JP7062358B2 - Semiconductor laser module - Google Patents

Description

The present invention relates to a semiconductor laser module.

In recent years, in optical communication, a multi-value modulation method has been studied in order to increase the communication speed. As the multi-value modulation method, a coherent communication method mainly composed of phase shift keying (PSK) is used. In such coherent communication, a tunable semiconductor laser module (for example, μTOSA (Transmitter Optical Sub-Assembly) / μITLA (Integrable Tunable Laser Assembly)) is required for the signal light source on the transmitting side and the local oscillation light source.

In coherent communication, since information is placed on the phase of light, 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 more complicated, the semiconductor laser module is further required to have high output and low power consumption.

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

Japanese Patent No. 5567226

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 an SSC (Spot Size Converter), which is an element for converting a mode field, is provided in a semiconductor laser element or a semiconductor optical amplifier is being studied. However, the SSC may have a large optical loss of its own and may not be able to increase the coupling efficiency. Therefore, it has been difficult to increase the output and power consumption, which are important characteristics of the tunable laser module.

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

In order to solve the above-mentioned problems and achieve the object, the semiconductor laser module according to one aspect of the present invention has a semiconductor laser element that outputs a laser beam and the laser beam is input from the input side to receive the laser beam. It comprises a semiconductor optical amplifier that amplifies and outputs from the output side, and an optical coupler that optically couples the laser beam output from the semiconductor laser element to the semiconductor optical amplifier, and is an active core of the semiconductor optical amplifier. The layer is characterized in that it 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 one aspect of the present invention, in the active core layer of the semiconductor optical amplifier, the core width on the input side is wider than the core width in the central portion, and the core width is directed from the input side toward the central portion. It is characterized in that 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 aspect of the present invention is characterized in that the length of the region in the longitudinal direction is 10 μm or more and 200 μm or less.

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 one aspect of the present invention is characterized in that the passive waveguide portion includes a bending waveguide.

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

The semiconductor laser module according to one aspect of the present invention is characterized by including a base on which the semiconductor optical amplifier is mounted in a junction-down state.

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 of 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 of the output side on the output 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 has a core width on the output side different from a core width at least in the central portion in the optical waveguide direction.

According to the present invention, there is an effect that a semiconductor laser module having high coupling efficiency between a semiconductor laser device and a semiconductor optical amplifier can be realized.

FIG. 1 is a schematic diagram showing 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 the line AA of FIG. FIG. 4 is a schematic cross-sectional view of the active core layer of the semiconductor optical amplifier shown in FIG. 1 in a cross section perpendicular to the longitudinal direction. FIG. 5 is a schematic diagram showing the configuration of a semiconductor optical amplifier having the SSC structure of Comparative Examples 1-1 to 1-3. FIG. 6 is a diagram illustrating the 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 a semiconductor laser device. FIG. 8 is a diagram showing an EE line cross section, an FF line cross section, and a GG line cross section of FIG. 7. FIG. 9 is a schematic diagram showing the 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 showing another configuration example of the semiconductor optical amplifier.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to this embodiment. Further, in the description of the drawings, the same or corresponding elements are appropriately designated by the same reference numerals. In addition, it should be noted that the drawings are schematic, and the relationship between the dimensions of each element, the ratio of each element, etc. may differ from the reality. Even between the drawings, there may be parts where the relationship and ratio of the dimensions are different from each other.

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

The bases 1002 and 1003 are respectively mounted on a temperature control element (not shown) in the housing 1001. The base 1002 is equipped with a 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 1001a of the housing 1001.

The temperature control element is, for example, a Pelche element. Each temperature control element can control the temperature of the semiconductor laser device 100 and the semiconductor optical amplifier 200 by cooling and, in some cases, heating each of the semiconductor laser element 100 and the semiconductor optical amplifier 200 by supplying a drive current.

The bases 1002 and 1003 are made of aluminum nitride (AlN) having a high thermal conductivity of 170 W / m · K, for example, but are not limited to AlN, and materials having a high thermal conductivity such as CuW, silicon carbide (SiC), and diamond. But it may be.

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

The collimator lens 1004 is arranged on the front side, which is the side that outputs the laser beam L1 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 beam L1 and outputs it to the condenser lens 1006, and at the same time, branches a part of the laser beam L1 (laser beam L3) and reflects it toward the beam splitter 1007.

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

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

On the other hand, the beam splitter 1007 splits the laser beam L3 into two branches, transmits one to the PD1008, and reflects the other toward the etalon filter 1009. The PD1008 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 at a transmittance corresponding to the transmission characteristic to the PD1010 for wavelength monitoring. input. The PD1010 detects the intensity of the laser beam 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 PD1008, 1010 is used for wavelength lock control (control for adjusting 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 the line AA of 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 of the semiconductor optical amplifier 200 to the output side 203, and its length is 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 waveguideing in the longitudinal direction (optical waveguide direction), and outputs the laser beam L2 as the laser beam L2 from the output side 203. Both end faces of the input side 202 and the output side 203 are coated with antireflection films.

Further, as shown in FIG. 3, the semiconductor optical amplifier 200 is composed of an n-side electrode 200a including, for example, AuGeNi, and an n-type InP in a cross section along the active core layer 201, and is an n-type including a substrate. It has a structure in which a semiconductor layer 200b, an active core layer 201, a p-type semiconductor layer 200c composed of p-type InP, a contact layer 200d, and a p-side electrode 200e including, for example, AuZn, are laminated in this order. are doing. The active core layer 201 has a multiple quantum well structure including a plurality of alternately stacked well layers and a plurality of barrier layers, and lower and upper light confinement layers sandwiching 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 the 1.55 μm band in the first embodiment. The lower light confinement layer is made of n-type InGaAsP. The upper light 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 of the base 1003, and the n-type semiconductor layer 200b including the growth substrate is located on the side opposite to the base 1003, that is. It may be installed in a junction down state. As a result, the heat generated in the active core layer 201 of the semiconductor optical amplifier 200 is easily dissipated 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 section 201a, an input-side monospaced section 201b, and a tapered section 201c. These portions are arranged in the order of the input side monospaced portion 201b, the taper portion 201c, and the main waveguide portion 201a from the input side 202 to the output side 203.

The main waveguide section 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 about 1 mm from each of the input side 202 and the output side 203. The core width W1 of the main waveguide section 201a is a value capable of waveguideing light in the 1.55 μm band in a single mode, and is 2 μm in the first embodiment.

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

The tapered portion 201c is a region in which the core width gradually narrows 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 of 10 μm or more and 200 μm or less in the optical waveguide direction. When the length of the tapered portion 201c is 10 μm or more, the tapered angle does not become excessively large, so that it is possible to suppress an increase in loss due to a sudden change in the core width. Further, since the core width of the tapered portion 201c is large, the luminous efficiency with respect to the injection current amount is low, but if the length is 200 μm or less, the luminous efficiency of the tapered portion 201c is lowered in the entire semiconductor optical amplifier 200. It does not pose a problem with 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, both sides (left-right direction of the paper surface) of the active core layer 201 having a stripe mesa structure have an embedded structure having a current blocking structure composed of a p-type InP embedded layer 200f and an n-type InP current blocking layer 200g. 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 via 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 on the input side 202 is larger than the core width W1 in the central portion 201aa. As a result, the coupling efficiency between the semiconductor laser element 100 and the semiconductor optical amplifier 200 is high.

Hereinafter, a specific description will be given. When the laser light from the semiconductor laser element is optically coupled to the semiconductor optical amplifier in the semiconductor laser module, when the laser light is coupled via the lens, the coupling efficiency to the semiconductor optical amplifier is increased by changing the image magnification of the lens. Is a common technique.

However, it is not possible to change the aspect ratio of the mode field of the laser beam from the semiconductor laser device only by performing image magnification conversion with the lens. Therefore, when the mode fields are different between the semiconductor laser element and the semiconductor optical amplifier, it may not be possible to sufficiently couple the laser light to the semiconductor optical amplifier. In particular, when the semiconductor laser element has an active region and a passive waveguide section and the laser light is output through the passive waveguide section, the passive waveguide section is in the vertical direction (semiconductor layer stacking direction). Since the light confinement is stronger than the light confinement in the horizontal direction (plane direction of the semiconductor layer), the laser beam output from the semiconductor laser element is in an elliptical mode field having a long axis in the vertical direction and a high flatness. Become. In this case, the laser beam imaged 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 a laser beam to a semiconductor optical amplifier only by changing the image magnification of the lens. Further, it is conceivable to use a mode field conversion element or a mode field conversion component together with a lens, but there are problems such as deterioration of assembling property and optical loss in the conversion element / conversion component.

On the other hand, on the output side of the semiconductor laser device and the input side of the semiconductor optical amplifier, the mode field is changed by changing both the width and the thickness of the core layer, and the coupling to the semiconductor optical amplifier is enhanced by using a known SSC structure. Can be considered. However, in order to fabricate the SSC structure, a semiconductor regrowth step using a crystal growth apparatus such as a MOCVD (Metal-Organic Chemical Vapor Deposition) apparatus is required, and the time required for the fabrication becomes long, so that the yield and the like are increased. It is disadvantageous in terms of. Furthermore, when the SSC structure is produced, regrowth is carried out as described above, so that light loss occurs at the regrowth interface to a considerable extent. Therefore, even if the aspect ratio of the mode field of the laser beam 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 by changing 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 of. This makes it possible to realize a semiconductor optical amplifier 200 in which the mode field is close to the aspect ratio of the mode field of the laser beam L1 imaged by the lenses 1004 and 1006. Moreover, it is not necessary to form a regrowth interface that causes 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 improved.

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 element 100 and the semiconductor optical amplifier 200 may be appropriately set according to the characteristics of the above.

An example of a manufacturing method of the semiconductor optical amplifier 200 will be described. First, an n-type InP-clad layer is grown on an n-type InP substrate using a crystal growth device such as a MOCVD crystal growth device to form an n-type semiconductor layer 200b, and a semiconductor layer to be an active core layer 201 is further formed. , A part of the p-type semiconductor layer 200c, the contact layer 200d is grown. Subsequently, a mask made of SiNx is formed on the p-type semiconductor layer 200c by the CVD method. Subsequently, the pattern of the active core layer 201 is resist-transferred using a resist and a photomask. At this time, a photomask having the 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 produced by wet etching using SiNx as an etching mask. Subsequently, a current blocking structure is formed using a MOCVD apparatus to form an embedded structure. Further, a MOCVD apparatus is used to form a contact layer 200d with the remaining portion of the p-type semiconductor layer 200c. Subsequently, the SiNx protective film 200h and the p-side electrode 200e are formed, and the back surface of the wafer is polished to form the n-side electrode 200a. This completes the wafer. Further, the completed wafer is cut into a bar element having an appropriate length, both end surfaces of the bar element are coated with a non-reflective film, and the bar element is further cut into a semiconductor optical amplifier 200. As a result, 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 and Comparative Examples 1-1 to 1-3 and 2-1 to 2-3 were produced. The semiconductor laser modules of Examples 1 to 3 have the same configuration as that of the first embodiment. As the semiconductor laser device, the one of the configuration example 1 of the semiconductor laser device described later was used. The image magnification m of the laser beam by the collimeter lens (focal distance f1) and the condenser lens (focal distance f2) arranged between the semiconductor laser element and the semiconductor optical amplifier is the same as that of Examples 1, 2 and 3. It was set to 1, 1.4, and 2, respectively.

Further, the semiconductor laser modules of Comparative Examples 1-1 to 1-3 have a structure in which the input side equal width portion and the tapered portion of the semiconductor optical amplifier are replaced with an SSC structure, except that the semiconductor laser modules are of Examples 1 to 1. It has the same configuration as that of the semiconductor laser module of 3. FIG. 5 is a schematic diagram showing the configuration of a semiconductor optical amplifier having 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 unit 1200A and an SSC structure unit 1200B are integrated. The semiconductor optical amplification unit 1200A has an n-side electrode 1200a, an n-type semiconductor layer 1200b composed of an n-type InP, an active core layer 1201A, and a p-type semiconductor layer composed of a p-type InP in a cross section along the active core layer 1201A. The 1200c, the contact layer 1200d, and the p-side electrode 1200e have a structure in which they are laminated in this order. The SSC structure portion 1200B also has a similar laminated structure, but the active core layer 1201A is replaced with the waveguide core layer 1201B, and the p-type contact layer 1200d and the p-side electrode 1200e are not provided in the laminated structure.

The active core layer 1201A of the semiconductor optical amplifier unit 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 are changed 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 surface) toward the semiconductor optical amplifier unit 1200A side. The waveguide core layer 1201B is made of InGaAsP having a bandgap wavelength of 1.2 μm.

Further, in the semiconductor laser modules of Comparative Examples 2-1 to 2-3, the core widths of the input side equal width portion and the tapered portion of the semiconductor optical amplifier are the same as those of the main waveguide portion, except that the core width is the same as that of the main waveguide portion. It has the same configuration as the semiconductor laser module.

Then, while outputting the laser light from the semiconductor laser element of the semiconductor laser module of each Example and Comparative Example, a reverse bias voltage was applied to the semiconductor optical amplifier, and the current flowing through the semiconductor optical amplifier was measured.

FIG. 6 is a diagram illustrating the characteristics of Comparative Examples 1-1 to 1-3, 2-1 to 2-3, and Examples 1 to 3. The horizontal axis shows the image magnification m, and the vertical axis shows 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, the higher the coupling efficiency between the semiconductor laser element and the semiconductor optical amplifier.

As shown in FIG. 6, in any of Examples 1 to 3, Isoa is larger than that 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 binding efficiency can be increased by about 20% with the same image magnification with respect to -3.

(Examples 4 and 5, Comparative Examples 3 and 4)
As Example 4 and Comparative Example 3, a semiconductor laser module having the same configuration as that of Example 1 and Comparative Example 1-1 but having a semiconductor optical amplifier element length of 1400 μm is manufactured and output from an optical fiber. When the operating currents of the semiconductor optical amplifiers for making the power of the laser light 100 mW were compared, the operating current of Example 4 could be reduced by about 4% as compared with the case of Comparative Example 3. Further, as Example 5 and Comparative Example 4, a semiconductor laser module having the same configuration as that of Example 4 and Comparative Example 3 but having a semiconductor optical amplifier element length of 1700 μm is manufactured and output from an optical fiber. When the operating currents of the semiconductor optical amplifiers for making the power of the laser light 100 mW were compared, the operating current of Example 5 could be reduced by about 3% as compared with the case of Comparative Example 4.

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

FIG. 7 is a schematic diagram of the semiconductor laser device according to the configuration example 1. As shown in FIG. 7, the semiconductor laser element 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. It has 120b and a high-mesa-type waveguide structure region 130 in which a waveguide is formed by a high-mesa-type waveguide.

The embedded waveguide structure region 110 has a structure in which a plurality of distributed feedback type (DFB: Distributed Feed-Back) laser elements 111 ₁ to 111 ₁₂ having different oscillation wavelengths are integrated, and is an input guide that is a bending waveguide. It is provided with a waveguide 113. The slab waveguide region 120a includes an input-side slab waveguide 141, the slab waveguide region 120b comprises an output-side slab waveguide 142, and the high-mess-type waveguide region 130 is an array guide that is a bending waveguide. It is equipped with a waveguide 143. The input side slab waveguide 141, the output side slab waveguide 142, and the array waveguide 143, which is a bending waveguide, together constitute an arrayed waveguide Grating (AWG) 140. Further, the input waveguide 113 and the AWG 140 form a passive waveguide section. Here, the present configuration example 1 will be described using the semiconductor laser element 100A provided with twelve DFB laser elements 111 ₁ to 111 ₁₂ having different oscillation wavelengths, but the present configuration example 1 is limited by the number of DFB laser elements. It's not something.

The DFB laser elements 111 ₁ to 111 ₁₂ which are laser oscillation units are one form of a semiconductor laser element, 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. Is designed for. The DFB laser elements 111 ₁ to 111 ₁₂ have a characteristic that the oscillation wavelength changes by changing the temperature. In the semiconductor laser element 100A, the output wavelength is roughly 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 device 100A as a whole operates as a tunable light source that oscillates a laser in a continuous wavelength range. The DFB laser elements 111 ₁ to 111 ₁₂ may be replaced with DR (Distributed Reflector) laser elements, respectively.

The laser light emitted from the DFB laser elements 111 ₁ to 111 ₁₂ is guided to the input side slab waveguide 141 via the input waveguide 113. The input side slab waveguide 141 is a waveguide in which no light is confined in a direction parallel to the substrate, and the laser beam input from the input waveguide 113 is diffracted in the direction parallel to the substrate while being diffracted into the array waveguide 143. Waveguide light.

The array waveguide 143 is composed of a large number of waveguides configured by bending the path, and is provided with an optical path length difference depending on the wavelength. Therefore, when the input position of the laser beam with respect to the input side slab waveguide 141 is changed in correspondence with the optical path length difference depending on this wavelength, the laser light of all wavelengths is at the same position at the output end of the output side slab waveguide 142. Will be combined with.

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, and 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-type waveguide constituting the array 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 array waveguide 143 is 16.3 μm. The focal length L _f of the AWG 140 is 480 μm. The waveguide spacing of the array waveguide 143 on the input end surface 141b of the input side slab waveguide 141 is 3.5 μm. Further, the waveguide spacing of the input waveguide 113 in the input end surface 141a of the input side slab waveguide 141 is 5 μm.

8 (a), (b), and (c) are views showing the EE line cross section, the FF line cross section, and the GG line cross section of FIG. 7, respectively. FIG. 8A illustrates one of the input waveguides 113 included in the EE line cross section. The input waveguide 113 is a waveguide core layer having a thickness of about 200 nm, which is composed of an n-side electrode 110a, an n-type InP, an n-type semiconductor layer 110b including a growth substrate, and an InGaAsP having a bandgap wavelength of 1.3 μm. It has a structure in which 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 laminated in this order. ing. The waveguide core layer 110c and the spacer layer 110j have a striped mesa structure having a width (for example, 2.0 to 2.5 μm) suitable for optical waveguide of 1.55 μm band light in a single mode. Both sides of the stripe mesa structure (in the left-right direction of the paper surface) have an embedded structure having a current blocking structure composed of a p-type InP embedded layer 110 g and an n-type InP current blocking layer 110h. The other input waveguide 113 also has the structure shown in FIG. 8 (a).

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

FIG. 8 (c) illustrates one of the array waveguide 143s included in the GG line cross section. The array 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 laminated in this order. A high-mess structure in which the upper portion 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 optical waveguide of 1.55 μm band light in a single mode. The surface of which is covered with the SiNx protective film 110i.

In a semiconductor laser element such as the semiconductor laser element 100A in which a passive waveguide is integrated on the output side of the laser beam, the output laser beam has an elliptical mode field having a long axis in the vertical direction and a high flatness. It is easy to become. In particular, when the passive waveguide includes a bending waveguide, the flatness of the mode field tends to be higher because the difference in the specific refractive index of the waveguide in the passive waveguide is set high in order to suppress bending loss. It is in. Therefore, it is preferable to combine such a semiconductor laser device with the semiconductor optical amplifier 200 to increase the coupling efficiency. As another example of the semiconductor laser element in which the passive waveguide portion is integrated on the output side of the laser beam, in the configuration of the semiconductor laser element 100A, the MMI (Multi-Mode Interferometer) element is provided instead of the AWG140. There are variable wavelength laser elements and the like.

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

Hereinafter, the 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 the laser beam L1. The central axis of the waveguide in which the laser beam L1 is guided to the optical output end surface 100Ba of the semiconductor laser element 100 is inclined by 7 ° with respect to the normal line of the optical output end surface 100Ba. As a result, the laser light L1 is output in a direction forming 23 ° with respect to the normal of the light output end face 100Ba of the semiconductor laser element 100B. As a result, it is suppressed that the reflected light generated at the light output end face 100Ba returns to the semiconductor laser element 100B and the laser characteristics become unstable. Since the laser beam L1 is output in the inclined direction in this way, the base 1002 is arranged to be inclined with respect to the traveling direction of the laser beam L1. The semiconductor laser device 100C may be a wavelength tunable laser device having a configuration as shown in FIG. 7.

The base 1013 mounts the base 1003, the beam splitters 1005, 1007, the condenser lens 1006, the PD1008, 1010, the etalon filter 1009, and the optical isolator 1014 in the housing 1001. The base 1013 is made of AlN having a high thermal conductivity of 170 W / m · K, for example, but 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 arranged between the collimator lens 1004 and the beam splitter 1005. The optical isolator 1014 passes the laser beam L1 from the collimator lens 1004 side to the beam splitter 1005 side and blocks the light traveling from the beam splitter 1005 side to prevent the light from being input to the semiconductor laser element 100B. 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 of the semiconductor optical amplifier 200A to the output side 203A, and its length is about 2 mm. The active core layer 201A amplifies the laser beam L1 input from the input side 202A while waveguideing in the longitudinal direction (optical waveguide direction), and outputs the laser beam L2 as the laser beam L2 from the output side 203A. The cross-sectional structure 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 structures 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. Further, as shown in FIG. 10, the active core layer 201A includes a main waveguide section 201Aa, an input-side monospaced section 201Ab, a tapered section 201Ac, and a curved waveguide section 201Ad. Although not clearly described in FIG. 10, the curved waveguide section 201Ad is a gently and continuously curved waveguide connecting the tapered section 201Ac and the main waveguide section 201Aa. The curved waveguide portion 201Ad can be integrated with the tapered portion 201Ac to have a change in width and a bend at the same time. The main waveguide section 201Aa includes an input side main waveguide section 201Aaa, an output side main waveguide section 201Aab, and a curved waveguide section 201Ae. Although not clearly described in FIG. 10, the curved waveguide section 201Ae is a gently and continuously curved waveguide connecting the input side main waveguide section 201Aaa and the output side main waveguide section 201Aab.

The main waveguide section 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 a region 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 section 201Aa is a value capable of waveguideing light in the 1.55 μm band in a single mode, and is 2 μm in the second embodiment. Further, the central axis X1 of the output side main waveguide section 201Aa of the main waveguide section 201Aa is inclined by an angle θ1 = 7 ° with respect to the normal line N1 of the optical output end face 204A of the semiconductor optical amplifier 200A.

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

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

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 at the input side 202A is larger than the core width W3 at the central portion 201Aac. As a result, the coupling efficiency between the semiconductor laser element 100B and the semiconductor optical amplifier 200A is high.

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

(Other configuration examples of semiconductor optical amplifiers)
FIG. 11 is a schematic diagram showing another configuration example of the semiconductor optical amplifier. The semiconductor optical amplifier 200B shown in FIG. 11A includes an input side monospaced portion 201Bb and a tapered portion 201Bc on the input side 202B with respect to the main waveguide portion 201B in the active core layer 201B, and also on the output side 203B. The output side is provided with a monospaced portion 201Bf and a tapered portion 201Bg. The length and width of the input-side monospaced portion 201Bb and the output-side monospaced portion 201Bf may be the same as the length and width of the input-side monospaced portion 201b of the active core layer 201 of the semiconductor optical amplifier 200. The length and width of the tapered portion 201Bc may be the same as the length and width of the tapered portion 201c of the active core layer 201. In the active core layer 201B, the core width of the output side 203B is wider than the core width at the central portion in the optical waveguide direction. As a result, the resistance at the time of injecting current is lowered in the output side monospaced portion 201Bf and the tapered portion 201Bg, 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 lowering the resistance can be increased. That is, the length of the tapered portion 201Bc is selected to be as small as possible within the range in which the increase in loss due to a sudden change in the core width can be suppressed, but the length of the tapered portion 201Bg is longer than that, for example, 500 μm. Efficiency is improved by setting the degree.

In the active core layer 201C, the semiconductor optical amplifier 200C shown in FIG. 11B includes an input side monospaced portion 201Cb, a tapered 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 is also provided with an output side monospaced portion 201Cf, a tapered portion 201Cg, and a curved waveguide portion 201Ch. Although not clearly shown in FIG. 11, the curved waveguides 201Cd and 201Ch are gently and continuously bent. The length and width of the input-side monospaced portion 201Cb and the output-side monospaced portion 201Cf may be the same as the length and width of the input-side monospaced 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 curved waveguide 201Cd may be the same as the shape of the curved waveguide 201Ad of the active core layer 201A. The curved waveguide portion 201Cd may be integrated with the tapered portion 201Cc to have a change in width and a bend at the same time. The curved waveguide portion 201Ch may be integrated with the tapered portion 201Cg to 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 central portion in the optical waveguide direction. As a result, in the output side monospaced portion 201Cf and the tapered portion 201Cg, the resistance at the time of injecting a current 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 core width on the input side may be narrower than the core width at the center to improve the coupling efficiency between the semiconductor laser device and the semiconductor optical amplifier. You may. Further, the length of the monospaced portion on the input side may be substantially zero, and the tapered portion is not an essential configuration. That is, it is sufficient 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 device and the semiconductor optical amplifier can be improved. Further, the core width on the output side of the active core layer may be narrower than the core width at the central portion in the optical waveguide direction.

Further, the present invention is not limited to the above embodiments. The present invention also includes a configuration in which the above-mentioned components are appropriately combined. For example, in the semiconductor laser module 1000 shown in FIG. 1, an optical isolator may be arranged between the collimator lens 1004 and the beam splitter 1005. Further, 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 embodiment, and various modifications can be made.

201, 201A, 201B, 201C Active core layer 110b, 200b n type semiconductor layer 110j Spacer layer 110g, 200fp type InP embedded layer 110h, 200g n type InP current blocking layer 110d, 200c p type semiconductor layer 110e, 200d contact layer 200e p-side electrode 110i, 200h SiNx protective film 200ha Opening 110a, 200an-side electrode 100, 100A, 100B Semiconductor laser element 100Ca Optical output end face 110 Embedded waveguide structure region 110c waveguide core layer 113 Input waveguide 120a, 120b Slab Waveguide structure region 130 High-mess type waveguide structure region 141 Input side slab waveguide 141a, 141b Input end face 142 Output side slab waveguide 142a Output end 143 Array waveguide 200, 200A, 200B, 200C Semiconductor optical amplifier 201a, 201Aa, 201Ba , 201Ca Main waveguide section 201Aaa Input side main waveguide section 201Aab Output side main waveguide section 201aa, 201Aac Central section 201b, 201Ab, 201Bb, 201BCb, 201Cb Input side equal width section 201c, 201Ac, 201Bc, 201Bg, 201Cc, 201Cg Tapered section 201Ad , 201Ae, 201Cd, 201Ch Curved waveguide 201Bf, 201Cf Output side equal width part 202, 202A, 202B, 202C Input side 203, 203A, 203B, 203C Output side 204A Optical output end surface 205A Optical input end surface 1000, 1000A Semiconductor laser module 1001 Housing 1001a Mounting part 1002, 1003, 1013 Base 1004 Collimeter lens 1005, 1007 Beam splitter 1006, 1011 Condensing lens 1009 Etalon filter 1008, 1010 PD
1012 Optical fiber 1014 Optical isolator ₁₁₁ 1-111 ₁₂ DFB laser element L1, L2, L3 Laser light N1, N2 Normal line X1, X2 Central axis

Claims (9)

A semiconductor laser device that outputs laser light and
A semiconductor optical amplifier in which the laser beam is input from the input side, the laser beam is amplified and output from the output side, and the like.
An optical coupler that optically couples the laser beam output from the semiconductor laser element to the semiconductor optical amplifier.
Equipped with
The semiconductor optical amplifier does not have a semiconductor regrowth interface.
The active core layer of the semiconductor optical amplifier is
Intervening between two semiconductor layers in the stacking direction,
It extends from the input side of the semiconductor optical amplifier to the output side, and has a monospaced portion, a tapered portion, and a main waveguide portion from the input side.
The core thickness, which is the thickness in the stacking direction, has a uniform core thickness, and the core width, which is the width in the direction orthogonal to the stretching direction when viewed from the stacking direction, is input from the main waveguide . The core width on the side is wider than the core width in the central portion, unlike the core width in the central portion including at least the center in the longitudinal direction which is the direction of the stretching in the main waveguide portion, and is wider on the input side. A region in which the core width narrows toward the central portion is provided as the tapered portion at a position closer to the input side than the main waveguide including the central portion, and the equal width portion is larger than the tapered portion. On the input side, the core width is constant,
The length of the region in the longitudinal direction is 10 μm or more and 200 μm or less .
The optical coupler is a lens.
A semiconductor laser module characterized in that the laser light coupled to the semiconductor optical amplifier by the optical coupler is an elliptical mode field having a long axis in the plane direction of the semiconductor layer . 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 the output side of the laser beam. The semiconductor laser module according to claim 2, wherein the passive waveguide includes a bending waveguide. The semiconductor laser module according to claim 2 or 3, wherein the passive waveguide includes a slab emitting array waveguide diffraction grating. The semiconductor laser module according to any one of claims 1 to 4, wherein the semiconductor laser element has a configuration in which a plurality of laser oscillation units are integrated. The semiconductor laser module according to any one of claims 1 to 5, further comprising a base on which the semiconductor optical amplifier is mounted in a junction-down state. The semiconductor according to any one of claims 1 to 6, wherein the active core layer of the semiconductor optical amplifier is inclined with respect to the end face of the input side on the input side of the semiconductor optical amplifier. Laser module. The semiconductor according to any one of claims 1 to 6, wherein the active core layer of the semiconductor optical amplifier is inclined with respect to the end face of the output side on the output side of the semiconductor optical amplifier. Laser module. The active core layer of the semiconductor optical amplifier according to any one of claims 1 to 8, wherein the core width on the output side is different from the core width at least in the central portion in the optical waveguide direction. Semiconductor laser module.

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