JP5682197B2 - Optical semiconductor device - Google Patents

Description

  The present invention relates to an optical semiconductor element.

  In recent years, an optical transmitter in which a semiconductor laser and a Mach-Zehnder interferometer type optical modulator (hereinafter also simply referred to as an MZ optical modulator) are combined has been developed. This type of optical transmitter is used, for example, in a wavelength division multiplexing transmission system. Further, there is a demand for a small optical transmitter.

As the MZ light modulator, for example, there is an MZ light modulator (hereinafter, also simply referred to as an LN-MZ light modulator) using an electro-optic effect of lithium niobate (LiNbO ₃ : LN) which is a nonlinear optical crystal. The LN-MZ optical modulator has a wide operating wavelength band and can be chirped. Then, it has been proposed to combine a semiconductor laser and an LN-MZ optical modulator together with optical components such as a lens and an isolator and integrate them in the same module to reduce the size of the optical transmitter.

  However, the size of the optical transmitter is limited by the large size of the LN-MZ optical modulator itself and the combination of a plurality of optical components such as a lens and an isolator.

  In addition, by using a planar lightwave circuit (PLC) element formed of a quartz-based material, a semiconductor laser and an LN-MZ optical modulator are integrated in a hybrid manner, thereby further reducing the size of the optical transmitter. It has been proposed to

  However, such an optical transmitter is difficult to manufacture because it is not easy to optically couple the formed parts.

  An optical semiconductor element in which a semiconductor Mach-Zehnder interferometer type optical modulator (hereinafter also referred to as a semiconductor MZ optical modulator) using a semiconductor having a lattice constant comparable to that of the substrate is formed on the same substrate on which the semiconductor laser is formed. Has been proposed. In this case, the semiconductor laser, the semiconductor MZ optical modulator, and the optical waveguide connecting them are linearly arranged on the same substrate. In this optical semiconductor device, the semiconductor laser and the semiconductor MZ optical modulator can be manufactured in-line on the same substrate.

  In the semiconductor MZ optical modulator, in particular, in a semiconductor MZ optical modulator using a quantum confined stark effect (QCSE) that changes the refractive index by applying an electric field to the quantum well structure, LN-MZ light is used. Compared with the modulator, the amount of change in the refractive index is large. Therefore, it is expected that the semiconductor MZ optical modulator can reduce the size and driving voltage of the optical semiconductor element.

  When the semiconductor laser is a Fabry-Perot laser or a distributed feedback (DFB) laser, the element length of the laser is about several hundred μm. On the other hand, in the case of a semiconductor laser in which the wavelength of the output light is variable, particularly in the case of a wavelength variable semiconductor laser having a wide wavelength variable band, the element length of the laser may be several mm.

  In addition, since the combined length of the bent waveguide, the optical coupler, and other elements such as the phase modulation unit is about several millimeters, it is impossible to arrange the semiconductor laser and the semiconductor MZ optical modulator in a straight line. The dimension in the longitudinal direction of the optical semiconductor element is increased.

  Furthermore, the large size of the optical semiconductor element in the longitudinal direction reduces the number of elements that can be manufactured from a single substrate, and the increase in the aspect ratio (aspect ratio) of the element means that the yield in the manufacture of the element. It can also be a cause of lowering.

  Therefore, it is expected to reduce the size of the optical semiconductor element provided with the semiconductor laser and the semiconductor MZ optical modulator.

JP 2007-94336 A JP 2004-22618 A JP-A-2005-159118 JP 2007-93717 A JP 2009-146992 A

  The present specification aims to provide an optical semiconductor device with reduced dimensions.

  In order to solve the above problems, according to one embodiment of the optical semiconductor element disclosed in this specification, a semiconductor laser formed on a substrate, a first phase modulation unit formed on the substrate and having a first optical waveguide, A second phase modulator formed on the substrate and having a second optical waveguide; and an output light of the semiconductor laser formed on the substrate that is split into two, and the branched light is split into the first optical waveguide and the second optical waveguide. A semiconductor laser and a first optical waveguide, comprising: a first optical coupler that outputs; and a second optical coupler that is formed on the substrate and that combines and outputs the output light from the first optical waveguide and the second optical waveguide. The second optical waveguide is at least partially arranged in parallel.

  According to one embodiment of the optical semiconductor element disclosed in the present specification described above, the size is reduced.

  The objects and advantages of the invention will be realized and obtained by means of the elements and combinations particularly pointed out in the appended claims.

  Both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed.

1 is a diagram illustrating a first embodiment of an optical semiconductor device disclosed in this specification. FIG. It is an AA line expanded sectional view of FIG. It is a BB line expanded sectional view of Drawing 1. It is the C-C 'line expanded sectional view of FIG. (A) is an enlarged view of the main part of FIG. 1, (B) shows the intensity distribution of light propagating through the core layer embedded in the first embedded layer, and (C) shows the second embedded layer. The intensity distribution of the light which propagates the core layer embedded in the layer is shown. FIG. 2 is an enlarged sectional view taken along line D-D ′ in FIG. 1. It is FIG. (The 1) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. It is FIG. (2) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. FIG. 9 is a view (No. 3) showing a manufacturing step of the optical semiconductor element of the first embodiment, which is an enlarged sectional view taken along line E-E ′ of FIG. 8; It is FIG. (The 4) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. FIG. 11 is a diagram (No. 5) illustrating a process for manufacturing the optical semiconductor element according to the first embodiment, which is an enlarged cross-sectional view taken along the line F-F ′ in FIG. 10; It is FIG. (6) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. It is FIG. (The 7) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. FIG. 14 is a view (No. 8) showing a manufacturing step of the optical semiconductor element of the first embodiment, which is an enlarged sectional view taken along the line GG of FIG. 13; FIG. 14 is a drawing (No. 9) showing a manufacturing step of the optical semiconductor element of the first embodiment, which is an enlarged sectional view taken along the line H-H in FIG. 13; It is FIG. (10) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. FIG. 17 is a view (No. 11) showing a manufacturing step of the optical semiconductor element according to the first embodiment, which is an enlarged sectional view taken along the line II in FIG. 16; FIG. 17 is a view (No. 12) illustrating a manufacturing step of the optical semiconductor element of the first embodiment, which is an enlarged sectional view taken along the line JJ of FIG. 16; It is FIG. (13) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. FIG. 20 is a view (No. 14) showing a manufacturing step of the optical semiconductor element according to the first embodiment, which is an enlarged sectional view taken along the line KK of FIG. 19; FIG. 20 is a view (No. 15) showing a manufacturing step of the optical semiconductor element of the first embodiment, which is an enlarged sectional view taken along the line LL of FIG. 19; It is FIG. (16) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. It is FIG. (17) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. It is FIG. (18) which shows the manufacturing process of the optical semiconductor element of 1st Embodiment. It is a figure which shows the modification 1 of the optical semiconductor element of 1st Embodiment. It is a figure which shows the modification 2 of the optical semiconductor element of 1st Embodiment. It is the N-N 'line enlarged sectional view of FIG. It is a figure which shows 2nd Embodiment of the optical semiconductor element disclosed to this specification. It is a figure which shows the modification 1 of the optical semiconductor element of 2nd Embodiment. It is a figure which shows the modification 2 of the optical semiconductor element of 2nd Embodiment. It is a figure which shows 3rd Embodiment of the optical semiconductor element disclosed in this specification. It is a figure which shows the other example of the optical semiconductor element disclosed to this specification.

  Hereinafter, a preferred first embodiment of an optical semiconductor device disclosed in this specification will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

  FIG. 1 is a diagram showing a first embodiment of an optical semiconductor device disclosed in this specification. FIG. 2 is an enlarged cross-sectional view taken along line AA in FIG. FIG. 3 is an enlarged sectional view taken along line BB in FIG.

  The optical semiconductor element 10 of the present embodiment is formed on a semiconductor laser 11 formed on a semiconductor substrate 30, a first phase modulation unit 12 formed on the substrate 30 and having a first optical waveguide 12a, and the substrate 30. And a second phase modulator 13 having a second optical waveguide 13a.

  Further, the optical semiconductor element 10 is formed on the substrate 30 and branches the output light of the semiconductor laser 11 into two, and outputs the branched light to the first optical waveguide 12a and the second optical waveguide 13a. 14. The optical semiconductor element 10 includes a second optical coupler 15 that is formed on the substrate 30 and that combines and outputs the output light from the first optical waveguide 12a and the second optical waveguide 13a.

  The first phase modulation section 12 includes a first phase modulation electrode 12b that changes the refractive index of the optical waveguide by applying a modulation electric field to the first optical waveguide 12a together with the first optical waveguide 12a. The first optical waveguide 12a is formed in a straight vertically long shape. The first phase modulation electrode 12b is vertically long and covers the entire longitudinal direction of the first optical waveguide 12a. As shown in FIG. 1, the first phase modulation section 12 is vertically long, and the longitudinal direction thereof coincides with the longitudinal directions of the first optical waveguide 12a and the first phase modulation electrode 12b. The phase of light propagating through the first optical waveguide 12a changes in accordance with the refractive index of the optical waveguide. As shown in FIG. 3, the first phase modulation electrode 12b is disposed above the first optical waveguide 12a.

  The second phase modulation unit 13 includes a second phase modulation electrode 13b that applies a modulation electric field to the second optical waveguide 13a together with the second optical waveguide 13a. The structure of the second phase modulation unit 13 is the same as that of the first phase modulation unit 12 described above.

  The first phase modulation unit 12 and the second phase modulation unit 13 are spaced apart in the width direction and are arranged next to each other in parallel. Here, the width direction is a direction orthogonal to the longitudinal direction of the first optical waveguide 12a and the second optical waveguide 13a. In the optical semiconductor element 10, the first optical waveguide 12a and the second optical waveguide 13a have the same length.

  It is preferable that the distance between the first phase modulation unit 12 and the second phase modulation unit 13 in the width direction is such that no crosstalk occurs between the phase modulation electrodes 12b and 13b. For example, the distance in the width direction of the first phase modulation unit 12 and the second phase modulation unit 13 can be set to 100 to 200 μm.

  Next, the semiconductor laser 11 will be further described. As shown in FIG. 1, the semiconductor laser 11 is vertically long, and the longitudinal direction thereof coincides with the longitudinal directions of the first phase modulator 12 and the second phase modulator 13. These longitudinal directions coincide with the longitudinal direction of the optical semiconductor element 10.

  As shown in FIGS. 1 and 2, the semiconductor laser 11 includes a laser mesa unit 11a and a laser drive electrode 11b that injects a drive current into the laser mesa unit 11a. As shown in FIG. 1, the laser drive electrode 11 is vertically long and covers the entire length of the laser mesa portion 11a. As shown in FIG. 2, the laser drive electrode 11b is disposed above the first optical waveguide 12a.

  The semiconductor laser 11 and the second phase modulator 13 are separated from each other in the width direction. The distance at which the semiconductor laser 11 and the second phase modulation section 13 are separated in the width direction is preferably set such that no crosstalk occurs between the laser drive electrode 11b and the second phase modulation electrode 13b. For example, the distance in the width direction between the semiconductor laser 11 and the second phase modulation unit 13 can be set to 100 to 200 μm.

  As shown in FIG. 1, in the optical semiconductor element 10, the semiconductor laser 11 formed on the same substrate 30, and the first optical waveguide 12a and the second optical waveguide 13a are arranged in parallel so that at least a part thereof overlaps in the longitudinal direction. Placed in.

  In the example shown in FIG. 1, a part of the semiconductor laser 11 in the longitudinal direction overlaps the first optical waveguide 12a and the second optical waveguide 13a in the longitudinal direction. Further, when the length of the semiconductor laser 11 is shorter than the first optical waveguide 12a and the second optical waveguide 13a, the semiconductor laser 11 is entirely in the longitudinal direction of the first optical waveguide 12a and the second optical waveguide 13a. May overlap. When the lengths of the first optical waveguide 12 a and the second optical waveguide 13 a are shorter than the semiconductor laser 11, the first optical waveguide 12 a and the second optical waveguide 13 a are entirely in the longitudinal direction of the semiconductor laser 11. May overlap. By arranging in this way, the dimension in the longitudinal direction of the optical semiconductor element 10 can be further reduced.

  The semiconductor laser 11 is preferably a single mode laser. The semiconductor laser 11 may be a wavelength tunable laser. Specifically, the semiconductor laser 11 includes a distributed feedback (DFB) type laser, a distributed Bragg reflector (DBR) type laser, a super structure grating (SSG) type DBR laser, and the like. Alternatively, a CSG-DR (Chirped Sampled Distributed Distributor) type laser may be used.

  In the present embodiment, the following description is given by taking the case where the semiconductor laser 11 is a DFB type laser as an example.

  Next, the cross-sectional structure of the semiconductor laser 11 will be described below with reference to the drawings.

  As shown in FIG. 2, the semiconductor laser 11 includes a laser mesa portion 11a formed on the substrate 30 and a laser drive electrode 11b formed thereon.

  The laser mesa unit 11 a includes a lower cladding layer 31 disposed on the substrate 30, a diffraction grating layer 32 disposed on the lower cladding layer 31, a spacer layer 33 disposed on the diffraction grating layer 32, and a spacer layer 33. And a core layer 34 of the semiconductor laser disposed on the semiconductor laser. In the diffraction grating layer 32, a diffraction grating having periodicity in the light propagation direction is formed. The laser mesa unit 11a includes a first upper cladding layer 36 disposed on the core layer 34 of the semiconductor laser, a third upper cladding layer 38 disposed on the first upper cladding layer 36, and a third upper cladding layer. And a first contact layer 39 disposed on 38. Further, the portion of the substrate 30 located under the lower cladding layer 31 also forms part of the laser mesa portion 11a.

  The laser drive electrode 11 b includes a first electrode 40 and a second electrode 41. The laser drive electrode 11b is electrically connected to the laser mesa unit 11a through the first electrode 40 and the second electrode 41.

  The laser mesa unit 11 a is embedded by the first embedded layer 42. A first passivation layer 43 is disposed on the first buried layer 42, a second buried layer 44 is disposed on the first passivation layer 43, and a second passivation layer 45 is disposed on the second buried layer 44. Is done. The lower part of the laser drive electrode 11 b is buried with the second buried layer 44.

  The laser mesa unit 11a receives current injection from the laser drive electrode 11b, oscillates laser light, generates heat, and thermally expands. The first buried layer 42 is also heated by the laser mesa unit 11a and thermally expands. Therefore, it is preferable that the laser mesa portion 11a and the first buried layer 42 have no difference in thermal expansion coefficient in order to prevent thermal stress from being generated in the laser mesa portion 11a or the first buried layer 42. If thermal stress is generated in the laser mesa unit 11a or the first buried layer 42, the life of the semiconductor laser 11 may be shortened due to generation of cracks or the like.

  For example, the difference between the thermal expansion coefficients of the first buried layer 42 and the core layer 34 of the semiconductor laser is preferably within ± several% from the viewpoint described above. The material for forming the first buried layer 42 is preferably formed using a semiconductor similar to the substrate. The first buried layer 42 preferably has semi-insulating conductivity in order to increase the efficiency of current injection into the core layer 34.

  In FIG. 1, a region where the first buried layer 42 is formed is shown as a first buried region B1. In the first buried region B1, the semiconductor laser 11 is buried with the first buried layer. Further, the first embedded region B1 is embedded with a first embedded layer 42 in the input side portion of the first bent optical waveguide 16 described later.

  Next, the cross-sectional structure of the first phase modulation unit 12 will be described below with reference to the drawings.

  As shown in FIG. 3, the first optical waveguide 12a of the first phase modulator 12 has a mesa structure.

  The first optical waveguide 12a has the same structure as the laser mesa 11a of the semiconductor laser 11 except for the following points. In the first optical waveguide 12 a, no diffraction grating is formed in the diffraction grating layer 32. An optical waveguide core layer 35 is disposed on the spacer layer 33, and a second upper clad layer 37 is disposed on the optical waveguide core layer 35. Further, both side surfaces of the first optical waveguide 12 a are covered with the first passivation layer 43. The first passivation layer 43 also covers the substrate 30 on both sides of the first optical waveguide 12a. A first phase modulation electrode 12b is disposed on the first optical waveguide 12a. The lower portion of the first phase modulation electrode 12 b is embedded with the second embedded layer 44.

  The first optical waveguide 12a is embedded with a second embedded layer 44 having a lower refractive index than the core layer 35 of the first optical waveguide 12a. From the viewpoint of confinement of light propagating through the first optical waveguide 12a, the difference between the refractive index of the second buried layer 44 and the refractive index of the core layer 35 of the first optical waveguide is preferably large.

  As a material for forming the second embedded layer 44, for example, a resin having a low dielectric constant or air can be used.

  The second phase modulation unit 13 has the same cross-sectional structure as the first phase modulation unit 12, and the above description is also applied to the second phase modulation unit 13 as appropriate.

  In FIG. 1, a region where a mesa structure such as an optical waveguide is embedded by the second embedded layer 44 is shown as a second embedded region B2. In the second embedded region B2, the first optical waveguide 12a, the second optical waveguide 13a, the first optical coupler 14, and the second optical coupler 15 are embedded with the second embedded layer 44. In the second embedded region B2, the output side portion of the first bent optical waveguide 16 described later is embedded by the second embedded layer 44.

  Further, on the back side of the substrate 30, lower electrodes (not shown) are arranged corresponding to the laser drive electrode 11 b and the first and second phase modulation electrodes 12 b and 13 b.

  Next, the first bent optical waveguide 16 that receives the output light of the semiconductor laser 11 and curves in the opposite direction and propagates the light to the first optical coupler 14 will be described below with reference to the drawings.

  As shown in FIG. 1, the optical semiconductor element 10 includes a first bent optical waveguide 16 formed on a substrate 30. The first bent optical waveguide 16 receives the output light of the semiconductor laser 11 and propagates the light by bending the propagation direction by 180 degrees. As described above, the optical semiconductor element 10 includes the first optical coupler between the semiconductor laser 11 arranged in parallel and the first optical waveguide 12a and the second optical waveguide 13a using the first bent optical waveguide 16. The light propagates through 14.

  Next, the cross-sectional structure of the joint portion between the first bent optical waveguide 16 and the semiconductor laser 11 will be described below with reference to the drawings.

  FIG. 4 is an enlarged sectional view taken along line C-C ′ of FIG. 1. FIG. 4 shows a cross-sectional structure in the longitudinal direction at the joint between the first bent optical waveguide 16 and the semiconductor laser 11.

  As shown in FIG. 4, the first bent optical waveguide 16 has the same structure as the first optical waveguide 12a described above except for the following points. In the first bent optical waveguide 16, the first phase modulation electrode 12b is not disposed. Further, the first contact layer 39 is covered with a first passivation layer 43.

  At the junction between the first bent optical waveguide 16 and the semiconductor laser 11, a junction interface S1 between the core layer 35 of the optical waveguide and the core layer 34 of the semiconductor laser is formed. The joining interface S1 is a so-called butt joint interface. Further, at the position of the junction interface S1, the junction interface between the first upper cladding layer 36 disposed on the core layer 34 of the semiconductor laser and the second upper cladding layer 37 disposed on the core layer 35 of the optical waveguide. Is also formed.

  The core layer 35 of the optical waveguide extends on an arc toward the first optical coupler 14 from the junction interface S1 which is the end face of the core layer 34 of the linear semiconductor laser.

  The radius of curvature of the first bent optical waveguide 16 can be determined so as to ensure a preferable separation distance between the semiconductor laser 11 and the second phase modulator 13 described above. In addition, the lower limit value of the radius of curvature of the first bent optical waveguide 16 may be restricted in the manufacturing process. From such a viewpoint, the radius of curvature of the first bent optical waveguide 16 can be set to 100 μm, for example.

  Further, as shown in FIG. 1, the input-side portion of the first bent optical waveguide 17a is included in the first embedded region B1 similarly to the laser mesa portion 11a.

  On the other hand, as shown in FIG. 1, the output-side portion of the first bent optical waveguide 17a connected to the first optical coupler 14 is included in the second buried region B2, and is in the middle of the first bent optical waveguide 17a. The junction interface S <b> 2 between the first buried layer 42 and the second buried layer 44 is formed at this position.

  Next, the position of the bonding interface S2 between the first buried layer 42 and the second buried layer 44 will be described below with reference to the drawings.

  FIG. 5A is an enlarged view of a main part of FIG. FIG. 5B shows the intensity distribution of light propagating through the core layer 35 embedded in the first embedded layer 42. FIG. 5C shows the intensity distribution of light propagating through the core layer 35 embedded in the second embedded layer 44.

  FIG. 5A shows a portion of the first bent optical waveguide 16 extending on the arc from the bonding interface S1 of the laser mesa portion 11a. Further, in FIG. 5A, a bonding interface S2 formed at a position P in the middle of the first bent optical waveguide 16 is indicated by a one-dot chain line. 5A shows a tangent line L1 at the position P of the arc-shaped first bent optical waveguide 16. Further, in FIG. 5A, the straight traveling direction of the light output from the bonding interface S1 is indicated by a straight line L2.

  The position P in the middle of the first bent optical waveguide 16 where the bonding interface S2 is formed is determined by the angle α formed by the tangent line L1 and the straight line L2. The angle α is also the center angle of the arc formed by the position of the bonding interface S1 and the position P with the center of curvature O of the first bent optical waveguide 16 as the center.

  As shown in FIG. 5B, in the portion of the first bent optical waveguide 16 embedded in the first embedded layer 42, the intensity of light propagating through the core layer 35 in the mesa portion 16a of the first bent optical waveguide 16 The distribution extends beyond the width of the core layer 35. On the other hand, as shown in FIG. 5C, in the portion of the first bent optical waveguide 16 embedded in the second embedded layer 44, the intensity distribution of light propagating through the core layer 35 of the mesa portion 16a is the core layer 35. Is almost confined within the width of.

  When light having an intensity distribution as shown in FIG. 5B passes through the junction interface S2, the light is reflected by the junction interface S2 having a different equivalent refractive index, and the first bent optical waveguide 16 is directed toward the semiconductor laser 11. Light that returns inside is generated.

  Therefore, in the optical semiconductor element 10, the junction interface S <b> 2 between the first buried layer 42 and the second buried layer 44 is formed at a position in the middle of the first bent optical waveguide 16, and the second semiconductor layer 11 is reflected toward the semiconductor laser 11. The amount of light returning through the bent optical waveguide 16 is reduced.

  The amount of light that returns to the semiconductor laser 11 due to reflection and returns in the optical waveguide 16 decreases as the value of the angle α that determines the position P of the bonding interface increases.

  On the other hand, the upper limit of the angle α may be determined due to restrictions on the manufacturing process. For example, when the angle α increases, the first buried layer 42 may grow so as to rise on the mesa structure of the first bent optical waveguide 16. In such a case, the angle α is preferably set to a size within a range where the first buried layer 42 does not grow abnormally.

  Therefore, in the present embodiment, the angle α is set to an upper limit value at which the first embedded layer 42 does not grow abnormally when the mesa structure of the first bent optical waveguide 16 is embedded. In this way, by determining the angle α, the position P of the bonding interface S2 between the first buried layer 42 and the second buried layer 44 is determined. For example, the angle α may be 10 degrees.

  Next, the first optical coupler 14 will be described. As the first optical coupler 14, for example, a multimode interference coupler having one input port and two output ports can be used. The cross-sectional structure of the first optical coupler 14 is the same as that of the first bent optical waveguide 16 described above. Note that a multimode interference coupler having two input ports and two output ports may be used as the first optical coupler 14. In this case, the light from the semiconductor laser 11 is input from one input port.

  Next, the second optical coupler 15 will be described. The second optical coupler 15 causes the input two lights to interfere with each other and outputs light having light intensity corresponding to the phase difference. As the second optical coupler 15, for example, a multimode interference coupler having two input ports and two output ports can be used. The cross-sectional structure of the second optical coupler 15 is the same as that of the first bent optical waveguide 16 described above. Note that a multimode interference coupler having two input ports and one output port may be used as the second optical coupler 15.

  As shown in FIG. 1, the optical semiconductor element 10 is formed on the substrate 30 and inputs one of the two output lights of the first optical coupler 14 and bends the propagation direction to make the first optical waveguide 12a. Are provided with a second bent optical waveguide 17a for propagating light. In addition, the optical semiconductor element 10 is formed on the substrate 30, receives the other of the two output lights of the first optical coupler 14, bends the propagation direction, and propagates light to the second optical waveguide 12 b. A bent optical waveguide 17b is provided.

  As shown in FIG. 1, the optical semiconductor element 10 is formed on the substrate 30, receives the output light of the first optical waveguide 12 a, bends the propagation direction, and propagates the light to the second optical coupler 15. A four-bend optical waveguide 18a is provided. The optical semiconductor element 10 includes a fifth bent optical waveguide 18b that is formed on the substrate 30 and that receives the output light of the second optical waveguide 13a, bends the propagation direction, and propagates the light to the second optical coupler 15. .

  The optical semiconductor element 10 includes sixth and seventh optical waveguides 19a and 19b that input light from the two output ports of the second optical coupler 15 and output the light to the outside. The exposed end surfaces of the sixth and seventh optical waveguides 19a and 19b are preferably coated with antireflection, for example.

  The cross-sectional structures of the second to fifth bent optical waveguides 17a, 17b, 18a and 18b and the sixth and seventh optical waveguides 19a and 19b are the same as those of the first bent optical waveguide 16 described above.

  In the second buried region B2, the second and third bent optical waveguides 17a and 17b, the fourth and fifth bent optical waveguides 18a and 18b, and the sixth and seventh optical waveguides 19a and 19b are provided. 2 embedded in the embedded layer 44.

  Further, the first optical coupler 14, the first phase modulator 12 and the second phase modulator 13, the second optical coupler 15, the second and third bent optical waveguides 17a and 17b, the fourth, The fifth bent optical waveguides 18a and 18b and the sixth and seventh optical waveguides 19a and 19b form a semiconductor MZ optical modulator on the same substrate 30.

  As shown in FIG. 1, in the optical semiconductor element 10, the semiconductor laser 11 is disposed on one side of the first phase modulation unit 12 and the second phase modulation unit 13 that are adjacently arranged in parallel. In the optical semiconductor element 10, the heater 22 formed on the substrate 30 is disposed on the other side of the first phase modulation unit 12 and the second phase modulation unit 13.

  The heater 22 includes a vertically long heater body 22a and a pair of heater electrodes 22b and 22c that supply electric power to the heater body 22a. The heater electrodes 22b and 22c are connected to both ends of the heater body 22a.

  The longitudinal direction of the heater body 22a coincides with the longitudinal directions of the semiconductor laser 11, the first optical waveguide 12a, and the second optical waveguide 13a.

  The distance between the heater body 22a and the first phase modulation unit 12 is preferably the same as the distance between the semiconductor laser 11 and the second phase modulation unit 13.

  In the optical semiconductor element 10, since the semiconductor laser 11 into which the current has been injected generates heat, a temperature gradient is formed in the width direction of the optical semiconductor element 10, and the temperature on the second phase modulation unit 13 side is high and the first phase modulation is performed. The temperature of the part 12 becomes relatively low. When a temperature difference is generated between the optical paths constituting the interferometer of the MZ modulator, the optical path length of the interferometer changes, so that the phase difference changes. Thus, it is very difficult to adjust the phase difference that changes depending on the driving state of the semiconductor laser 11. Further, the first optical waveguide 12a and the second optical waveguide 13a also have a problem that the amount of change in refractive index when an electric field is applied differs depending on the generated temperature difference.

  Therefore, in the optical semiconductor element 10, the heater 22 is used to cancel the temperature gradient in the width direction of the optical semiconductor element 10 so that the first optical waveguide 12a and the second optical waveguide 13a have the same temperature.

  In the optical semiconductor element 10, as the method for driving the heater 22, the same amount of electric power as that injected into the semiconductor laser 11 is supplied to the heater electrode 22.

  Further, a temperature sensor may be disposed in each of the first optical waveguide 12a and the second optical waveguide 13a, and the heater 22 may be driven so that the temperatures of the respective optical waveguides are the same.

  Next, the cross-sectional structure of the heater 22 will be described below with reference to the drawings.

  6 is an enlarged sectional view taken along line D-D ′ of FIG. 1. FIG. 6 shows a cross-sectional structure in the longitudinal direction of the joint portion between the heater body 22a and the heater electrode 22b.

  As shown in FIG. 6, the heater body 22 a is formed on the first embedded layer 42 disposed on the substrate 30, the first passivation layer 43 disposed on the first embedded layer 42, and the first passivation layer 43. A second buried layer 44 disposed thereon. The heater main body 22 a includes a heat generation layer 46 disposed on the second embedded layer 44 and a second passivation layer 45 disposed on the heat generation layer 46. The heat generating layer 46 can be formed of Ti, for example.

  Further, as shown in FIG. 6, the heater electrode 22 b is arranged on the heat generating layer 46 with the first electrode 40 and the second electrode 41 interposed in order.

  Next, an example of a preferable method for manufacturing the above-described optical semiconductor element 10 of the present embodiment will be described below with reference to the drawings.

  First, as shown in FIG. 7, the lower cladding layer 31 is formed on the substrate 30. As a method for forming the lower cladding layer 31, for example, epitaxial growth by metal organic chemical vapor deposition (MOCVD) can be used. Similarly, the diffraction grating layer 32 to the first upper cladding layer 36 to be described later can also be formed using the MOCVD method. For example, n-InP can be used as a material for forming the substrate 30. For example, the lower cladding layer 31 can be made to have a thickness of 200 nm by using n-InP as a forming material.

  A diffraction grating layer 32 is formed on the lower cladding layer 31. As a material for forming the diffraction grating layer 32, for example, n-InGaAsP having a composition wavelength of 1.2 μm can be used. The thickness of the diffraction grating layer 32 can be set to, for example, 70 nm. In addition, for example, a diffraction grating having a period of about 240 nm in the light propagation direction can be formed in the region to be the semiconductor laser of the diffraction grating layer 32 using electron beam (EB) exposure and dry etching. Note that a diffraction grating is not formed in a region of the diffraction grating layer 32 that does not become a semiconductor laser.

  Then, the spacer layer 33 is formed on the diffraction grating layer 32. For example, the spacer layer 33 can be made to have a thickness of 100 nm by using n-InP as a forming material.

  Then, the core layer 34 of the semiconductor laser is formed on the spacer layer 33. The core layer 34 is formed by a multilayer quantum well (MQW) active layer and SCH layers disposed above and below the MQW active layer. The MQW active layer is formed by, for example, using i-InGaAsP as a forming material and laminating a barrier layer having a thickness of 15 nm and a well layer having a thickness of 5 nm by eight periods, and a PL emission wavelength of 1.55 μm. can do. A barrier layer is disposed inside each SCH layer. For example, i-InGaAsP having a composition wavelength of 1.15 μm is used as a forming material, and the thickness of the SCH layer can be 12.5 nm. The core layer 34 can be, for example, 200 nm.

  A first upper cladding layer 36 is formed on the core layer 34 of the semiconductor laser. For example, the first upper cladding layer 36 can be made to have a thickness of 200 nm by using p-InP as a forming material.

Next, as shown in FIG. 8, a patterned first mask layer M <b> 1 is formed on the region of the first upper cladding layer 36 to be a semiconductor laser using a technique such as photolithography. For the first mask layer M1, for example, SiO ₂ can be used as a forming material. As a method for forming the first mask layer M1, for example, a chemical vapor deposition (CVD) method can be used.

  Next, as shown in FIG. 9, using the first mask layer M1 as a mask, the first upper cladding layer 36 and the core layer are formed on the region where the first mask layer M1 is not formed using wet etching or the like. 34 is selectively removed and the spacer layer 33 is exposed.

  Next, as shown in FIGS. 10 and 11, using the first mask layer M1 as a selective growth mask, the core layer 35 of the optical waveguide on the spacer layer 33 in the region where the first mask layer M1 is not formed, The second upper cladding layer 37 is formed in order. As a method for forming the core layer 35 and the second upper cladding layer 37, for example, epitaxial growth by MOCVD method can be used. For example, the core layer 35 may be made of i-InGaAsP having a composition wavelength of 1.38 μm as a forming material and may have a thickness of 200 nm. The second upper cladding layer 37 can be made to be 200 nm in thickness by using p-InP as a forming material. In this way, the core layer 35 of the optical waveguide is butt-joint grown with respect to the core layer 34 of the semiconductor laser to form a bonding interface S1 between the core layer 35 of the optical waveguide and the core layer 34 of the semiconductor laser. Then, the first mask layer M1 is removed.

  In addition, in the future, the optical waveguide structure including the core layer 35 of the optical waveguide will have a first bent optical waveguide 16, first and second optical waveguides 12 a and 13 a, and first and second optical couplers 14 and 15. The second to fifth bent optical waveguides 17a, 17b, 18a, 18b and the sixth and seventh optical waveguides 19a, 19b are formed.

  Next, as shown in FIG. 12, a third upper cladding layer 38 and a first contact layer 39 are sequentially formed on the first upper cladding layer 36 and the second upper cladding layer 37. As a method for forming the third upper cladding layer 38 and the first contact layer 39, for example, MOCVD can be used. For example, the third upper cladding layer 38 may be 1200 nm in thickness by using p-InP as a forming material. For example, the first contact layer 39 may be formed using p-InGaAs as a forming material and may have a thickness of 300 nm.

Next, as shown in FIG. 13, a patterned second mask layer M2 is formed on the first contact layer 39 using a technique such as photolithography. SiO ₂ was used as a material for forming the second mask layer M2. Then, using the second mask layer M2 as a mask, a region where the second mask layer M2 is not formed is removed by etching, and a mesa structure as shown in FIGS. 14 and 15 is formed. As an etching method, for example, ICP-RIE can be used. By this etching, a portion having a thickness of about 3 μm is removed from the surface to form a mesa structure. In addition, a part of the surface of the substrate 30 is also removed by this etching. FIG. 14 is an enlarged sectional view taken along line GG in FIG. 13 of the mesa structure for forming the semiconductor laser. FIG. 15 is an enlarged sectional view taken along the line HH of FIG. 13 of the mesa structure forming the first optical waveguide. As shown in FIG. 13, the core layer forming the first bent optical waveguide is bent and formed in the same manner as the second mask layer M2.

  Next, as shown in FIGS. 16 and 17, a patterned third mask layer M3 is formed on the substrate 30 on which the mesa structure is formed using a technique such as photolithography. For example, SiN can be used as a material for forming the third mask layer M3. The region where the third mask layer M3 is formed will become the second buried region B2 in the future. For the mesa structure portion forming the first bent optical waveguide, the third mask layer M3 is formed so as to cover up to the position P described with reference to FIG. In other words, the third mask layer M3 is not formed on the mesa structure portion for forming the semiconductor laser and the portion on the semiconductor laser side from the position P of the mesa structure for forming the first bent optical waveguide.

  Then, as shown in FIG. 18, using the second mask layer M2 and the third mask layer M3 as a selective growth mask, the first buried layer is formed on the region where the second mask layer M2 and the third mask layer M3 are not formed. 42 is formed, and the mesa structure on the substrate 30 is embedded by the first embedded layer 42. As a method for forming the first buried layer 42, for example, an MOCVD method can be used. As a material for forming the first buried layer 42, for example, semi-insulating InP (SemiInsulating-InP) can be used. The portion where the first buried layer 42 is formed becomes the first buried region B1.

  Then, the second mask layer M2 and the third mask layer M3 are removed. These mask layers are removed using, for example, a hydrofluoric acid-based etchant.

Next, a first passivation layer 43 is formed on the entire surface of the substrate 30. As a method for forming the first passivation layer 43, for example, a CVD method can be used. As a material for forming the first passivation layer 43, for example, SiO ₂ can be used.

  Then, as shown in FIGS. 19 and 20, the second embedded layer 44 is formed on the first passivation layer 43, and the mesa structure of the second embedded region B <b> 2 is embedded by the second embedded layer 44. As a method for forming the second buried layer 44, for example, a spin coating method can be used. In addition, as a material for forming the second embedded layer 44, for example, a low refractive index material such as benzocyclobutene (BCB) can be used. The substrate 30 on which the BCB is spin-coated is subjected to an appropriate heat treatment. Here, FIG. 20 shows a cross-sectional structure corresponding to the position shown in FIG.

  As shown in FIG. 21, the second buried layer 44 is also formed on the first buried layer 42 included in the first buried region B <b> 1 via the first passivation layer 43. Here, FIG. 21 shows a cross-sectional structure corresponding to the position shown in FIG.

  Next, the heat generating layer 46 is formed on the entire surface of the second embedded layer 44. As a method for forming the heat generating layer 46, for example, sputtering can be used. Moreover, as a forming material of the heat generating layer 46, for example, Ti can be used. Then, a mask pattern (not shown) having an opening in the region where the heater body is formed is formed on the heat generating layer 46, and the heat generating layer 46 in the region where the mask pattern is not formed is formed by ICP-RIE or the like. It is removed using dry etching. Then, after the mask pattern is removed, a second passivation layer 45 is formed on the entire surface of the substrate 30. As a method for forming the second passivation layer 45, for example, plasma CVD can be used. Further, as a material for forming the second passivation layer 45, for example, SiN can be used.

  Then, a patterned fourth mask layer M4 having an opening in a region where the laser driving electrode, the first and second phase modulation electrodes, and the heater electrode are formed is formed, and using this fourth mask layer M4, The second passivation layer 45 exposed in the opening is removed by wet etching or the like. As a material for forming the fourth mask layer M4, for example, a photoresist can be used.

  Subsequently, the portion of the second embedded layer 44 exposed in the region where the laser drive electrode and the first and second phase modulation electrodes are formed is removed using dry etching such as ICP-RIE, The first passivation layer 43 is exposed. As sectional views in this state, FIG. 22 shows an enlarged sectional view at a position corresponding to the line KK in FIG. 19, and FIG. 23 shows an enlarged sectional view at a position corresponding to the line LL in FIG. . As a cross-sectional view of this state, FIG. 24 shows an enlarged cross-sectional view corresponding to the line M-M ′ of FIG. 19.

  Next, the portion of the first passivation layer 43 exposed at the opening of the fourth mask layer M4 in the region where the laser driving electrode and the first and second phase modulation electrodes are formed is removed using wet etching or the like. As a result, the first contact layer 39 having a mesa structure is exposed.

  Then, the first electrode 40 is formed on the entire surface of the substrate 30. The first electrode 40 is formed on the first contact layer 39 in the opening of the fourth mask layer M4 in the region where the laser driving electrode and the first and second phase modulation electrodes are formed. The first electrode 40 is formed so as to cover the heat generating layer 46 in the opening of the fourth mask layer M4 in the region where the heater electrode is formed. The first electrode 40 is formed as an Au / Zn / Au film, for example, using a vacuum deposition method. Then, the portion of the first electrode 40 formed on the fourth mask layer M4 is removed together with the fourth mask layer M4.

  Then, the second electrode 41 is formed on the entire surface of the substrate 30. The second electrode 41 is formed as a Ti / Pt / Au film by using, for example, a sputtering method. A mask pattern (not shown) having an opening in a region where the laser driving electrode, the first and second phase modulation electrodes, and the heater electrode are formed is formed on the second electrode 41. Then, using the second electrode 41 as an electrode, a conductive layer is plated on a portion on the second electrode 41 exposed at the opening of the mask pattern. Au can be used as a material for forming the conductive layer. Then, after the mask pattern is removed, the portion of the second electrode 41 in the region where the conductive layer is not formed is removed using dry etching or the like using the conductive layer formed by plating as a mask.

  Thus, the portion of the conductive layer plated in the region to be the laser drive electrode becomes the laser drive electrode, and the portion of the conductive layer plated in the region to be the first and second phase modulation electrodes is the first and second. It becomes a phase modulation electrode. Further, the portion of the conductive layer plated in the region to be the heater electrode becomes the heater electrode.

  In this way, the structure shown in FIGS. 1 to 4 and 6 is formed.

  Then, the back surface of the substrate 30 (the surface opposite to the surface on which the electrodes and the like are formed) is polished so that the thickness of the substrate 30 is about 150 μm, and is formed on the entire surface of the back surface by, for example, vacuum deposition. An AuGe / Au film is formed. Then, a mask pattern having an opening appropriately patterned using a photoresist is formed on the AuGe / Au film, and then Au plating is formed on the AuGe / Au portion exposed in the opening, so that the lower electrode is formed. It is formed. Thereafter, the substrate 30 from which the mask pattern has been removed is appropriately subjected to heat treatment, and contacts having good ohmic properties are obtained on the front surface and the back surface of the substrate 30 to complete the optical semiconductor device shown in FIG. .

  According to the optical semiconductor element 10 of the present embodiment described above, the semiconductor laser 11 and the semiconductor MZ optical modulator are formed on the same substrate, and the longitudinal dimension thereof is reduced.

  Further, according to the optical semiconductor element 10, the heater 22 is supplied with electric power equivalent to the electric power supplied to the semiconductor laser 11, thereby driving the semiconductor laser 11 in the width direction of the optical semiconductor element 10. By canceling the temperature gradient, the temperatures of the first optical waveguide 12a and the second optical waveguide 13a can be made the same. Accordingly, the phase adjustment between the two optical waveguides can be performed without considering the temperature difference between the two optical waveguides.

  Further, according to the optical semiconductor element 10, the number of elements that can be manufactured from one substrate is increased by reducing the longitudinal dimension.

  Furthermore, according to the optical semiconductor element 10, since the dimension in the longitudinal direction is reduced, the aspect ratio (aspect ratio) of the element is reduced, so that the yield in manufacturing the element is improved.

  Next, modifications of the optical semiconductor device of the first embodiment described above will be described below with reference to the drawings.

  FIG. 25 is a diagram illustrating a first modification of the optical semiconductor device according to the first embodiment.

  As illustrated in FIG. 25, in the optical semiconductor element 10 a of Modification Example 1, each of the first phase modulation unit 12 and the second phase modulation unit 13 includes a phase adjustment unit 23 formed on the substrate 30. The phase adjustment unit 23 is formed by a portion of the first optical waveguide 12a on the second bent optical waveguide 17a side, a portion of the second optical waveguide 13a on the third bent optical waveguide 17b side, and the phase adjustment electrode 23a.

  The phase adjustment unit 23 applies a voltage to the phase adjustment electrode 23a to change the phase of light propagating in the first optical waveguide 12a or the second optical waveguide 13a to the first phase modulation electrode 12b or the second phase modulation electrode. It can be controlled independently of the modulation by 13b.

  There may be a deviation due to processing accuracy in the width of the optical waveguide or the dimensions of the optical coupler. Due to such a displacement, a phase difference occurs between the light incident on the first optical waveguide 12a and the light incident on the second optical waveguide 13a.

  Therefore, in the first modification, the phase adjustment unit 23 is disposed in each of the first phase modulation unit 12 and the second phase modulation unit 13, and the light incident on the first optical waveguide 12a and the second optical waveguide 13a are incident. The phase difference from the light is adjusted.

  The arrangement of the phase adjusting unit 23 in each of the first phase modulating unit 12 and the second phase modulating unit 13 as in the optical semiconductor element 10a of the modified example 1 may be applied to other embodiments or modified examples thereof. good.

  The phase adjustment unit 23 may be disposed between each of the first phase modulation unit 12 and the second phase modulation unit 13 and the second optical coupler 15.

  FIG. 26 is a diagram illustrating a second modification of the optical semiconductor device according to the first embodiment. FIG. 27 is an enlarged sectional view taken along line N-N ′ of FIG. 26.

  The optical semiconductor element 10b of Modification 2 includes a semiconductor laser 24 whose output light wavelength is variable. Specifically, as the semiconductor laser 24, a super structure grating (SSG) type DBR laser (hereinafter also simply referred to as SSG-DBR) is used.

  As shown in FIG. 26, the semiconductor laser 24 has a front DBR region 24a, a phase adjustment region 24b, a gain region 24c, and a rear DBR region 24d. The semiconductor laser 24 also includes a first drive electrode 24e that injects current into the front DBR region 24a, a second drive electrode 24f that injects current into the phase adjustment region 24b, and a third drive that injects current into the gain region 24c. An electrode 24g and a fourth drive electrode 24h for injecting current into the rear DBR region 24d are provided. In the SSG-DBR type laser, a wide wavelength tunable operation can be obtained using the vernier effect by individually controlling the front and rear two DBR regions. Therefore, the optical semiconductor element 60 can output signal light at a plurality of wavelengths.

  The front DBR region 24 a, the phase adjustment region 24 b, the gain region 24 c, and the rear DBR region 24 d are arranged in series on the substrate 30. Similarly, the laser mesa portions forming the respective regions are arranged in series.

  The front DBR region 24a and the phase adjustment region 24b are integrally formed with a core layer. The core layer forming the rear DBR region 24d is formed of the same material as the front DBR region 24a and the phase adjustment region 24b. The front DBR region 24a, the phase adjustment region 24b, and the rear DBR region 24d are collectively referred to as a refractive index control region. The core layer of the gain region 24c is formed of a material different from that of the core layer of the refractive index control region.

  As shown in FIG. 26, the first bent optical waveguide 16 extends in an arc shape from one end face of the front DBR region 24 a toward the first optical coupler 14.

  The output light of the semiconductor laser 24 is output to the first bent optical waveguide 16 from one end face of the front DBR region 24a. The first bent optical waveguide 16 has a core layer that inputs light from the input-side core layer, and that bends and propagates the light to the output-side core layer.

  In the second modification, the portion on the front DBR region 24a side on the input side of the core layer forming the first bent optical waveguide 16 is formed integrally with the core layer of the front DBR region 24a on the input side. On the other hand, the first optical coupler 14 side on the output side of the core layer of the first bent optical waveguide 16 is formed integrally with the core layer of the first optical coupler 14 on the output side.

  As shown in FIG. 27, a junction interface S3 between the core layer 34a of the input-side front DBR region 24a and the core layer 35 of the output-side first optical coupler 14 is located at a position in the middle of the first bent optical waveguide 16. It is formed.

  In the optical semiconductor device 10b of Modification 2, the bonding interface S3 of the different core layers 34a and 35 is disposed at a position in the middle of the first bent optical waveguide 16, and the first bent optical waveguide 16 is reflected by reflection at the bonding interface S3. The amount of light returning to the semiconductor laser 24 is reduced.

  Further, the joint interface S2 between the first buried layer 42 and the second buried layer 44 is disposed at a position in the middle of the first bent optical waveguide 16 as in the first embodiment described above.

  Next, a method for manufacturing the optical semiconductor element 10b of Modification 2 will be described below.

  The manufacturing method of Modification 2 is the same as the manufacturing method of the optical semiconductor element 10 described above except for the method of forming the semiconductor laser 24. Therefore, the formation of the semiconductor laser 24 will be described below.

  The major difference between the method of forming the semiconductor laser 24 and the method of forming the semiconductor laser 11 in the method of manufacturing the optical semiconductor element 10 described above is that the core layer in the refractive index control region is grown by butt joint with respect to the core layer in the gain region 24c. And the fact that diffraction gratings are formed in the front DBR region 24a and the rear DBR region 24d, but no diffraction grating is formed in the core layer of the gain region 24c.

  Specifically, in FIG. 7, after the core layer of the gain region 24c and the first upper cladding layer 36 are formed on the entire surface of the spacer layer 32, only on the region of the core layer where the gain region 24c is formed. A mask pattern is formed. Then, the first upper cladding layer 36, the core layer of the gain region 24c, and the spacer layer 32 in the region where the mask pattern is not formed are removed by etching. Then, a diffraction grating is formed using dry etching or the like in a portion of the diffraction grating layer 32 in a region where the front DBR region 24a and the rear DBR region 24d are formed. Then, the spacer layer 32, the core layer 34a of the refractive index control region, and the first upper cladding layer 36a are formed in the region where the mask pattern is not formed, and refracted with respect to the core layer of the gain region 24c. The core layer of the rate control region is grown by butt joint. Then, a mask pattern is formed in the region where the semiconductor laser 24 is formed and the portion on the semiconductor laser side in the first bent optical waveguide (up to the portion where the junction interface S3 in FIG. 26 is formed), and this mask pattern is formed. Even the core layer in the unprocessed region is removed by wet etching or the like. Then, the core layer 35 and the second upper cladding layer 37 of the optical waveguide are formed on the region other than where the semiconductor laser side portion of the semiconductor laser and the first bent optical waveguide is formed. Subsequent steps are the same as in the manufacturing method described above. In addition, regarding the formation of the drive electrode of the semiconductor laser 24 of Modification 2, the mask pattern may be changed as appropriate.

  Further, in the optical semiconductor element 10b of Modification 2, the core layer of a passive optical waveguide such as a bent optical waveguide may be formed using the core layer in the refractive index control region.

  A core layer of an optical waveguide integrally formed with an input-side core layer, such as a core layer of a semiconductor laser, in the middle of the first bent optical waveguide, as in the optical semiconductor element 10b of Modification 2, and the first light Arrangement of the bonding interface between the core layer of the optical waveguide formed integrally with the core layer on the output side such as the core layer of the coupler may be applied to other embodiments or modifications thereof.

  Next, the optical semiconductor elements of the second and third embodiments disclosed in this specification will be described below with reference to the drawings. Regarding points that are not particularly described in the second and third embodiments, the description in detail regarding the first embodiment is applied as appropriate. 28 to 31, the same reference numerals are given to the same forming elements as those in FIGS. 1 to 27.

  FIG. 28 is a diagram illustrating a second embodiment of the optical semiconductor element disclosed in this specification.

  In the optical semiconductor device 50 of the present embodiment, the semiconductor laser 11 is disposed between the first optical waveguide 12a and the second optical waveguide 13a. Each of the first optical waveguide 12a and the second optical waveguide 13a is separated from the semiconductor laser 11 by an equal distance.

  In the optical semiconductor element 50, the heat generated by the semiconductor laser 11 is evenly transmitted to the first optical waveguide 12a and the second optical waveguide 13a, so that there is a temperature difference between the first optical waveguide 12a and the second optical waveguide 13a. Does not occur. For this reason, in the optical semiconductor element 50, the phase difference due to the temperature gradient does not occur between the first optical waveguide 12a and the second optical waveguide 13a. Therefore, the heater of the first embodiment described above is not disposed.

  The optical semiconductor element 50 includes an eighth optical waveguide 25 that receives the output light of the semiconductor laser 11 and propagates the light to the first optical coupler 14. The eighth optical waveguide 25 extends linearly from one end face from which the semiconductor laser 11 outputs light toward the first optical coupler 14 toward the first optical coupler 14.

  In the optical semiconductor element 50, the second bent optical waveguide 17a receives one of the two output lights from the first optical coupler 14 and bends 180 degrees in the opposite direction to transmit light to the first optical waveguide 12a. Propagate. Similarly, the third bent optical waveguide 17b inputs the other of the two output lights of the first optical coupler 14 and bends it 180 degrees in the opposite direction to propagate the light to the second optical waveguide 13a.

  The radius of curvature of the second and third bent optical waveguides 17a and 17b ensures a preferable separation distance between the semiconductor laser 11 and the first and second phase modulators 12 and 13 as described in the description of the first embodiment. Can be determined as follows. Further, the lower limit value of the radius of curvature of the second and third bent optical waveguides 17a and 17b may be restricted in the manufacturing process. From such a viewpoint, the curvature radii of the second and third bent optical waveguides 17a and 17b can be set to 100 μm, for example.

  The semiconductor laser 11 has a reflection film 11c that reflects light toward one end surface on the end surface opposite to the one end surface that outputs light toward the first optical coupler. Thus, in the optical semiconductor element 50, stray light is prevented from leaking from the other end face of the semiconductor laser 11 to the semiconductor MZ optical modulator.

  In the optical semiconductor element 50, the first buried region B1 includes the first of the semiconductor laser 11, the eighth optical waveguide 25, the first optical coupler 14, the second bent optical waveguide 17a, and the third bent optical waveguide 17b. A portion on the optical coupler 14 side is included. Accordingly, portions of the second bent optical waveguide 17 a and the third bent optical waveguide 17 b on the first optical coupler 14 side are embedded in the first embedded layer 42.

  Further, in the optical semiconductor element 50, the second embedded region B2 includes a portion of the second bent optical waveguide 17a and the third bent optical waveguide 17b on the first optical waveguide 12a or second optical waveguide 13a side. Therefore, portions of the second bent optical waveguide 17 a and the third bent optical waveguide 17 b on the first optical waveguide 12 a or the second optical waveguide 13 a side are embedded by the second embedded layer 44. The second buried region B2 includes first and second optical waveguides 12a and 13a, fourth and fifth bent optical waveguides 18a and 18b, a second optical coupler 15, and sixth and seventh optical waveguides. 19a, 19b.

  As shown in FIG. 28, a junction interface S2 between the first embedded layer 42 and the second embedded layer 44 is formed at a position in the middle of the second bent optical waveguide 17a and the third bent optical waveguide 17b. Thus, the reflection of light is reduced by disposing the bonding interface S2 at a position in the middle of the second bent optical waveguide 17a and the third bent optical waveguide 17b.

  Next, the manufacturing method of the optical semiconductor element 50 of 2nd Embodiment is demonstrated below.

  The manufacturing method of the optical semiconductor device 50 of the second embodiment is the same as the manufacturing method of the optical semiconductor device 10 described above except for the shape of the mask pattern to be used. In the optical semiconductor element 50, the shape or arrangement of the semiconductor laser, the first and second phase modulation units, and other optical waveguides are different from those of the first embodiment. Therefore, if the mask pattern used for manufacturing the optical semiconductor element 50 of the second embodiment is appropriately changed, it can be manufactured in the same manner as in the first embodiment described above. Moreover, the modification of 2nd Embodiment mentioned later can be manufactured similarly.

  According to the optical semiconductor element 50 of the present embodiment described above, the same effects as those of the first embodiment described above are exhibited.

  Moreover, according to the optical semiconductor element 50, since a heater like 1st Embodiment mentioned above is not used, power consumption is reduced.

  Next, a modification of the optical semiconductor device of the second embodiment described above will be described below with reference to the drawings.

  FIG. 29 is a diagram illustrating a first modification of the optical semiconductor device according to the second embodiment.

  The optical semiconductor element 50 a of Modification 1 includes a light absorbing unit 26 adjacent to an end surface opposite to one end surface from which the semiconductor laser 11 outputs light toward the first optical coupler 14.

  The light absorption unit 26 includes a light absorption mesa unit 26a formed by extending the laser mesa unit 11a of the semiconductor laser 11, and a light absorption drive electrode 26b that applies a reverse voltage to the light absorption mesa unit 26a.

  The light absorption unit 26 absorbs light by applying a voltage to the light absorption drive electrode 26b in a direction opposite to that of the semiconductor laser 11. In this way, in the optical semiconductor element 50a, stray light is prevented from leaking from the other end face of the semiconductor laser 11 to the semiconductor MZ optical modulator.

  Further, it may be used to adjust the diffraction grating provided in the diffraction grating layer 34 of the laser mesa portion 11a of the semiconductor laser 11 to reduce the amount of light leaking from the other end face.

  FIG. 30 is a diagram illustrating a second modification of the optical semiconductor device according to the second embodiment.

  The optical semiconductor element 50b of Modification 2 is different from the optical semiconductor element of the second embodiment described above in the position of the junction interface S2 between the first embedded region B1 and the second embedded region B2.

  As shown in FIG. 30, in the optical semiconductor element 50b, the semiconductor laser side of the semiconductor laser 11, the eighth optical waveguide 25, and the first optical coupler 14, which is a multimode interference coupler, is included in the first buried region B1. 11 parts are included. Specifically, the first optical coupler 14 is embedded in the first buried layer 42 up to the vicinity of the end of the first optical coupler 14 on the semiconductor laser 11 side.

  Further, in the optical semiconductor element 50b, the second embedded region B2 includes a portion of the first optical coupler 14 on the second bent optical waveguide 17a side and the third bent optical waveguide 17b side. Portions of the first optical coupler 14 on the second bent optical waveguide 17a side and the third bent optical waveguide 17b side are embedded with a second embedded layer 44. The second embedded region B2 includes second and third bent optical waveguides 17a and 17b, first and second optical waveguides 12a and 13a, fourth and fifth bent optical waveguides 18a and 18b, and second An optical coupler 15 and sixth and seventh optical waveguides 19a and 19b are included.

  As shown in FIG. 30, the junction interface S <b> 2 between the first buried layer 42 and the second buried layer 44 is formed in the vicinity of the end portion of the first optical coupler 14 on the semiconductor laser 11 side.

  In the vicinity of the input side end of the first optical coupler 14 which is a multimode interference coupler, the distribution of light is concentrated at the center in the width direction to which the eighth optical waveguide 25 is connected. The amount of light distributed is small. Therefore, by arranging the junction interface S2 between the first buried layer 42 and the second buried layer 44 in the vicinity of the end of the first optical coupler 14 on the semiconductor laser 11 side, the influence of light reflection is reduced. The

  From the same concept, the junction interface S <b> 2 between the first buried layer 42 and the second buried layer 44 may be disposed in the vicinity of the output side end of the first optical coupler 14. In the vicinity of the output side end portion of the first optical coupler 14, the multimode interference light propagating through the first optical coupler 14 is self-imaged, and the second and third bent optical waveguides 17a and 17b. Concentrate on the connection. Therefore, even in the vicinity of the output-side end portion of the first optical coupler 14, the distribution of light in places other than the connection portion of the optical waveguide is reduced.

  FIG. 31 is a diagram illustrating a third embodiment of the optical semiconductor element disclosed in this specification.

  The optical semiconductor device 60 of the present embodiment differs from the second embodiment described above in the structure of the first optical coupler 14 and the shapes of the second and third bent optical waveguides 17a and 17b.

  In the optical semiconductor element 60, the first optical coupler 14, which is a multimode interference coupler, is opposed to the first end face 14 a for inputting the output light of the semiconductor laser 11 and the first end face 14 a, and the multimode is propagated inside. A second end face b that reflects the interference light and folds it back in the direction of the first end face a. The first optical coupler 14 outputs two lights branched from the first end face 14a.

  The first optical coupler 14 folds the optical path of the multimode interference coupler having one input port and two output ports at an intermediate position, thereby maintaining the optical path length and halving the dimension in the light propagation direction. Has a reduced structure. The light input from the eighth optical waveguide 25 to the first end face 14a of the first optical coupler 14 propagates toward the second end face 14b, is reflected by the second end face 14b and is turned back, and then the first end face 14a. , And the light branched into two on both sides of the connection portion of the eighth optical waveguide 25 forms a self-image.

  The position of the second end face 14a may be determined by cleaving, but is preferably determined using a technique such as dry etching from the viewpoint of improving the accuracy of the reflection position. In this case, the position of the second end face 14a is determined by using a mask pattern as in the formation of the mesa structure of the optical coupler or the optical waveguide. If this technique is used, the position of the second end face 14a can be determined with submicron accuracy.

In addition, it is preferable to form a reflective film 14c having a high reflectance on the second end face 14a in order to reduce light loss. As the reflective film 14c, for example, a multilayer film formed by laminating SiO ₂ and Si may be used. The reflective film 14c may be formed on the entire end surface of the optical semiconductor element 60 on the first optical coupler 14 side.

  In the optical semiconductor element 60, the second bent optical waveguide 17a inputs one of the two output lights of the first optical coupler 14, bends the propagation direction, and propagates the light to the first optical waveguide 12a. The third bent optical waveguide 17b inputs the other of the two output lights of the first optical coupler 14, bends the propagation direction, and propagates the light to the second optical waveguide 13a.

  In the optical semiconductor element 60, since the first optical coupler 14 using reflection is used, the second and third bent optical waveguides 17a and 17b propagate with the propagation direction of the input light bent obliquely. As in the second embodiment, the input light is not propagated by being bent 180 degrees in the opposite direction.

  Therefore, in the optical semiconductor element 60, the dimension in the width direction of the optical semiconductor element 60 is reduced as compared with the second embodiment described above. Moreover, in the optical semiconductor element 60, since the dimension of the first optical coupler 14 in the light propagation direction is halved, the dimension of the optical semiconductor element 60 in the longitudinal direction is also reduced.

  In the optical semiconductor device 60, the first buried region B1 includes the first of the semiconductor laser 11, the eighth optical waveguide 25, the first optical coupler 14, the second bent optical waveguide 17a, and the third bent optical waveguide 17b. A portion on the optical coupler 14 side is included. Accordingly, portions of the second bent optical waveguide 17 a and the third bent optical waveguide 17 b on the first optical coupler 14 side are embedded in the first embedded layer 42.

  In the optical semiconductor element 60, the second embedded region B2 includes a portion of the second bent optical waveguide 17a and the third bent optical waveguide 17b on the first optical waveguide 12a or second optical waveguide 13a side. Therefore, portions of the second bent optical waveguide 17 a and the third bent optical waveguide 17 b on the first optical waveguide 12 a or the second optical waveguide 13 a side are embedded by the second embedded layer 44. The second buried region B2 includes first and second optical waveguides 12a and 13a, fourth and fifth bent optical waveguides 18a and 18b, a second optical coupler 15, and sixth and seventh optical waveguides. 19a, 19b.

  As shown in FIG. 31, a bonding interface S2 between the first embedded layer 42 and the second embedded layer 44 is formed at a position in the middle of the second bent optical waveguide 17a and the third bent optical waveguide 17b. Thus, the reflection of light is reduced by disposing the bonding interface S2 at a position in the middle of the second bent optical waveguide 17a and the third bent optical waveguide 17b.

  Next, the manufacturing method of the optical semiconductor element 60 of 3rd Embodiment is demonstrated below.

  The manufacturing method of the optical semiconductor element 60 of the third embodiment is the same as the manufacturing method of the optical semiconductor element 10 of the first embodiment described above, except for the shape of the mask pattern used. In the optical semiconductor device 60, the shape or arrangement of the first optical coupler, the first and second phase modulation units, and other optical waveguides is different from that of the first embodiment. Therefore, if the mask pattern used for manufacturing the optical semiconductor element 50 of the second embodiment is appropriately changed, it can be manufactured in the same manner as the second embodiment described above. Further, the shape of the mask pattern can be changed depending on whether the position of the second end face of the first optical coupler is determined by cleavage or etching.

  According to the optical semiconductor element 60 of the present embodiment described above, the dimensions of the optical semiconductor element 60 in the longitudinal direction and the width direction are reduced. Moreover, the same effect as 2nd Embodiment mentioned above is show | played.

  In the optical semiconductor device 60 of the third embodiment, the first optical coupler 14 is disposed in the second buried region B2, and the junction interface S2 between the first buried layer 42 and the second buried layer 44 is defined as Eight optical waveguides 25 may be provided in the middle.

  In the present invention, the optical semiconductor element and the manufacturing method thereof according to the above-described embodiments can be appropriately changed without departing from the gist of the present invention. In addition, the requirements in the above-described embodiment or modification can be appropriately interchanged between the embodiment and the modification as appropriate.

  For example, the heater in the first embodiment described above may not be arranged as shown in FIG. In this case, the drive signal voltage to the first phase modulation electrode or the second phase modulation electrode may be adjusted to compensate for the phase difference due to the temperature difference between the first optical waveguide and the second optical waveguide.

  In the embodiment of the optical semiconductor element described above, each of the first phase modulation unit and the second phase modulation unit has the phase modulation electrode. However, the phase modulation electrode may be the first phase modulation unit or the second phase modulation unit. You may arrange | position only to either one of a phase modulation part.

  In each of the above-described embodiments, the description has been made using InP as the substrate forming material, but other materials may be used as the substrate forming material. Further, the structure or forming material of the laser mesa portion or the optical waveguide may be other structures or forming materials. For example, the core layers of the first and second optical waveguides may use InAlGaAs as a forming material. The core layer of the optical waveguide may have an MQW structure.

  Moreover, the manufacturing method of the optical semiconductor element mentioned above is an example, and you may form an optical semiconductor element using another manufacturing method.

  All examples and conditional words mentioned herein are intended for educational purposes to help the reader deepen and understand the inventions and concepts contributed by the inventor. All examples and conditional words mentioned herein are to be construed without limitation to such specifically stated examples and conditions. Also, such exemplary mechanisms in the specification are not related to showing the superiority and inferiority of the present invention. While embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions or modifications can be made without departing from the spirit and scope of the invention.

  Regarding the above-described embodiments, the following additional notes are disclosed.

(Appendix 1)
A semiconductor laser formed on a substrate;
A first phase modulation unit formed on the substrate and having a first optical waveguide;
A second phase modulation unit formed on the substrate and having a second optical waveguide;
A first optical coupler formed on the substrate, for branching the output light of the semiconductor laser into two, and outputting the branched light to the first optical waveguide and the second optical waveguide;
A second optical coupler formed on the substrate and coupling and outputting the output light from the first optical waveguide and the second optical waveguide;
An optical semiconductor element in which at least a part of the semiconductor laser and the first optical waveguide and the second optical waveguide are arranged in parallel.

(Appendix 2)
The semiconductor laser has a first mesa portion embedded by a first embedded layer,
The first optical waveguide and the second optical waveguide are embedded by a second embedded layer having a refractive index smaller than that of the core layer of the first optical waveguide and the second optical waveguide,
Formed on the substrate, comprising a bent optical waveguide that inputs light and bends the propagation direction to propagate the light,
An input side portion of the bent optical waveguide is embedded by the first embedded layer, and an output side portion of the bent optical waveguide is embedded by the second embedded layer. The optical semiconductor element according to appendix 1, wherein a bonding interface between the first buried layer and the second buried layer is formed at the position of.

(Appendix 3)
A bent optical waveguide formed on the substrate, having a core layer that inputs light from the core layer on the input side, propagates the light to the core layer on the output side, and is bent;
The input side portion of the core layer of the bent optical waveguide is formed integrally with the input side core layer,
The output side portion of the core layer of the bent optical waveguide is formed integrally with the output side core layer,
The optical semiconductor device according to appendix 1, wherein a bonding interface between the input-side core layer and the output-side core layer is formed at a position in the middle of the bent optical waveguide.

(Appendix 4)
The first phase modulator and the second phase modulator are arranged next to each other,
As the bent optical waveguide,
4. The optical semiconductor element according to appendix 2 or 3, further comprising a first bent optical waveguide formed on the substrate and configured to input the output light of the semiconductor laser and bend it in the opposite direction to propagate the light to the first optical coupler.

(Appendix 5)
The semiconductor laser is disposed on one side of the first phase modulation unit and the second phase modulation unit that are disposed adjacent to each other in parallel,
The optical semiconductor element according to appendix 4, wherein a heater formed on the substrate is disposed on the other side of the first phase modulation unit and the second phase modulation unit.

(Appendix 6)
4. The optical semiconductor element according to appendix 2 or 3, wherein the semiconductor laser is disposed between the first optical waveguide and the second optical waveguide.

(Appendix 7)
The optical semiconductor device according to appendix 6, wherein each of the first optical waveguide and the second optical waveguide is separated from the semiconductor laser by an equal distance.

(Appendix 8)
As the bent optical waveguide,
A second bent optical waveguide formed on the substrate and configured to input one of the two output lights of the first optical coupler and bend in the opposite direction to propagate the light to the first optical waveguide;
And a third bent optical waveguide formed on the substrate and configured to input the other of the two output lights of the first optical coupler and bend in the opposite direction to propagate the light to the second optical waveguide. 8. The optical semiconductor element according to 6 or 7.

(Appendix 9)
The first optical coupler is a multimode interference coupler that branches the output light of the semiconductor laser into two,
The first optical coupler reflects a multi-mode interference light that is opposed to the first end face for inputting the output light of the semiconductor laser and propagates through the first end face, and is folded back in the direction of the first end face. The optical semiconductor element according to appendix 6 or 7, wherein the optical semiconductor element has a second end face to be output, and outputs two lights branched from the first end face.

(Appendix 10)
As the bent optical waveguide,
A fourth bent optical waveguide formed on the substrate and receiving one of two output lights of the first optical coupler and propagating the light to the first optical waveguide;
The optical semiconductor according to appendix 9, further comprising: a fifth bent optical waveguide formed on the substrate and receiving the other of the two output lights of the first optical coupler and propagating the light to the second optical waveguide. element.

(Appendix 11)
The semiconductor laser is disposed between the first optical waveguide and the second optical waveguide;
A sixth bent optical waveguide formed on the substrate and configured to input one of the two output lights of the first optical coupler and bend it in the opposite direction to propagate the light to the first optical waveguide;
A seventh bent optical waveguide formed on the substrate and configured to input the other of the two output lights of the first optical coupler and bend it in the opposite direction to propagate the light to the second optical waveguide;
The semiconductor laser has a first mesa portion having a first core layer, and the first mesa portion is buried by a first buried layer,
The sixth bent optical waveguide and the seventh bent optical waveguide are embedded by a second embedded layer;
The portion of the first optical coupler on the side of the semiconductor laser is buried by the first buried layer, and the portions of the first optical coupler on the side of the second bent optical waveguide and the third bent optical waveguide are Embedded with a second buried layer,
The optical semiconductor element according to appendix 1, wherein a junction interface between the first buried layer and the second buried layer is formed in the vicinity of an end portion of the first optical coupler on the semiconductor laser side.

(Appendix 12)
The optical semiconductor according to any one of appendices 6 to 11, further comprising a light absorption unit adjacent to an end surface opposite to one end surface from which the semiconductor laser outputs light toward the first optical coupler. element.

(Appendix 13)
Any one of appendices 6 to 11, wherein the semiconductor laser has a reflection film that reflects light toward the one end surface on an end surface opposite to the one end surface that outputs light toward the first optical coupler. An optical semiconductor device according to claim 1.

(Appendix 14)
Each of the said 1st phase modulation | alteration part and the said 2nd phase modulation | alteration part is an optical semiconductor element as described in any one of Additional remarks 1-13 which has the phase adjustment part formed in the said board | substrate.

(Appendix 15)
15. The optical semiconductor element according to any one of appendices 1 to 14, wherein the semiconductor laser has a variable wavelength.

10, 50, 60 Optical semiconductor element 11 Semiconductor laser 11a Laser mesa unit 11b Laser drive electrode 11c Reflective film 12 First phase modulation unit 12a First optical waveguide 12b First phase modulation electrode 13 Second phase modulation unit 13a Second optical waveguide 13b Second phase modulation electrode 14 First optical coupler 14a First end face 14b Second end face 14c Reflective film 15 Second optical coupler 16 First bent optical waveguide 16a Mesa portion of first bent optical waveguide 17a Second bent optical waveguide 17b 3rd bent optical waveguide 18a 4th bent optical waveguide 18b 5th bent optical waveguide 19a 6th optical waveguide 19b 7th optical waveguide 22 heater 22a heater main body 22b, 22c heater electrode 23 phase adjusting unit 23a phase adjusting electrode 24 semiconductor laser 24a front DBR region 24b Phase adjustment region 24c Gain region 24 Rear DBR region 24e First drive electrode 24f Second drive electrode 24g Third drive electrode 24h Fourth drive electrode 25 Eighth optical waveguide 26 Light absorption part 26a Light absorption mesa part 26b Light absorption drive electrode 30 Substrate 31 Lower cladding layer 32 Diffraction Lattice layer 33 Spacer layer 34 Semiconductor laser core layer 35 Optical waveguide core layer 36 First upper cladding layer 37 Second upper cladding layer 38 Third upper cladding layer 39 First contact layer 40 First electrode 41 Second electrode 42 Second 1 buried layer 43 first passivation layer 44 second buried layer 45 second passivation layer 46 heat generation layer B1 first buried region B2 second buried region S1, S3 core layer junction interface S2 buried junction interface M1 first mask layer M2 second Mask layer M3 Third mask layer M4 Fourth mask layer

Claims (5)

A semiconductor laser formed on a substrate;
A first phase modulation unit formed on the substrate and having a first optical waveguide;
A second phase modulation unit formed on the substrate and having a second optical waveguide;
A first optical coupler formed on the substrate, for branching the output light of the semiconductor laser into two, and outputting the branched light to the first optical waveguide and the second optical waveguide;
A second optical coupler formed on the substrate and coupling and outputting the output light from the first optical waveguide and the second optical waveguide;
The semiconductor laser and the first optical waveguide and the second optical waveguide are at least partially arranged in parallel ,
The semiconductor laser has a first mesa portion embedded by a first embedded layer,
The first optical waveguide and the second optical waveguide are embedded by a second embedded layer having a refractive index smaller than that of the core layer of the first optical waveguide and the second optical waveguide,
Formed on the substrate, comprising a bent optical waveguide that inputs light and bends the propagation direction to propagate the light,
An input side portion of the bent optical waveguide is embedded by the first embedded layer, and an output side portion of the bent optical waveguide is embedded by the second embedded layer. An optical semiconductor element in which a bonding interface between the first buried layer and the second buried layer is formed at the position of . The semiconductor laser is disposed on one side of the first phase modulation unit and the second phase modulation unit that are disposed adjacent to each other in parallel,
As the bent optical waveguide,
A first bent optical waveguide which is formed on the substrate and receives the output light of the semiconductor laser and bends in the opposite direction to propagate the light to the first optical coupler;
Wherein the other side of the first phase modulator section and said second phase modulator section, an optical semiconductor device according to claim 1 in which the heater formed on the substrate is placed. The optical semiconductor device according to claim 1, wherein the semiconductor laser is disposed between the second optical waveguide and the first waveguide. As the bent optical waveguide,
A second bent optical waveguide formed on the substrate and configured to input one of the two output lights of the first optical coupler and bend in the opposite direction to propagate the light to the first optical waveguide;
And a third bent optical waveguide formed on the substrate and configured to input the other of the two output lights of the first optical coupler and bend it in the opposite direction to propagate the light to the second optical waveguide. Item 4. The optical semiconductor device according to Item 3 . The first optical coupler is a multimode interference coupler that branches the output light of the semiconductor laser into two,
The first optical coupler reflects a multi-mode interference light that is opposed to the first end face for inputting the output light of the semiconductor laser and propagates through the first end face, and is folded back in the direction of the first end face. A second end face that outputs the two lights branched from the first end face,
As the bent optical waveguide,
A fourth bent optical waveguide formed on the substrate and receiving one of two output lights of the first optical coupler and propagating the light to the first optical waveguide;
4. The light according to claim 3 , further comprising: a fifth bent optical waveguide that is formed on the substrate and that inputs the other of the two output lights of the first optical coupler and propagates the light to the second optical waveguide. Semiconductor element.

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