JP2016018894A - Integrated semiconductor optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor optical element capable of removing the higher order mode, while keeping the short length of a circuit board.SOLUTION: An integrated semiconductor optical element has a semiconductor substrate, a light source section formed on the semiconductor substrate, a higher order mode filter section formed on the semiconductor substrate, while connected with the light source section, and having a higher order mode filter for removing the higher order mode generated by the light from the light source section, in a waveguide formed on the semiconductor substrate, and an oblique emission waveguide formed on the semiconductor substrate, and connected to the output side of the higher order mode filter. The higher order mode filter has a first arcuate waveguide for guiding the light from the light source section formed on the semiconductor substrate, and a second arcuate waveguide connected to the output side of the first arcuate waveguide, and having a bending direction in the opposite direction from the first arcuate waveguide.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a semiconductor optical device, and more particularly to an integrated semiconductor optical device in which a plurality of semiconductor lasers are integrated on a semiconductor substrate.

  In a wavelength division multiplexing communication system in optical fiber communication, a plurality of optical signals having different wavelengths are transmitted through a single optical fiber. Generally, a semiconductor distributed feedback (DFB) laser operating in a single mode is used as a light source for optical fiber communication. Therefore, for wavelength multiplex communication, a plurality of DFB lasers operating at different wavelengths are used, each DFB laser is directly modulated or laser light from the DFB laser is externally modulated, and each modulated output laser light is Combine and transmit using a multiplexer.

  An integrated semiconductor in which a plurality of DFB lasers, a plurality of modulators for modulating laser light from the DFB lasers, and a multiplexer are integrated on a single semiconductor substrate in order to reduce the size and power consumption of the system. Optical elements are also being developed.

  FIG. 1 is a diagram showing an example of the configuration of an EA-DFB laser array element 100 which is a conventional integrated semiconductor optical element.

  The EA-DFB laser array element 100 shown in FIG. 1 is configured to receive output laser light from four DFB lasers 111 to 114 formed on a semiconductor substrate 101, respectively, on an electric field absorption type (EA : An integrated semiconductor optical device having an optical circuit that is modulated by external modulators (EA modulators) 121 to 124 of electro-absorption and multiplexed into a single optical waveguide by a multiplexer (MMI multiplexer) 131 It is. Photodiodes 141 to 144 are provided on the side of the DFB lasers 111 to 114 opposite to the EA modulators 121 to 124 so that the output laser light of the DFB lasers 111 to 114 can be monitored.

  Since a plurality of DFB lasers, a plurality of EA modulators, a plurality of photodiodes, and an MMI multiplexer can be combined on one semiconductor substrate, a single package can be obtained. Compared with a case where a lens or a lens is provided, it is possible to reduce power consumption and cost.

  There are various waveguide structures used in semiconductor optical devices, and in an integrated device, a plurality of types of optical waveguides are combined and manufactured.

  2A and 2B are cross-sectional views showing examples of waveguides used in a semiconductor optical device. FIG. 2A is a shallow ridge waveguide, FIG. 2B is a buried heterostructure waveguide, and FIG. 2C is a high mesa waveguide. FIG. 2 is a cross-sectional view of a light guide direction of light. (A) A waveguide having a shallow ridge structure has a core 201 surrounded by a semiconductor 202 having a narrower width than the core and 203 having the same width as the core, and (b) a waveguide having a buried heterostructure has a core 211 having a semiconductor 212. In the structure surrounded by, the difference in refractive index between the portion where the light is guided and its both sides is small, and the lateral light confinement is weak. Therefore, for example, when used for a curved waveguide, the loss of light is large. On the other hand, a waveguide with a shallow ridge structure and a waveguide with a buried hetero structure have few crystal defects and good light emission efficiency. Therefore, they are used for elements in which the core of an optical waveguide emits light, such as a semiconductor laser. On the other hand, the (c) high-mesa waveguide has a structure in which both sides of the core 221 are sandwiched between air, and the optical confinement in the lateral direction becomes strong because the refractive index difference between the semiconductor and air is large. Therefore, there is little bending loss and it can be used for a curved waveguide. An integrated semiconductor optical device can create an optimum waveguide structure by combining waveguides such as a buried hetero structure, a shallow ridge structure, and a high mesa waveguide structure.

  Usually, a semiconductor laser or optical waveguide for optical communication is operated in a single mode. Waveguides used in integrated semiconductor optical devices include not only straight waveguides but also curved waveguides, waveguide junctions having different structures, and multiplexers. Among the waveguides, for shallow ridge waveguides and buried heterostructure waveguides, the inflection point from the curved waveguide to the curved waveguide, the inflection point from the straight waveguide to the curved waveguide, the waveguide It is known that higher-order modes are generated at joints, multiplexers, and the like.

  When the higher order mode occurs, not only the performance of the original optical circuit cannot be obtained, but also the coupling loss with the single mode fiber becomes large, and light rays meander in the waveguide. As the light beam meanders in the waveguide, the direction of light emitted from the chip differs for each chip or for each laser that emits light, resulting in problems such as difficulty in lens coupling with the fiber.

  Even in a circuit including a higher-order mode, the higher-order mode is removed as long as it propagates through the single-mode waveguide. However, a long distance, for example, 10 mm is required to completely eliminate higher-order modes, which is not practical.

For this reason, for example, at the inflection point from a straight line to a curved waveguide, in order to suppress the generation of a higher-order mode, an offset junction that is joined by shifting the waveguide center axis is introduced (non-patent document). Reference 1).
Further, it is known that a single mode laser such as a DFB laser operating in a single mode is generally weak against reflected light. That is, once the light emitted to the outside of the laser resonator is reflected and reenters the inside of the resonator, the line width increases according to the intensity and phase of the reflected wave, and the communication quality deteriorates. The influence of this reflected wave is more problematic in the far reflection than in the vicinity of the laser emission end face. Therefore, in the case of an integrated semiconductor optical device in which the waveguide continues for a long time before it is emitted from the semiconductor into the air after the laser, not only the non-reflective coating is applied to the semiconductor end face (open surface) but also the end face of the semiconductor. The waveguide (shallow ridge structure waveguide or buried heterostructure waveguide) is disposed obliquely with respect to the cleaved surface (so-called oblique emission waveguide). By adopting the oblique emission waveguide in the shallow ridge structure waveguide or buried heterostructure waveguide, a structure is adopted in which slight reflected light on the open surface with the antireflection coating does not return to the waveguide.

Vijaya Subramaniam et at., “Measurement of mode field profiles and bending and transition losses in curved optical channel waveguides”, Journal of Lightwave Technology, vol.15, no.6, pp. 990-997, June 1997. Masaki Kohtoku et al., “Evaluation of the rejection ratio of an MMI-based higher order mode filter using optical low coherence reflectometry”, IEEE Photonics Technology Letters, vol. 14, no. 7, pp. 968-970, July 2002.

  The integrated semiconductor optical device is manufactured so as to minimize the optical loss by using the respective waveguide structures, such as the adoption of the three types of waveguides shown in FIG. 2 and the introduction of the offset of the curved waveguide described in Non-Patent Document 1. If it is possible, it will be possible to suppress the generation of higher order modes, but there will be a lot of manufacturing errors including in-plane distribution on the semiconductor. It is thought that it cannot be suppressed. In addition, when an MMI multiplexer or the like is manufactured with a waveguide structure with a weak lateral confinement, such as a shallow ridge structure or a buried heterostructure, higher-order modes are likely to be mixed into the waveguide after multiplexing.

  It goes without saying that each individual part should be designed so that higher order modes do not occur as much as possible. However, even if there are manufacturing errors or various waveguide structures are used, light does not meander without including higher order modes. In order to obtain a stable light output, it is necessary to install a high-order mode filter for effectively removing the high-order mode with as short a length as possible in the final stage of the optical circuit. As a high-order mode filter, it is known that a 1-input 1-output MMI is used in a high-mesa waveguide (Non-Patent Document 2). However, in the 1-input 1-output MMI, the high-order mode removal performance deteriorates due to a manufacturing dimension error of about 0.5 μm or less. Therefore, in order to secure the manufacturing yield, high manufacturing condition reproducibility and high manufacturing condition in-plane uniformity are required. It was necessary.

  FIG. 3 is a configuration diagram showing an EA-DFB racer element 300 that uses a high-mesa waveguide as a curved waveguide and uses a shallow ridge-structure oblique emission waveguide as each waveguide including a laser emission port. A high mesa waveguide with low bending loss is used for the curved waveguide, and a shallow ridge waveguide is used for the output waveguide.

  In the EA-DFB laser array element 300 of FIG. 3, a high-order mode filter based on a 1-input 1-output MMI 333 is inserted into a high-mesa waveguide 332 to introduce a shallow ridge structure into a high-mesa waveguide 334 that is a curved waveguide. The waveguide 335 is joined to form an oblique emission waveguide at the laser beam exit of the shallow ridge structure 335.

  However, in the structure of the EA-DFB laser array element 300, since conversion from the high-mesa waveguide 334 to the shallow ridge-structure waveguide 335 is necessary, there is a problem that the higher-order modes cannot be sufficiently removed.

  Here, in FIG. 3, if all waveguides including the curved waveguide are formed by shallow ridges, there is a problem that a high-order mode is included in the 1-input 1-output MMI 333. When all the waveguides are manufactured with a shallow ridge, in order to remove higher-order modes, for example, the output waveguide needs to be as long as several tens of millimeters, and the semiconductor optical device cannot be reduced in size.

  On the other hand, if all the waveguides in FIG. 3 are made of high-mesa waveguides, there is no concern about higher-order modes due to the 1-input 1-output MMI 333. There is a problem that the light reflected from the end face returns to the waveguide because of its high confinement capability.

  Therefore, the present invention adopts a shallow ridge structure or buried heterostructure waveguide as the waveguide at the semiconductor end face in order to prevent laser light reflection at the time of output of the laser light from the semiconductor optical device, thereby forming an oblique emission waveguide. It is an object of the present invention to eliminate higher-order modes while the length of the semiconductor optical device is short.

  In order to achieve such an object, the first aspect of the present invention provides a semiconductor substrate, a light source unit formed on the semiconductor substrate, a light source unit formed on the semiconductor substrate, and the light source A connected high-order mode filter unit, wherein the high-order mode filter unit removes a high-order mode of light generated by light from the light source in a waveguide formed on the semiconductor substrate. An integrated semiconductor optical device comprising a high-order mode filter section having a second-order mode filter, and an oblique emission waveguide formed on the semiconductor substrate and connected to the output side of the higher-order mode filter, The next mode filter is connected to the first arc-shaped waveguide that guides light from the light source formed on the semiconductor substrate, and to the output side of the first arc-shaped waveguide, and the first mode filter Opposite to arc waveguide And having a second circular waveguide formed in said semiconductor substrate having a bending direction of the direction.

  The second aspect of the present invention is the integrated semiconductor optical device according to the first aspect, wherein the high-order mode filter further includes at least one third arcuate waveguide, The third arcuate waveguide is connected in series to the output side of the second arcuate waveguide, and the second arcuate waveguide and the at least one third arcuate waveguide are adjacent to each other. The arc-shaped waveguides have bending directions opposite to each other.

  According to a third aspect of the present invention, there is provided an integrated semiconductor optical device according to the first or second aspect, wherein a junction between the first arcuate waveguide and the second arcuate waveguide, A junction of a second arcuate waveguide and the at least one third arcuate waveguide, a junction of each of a plurality of third arcuate waveguides, and the second arcuate waveguide or The junction between at least one third arcuate waveguide and the oblique emission waveguide is connected to each other with an offset.

  A fourth aspect of the present invention is the integrated semiconductor optical device according to any one of the first to third aspects, wherein the semiconductor substrate is a (100) InP substrate, the first arcuate waveguide, The second arc-shaped waveguide, the at least one third arc-shaped waveguide, and the oblique emission waveguide each have a shallow ridge structure or a buried heterostructure, and are arranged in the direction of light waveguide. The angle formed with the <011> direction is 10 degrees or less.

  According to a fifth aspect of the present invention, there is provided the integrated semiconductor optical device according to any one of the first to fourth aspects, wherein the light source includes a plurality of semiconductor lasers and a modulation connected to the plurality of semiconductor lasers, respectively. , A waveguide connected to each of the EA modulators, and a multiplexer connected to all of the waveguides, wherein the optical modulator is a plurality of external modulators, Is characterized in that the modulated light from the modulator is multiplexed and output to the higher-order mode filter.

  As described above, according to the present invention, the waveguide of the semiconductor end face employs a shallow ridge structure or buried heterostructure waveguide and an oblique emission waveguide, and the length of the integrated semiconductor optical device remains short. Higher order modes can be eliminated.

It is a figure which shows an example of a structure of the EA-DFB laser array element which is the conventional integrated semiconductor optical element. FIG. 4 is a cross-sectional view showing an example of a waveguide used in an integrated semiconductor optical device, where (a) is a shallow ridge structure waveguide, (b) is a buried heterostructure waveguide, and (c) is a high mesa waveguide. FIG. 3 is a cross-sectional view in the light guiding direction. It is a block diagram which shows the EA-DFB racer element which uses the waveguide of a high mesa structure for a curved waveguide, and uses the diagonal emission waveguide of a shallow ridge structure for each waveguide including a laser emission port. It is a block diagram which shows the EA-DFB laser element which is the 1st Embodiment of this invention. It is the block diagram which expanded the higher order mode filter part of the output waveguide. (A) And (b) is sectional drawing of the waveguide direction of the light of the waveguide of a shallow ridge structure. FIG. 7A is a diagram showing a junction of each waveguide of the high-order mode filter unit, FIG. 7A is a junction between a straight waveguide and an arcuate waveguide, FIG. 7B is two arcuate waveguides, It is a figure which shows a junction part with an oblique emission waveguide. It is a block diagram which shows the high order mode filter part of the EA-DFB laser element which is the 2nd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

[First embodiment]
FIG. 4 is a block diagram showing an EA-DFB laser array element 400 which is the first embodiment of the integrated semiconductor optical element of the present invention. The EA-DFB laser array element 400 in FIG. 4 includes a semiconductor substrate 401, a light source unit 410 formed on the semiconductor substrate 401, and light from the light source unit 410 in a waveguide formed on the semiconductor substrate 401. A higher-order mode filter unit 450 that removes higher-order modes of generated light, and an oblique emission waveguide 454 formed on the semiconductor substrate 401 and connected to the higher-order mode filter unit 450 are provided.

  The light source unit 410 includes two DFB lasers 411 and 412, EA modulators 421 and 422 that modulate output laser beams from the DFB lasers 411 and 412, and modulated laser beams from the EA modulators 421 and 422, respectively. An MMI multiplexer 431 that multiplexes into one optical waveguide, and connection waveguides 432 and 433 connected between the EA modulators 421 and 422 and the input side of the MMI multiplexer 431, respectively. The EA-DFB laser array element 400 is provided with photodiodes 441 and 442 on the opposite side of the EA modulators 421 and 422 of the DFB lasers 411 and 412 so that the output laser light of the DFB lasers 411 and 412 can be monitored. It has become.

  The high-order mode filter unit includes an output waveguide 434 constituting a high-order mode filter connected to the output side of the MMI multiplexer 431 of the light source unit 410. The oblique emission waveguide 454 is connected to the output waveguide 434.

  The semiconductor substrate 401 is an InP substrate, and the DFB lasers 411 and 412 have a GaInAsP multiple quantum well structure having a gain in the vicinity of a wavelength of 1.3 μm in an active layer, and can operate in a single mode by forming a diffraction grating. DFB laser. The EA modulators 421 and 422 have an AlGaInAs multiple quantum well structure having an absorption peak on the shorter wavelength side than the wavelength of 1.3 μm as an absorption layer. The multiplexer 431 is a 2-input 1-output MMI multiplexer, and uses GaInAsP having a 1.1 μm wavelength band gap as a core. The connection waveguides 432 and 433 and the output waveguide 434 also have GaInAsP having a band gap of 1.1 μm as a core, and the waveguide structures are all shallow ridge structures.

  FIG. 5 is an enlarged configuration diagram of the high-order mode filter unit 450 and the oblique emission waveguide 454 of FIG. The output waveguide 434 is connected to the output side of the multiplexer 431, and is arranged in the order of the straight waveguide 451, the first arc-shaped waveguide 452, and the second arc-shaped waveguide 453 from the multiplexer 431 side. ing.

  From the wavelength of the laser beam to propagate and the refractive index of the semiconductor, if the appropriate waveguide width is set to satisfy the single mode condition, even if the laser beam is propagated to the straight waveguide, Higher order modes are emitted from the side of the core. However, by forming the waveguide in an arc shape, higher-order mode radiation becomes more prominent. This is because higher order modes cannot be propagated along the waveguide and are radiated from the side of the core. In this embodiment, light having a wavelength in the vicinity of 1.3 μm is propagated through the waveguide, but the waveguide width is 1.6 μm.

  In this embodiment, the waveguide structures are all shallow ridge structures. 6A and 6B are cross-sectional views in the light guiding direction of a waveguide having a shallow ridge structure. When a waveguide having a shallow ridge structure is formed by a semiconductor optical device using an InP-based material, only the upper cladding layers 601 and 611 made of InP are selectively etched as shown in FIG. 6A, and GaInAsP, AlGaInAs, or the like is used. For the core layers 602 and 612 and the lower clad layers 603 and 613, the waveguide can be easily manufactured by using a wet etching solution that is not etched.

  However, in wet etching, the etching shape largely depends on the crystal plane orientation. That is, in the <011> -direction waveguide fabricated on the (100) substrate, the upper cladding layer 601 has a substantially vertical mesa shape as shown in FIG. That is, when the direction of the waveguide is angled from the <011> direction, the lower part of the upper cladding layer 611 gradually becomes thin as shown in FIG. Therefore, considering the stable production of the upper clad, it is necessary to suppress the waveguide direction to about 10 degrees or less from the <011> direction. That is, the arc angle θ1 of the first arcuate waveguide 452 in FIG. 5 needs to be 10 degrees or less.

  Here, the length of the arc of the first arcuate waveguide 452 is π × R1 × θ1 / 180, where the radius of curvature of the arc of the arcuate waveguide 452 is R1, and thus when θ1 is limited, The length of the arc is also limited. If R1 is large, the length of the arc increases. However, the larger R1, the closer to the straight line, the higher order mode radiation becomes gentle and the size of the higher order mode filter unit 450 also becomes larger. The merit of miniaturization by integration is lost.

  Therefore, in the present embodiment, as shown in FIG. 5, a second arcuate waveguide 453 having a bending direction opposite to that of the first arcuate waveguide 452 is provided after the first arcuate waveguide 452. Thus, the length of the arc of the arcuate waveguide is increased. If the second arcuate waveguide 453 is an arc having the same angle as that of the first arcuate waveguide 452, it returns to the original linear axis, and therefore the waveguide is output perpendicular to the element end face. Here, reflection countermeasures are also considered, and for the reflection countermeasures, an oblique emission waveguide 454 that outputs from the end face of the EA-DFB laser array element 400 at an angle θ3 with respect to the <011> direction is further formed in the second arc shape. It is connected to the waveguide 453.

  Therefore, if the angle θ2 of the arc of the second arcuate waveguide 453 in FIG. 5 is θ2 = θ1 + θ3, a reflection countermeasure can be performed simultaneously with the function of the high-order mode filter. Here, from the viewpoint of the crystal plane orientation dependence of the etching shape, the maximum angle of θ3 has the same restrictions as the maximum angle of θ1, and θ3 needs to be 10 degrees or less. Therefore, when θ1 and θ3 are set to a maximum angle of 10 degrees, θ2 becomes a maximum angle of 20 degrees. In this embodiment, the radius of curvature R2 of the arc of R1 and the second arcuate waveguide 452 is 600 μm. Also, θ1, θ2, and θ3 were set to 10 degrees, 17 degrees, and 7 degrees, respectively.

  When a high-order mode filter using an arcuate waveguide is used, the connection part from the straight waveguide 451 to the first arcuate waveguide 452, the first arcuate waveguide 452 and the second arcuate waveguide 453 By introducing an offset to the waveguide junction at an inflection point such as a junction, it is possible to prevent the generation of a new higher-order mode and enhance the filter effect of the higher-order mode filter. FIG. 7 is a diagram showing a junction portion of each waveguide of the higher-order mode filter unit 450 in FIG. 5. FIG. 7A is a junction portion between the straight waveguide 451 and the arc-shaped waveguide 452, and FIG. FIG. 7B is a diagram illustrating a joint portion between the arc-shaped waveguide 452, the arc-shaped waveguide 453, and the oblique emission waveguide 454. In this embodiment, a slight offset of 0.05 μm is introduced at the junction of each waveguide.

  The material for fabricating the integrated semiconductor optical device of the present invention is not limited to the InP substrate and the core of GaInAsP, AlGaAsP, InGaAlAs, but other optical semiconductor devices such as a GaAs substrate, a core of GaInAs, AlGaAs, and GaInNAs. The material which can produce can be used. Further, since the feature of the present invention is the arrangement of the individual elements of the integrated device, the method for producing the waveguide is not limited to wet etching, and an exposure method using a mask, an EB exposure using an electron beam, and the like. It may be used.

  In the first embodiment, a waveguide having a shallow ridge structure is used, but a similar effect can be obtained even in a buried heterostructure having a lower lateral confinement than a high mesa structure. In addition, in the case of the shallow ridge structure, it has been explained that the angle can be tilted only up to about 10 degrees due to the limitation of the crystal plane orientation dependency of etching. However, the shape of the buried heterostructure also depends on the crystal plane orientation. . Therefore, the angle is still limited, and it is very effective to use a two-stage arc filter.

[Second Embodiment]
FIG. 8 is a block diagram showing a high-order mode filter 800 of the EA-DFB laser array device according to the second embodiment of the integrated semiconductor optical device of the present invention. In the first embodiment, a filter structure with a two-stage arc composed of the first arc-shaped waveguide 452 and the second arc-shaped waveguide 453 is adopted. However, as shown in FIG. In order to enhance the filtering function, the first arcuate waveguide 802, the second arcuate waveguide 803, and the third arcuate waveguide 804 are provided between the straight waveguide 801 and the oblique exit waveguide 805. A filter structure with stepped arcs may be used. When the oblique output waveguide 805 is θ4 with respect to the <011> direction as a countermeasure against reflection, the arc angle θ1 of the first arc waveguide 802, the arc angle θ2 of the second arc waveguide 803, If the angle θ3 of the arc of the third arc waveguide 804 is θ1 + θ3 = θ2 + θ4, reflection countermeasures can be performed simultaneously with the function of the high-order mode filter.

  Moreover, the number of stages can be increased depending on the application, not limited to three stages. In the arc-shaped waveguides at each stage, adjacent arc-shaped waveguides have bending directions opposite to each other. When using a waveguide with a shallow ridge structure, the direction of the curved waveguide is set to 10 degrees or less from the <011> direction, and the number of steps is increased. While satisfying the angle requirement for the waveguide, the higher-order mode filtering function can be enhanced to any extent.

  Further, for example, depending on the layout of the integrated optical circuit to be manufactured, there may be a straight waveguide between each arc-shaped waveguide.

  The present invention provides not only an EA-DFB laser array element integrated with an EA modulator, but also a semiconductor laser array element integrated with another type of modulator, a semiconductor laser array element capable of direct modulation, and only a modulator. It can also be applied to array elements.

100, 300, 400 Integrated semiconductor optical devices 101, 301, 401 Semiconductor substrates 111-114, 311-314, 411, 412 DFB lasers 121-124, 321-324, 421, 422 EA modulators 141-144, 321-324 , 441, 442 Photodiode 131, 331, 431 Multiplexer 201, 211, 221, 602, 612 Core 202, 203, 212, 222, 223, 601, 603, 611, 613 Clad 410 Light source 434 Output waveguide 450 , 800 High-order mode filter sections 451, 801 Linear waveguides 452, 453, 802-804 Arc-shaped waveguides 454, 335, 805 Diagonal exit waveguide 332 High-mesa linear waveguide 333 1-input 1-output MMI
334 Curved waveguide with high mesa structure

Claims (5)

A semiconductor substrate;
A light source unit formed on the semiconductor substrate;
A high-order mode filter section having a high-order mode filter for removing a high-order mode of light generated by light from the light source in a waveguide formed on the semiconductor substrate and connected to the light source section;
An integrated semiconductor optical device comprising an oblique emission waveguide formed on the semiconductor substrate and connected to the output side of the higher-order mode filter,
The high-order mode filter is connected to a first arcuate waveguide that guides light from the light source unit formed on the semiconductor substrate, and an output side of the first arcuate waveguide, An integrated semiconductor optical device comprising: a first arcuate waveguide; and a second arcuate waveguide formed on the semiconductor substrate having a bending direction opposite to the first arcuate waveguide.   The higher-order mode filter further includes at least one third arcuate waveguide, and the at least one third arcuate waveguide is connected in series to the output side of the second arcuate waveguide. 2. The second arc-shaped waveguide and the at least one third arc-shaped waveguide are characterized in that adjacent arc-shaped waveguides have bending directions opposite to each other. Integrated semiconductor optical device.   A junction between the first arcuate waveguide and the second arcuate waveguide; a junction between the second arcuate waveguide and the at least one third arcuate waveguide; Each of the three arc-shaped waveguides, and each of the second arc-shaped waveguide or the junction of the at least one third arc-shaped waveguide and the oblique emission waveguide has an offset. The integrated semiconductor optical device according to claim 1, wherein the integrated semiconductor optical device is connected. The semiconductor substrate is a (100) InP substrate;
The first arc-shaped waveguide, the second arc-shaped waveguide, the at least one third arc-shaped waveguide, and the oblique emission waveguide have a shallow ridge structure or a buried heterostructure. 4. The integrated semiconductor optical device according to claim 1, wherein an angle formed between the light guiding direction and the <011> direction in the substrate is 10 degrees or less. 5. The light source unit is
A plurality of semiconductor lasers;
A modulator connected to each of the plurality of semiconductor lasers;
Waveguides connected to each of the EA modulators;
And a multiplexer connected to all the waveguides,
The optical modulator is a plurality of external modulators;
5. The integrated semiconductor optical device according to claim 1, wherein the multiplexer multiplexes the modulated light from the modulator and outputs the combined light to the higher-order mode filter unit. 6.

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