface Z 4 on the + Z side of the birefringent plate 19. 24 to 26, for easy understanding, the birefringent plate 17, the Faraday rotator 20, and the birefringent plate 19 are viewed in the −Z direction, and the reflecting plates 36a and 36b are disposed in the −Y direction. It is schematically shown together with the seen state.

  FIG. 24 shows light that enters from the light incident / exit port P1 and exits to the outside from the light incident / exit port P2, as indicated by the solid line in FIG. As shown on the left side of FIG. 24A, the light L <b> 121 incident from the light incident / exit port P <b> 1 enters the birefringent plate 17. As shown on the left side of FIG. 24B, the light L121 is separated into the ordinary light L122a and the extraordinary light L122b shifted in the + X direction and emitted from the birefringent plate 17. The ordinary light component light L 122 a is incident on the magnetic domain B of the Faraday rotator 20, and the extraordinary light component light L 122 b is incident on the magnetic domain A of the Faraday rotator 20. For example, the Faraday rotation angle of the magnetic domain A of the Faraday rotator 20 is + 45 ° with respect to the Z axis when viewed in the −Z direction, and the Faraday rotation angle of the magnetic domain B is −45 ° with respect to the Z axis when viewed in the −Z direction. As shown on the left side of FIG. 24C, the light L122a is emitted from the Faraday rotator 20 as light L123a whose polarization direction is rotated 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and the light L122b is polarized. The light is emitted from the Faraday rotator 20 as light L123b whose azimuth is rotated 45 ° clockwise. Thereby, the polarization azimuth | direction of light L123a, L123b becomes perpendicular | vertical to the plane formed by the straight line parallel to the advancing direction of light L123a, L123b, and the straight line parallel to the optical axis of the birefringent plate 19 intersecting. Lights L123a and L123b are incident on one surface of the birefringent plate 19 as ordinary light, and as shown on the left side of FIG. 24 (d), light L124a and L124b are transmitted from the other surface of the birefringent plate 19 without being misaligned. Exit. The lights L124a and L124b are reflected by the reflecting plates 36a and 36b, and enter the other surface of the birefringent plate 19 as light L125a and L125b whose optical paths are changed, respectively, as shown on the right side of FIG.

  As shown on the right side of FIG. 24C, the lights L125a and L125b are emitted as light L126a and L126b from one surface of the birefringent plate 19 without being misaligned. The light L 126 a is incident on the magnetic domain B of the Faraday rotator 20, and the light L 126 b is incident on the magnetic domain A of the Faraday rotator 20. Here, the magnetic domain B where the light L126a is incident is formed in the same region as the magnetic domain B where the light L122a is incident, and the magnetic domain A where the light L126b is incident is formed in a region different from the magnetic domain A where the light L122b is incident. Has been. As shown on the right side of FIG. 24 (b), the light L126a is emitted from the Faraday rotator 20 as light L127a rotated 45 ° counterclockwise with respect to the Z axis when the polarization direction is seen in the −Z direction, and the light L126b is polarized. The light is emitted from the Faraday rotator 20 as light L127b whose azimuth is rotated 45 ° clockwise. The lights L127a and L127b respectively enter the birefringent plate 17, the light L127a passes through the birefringent plate 17 as extraordinary light, and the light L127b passes through the birefringent plate 17 as ordinary light. As shown on the right side of FIG. 24A, the light L127a is offset in the −X direction and combined with the light L127b, and is emitted from the birefringent plate 17 as light L128. The light L128 enters the light incident / exit port P2 and exits to the outside.

  FIG. 25 shows light that enters from the light incident / exit port P2 and exits to the outside from the light incident / exit port P3, like a light beam indicated by a broken line in FIG. As shown on the right side of FIG. 25A, the light L131 incident from the light incident / exit port P2 enters the birefringent plate 17. As shown on the right side of FIG. 25 (b), the light L 131 is separated into the ordinary light L 132 a and the extraordinary light L 132 b shifted in the + X direction, and is emitted from the birefringent plate 17. The ordinary light component light L 132 a is incident on the magnetic domain A of the Faraday rotator 20, and the extraordinary light component light L 132 b is incident on the magnetic domain B of the Faraday rotator 20. As shown on the right side of FIG. 25 (c), the light L132a is emitted from the Faraday rotator 20 as light L133a rotated in the clockwise direction by 45 ° with respect to the Z axis as viewed in the −Z direction, and the light L132b is polarized. Is emitted from the Faraday rotator 20 as light L133b rotated 45 ° counterclockwise. Thereby, the polarization directions of the lights L133a and L133b are parallel to a plane formed by intersecting a straight line parallel to the traveling direction of the lights L133a and L133b and a straight line parallel to the optical axis of the birefringent plate 19. The lights L133a and L133b are incident on one surface of the birefringent plate 19 as extraordinary light, and are offset in both the −X and + Y directions as shown on the right side of FIG. 19 is emitted as light L134a and L134b from the other surface. The lights L134a and L134b are reflected by the reflecting plates 36b and 36a, and enter the other surface of the birefringent plate 19 as the lights L135a and L135b whose optical paths are changed, respectively, as shown on the left side of FIG.

  As shown on the left side of FIG. 25 (c), the lights L135a and L135b are offset in both directions of the + X direction and the −Y direction, and are emitted as light L136a and L136b from one surface of the birefringent plate 19. The light L136a is incident on the magnetic domain A of the Faraday rotator 20, and the light L136b is incident on the magnetic domain B of the Faraday rotator 20. Here, the magnetic domain A in which the light L136a is incident is formed in a region different from the magnetic domain A in which the light L132a is incident, and the magnetic domain B in which the light L136b is incident is in a region different from the magnetic domain B in which the light L132b is incident. Is formed. As shown on the left side of FIG. 25 (b), the light L136a is emitted from the Faraday rotator 20 as light L137a rotated in the clockwise direction by 45 ° with respect to the Z axis as viewed in the −Z direction, and the light L136b is polarized. Is emitted from the Faraday rotator 20 as light L137b rotated 45 ° counterclockwise. The lights L137a and L137b are incident on the birefringent plate 17, respectively, the light L137a passes through the birefringent plate 17 as extraordinary light, and the light L137b passes through the birefringent plate 17 as ordinary light. As shown on the left side of FIG. 25A, the light L137a is shifted in the -X direction and combined with the light L137b, and is emitted from the birefringent plate 17 as light L138. The light L138 enters the light incident / exit port P3 disposed next to the light incident / exit port P1 and exits to the outside.

  FIG. 26 shows light that enters from the light incident / exit port P3 and exits to the outside from the light incident / exit port P4, like a light beam indicated by a one-dot chain line in FIG. As shown on the left side of FIG. 26A, the light L141 incident from the light incident / exit port P3 enters the birefringent plate 17. As shown on the left side of FIG. 26B, the light L141 is separated into the ordinary light L142a and the extraordinary light L142b shifted in the + X direction and emitted from the birefringent plate 17. The ordinary light component light L 142 a is incident on the magnetic domain B of the Faraday rotator 20, and the extraordinary light component light L 142 b is incident on the magnetic domain A of the Faraday rotator 20. As shown on the left side of FIG. 26 (c), the light L142a is emitted from the Faraday rotator 20 as light L143a whose polarization orientation is rotated 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and the light L142b is polarized. The light is emitted from the Faraday rotator 20 as light L143b whose azimuth is rotated 45 ° clockwise. Thereby, the polarization directions of the lights L143a and L143b are perpendicular to a plane formed by intersecting a straight line parallel to the traveling direction of the lights L143a and L143b and a straight line parallel to the optical axis of the birefringent plate 19. Lights L143a and L143b are incident on one surface of the birefringent plate 19 as ordinary light, and light L144a and L144b are transmitted from the other surface of the birefringent plate 19 as shown on the left side of FIG. Exit. The lights L144a and L144b are reflected by the reflecting plates 36a and 36b, and enter the other surface of the birefringent plate 19 as light L145a and L145b whose optical paths are changed as shown on the right side of FIG.

  As shown on the right side of FIG. 26 (c), the light beams L145a and L145b are emitted as light beams L146a and L146b from one surface of the birefringent plate 19 without being misaligned. The light L146a is incident on the magnetic domain B of the Faraday rotator 20, and the light L146b is incident on the magnetic domain A of the Faraday rotator 20. Here, the magnetic domain B in which the light L146a is incident is formed in a region different from the magnetic domain B in which the light L142a is incident, and the magnetic domain A in which the light L146b is incident is in a region different from the magnetic domain A in which the light L142b is incident. Is formed. As shown on the right side of FIG. 26B, the light L146a is emitted from the Faraday rotator 20 as light L147a whose polarization direction is rotated 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and the light L146b is polarized. The light is emitted from the Faraday rotator 20 as light L147b whose azimuth is rotated 45 ° clockwise. The lights L147a and L147b are respectively incident on the birefringent plate 17, the light L147a passes through the birefringent plate 17 as extraordinary light, and the light L147b passes through the birefringent plate 17 as ordinary light. As shown on the right side of FIG. 26A, the light L147a is shifted in the -X direction and combined with the light L147b, and is emitted from the birefringent plate 17 as light L148. The light L148 enters the light incident / exit port P4 disposed next to the light incident / exit port P2, and exits to the outside.

  Thus, in the reflective optical circulator 5 according to the present embodiment, the input light from the light incident / exit port P1 is output from the light incident / exit port P2, and the input light from the light incident / exit port P2 is the light incident / exit port P3. The input light from the light incident / exit port P3 is output from the light incident / exit port P4.

  In the present embodiment, the reflective optical circulator 5 can be configured using three optical elements (two birefringent plates 17 and 19 and one Faraday rotator 20). Therefore, according to the present embodiment, the element configuration of the reflection type optical circulator 5 becomes extremely simple, and it is easy to reduce the size and the price. Further, since the optical fibers 41, 42, 43, and 44 can be arranged in parallel and in the same plane, it is possible to form an array in which a plurality of reflective optical circulators 5 are arranged adjacent to each other in the ± Y direction, for example.

  The reflective optical circulator 5 according to the present embodiment has a configuration connected to the four light incident / exit ports P1 to P4, but is connected to three or more light incident / exit ports. It may be a configuration. For example, in the configuration connected to three light incident / exit ports, the Faraday rotator 20 may have a five-domain structure.

[Sixth Embodiment]
Next, a reflective optical component according to a sixth embodiment of the present invention will be described with reference to FIGS. FIG. 27 schematically shows the configuration of a reflective optical circulator according to this embodiment. As shown in FIG. 27, the reflective optical circulator 6 is connected to four optical fibers 41, 42, 43, 44. As in the fifth embodiment, the optical fibers 41, 42, 43, and 44 are arranged in a plane parallel to the XZ plane and are arranged substantially parallel to each other. The optical fiber 43 is arranged on the most + X side, and the optical fibers 41, 42, 44 are arranged in this order at equal intervals, for example, on the −X side of the optical fiber 43. The ends of the optical fibers 41, 42, 43, and 44 on the −Z side are indicated by four light input / output ports P1, P2, P3, and P4 (in the drawing, numbers (1) to (4), respectively). )It has become. Lenses 51, 52, 53, and 54 are fused to the + Z side ends of the optical fibers 41, 42, 43, and 44, respectively.

  A birefringent plate 17 is disposed in the + Z direction of the lenses 51, 52, 53, and 54. The birefringent plate 17 has an optical axis OA parallel to a direction tilted 45 ° counterclockwise about the Y axis when viewed in the −Y direction (in FIG. 27, the direction of the optical axis OA is a double-headed arrow). ).

  A Faraday rotator 20 is disposed in the + Z direction of the birefringent plate 17. The Faraday rotator 20 has a seven-domain structure formed by a magnetic field applied by a permanent magnet (not shown). Light that has entered through the light incident / exit port P1 and passed through the birefringent plate 17 as ordinary light enters the magnetic domain B of the Faraday rotator 20, and light that has passed through the birefringent plate 17 as extraordinary light passes through the magnetic domain of the Faraday rotator 20. It is incident on A. Light that has entered through the light incident / exit port P2 and passed through the birefringent plate 17 as ordinary light enters the magnetic domain A of the Faraday rotator 20, and light that has passed through the birefringent plate 17 as abnormal light passes through the magnetic domain of the Faraday rotator 20. It is incident on B. Light that has entered through the light incident / exit port P3 and passed through the birefringent plate 17 as ordinary light is incident on the magnetic domain B of the Faraday rotator 20, and light that has passed through the birefringent plate 17 as extraordinary light is in the magnetic domain of the Faraday rotator 20. It is incident on A. Light that has entered through the light incident / exit port P4 and passed through the birefringent plate 17 as ordinary light enters the magnetic domain A of the Faraday rotator 20, and light that has passed through the birefringent plate 17 as abnormal light passes through the magnetic domain of the Faraday rotator 20. It is incident on B.

  A half-wave plate 25 is disposed in the + Z direction of the Faraday rotator 20. The half-wave plate 25 is disposed so as to rotate the polarization azimuth of the light incident in the + Z direction by 45 ° clockwise as viewed in the −Z direction. A birefringent plate 27 is disposed in the + Z direction of the half-wave plate 25. The birefringent plate 27 has an optical axis OA that is parallel to a direction tilted 45 ° clockwise with respect to the Y axis when viewed in the −Y direction. For the birefringent plate 27, an element having the same specifications as the birefringent plate 17 is used. In the + Z direction of the birefringent plate 27, reflecting plates 36a and 36b that change the optical path by two-surface reflection are arranged.

  Next, the operation of the reflective optical circulator according to this embodiment will be described. FIG. 28 to FIG. 30 are diagrams in which the polarization state of light passing through each optical element constituting the reflective optical circulator 6 is viewed in the −Z direction. (A) of FIG. 28 thru | or 30 has shown the polarization state of the light in the light entrance / exit surface Z1 of the -Z side of the birefringent plate 17, as shown in FIG. FIG. 28 to FIG. 30B show the polarization state of light on the light incident / exit surface Z2 on the + Z side of the birefringent plate 17. FIG. 28 to FIG. 30C show the polarization state of the light on the light incident / exit surface Z3 on the −Z side of the birefringent plate 27. FIG. (D) of FIG. 28 thru | or FIG. 30 has shown the polarization state of the light in the light entrance / exit surface Z4 of the + Z side of the birefringent plate 27. FIG. 28 to 30, for easy understanding, a state in which the birefringent plate 17, the Faraday rotator 20, the half-wave plate 25, and the birefringent plate 27 are viewed in the −Z direction, and the reflecting plate 36 a. , 36b are schematically illustrated together with the state when viewed in the -Y direction.

  FIG. 28 shows light that enters from the light incident / exit port P1 and exits to the outside from the light incident / exit port P2, as indicated by the solid line in FIG. As shown on the left side of FIG. 28A, the light L151 incident from the light incident / exit port P1 enters the birefringent plate 17. As shown on the left side of FIG. 28 (b), the light L 151 is separated into the ordinary light L 152 a and the extraordinary light L 152 b shifted in the + X direction and emitted from the birefringent plate 17. The ordinary light component light L152a is incident on the magnetic domain B (first Faraday rotator) of the Faraday rotator 20, and the extraordinary light component light L152b is incident on the magnetic domain A (second Faraday rotator) of the Faraday rotator 20. . For example, the Faraday rotation angle of the magnetic domain A of the Faraday rotator 20 is + 45 ° with respect to the Z axis when viewed in the −Z direction, and the Faraday rotation angle of the magnetic domain B is −45 ° with respect to the Z axis when viewed in the −Z direction. The light L152a is emitted from the Faraday rotator 20 as light whose polarization direction is rotated by 45 ° counterclockwise with respect to the Z axis when viewed in the −Z direction, and is incident on the half-wave plate 25, and the light L152a is shown in FIG. As shown on the left side of), the light is emitted as light L153a whose polarization direction is rotated by 45 ° clockwise about the Z axis when viewed in the −Z direction. The light L152b is emitted from the Faraday rotator 20 as light whose polarization direction is rotated by 45 ° clockwise with respect to the Z axis when viewed in the −Z direction, and is incident on the half-wave plate 25 and has a polarization direction of −Z. The light L153b is rotated 45 ° clockwise about the Z axis when viewed in the direction. Thereby, the polarization directions of the lights L153a and L153b are perpendicular to a plane formed by intersecting a straight line parallel to the traveling direction of the light L153a and L153b and a straight line parallel to the optical axis of the birefringent plate 27. Lights L153a and L153b are incident on one surface of the birefringent plate 27 as ordinary light, and light L154a and L154b are transmitted from the other surface of the birefringent plate 27 without being misaligned as shown on the left side of FIG. Exit. The lights L154a and L154b are reflected by the reflecting plates 36a and 36b, and enter the other surface of the birefringent plate 27 as the lights L155a and L155b whose optical paths are changed as shown on the right side of FIG.

  As shown on the right side of FIG. 28 (c), the lights L 155 a and L 155 b are emitted as light L 156 a and L 156 b from one surface of the birefringent plate 27 without being misaligned, and enter the half-wave plate 25. The light L156a is emitted from the half-wave plate 25 as light whose polarization direction is rotated by 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and further enters the magnetic domain B of the Faraday rotator 20. As shown on the right side of FIG. 28 (b), the light is emitted as light L157a whose polarization direction is rotated 45 ° counterclockwise about the Z axis when viewed in the −Z direction. The light L156b is emitted from the half-wave plate 25 as light whose polarization direction is rotated by 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and is incident on the magnetic domain A of the Faraday rotator 20 to be polarized. The light is emitted as light L157b whose azimuth is rotated 45 ° clockwise about the Z axis when viewed in the −Z direction. Here, the magnetic domain B where the light L156a is incident is formed in the same region as the magnetic domain B where the light L152a is incident, and the magnetic domain A where the light L156b is incident is formed in a region different from the magnetic domain A where the light L152b is incident. Has been. The lights L157a and L157b respectively enter the birefringent plate 17, the light L157a passes through the birefringent plate 17 as extraordinary light, and the light L157b passes through the birefringent plate 17 as ordinary light. As shown on the right side of FIG. 28A, the light L157a is shifted in the -X direction and combined with the light L157b, and is emitted from the birefringent plate 17 as light L158. The light L158 enters the light incident / exit port P2 and exits to the outside.

  FIG. 29 shows light that enters from the light incident / exit port P2 and exits to the outside from the light incident / exit port P3, as shown by a broken line in FIG. As shown on the right side of FIG. 29A, the light L161 incident from the light incident / exit port P2 enters the birefringent plate 17. As shown on the right side of FIG. 29B, the light L161 is separated into ordinary light L162a and extraordinary light L162b shifted in the + X direction, and is emitted from the birefringent plate 17. The ordinary light component light L 162 a is incident on the magnetic domain A of the Faraday rotator 20, and the abnormal light component light L 162 b is incident on the magnetic domain B of the Faraday rotator 20. The light L162a is emitted from the Faraday rotator 20 as light whose polarization direction is rotated by 45 ° clockwise with respect to the Z axis when viewed in the −Z direction, and is incident on the half-wave plate 25 as shown in FIG. As shown on the right side, the light is emitted as light L163a whose polarization direction is rotated by 45 ° clockwise about the Z axis when viewed in the −Z direction. The light L162b is emitted from the Faraday rotator 20 as light whose polarization direction is rotated by 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and is incident on the half-wave plate 25 and has a polarization direction of − It is emitted as light L163b rotated 45 ° clockwise about the Z axis when viewed in the Z direction. Thereby, the polarization directions of the lights L163a and L163b are parallel to a plane formed by intersecting a straight line parallel to the traveling direction of the lights L163a and L163b and a straight line parallel to the optical axis of the birefringent plate 27. Lights L163a and L163b are incident on one surface of the birefringent plate 27 as extraordinary light, and are shifted from the other surface of the birefringent plate 27 with an axis offset in the −X direction, as shown on the right side of FIG. The light is emitted as L164a and L164b. The lights L164a and L164b are reflected by the reflecting plates 36b and 36a, and enter the other surface of the birefringent plate 27 as the lights L165a and L165b whose optical paths are changed as shown on the left side of FIG.

  As shown on the left side of FIG. 29 (c), the lights L165a and L165b are off-axis in the + X direction and are emitted as light L166a and L166b from one surface of the birefringent plate 27 and enter the half-wave plate 25. To do. The light L166a is emitted from the half-wave plate 25 as light whose polarization direction is rotated by 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and is incident on the magnetic domain A of the Faraday rotator 20. As shown on the left side of 29 (b), the polarization azimuth is emitted as light L167a rotated 45 ° clockwise about the Z axis when viewed in the −Z direction. The light L166b is emitted from the half-wave plate 25 as light whose polarization orientation is rotated by 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and is incident on the magnetic domain B of the Faraday rotator 20 to be polarized. The light is emitted as light L167b whose azimuth is rotated by 45 ° counterclockwise about the Z axis when viewed in the −Z direction. Here, the magnetic domain A in which the light L166a is incident is formed in a region different from the magnetic domain A in which the light L162a is incident, and the magnetic domain B in which the light L166b is incident is in a region different from the magnetic domain B in which the light L162b is incident. Is formed. The lights L167a and L167b respectively enter the birefringent plate 17, the light L167a passes through the birefringent plate 17 as extraordinary light, and the light L167b passes through the birefringent plate 17 as ordinary light. As shown on the left side of FIG. 29A, the light L167a is shifted in the -X direction and combined with the light L167b, and is emitted from the birefringent plate 17 as light L168. The light L168 is incident on the light incident / exit port P3 arranged next to the light incident / exit port P1, and is emitted to the outside.

  FIG. 30 shows light that enters from the light incident / exit port P3 and exits to the outside from the light incident / exit port P4, like a light beam indicated by a one-dot chain line in FIG. As shown on the left side of FIG. 30A, the light L171 incident from the light incident / exit port P3 enters the birefringent plate 17. As shown on the left side of FIG. 30 (b), the light L 171 is separated into ordinary light L 172 a and extraordinary light L 172 b shifted in the + X direction and emitted from the birefringent plate 17. The ordinary light component light L 172 a is incident on the magnetic domain B of the Faraday rotator 20, and the extraordinary light component light L 172 b is incident on the magnetic domain A of the Faraday rotator 20. The light L172a is emitted from the Faraday rotator 20 as light whose polarization orientation is rotated by 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and is incident on the half-wave plate 25, and the light L172a in FIG. As shown on the left side of (), the light is emitted as light L173a whose polarization direction is rotated by 45 ° clockwise about the Z axis when viewed in the -Z direction. The light L172b is emitted from the Faraday rotator 20 as light whose polarization orientation is rotated by 45 ° clockwise with respect to the Z axis when viewed in the −Z direction, and is incident on the half-wave plate 25 and has a polarization orientation of −Z. It is emitted as light L173b rotated 45 degrees clockwise about the Z axis when viewed in the direction. Thereby, the polarization directions of the lights L173a and L173b are perpendicular to a plane formed by intersecting a straight line parallel to the traveling direction of the lights L173a and L173b and a straight line parallel to the optical axis of the birefringent plate 27. Lights L173a and L173b are incident on one surface of the birefringent plate 27 as ordinary light, and light L174a and L174b are transmitted from the other surface of the birefringent plate 27 as shown on the left side of FIG. Exit. The lights L174a and L174b are reflected by the reflecting plates 36a and 36b, and enter the other surface of the birefringent plate 27 as the lights L175a and L175b whose optical paths are changed as shown on the right side of FIG.

  As shown on the right side of FIG. 30 (c), the lights L 175 a and L 175 b are emitted as light L 176 a and L 176 b from one surface of the birefringent plate 27 without being misaligned, and enter the half-wave plate 25. The light L176a is emitted from the half-wave plate 25 as light whose polarization direction is rotated by 45 ° counterclockwise about the Z-axis when viewed in the −Z direction, and further enters the magnetic domain B of the Faraday rotator 20, As shown on the right side of 30 (b), the polarization direction is emitted as light L177a rotated 45 ° counterclockwise about the Z axis when viewed in the −Z direction. The light L176b is emitted from the half-wave plate 25 as light whose polarization direction is rotated by 45 ° counterclockwise about the Z axis when viewed in the −Z direction, and is incident on the magnetic domain A of the Faraday rotator 20 to be polarized. The light is emitted as light L177b whose azimuth is rotated 45 ° clockwise about the Z axis when viewed in the −Z direction. Here, the magnetic domain B into which the light L176a is incident is formed in a region different from the magnetic domain B into which the light L172a is incident, and the magnetic domain A into which the light L176b is incident is in a region different from the magnetic domain A into which the light L172b is incident. Is formed. Lights L177a and L177b respectively enter the birefringent plate 17, the light L177a passes through the birefringent plate 17 as extraordinary light, and the light L177b passes through the birefringent plate 17 as ordinary light. As shown on the right side of FIG. 30A, the light L177a is offset in the −X direction and combined with the light L177b, and is emitted from the birefringent plate 17 as light L178. The light L178 enters the light incident / exit port P4 disposed next to the light incident / exit port P2, and exits to the outside.

  Thus, in the reflective optical circulator 6 according to the present embodiment, the input light from the light incident / exit port P1 is output from the light incident / exit port P2, and the input light from the light incident / exit port P2 is output to the light incident / exit port P3. The input light from the light incident / exit port P3 is output from the light incident / exit port P4.

  In the present embodiment, the reflective optical circulator 6 is configured using four optical elements (two birefringent plates 17 and 27, one Faraday rotator 20, and one half-wave plate 25). it can. The reflection-type optical circulator 6 is an element having the same specifications as the two birefringence plates 17 and 27, although a half-wave plate 25 is newly required as compared with the reflection-type optical circulator 5 according to the fifth embodiment. Can be used. Therefore, according to the present embodiment, the element configuration of the reflective optical circulator 6 becomes extremely simple, and it is easy to reduce the size and the cost. Further, since the optical fibers 41, 42, 43, and 44 can be arranged in parallel and in the same plane, it is possible to form an array in which a plurality of reflective optical circulators 6 are arranged adjacent to each other in the ± Y direction, for example.

  The reflective optical circulator 5 according to the present embodiment has a configuration connected to the four light incident / exit ports P1 to P4, but is connected to three or more light incident / exit ports. It may be a configuration. For example, in the configuration connected to three light incident / exit ports, the Faraday rotator 20 may have a five-domain structure.

The present invention is not limited to the above embodiment, and various modifications can be made.
For example, in the above embodiment, the reflection type optical circulators 1, 1 ', 5, 6 and the reflection type optical isolators 2, 4 are exemplified as the reflection type optical components. However, the present invention is not limited to this, and the Faraday rotation is not limited thereto. It can also be applied to an optical switch by adding a mechanism for reversing the magnetization of the child 20.

  In the first and second embodiments, four light incident / exit ports are provided. However, the present invention is not limited to this, and it is of course possible to provide three or five or more light incident / exit ports. It is.

  Further, in the first to third embodiments, the lenses 51, 52, 53, 54 are provided between the optical fibers 41, 42, 43, 44 and the birefringent plates 11, 12 (or 14, 14 ′). However, the lens 51, 52, 53, 54 may not be provided, and the surface of the reflecting mirror on which the reflecting film 30 is formed may be formed in a spherical shape to have a lens function. In addition, the reflecting mirror may have a lens function and the lenses 51, 52, 53, and 54 may be provided together.

  In the above embodiment, the reflective optical circulator and the reflective optical isolator have the permanent magnets 61 and 62, but the latching type Faraday rotator 20 is manufactured using a material having a relatively high holding force. By forming a two-domain structure in advance, the reflective optical circulator and the reflective optical isolator may be configured without using the permanent magnets 61 and 62. In this case, for example, as shown in FIG. 1B, permanent magnets 61 and 62 are arranged in the vicinity of the Faraday rotator 20 to form a two-domain structure, and then the permanent magnets 61 and 62 are removed. As a result, the permanent magnets 61 and 62 are not required, and the reflective optical circulator and the reflective optical isolator can be greatly reduced in size.

  Further, in the above embodiment, a birefringent plate is used as the polarization separation / combination unit, but a polarization beam splitter or the like can also be used as the polarization separation / combination unit.

It is a figure which shows typically the structure of the reflection type optical component by the 1st Embodiment of this invention. It is a figure which shows the example of a structure of the lens which can be reduced in size. It is a figure explaining the optical axis of a birefringent plate. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical circulator. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical circulator. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical circulator. It is a figure which shows typically the structure of the reflection type optical component by the 2nd Embodiment of this invention. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical circulator. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical circulator. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical circulator. It is a figure which shows the modification of the reflection type optical component by the 2nd Embodiment of this invention. It is a figure which shows the modification of the reflection type optical component by the 2nd Embodiment of this invention. It is a figure which shows typically the structure of the reflection type optical component by the 3rd Embodiment of this invention. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical isolator. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical isolator. It is a figure explaining the problem which may arise in the reflection type optical component by the 3rd Embodiment of this invention. It is a figure explaining the problem which may arise in the reflection type optical component by the 3rd Embodiment of this invention. It is a figure which shows the modification of the reflection type optical component by the 3rd Embodiment of this invention. It is a figure which shows typically the structure of the reflection type optical component by the 4th Embodiment of this invention. It is a figure which shows arrangement | positioning of the Faraday rotator and permanent magnet of the reflection type optical component by the 4th Embodiment of this invention. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical isolator. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical isolator. It is a figure which shows typically the structure of the reflection type optical component by the 5th Embodiment of this invention. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical circulator. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical circulator. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical circulator. It is a figure which shows typically the structure of the reflection type optical component by the 6th Embodiment of this invention. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical circulator. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical circulator. It is a figure which shows the polarization state of the light which passes each optical element which comprises a reflection type optical circulator. It is a figure which shows the structure of the conventional reflection type optical circulator described in patent document 1. FIG. It is a figure which shows the structure of the other conventional reflection type optical circulator described in patent document 1. FIG. It is a figure which shows the structure of the conventional reflection type optical circulator described in patent document 2. FIG. It is a figure which shows the structure of the conventional reflection type optical circulator described in patent document 3. FIG.

Explanation of symbols

1, 1 ′, 5, 6 Reflective optical circulator 2, 2 ′, 2 ″, 4 Reflective optical isolator 11, 12, 13, 14, 14 ′, 15, 17, 19, 27 Birefringent plate 11a Emitting surface 16 Polarizing glass 18 Wedge birefringent crystal 20 Faraday rotator 22, 23, 24, 25 Half wave plate 30 Reflecting film 32 Two-sided reflector 34 Lens 36 Reflecting mirrors 36a, 36b Reflecting plates 40, 41, 42, 43, 44 Optical fibers 50, 71, 72, 73, 74 GI lens 50a End surfaces 51, 52, 53, 54 Lens 55 Ball lenses 61, 62, 63, 64, 65 Permanent magnets P1, P2, P3, P4 Light incident / exit port

Claims (22)

A first polarization separation / multiplexing unit that separates and emits light incident from the first port into first light of an ordinary light component and second light of an extraordinary light component;
A first Faraday rotator that rotates the polarization direction of the first light by 45 ° and emits it as third light;
A second Faraday rotator for rotating the polarization direction of the second light in the opposite direction by 45 ° and emitting it as a fourth light having a polarization direction substantially parallel to the polarization direction of the third light;
A first birefringent plate that transmits the third and fourth lights as either ordinary light or extraordinary light ;
A reflection unit that reflects the third and fourth light beams transmitted through the first birefringent plate and re-enters the first birefringent plate ;
The reflected by the reflecting portion of the light as the extraordinary light of the third light transmitted through the first birefringent plate and the third Faraday rotation portion, said first birefringent plate is reflected by the reflective portion And the fourth polarization separation and multiplexing that transmits the fourth light that has passed through the fourth Faraday rotator as ordinary light, combines the third and fourth lights, and emits them from the second port. And a reflection type optical circulator . The reflective optical circulator according to claim 1,
The reflection type optical circulator, wherein the first to fourth Faraday rotators are composed of the same magneto-optical element. A reflective optical circulator according to claim 1 or 2,
The first polarization separating / combining unit is configured by a second birefringent plate ,
The second polarization separating / combining portion is constituted by a third birefringent plate ,
The first and third Faraday rotators are constituted by the same region of the same magneto-optical element,
The reflection type optical circulator, wherein the second and fourth Faraday rotators are constituted by the same region of the same magneto-optical element. A reflective optical circulator according to claim 3,
The reflection type optical circulator, wherein the second and third birefringent plates are elements having the same specifications. A reflection type optical circulator according to claim 3 or 4,
The reflection type optical circulator, wherein the reflection part is a two-surface reflector. A reflective optical circulator according to claim 1 or 2,
The first and second polarization separation / multiplexing units are configured by the same birefringent plate,
The first and fourth Faraday rotators are constituted by the same region of the same magneto-optical element,
The reflection type optical circulator, wherein the second and third Faraday rotators are constituted by the same region of the same magneto-optical element. The reflective optical circulator according to claim 6 ,
Including at least one half-wave plate that rotates the polarization orientation by 90 °;
Reflective optical circulator, wherein the reflective portion is configured by a lens and the reflective film. A reflection type optical circulator according to any one of claims 3 to 7 ,
The reflection type optical circulator, wherein the first Faraday rotator and the second Faraday rotator each have a Faraday rotator having the same material composition and having opposite magnetization directions. A reflection type optical circulator according to any one of claims 3 to 7 ,
The first Faraday rotator has a magnetic domain A in which magnetization is uniformly made in one direction in a region of the Faraday rotator,
The reflection type optical circulator, wherein the second Faraday rotator has a magnetic domain B in which magnetization is uniform in a direction opposite to the magnetic domain A in the other region of the Faraday rotator. A reflective optical circulator according to claim 1 or 2,
The reflection-type optical circulator, wherein the first and second polarization separation / combining sections are formed of the same birefringent plate.   A first polarization separation / multiplexing unit that separates and emits light incident from the first port into first light of an ordinary light component and second light of an extraordinary light component;
  A first Faraday rotator that rotates the polarization direction of the first light by 45 ° and emits it as third light;
  A second Faraday rotator that rotates the polarization direction of the second light in the opposite direction by 45 ° and emits it as a fourth light having a polarization direction substantially parallel to the polarization direction of the third light;
  A polarizer having a transmission axis parallel to the polarization orientation of the third and fourth lights and transmitting the third and fourth lights;
  A reflection unit that reflects the third and fourth lights transmitted through the polarizer and re-enters the polarizer;
  The third light reflected by the reflection unit and passed through the polarizer and the third Faraday rotation unit is transmitted as abnormal light, reflected by the reflection unit, and the polarizer and the fourth Faraday rotation unit are transmitted. A second polarization separating / combining unit that transmits the passed fourth light as ordinary light, combines the third light and the fourth light, and emits the light from the second port;
  A reflective optical isolator characterized by comprising: A first polarization separation / multiplexing unit that separates and emits light incident from the first port into first light of an ordinary light component and second light of an extraordinary light component;
  A first Faraday rotator that rotates the polarization direction of the first light by 45 ° and emits it as third light;
  A second Faraday rotator that rotates the polarization direction of the second light in the opposite direction by 45 ° and emits it as a fourth light having a polarization direction substantially parallel to the polarization direction of the third light;
  A polarizer made of a birefringent plate, which separates and transmits each of the third and fourth lights into ordinary light and extraordinary light;
  A reflection unit that reflects the third and fourth lights transmitted through the polarizer and re-enters the polarizer;
  The third light reflected by the reflection unit and passed through the polarizer and the third Faraday rotation unit is transmitted as abnormal light, reflected by the reflection unit, and the polarizer and the fourth Faraday rotation unit are transmitted. A second polarization separating / combining unit that transmits the passed fourth light as ordinary light, combines the third light and the fourth light, and emits the light from the second port;
  A reflective optical isolator characterized by comprising: The reflective optical isolator according to claim 11 or 12,
  The first to fourth Faraday rotators are composed of the same magneto-optical element.
  A reflection type optical isolator characterized by the above. The reflective optical isolator according to any one of claims 11 to 13,
  The first polarization separation / combination unit is constituted by a first birefringent plate,
  The second polarization separating / combining unit is constituted by a second birefringent plate,
  The first and third Faraday rotators are constituted by the same region of the same magneto-optical element,
  The second and fourth Faraday rotators are configured by the same region of the same magneto-optical element.
  A reflection type optical isolator characterized by the above. The reflective optical isolator according to claim 14, wherein
  The first and second birefringent plates are elements having the same specifications.
  A reflection type optical isolator characterized by the above. The reflective optical isolator according to claim 14 or 15,
  The reflector is a two-sided reflector
  A reflection type optical isolator characterized by the above. The reflective optical isolator according to claim 12,
  The first polarization separation / combination unit is constituted by a first birefringent plate,
  The second polarization separating / combining unit is constituted by a second birefringent plate,
  The first and third Faraday rotators are constituted by the same region of the same magneto-optical element,
  The second and fourth Faraday rotators are constituted by the same region of the same magneto-optical element,
  The polarizer is a wedge birefringent crystal
  A reflection type optical isolator characterized by the above. The reflective optical isolator according to any one of claims 11 to 13,
  The first and second polarization separation / multiplexing units are configured by the same birefringent plate,
  The first and fourth Faraday rotators are constituted by the same region of the same magneto-optical element,
  The second and third Faraday rotators are configured by the same region of the same magneto-optical element.
  A reflection type optical isolator characterized by the above. The reflective optical isolator according to claim 18, wherein
  Including at least one half-wave plate that rotates the polarization orientation by 90 °;
  The reflection part is composed of a lens and a reflection film.
  A reflection type optical isolator characterized by the above. The reflective optical isolator according to any one of claims 14 to 19,
  The first Faraday rotator and the second Faraday rotator each have a Faraday rotator having the same material composition and having opposite magnetization directions.
  A reflection type optical isolator characterized by the above. The reflective optical isolator according to any one of claims 14 to 19,
  The first Faraday rotator has a magnetic domain A in which magnetization is uniformly made in one direction in a region of the Faraday rotator,
  The second Faraday rotator has a magnetic domain B in which magnetization is made uniform in the opposite direction to the magnetic domain A in the other region of the Faraday rotator.
  A reflection type optical isolator characterized by the above. The reflective optical isolator according to any one of claims 11 to 13,
  The first and second polarization separation / combining sections are configured by the same birefringent plate.
  A reflection type optical isolator characterized by the above.

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