JP2017022247A - Wavelength selection device and tunable light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable wavelength selection device and tunable light source that have a wide wavelength tuning range, can stably operate with high output and can stably oscillate efficiently and stably only at a desired wavelength.SOLUTION: A wavelength selection device comprises an optical demultiplexer 11 having output waveguides 12a to 12d. At least one of the output waveguides 12a to 12d is provided with a distributed reflection type mirror structure 14 having a chirped diffraction grating whose diffraction grating period has been changed. At least another one of the output waveguides 12a to 12d is a light output port to the outside.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wavelength selection element and a wavelength tunable light source including the wavelength selection element.

  In recent years, a tunable laser capable of changing the wavelength in a wide wavelength range has been attracting attention for digital coherent communication whose market scale is expanding as a long-distance large-capacity optical transmission system. As an example of the wavelength tunable laser, there is one that selects an arbitrary wavelength in a wide wavelength range by combining vernier type wavelength filters (vernier type filters) having periodic wavelength selection characteristics.

  In this wavelength tunable laser, laser oscillation can be performed only at a wavelength where the selected wavelengths of the two wavelength filters overlap each other by minutely changing the period of the two wavelength filters. In the vernier type filter, the filter characteristics are determined by the period and sharpness (finesse) of the two wavelength filters. Therefore, by appropriately adjusting these parameters, a wavelength variable operation in a wide wavelength range is possible.

  As a specific example of a wavelength tunable laser using a vernier filter, there is one in which two ring resonators and semiconductor optical amplifiers (SOA) are hybrid-mounted as a vernier filter. The SOA has a reflectance of about 30% on the output end side, and has a non-reflective structure on the coupling side with the ring resonator. The ring resonator can be reduced in size to a radius of about several μm to several tens of μm.

  On the other hand, the size (form factor) of the optical module is changed from CFP to CFP2 so that the number of optical modules that can be mounted on the optical transmission device can be increased in order to cope with the increase in capacity of the long-distance large-capacity optical transmission system in recent years. Furthermore, it has become increasingly smaller to CFP4. The current optical module for 100 gigabit ether uses 4 multi-wavelengths (LAN-WDM), and as a laser light source mounted in one optical module, individual laser elements corresponding to the number of wavelengths or monolithically integrated. A laser array or the like is used. On the other hand, due to demands for module miniaturization and low power consumption, realization of a multi-wavelength light source that simultaneously oscillates a plurality of wavelengths is required.

JP 2006-245346 A International Publication No. 2009/119284 International Publication No. 2007/029647

  In a conventional wavelength tunable laser using a ring resonator, the interval at which the recursive mode (the wavelength where the selected wavelengths of the two ring resonators overlap again on the long wave side and the short wave side with respect to the selected wavelength) appears is set wide. Yes. As a result, adjacent recursive modes are less likely to receive the SOA gain and suppress oscillation. However, in this case, a suppression ratio between the oscillation mode and the adjacent mode cannot be obtained, which may cause a problem in oscillation mode stability.

  On the other hand, the conventional multi-wavelength light source cannot completely cut out only the desired four multiplexed wavelengths. Therefore, although the light intensity is weak on both the long and short sides, there is a problem that light having an oscillating wavelength exists and cannot be completely removed.

  In either case, the cleavage plane of the laser element is used as the reflection surface on the output end side, and there is a problem that the wavelength selectivity is limited because the reflectance does not have wavelength dependency. In addition, a waveguide type filter structure that has a finite reflectance of about 30% within the wavelength range required in the conventional example and can be monolithically integrated or hybrid integrated with an optical amplifier has not been realized.

  The present invention has been made in view of the above problems, has a wide wavelength variable range, can operate stably at high output, and can oscillate efficiently and stably only at a desired wavelength. An object of the present invention is to provide a highly reliable wavelength selection element and wavelength tunable light source capable of performing the above.

  One aspect of the wavelength selection element includes an optical demultiplexer having a plurality of output waveguides, and at least one of the plurality of output waveguides has a distributed reflection type having a chirped diffraction grating having a changed diffraction grating period A mirror structure is provided, and at least one of the plurality of output waveguides is an optical output port to the outside.

  One aspect of the wavelength tunable light source includes the wavelength selection element described above and another wavelength selection element connected to the wavelength selection element.

  According to the above aspects, a highly reliable wavelength that has a wide wavelength tunable range, can operate stably at a high output, and can oscillate efficiently and stably only at a desired wavelength. A selection element and a wavelength tunable light source are realized.

It is a schematic diagram which shows schematic structure of the wavelength variable light source provided with the wavelength selection element by 1st Embodiment. It is a characteristic view which shows the relationship between the wavelength of the wavelength selection element by 1st Embodiment, a filter characteristic, etc. FIG. It is a schematic diagram which shows the chirped diffraction grating of a DBR mirror. It is a characteristic view which shows the relationship between a wavelength, a reflectance, etc. It is a characteristic view which shows the relationship between a wavelength and a reflectance. It is a schematic perspective view which shows the manufacturing method of the wavelength tunable light source provided with the wavelength selection element by 1st Embodiment. FIG. 7 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 6. FIG. 8 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 7. FIG. 9 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 8. FIG. 10 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 9. FIG. 11 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 10. FIG. 12 is a schematic perspective view illustrating a manufacturing method of the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 11. FIG. 13 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 12. FIG. 14 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 13. FIG. 15 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 14. FIG. 16 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 15. FIG. 17 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 16. FIG. 18 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 17. FIG. 19 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 18. FIG. 20 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the first embodiment, following FIG. 19. It is a schematic diagram which shows schematic structure of the wavelength variable light source provided with the wavelength selection element by 2nd Embodiment. It is a schematic perspective view which shows the manufacturing method of the wavelength tunable light source provided with the wavelength selection element by 2nd Embodiment. FIG. 23 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 22. FIG. 24 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 23. FIG. 25 is a schematic perspective view illustrating a manufacturing method of the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 24. FIG. 26 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 25. FIG. 27 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 26. FIG. 28 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 27. FIG. 29 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 28. FIG. 30 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 29. FIG. 31 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 30. FIG. 32 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 31. FIG. 33 is a schematic perspective view illustrating a method for manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 32. FIG. 34 is a schematic perspective view illustrating a method for manufacturing a wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 33. FIG. 35 is a schematic perspective view illustrating a method for manufacturing a wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 34. FIG. 36 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 35. It is a schematic diagram which shows schematic structure of the wavelength variable light source provided with the wavelength selection element by 3rd Embodiment. It is a schematic perspective view which shows the manufacturing method of the wavelength tunable light source provided with the wavelength selection element by 3rd Embodiment. FIG. 39 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 38. FIG. 40 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 39. FIG. 41 is a schematic perspective view illustrating a method for manufacturing a wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 40. FIG. 42 is a schematic perspective view illustrating a manufacturing method of the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 41. FIG. 43 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 42. FIG. 44 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 43. FIG. 45 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 44. FIG. 46 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 45. FIG. 47 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 46. FIG. 48 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selecting element according to the second embodiment, following FIG. 47. FIG. 49 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 48. FIG. 50 is a schematic perspective view illustrating a method of manufacturing the wavelength tunable light source including the wavelength selection element according to the second embodiment, following FIG. 49. It is a schematic diagram which shows schematic structure of the other example of the wavelength variable light source provided with the wavelength selection element by this embodiment. It is a schematic diagram which shows schematic structure of the other example of the wavelength variable light source provided with the wavelength selection element by this embodiment. It is a schematic diagram which shows schematic structure of the optical module by 4th Embodiment.

  Hereinafter, embodiments of the wavelength selection element and the wavelength tunable light source will be described in detail with reference to the drawings.

(First embodiment)
First, the first embodiment will be described.

[Schematic configuration of wavelength tunable light source]
FIG. 1 is a schematic diagram illustrating a schematic configuration of a wavelength tunable light source including a wavelength selection element according to the first embodiment.
This wavelength tunable light source is configured by connecting a wavelength selection element 1 and a wavelength filter element 2.

  The wavelength selection element 1 includes a multi-mode interference (MMI) demultiplexer 11 as an optical demultiplexer. In the MMI demultiplexer 11, optical waveguides 12a, 12b, 12c, and 12d are formed. An SOA 13 is formed in the optical waveguide 12b. A DBR mirror 14 is formed in the optical waveguide 12c.

  As shown in FIG. 2, the DBR mirror 14 has a flat and finite reflectance in the wavelength band used as the wavelength variable region, and a filter having a bandpass filter shape in which the reflectance rapidly decreases outside the wavelength band. Has characteristics. Furthermore, the recurrence mode interval is made substantially equal to the wavelength band (used wavelength band) used as the wavelength variable region. As shown in FIG. 3, the DBR mirror 14 has a chirped diffraction grating whose diffraction grating period is changed. Here, the case where the diffraction grating period is changed to Λ1, Λ2,. With such a chirped diffraction grating, the reflection band in the DBR mirror 14 can be expanded.

  When the DBR mirror 14 has a finite reflectance of, for example, about 30%, the reflectance is difficult to be flat within a required wavelength range, and a ripple of about 10% is generated as shown in FIG. In this case, a gain difference between adjacent modes cannot be secured, and there is a problem in mode stability. For this reason, as shown in FIG. 5, a DBR mirror 14 having a reflectance that makes the reflection band substantially flat is 90% or more (approximately 100%). However, in this case, if all the light is reflected by the DBR mirror 14, the output light cannot be extracted. In the present embodiment, part of the output light from the SOA 13 is guided to the DBR mirror 14 by the MMI demultiplexer 11 and reflected, and then returned to the SOA 13 to realize the wavelength filter effect, and is guided to the DBR mirror 14. Unused light is taken out as output light.

  The wavelength filter element 2 is configured such that two ring modulators 15 and 16 are provided in an optical waveguide, and a loop mirror 17 is provided at one end of the optical waveguide. The wavelength selection element 1 and the wavelength filter element 2 are combined by connecting the SOA 13 of the wavelength selection element 1 to the other end of the optical waveguide of the wavelength filter element 2 to constitute a wavelength variable light source.

[Manufacturing method of wavelength tunable light source]
6 to 20 are schematic perspective views illustrating a method of manufacturing a wavelength tunable light source including the wavelength selection element according to the first embodiment in the order of steps.

First, as shown in FIG. 6, a quantum well active layer 102, a p-type doped InP cladding layer 103, and a SiO ₂ film 104 are sequentially formed on an n-type doped InP substrate 101.
Specifically, the quantum well active layer 102 and the p-type doped InP cladding layer 103 are sequentially grown on the n-type doped InP substrate 101 by using, for example, metal organic vapor phase epitaxy (MOVPE). The quantum well active layer 102 includes an undoped GaInAsP quantum well layer having a thickness of about 5.1 nm and a compressive strain of about 1.0%, and an undoped GaInAsP barrier layer having a composition wavelength of 1.20 μm and a thickness of about 10 nm. The number of quantum well layers is six, and the emission wavelength is 1550 nm. These quantum well layers / barrier layers are sandwiched between undoped GaInAsP · SCH layers having a wavelength of 1.15 μm and a thickness of 50 nm. The p-type doped InP cladding layer 103 is formed with a thickness of about 150 nm.
Next, the SiO ₂ film 104 is deposited and formed on the p-type doped InP clad layer 103 to a thickness of about 400 nm by using an ordinary chemical vapor deposition method (CVD method).

Subsequently, as shown in FIG. 7, an etching mask for the SiO ₂ film 104 is formed.
More specifically, the SiO ₂ film 104 is processed by photolithography and dry etching, and the SiO ₂ film 104 is left so as to cover only a portion to be an active region of the SOA, thereby forming an etching mask.

Subsequently, as shown in FIG. 8, the p-type doped InP cladding layer 103 and the quantum well active layer 102 are processed.
Specifically, the p-type doped InP cladding layer 103 and the quantum well active layer 102 are dry-etched using the etching mask of the SiO ₂ film 104, and the quantum well active layer 102 and the p-type doped InP are formed into a shape following the etching mask. The cladding layer 103 is left.

Subsequently, as shown in FIG. 9, an undoped GaInAsP layer 105 and an undoped InP layer 106 are sequentially formed.
Specifically, an undoped GaInAsP layer 105 having a composition wavelength of 1.25 μm and a thickness of approximately 200 nm and an undoped InP layer 106 having a thickness of approximately 150 nm are sequentially grown on the n-type doped InP substrate 101 by using the MOVPE method. At this time, the undoped GaInAsP layer 105 and the undoped InP layer 106 do not grow on the etching mask of the SiO ₂ film 104 due to the selective growth effect, but are removed by etching the quantum well active layer 102 and the p-type doped InP cladding layer 103. It grows only on the part that was made. The etching mask of the SiO ₂ film 104 is peeled and removed by wet processing using a chemical solution such as hydrofluoric acid.

Subsequently, as shown in FIG. 10, an etching mask for the SiO ₂ film 107 is formed.
Specifically, the SiO ₂ film 107 is deposited to a thickness of about 400 nm on the p-type doped InP clad layer 103 and the undoped InP layer 106 by using a normal CVD method.
Next, the SiO ₂ film 104 is processed by photolithography and dry etching, and the SiO ₂ film 107 is left so as to open only a portion to be a region for forming a DBR chirped diffraction grating, thereby forming an etching mask.

Subsequently, as shown in FIG. 11, the undoped InP layer 106 is processed.
Specifically, the undoped InP layer 106 is dry-etched using the etching mask for the SiO ₂ film 107, leaving the undoped InP layer 106 in a shape that follows the etching mask.

Subsequently, as shown in FIG. 12, an undoped InP layer 108 and an undoped GaInAsP layer 109 are sequentially formed.
Specifically, an undoped InP layer 108 having a thickness of about 30 nm and an undoped GaInAsP layer 109 having a composition wavelength of 1.25 μm and a thickness of about 100 nm are sequentially grown on the undoped GaInAsP layer 105 by using the MOVPE method. At this time, due to the selective growth effect, the undoped InP layer 108 and the undoped GaInAsP layer 109 do not grow on the etching mask of the SiO ₂ film 107 but grow only on the portion removed by the etching of the undoped InP layer 106. The etching mask of the SiO ₂ film 107 is peeled and removed by wet processing using a chemical solution such as hydrofluoric acid.

Subsequently, as shown in FIG. 13, a diffraction grating mask 110 is formed.
Specifically, an electron beam resist (trade name: ZEP520 manufactured by Nippon Zeon Co., Ltd.) is applied on the undoped InP layer 106 and the undoped GaInAsP layer 109. The resist is processed by an electron beam exposure method to form a diffraction grating mask 110. In this diffraction grating mask 110, the region length of the distributed reflector (DBR mirror) is about 100 μm. The diffraction grating period gradually changes from about 237.5 nm to about 249.375 nm.

Subsequently, as shown in FIG. 14, a chirped diffraction grating is formed in the undoped GaInAsP layer 109.
Specifically, the undoped GaInAsP layer 109 is etched using the diffraction grating mask 110 until the surface of the undoped InP layer 108 is exposed. As the etching, reactive ion etching using an ethane / hydrogen mixed gas is applied. A chirped diffraction grating following the diffraction grating mask 110 is transferred and formed on the undoped GaInAsP layer 109. At this time, the depth of the chirped diffraction grating is about 100 nm.

  Subsequently, as shown in FIG. 15, the diffraction grating mask 110 is peeled and removed by a wet process using a predetermined chemical solution.

Subsequently, as shown in FIG. 16, a p-type InP clad layer 111, a p-type GaInAs contact layer 112, and an SiO ₂ film 113 are sequentially formed.
Specifically, a p-type GaInAs contact doped with Zn and having a p-type InP cladding layer 111 doped with Zn to a thickness of about 2.0 μm on the undoped InP layer 106 and the undoped GaInAsP layer 109 again using the MOVPE method. The layer 112 is sequentially grown to a thickness of about 300 nm. Next, a SiO ₂ film 113 is deposited on the p-type GaInAs contact layer 112 to a thickness of about 400 nm using a normal CVD method.

Subsequently, as shown in FIG. 17, an etching mask for the SiO ₂ film 113 is formed.
Specifically, the SiO ₂ film 113 is processed by photolithography and dry etching to leave the SiO ₂ film 113 in a shape such that the four optical waveguides merge with the MMI duplexer, and an etching mask is formed.

Subsequently, as illustrated in FIG. 18, a semiconductor multilayer structure including the quantum well active layer 102 to the p-type GaInAs contact layer 112 on the n-type doped InP substrate 101 is processed.
More specifically, using the etching mask for the SiO ₂ film 113, the semiconductor multilayer structure is dry etched to a depth in which the surface of the n-type doped InP substrate 101 is dug to about 0.7 μm and processed into a mesa stripe shape.

Subsequently, as shown in FIG. 19, a current confinement layer 114 is formed.
Specifically, the current confinement layer 114 made of Fe-doped semi-insulating InP 3 is grown on both sides of the mesa stripe-shaped semiconductor multilayer structure by using the MOVPE method. The etching mask of the SiO ₂ film 113 is peeled and removed by wet processing using a chemical solution such as hydrofluoric acid.

Subsequently, as shown in FIG. 20, a wavelength selection element is formed.
Specifically, first, a passivation film 115 made of SiN is formed on the p-type GaInAs contact layer 112 and the current confinement layer 114. Next, only the portion of the passivation film 115 that becomes the SOA is removed using photolithography and dry etching to form an opening. Next, an SOA p-electrode 116 is formed in the opening of the passivation film 115, and an SOA n-electrode 117 is formed on the back surface of the n-type doped InP substrate 101. Then, non-reflective coatings 118 and 119 are formed on both end portions. Thus, the wavelength selection element according to the present embodiment is formed.

  Thereafter, the wavelength selection element is combined with a wavelength filter element having two ring resonators and a loop mirror formed on the silicon substrate. As described above, the variable wavelength light source according to the present embodiment is obtained. With this wavelength tunable light source, laser oscillation light having characteristics of an optical output of about 13 dBm and a spectral line width of about 100 kHz is acquired in a wavelength tunable range from C band 1520 nm to 1570 nm.

  As described above, according to the present embodiment, it has a wide wavelength variable range, can operate stably at high output, and can oscillate efficiently and stably only at a desired wavelength. A highly reliable wavelength selection element and wavelength tunable light source are realized.

(Second Embodiment)
Next, a second embodiment will be described.

[Schematic configuration of wavelength tunable light source]
FIG. 21 is a schematic diagram illustrating a schematic configuration of a wavelength tunable light source including a wavelength selection element according to the second embodiment.
This wavelength tunable light source is configured by connecting a wavelength selection element 3 and a wavelength filter element 2 similar to that of the first embodiment.

  The wavelength selection element 1 includes an MMI demultiplexer 11 as an optical demultiplexer. In the MMI demultiplexer 11, optical waveguides 12a, 12b, 12c, and 12d are formed. An SOA 13 is formed in the optical waveguide 12b. A DBR mirror 14 is formed in the optical waveguide 12c. An SOA 18 is formed in the optical waveguide 12d.

  The DBR mirror 14 has a flat and finite reflectance in the wavelength band used as the wavelength variable region, and has a band-pass filter-shaped filter characteristic in which the reflectance rapidly decreases outside the wavelength band. Furthermore, the recurrence mode interval is made substantially equal to the wavelength band (used wavelength band) used as the wavelength variable region. The DBR mirror 14 has a chirped diffraction grating whose diffraction grating period is changed. With such a chirped diffraction grating, the reflection band in the DBR mirror 14 can be expanded.

  In the present embodiment, the SOA 18 is integrated in the optical waveguide 12d that is an output waveguide that performs optical output of the MMI demultiplexer 11. According to this configuration, it is possible to increase the light output while suppressing the occurrence of two-photon absorption that becomes a problem when the light intensity in the optical waveguide is strong.

[Manufacturing method of wavelength tunable light source]
22 to 36 are schematic perspective views showing a method of manufacturing a wavelength tunable light source including the wavelength selection element according to the second embodiment in the order of steps.

First, as shown in FIG. 22, a quantum well active layer 302, a p-type doped InP cladding layer 203, and a SiO ₂ film 204 are sequentially formed on an n-type doped InP substrate 201.
Specifically, the quantum well active layer 202 and the p-type doped InP cladding layer 203 are sequentially grown on the n-type doped InP substrate 201 by using, for example, metal organic vapor phase epitaxy (MOVPE). The quantum well active layer 202 includes an undoped GaInAsP quantum well layer having a thickness of approximately 5.1 nm and a compressive strain of approximately 1.0%, and an undoped GaInAsP barrier layer having a composition wavelength of 1.20 μm and a thickness of approximately 10 nm. The number of quantum well layers is six, and the emission wavelength is 1550 nm. These quantum well layers / barrier layers are sandwiched between undoped GaInAsP · SCH layers having a wavelength of 1.15 μm and a thickness of 50 nm. The p-type doped InP cladding layer 203 is formed with a thickness of about 150 nm.
Next, the SiO ₂ film 204 is deposited on the p-type doped InP clad layer 203 to a thickness of about 400 nm by using an ordinary chemical vapor deposition method (CVD method).

Subsequently, as shown in FIG. 23, an etching mask for the SiO ₂ film 204 is formed.
More specifically, the SiO ₂ film 204 is processed by photolithography and dry etching, and the etching mask is formed by leaving the SiO ₂ film 204 so as to cover only the portions that are to be active regions of the SOA (in this embodiment, two locations). To do.

Subsequently, as shown in FIG. 24, the p-type doped InP cladding layer 203 and the quantum well active layer 202 are processed.
Specifically, the p-type doped InP cladding layer 203 and the quantum well active layer 202 are dry-etched using the etching mask of the SiO ₂ film 204, and the quantum well active layer 202 and the p-type doped InP are formed in a shape following the etching mask. The cladding layer 203 is left.

Subsequently, as shown in FIG. 25, an undoped GaInAsP layer 205 and an undoped InP layer 206 are sequentially formed.
More specifically, an undoped GaInAsP layer 205 having a composition wavelength of 1.25 μm and a thickness of approximately 200 nm and an undoped InP layer 206 having a thickness of approximately 150 nm are sequentially grown on the n-type doped InP substrate 201 using the MOVPE method. At this time, the undoped GaInAsP layer 105 and the undoped InP layer 106 do not grow on the etching mask of the SiO ₂ film 204 due to the selective growth effect, but are removed by etching the quantum well active layer 202 and the p-type doped InP cladding layer 203. It grows only on the part that was made. The etching mask of the SiO ₂ film 204 is peeled and removed by wet processing using a chemical solution such as hydrofluoric acid.

Subsequently, as shown in FIG. 26, an etching mask for the SiO ₂ film 207 is formed.
Specifically, an SiO ₂ film 207 is deposited and formed on the p-type doped InP clad layer 203 and the undoped InP layer 206 by a normal CVD method to a thickness of about 400 nm.
Next, the SiO ₂ film 204 is processed by photolithography and dry etching to leave the SiO ₂ film 207 so as to open only a portion to be a region for forming a DBR chirped diffraction grating, thereby forming an etching mask.

Subsequently, as shown in FIG. 27, the undoped InP layer 206 is processed.
Specifically, the undoped InP layer 206 is dry-etched using the etching mask for the SiO ₂ film 207 to leave the undoped InP layer 206 in a shape following the etching mask.

Subsequently, as shown in FIG. 28, an undoped GaInAsP layer 208 is sequentially formed.
Specifically, an undoped GaInAsP layer 208 having a composition wavelength of 1.25 μm and a thickness of about 150 nm is sequentially grown on the undoped GaInAsP layer 205 by using the MOVPE method. At this time, due to the selective growth effect, the undoped GaInAsP layer 208 does not grow on the etching mask of the SiO ₂ film 207 but grows only on the portion removed by the etching of the undoped InP layer 206. The etching mask for the SiO ₂ film 207 is peeled and removed by wet treatment using a chemical solution such as hydrofluoric acid.

Subsequently, as shown in FIG. 29, a diffraction grating mask 209 is formed.
Specifically, an electron beam resist (trade name: ZEP520 manufactured by Nippon Zeon Co., Ltd.) is applied on the undoped InP layer 206 and the undoped GaInAsP layer 208. The resist is processed by an electron beam exposure method to form a diffraction grating mask 209. In the diffraction grating mask 209, the region length of the distributed reflector (DBR mirror) is about 100 μm. The diffraction grating period gradually changes from about 237.5 nm to about 249.375 nm.

Subsequently, as shown in FIG. 30, a chirped diffraction grating is formed in the undoped GaInAsP layer 208.
Specifically, the undoped GaInAsP layer 208 is etched using the diffraction grating mask 209. As the etching, reactive ion etching using an ethane / hydrogen mixed gas is applied. A chirped diffraction grating following the diffraction grating mask 209 is transferred and formed on the undoped GaInAsP layer 208. At this time, the depth of the chirped diffraction grating is about 100 nm.

  Subsequently, as shown in FIG. 31, the diffraction grating mask 209 is peeled and removed by wet processing using a predetermined chemical solution.

Subsequently, as shown in FIG. 32, a p-type InP clad layer 210, a p-type GaInAs contact layer 211, and an SiO ₂ film 212 are sequentially formed.
Specifically, a Zn-doped p-type InP cladding layer 210 having a thickness of about 2.0 μm and a Zn-doped p-type GaInAs contact are again formed on the undoped InP layer 206 and the undoped GaInAsP layer 208 by using the MOVPE method. The layer 211 is sequentially grown to a thickness of about 300 nm. Next, a SiO ₂ film 212 is deposited on the p-type GaInAs contact layer 211 to a thickness of about 400 nm using a normal CVD method.

Subsequently, as shown in FIG. 33, an etching mask for the SiO ₂ film 212 is formed.
Specifically, the SiO ₂ film 212 is processed by photolithography and dry etching, and the etching mask is formed by leaving the SiO ₂ film 212 in a shape in which four optical waveguides merge with the MMI duplexer.

Subsequently, as shown in FIG. 34, a semiconductor multilayer structure including the quantum well active layer 202 to the p-type GaInAs contact layer 211 on the n-type doped InP substrate 201 is processed.
Specifically, using the etching mask for the SiO ₂ film 212, the semiconductor multilayer structure is dry etched to a depth of about 0.7 μm in the surface of the n-type doped InP substrate 201 and processed into a mesa stripe shape.

Subsequently, as shown in FIG. 35, a current confinement layer 213 is formed.
More specifically, a current confinement layer 213 made of Fe-doped semi-insulating InP 2 is grown on both sides of the mesa stripe-shaped semiconductor multilayer structure by using the MOVPE method. The etching mask of the SiO ₂ film 212 is peeled and removed by wet processing using a chemical solution such as hydrofluoric acid.

Subsequently, as shown in FIG. 36, a wavelength selection element is formed.
Specifically, first, a passivation film 214 made of SiN is formed on the p-type GaInAs contact layer 211 and the current confinement layer 213. Next, only the portions (two locations in the present embodiment) to be the SOA of the passivation film 214 are removed using photolithography and dry etching to form openings. Next, SOA p-electrodes 215 and 216 are formed in two openings of the passivation film 214, and an SOA n-electrode 217 is formed on the back surface of the n-type doped InP substrate 201. Then, anti-reflective coatings 218 and 219 are formed on both end portions. Thus, the wavelength selection element according to the present embodiment is formed.

  Thereafter, the wavelength selection element is combined with a wavelength filter element having two ring resonators and a loop mirror formed on the silicon substrate. As described above, the variable wavelength light source according to the present embodiment is obtained. With this wavelength tunable light source, laser oscillation light having characteristics of an optical output of about 13 dBm and a spectral line width of about 100 kHz is acquired in a wavelength tunable range from C band 1520 nm to 1570 nm.

  As described above, according to the present embodiment, it has a wide wavelength variable range, can operate stably at high output, and can oscillate efficiently and stably only at a desired wavelength. A highly reliable wavelength selection element and wavelength tunable light source are realized.

(Third embodiment)
Next, a third embodiment will be described.

[Schematic configuration of wavelength tunable light source]
FIG. 37 is a schematic diagram showing a schematic configuration of a wavelength tunable light source including a wavelength selection element according to the third embodiment.
This wavelength tunable light source is configured by connecting a wavelength selection element 4 and a quantum dot SOA5. A quantum well SOA may be used instead of the quantum dot SOA5.

  The wavelength selection element 4 has two optical waveguides 21a and 21b, and the optical waveguides 21a and 21b are close to each other at a predetermined portion to form a directional coupler. A DBR mirror 14 is formed in the optical waveguide 21a. An SOA 18 is formed in the optical waveguide 21b.

  The DBR mirror 14 has a flat and finite reflectance in a wavelength band used as a multi-wavelength oscillation region, and has a band-pass filter-shaped filter characteristic in which the reflectance rapidly decreases outside the wavelength band. The DBR mirror 14 has a chirped diffraction grating whose diffraction grating period is changed. With such a chirped diffraction grating, the reflection band in the DBR mirror 14 can be expanded.

  In the present embodiment, the SOA 18 is integrated at the light output portion of the optical waveguide 21b. According to this configuration, it is possible to increase the light output while suppressing the occurrence of two-photon absorption which becomes a problem when the light intensity in the optical waveguide is strong.

  When the DBR mirror 14 has a finite reflectance of, for example, about 30%, the reflectance hardly becomes flat within a required wavelength range, and a ripple of about 10% is generated. In this case, a gain difference between adjacent modes cannot be secured, and there is a problem in mode stability. For this reason, a DBR mirror 14 having a reflectivity of 90% or more (nearly 100%) with a substantially flat reflection band is used. However, in this case, if all the light is reflected by the DBR mirror 14, the output light cannot be extracted. In the present embodiment, a part of the output light from the quantum dot SOA5 is guided to the DBR mirror 14 by the directional coupler, reflected, and returned again to realize the wavelength filter effect, but not guided to the DBR mirror 14. Light is extracted as output light. Further, even in the case of a multi-wavelength light source, unnecessary carrier consumption in the quantum dot SOA5 can be suppressed by cutting unnecessary oscillation modes, and loss due to the directional coupler can be compensated.

  The quantum dot SOA5 is hybrid-mounted on the Si platform 22, and further provided with a lens 23, for example, an etalon 24 having peaks at intervals of 800 GHz, and a total reflection mirror 25. The wavelength selection element 4 and the quantum well laser 5 are combined with the optical waveguide 21b of the wavelength selection element 1 connected to the output part of the quantum dot SOA5 to constitute a wavelength variable light source.

[Manufacturing method of wavelength tunable light source]
38 to 50 are schematic perspective views showing a method of manufacturing a wavelength tunable light source including the wavelength selection element according to the third embodiment in the order of steps.

First, as shown in FIG. 38, an undoped GaInAsP layer 302 and a resist layer 303 are sequentially formed on an n-type doped InP substrate 301.
Specifically, an undoped GaInAsP layer 302 having a composition wavelength of 1.15 μm and a thickness of 100 nm is grown on the n-type doped InP substrate 301 by using, for example, the MOVPE method. Next, an electron beam resist (trade name: ZEP520 manufactured by Nippon Zeon Co., Ltd.) is applied on the undoped GaInAsP layer 302 to form a resist layer 303.

Subsequently, as shown in FIG. 39, a diffraction grating mask of the resist layer 303 is formed.
Specifically, the resist layer 303 is processed by an electron beam exposure method to form a diffraction grating mask. In this diffraction grating mask, the region length of the distributed reflector (DBR mirror) is 100 μm. The diffraction grating period gradually changes from 198 nm to 202 nm.

Subsequently, as shown in FIG. 40, a chirped diffraction grating is formed in the undoped GaInAsP layer 302.
Specifically, the undoped GaInAsP layer 302 is etched using the diffraction grating mask of the resist layer 303. Here, reactive ion etching using an ethane / hydrogen mixed gas is applied to penetrate the undoped GaInAsP layer 302 and etch from the surface of the n-type doped InP substrate 301 to about 15 nm. A chirped diffraction grating following the diffraction grating mask of the resist layer 303 is transferred and formed on the undoped GaInAsP layer 302.

  Subsequently, as shown in FIG. 41, the diffraction grating mask of the resist layer 303 is peeled and removed by wet processing using a predetermined chemical solution.

Subsequently, as shown in FIG. 42, an n-type doped InP layer 304, a quantum well active layer 305, a p-type doped InP clad layer 306, and a SiO ₂ film 307 are sequentially formed.
Specifically, after growing the n-type doped InP layer 304 using the MOVPE method and filling the chirped diffraction grating of the undoped GaInAsP layer 302, the n-type is doped until the thickness on the part without the chirped diffraction grating reaches about 50 nm. A doped InP layer 304 is grown. Subsequently, a quantum well active layer 305 and a p-type doped InP cladding layer 306 having a thickness of about 150 nm are grown by MOVPE. Next, an SiO ₂ film 307 is deposited on the p-type doped InP clad layer 306 to a thickness of about 400 nm using a normal CVD method.

  Here, the quantum well active layer 305 includes an undoped AlGaInAs quantum well layer having a thickness of about 4.8 nm and a compressive strain of about 1.0%, and an undoped AlGaInAs barrier layer having a composition wavelength of 1.05 μm and a thickness of about 10 nm. Is done. The number of undoped AlGaInAs quantum well layers is eight, and the emission wavelength is 1310 nm. These quantum well layers / barrier layers are sandwiched between undoped AlGaInAs · SCH layers having a wavelength of about 1.0 μm and a thickness of about 20 nm.

Subsequently, as shown in FIG. 43, an etching mask for the SiO ₂ film 307 is formed.
Specifically, the SiO ₂ film 307 is processed by photolithography and dry etching, and the etching mask is formed by leaving the SiO ₂ film 307 so as to cover only the portion that should be the active region of the SOA.

Subsequently, as shown in FIG. 44, the p-type doped InP cladding layer 306 and the quantum well active layer 305 are processed.
Specifically, using the etching mask for the SiO ₂ film 307, the p-type doped InP cladding layer and the 306 quantum well active layer 305 are dry-etched until the surface of the n-type doped InP layer 304 is exposed, and the SiO ₂ film 307 is etched. It remains in a shape following the etching mask.

Subsequently, as shown in FIG. 45, an undoped AlGaInAsP layer 308 and an undoped InP layer 309 are sequentially formed.
Specifically, an undoped AlGaInAsP layer 308 having a composition wavelength of 1.15 μm and a thickness of about 170 nm and an undoped InP layer 309 having a thickness of about 150 nm are sequentially grown on the n-type doped InP layer 304 by using the MOVPE method. At this time, the undoped AlGaInAsP layer 308 and the undoped InP layer 309 do not grow on the etching mask of the SiO ₂ film 307 due to the selective growth effect, but are removed by etching of the quantum well active layer 305 and the p-type doped InP cladding layer 306. It grows only on the part that was made. The etching mask of the SiO ₂ film 307 is peeled and removed by wet processing using a chemical solution such as hydrofluoric acid.

Subsequently, as shown in FIG. 46, a p-type InP clad layer 310, a p-type GaInAs contact layer 311 and an SiO ₂ film 312 are sequentially formed.
Specifically, a p-type InP clad layer 310 doped with Zn is formed on the p-type doped InP clad layer 306 and the undoped AlGaInAsP layer 308 again by using the MOVPE method. A type GaInAs contact layer 311 is sequentially grown to a thickness of about 300 nm. Next, a SiO ₂ film 312 is deposited on the p-type GaInAs contact layer 311 to a thickness of about 400 nm using a normal CVD method.

Subsequently, as shown in FIG. 47, an etching mask for the SiO ₂ film 312 is formed.
Specifically, the SiO ₂ film 312 is processed by photolithography and dry etching, and the two waveguides are close to each other to leave the SiO ₂ film 312 in a shape constituting the directional coupler, thereby forming an etching mask. .

Subsequently, as shown in FIG. 48, a semiconductor multilayer structure including the undoped GaInAsP layer 302 to the p-type GaInAs contact layer 311 of the n-type doped InP substrate 301 is processed.
More specifically, using the etching mask for the SiO ₂ film 312, the semiconductor multilayer structure is dry-etched to a depth in which the surface of the n-type doped InP substrate 301 is dug by about 0.7 μm and processed into a mesa stripe shape.

Subsequently, as shown in FIG. 49, a current confinement layer 313 is formed.
More specifically, a current confinement layer 313 made of Fe-doped semi-insulating InP 3 is grown on both sides of the mesa stripe-shaped semiconductor multilayer structure by using the MOVPE method. The etching mask of the SiO ₂ film 312 is peeled and removed by wet processing using a chemical solution such as hydrofluoric acid.

Subsequently, as shown in FIG. 50, a wavelength selection element is formed.
Specifically, first, a passivation film 314 made of SiN is formed on the p-type GaInAs contact layer 311 and the current confinement layer 313. Next, only the portion of the passivation film 314 that becomes the SOA is removed using photolithography and dry etching to form an opening. Next, an SOA p-electrode 315 is formed in the opening of the passivation film 314, and an SOA n-electrode 316 is formed on the back surface of the n-type doped InP substrate 301. Then, non-reflective coatings 317 and 318 are formed on both end surface portions. Thus, the wavelength selection element according to the present embodiment is formed.

  Thereafter, a quantum dot SOA (or quantum well SOA) having a non-reflective coating on the wavelength selection element and both end faces is hybrid-mounted on the Si platform. Furthermore, a multi-wavelength simultaneous oscillation laser light source can be obtained by combining a lens, an etalon having peaks at intervals of 800 GHz, and a total reflection mirror. With this multi-wavelength simultaneous oscillation laser light source, laser oscillation light having four wavelengths used in LAN-WDM can be obtained.

  As described above, according to the present embodiment, it has a wide wavelength variable range, can operate stably at high output, and can oscillate efficiently and stably only at a desired wavelength. A highly reliable wavelength selection element and wavelength tunable light source are realized.

  In the first embodiment, each output end of the optical waveguide 12d of the MMI demultiplexer 11, the SOA 18 of the optical waveguide 12d in the second embodiment, and the SOA 18 of the optical waveguide 21b of the directional coupler in the third embodiment. Exemplifies those extending in a direction perpendicular to the end face. In order to suppress light reflection at the end face, each output end may be bent halfway to extend obliquely with respect to the end face.

  Further, in order to improve optical coupling with other optical elements, for example, a spot size converter in which the width and thickness of the optical waveguide are gently changed may be integrated on the end face portion of the optical waveguide. Further, as the optical multiplexer / demultiplexer, the MMI demultiplexer is used in the first and second embodiments, and the directional coupler is used in the third embodiment, but other optical multiplexer / demultiplexers may be used. . For example, each optical multiplexer / demultiplexer may use a different optical multiplexer / demultiplexer. As shown in FIG. 51, the wavelength selection element may include a Y-branch waveguide 31 that stimulates the optical waveguides 31a and 31b from the optical waveguide in which the SOA 13 is integrated.

  In the first and second embodiments, the MMI duplexer having a 2 × 2 port is used. However, the same effect can be obtained with an MMI duplexer having a 1 × 2 port. As shown in FIG. 52, a photodetector (waveguide type PD32) may be integrated into a port of an empty optical waveguide of the MMI demultiplexer 11 (for example, the optical waveguide 12b) to form an optical monitor. it can.

  Further, as the active region of the semiconductor optical amplifier, a GaInAsP-based material is used in the first and second embodiments, and an AlGaInAs-based material is used in the third embodiment. Absent. It is clear that the same effect can be obtained even if the active layer is formed of a bulk type semiconductor instead of a quantum well. In the first to third embodiments, all the wavelength selection elements are fabricated on the InP substrate, but may be fabricated on a GaAs substrate or the like. In addition, when the optical amplification function is not necessary, the material constituting the wavelength selection element is loaded with a chirped diffraction grating in the vicinity of the optical waveguide even if it is composed of not only a compound semiconductor but also an organic or inorganic material Obviously, it is applicable to all devices.

  In the first to third embodiments, the wavelength selection element is formed on the substrate having n-type conductivity, but the first to third layers are formed using a substrate having p-type conductivity. It is obvious that the same effect can be obtained even if a structure having a conductivity opposite to that of the embodiment is used. It is obvious that the same effect can be obtained even if the wavelength selection element is manufactured on a semi-insulating substrate, for example, by a bonding method on a silicon substrate.

  In the first to third embodiments, the current confinement structure using the current confinement buried structure using a semi-insulating material is exemplified as the buried structure, but the current confinement structure having the pnpn thyristor structure is applied. I do not care. Furthermore, in the first to third embodiments, the embedded type optical waveguide is exemplified, but it is apparent that the present invention can be applied to lasers having other optical waveguide structures such as a ridge type waveguide.

  In the second embodiment, the surface diffraction grating structure is exemplified as the chirped diffraction grating structure, but an embedded diffraction grating structure may be applied as in the first and third embodiments. The second embodiment and the first and third embodiments may be reversed. In the third embodiment, the chirped diffraction grating is loaded on the substrate side with respect to the optical waveguide. However, as in the first and second embodiments, the chirped diffraction grating is loaded on the opposite side of the substrate. It is clear that a similar effect can be obtained. The third embodiment may be reversed from the first and second embodiments. In the first to third embodiments, the value of the chirped diffraction grating depth (= coupling coefficient) of the DBR mirror is not changed, but it may be different in the resonator direction depending on the element design. .

(Fourth embodiment)
Next, a fourth embodiment will be described. In the present embodiment, an optical module including one type of wavelength tunable light source in the first to third embodiments is disclosed.

FIG. 53 is a schematic diagram showing a schematic configuration of the optical module according to the fourth embodiment.
The optical module includes a transmission module unit 41 and a reception module unit 42, and the transmission module unit 41 and the reception module unit 42 are connected by an optical fiber 43.

  The transmission module unit 41 includes a modulation light circuit 44, a driver IC 45 for driving the modulation light circuit 44, a monitor PD 48 for monitoring light emission in the modulation light circuit 44, an isolator 47, a lens 49, and the like. . In the present embodiment, the modulation light circuit 44 uses one of the variable wavelength light sources of the first to third embodiments. In the transmission module unit 41, the laser light emitted from the modulation light circuit 44 driven by the driver IC 45 is incident from one end 43 a of the optical fiber 43 through the isolator 47 and the lens 49.

  The reception module unit 42 includes a signal demodulation circuit 51, a driver IC 52 that drives the signal demodulation circuit 51, a lens 53, and the like. Laser light that has entered the one end portion 43 a of the optical fiber 430 from the transmission module portion 42 propagates through the optical fiber 43 and is emitted from the other end portion 43 b of the optical fiber 43. The laser light emitted from the other end 43 b of the optical fiber 43 is incident on the reception module unit 42 and is incident on the signal demodulation circuit 51 through the lens 53 in the reception module unit 42.

  According to the present embodiment, modulated light having a wavelength tunable light source that has a wide wavelength tunable range, can operate stably with high output, and can oscillate efficiently and stably only at a desired wavelength. A highly reliable optical module including the circuit 44 is realized.

  Hereinafter, various aspects of the wavelength selection element and the wavelength tunable light source will be collectively described as additional notes.

(Supplementary Note 1) An optical demultiplexer having a plurality of output waveguides is provided,
At least one of the plurality of output waveguides is provided with a distributed reflection type mirror structure having a diffraction grating,
The wavelength selection element according to claim 1, wherein at least one of the plurality of output waveguides is an optical output port to the outside.

  (Supplementary note 2) The wavelength selection element according to supplementary note 1, wherein one waveguide input to the optical demultiplexer includes a first optical amplifier.

  (Supplementary note 3) The wavelength selection element according to supplementary note 1 or 2, wherein the output waveguide which is the optical output port includes a second optical amplifier.

  (Supplementary note 4) The wavelength selection element according to supplementary note 3, wherein the other waveguide input to the optical demultiplexer includes a photodetector.

  (Supplementary Note 5) The distributed reflection type mirror structure has a flat and finite reflectivity in the wavelength band used as the wavelength variable region or the multi-wavelength oscillation region, and the reflectivity rapidly decreases outside the wavelength band. 5. The wavelength selection element according to any one of supplementary notes 1 to 4, wherein the wavelength selection element has a filter characteristic of a filter shape.

  (Supplementary note 6) The wavelength selection element according to any one of Supplementary notes 1 to 5, wherein the first output waveguide has a light reflectance of the distributed reflection mirror structure of 90% or more.

(Supplementary note 7) The wavelength selection element according to any one of supplementary notes 1 to 6,
A second wavelength selection element connected to the first optical amplifier at an end opposite to the optical demultiplexer;
A wavelength tunable light source comprising a reflection mirror connected to the second wavelength selection element at an end opposite to the first optical amplifier.

  (Additional remark 8) The said 2nd wavelength selection element has a vernier type | mold wavelength filter which consists of a some wavelength filter, The variable wavelength light source of Additional remark 7 characterized by the above-mentioned.

  (Supplementary note 9) The wavelength variable light source according to supplementary note 7, wherein the first optical amplifier includes a quantum dot SOA.

1, 3, 4, 6, 7 Wavelength selection element 2 Wavelength filter element 5 Quantum dot SOA
11 MMI demultiplexers 12a, 12b, 12c, 12d, 21a, 21b, 31a, 31b Optical waveguides 13, 18 SOA
14 DBR mirrors 15 and 16 Ring resonator 17 Loop mirror 22 Si platform 23 Lens 24 Etalon 25 Total reflection mirror 31 Y-branch waveguide 32 Waveguide type PD
41 transmitting module section 42 receiving module section 43 optical fiber 43a one end 43b other end 44 modulating optical circuit 45, 52 driver IC
46 Beam splitter 47 Isolator 48 Monitor PD
49, 53 Lens 51 Signal demodulation circuit

Claims (7)

Comprising an optical demultiplexer having a plurality of output waveguides;
At least one of the plurality of output waveguides is provided with a distributed reflection type mirror structure having a diffraction grating,
The wavelength selection element according to claim 1, wherein at least one of the plurality of output waveguides is an optical output port to the outside.   The wavelength selection element according to claim 1, wherein one waveguide input to the optical demultiplexer includes a first optical amplifier.   3. The wavelength selection element according to claim 1, wherein the output waveguide configured as the optical output port includes a second optical amplifier. 4.   The wavelength selection element according to claim 3, wherein another waveguide input to the optical demultiplexer includes a photodetector.   The distributed reflection type mirror structure has a flat and finite reflectance in a wavelength band used as a wavelength variable region or a multi-wavelength oscillation region, and a filter having a bandpass filter shape in which the reflectance rapidly decreases outside the wavelength band. The wavelength selection element according to claim 1, wherein the wavelength selection element has characteristics.   6. The wavelength selection element according to claim 1, wherein the first output waveguide has a light reflectance of 90% or more of the distributed reflection type mirror structure. The wavelength selection element according to any one of claims 1 to 6,
A second wavelength selection element connected to the first optical amplifier at an end opposite to the optical demultiplexer;
A wavelength tunable light source comprising a reflection mirror connected to the second wavelength selection element at an end opposite to the first optical amplifier.

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