JP2018107310A - Semiconductor laser module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser module with high coupling efficiency between a semiconductor laser element and a semiconductor optical amplifier.SOLUTION: A semiconductor laser module includes a semiconductor laser element for outputting laser light, a semiconductor optical amplifier that receives laser light from an input side, amplifies the laser light, and outputs the amplified laser light through an output side, and an optical coupler optically coupling the laser light output from the semiconductor laser device to the semiconductor optical amplifier, and an active core layer of the semiconductor optical amplifier has a uniform core thickness and the input side core width is different from the core width at least in the center part in the optical waveguide direction.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a semiconductor laser module.

  In recent years, multi-level modulation schemes have been studied in optical communication to increase the communication speed. As the multi-level modulation method, a coherent communication method mainly using phase shift keying (PSK) is used. In such coherent communication, a wavelength-variable semiconductor laser module (for example, μTOSA (Transmitter Optical Sub-Assembly) / μITLA (Integrable Tunable Laser Assembly)) is required for the signal light source on the transmission side and the local oscillation light source.

  In coherent communication, information is placed on the phase of light, so that the signal light source and the local oscillation light source are required to have a small phase fluctuation (that is, a small spectral line width). Further, as the configuration of the communication system becomes complicated, the semiconductor laser module is further required to have higher output and lower power consumption.

  As a method of obtaining a semiconductor laser module that outputs laser light having a low spectral line width as described above, a semiconductor laser element chip and a semiconductor optical amplifier (SOA) chip are manufactured as separate chips, and a semiconductor laser is obtained. Patent Document 1 discloses a method of optically coupling two chips using a lens or the like in a module.

Japanese Patent No. 5567226 International Publication No. 2016/053463

  However, since the semiconductor laser element and the semiconductor optical amplifier often have different mode fields, the coupling efficiency between the semiconductor laser element and the semiconductor optical amplifier may not be high simply by optically coupling with a lens. . As a method for increasing the coupling efficiency, a structure in which a semiconductor laser element or a semiconductor optical amplifier is provided with an SSC (Spot Size Converter) that is an element for converting a mode field has been studied. However, the SSC itself may have a large optical loss, and the coupling efficiency may not be improved. For this reason, it has been difficult to achieve high output and low power consumption, which are important characteristics of the wavelength tunable laser module.

  The present invention has been made in view of the above, and an object thereof is to provide a semiconductor laser module having high coupling efficiency between a semiconductor laser element and a semiconductor optical amplifier.

  In order to solve the above-described problems and achieve the object, a semiconductor laser module according to one embodiment of the present invention includes a semiconductor laser element that outputs laser light, the laser light input from an input side, A semiconductor optical amplifier that amplifies and outputs from the output side; and an optical coupler that optically couples the laser light output from the semiconductor laser element to the semiconductor optical amplifier, and an active core of the semiconductor optical amplifier The layer has a uniform core thickness, and the core width on the input side is different from the core width at least in the central portion in the longitudinal direction.

  In the semiconductor laser module according to an aspect of the present invention, the active core layer of the semiconductor optical amplifier has a core width on the input side that is wider than a core width on the center portion, and extends from the input side toward the center portion. Thus, a region where the core width is narrowed is provided at a position closer to the input side than the central portion.

  The semiconductor laser module according to one embodiment of the present invention is characterized in that the length of the region in the longitudinal direction is not less than 10 μm and not more than 200 μm.

  The semiconductor laser module according to one aspect of the present invention is characterized in that the semiconductor laser element has a configuration in which a passive waveguide portion is integrated on the output side of the laser beam.

  The semiconductor laser module according to an aspect of the present invention is characterized in that the passive waveguide section includes a bent waveguide.

  The semiconductor laser module according to an aspect of the present invention is characterized in that the passive waveguide section includes a slab emission type arrayed waveguide diffraction grating.

  The semiconductor laser module according to one aspect of the present invention is characterized in that the semiconductor laser element has a configuration in which a plurality of laser oscillation units are integrated.

  A semiconductor laser module according to an aspect of the present invention includes a base on which the semiconductor optical amplifier is mounted in a junction-down state.

  The semiconductor laser module according to an aspect of the present invention is characterized in that the active core layer of the semiconductor optical amplifier is inclined with respect to the end face on the input side on the input side of the semiconductor optical amplifier.

  The semiconductor laser module according to one aspect of the present invention is characterized in that the active core layer of the semiconductor optical amplifier is inclined with respect to the end face on the output side on the output side of the semiconductor optical amplifier.

  In the semiconductor laser module according to an aspect of the present invention, the active core layer of the semiconductor optical amplifier has a core width on the output side that is different from a core width at least in a central portion in the optical waveguide direction.

  According to the present invention, it is possible to realize a semiconductor laser module having high coupling efficiency between a semiconductor laser element and a semiconductor optical amplifier.

FIG. 1 is a schematic diagram illustrating the configuration of the semiconductor laser module according to the first embodiment. FIG. 2 is a schematic diagram showing the configuration of the semiconductor optical amplifier shown in FIG. FIG. 3 is a cross-sectional view taken along line AA in FIG. FIG. 4 is a schematic cross-sectional view in a cross section perpendicular to the longitudinal direction of the active core layer of the semiconductor optical amplifier shown in FIG. FIG. 5 is a schematic diagram illustrating a configuration of a semiconductor optical amplifier including the SSC structure of Comparative Examples 1-1 to 1-3. FIG. 6 is a diagram illustrating characteristics of Comparative Examples 1-1 to 1-3, 2-1 to 2-3, and Examples 1 to 3. FIG. 7 is a schematic diagram showing a configuration example 1 of the semiconductor laser element. FIG. 8 is a diagram showing a cross section taken along line EE, line FF, and line GG in FIG. FIG. 9 is a schematic diagram illustrating a configuration of the semiconductor laser module according to the second embodiment. FIG. 10 is a schematic diagram showing the configuration of the semiconductor optical amplifier shown in FIG. FIG. 11 is a schematic diagram illustrating another configuration example of the semiconductor optical amplifier.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, this invention is not limited by this embodiment. In the description of the drawings, the same or corresponding elements are denoted by the same reference numerals as appropriate. It should be noted that the drawings are schematic, and the relationship between the dimensions of each element, the ratio of each element, and the like may differ from the actual situation. Even between the drawings, there are cases in which portions having different dimensional relationships and ratios are included.

(Embodiment 1)
FIG. 1 is a schematic diagram illustrating the configuration of the semiconductor laser module according to the first embodiment. As shown in FIG. 1, a semiconductor laser module 1000 includes a housing 1001, bases 1002 and 1003, a semiconductor laser element 100, a collimator lens 1004, beam splitters 1005 and 1007, condenser lenses 1006 and 1011, and a photodiode (PD). 1008, 1010, an etalon filter 1009, an optical fiber 1012, and a semiconductor optical amplifier 200. The semiconductor laser module 1000 is connected to a controller.

  Each of the bases 1002 and 1003 is placed on a temperature control element (not shown) in the housing 1001. The base 1002 mounts the semiconductor laser element 100. The base 1003 is equipped with a semiconductor optical amplifier 200. The condenser lens 1011 and the optical fiber 1012 are attached to the attachment portion 1001 a of the housing 1001.

  The temperature adjustment element is, for example, a Peltier element. Each temperature adjusting element can adjust the temperature by cooling, in some cases, heating the semiconductor laser element 100 and the semiconductor optical amplifier 200 when a driving current is supplied.

  The bases 1002 and 1003 are made of aluminum nitride (AlN) having a high thermal conductivity of 170 W / m · K, for example. But you can.

  The semiconductor laser element 100 is supplied with a drive current from the controller and outputs a laser beam L1. The wavelength of the laser beam L1 is a wavelength within a wavelength band (for example, 1520 nm to 1620 nm) used for optical communication.

  The collimator lens 1004 is disposed on the front side, which is the side that outputs the laser light L <b> 1 of the semiconductor laser element 100. The collimator lens 1004 converts the laser light L1 output from the semiconductor laser element 100 into parallel light.

  The beam splitter 1005 transmits most of the laser light L1 and outputs it to the condenser lens 1006, and part of the laser light L1 (laser light L3) is branched and reflected toward the beam splitter 1007.

  The condensing lens 1006 condenses the laser light L1 output from the beam splitter 1005 and inputs it to the semiconductor optical amplifier 200. That is, the condensing lens 1006 is an optical coupler that optically couples the laser light L1 output from the semiconductor laser element 100 to the semiconductor optical amplifier 200.

  The semiconductor optical amplifier 200 amplifies the laser beam L1 input from the input side and outputs the amplified laser beam L2 from the output side. The condensing lens 1011 condenses the laser beam L2 and inputs it to the optical fiber 1012. The optical fiber 1012 transmits the laser light L2 to a predetermined device or the like.

  On the other hand, the beam splitter 1007 splits the laser light L3 into two branches, transmits one of them and outputs it to the PD 1008, and reflects the other toward the etalon filter 1009. The PD 1008 detects the intensity of the laser beam input from the beam splitter 1007 and outputs a current corresponding to the detected intensity to the controller.

  The etalon filter 1009 has a periodic transmission characteristic of light, and selectively transmits the laser light reflected by the beam splitter 1007 to the wavelength monitoring PD 1010 with a transmittance according to the transmission characteristic. input. The PD 1010 detects the intensity of the laser light transmitted through the etalon filter 1009, and outputs a current having a value corresponding to the detected intensity to the controller.

  The intensity of the laser beam detected by the PDs 1008 and 1010 is used for wavelength lock control (control for setting the laser beam L1 to a desired wavelength and intensity) by the controller.

  Next, the semiconductor optical amplifier 200 will be specifically described. FIG. 2 is a schematic diagram showing the configuration of the semiconductor optical amplifier 200. FIG. 3 is a cross-sectional view taken along line AA in FIG.

  The semiconductor optical amplifier 200 has a width of about 0.4 mm and a length of about 2 mm, and includes an active core layer 201. The active core layer 201 extends from the input side 202 to the output side 203 of the semiconductor optical amplifier 200 and has a length of about 2 mm, which is the same as that of the semiconductor optical amplifier 200. The active core layer 201 amplifies the laser beam L1 input from the input side 202 while guiding it in the longitudinal direction (optical waveguide direction), and outputs the laser beam L2 from the output side 203. Note that antireflection films are coated on both end faces of the input side 202 and the output side 203.

  As shown in FIG. 3, the semiconductor optical amplifier 200 includes an n-side electrode 200a configured to include, for example, AuGeNi and an n-type InP including a substrate in a cross section along the active core layer 201. The semiconductor layer 200b, the active core layer 201, the p-type semiconductor layer 200c made of p-type InP, the contact layer 200d, and the p-side electrode 200e composed of, for example, AuZn are stacked in this order. doing. The active core layer 201 has a multiple quantum well structure including a plurality of well layers and a plurality of barrier layers that are alternately stacked, and a lower and upper optical confinement layer that sandwich the multiple quantum well structure from above and below. ing. The well layer and the barrier layer constituting the multiple quantum well structure of the active core layer 201 are made of InGaAsP having different compositions, and the emission wavelength band of the well layer is 1.55 μm band in the first embodiment. The lower optical confinement layer is made of n-type InGaAsP. The upper optical confinement layer is made of p-type InGaAsP. The contact layer 200d is made of p-type InGaAs.

  In the semiconductor optical amplifier 200, the p-type semiconductor layer 200c is located on the base 1003 side, and the n-type semiconductor layer 200b including the growth substrate is located on the opposite side of the base 1003. It may be mounted in a junction-down state. As a result, heat generated in the active core layer 201 of the semiconductor optical amplifier 200 is easily radiated through the base 1003.

  Here, as shown in FIG. 3, the active core layer 201 of the semiconductor optical amplifier 200 has a uniform core thickness of 160 nm in the semiconductor optical amplifier 200. Further, as shown in FIG. 2, the active core layer 201 includes a main waveguide portion 201a, an input-side equal width portion 201b, and a tapered portion 201c. These portions are arranged from the input side 202 to the output side 203 in the order of the input side equal width portion 201b, the taper portion 201c, and the main waveguide portion 201a.

  The main waveguide 201a includes a central portion 201aa in the longitudinal direction of the active core layer 201, and is a portion having a constant core width. The central portion 201aa is a region located at a position of about 1 mm from each of the input side 202 and the output side 203. The core width W1 of the main waveguide portion 201a is a value that can guide light in a 1.55 μm band in a single mode, and is 2 μm in the first embodiment.

  The input-side equal width portion 201b is located on the input side 202, has a length in the optical waveguide direction of about 20 μm, and a constant core width. The core width W2 of the input side equal width portion 201b is 3 μm in the first embodiment, and is 1 μm wider than the core width W1 of the main waveguide portion 201a. That is, the core width W2 on the input side 202 of the active core layer 201 is wider than the core width W1 at the central portion 201aa. Further, since the length of the input-side equal width portion 201b is as long as about 20 μm, when the semiconductor optical amplifier 200 is formed on a semiconductor wafer and is cut into individual chips, a positional shift depending on the cutting accuracy is caused in the longitudinal direction. Even if it occurs, it is possible to prevent the input-side equal width portion 201b from being completely cut.

  The tapered portion 201c is a region where the core width gradually decreases from the input side 202 toward the central portion 201aa, and the length thereof is about 100 μm. The tapered portion 201c is located closer to the input side 202 than the central portion 201aa. The tapered portion 201c preferably has a length in the optical waveguide direction of 10 μm or more and 200 μm or less. If the length of the taper portion 201c is 10 μm or more, the taper angle does not become excessively large, so that an increase in loss due to a rapid change in the core width can be suppressed. In addition, since the taper portion 201c has a large core width, the light emission efficiency with respect to the injected current amount is low. However, if the length is 200 μm or less, the decrease in the light emission efficiency in the taper portion 201c is caused in the entire semiconductor optical amplifier 200. It becomes a level which does not become a problem with respect to luminous efficiency.

  Further, the semiconductor optical amplifier 200 shown in FIG. 1 has the structure shown in FIG. 4 in a cross section perpendicular to the longitudinal direction of the active core layer 201. That is, in the semiconductor optical amplifier 200, the embedded structure having a current blocking structure including the p-type InP buried layer 200f and the n-type InP current blocking layer 200g on both sides (left and right direction in the drawing) of the active core layer 201 having the stripe mesa structure. It has become. Further, a SiNx protective film 200h is formed on the contact layer 200d. The p-side electrode 200e is in ohmic contact with the contact layer 200d through the opening 200ha of the SiNx protective film 200h.

  In the semiconductor laser module 1000, the active core layer 201 of the semiconductor optical amplifier 200 has a uniform core thickness in the semiconductor optical amplifier 200, and the core width W2 at the input side 202 is larger than the core width W1 at the central portion 201aa. As a result, the coupling efficiency between the semiconductor laser device 100 and the semiconductor optical amplifier 200 is increased.

  This will be specifically described below. When optically coupling laser light from a semiconductor laser element to a semiconductor optical amplifier in a semiconductor laser module, the coupling efficiency to the semiconductor optical amplifier is improved by changing the image magnification of the lens. Is a general technique.

  However, the aspect ratio (aspect ratio) of the mode field of the laser light from the semiconductor laser element cannot be changed only by performing image magnification conversion with a lens. Therefore, when the mode field differs between the semiconductor laser element and the semiconductor optical amplifier, the laser light may not be sufficiently coupled to the semiconductor optical amplifier. In particular, when the semiconductor laser element has an active region and a passive waveguide portion, and laser light is output through the passive waveguide portion, the vertical direction (semiconductor layer stacking direction) in the passive waveguide portion. Since the optical confinement is stronger than the optical confinement in the lateral direction (plane direction of the semiconductor layer), the laser light output from the semiconductor laser element is converted into an elliptical mode field having a long axis in the vertical direction and a high flatness. Become. In this case, the laser beam focused on the semiconductor optical amplifier by the lens tends to be an elliptical mode field having a long axis in the lateral direction and a high flatness. It is difficult to sufficiently couple such laser light to the semiconductor optical amplifier only by changing the image magnification of the lens. In addition, it is conceivable to use a mode field conversion element or a mode field conversion component in combination with a lens, but there are problems such as deterioration in assemblability and light loss in the conversion element / conversion component.

  On the other hand, the mode field is changed by changing both the width and thickness of the core layer on the output side of the semiconductor laser element and the input side of the semiconductor optical amplifier, and the coupling to the semiconductor optical amplifier is enhanced by using a known SSC structure. It is possible. However, in order to fabricate the SSC structure, a semiconductor regrowth process using a crystal growth apparatus such as a MOCVD (Metal-Organic Chemical Vapor Deposition) apparatus is required, and the time required for the production becomes longer, resulting in a yield. This is disadvantageous. Furthermore, when the SSC structure is manufactured, regrowth is performed as described above, so that light loss occurs at the regrowth interface. Therefore, even if the mode ratio of the laser light mode field is changed by the SSC structure to be the same as the mode field of the semiconductor optical amplifier, the effect of improving the coupling efficiency due to the change of the aspect ratio is diminished by the optical loss at the regrowth interface. It may be done.

  On the other hand, in the semiconductor laser module 1000, the active core layer 201 of the semiconductor optical amplifier 200 has a uniform core thickness in the semiconductor optical amplifier 200, and the core width W2 on the input side 202 is the central portion 201aa. It is wider than the core width W1. Thereby, the semiconductor optical amplifier 200 in which the mode field is brought close to the mode field aspect ratio of the laser light L1 formed by the lenses 1004 and 1006 can be realized. In addition, it is not necessary to form a regrowth interface that generates optical loss when the semiconductor optical amplifier 200 is manufactured. As a result, the coupling efficiency between the semiconductor laser device 100 and the semiconductor optical amplifier 200 can be increased.

  In the first embodiment, the core width W2 of the input-side equal width portion 201b is 3 μm, but the core width W2 is the characteristics of the semiconductor laser element 100, the characteristics of the laser light L1, the collimator lens 1004, and the condenser lens 1006. The coupling efficiency between the semiconductor laser device 100 and the semiconductor optical amplifier 200 may be appropriately set according to the characteristics.

  An example of a method for manufacturing the semiconductor optical amplifier 200 will be described. First, an n-type InP-cladding layer is grown on a n-type InP substrate using a crystal growth apparatus such as an MOCVD crystal growth apparatus to form an n-type semiconductor layer 200b, and a semiconductor layer that becomes an active core layer 201 Then, a part of the p-type semiconductor layer 200c and the contact layer 200d are grown. Subsequently, a mask made of SiNx is formed on the p-type semiconductor layer 200c by a CVD method. Subsequently, the pattern of the active core layer 201 is transferred using a resist and a photomask. At this time, a photomask having a pattern of the active core layer 201 is used. Thereby, the shape of the active core layer 201 of the semiconductor optical amplifier 200 can be easily realized. Subsequently, SiNx etching is performed on the resist-transferred wafer by reactive ion etching. Subsequently, a mesa stripe shape is formed by wet etching using SiNx as an etching mask. Subsequently, a current blocking structure is formed using an MOCVD apparatus to form a buried structure. Further, the remaining part of the p-type semiconductor layer 200c and the contact layer 200d are formed using an MOCVD apparatus. Subsequently, the SiNx protective film 200h and the p-side electrode 200e are formed, the back surface of the wafer is polished, and the n-side electrode 200a is formed. Thereby, the wafer is completed. Further, the completed wafer is cut into a bar element having an appropriate length, antireflection films are coated on both end faces of the bar element, and the bar element is further cut into the semiconductor optical amplifier 200. Thereby, the semiconductor optical amplifier 200 can be manufactured.

(Examples 1 to 3, Comparative Examples 1-1 to 1-3, 2-1 to 2-3)
Semiconductor laser modules of Examples 1 to 3, Comparative Examples 1-1 to 1-3, and 2-1 to 2-3 were manufactured. The semiconductor laser modules of Examples 1 to 3 have the same configuration as that of the first embodiment. As the semiconductor laser element, a semiconductor laser element configuration example 1 described later was used. Note that the image magnification m of the laser beam by the collimator lens (focal length f1) and the condensing lens (focal length f2) disposed between the semiconductor laser element and the semiconductor optical amplifier is different from that in Examples 1, 2, and 3. And set to 1, 1.4 and 2, respectively.

  In addition, the semiconductor laser modules of Comparative Examples 1-1 to 1-3 are the same as those in Examples 1 to 3 except that the portions where the input-side equal-width portion and the tapered portion of the semiconductor optical amplifier are replaced with the SSC structure. Each of the semiconductor laser modules 3 had the same configuration. FIG. 5 is a schematic diagram illustrating a configuration of a semiconductor optical amplifier including the SSC structure of Comparative Examples 1-1 to 1-3. The semiconductor optical amplifier 1200 has a structure in which a semiconductor optical amplifier 1200A and an SSC structure 1200B are integrated. In the cross section along the active core layer 1201A, the semiconductor optical amplifier 1200A includes an n-side electrode 1200a, an n-type semiconductor layer 1200b made of n-type InP, an active core layer 1201A, and a p-type semiconductor layer made of p-type InP. 1200c, contact layer 1200d, and p-side electrode 1200e are stacked in this order. The SSC structure portion 1200B has a similar stacked structure, but the active core layer 1201A is replaced with a waveguide core layer 1201B, and has a stacked structure that does not include the p-type contact layer 1200d and the p-side electrode 1200e.

  The active core layer 1201A of the semiconductor optical amplifier 1200A has a constant core width of 2 μm and a constant core thickness. In the waveguide core layer 1201B of the SSC structure portion 1200B, both the core width and the core thickness change in the longitudinal direction. Specifically, the core thickness changes from 90 nm to 160 nm and the core width changes from 3 μm to 2 μm in a tapered shape from the input side (left side of the paper) toward the semiconductor optical amplifier 1200A side. The waveguide core layer 1201B is made of InGaAsP having a band gap wavelength of 1.2 μm.

  In addition, the semiconductor laser modules of Comparative Examples 2-1 to 2-3 are the same as those of Examples 1 to 3 except that the input-side equal-width portion and the tapered portion of the semiconductor optical amplifier have the same constant core width as the main waveguide portion. Each of the semiconductor laser modules has the same configuration.

  Then, a reverse bias voltage was applied to the semiconductor optical amplifier while laser light was output from the semiconductor laser elements of the semiconductor laser modules of the examples and comparative examples, and the current flowing through the semiconductor optical amplifier was measured.

  FIG. 6 is a diagram illustrating characteristics of Comparative Examples 1-1 to 1-3, 2-1 to 2-3, and Examples 1 to 3. The horizontal axis indicates the image magnification m, and the vertical axis indicates the current Isoa flowing through the semiconductor optical amplifier. Since the current Isoa is proportional to the power of the laser beam coupled to the semiconductor optical amplifier, the larger the value of Isoa means that the coupling efficiency between the semiconductor laser element and the semiconductor optical amplifier is higher.

  As shown in FIG. 6, in any of Examples 1 to 3, Isoa is larger than any of Comparative Examples 1-1 to 1-3 and 2-1 to 2-3, and Comparative Examples 2-1 to 2 It was confirmed that the coupling efficiency can be increased by about 20% at the same image magnification with respect to -3.

(Examples 4 and 5, Comparative Examples 3 and 4)
Example 4 and Comparative Example 3 have the same configurations as those of Example 1 and Comparative Example 1-1, respectively, but a semiconductor laser module having a semiconductor optical amplifier element length of 1400 μm is manufactured and output from an optical fiber. When the operating current of the semiconductor optical amplifier for setting the laser beam power to 100 mW was compared, the operating current in Example 4 could be reduced by about 4% compared to the case of Comparative Example 3. Further, as Example 5 and Comparative Example 4, the configurations are the same as those of Example 4 and Comparative Example 3, respectively, but a semiconductor laser module in which the element length of the semiconductor optical amplifier is 1700 μm is manufactured and output from the optical fiber. When the operating current of the semiconductor optical amplifier for setting the laser beam power to 100 mW was compared, in the case of Example 5, the operating current could be reduced by about 3% compared to the case of Comparative Example 4.

(Configuration Example 1 of Semiconductor Laser Element)
Next, a configuration example 1 of the semiconductor laser element will be described. The semiconductor laser device according to Configuration Example 1 is a wavelength tunable laser device having a configuration in which a passive waveguide portion is integrated on the laser light output side.

  FIG. 7 is a schematic diagram of a semiconductor laser device according to Configuration Example 1. As shown in FIG. 7, the semiconductor laser device 100A includes an embedded waveguide structure region 110 in which a waveguide is formed by an embedded waveguide, and a slab waveguide structure region 120a in which a waveguide is formed by a slab waveguide. 120 b and a high mesa waveguide structure region 130 in which a waveguide is formed by a high mesa waveguide.

The buried waveguide structure region 110 has a structure in which a plurality of distributed feedback (DFB: Distributed Feed-Back) laser elements 111 _{1 to} 111 ₁₂ having different oscillation wavelengths are integrated, and is an input waveguide that is a bent waveguide. A waveguide 113 is provided. The slab waveguide structure region 120a includes an input-side slab waveguide 141, the slab waveguide structure region 120b includes an output-side slab waveguide 142, and the high mesa waveguide structure region 130 is an array waveguide that is a bending waveguide. A waveguide 143 is provided. The input-side slab waveguide 141, the output-side slab waveguide 142, and the arrayed waveguide 143, which is a bending waveguide, integrally form an arrayed waveguide grating (AWG) 140. The input waveguide 113 and the AWG 140 constitute a passive waveguide section. Here, explanation of the present configuration example 1 using a semiconductor laser element 100A including 12 pieces of the DFB laser element ₁₁₁ 1-111 ₁₂ having different oscillation wavelengths, but the present configuration example 1 is limited by the number of the DFB laser element It is not something.

The DFB laser elements 111 _{1 to} 111 _{12 serving as} laser oscillation units are one form of semiconductor laser elements, and for example, the oscillation wavelengths of the DFB laser elements 111 _{1 to} 111 ₁₂ are different by 3.5 nm in the 1.55 μm wavelength band. Designed to. The DFB laser elements 111 _{1 to} 111 ₁₂ have a characteristic that the oscillation wavelength is changed by changing the temperature. In the semiconductor laser element 100A, the output wavelength is coarsely adjusted by selecting one of the plurality of DFB laser elements 111 _{1 to} 111 ₁₂ , and the output wavelength is finely adjusted by changing the temperature. As a result, the semiconductor laser element 100A as a whole operates as a wavelength variable light source that performs laser oscillation in a continuous wavelength range. The DFB laser elements 111 _{1 to} 111 ₁₂ may be replaced with DR (Distributed Reflector) laser elements.

Laser light emitted from the DFB laser elements 111 _{1 to} 111 ₁₂ is guided to the input side slab waveguide 141 through the input waveguide 113. The input-side slab waveguide 141 is a waveguide in which light is not confined in the direction parallel to the substrate, and the laser beam input from the input waveguide 113 is diffracted in the direction parallel to the substrate, and the laser is transmitted to the arrayed waveguide 143. Guides light.

  The arrayed waveguide 143 is composed of a large number of waveguides formed by bending paths, and is provided with an optical path length difference depending on the wavelength. Therefore, when the input position of the laser beam to the input-side slab waveguide 141 is changed in accordance with the optical path length difference depending on this wavelength, the laser beams of all wavelengths are at the same position at the output end of the output-side slab waveguide 142. Will be bound to.

  In the present configuration example 1, the AWG 140 is a slab emission type AWG, and laser light is directly emitted from the output end 142a of the output-side slab waveguide 142, which also serves as the output end of the semiconductor laser element 100A.

  Here, a specific configuration example of the AWG 140 according to the present embodiment will be disclosed.

The group refractive index _ng of the high-mesa waveguide constituting the arrayed waveguide 143 is 3.54, and the equivalent refractive index n _eff is 3.19. Further, the optical path length difference ΔL between adjacent waveguides in the waveguide constituting the arrayed waveguide 143 is 16.3 μm. Focal length _{L f} of AWG140 is 480 .mu.m. The waveguide interval of the arrayed waveguides 143 at the input end face 141b of the input side slab waveguide 141 is 3.5 μm. The waveguide interval of the input waveguide 113 on the input end face 141a of the input side slab waveguide 141 is 5 μm.

  FIGS. 8A, 8B, and 8C are views showing a cross section taken along the line EE, a line FF, and a line GG, respectively, in FIG. FIG. 8A illustrates one of the input waveguides 113 included in the cross section taken along the line EE. The input waveguide 113 is made of an n-side electrode 110a, an n-type InP, an n-type semiconductor layer 110b including a growth substrate, and a waveguide core layer having a thickness of about 200 nm made of InGaAsP having a band gap wavelength of 1.3 μm. 110c, a spacer layer 110j made of p-type InP, a p-type semiconductor layer 110d made of p-type InP, a contact layer 110e made of p-type InGaAs, and a SiNx protective film 110i are stacked in this order. ing. The waveguide core layer 110c and the spacer layer 110j have a stripe mesa structure having a width (for example, 2.0 to 2.5 μm) suitable for optically guiding light in a 1.55 μm band in a single mode. Both sides of the stripe mesa structure (left and right direction in the drawing) have a buried structure having a current blocking structure including a p-type InP buried layer 110g and an n-type InP current blocking layer 110h. The other input waveguide 113 has the structure shown in FIG.

  FIG. 8B illustrates the input-side slab waveguide 141 included in the FF line cross section. The input-side slab waveguide 141 includes an n-side electrode 110a, an n-type semiconductor layer 110b, a waveguide core layer 110c, a p-type semiconductor layer 110d, a contact layer 110e, and a SiNx protective film 110i in this order. It has the structure. Note that the output-side slab waveguide 142 also has the structure shown in FIG.

  FIG. 8C illustrates one of the arrayed waveguides 143 included in the GG line cross section. The arrayed waveguide 143 has a structure in which an n-side electrode 110a, an n-type semiconductor layer 110b, a waveguide core layer 110c, a p-type semiconductor layer 110d, and a contact layer 110e are stacked in this order. A high mesa structure in which the upper part of the n-type semiconductor layer 110b to the contact layer 110e has a width (for example, 2.0 to 2.5 μm) suitable for optically guiding light in a 1.55 μm band in a single mode; The surface is covered with the SiNx protective film 110i.

  Like the semiconductor laser element 100A, a semiconductor laser element in which a passive waveguide portion is integrated on the laser beam output side has an elliptical mode field in which the output laser beam has a long axis in the vertical direction and a high flatness. It is easy to become. In particular, when the passive waveguide portion includes a bending waveguide, the relative refractive index difference of the waveguide in the passive waveguide portion is set high in order to suppress bending loss, so that the flatness of the mode field tends to be higher. It is in. Therefore, such a semiconductor laser device is preferably combined with the semiconductor optical amplifier 200 to increase the coupling efficiency. As another example of the semiconductor laser device in which the passive waveguide section is integrated on the laser beam output side, the semiconductor laser device 100A has a configuration including an MMI (Multi-Mode Interferometer) device instead of the AWG 140. There are tunable laser elements and the like.

(Embodiment 2)
FIG. 9 is a schematic diagram illustrating a configuration of the semiconductor laser module according to the second embodiment. As shown in FIG. 9, in the configuration of the semiconductor laser module 1000A shown in FIG. 1, the semiconductor laser module 100A is replaced with the semiconductor laser element 100B, the semiconductor optical amplifier 200 is replaced with the semiconductor optical amplifier 200A, It has a configuration in which a table 1013 and an optical isolator 1014 are added. The semiconductor laser module 1000A is connected to a controller.

  Hereinafter, differences between the semiconductor laser module 1000A and the semiconductor laser module 1000 will be described. Similar to the semiconductor laser element 100, the semiconductor laser element 100B is supplied with a drive current from the controller and outputs a laser beam L1. The central axis of the waveguide that guides the laser light L1 to the light output end face 100Ba of the semiconductor laser element 100 is inclined by 7 ° with respect to the normal line of the light output end face 100Ba. As a result, the laser beam L1 is output in a direction that forms 23 ° with respect to the normal line of the light output end surface 100Ba of the semiconductor laser element 100B. As a result, the reflected light generated at the light output end face 100Ba is prevented from returning into the semiconductor laser element 100B and the laser characteristics becoming unstable. Thus, since the laser beam L1 is output in the tilted direction, the base 1002 is tilted with respect to the traveling direction of the laser beam L1. The semiconductor laser element 100C may be a wavelength tunable laser element configured as shown in FIG.

  A base 1013 mounts a base 1003, beam splitters 1005 and 1007, condenser lenses 1006, PDs 1008 and 1010, an etalon filter 1009, and an optical isolator 1014 in a housing 1001. The base 1013 is made of AlN having a high thermal conductivity of 170 W / m · K, for example. However, the base 1013 is not limited to AlN, and may be a material having a high thermal conductivity such as CuW, SiC, or diamond.

  The optical isolator 1014 is disposed between the collimator lens 1004 and the beam splitter 1005. The optical isolator 1014 passes the laser light L1 from the collimator lens 1004 side to the beam splitter 1005 side, blocks light traveling from the beam splitter 1005 side, and prevents the light from being input to the semiconductor laser element 100B. To do.

  Next, the semiconductor optical amplifier 200A will be specifically described. FIG. 10 is a schematic diagram showing the configuration of the semiconductor optical amplifier 200A.

  The semiconductor optical amplifier 200A has a width of about 0.4 mm and a length of about 2 mm, and includes an active core layer 201A. The active core layer 201A extends from the input side 202A to the output side 203A of the semiconductor optical amplifier 200A, and its length is about 2 mm. The active core layer 201A amplifies the laser beam L1 input from the input side 202A while being guided in the longitudinal direction (optical waveguide direction), and outputs the laser beam L2 from the output side 203A. The cross section of the semiconductor optical amplifier 200A along the active core layer 201A and the cross sectional structure perpendicular to the longitudinal direction of the active core layer 201A are the same as the corresponding cross sectional structure of the semiconductor optical amplifier 200.

  The active core layer 201A of the semiconductor optical amplifier 200A has a uniform core thickness of 160 nm in the semiconductor optical amplifier 200A. As shown in FIG. 10, the active core layer 201A includes a main waveguide portion 201Aa, an input-side equal width portion 201Ab, a tapered portion 201Ac, and a bent waveguide portion 201Ad. Although not clearly described in FIG. 10, the bent waveguide portion 201Ad is a gently and continuously bent waveguide that connects the tapered portion 201Ac and the main waveguide portion 201Aa. The bent waveguide portion 201Ad can be integrated with the tapered portion 201Ac and have a change in width and a bend at the same time. The main waveguide 201Aa includes an input-side main waveguide 201Aaa, an output-side main waveguide 201Aab, and a bent waveguide 201Ae. Although not clearly shown in FIG. 10, the bent waveguide 201Ae is a gently and continuously bent waveguide that connects the input main waveguide 201Aaa and the output main waveguide 201Aab.

  The main waveguide portion 201Aa includes a central portion 201Aac in the longitudinal direction of the active core layer 201A, and is a portion having a constant core width. The central portion 201Aac is an area including a position of about 1 mm from each of the input side 202A and the output side 203A. The core width W3 of the main waveguide portion 201Aa is a value that can guide light in a 1.55 μm band in a single mode, and is 2 μm in the second embodiment. The central axis X1 of the output main waveguide 201Aab of the main waveguide 201Aa is inclined by an angle θ1 = 7 ° with respect to the normal N1 of the optical output end surface 204A of the semiconductor optical amplifier 200A.

  The input-side equal width portion 201Ab is located on the input side 202A, has a length of about 20 μm in the central axis X2, and has a constant core width. The core width W4 of the input-side equal width portion 201Ab is 3 μm in the second embodiment, and is wider than the core width W3 in the central portion 201Aac. Further, the central axis X2 of the input-side equal-width portion 201Ab is inclined by an angle θ2 = 7 ° with respect to the normal line N2 of the optical input end face 205A of the semiconductor optical amplifier 200A. Therefore, the output side main waveguide portion 201Aab and the input side equal width portion 201Ab are parallel to each other. The laser beam L1 output from the semiconductor laser element 100C is input to the semiconductor optical amplifier 200A from a direction that forms 23 ° with respect to the normal line N2 of the optical input end face 205A of the semiconductor optical amplifier 200A. The laser light L2 is output from the semiconductor optical amplifier 200A in a direction that forms 23 ° with respect to the normal line N1 of the light output end face 204A.

  The taper portion 201Ac is a region where the core width gradually decreases from the input side 202A toward the center portion 201Aac, and the length thereof is about 100 μm. The taper portion 201Ac is located closer to the input side 202A than the central portion 201Aac. The taper portion 201Ac preferably has a length in the optical waveguide direction of 10 μm or more and 200 μm or less.

  In the semiconductor laser module 1000A, the active core layer 201A of the semiconductor optical amplifier 200A has a uniform core thickness in the semiconductor optical amplifier 200A, and the core width W4 on the input side 202A is larger than the core width W3 on the central portion 201Aac. As a result, the coupling efficiency between the semiconductor laser device 100B and the semiconductor optical amplifier 200A is increased.

  The active core layer 201A is inclined with respect to the light input end face 205A and the light output end face 204A on the input side 202A and the output side 203A of the semiconductor optical amplifier 200A, respectively. Thereby, it is suppressed that the reflected light generated at each end face is coupled to the active core layer 201A and the operation becomes unstable.

(Other configuration examples of semiconductor optical amplifier)
FIG. 11 is a schematic diagram illustrating another configuration example of the semiconductor optical amplifier. In the active core layer 201B, the semiconductor optical amplifier 200B shown in FIG. 11A includes an input-side equal width portion 201Bb and a tapered portion 201Bc on the input side 202B with respect to the main waveguide portion 201Ba, and also on the output side 203B. The output side equal width part 201Bf and the taper part 201Bg are provided. The length and width of the input-side equal width portion 201Bb and the output-side equal width portion 201Bf may be the same as the length and width of the input-side equal width portion 201b of the active core layer 201 of the semiconductor optical amplifier 200. The length and width of the taper portion 201Bc may be the same as the length and width of the taper portion 201c of the active core layer 201. In the active core layer 201B, the core width on the output side 203B is wider than the core width at the center in the optical waveguide direction. Thereby, in the output side equal width part 201Bf and the taper part 201Bg, the resistance at the time of current injection is lowered, so that the power efficiency is improved. By making the length of the tapered portion 201Bg longer than the length of the tapered portion 201Bc, the effect of reducing the resistance can be increased. That is, the length of the taper portion 201Bc is selected to be as small as possible within a range in which an increase in loss due to a rapid change in the core width can be suppressed, but the length of the taper portion 201Bg is longer than that, for example, 500 μm. By improving the degree, the efficiency is improved.

  A semiconductor optical amplifier 200C shown in FIG. 11B includes, in the active core layer 201C, an input side equal width portion 201Cb, a taper portion 201Cc, and a curved waveguide portion 201Cd on the input side 202C with respect to the main waveguide portion 201Ca. The output side 203C also includes an output side equal width portion 201Cf, a taper portion 201Cg, and a curved waveguide portion 201Ch. Although not clearly shown in FIG. 11, the bent waveguide portions 201Cd and 201Ch are bent gently and continuously. The length and width of the input side equal width portion 201Cb and the output side equal width portion 201Cf may be the same as the length and width of the input side equal width portion 201Ab of the active core layer 201A of the semiconductor optical amplifier 200A. The length and width of the tapered portion 201Cc may be the same as the length and width of the tapered portion 201Ac of the active core layer 201A. The shape of the bent waveguide portion 201Cd may be the same as the shape of the bent waveguide portion 201Ad of the active core layer 201A. The bent waveguide portion 201Cd may be integrated with the tapered portion 201Cc and have a change in width and a bend at the same time. The bent waveguide portion 201Ch may be integrated with the tapered portion 201Cg and have a change in width and a bend at the same time. In the active core layer 201C, the core width of the output side 203C is wider than the core width at the center in the optical waveguide direction. Thereby, in the output side equal width part 201Cf and the taper part 201Cg, the resistance at the time of current injection is lowered, so that the power efficiency is improved. The length of the tapered portion 201Cg may be longer than the length of the tapered portion 201Cc.

  In the above embodiment, the active core layer of the semiconductor optical amplifier has a shape in which the core width on the input side is wider than the core width in the central portion. However, depending on the characteristics of the semiconductor laser device, the coupling width between the semiconductor laser device and the semiconductor optical amplifier is increased by making the core width on the input side narrower than the core width at the center. May be. Further, the input-side equal width portion may be substantially zero in length, and the tapered portion is not an essential configuration. That is, it is only necessary that the core width on the input side of the active core layer is different from the core width at least in the central portion in the longitudinal direction, so that the coupling efficiency between the semiconductor laser element and the semiconductor optical amplifier can be increased. Further, the core width on the output side of the active core layer may be narrower, unlike the core width at the center in the optical waveguide direction.

  Further, the present invention is not limited by the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. For example, an optical isolator may be disposed between the collimator lens 1004 and the beam splitter 1005 in the semiconductor laser module 1000 shown in FIG. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

201, 201A, 201B, 201C active core layer 110b, 200b n-type semiconductor layer 110j spacer layer 110g, 200f p-type InP buried layer 110h, 200g n-type InP current blocking layer 110d, 200cp p-type semiconductor layer 110e, 200d contact layer 200e p-side electrode 110i, 200h SiNx protective film 200ha opening 110a, 200a n-side electrode 100, 100A, 100B semiconductor laser device 100Ca light output end face 110 buried waveguide structure region 110c waveguide core layer 113 input waveguide 120a, 120b slab Waveguide structure region 130 High-mesa waveguide structure region 141 Input side slab waveguides 141a and 141b Input end surface 142 Output side slab waveguide 142a Output end 143 Array waveguides 200, 200A, 200B 200C Semiconductor optical amplifier 201a, 201Aa, 201Ba, 201Ca Main waveguide portion 201Aaa Input side main waveguide portion 201Aab Output side main waveguide portion 201aa, 201Aac Center portion 201b, 201Ab, 201Bb, 201BCb, 201Cb Input side equal width portion 201c, 201Ac, 201Bc 201Bg, 201Cc, 201Cg Tapered portions 201Ad, 201Ae, 201Cd, 201Ch Curved waveguide portions 201Bf, 201Cf Output side equal width portions 202, 202A, 202B, 202C Input side 203, 203A, 203B, 203C Output side 204A Light output end face 205A Optical input end face 1000, 1000A Semiconductor laser module 1001 Case 1001a Mounting portion 1002, 1003, 1013 Base 1004 Collimator lens 1005, 10 07 Beam splitter 1006, 1011 Condensing lens 1009 Etalon filter 1008, 1010 PD
1012 Optical fiber 1014 Optical isolators 111 _{1 to} 111 ₁₂ DFB laser elements L1, L2, L3 Laser light N1, N2 Normal lines X1, X2 Central axis

Claims (11)

A semiconductor laser element for outputting laser light;
A semiconductor optical amplifier that receives the laser beam from the input side, amplifies the laser beam, and outputs the laser beam from the output side;
An optical coupler for optically coupling the laser light output from the semiconductor laser element to the semiconductor optical amplifier;
With
The active laser layer of the semiconductor optical amplifier has a uniform core thickness, and the core width on the input side is different from the core width at least in the central portion in the longitudinal direction. The active core layer of the semiconductor optical amplifier is:
The core width on the input side is wider than the core width at the central portion,
2. The semiconductor laser module according to claim 1, wherein a region where the core width becomes narrower from the input side toward the central portion is provided at a position closer to the input side than the central portion.   3. The semiconductor laser module according to claim 2, wherein a length of the region in a longitudinal direction is not less than 10 μm and not more than 200 μm.   The semiconductor laser module according to claim 1, wherein the semiconductor laser element has a configuration in which a passive waveguide portion is integrated on an output side of the laser light.   The semiconductor laser module according to claim 4, wherein the passive waveguide portion includes a bent waveguide.   6. The semiconductor laser module according to claim 4, wherein the passive waveguide section includes a slab emission type arrayed waveguide diffraction grating.   The semiconductor laser module according to claim 1, wherein the semiconductor laser element has a configuration in which a plurality of laser oscillation units are integrated.   The semiconductor laser module according to claim 1, further comprising a base on which the semiconductor optical amplifier is mounted in a junction-down state.   9. The semiconductor according to claim 1, wherein an active core layer of the semiconductor optical amplifier is inclined with respect to an end face of the input side on an input side of the semiconductor optical amplifier. Laser module.   9. The semiconductor according to claim 1, wherein an active core layer of the semiconductor optical amplifier is inclined with respect to an end face on the output side on an output side of the semiconductor optical amplifier. Laser module.   The active core layer of the semiconductor optical amplifier has a core width on the output side that is different from a core width at least in a central portion in an optical waveguide direction. Semiconductor laser module.

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