JP2005123345A - Laser emission module - Google Patents

Abstract

In a laser light emitting module having an SOA and an etalon in a resonator, a laser light emitting module capable of shortening the resonator length and having excellent characteristics is provided.
An SOA having a base substrate and an active layer waveguide formed on the main surface of the base substrate, and a light emitted from one end surface are arranged outside the one end surface of the SOA. Between the reflective wavelength tunable filter 12 that reflects, a resonator formed on the other end face of the SOA 10 and a reflective film 30 that reflects light emitted from the other end face, and between the SOA 10 and the reflective tunable filter 12 In the laser light emitting module having the etalon 36 arranged, the etalon 36 is a resonator so that the angle formed by the normal line of the first light incident / exit surface 36a and the normal line of the main surface of the base substrate 14 is an acute angle. Are inclined with respect to the optical axis.
[Selection] Figure 1

Description

  The present invention relates to a laser light emitting module, and more particularly to a laser light emitting module including an etalon in a resonator.

  Up to now, as one of lasers used as a transmission light source in a large-capacity optical network system, a semiconductor optical amplifier (SOA), a wavelength tunable filter, and a sharp comb-shaped transmission peak at a certain frequency interval are used. There is known a wavelength tunable laser module in combination with an etalon (see, for example, Patent Documents 1 and 2).

  FIG. 7 is a plan view showing a configuration of a conventional wavelength tunable laser module in which an SOA having a wide band gain characteristic and an etalon are arranged in a resonator.

  As shown in the figure, the ASE (Amplified Spontaneous Emission) light is generated, the SOA 100 that amplifies the light traveling inside the resonator, and the selective light having a predetermined wavelength among the light incident from the SOA 100 side is reflected to the SOA 100 side. The reflection type wavelength tunable filter 102 is disposed so that the end faces face each other.

  An antireflection film 104 is formed on one end face of the SOA 100 facing the reflective wavelength tunable filter 102. A reflective film 106 is formed on the other end surface of the SOA 100 facing the end surface facing the reflective wavelength tunable filter 102.

  Thus, the reflection film 106 formed on the end face of the SOA 100 and the reflective wavelength tunable filter 102 constitute a laser resonator.

  In the resonator between the SOA 100 and the reflection type wavelength tunable filter 102, light incident from the SOA 100 side out of the light traveling back and forth through the resonator is collimated into parallel light and emitted to the reflection type wavelength tunable filter 102 side. In addition, a lens 110 is provided that collects light incident from the reflective wavelength tunable filter 102 side and enters the active layer waveguide of the SOA 100. Further, an etalon 112 having a sharp comb-shaped transmission peak at a constant frequency interval is disposed between the lens 110 and the reflective wavelength tunable filter 102.

  Of the ASE light generated in the SOA 100, light having a predetermined wavelength selected by the reflective wavelength tunable filter 102 is amplified by reciprocating the resonator.

  Here, even when the filter characteristics of the reflection type tunable filter 108 are not sharp enough to select one resonator longitudinal mode, the oscillating longitudinal mode of the etalon 112 is used to select a single oscillating longitudinal mode. Is possible.

  In inserting the etalon into the resonator in the wavelength tunable laser module as shown in FIG. 7, it is necessary to prevent the reflected light from the etalon 112 from being coupled to the active layer waveguide of the SOA 100. For this reason, the etalon 112 must be inserted while being inclined with respect to the optical axis of the resonator. However, if the etalon 112 is tilted, the finesse is reduced and the insertion loss is increased.

Therefore, when the etalon 112 is disposed between the SOA 100 and the reflective variable wavelength filter 102 in order to avoid such a decrease in finesse and an increase in insertion loss due to the inclination of the etalon 112, the relationship between the SOA 100 and the etalon 112 can be reduced. The inclination of the etalon 112 is kept as small as possible by separating the distance between them.
Japanese Patent Laid-Open No. 4-99389 JP 2002-232050 A

  As described above, the conventional laser light emitting module as shown in FIG. 7 in which SOA and etalon are combined has a close proximity between SOA and etalon in order to avoid a decrease in finesse and an increase in insertion loss due to the inclination of the etalon. It was difficult to arrange. For this reason, the resonator length has become long. When the resonator length is increased, the longitudinal mode interval is narrowed, so that the competition of the longitudinal mode is likely to occur.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a laser light emitting module having excellent characteristics in which the resonator length can be shortened in a laser light emitting module having an SOA and an etalon in the resonator.

  The above-mentioned object is disposed outside the one end face side of the semiconductor optical amplifier, and is emitted from the one end face, having a base substrate and an active layer waveguide formed on the main surface of the base substrate. A resonator having a first reflecting means for reflecting the emitted light, and a second reflecting means arranged on the other end face side of the semiconductor amplifier and reflecting the light emitted from the other end face; and the semiconductor light An etalon disposed between an amplifier and the first reflecting means, and a normal line of the light incident / exit surface of the etalon on the semiconductor optical amplifier side and a normal line of the main surface of the base substrate This is achieved by a laser light emitting module characterized in that the etalon is disposed to be inclined with respect to the optical axis of the resonator so that the angle formed is an acute angle.

  Also, the object is to provide a semiconductor optical amplifier having a base substrate and an active layer waveguide formed on the main surface of the base substrate, and the one end face disposed outside the one end face side of the semiconductor optical amplifier. A resonator having a first reflecting means for reflecting the light emitted from the semiconductor amplifier, and a second reflecting means disposed on the other end face side of the semiconductor amplifier and reflecting the light emitted from the other end face; An etalon disposed between the semiconductor optical amplifier and the first reflecting means so that the base substrate is not positioned in the normal direction of the light incident / exit surface of the etalon on the semiconductor optical amplifier side The etalon is achieved by a laser light emitting module, wherein the etalon is inclined with respect to the optical axis of the resonator.

  As described above, according to the present invention, the first reflecting means that is disposed outside the one end face side of the semiconductor optical amplifier and reflects light emitted from the one end face, and the other end face side of the semiconductor amplifier are disposed. An etalon semiconductor comprising: a resonator having a second reflecting means for reflecting light emitted from the other end face; and an etalon disposed between the semiconductor optical amplifier and the first reflecting means. Since the etalon is arranged at an angle with respect to the optical axis of the resonator so that the angle formed by the normal of the light incident / exit surface on the optical amplifier side and the normal of the main surface of the base substrate is an acute angle, The influence of the reflected light at the etalon can be eliminated without reducing and increasing the insertion loss. As a result, the etalon can be arranged in the vicinity of the semiconductor optical amplifier, and the cavity length of the laser can be shortened.

  In addition, according to the present invention, since the reflective acoustooptic wavelength tunable filter is used as the wavelength tunable filter, the assembly process can be simplified, the number of optical components can be reduced, and the cost can be reduced. . Furthermore, since the resonator loss can be reduced by the amount of the unnecessary optical system, various characteristics of laser oscillation can be improved.

[First Embodiment]
A laser light emitting module according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram illustrating the structure of the laser light emitting module according to the present embodiment, FIG. 2 is a diagram illustrating the inclination of the etalon in the laser light emitting module according to the present embodiment, and FIG. 3 is a view from the reflective film side of the SOA with respect to the inclination angle of the etalon. FIG. 4 is a side view showing the reflected light on the etalon surface toward the SOA side.

  First, the structure of the laser light emitting module according to the present embodiment will be described with reference to FIGS. FIG. 1A is a plan view showing the structure of the laser light emitting module according to the present embodiment, and FIG. 1B is a side view showing the structure of the laser light emitting module according to the present embodiment.

  As shown in FIG. 1A and FIG. 1B, the SOA 10 that generates ASE light and amplifies the light traveling inside, and the selected light having a predetermined wavelength among the light incident from the SOA 10 side is the SOA 10. The reflection type wavelength tunable filter 12 that reflects to the side is disposed so that the end faces thereof face each other.

  The stacked structure of the SOA 10 has a structure as shown in FIG. For example, on the main surface of the base substrate 14 made of n-type InP, for example, a buffer layer 16 made of n-type InP, an active layer waveguide 18 having a 1.55 μm band multiple quantum well (MQW) structure, and a p-type InP, for example. A clad layer 20 is sequentially laminated. A p-type contact layer (not shown) and a p-side electrode 22 are sequentially formed on the cladding layer 20. An n-side electrode 24 is formed on the lower surface of the base substrate 14. The thickness of the SOA 10, that is, the thickness from the lower surface of the n-side electrode 24 to the upper surface of the p-side electrode 22 is, for example, 100 μm. The active layer waveguide 18 is formed at a position of, for example, about 5 μm from the upper surface of the p-side electrode 22. The SOA 10 having such a laminated structure is placed on a heat sink 26 for cooling the SOA 10.

  An antireflection film 28 is formed on one end surface of the SOA 10 that faces the reflective wavelength tunable filter 12. A reflective film 30 is formed on the other end face of the SOA 10 that faces the end face that faces the reflective wavelength tunable filter 12.

  Thus, the reflection film 30 formed on the end face of the SOA 10 and the reflective wavelength tunable filter 12 constitute a laser resonator.

  In the resonator between the SOA 10 and the reflective wavelength tunable filter 12, the light incident from the SOA 10 side out of the light traveling back and forth through the resonator is collimated into parallel light and emitted to the reflective wavelength tunable filter 12 side. In addition, a lens 34 that collects light incident from the reflective wavelength tunable filter 12 side and enters the active layer waveguide 28 of the SOA 10 is disposed. Further, an etalon 36 having a sharp comb-shaped transmission peak at a constant frequency interval is disposed between the lens 34 and the reflective wavelength tunable filter 12. The etalon 36 has a parallel plate shape made of, for example, optical glass, quartz glass, or the like, and has a first light incident / exit surface 36a from which light from the SOA 10 side is incident and light from the reflective wavelength tunable filter 12 side is emitted. And a second light incident / exit surface 36b facing substantially parallel to the first light incident / exit surface 36a on which light from the SOA 10 side is emitted and light from the reflective tunable filter 12 side is incident. Yes.

The etalon 36 has a direction in which the angle formed by the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10 becomes an acute angle (+ θ _y direction in FIG. 1B). Further, they are arranged in an inclined state with respect to the optical axis of the laser resonator. In other words, the etalon 36 is inclined with respect to the optical axis of the laser resonator so that the base substrate 14 of the SOA 10 is not positioned in the normal direction of the first light incident / exit surface 36a on the SOA 10 side of the etalon 10. Is arranged in. With such an inclination, the reflected light from the first light incident / exit surface 36 a of the etalon 36 travels in the direction opposite to the base substrate 14 with respect to the active layer waveguide 18. Incidentally, the etalon 36 is inclined in the horizontal direction and the base substrate 14 in SOA10 (FIGS. 1 (a) in ± theta _x-direction) is zero. That is, the first light incident / exit surface 36a on the SOA 10 side of the etalon 36 is orthogonal to a plane including the normal of the main surface of the base substrate 14 of the SOA 10 and the optical axis of the laser resonator. The setting of the inclination angle of the etalon 36 will be described in detail below.

  Thus, the laser light emitting module according to the present embodiment is configured.

  The laser light emitting module according to the present embodiment is the first light on the SOA 10 side so that the reflected light on the surface of the etalon 36 on the SOA 10 side travels in the direction opposite to the base substrate 14 with respect to the active layer waveguide 18. The etalon 36 is arranged in an inclined state with respect to the optical axis of the laser resonator in a direction in which the angle formed by the normal line of the incident / exit surface 36a and the normal line of the main surface of the base substrate 14 of the SOA 10 is an acute angle. The main characteristic is that That is, the main feature is that the base substrate 14 of the SOA 10 is not arranged in the direction of the normal line of the first light incident / exit surface 36a on the SOA 10 side of the etalon 10.

  The inventors of the present application inclined the etalon 36 in a direction in which the angle formed by the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10 is an acute angle. It has been experimentally confirmed that the influence of reflection on the surface of the etalon 36 can be suppressed while suppressing the inclination even when the etalon 36 is disposed in the vicinity of the SOA 10.

FIG. 2 is a side view of the vicinity of the SOA 10, the lens 34, and the etalon 36. The ASE light emitted from the end face on which the antireflection film 28 of the SOA 10 is formed is collimated into parallel light by the lens 34 and enters the etalon 36. Here, when the reflected light from the etalon 36 does not affect the SOA 10, only the ASE light is emitted from the end face on which the reflective film 30 of the SOA 10 is formed. On the other hand, when the reflected light from the etalon 36 affects the SOA 10, the reflected light component is also amplified by the SOA 10. Therefore, the optical output P _f from the end face of the reflective film 30 of SOA10 is formed, so that the increase in comparison with the case where only the ASE light is emitted.

Therefore, the direction formed by the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10 is an acute angle or an obtuse angle (in FIGS. 1B and 3). The optical output P _f was detected while tilting the etalon 36 in the indicated ± θ _y direction) to examine whether the reflected light from the etalon 36 has an effect on the SOA 10. The distance between the lens 34 and the etalon 36 is set to about 2 mm. The slope of the etalon 36 in the base substrate 14 and the horizontal direction (± theta _x direction shown in FIG. 1 (a)) is set to zero. That is, the first light incident / exit surface 36a on the SOA 10 side of the etalon 10 is in a state orthogonal to a plane including the normal of the main surface of the base substrate 14 of the SOA 10 and the optical axis of the laser resonator. Yes.

FIG. 3 is a graph showing the above experimental results. The horizontal axis represents the inclination angle θ _y of the etalon 36, and the vertical axis represents the detected light output P _f .

When the etalon 36 is inclined in a direction (−θ _y direction) in which the angle formed by the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10 is an obtuse angle, The following can be said from the graph of FIG. That is, even if increasing the inclination of the etalon 36, the light reflected by the etalon 36 is larger optical output P _f than when only the amplified ASE light is measured by SOA10.

In contrast, the etalon 36 is inclined in a direction (+ θ _y direction) in which the angle formed by the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10 is an acute angle. In this case, the following can be said from the graph of FIG. That is, by setting the angle of inclination of the etalon 36, that is, the angle formed by the normal line of the first light incident / exit surface 36a and the optical axis of the laser resonator to about 0.25 ° or more, in the graph of FIG. The optical output P _{f of the} same level as the optical output P _f level when the etalon indicated by the dotted line is not inserted is measured.

FIG. 4 is a side view showing the reflected light from the etalon 36 toward the SOA 10 side. In the drawing, an arrow with x indicates a direction in which the angle formed by the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10 is an obtuse angle (−θ _y direction). The traveling direction of the reflected light when the etalon 36 is inclined is shown. Also, the arrow marked with ○ in the figure indicates a direction (+ θ _y direction) in which the angle formed by the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10 is an acute angle. ) Shows the traveling direction of the reflected light when the etalon 36 is tilted.

When the etalon 36 is inclined in the −θ _y direction, the reflected light from the etalon 36 is positioned on the base substrate 14 side with respect to the active layer waveguide 18 of the SOA 10 as indicated by an arrow marked with x in FIG. Proceed toward. Further, in such a case, the reflected light is reflected at the interface in the SOA 10 such as the interface between the n-side electrode 24 and the base substrate 14 or the interface between the heat sink 26 and the n-side electrode 24 of the SOA 10. The layer waveguide 18 is coupled. For this reason, in the above experiment, a larger optical output _Pf is measured than in the case of only ASE light. Therefore, when the etalon 36 is tilted in the -θ _y direction, the angle at which the etalon 36 is tilted must be further increased in order to prevent the reflected light at the interface or the like in the SOA 10 from being coupled to the active layer waveguide 18. I must. In that case, however, the finesse decreases and the insertion loss increases.

On the other hand, when the etalon 36 is tilted in the + θ _y direction, the reflected light from the etalon 36 is opposite to the base substrate 14 with respect to the active layer waveguide 18 of the SOA 10 as indicated by the arrows marked with ◯ in FIG. Proceed toward the side position. Here, the thickness of the SOA 10 is about 100 μm, for example, while the active layer waveguide 18 is at a position of about 5 μm, for example, from the surface opposite to the base substrate 14. Therefore, by slightly tilting the etalon 36 to + theta _y-direction, can be reflected light from the etalon 36 is prevented from binding to the active layer waveguide 18. For this reason, in the above experiment, by tilting the etalon 36 at a slight angle of about 0.25 ° in the + θ _y direction, the optical output P _f level is almost the same as the optical output P _f level when no etalon is inserted. P _f is measured. This measurement result shows that the influence of the reflected light from the etalon 36 on the SOA 10 can be removed with a slight inclination of about 0.25 °.

Note that when tilting the etalon 36 ± theta _x-direction by fixing the tilt angle of theta _y-direction to zero to remove the influence of reflection at the similarly etalon 36 surface by tilting the - [theta] _y direction It has been confirmed that this is difficult.

As shown in the above results, the etalon is in the direction (+ θ _y direction) in which the angle between the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10 becomes an acute angle. By inclining 36, the influence of the reflected light from the etalon 36 can be removed with a slight inclination angle. Thereby, the etalon 36 can be disposed in the vicinity of the SOA 10.

  Based on the above knowledge, the laser light emitting module according to the present embodiment is configured so that the reflected light on the surface of the etalon 36 on the SOA 10 side proceeds in the direction opposite to the base substrate 14 with respect to the active layer waveguide 18. By disposing the etalon 36 in a state where the angle formed by the normal of the first light incident / exit surface 36a on the side and the normal of the main surface of the base substrate 14 of the SOA 10 is inclined, the finesse is reduced. In addition, the influence of the reflected light from the etalon 36 is eliminated without increasing the insertion loss, and the etalon 36 can be arranged in the vicinity of the SOA 10. Thereby, the distance between the SOA 10 into which the etalon 36 is inserted and the reflective wavelength tunable filter 12, that is, the resonator length can be shortened, and the total length of the laser can be shortened.

  The angle formed between the normal line of the first light incident / exit surface 36a of the etalon 36 and the optical axis of the laser resonator is, for example, 0.25 ° according to the above experimental results in order to eliminate the influence of the reflected light. The degree is sufficient.

  Next, the operation of the laser light emitting module according to the present embodiment will be described with reference to FIG.

  The ASE light generated in the active layer waveguide 18 of the SOA 10 by injecting current into the active layer waveguide 18 by the p-side electrode 22 and the n-side electrode 24 is the end face on which the antireflection film 28 is formed or the reflection film 30. It progresses toward the end surface where it was formed. The reflection film 30 reflects a part of the ASE light, and the reflected light travels toward the end surface on which the antireflection film 28 is formed.

  The ASE light traveling toward the end surface on which the antireflection film 28 is formed in this way is emitted from the end surface on which the antireflection film 28 is formed.

  The ASE light emitted from the end surface on which the antireflection film 28 of the SOA 10 is formed is collimated by the lens 34 into parallel light. The ASE light collimated into parallel light by the lens 34 passes through the etalon 36 and then enters the reflective wavelength tunable filter 12. When the ASE light is transmitted through the etalon 36, the etalon 36 is inclined in a direction in which the angle formed by the normal line of the first light incident / exit surface 36a and the normal line of the main surface of the base substrate 14 of the SOA 10 becomes an acute angle. Thus, the reflected light from the etalon 36 is not coupled to the active layer waveguide 18 of the SOA 10.

  In the reflection-type wavelength tunable filter 12, only the selection light having a predetermined wavelength is reflected from the incident ASE light, and proceeds toward the SOA 10. By controlling the wavelength of the selective light reflected by the reflective wavelength tunable filter 12, the oscillation wavelength of the laser can be controlled.

  The selection light reflected by the reflection type wavelength tunable filter 12 passes through the etalon 36, is collected by the lens 34, and enters the active layer waveguide 18 of the SOA 10.

  The selective light incident on the active layer waveguide 18 is amplified by traveling through the active layer waveguide 18, and a part thereof is reflected by the reflective film 30. This reflected light is emitted again from the end surface on which the antireflection film 28 of the SOA 10 is formed.

  In this way, the selected light having a predetermined wavelength selected by the reflective wavelength tunable filter 12 reciprocates between resonators constituted by the reflective film 30 of the SOA 10 and the reflective wavelength tunable filter 12. At this time, the selection light is amplified while traveling in the active layer waveguide 18 of the SOA 10. Laser oscillation is thus obtained. This laser oscillation becomes a single longitudinal mode oscillation due to the transmission characteristics of the etalon 36 inserted in the resonator.

  The laser beam thus obtained is emitted from the end face on which the reflective film 30 of the SOA 10 is formed.

  As described above, according to the present embodiment, the angle of the laser between the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10 is an acute angle. Since the etalon 36 is disposed in an inclined state with respect to the optical axis of the resonator, the influence of the reflected light from the etalon 36 is eliminated without causing a decrease in finesse and an increase in insertion loss, and the etalon 36 is disposed in the vicinity of the SOA 10. It becomes possible to do. As a result, the distance between the SOA 10 into which the etalon 36 is inserted and the reflective wavelength tunable filter, that is, the resonator length can be shortened, and the total length of the laser can be shortened.

[Second Embodiment]
A laser light emitting module according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a plan view showing the structure of a laser emission module having an SOA and an etalon using AOTF as a wavelength tunable filter, and FIG. 6 is a schematic view showing the structure of the laser emission module according to the present embodiment. In addition, the same code | symbol is attached | subjected to the component same as the laser light emission module by 1st Embodiment, and description is abbreviate | omitted or simplified.

  The basic configuration of the laser light emitting module according to the present embodiment is substantially the same as that of the laser light emitting module according to the first embodiment. The laser light emitting module according to the present embodiment is an acoustic optical wavelength tunable filter (Acousto-Optic Tunable Filter: AOTF) that performs wavelength selection of incident light by the acoustooptic effect as the reflective wavelength tunable filter 12 in the laser light emitting module according to the first embodiment. ).

  Conventionally, in a laser light emitting module including an SOA and an etalon in a resonator, an AOTF is used as a wavelength tunable filter. FIG. 5 is a plan view showing the structure of a laser light emitting module using AOTF as a wavelength tunable filter. Since the AOTF can have a transmission type structure, in this laser light emitting module, the transmission type AOTF is disposed between the SOA and the etalon.

  As shown in FIG. 5, a mirror 38 is arranged to face one end face of the SOA 10. An antireflection film 28 is formed on one end face of the SOA 10 facing the mirror 38. A reflective film 30 is formed on the other end face of the SOA 10 facing the end face facing the mirror 38. The reflective film 30 of the SOA 10 and the mirror 38 constitute a laser resonator.

  An etalon 36 is disposed between the SOA 10 and the mirror 38.

  Between the SOA 10 and the etalon 36, a transmission type AOTF 40 as a wavelength tunable filter that transmits selective light of a predetermined wavelength is disposed.

  Between the SOA 10 and the transmissive AOTF 40, a lens group (lenses 42 and 44) for optically coupling the active layer waveguide of the SOA 10 and one port of the transmissive AOTF 40 is disposed.

  Between the other port of the transmission type AOTF 40 and the etalon 36, the light emitted from the other port of the transmission type AOTF 40 is collimated into parallel light and emitted to the etalon 38 side, and is reflected by the mirror 38 and reflected by the etalon. A lens 46 that collects the light transmitted through 36 and collects and enters the port of the transmission type AOTF 40 is disposed.

  By inserting the transmission type AOTF 40 between the SOA 10 and the etalon 36 as described above, the SOA 10 and the etalon 36 can be arranged at a distance. For example, the distance between the SOA 10 and the etalon 36 can be about 50 mm, for example. Therefore, the etalon 36 required for preventing the reflected light from the etalon 36 from being coupled to the resonator may be a minute one having an inclination angle of about 0.3 °. Thereby, it is possible to suppress a decrease in finesse and an increase in insertion loss due to the inclination of the etalon 36.

  However, in the laser light emitting module in which the transmission type AOTF 40 shown in FIG. 5 is arranged between the SOA 10 and the etalon 36, when assembling each component, first, the step of adjusting the coupling between the SOA 10 and the transmission type AOTF 40 is performed. Necessary. Furthermore, a step of adjusting the lens 46 for collimating the selection light by the transmission type AOTF 40 and the optical system including the mirror 38 used as the resonator end is required. For this reason, the laser light emitting module shown in FIG. 5 has a drawback that it takes time to assemble and the cost increases. In addition, a large number of optical components also causes an increase in cost. Furthermore, the total resonator loss increases by the amount of loss that occurs when reciprocating these optical systems. When the resonator loss increases, various characteristics of the laser deteriorate, such as an increase in the oscillation threshold current.

  Compared with the laser light emitting module using the transmission type AOTF, the laser light emitting module according to the present embodiment uses a reflection type AOTF as a wavelength tunable filter instead of the transmission type AOTF, thereby simplifying the assembly process. At the same time, the cost is reduced by reducing the number of optical components, and the resonator loss is reduced to realize excellent laser characteristics. Hereinafter, the laser light emitting module according to the present embodiment will be described in detail.

  First, the structure of the laser light emitting module according to the present embodiment will be described with reference to FIG. FIG. 6A is a plan view showing the structure of the laser light emitting module according to the present embodiment, and FIG. 6B is a side view showing the structure of the laser light emitting module according to the present embodiment.

  As shown in FIGS. 6A and 6B, the SOA 10 and a reflective AOTF 48 as a reflective wavelength tunable filter that emits selective light of a predetermined wavelength to the SOA 10 side out of the light incident from the SOA 10 side are mutually connected. It arrange | positions so that an end surface may oppose. Between the SOA 10 and the reflective AOTF 48, as in the laser light emitting module according to the first embodiment, the normal of the first light incident / exit surface 36a on the SOA 10 side and the normal of the main surface of the base substrate 14 of the SOA 10 are The etalon 36 is disposed in an inclined state with respect to the optical axis of the laser resonator so that the formed angle is an acute angle.

  Between the SOA 10 and the etalon 36, the light incident from the SOA 10 side is collimated into parallel light and emitted to the etalon 36 side, and the light incident from the etalon 36 side is condensed on the active layer waveguide 18 of the SOA 10. The incident lens 50 is arranged.

  Between the etalon 36 and the reflective AOTF 48, the light incident from the etalon 36 side is condensed and incident on one port of the reflective AOTF 48, and the light emitted from one port of the reflective AOTF 48 is reflected. A lens 52 that collimates the parallel light and emits it to the etalon 36 side is disposed.

  Here, the structure of the reflective AOTF 48 will be described with reference to FIG.

  Near the center of the substrate 54, a polarization beam splitter (PBS) 56 as a mode splitter is provided. Optical waveguides 58a and 58b formed in parallel with each other are formed on the substrate 54 on the SOA 10 side of the PBS 56, respectively. The end portions of the optical waveguides 58a and 58b are positioned at one end of the substrate 54 facing the SOA 10, respectively. On the opposite side of the PBS 56 from the SOA 10, optical waveguides 60a and 60b are formed on the substrate 54 in parallel with each other. The end portions 60 a and 60 b of the optical waveguide are respectively located at the other end of the substrate 54.

  The optical waveguide 58a is provided with a PBS 62 as a mode branching device, and one end side portion and the other end side portion of the substrate 54 of the optical waveguide 58a are formed so as to be positioned on the cross side of the PBS 62, respectively. Yes.

  Further, on the optical waveguide 58 a between the PBS 62 and the PBS 56, a comb-shaped electrode 64 that generates a surface acoustic wave (SAW) having a predetermined frequency, and the SAW generated by the comb-shaped electrode 64 is optically waveguided. A SAW guide 66 for propagating along 58a is provided. An AC power supply 68 that applies an RF signal to the comb electrode 64 is connected to the comb electrode 64. Thus, the comb-shaped electrode 64 and the SAW guide 66 constitute a mode conversion unit 70 that mode-converts a light component centered on a predetermined wavelength.

  Further, the optical waveguide 60a is provided with a comb electrode 72 that generates SAW of a predetermined frequency, and a SAW guide 74 for propagating the SAW generated by the comb electrode 72 along the optical waveguide 60a. . An AC power supply 68 that applies an RF signal to the comb electrode 72 is connected to the comb electrode 72. Thus, the comb-shaped electrode 72 and the SAW guide 74 constitute a mode conversion unit 76 that mode-converts a light component centered on a predetermined wavelength.

Further, the optical waveguide 60a between the mode conversion unit 76 and the other end of the substrate 54 is provided with a PBS 78 as a mode branching device, and one end side portion and the other end side portion of the substrate 54 of the optical waveguide 60a are provided. Are formed so as to be positioned on the cross sides of the PBS 78. One end of an optical waveguide 79 formed on the substrate 54 is connected to the other end of the substrate 78 of the PBS 78. The other end of the optical waveguide 79 is located at the other end of the substrate 54, and is a non-selected light port _Pu1 from which non-selected light other than the selected light having a predetermined wavelength is output.

The end portion of the optical waveguide 60a located at the other end of the substrate 54 is a selection light port P _{s from} which selection light having a selected predetermined wavelength is output. A reflective film 80 for reflection is formed.

On the other hand, the end portion of the optical waveguide 60b located at the other end of the substrate 54 is a non-selected light port _Pu2 through which non-selected light other than the selected light having a predetermined wavelength is output.

  With respect to the reflective AOTF 48 having the above-described structure, light from the SOA 10 side is incident on one end of an optical waveguide 58a in which the PBS 62 and the mode conversion unit 70 are provided. The reflective film 30 of the SOA 10 and the reflective film 80 provided at the end of the optical waveguide 60a constitute a laser resonator.

  Thus, the laser light emitting module according to the present embodiment is configured.

  In the laser light emitting module according to the present embodiment, the angle formed between the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10 is the same as the laser light emitting module according to the first embodiment. Has an etalon 36 disposed so as to be inclined with respect to the optical axis of the laser resonator, and further has a reflection type AOTF 48 as a wavelength tunable filter for selecting a selection light of a predetermined wavelength. There is a main feature.

  As in the laser light emitting module according to the first embodiment, the angle between the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10 is inclined in an acute angle direction. By disposing the etalon 36, it is possible to remove the influence of the reflected light from the etalon 36 without lowering finesse and increasing insertion loss, and to dispose the etalon 36 in the vicinity of the SOA 10. As a result, the distance between the SOA 10 into which the etalon 36 is inserted and the reflective AOTF 48, that is, the resonator length, can be shortened, and the total length of the laser can be shortened.

  Further, by using a reflective AOTF 48 instead of the transmissive AOTF 40 shown in FIG. 5 as a wavelength tunable filter, a mirror 46 serving as a resonator end and a lens 46 for collimating the selection light required when the transmissive AOTF 40 is used. 38 can be omitted. Therefore, in the optical axis adjustment at the time of assembly, it is only necessary to adjust the coupling between the SOA 10 and the reflective AOTF 48. Therefore, as compared with the case where the transmission type AOTF 40 shown in FIG. 5 is used, the assembly process is simplified, and the number of optical components is reduced, so that the cost can be reduced. Furthermore, since the resonator loss can be reduced by an amount corresponding to the unnecessary optical system, various characteristics of laser oscillation can be improved, for example, the oscillation threshold current can be reduced.

  Next, the operation of the laser light emitting module according to the present embodiment will be described with reference to FIG.

  As in the laser light emitting module according to the first embodiment, the ASE light emitted from the end surface of the SOA 10 on which the antireflection film 28 is formed is collimated into parallel light by the lens 34 and then passes through the etalon 36. At this time, as in the laser light emitting module according to the first embodiment, the etalon 36 has an acute angle formed between the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10. Therefore, the reflected light from the etalon 36 is not coupled to the active layer waveguide 18 of the SOA 10.

  The ASE light that has passed through the etalon 36 is collected by the lens 52 and is incident on one end of the optical waveguide 58 a of the reflective AOTF 48.

  The light incident on the optical waveguide 58 a first passes through the PBS 62, and only the TE mode component is guided to the mode conversion unit 70.

  In the mode conversion unit 70, by applying an RF signal to the comb electrode 64, a SAW having a frequency corresponding to the frequency of the RF signal is generated. The generated SAW is propagated along the optical waveguide 58 a by the SAW guide 66. The SAW propagating through the SAW guide 66 interacts with the light propagating through the optical waveguide 58a, and a component centered on a predetermined wavelength is converted into the TM mode.

The light component converted into the TM mode is guided by the PBS 56 to the mode conversion unit 76 of the optical waveguide 60a. On the other hand, the light component that is not converted into TM mode is guided to the optical waveguide 60b by PBS56, and is emitted from the end portion of the optical waveguide 60b is a non-selective optical port _{P u2.}

  In the mode conversion unit 76, by applying an RF signal to the comb-shaped electrode 72, a SAW having a frequency corresponding to the frequency of the RF signal is generated. The generated SAW is propagated along the optical waveguide 60 a by the SAW guide 74. The SAW propagating through the SAW guide 74 interacts with the light propagating through the optical waveguide 60a, and a component in a narrower wavelength band centered on the predetermined wavelength selected by the previous mode converter 70 is now TE mode. Is converted to Here, by appropriately controlling the frequency of the RF signal applied to the comb electrodes 64 and 72, the wavelength component that is mode-converted by the mode converters 70 and 76 can be controlled, and the oscillation wavelength of the laser is controlled. be able to.

Light component is converted into TE mode in the mode conversion section 76, by PBS78, is separated into the optical waveguide 60a end is selective optical port P _s of the reflective film 80 is formed. On the other hand, the light component that is not converted into TE mode, emitted from the end portion of the optical waveguide 79 is a non-selective optical port P _u1 by PBS78.

Thus, of the light incident from the SOA 10, the selected light component having a predetermined wavelength and the non-selected light component are separated into different ports. The end portion of the optical waveguide 60b is a non-selective optical port _{P u2} is a port incident light from SOA10 when applying no RF signals to the comb electrodes 64 and 72 is directly emitted. The light emitted from the end of the optical waveguide 60b is used as monitor light when adjusting the optical axes of the SOA 10 and the reflective AOTF 48.

  Here, the reason why the SAW guides 66 and 74 are configured in two stages in series is to cancel the frequency shift in the TE / TM mode conversion.

Predetermined selective optical wavelengths separated in the optical waveguide 60a end is selective optical port P _s is reflected by the reflecting film 80. The selection light reflected by the reflecting film 80 propagates in the opposite direction through the propagated optical waveguides 60a and 58a, and is emitted from the end of the optical waveguide 58a to the SOA 10 side.

  The selection light emitted from the end of the optical waveguide 58a is collimated into parallel light by the lens 52, passes through the etalon 36, is collected by the lens 50, and enters the active layer waveguide 18 of the SOA 10.

  The selective light incident on the active layer waveguide 18 is amplified by traveling through the active layer waveguide 18, and a part thereof is reflected by the reflective film 30. This reflected light is emitted again from the end surface on which the antireflection film 28 of the SOA 10 is formed.

  The light emitted again from the SOA 10 enters the reflective AOTF 48, and the reflective AOTF 48 selects a predetermined wavelength in the same manner as described above.

  Thus, the selected light having a predetermined wavelength selected by the reflective AOTF 48 reciprocates between the resonators constituted by the reflective film 30 of the SOA 10 and the reflective film 80 formed at the end of the optical waveguide 60a of the reflective AOTF 48. To do. At this time, the selection light is amplified while traveling in the active layer waveguide 18 of the SOA 10. Laser oscillation is thus obtained. This laser oscillation becomes a single longitudinal mode oscillation due to the transmission characteristics of the etalon 36 inserted in the resonator.

  As described above, according to the present embodiment, the angle of the laser between the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10 is an acute angle. Since the etalon 36 is disposed in an inclined state with respect to the optical axis of the resonator, the influence of the reflected light from the etalon 36 is eliminated without causing a decrease in finesse and an increase in insertion loss, and the etalon 36 is disposed in the vicinity of the SOA 10. It becomes possible to do. As a result, the distance between the SOA 10 into which the etalon 36 is inserted and the reflective wavelength tunable filter, that is, the resonator length can be shortened, and the total length of the laser can be shortened.

  Furthermore, according to the present embodiment, since the reflective AOTF 48 is used as the wavelength tunable filter, the assembly process can be simplified, the number of optical components can be reduced, and the cost can be reduced. Furthermore, since the resonator loss can be reduced by the amount of the unnecessary optical system, various characteristics of laser oscillation can be improved.

[Modified Embodiment]
The present invention is not limited to the above embodiment, and various modifications can be made.

  For example, in the above embodiment, the case where AOTF is used as the wavelength tunable filter has been described as an example, but various wavelength tunable filters as well as AOTF can be applied to the present invention.

  In the above embodiment, the first light incident / exit surface 36a on the SOA 10 side of the etalon 36 is orthogonal to a plane including the normal of the main surface of the base substrate 14 of the SOA 10 and the optical axis of the laser resonator. However, the present invention is not necessarily limited to the case of being orthogonal, but the first light incident / exit surface 36a, the normal of the main surface of the base substrate 14 of the SOA 10, and the optical axis of the laser resonator May intersect at a predetermined angle other than 90 °.

  In the above embodiment, the case where the SOA 10 is placed on the heat sink 26 with the n-side electrode 24 facing the heat sink 26 has been described. However, the SOA 10 has the p-side electrode 22 facing the heat sink 26 and the heat sink 26 may be placed. Also in this case, with respect to the etalon 36, the angle formed by the normal line of the first light incident / exit surface 36a on the SOA 10 side and the normal line of the main surface of the base substrate 14 of the SOA 10 with respect to the base substrate 14 of the SOA 10 is used. What is necessary is just to arrange | position in the state inclined in the direction used as an acute angle.

(Appendix 1)
A semiconductor optical amplifier having a base substrate and an active layer waveguide formed on the main surface of the base substrate;
A first reflecting means that is disposed outside the one end face side of the semiconductor optical amplifier and reflects light emitted from the one end face, and is disposed on the other end face side of the semiconductor amplifier and is emitted from the other end face. A resonator having a second reflecting means for reflecting light;
An etalon disposed between the semiconductor optical amplifier and the first reflecting means;
The etalon is relative to the optical axis of the resonator so that the angle formed by the normal of the light incident / exit surface of the etalon on the semiconductor optical amplifier side and the normal of the main surface of the base substrate is an acute angle. A laser light emitting module characterized by being arranged at an angle.

(Appendix 2)
A semiconductor optical amplifier having a base substrate and an active layer waveguide formed on the main surface of the base substrate;
A first reflecting means that is disposed outside the one end face side of the semiconductor optical amplifier and reflects light emitted from the one end face, and is disposed on the other end face side of the semiconductor amplifier and is emitted from the other end face. A resonator having a second reflecting means for reflecting light;
An etalon disposed between the semiconductor optical amplifier and the first reflecting means;
The etalon is disposed so as to be inclined with respect to the optical axis of the resonator so that the base substrate is not positioned in the normal direction of the light incident / exit surface of the etalon on the semiconductor optical amplifier side. A laser emission module.

(Appendix 3)
In the laser light emitting module according to appendix 1 or 2,
The laser light emitting module, wherein the light incident / exit surface of the etalon is orthogonal to a plane including a normal line of the main surface of the base substrate and the optical axis of the resonator.

(Appendix 4)
In the laser light emitting module according to any one of appendices 1 to 3,
The laser light emitting module, wherein the first reflecting means is a wavelength tunable filter that reflects selective light having a predetermined wavelength out of light incident from the semiconductor optical amplifier side.

(Appendix 5)
In the laser light emitting module according to appendix 4,
The wavelength tunable filter is an acousto-optic wavelength tunable filter.

(Appendix 6)
In the laser light emitting module according to appendix 5,
The acousto-optic tunable filter is formed on a first port to which light is input from the semiconductor optical amplifier, a second port from which the selection light is output, and an end face of the second port, and the selection A reflective film that reflects light,
The laser light emitting module, wherein the selection light is output from the first port.

(Appendix 7)
In the laser light emitting module according to any one of appendices 1 to 6,
The laser light emitting module, wherein the second reflecting means is a reflecting film formed on the other end face of the semiconductor optical amplifier.

It is the schematic which shows the structure of the laser light emitting module by 1st Embodiment of this invention. It is a figure explaining the inclination of the etalon in the laser light emitting module by 1st Embodiment of this invention. It is a graph which shows the dependence with respect to the inclination angle of the etalon of the optical output from SOA. It is a side view which shows the laminated structure of SOA, and the reflected light from an etalon. It is a top view which shows the structure of the laser emission module which has SOA and etalon which used transmission type AOTF as a wavelength variable filter. It is the schematic which shows the structure of the laser light emission module by 2nd Embodiment of this invention. It is a top view which shows the structure of the conventional laser light emitting module which contains SOA and an etalon in a resonator.

Explanation of symbols

10 ... SOA
DESCRIPTION OF SYMBOLS 12 ... Reflection type wavelength tunable filter 14 ... Base substrate 16 ... Buffer layer 18 ... Active layer waveguide 20 ... Cladding layer 22 ... P side electrode 24 ... N side electrode 26 ... Heat sink 28 ... Antireflection film 30 ... Reflection film 34 ... Lens 36 ... Etalon 36a ... First light entrance / exit surface 36b ... Second light entrance / exit surface 38 ... Mirror 40 ... Transmission type AOTF
42, 44, 46 ... lens 48 ... reflective AOTF
50, 52 ... lens 54 ... substrate 56 ... PBS
58a, 58b ... Optical waveguide 60a, 60b ... Optical waveguide 62 ... PBS
64 ... Comb electrode 66 ... SAW guide 68 ... AC power supply 70 ... Mode converter 72 ... Comb electrode 74 ... SAW guide 76 ... Mode converter 78 ... PBS
79 ... Optical waveguide 80 ... Reflective film 100 ... SOA
DESCRIPTION OF SYMBOLS 102 ... Reflection type wavelength variable filter 104 ... Antireflection film 106 ... Reflection film 110 ... Lens 112 ... Etalon

Claims (5)

A semiconductor optical amplifier having a base substrate and an active layer waveguide formed on the main surface of the base substrate;
A first reflecting means that is disposed outside the one end face side of the semiconductor optical amplifier and reflects light emitted from the one end face, and is disposed on the other end face side of the semiconductor amplifier and is emitted from the other end face. A resonator having a second reflecting means for reflecting light;
An etalon disposed between the semiconductor optical amplifier and the first reflecting means;
The etalon is relative to the optical axis of the resonator so that the angle formed by the normal of the light incident / exit surface of the etalon on the semiconductor optical amplifier side and the normal of the main surface of the base substrate is an acute angle. A laser light emitting module characterized by being arranged at an angle. A semiconductor optical amplifier having a base substrate and an active layer waveguide formed on the main surface of the base substrate;
A first reflecting means that is disposed outside the one end face side of the semiconductor optical amplifier and reflects light emitted from the one end face, and is disposed on the other end face side of the semiconductor amplifier and is emitted from the other end face. A resonator having a second reflecting means for reflecting light;
An etalon disposed between the semiconductor optical amplifier and the first reflecting means;
The etalon is disposed so as to be inclined with respect to the optical axis of the resonator so that the base substrate is not positioned in the normal direction of the light incident / exit surface of the etalon on the semiconductor optical amplifier side. A laser emission module. The laser light emitting module according to claim 1 or 2,
The laser light emitting module, wherein the light incident / exit surface of the etalon is orthogonal to a plane including a normal line of the main surface of the base substrate and the optical axis of the resonator. The laser light emitting module according to any one of claims 1 to 3,
The laser light emitting module, wherein the first reflecting means is a wavelength tunable filter that reflects selective light having a predetermined wavelength out of light incident from the semiconductor optical amplifier side. The laser light emitting module according to claim 4, wherein
The wavelength tunable filter is an acousto-optic wavelength tunable filter.

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