JP5420388B2 - Optical module, method for manufacturing optical module, and method for adjusting optical module - Google Patents

Description

  The present invention relates to an optical module, an optical module manufacturing method, and an optical module adjustment method.

  Some optical modules for optical communication on the transmission side emit light of a specific wavelength, and have a function of modulating and outputting the light. There are cases where light emission and modulation are realized by a single element and cases where they are realized by separate elements. Patent Document 1 describes an example of an optical module in which a light emitting function and a modulation function are realized by separate elements.

  In the optical module described in Patent Document 1, two optical elements are mounted on one platform substrate, and an optical system including a lens or the like is disposed between the optical elements to realize optical coupling between the two optical elements. . In this optical system, it is a common practice to make light rays passing between lenses parallel light. By making the light beam passing between the lenses parallel light, the distance between the two optical elements can be arbitrarily set, and components can be easily arranged between the lenses. In addition, making the light beam between the two lenses parallel light has an advantage that the influence of the positional deviation of each optical element on the optical coupling efficiency is small.

  Next, alignment of the optical module for communication will be described. In an optical module for communication, it is generally performed to ensure optical coupling by adjusting the positions of a coupling lens, an optical fiber that is a light propagation medium, or both. Such an operation of adjusting the position of a component that maximizes the optical coupling efficiency or ensures a certain value or more is generally called alignment. As described above, in an optical module that optically couples two optical elements with a lens, for example, the optical element is first fixed on the platform substrate, and then the position of the lens is adjusted (alignment). It has been done to maximize the optical coupling efficiency. When the coupling optical system between two elements is composed of two lenses, for example, after fixing the first lens, the position of the second lens is adjusted (alignment) to maximize the optical coupling efficiency. Things have been done.

  By the way, after fixing an optical element such as a lens constituting the optical coupling optical system, an optical axis shift occurs due to insufficient accuracy at the time of fixing or stress in the fixing process, and the optical coupling efficiency decreases due to the shift. Sometimes. As an example of an optical system that can correct this shift and improve the optical coupling efficiency, Patent Document 2 discloses that an parallel plate is inserted between a lens and an optical element, and the inclination of the parallel plate is adjusted. An optical system capable of shifting the optical axis of the light beam is described. If the inclination of the parallel plate inserted in the optical path is changed, the optical axis of transmitted light moves in parallel, which is the principle of improving the optical coupling efficiency.

US Pat. No. 6,275,317 JP 2007-10854 A

  However, in a small optical module, a small lens with a short focal point is often used, and the distance between the lens and the optical element is often small. For example, a collimating lens with a focal length of 0.5 mm has a size of about 1 mm and is often used for a small optical module. However, since the operating distance of this lens is 0.2 mm or less, this lens and the optical element are used. It is difficult to perform alignment by changing the inclination of the parallel plate inserted between the two.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical module, an optical module manufacturing method, and an optical module adjustment method that can be easily aligned even when downsized. To do.

  In order to solve the above-described problems, an optical module according to the present invention includes a first optical element that emits light, a first lens through which outgoing light emitted from the first optical element passes, A second lens through which the outgoing light passing through the first lens passes, a second optical element to which the outgoing light passing through the second lens is optically coupled, and through the first lens. An optical path changing unit that changes an optical path of the emitted light reaching the second lens, and the first lens is separated from a position where the emitted light is emitted by a focal length of the first lens. The second lens is disposed at a position deviated from the position away from the position where the emitted light is to be optically coupled by the focal length of the second lens. The emitted light at the position where the first lens is disposed The second lens from the position where the second lens is disposed and the position where the second lens is disposed should be optically coupled with the deviation from the position where the first lens is separated from the position where it is emitted. This is characterized in that a deviation from a position separated by the focal length corresponds to this.

  The method of manufacturing an optical module according to the present invention includes a step of arranging a first optical element that emits light, and a second optical element to which light emitted from the first optical element is optically coupled. The first lens through which the emitted light emitted from the first optical element passes is shifted from a position away from a position where the emitted light is emitted by a focal length of the first lens. The outgoing light is optically coupled so that the step of placing the second lens through which the outgoing light passing through the first lens passes is optically coupled to the position where the outgoing light is to be optically coupled. The first lens is passed between the first lens and the second lens, and the step of disposing the first lens and the second lens from the position to be shifted from the position away from the position by the focal length of the second lens. And changing the optical path of the emitted light reaching the second lens. Characterized in that it comprises the steps of placing a road-changing unit.

  The optical module adjustment method according to the present invention includes a first optical element that emits light, a first lens through which outgoing light emitted from the first optical element passes, and the first lens. The second lens through which the outgoing light passes, the second optical element to which the outgoing light through the second lens is optically coupled, and the second lens through the first lens. An optical path changing unit that changes an optical path of the emitted light reaching the lens of the first lens, and the first lens is displaced from a position separated from a position where the emitted light is emitted by a focal length of the first lens. The second lens is disposed at a position shifted from a position away from a position where the emitted light is to be optically coupled by a focal length of the second lens, The emitted light at the position where one lens is disposed is emitted. The focal length of the second lens from the position where the outgoing light at the position where the second lens is disposed and the outgoing light at the position where the second lens is to be optically coupled are shifted from the position by the focal length of the first lens. The position where the outgoing light is optically coupled is changed by changing the inclination of the optical path changing unit included in the optical module included in the optical module corresponding to the deviation from the position far away from the optical axis. An optical coupling position changing procedure.

  According to the present invention, the optical axis misalignment between the second lens and the second optical element is corrected by adjusting the inclination of the optical path changing unit disposed between the first lens and the second lens. Thus, since the optical coupling efficiency can be improved, the alignment can be easily performed even if the size is reduced.

  In one embodiment of the present invention, the first lens and the second lens are mounted on different substrates.

  In this aspect, the substrate on which the first lens is mounted and the substrate on which the second lens is mounted may be mounted on different thermoelectric coolers.

  In one embodiment of the present invention, the optical path changing unit is an optical isolator.

  In one embodiment of the present invention, the optical path changing unit is a parallel plate.

  In one embodiment of the present invention, the first optical element is capable of changing a wavelength of emitted light, and splits incident light between the first lens and the second lens. A wavelength of light passing through which a branching portion is disposed, one light branched by the light branching portion passes through the second lens, and the other light branched by the light branching portion passes An optical filter whose transmittance is changed by the optical filter, and a control unit that controls the wavelength tunable light source so that the wavelength of the light emitted from the wavelength tunable light source changes according to the intensity of light passing through the optical filter. It is further provided with the feature.

It is explanatory drawing explaining an example of schematic structure of the internal structure of the optical module which concerns on one Embodiment of this invention. It is explanatory drawing explaining the adjustment principle of the optical axis in the optical module which concerns on one Embodiment of this invention. It is explanatory drawing explaining the adjustment principle of the optical axis in the optical module which concerns on one Embodiment of this invention. It is explanatory drawing explaining the adjustment principle of the optical axis in the optical module which concerns on one Embodiment of this invention. It is explanatory drawing explaining the adjustment principle of the optical axis in the optical module which concerns on one Embodiment of this invention. It is explanatory drawing explaining the adjustment principle of the optical axis in the optical module which concerns on one Embodiment of this invention. It is a figure which shows the relationship between the difference between the distance between an optical element and a lens, and a focal distance, and the shift | offset | difference from the point on the optical axis of the lens of the position which the light radiate | emitted from the optical element optically couples. It is a flowchart which shows an example of the outline | summary of the manufacturing process of the optical module which concerns on one Embodiment of this invention. It is explanatory drawing explaining an example of schematic structure of the internal structure of the optical module of a comparative example. It is explanatory drawing explaining the influence by the temperature change of TEC. It is explanatory drawing explaining the influence by the temperature change of TEC. It is explanatory drawing explaining an example of schematic structure of the internal structure of the optical module which concerns on the modification of this invention.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory diagram illustrating an example of a schematic configuration of the internal structure of the optical module 1 according to the present embodiment. FIG. 1 illustrates a state in which the internal structure of the optical module 1 according to the present embodiment is viewed from the side surface of the optical module 1.

  The optical module 1 according to the present embodiment includes, for example, two thermoelectric coolers (TEC) 12 (first TEC 12-1 and second TEC 12-2) and two platform boards 14 (first 1 platform substrate 14-1 and second platform substrate 14-2), two optical elements 16 (first optical element 16-1 and second optical element 16-2), and three lenses 18 (first Lens 18-1, second lens 18-2, and third lens 18-3), and parallel plate 20 are disposed. The optical module 1 according to this embodiment is connected to the optical fiber 22.

  A first TEC 12-1 and a second TEC 12-2 are mounted on the housing 10 of the optical module 1 shown in FIG. The first platform board 14-1 is mounted on the first TEC 12-1, and the second platform board 14-2 is mounted on the second TEC 12-2. And on the 1st platform board | substrate 14-1, the 1st optical element 16-1, the 1st lens 18-1, and the parallel plate 20 are mounted. The second lens 18-2, the second optical element 16-2, and the third lens 18-3 are mounted on the second platform substrate 14-2. The third lens 18-3 is disposed on the opposite side of the second optical element 16-2 from the position where the second lens 18-2 is disposed.

  In the optical module 1 according to the present embodiment, the first optical element 16-1 is, for example, a light source (semiconductor laser or the like) that emits light, and the second optical element 16-2 is, for example, an optical amplification function. Is an optical modulator. And in the optical module 1 which concerns on this embodiment, the emitted light from the 1st optical element 16-1 turns into the pseudo-parallel light which passes the 1st lens 18-1, and converges slightly rather than parallel light, The light passes through the parallel plate 20 and enters the second lens 18-2. Then, the light incident on the second lens 18-2 is converged and combined and incident on the second optical element 16-2. The second optical element 16-2 performs processing such as modulation and amplification on the light incident on the second optical element 16-2. And the processed light is radiate | emitted from the opposite side to the light-incident side of the 2nd optical element 16-2. The light emitted from the second optical element 16-2 is coupled and incident on the optical fiber 22 via the third lens 18-3. This light is output from the optical fiber 22 to the outside. In this way, the light emitted from the first optical element 16-1 is output from the optical fiber 22 to the outside. The optical module 1 according to this embodiment is provided with a lid 24.

  Here, the principle of this embodiment will be described.

  2A, 2B, 2C, 2D, and 2E are explanatory diagrams for explaining the principle of adjusting the optical axis in the optical module 1 according to the present embodiment. In the following description, paraxial ray approximation that does not consider the thickness of the lens 18 will be used. Further, it is assumed that the focal lengths of the first lens 18-1 and the second lens 18-2 are both f. The light traveling direction is the z-axis direction, and the downward direction in each figure is the y-axis direction. Further, the distance between the first optical element 16-1 and the first lens 18-1 is d0, the distance between the first lens 18-1 and the second lens 18-2 is d1, and the first The distance between the second lens 18-2 and the second optical element 16-2 is d2.

  FIG. 2A is a diagram illustrating a situation in which light between the first lens 18-1 and the second lens 18-2 becomes parallel light. In the example of FIG. 2A, the optical axes of the first optical element 16-1, the first lens 18-1, the second lens 18-2, and the second optical element 16-2 are on a straight line. In the example of FIG. 2A, the distance d0 between the first optical element 16-1 and the first lens 18-1 is the focal length f of the first lens 18-1. That is, the first lens 18-1 is disposed away from the first optical element 16-1 by a distance f in the positive direction of the z-axis. The distance d2 between the second lens 18-2 and the second optical element 16-2 is the focal length f of the second lens 18-2. That is, the second lens 18-2 is disposed away from the second optical element 16-2 by a distance f in the negative z-axis direction. Therefore, the light emitted from the first optical element 16-1 and passing through the first lens 18-1 becomes parallel light. The light passes through the second lens 18-2 and is optically coupled to the second optical element 16-2 disposed on the optical axis of the second lens 18-2.

  FIG. 2B is a diagram illustrating a situation where the position of the second optical element 16-2 is shifted in the positive direction of the y-axis from the situation shown in FIG. 2A. FIG. 2C shows a parallel plate 20 (thickness L, refractive index n, optical axis) between the first lens 18-1 and the second lens 18-2 in the situation shown in FIG. 2B. It is a figure explaining a mode that inclination (theta) is arranged. At this time, the light emitted from the first optical element 16-1 is shifted in the positive direction of the y axis by a distance d calculated by the following equation when passing through the parallel plate 20.

  At this time, the inclination of the optical axis of this light does not change. Therefore, the light emitted from the first optical element 16-1 enters the second lens 18-2 in parallel to the optical axis of the second lens 18-2. Therefore, the light passing through the second lens 18-2 is optically coupled to a point on the optical axis of the second lens 18-2 whose distance from the second lens 18-2 is f. As described above, in the example of FIG. 2C, even if the parallel plate 20 is tilted, the position where the emitted light from the first optical element 16-1 is optically coupled does not change. Therefore, in the situation shown in FIG. 2C, the emitted light from the first optical element 16-1 is not optically coupled to the second optical element 16-2.

  FIG. 2D shows the distance d0 between the first optical element 16-1 and the first lens 18-1 as f + δ, and the distance between the second optical element 16-2 and the second lens 18-2. It is a figure explaining the condition which made d2 into f-delta. 2E shows a parallel flat plate 20 (thickness L, refractive index n, inclination θ with respect to the optical axis) between the first lens 18-1 and the second lens 18-2 in the situation shown in FIG. 2D. It is a figure explaining the condition where is arrange | positioned. In the optical module 1 shown in FIG. 1, as in FIG. 2E, the first lens 18-1 moves from the position where the emitted light is emitted from the first optical element 16-1 to the first lens 18-1. It is arranged at a position shifted from a position separated by the focal length f (for example, a position where d0 = f + δ). Then, the second lens 18-2 is displaced from a position away from the position where the emitted light from the first optical element 16-1 is optically coupled by the focal length f of the second lens (for example, (position where d2 = f−δ).

  In the example of FIG. 2E, as in the situation shown in FIG. 2C, the light of the central optical axis of the first lens 18-1 emitted from the first optical element 16-1 passes through the parallel plate 20. , The distance d is shifted in the positive direction of the y-axis. As described above, when the outgoing light from the first optical element 16-1 passes through the parallel plate 20, the optical path is changed.

  Here, the light of the central optical axis is incident on the second lens 18-2 in parallel with the optical axis of the second lens 18-2, so that the light of the central optical axis is the second lens 18-. 2 passes through the second optical element 16-2 with a slope of d / f with respect to the positive direction of the z-axis, and the distance from the second lens 16-2 is the second lens 18-2. That is, it intersects the optical axis of the second lens 16-2 at a point separated by the focal length f. The paraxial ray imaging formula (1 / z1 + 1) showing the relationship between the exit position of the exit light (distance z1 from the lens 18) and the position where the exit light is optically coupled (distance z2 from the lens 18). / Z2 = 1 / f), the light emitted from the first optical element 16-1 is optically coupled at a distance that is approximately f-δ away from the second lens 18-2. It becomes. Therefore, the position at which the light emitted from the first optical element 16-1 is optically coupled is a position shifted by b = dδ / f from the optical axis of the second lens 18-2 in the y-axis direction.

  As described above, in the optical module 1 shown in FIG. 1, the first lens 18 from the position where the emitted light is emitted from the first optical element 16-1 at the position where the first lens 18-1 is disposed. −1 from a position separated by a focal distance f of −1 (for example, δ) and the light emitted from the first optical element 16-1 at the position where the second lens 18-2 is disposed are optically coupled. The deviation (for example, δ) from the position away from the position to be made by the focal length f of the second lens 18-2 corresponds.

  For example, the focal length f of the first lens 18-1 and the second lens 18-2 is 0.5 mm, the thickness L of the parallel plate 20 is 2 mm, the refractive index n of the parallel plate 20 is 2.0, and the first When the difference δ between the distance between the optical element 16-1 and the first lens 18-1 and the length of the focal length of the first lens 18-1 is 10 μm, the parallel plate 20 is moved twice. When tilted, the light emitted from the first optical element 16-1 is shifted by 34.9 μm in the y-axis direction when passing through the parallel plate 20. And the position where this light is optically coupled is shifted in the 0.7 μmy axis direction. As described above, in the above-described example, by tilting the parallel plate 20 at a maximum of 2 degrees, the position in the y-axis direction to be optically coupled can be corrected by a maximum of 0.7 μm.

  As described above, the light that couples the two optical elements 16 is set as pseudo-parallel light, and the inclination of the parallel plate 20 inserted in the optical path is changed, so that the convergent light by the second lens 18-2 is in the y-axis direction. The position at can be changed. That is, in the optical module 1 according to this embodiment, the optical axis deviation between the second lens 18-2 and the second optical element 16-2 is corrected by adjusting the inclination of the parallel plate 20, and the light The coupling efficiency can be improved. Further, the parallel plate 20 can be tilted with respect to any direction perpendicular to the optical axis direction (z-axis direction) of the second lens 18-2. It goes without saying that adjustment is possible even if the optical axis and the optical axis of the second optical element 16-2 are displaced in two axial directions orthogonal to the z-axis direction.

  The optical axis misalignment between the second lens 18-2 and the second optical element 16-2 is caused by insufficient accuracy at the time of fixing the second lens 18-2, deformation of components, and the like. From the ability of those skilled in the art to manufacture the optical module 1 according to the present embodiment, it is estimated that it is 1 μm or less. FIG. 3 is a diagram illustrating the relationship between the above-described value of δ and the above-described value of b. In FIG. 3, the maximum inclination (θmax) with which the parallel plate 20 can be tilted is 1 degree, 2 degrees, and 3 degrees. The relationship with the value is shown. If the maximum inclination of the parallel flat plate 20 is 3 degrees and the value of b is 0.5 μm, the value of δ may be about 5 μm. On the other hand, if the maximum inclination of the parallel plate 20 is 1 degree and the value of b is 1 μm, the value of δ is about 30 μm. Therefore, when correcting the optical axis deviation of 0.5 μm to 1 μm, it is considered that the above-mentioned value of δ should be about 5 μm to 30 μm. However, this value varies depending on the alignment accuracy between the second lens 18-2 and the second optical element 16-2, the thickness L of the parallel plate 20, and the refractive index n. Needless to say, the value of δ may not be 5 μm to 30 μm.

  Next, the outline of the manufacturing process of the optical module 1 according to the present embodiment will be described with reference to the flowchart shown in FIG. First, the first optical element 16-1 is disposed on the first platform substrate 14-1, and the second optical element 16-2 is disposed on the second platform substrate 14-2 (S101). And the 1st optical element 16-1 is light-emitted, the light which passes the 1st lens 18-1 is measured using a parallel light measuring device etc., and the light which passes the 1st lens 18-1 is parallel. The first lens 18-1 is fixed at a position where light is emitted (S102). Then, in a state where the first optical element 16-1 is caused to emit light, the second lens 18-2 is temporarily disposed on the incident-side optical axis of the second optical element 16-2, and the second optical element The position of the second lens 18-2 is adjusted and fixed so that the amount of light incident on 16-2 is maximized, that is, the optical coupling efficiency is maximized (S103). There are various fixing means for the lens 18, such as YAG welding and adhesive fixing, but they will not be described in detail here. In the step shown in S103, even if the second lens 18-2 is disposed on the second platform substrate 14-2 alone, the TEC 12 is mounted in the housing 10, and the platform substrate 14 is placed on the TEC 12. The second lens 18-2 may be disposed on the second platform substrate 14-2 in a state where is mounted.

  By fixing the first lens 18-1 and the second lens 18-2, optical coupling between the two optical elements 16 is realized. The optical axis often shifts due to the influence of the assembly process, and the optical coupling efficiency decreases. Therefore, after the mounting of the two optical elements 16 and the lens 18 that optically couples them is completed on the platform substrate 14, the parallel plate 20 is placed between the first lens 18-1 and the second lens 18-2. It is inserted on the optical path (S104) and adjusted to maximize the optical coupling efficiency to the second optical element 16-2 by changing the inclination of the parallel plate 20 (S105). As described above, in the optical module 1 according to the present embodiment, since the light beam passing between the first lens 18-1 and the second lens 18-2 becomes pseudo-parallel light, alignment is possible. Yes. The mounting of the first optical element 16-1, the second optical element 16-2, the first lens 18-1, and the second lens 18-2 is completed, and the light from the second optical element 16-2 Is emitted, the third lens 18-3 is fixed on the second platform substrate 14-2 (S106).

  When the mounting of the components on the platform substrate 14 in the housing 10 is completed, the lid 24 is attached (S107), and the first optical element 16-1 and the second optical element 16-2 are operated, and the optical fiber The position of the optical fiber 22 is adjusted so that the optical coupling at 22 is maximized, and the optical fiber 22 is fixed to the housing 10 (S108).

  Thus, the optical module 1 according to the present embodiment is assembled.

  FIG. 5 is an explanatory diagram illustrating an example of a schematic configuration of the internal structure of the optical module 1 of the comparative example. For example, in a communication optical module 1 configured by combining a light source function and a modulation function as separate optical elements 16, a lens 18 is disposed for each optical element 16, and the two optical elements 16 are arranged. Realizes optical coupling. Therefore, as shown in FIG. 5, when a common platform substrate 14 is provided in the optical module 1, the length of the platform substrate 14 in the optical axis direction is set to the length of the elements of the two optical elements 16 and the middle thereof. And the length of the optical system to be arranged. Therefore, the platform substrate 14 is longer than the optical module 1 on which the single optical element 16 is mounted.

  In the optical module 1 of the comparative example shown in FIG. 5, the emitted light from the first optical element 16-1 serving as the light source is converted into parallel light by the first lens 18-1, and this parallel light is converted into the second optical element. 16-2 is incident-coupled via the second lens 18-2. The light modulated or amplified by the second optical element 16-2 is incident and coupled to the optical fiber 22 attached to the side wall of the housing 10 via the third lens 18-3. These optical elements 16 and lenses 18 are mounted on the platform substrate 14. In the optical module 1 shown in FIG. 5, a gap is provided between the first lens 18-1 and the second lens 18-2. This gap is a margin for arranging and mounting an optical isolator (not shown) and a member for branching light to a wavelength locker for detecting a wavelength shift. In this way, the platform substrate 14 has a long dimension in the optical axis direction in order to mount the two optical elements 16, the three lenses 18, and other optical elements.

  In the optical module 1 on the transmission side, a laser element made of a semiconductor is often used as a light source element. Since the specificity of the semiconductor laser varies depending on the temperature, the semiconductor laser is often operated under a constant temperature condition using the TEC 12. In the optical module 1 having such a configuration, if there is a temperature difference on the platform substrate 14 on which the optical element is mounted, a characteristic fluctuation is caused. Therefore, the TEC 12 has a size corresponding to the platform substrate 14 so that the temperature unevenness is reduced. Often to do. In the optical module 1 shown in FIG. 5, the TEC 12 is disposed between the platform substrate 14 and the bottom surface of the housing 10, and the size thereof is slightly shorter than the length of the platform substrate 14.

  6A and 6B are explanatory diagrams for explaining the influence of the temperature change of the TEC 12. 6A and 6B show a platform board 14 on which an element (not shown) such as a laser is mounted, a TEC 12 that keeps the temperature of the platform board 14 constant, and a housing 10 on which the TEC 12 is mounted. The TEC 12 includes a low temperature side substrate 12a, a high temperature side substrate 12b, and a plurality of thermoelectric chips 12c mounted therebetween.

  The low temperature side substrate 12 a is bonded to the platform substrate 14 on which the optical element is mounted, and the high temperature side substrate 12 b is bonded to the housing 10 of the optical module 1. Then, the heat of the low temperature side substrate 12a of the TEC 12 is transported to the high temperature side substrate 12b, and the temperature of the low temperature side substrate 12a is made constant. When the temperature on the housing 10 side is low, heat transport may be reversed. Since the TEC 12 has a temperature difference between the low temperature side substrate 12a and the high temperature side substrate 12b due to its operation, a stress acts on the thermoelectric chip 12c between the low temperature side and the high temperature side due to thermal expansion. If this stress is excessive, there is a possibility that the TEC 12 may malfunction or be damaged.

  FIG. 6A is a diagram showing a situation where there is no temperature difference between the low temperature side substrate 12a and the high temperature side substrate 12b of the TEC 12. FIG. In this situation, the thermoelectric chip 12c is not deformed. FIG. 6B shows a situation where there is a temperature difference between the low temperature side substrate 12a and the high temperature side substrate 12b, and the temperature of the high temperature side substrate 12b is high. The housing 10 and the high temperature side substrate 12b are expanded by thermal expansion. The thermoelectric chip 12c is deformed as shown in FIG. 6B due to the difference in thermal expansion between the low temperature side substrate 12a and the high temperature side substrate 12b. Due to this deformation, a stress acts on the thermoelectric chip 12c. As shown in FIG. 6B, the thermoelectric chip 12c arranged on the outer side is more deformed and the stress is also larger.

  In recent years, there is a strong demand for miniaturization of the optical module 1, and the TEC 12 is also in a trend of thinning. The operating temperature conditions of the low temperature side substrate 12a and the high temperature side substrate 12b of the TEC 12 do not change so much, and the magnitude of thermal expansion of the platform substrate 14 does not change. When the thermoelectric chip 12c is shortened by making the TEC 12 thinner, the deformation per length of the thermoelectric chip 12c increases, and the stress acting on the thermoelectric chip 12c also increases. As described above, when the size of the TEC 12 is large, the stress acting on the thermoelectric chip 12c is further increased, which may lead to breakage. According to the thermal stress simulation by the inventor, when the length of the TEC 12 exceeds 10 mm, the stress at the interface between the thermoelectric chip 12c and the substrate connecting the thermoelectric chip 12c becomes large enough to cause destruction. Got. Therefore, it is difficult to apply a thin and large-sized TEC 12 in a small optical module 1 that requires a thin component.

  In the optical module 1 according to the present embodiment as shown in FIG. 1, the two optical elements 16 are separately mounted on the two platform substrates 14, thereby reducing the length of each platform substrate 14. The size of the TEC 12 provided on the platform substrate 14 may be small. As described above, the small size of the TEC 12 reduces the stress due to the difference in thermal expansion even when the TEC 12 is used under the same temperature condition. In the optical module 1 of the comparative example as shown in FIG. 5, since the platform substrate 14 is long, if the thin TEC 12 is used, the stress due to the difference in thermal expansion becomes excessive and the optical module 1 may be damaged. In the optical module 1 according to the present embodiment, since the size of the TEC 12 is reduced, the possibility of damage to the TEC 12 due to the difference in thermal expansion is reduced, and the optical module 1 having high reliability can be realized.

  However, in the optical module 1 according to the present embodiment, the optical system of the first optical element 16-1 and the optical system of the second optical element 16-2 are mounted on different platform substrates 14, The occurrence of optical axis deviation is likely to occur. Therefore, it can be said that it is important to provide a function of adjusting the optical axis between the two optical elements 16. The method for adjusting the optical module 1 used in the optical module 1 according to the present embodiment is very useful in manufacturing the optical module 1 having a configuration divided into two platform substrates 14.

  In addition, about the parallel plate 20 inserted in an intermediate | middle optical path, what is necessary is just a plate which has a fixed refractive index, but it did not prepare and mount the components only for alignment, but it shared it with other optical components. It can also be implemented.

  For example, in the case where the first optical element 16-1 serving as a light source is a laser element, if there is a return light in the first optical element 16-1, the resonance state may be disturbed, and malfunction may occur. For this reason, an optical isolator that removes the return light may be disposed on the light emitting side. The optical isolator has a configuration in which a Faraday element and a polarizing element are combined, and has a configuration in which flat plates having a certain refractive index are overlapped. An optical isolator can be used as the parallel plate 20 for alignment.

  Further, when the first optical element 16-1 has a wavelength variable function, a function of monitoring the wavelength of the emitted light from the first optical element 16-1 and feeding back the wavelength shift is required. In order to monitor the wavelength of the light emitted from the first optical element 16-1, for example, a part of the light is branched, and the filter element (for example, the transmittance of the light changes with respect to the wavelength) (for example, A method of detecting a shift in wavelength of light emitted from the first optical element 16-1 based on the intensity of the transmitted light that enters the Fabry-Perot etalon is often used in the optical module 1. A beam splitter can be used for splitting and entering light into an optical system (wavelength locker) that detects wavelength shift. A beam splitter is an optical element that branches a part of a light beam, and its structure is a transparent flat plate having a surface or a surface coated with a reflective coating. Therefore, a beam splitter that branches a light beam to the wavelength shift detection optical system can also be used as the parallel plate 20 for alignment.

  Examples of simple methods for fixing the posture of the parallel plate 20 after adjusting the inclination of the parallel plate 20 include YAG welding, solder bonding, and adhesive bonding. Among them, the YAG welding process method has a high reliability with almost no positional deviation after fixing. In the case of fixing an adhesive, since the volume of the adhesive itself varies, it is not often used for fixing an alignment target component. Here, in the optical module 1 according to the present embodiment, the practicality of the case where an adhesive is used as a method for fixing the parallel plate 20 will be examined. For example, if the volume of the adhesive that fixes the parallel plate 20 is changed by 2% after the parallel plate 20 is adjusted to be inclined by 2 degrees, the inclination of the parallel plate 20 changes by 0.04 degree. In this case, the fluctuation amount of the value of d described above is 0.26 μm, and the value of b described above is 0.01 μm. This magnitude is a fluctuation that is negligible for the coupling optical system. That is, an adhesive may be used for fixing the parallel plate 20. Fixing with an adhesive reduces the restrictions on the material of the parts, and eliminates the need for expensive equipment in the equipment for the adjustment and fixing process. Fixing with an adhesive produces the advantage of enabling the production of the optical module 1 at a low cost. Further, in solder bonding, volume variation occurs when the solder is solidified. However, as described above, the volume variation does not cause a problem, and therefore, it is possible to use solder bonding for fixing the parallel plate 20.

  The present invention is not limited to the above embodiment.

  FIG. 7 is an explanatory diagram illustrating an example of a schematic configuration of the internal structure of the optical module 1 according to a modification of the present invention. In FIG. 7, the internal structure of the optical module 1 according to a modification of the present invention is shown by showing a state viewed from above.

  On the first platform substrate 14-1, a first optical element 16-1 serving as a light source, and a first lens 18-1 for converting emitted light from the first optical element 16-1 into pseudo-parallel light. The parallel plate 20, two beam splitters 26 (first beam splitter 26-1 and second beam splitter 26-2), optical filter 28, and two light intensity detection elements 30 (first light intensity). The wavelength of light emitted from the first optical element 16-1 depends on the intensity of the light detected by the detection element 30-1 and the second light intensity detection element 30-2) and the light intensity detection element 30. And a control circuit 32 for controlling the first optical element 16-1 so as to change. A second lens 18-2, a second optical element 16-2, and a third lens 18-3 are mounted on the second platform substrate 14-2. The first optical element 16-1 has a function of changing the wavelength of the emitted light. The second optical element 16-2 has at least one function of modulation and amplification. The beam splitter 26 is a dice-type beam splitter. In FIG. 7, the description of the TEC 12, the housing 10, and the optical fiber 22 shown in FIG. 1 is omitted.

  The beam splitter 26 has a function of branching a part of transmitted light. Note that the optical module 1 illustrated in FIG. 7 may include another member that branches light instead of the beam splitter 26. The light branched by the first beam splitter 26-1 is incident on the first light intensity detection element 30-1. The light branched by the second beam splitter 26-2 enters the second light intensity detection element 30-2 via the optical filter 28. The optical filter 28 has a characteristic that the transmittance varies depending on the wavelength of transmitted light. The control circuit 32 outputs an output indicating the detection result of the light intensity at the first light intensity detection element 30-1, and an output indicating the detection result of the light intensity at the second light intensity detection element 30-2. , And comparing these detection results, the shift of the wavelength of the light emitted from the first optical element 16-1 from the desired wavelength can be detected. This shift is fed back to the first optical element 16-1, that is, the control circuit 32 controls the first optical element 16-1 so that the wavelength of the emitted light changes according to the shift. The wavelength of the light emitted from one optical element 16-1 can be set to a desired wavelength. The configuration of this optical system is called a wavelength locker, and the wavelength shift can be detected by the optical module 1 having a wavelength variable function by using the wavelength locker. Note that the wavelength locker optical system for detecting the wavelength shift is not limited to that shown in FIG. 7 and may have other configurations.

  In the optical module 1 shown in FIG. 7, as in the optical module 1 shown in FIG. 1, the light passing through the first lens 18-1 is set as pseudo-parallel light, and the inclination of the parallel plate 20 is adjusted. The optical axis shift between the second lens 18-2 and the second optical element 16-2 can be corrected to compensate for the decrease in optical coupling efficiency caused by the optical axis shift. Therefore, in assembling, the problem of a decrease in optical coupling efficiency due to an optical axis shift can be solved, and the optical module 1 can be manufactured with a high yield.

  In the modified optical module 1 as shown in FIG. 7, the wavelength of the light emitted from the first optical element 16-1 is required to be within a predetermined range. The wavelength of light emitted from the first optical element 16-1 is required to be within a predetermined range even at the start of operation such as when the power is turned on or at the timing of switching the wavelength. In a transient state in which the state changes from one state to another state, the wavelength of the light emitted from the first optical element 16-1 may not be stable, and the wavelength shift may be larger than the allowable range. is there. Here, as described above, the second optical element 16-2 having at least one of the function of modulation and amplification may be capable of blocking the light output to the optical fiber 22. Then, in the transient state, the second optical element 16-2 is set in the light non-transmission mode to block the light beam output to the outside, and the wavelength shift of the light emitted from the first optical element 16-1 during that time is blocked. Feedback is made to fall within a desired wavelength shift range, and then the second optical element 16-2 is set in a light transmission mode, so that light having a small wavelength shift can be output even if there is a transient state outside. It becomes possible.

  As described above, according to the optical module 1 according to the present embodiment and the optical module 1 of the modified example, it is possible to manufacture the optical module 1 for communication with high reliability by incorporating the two optical elements 16 with high yield. it can. Further, in the optical module 1 according to the present embodiment and the optical module 1 of the modified example, it is possible to easily align even after the assembly is finished or the use is started.

  The function sharing between the first optical element 16-1 and the second optical element 16-2 is not limited to the optical module 1 described above. For example, the first optical element 16-1 may have a light emission function and a modulation function, and the second optical element 16-2 may have an amplification function.

  Further, in the optical module 1 shown in FIG. 1 or the optical module 1 shown in FIG. 7, the distance between the first optical element 16-1 and the first lens 18-1 is set to be equal to that of the first lens 18-1. The distance between the second optical element 16-2 and the second lens 18-2 may be longer than the focal length of the second lens 18-2 by making it shorter than the focal length. . By so doing, the light passing between the first lens 18-1 and the second lens 18-2 becomes pseudo-parallel light that diverges slightly.

  Further, the optical module 1 according to the present embodiment may be applied to the optical module 1 in which the first lens 18-1 and the second lens 18-2 are mounted on one platform substrate 14.

  Further, in the optical module 1 according to the present embodiment, instead of the parallel plate 20, the first optical element 16-1 passes through the first lens 18-1 and reaches the second lens 18-2. Other members that change the optical path of the emitted light may be used.

  DESCRIPTION OF SYMBOLS 1 Optical module, 10 housing | casing, 12 thermoelectric cooler (TEC), 12a low temperature side board | substrate, 12b high temperature side board | substrate, 12c thermoelectric chip, 14 platform board | substrate, 16 optical element, 18 lens, 20 parallel plate, 22 optical fiber, 24 lid , 26 Beam splitter, 28 optical filter, 30 light intensity detecting element, 32 control circuit.

Claims (7)

A first optical element that emits light;
A first lens through which outgoing light emitted from the first optical element passes;
A second lens through which the emitted light passes through the first lens;
A second optical element to which the outgoing light passing through the second lens is optically coupled;
A third lens through which the output light of the second optical element passes;
An optical fiber into which the output light passing through the third lens is incident;
An optical path changing unit that changes the optical path of the emitted light that passes through the first lens and reaches the second lens;
The first lens is disposed at a position deviated from a position away from a position where the emitted light is emitted by a focal length of the first lens;
The second lens is disposed at a position where the emitted light is optically coupled to the second optical element, and from the position where the emitted light is to be optically coupled, the focal length of the second lens. from a distance, is arranged at a position shifted in the same direction as the direction in which the first lens is shifted,
An optical module characterized by that. The first lens and the second lens are mounted on different substrates;
The optical module according to claim 1. The substrate on which the first lens is mounted and the substrate on which the second lens is mounted are mounted on different thermoelectric coolers,
The optical module according to claim 2. The optical path changing unit is an optical isolator;
The optical module according to any one of claims 1 to 3, wherein: The optical path changing portion is a parallel plate;
The optical module according to claim 1, wherein the optical module is an optical module. The first optical element can change the wavelength of the emitted light,
Between the first lens and the second lens, a light branching unit that branches incident light is disposed,
One light branched by the light branching portion passes through the second lens,
An optical filter in which the other light branched by the light branching unit passes, and the transmittance changes depending on the wavelength of the light passing through;
A control unit that controls the wavelength tunable light source so that the wavelength of light emitted from the wavelength tunable light source changes according to the intensity of light passing through the optical filter;
The optical module according to claim 1, wherein the optical module is an optical module. Disposing a first optical element that emits light;
Disposing a second optical element to which light emitted from the first optical element is optically coupled;
After disposing the first optical element and the second optical element, the first lens through which the outgoing light emitted from the first optical element passes is moved from the position where the outgoing light is emitted to the first lens. Placing the lens at a position shifted from a position away from the focal length of one lens;
After the first lens is disposed, the second lens through which the outgoing light passing through the first lens passes is coupled to the position where the outgoing light should be optically coupled. Is disposed in a position shifted in the same direction as the direction in which the first lens is shifted from the position to be optically coupled;
After the first lens and the second lens are arranged, the exit from the first lens to the second lens through the first lens between the first lens and the second lens. Arranging an optical path changing unit for changing an optical path of the light;
The manufacturing method of the optical module characterized by including.

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