WO2016152274A1 - Variable wavelength laser element and laser module - Google Patents

Variable wavelength laser element and laser module Download PDF

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Publication number
WO2016152274A1
WO2016152274A1 PCT/JP2016/053463 JP2016053463W WO2016152274A1 WO 2016152274 A1 WO2016152274 A1 WO 2016152274A1 JP 2016053463 W JP2016053463 W JP 2016053463W WO 2016152274 A1 WO2016152274 A1 WO 2016152274A1
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WIPO (PCT)
Prior art keywords
waveguide
comb
wavelength
tunable laser
reflection spectrum
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PCT/JP2016/053463
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French (fr)
Japanese (ja)
Inventor
泰雅 川北
康貴 比嘉
岩井　則広
黒部　立郎
Original Assignee
古河電気工業株式会社
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Priority claimed from JP2016008579A external-priority patent/JP6684094B2/en
Application filed by 古河電気工業株式会社 filed Critical 古河電気工業株式会社
Priority to CN201680012598.3A priority Critical patent/CN107431331B/en
Publication of WO2016152274A1 publication Critical patent/WO2016152274A1/en
Priority to US15/708,994 priority patent/US10193305B2/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region

Definitions

  • the present invention relates to a wavelength tunable laser device and a laser module using the same.
  • Non-Patent Document 1 The configuration and operation principle of the wavelength tunable laser element are described in detail, for example, in Non-Patent Document 1.
  • DBR distributed Bragg reflector
  • Sampled Grating sampled diffraction grating
  • the reflection spectra of the two DBR mirrors have a comb-like shape with a slightly different period. Further, by causing a change in refractive index to the DBR mirror by current injection or heating, it is possible to make its reflection wavelength characteristic variable. By multiplying the reflection characteristics of the two DBR mirrors, the reflectance of a specific wavelength region can be increased to form a resonator. At this time, if the resonator length is properly designed, the distance between the longitudinal modes, which are resonator modes, becomes approximately the same as the reflection band by two DBR mirrors, only one resonator mode is selected, and single mode oscillation is To be realized.
  • the resonator is made long enough to obtain a laser beam with a narrow line width required for coherent communication, the longitudinal mode spacing becomes narrow, and the reflection band of the resonator Since it is difficult to select only one resonator mode, it is in principle difficult to obtain single mode oscillation.
  • the resonator is configured using two ring resonators
  • the reflectance fluctuation of the overlapping portion is large. Therefore, in order to realize stable laser oscillation, it is necessary to ensure that the peaks of the two sharp reflection wavelength characteristics overlap with each other, but such control is difficult.
  • the present invention has been made in view of the above, and it is an object of the present invention to provide a wavelength tunable laser device which can realize narrowing of the width of laser light and stable single mode oscillation, and a laser module using the same. Do.
  • a wavelength tunable laser device includes a diffraction grating and a reflection mirror including a ring resonator filter optically coupled to the diffraction grating.
  • a tunable laser device comprising: a configured laser resonator; a gain unit disposed in the laser resonator; and a phase adjusting unit disposed in the laser resonator, wherein the diffraction grating is A first comb-like reflection spectrum is generated, and the ring resonator filter is optically coupled to the ring waveguide, each of which is optically coupled to the ring waveguide, and one end thereof is integrated to form the optical grating and the optical grating.
  • a second comb-like reflection spectrum having a wavelength interval between the first and second comb-like reflection spectra, and the diffraction grating and the ring resonator produce one of the peaks of the first comb-like reflection spectrum and one of the peaks of the second comb-like reflection spectrum.
  • the laser resonators are configured such that the spacing between the modes of the resonator modes is narrower than the full width at half maximum of the peak of the first comb-like reflection spectrum. ing.
  • a laser module according to an aspect of the present invention includes the wavelength tunable laser element according to the aspect of the present invention.
  • FIG. 1 is a schematic perspective view of the wavelength tunable laser device according to the first embodiment.
  • FIG. 2A is a schematic cross-sectional view of the wavelength tunable laser device shown in FIG.
  • FIG. 2B is a schematic cross-sectional view of the wavelength tunable laser device shown in FIG.
  • FIG. 2C is a schematic cross-sectional view of the wavelength tunable laser device shown in FIG.
  • FIG. 3A is a diagram showing a first comb-like reflection spectrum and a second comb-like reflection spectrum.
  • FIG. 3B is a diagram showing a first comb reflection spectrum, a second comb reflection spectrum, and a resonator mode.
  • FIG. 4 is a diagram showing a first comb-like reflection spectrum, a second comb-like reflection spectrum and an overlap thereof.
  • FIG. 5 is a diagram for explaining the optical feedback in the wavelength tunable laser device shown in FIG.
  • FIG. 6 is a diagram for explaining a method of selecting a laser oscillation wavelength in the wavelength tunable laser device shown in FIG.
  • FIG. 7AA is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG.
  • FIG. 7AB is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG.
  • FIG. 7AC is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG.
  • FIG. 7AA is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG.
  • FIG. 7AB is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown
  • FIG. 7BA is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG.
  • FIG. 7BB is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG.
  • FIG. 7BC is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG.
  • FIG. 7CA is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG.
  • FIG. 7CB is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG.
  • FIG. 7CC is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG.
  • FIG. 7CC is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG. FIG.
  • FIG. 8 is a view for explaining a waveguide portion which optically couples the ring waveguide and the two arm portions in the wavelength tunable laser device shown in FIG.
  • FIG. 9A is a view for explaining the structure of the waveguide section.
  • FIG. 9B is a view for explaining the structure of the waveguide section.
  • FIG. 10 is a diagram for explaining an example of the first waveguide section having a ridge waveguide structure.
  • FIG. 11 is a schematic perspective view of the wavelength tunable laser device according to the second embodiment.
  • FIG. 12A is a schematic perspective view of a wavelength tunable laser device according to a third embodiment. 12B is a schematic cross-sectional view of the wavelength tunable laser device according to Embodiment 3.
  • FIG. FIG. 13 is a schematic perspective view of the wavelength tunable laser device according to the fourth embodiment.
  • FIG. 14 is a schematic view of a laser module according to the fifth embodiment.
  • FIG. 15 is a schematic view of a laser module according to the sixth
  • the tunable laser device is a tunable laser device using the vernier effect, wherein the peak of the first comb-like reflection spectrum is narrower than the full width at half maximum of the peak of the first comb-like reflection spectrum. Having a second comb-like reflection spectrum having a wavelength spacing different from the wavelength spacing, and the spacing between the modes of the resonator modes being narrower than the full width at half maximum of the first comb-like reflection spectrum By being configured, narrowing of the line width of laser light and stable single mode oscillation can be realized.
  • FIG. 1 is a schematic perspective view of the wavelength tunable laser device according to the first embodiment.
  • the wavelength tunable laser device 100 is configured to emit a laser beam by performing laser oscillation in a 1.55 ⁇ m band.
  • the wavelength tunable laser device 100 includes a first waveguide section 10 and a second waveguide section 20 formed on a common base B.
  • the base B is made of, for example, n-type InP.
  • An n-side electrode 30 is formed on the back surface of the base B.
  • the n-side electrode 30 includes, for example, AuGeNi, and makes ohmic contact with the base B.
  • the first waveguide unit 10 includes a waveguide unit 11, a semiconductor multilayer unit 12, a p-side electrode 13, and microheaters 14 and 15 made of Ti.
  • the waveguide portion 11 is formed to extend in the z direction in the semiconductor multilayer portion 12.
  • a diffraction grating loading type gain unit 11a and a phase adjustment unit 11b are disposed.
  • the semiconductor multilayer portion 12 is configured by laminating semiconductor layers, and has a function of a cladding portion and the like with respect to the waveguide portion 11. The configurations of the waveguide portion 11 and the semiconductor laminated portion 12 will be described in detail later.
  • the p-side electrode 13 is disposed on the semiconductor laminated portion 12 along the diffraction grating loaded gain portion 11 a.
  • the SiN protective film mentioned later is formed in the semiconductor lamination part 12, and the p side electrode 13 is in contact with the semiconductor lamination part 12 via the opening part formed in the SiN protection film.
  • the micro heater 14 is disposed on the SiN protective film of the semiconductor lamination portion 12 so as to be along the phase adjustment portion 11 b.
  • the microheater 15 as a first refractive index changer is disposed along the p-side electrode 13 on the SiN protective film of the semiconductor multilayer portion 12.
  • FIG. 2A is a cross-sectional view taken along the line AA of a portion of the first waveguide section 10 including the diffraction grating loaded gain section 11a, which is cut along a plane parallel to the xy plane of FIG.
  • the diffraction grating loading type gain portion 11a is composed of an active core layer 11aa and a sampling grating provided along the active core layer 11aa in the vicinity of and directly on the active core layer 11aa. And 11ab.
  • Active core layer 11aa has a multiple quantum well structure including a plurality of well layers and a plurality of barrier layers alternately stacked, and a multiple quantum well structure from the top to the bottom and the upper light confinement layer It emits light by current injection.
  • the well layer and the barrier layer constituting the multiple quantum well structure of the active core layer 11aa are made of InGaAsP different in composition from each other, and the emission wavelength band from the active core layer 11aa is 1.55 ⁇ m band in the first embodiment.
  • the lower optical confinement layer is made of n-type InGaAsP.
  • the upper optical confinement layer is made of p-type InGaAsP.
  • the band gap wavelengths of the lower and upper optical confinement layers are set to be shorter than the band gap wavelength of the active core layer 11aa.
  • a sampling diffraction grating is formed in the p-type InGaAsP layer along the z direction, and the groove of the diffraction grating has a configuration embedded in InP.
  • the grating interval of the diffraction grating is constant but sampled, thereby exhibiting a reflection response that is substantially periodic with respect to the wavelength.
  • the band gap wavelength of the p-type InGaAsP layer of the diffraction grating layer 11ab is preferably shorter than the band gap wavelength of the active core layer 11aa, and is, for example, 1.2 ⁇ m.
  • the semiconductor laminated portion 12 in the portion including the diffraction grating loaded gain portion 11a has, for example, the following configuration.
  • the semiconductor multilayer portion 12 has an n-type semiconductor layer 12a of n-type InP formed of a buffer layer having a function of a lower cladding layer on an n-type InP substrate forming the base B.
  • Active core layer 11aa is stacked on n-type semiconductor layer 12a.
  • a spacer layer 12b made of p-type InP is stacked on the active core layer 11aa.
  • the diffraction grating layer 11ab is stacked on the spacer layer 12b.
  • Active core layer 11aa, spacer layer 12b and diffraction grating layer 11ab have a stripe mesa structure having a width (for example, 1.8 .mu.m) suitable for single-mode optical waveguide of 1.55 .mu.m band by etching or the like. It is done. Both sides of the stripe mesa structure (in the left-right direction in the drawing) have a buried structure having a current blocking structure including a p-type InP buried layer 12c and an n-type InP current blocking layer 12d.
  • the p-type semiconductor layer 12e is provided at least from immediately above the active core layer 11aa to a part of the embedded structure on both sides thereof.
  • a SiN protective film 16 is formed on the semiconductor laminated portion 12 so as to cover the semiconductor laminated portion 12.
  • the p-side electrode 13 contains AuZn, is formed on the contact layer 12eb, and is in ohmic contact with the contact layer 12eb via the opening 16a of the SiN protective film 16. With the above configuration, current injection from the n-side electrode 30 and the p-side electrode 13 to the active core layer 11aa is possible. Furthermore, the microheater 15 is disposed along the p-side electrode 13 on the SiN protective film 17 provided in the semiconductor laminated portion 12 in order to insulate the p-side electrode 13 from the microheater 15.
  • FIG. 2B is a cross-sectional view taken along the line BB taken along a plane parallel to the xy plane in FIG. 1, of a portion of the first waveguide 10 including the phase adjustment portion 11b.
  • the sectional structure of the first waveguide section 10 including the phase adjustment section 11b replaces the active core layer 11aa in the structure shown in FIG. 2A with the phase adjustment section 11b which is an optical waveguide layer made of InGaAsP.
  • the diffraction grating layer 11ab and the spacer layer 12b are replaced by the p-type InP layer 12f, and the contact layer 12eb is eliminated.
  • the band gap wavelength of the phase adjustment part 11b is preferably shorter than the band gap wavelength of the active core layer 11aa, for example, 1.3 ⁇ m or less is there.
  • the first waveguide section 10 has the embedded waveguide structure as the first waveguide structure.
  • the second waveguide portion 20 includes a bifurcated portion 21, two arm portions 22 and 23, a ring-shaped waveguide 24, and a micro heater 25 made of Ti.
  • the bifurcated portion 21 is composed of a 1 ⁇ 2 type branched waveguide including a 1 ⁇ 2 type multimode interference (MMI) waveguide 21 a, and the two port side is connected to each of the two arm portions 22 and 23. At the same time, one port side is connected to the first waveguide section 10 side. One end of the two arm portions 22 and 23 is integrated by the bifurcated portion 21 and optically coupled to the diffraction grating layer 11ab.
  • MMI multimode interference
  • Each of the arm portions 22 and 23 extends in the z direction, and is disposed so as to sandwich the ring waveguide 24.
  • the arm portions 22 and 23 are in close proximity to the ring waveguide 24 and both are optically coupled to the ring waveguide 24 with the same coupling coefficient ⁇ .
  • the value of ⁇ is, for example, 0.2.
  • the arm portions 22 and 23 and the ring waveguide 24 constitute a ring resonator filter RF1. Further, the ring resonator filter RF1 and the bifurcated portion 21 constitute a reflection mirror M1.
  • the microheater 25 as a second refractive index changer is ring-shaped, and is disposed on a SiN protective film formed to cover the ring-shaped waveguide 24.
  • FIG. 2C is a cross-sectional view of the arm portion 22 of the second waveguide portion 20 taken along line CC cut along a plane parallel to the xy plane of FIG.
  • a lower cladding layer 22a of n-type InP, an optical waveguide layer 22b of InGaAsP, and an upper cladding layer 22c of p-type InP are stacked in this order on the base B.
  • the high mesa waveguide structure is configured.
  • the SiN protective film 22 d is formed to cover the arm portion 22.
  • the other components of the second waveguide portion 20, such as the bifurcated portion 21, the arm portion 23, and the ring waveguide 24 also have a high mesa waveguide structure, and are covered with a SiN protective film. There is. That is, the second waveguide section 20 has a second waveguide structure different from the first waveguide structure of the first waveguide section 10.
  • the first waveguide unit 10 and the second waveguide unit 20 are configured of a laser resonator C1 configured of the diffraction grating layer 11ab of the diffraction grating loading type gain unit 11a optically connected to each other and the reflection mirror M1. Configured.
  • the active core layer 11aa as the gain portion of the diffraction grating loading type gain portion 11a and the phase adjustment portion 11b are disposed in the laser resonator C1.
  • FIGS. 3A and 3B the vertical axis indicates reflectivity.
  • the diffraction grating layer 11ab generates a first comb-like reflection spectrum having substantially periodic reflection characteristics at substantially predetermined wavelength intervals, as shown by a curve in a legend “SG” in FIG. 3A.
  • the ring resonator filter RF1 generates a second comb-like reflection spectrum having periodic reflection characteristics at predetermined wavelength intervals, as shown by a curve in a legend “Ring” in FIG. 3A.
  • the legend "Mode” indicates the resonator mode of the laser resonator C1.
  • the resonator modes exist over at least the wavelength range of 1530 nm to 1570 nm shown in FIG. 3A.
  • the second comb reflection spectrum has a peak SC2 of full width at half maximum narrower than the full width at half maximum of the spectral component SC1 of the first comb reflection spectrum, and the first comb reflection is It has substantially periodic reflection characteristics at wavelength intervals different from the wavelength intervals of the spectrum.
  • the spectral components are not strictly equal wavelength intervals in consideration of the wavelength dispersion of the refractive index.
  • the wavelength interval between the peaks of the first comb-like reflection spectrum (free spectral range: FSR) is 373 GHz in terms of light frequency, and the full width at half maximum of each peak is light The frequency is 43 GHz.
  • the wavelength interval (FSR) between the peaks of the second comb-like reflection spectrum is 400 GHz in terms of the light frequency, and the full width at half maximum of each peak is 25 GHz in terms of the light frequency. That is, the full width at half maximum (25 GHz) of the peak of the second comb reflection spectrum is narrower than the full width at half maximum (43 GHz) of the peak of the first comb reflection spectrum.
  • the peak of the second comb-like reflection spectrum has a shape that changes sharply with respect to the wavelength, and the second derivative of the reflectance with respect to the wavelength takes positive values on the short wavelength side and long wavelength side from the peak There is a wavelength range.
  • the peak of the second comb reflection spectrum is, for example, in the form of a double exponential distribution (Laplace distribution) type.
  • the peak of the first comb-like reflection spectrum has a shape that changes gently with respect to the wavelength, compared to the peak of the second comb-like reflection spectrum, and the second derivative of the reflectance with respect to wavelength
  • the peak of the first comb-like reflection spectrum is, for example, a Gaussian shape.
  • FIG. 4 is a diagram showing a first comb-like reflection spectrum, a second comb-like reflection spectrum and an overlap thereof.
  • the curve indicated by the legend "Overlap” indicates spectral overlap. In the example shown in FIG. 4, the overlap is largest at a wavelength of 1550 nm.
  • thermo-optical effect is performed by heating the diffraction grating layer 11ab by the microheater 15 using at least one of the microheater 15 and the microheater 25 to change its refractive index by the thermo-optical effect.
  • One comb-like reflection spectrum is moved entirely on the wavelength axis, and the ring-shaped waveguide 24 is heated by the microheater 25 to change its refractive index to make the second comb-like reflection spectrum on the wavelength axis
  • This can be realized by performing at least one of moving the whole in
  • the resonator length of the laser resonator C1 is set such that the distance between the resonator modes (longitudinal mode distance) is 25 GHz or less. In this setting, the resonator length of the laser resonator C1 is 1800 ⁇ m or more, and narrowing of the line width of the oscillated laser light can be expected.
  • the wavelength tunable laser device 100 injects a current from the n-side electrode 30 and the p-side electrode 13 to the active core layer 11aa to cause the active core layer 11aa to emit light
  • the peak of the spectral component of the first comb reflection spectrum, The peak of the spectral component of the second comb-like reflection spectrum, and one of the resonator modes of the laser resonator are configured to emit a laser at a coincident wavelength, ie 1550 nm, and to output the laser light L1 (see FIG. 1) ing.
  • the wavelength of the resonator mode of the laser resonator C1 heats the phase adjustment unit 11b using the microheater 14 to change its refractive index, and the wavelength of the resonator mode is moved entirely on the wavelength axis. Fine adjustment can be done by That is, the phase adjustment unit 11b is a portion for actively controlling the optical path length of the laser resonator C1.
  • the second comb reflection spectrum by the ring resonator filter RF1 has a full width at half maximum narrower than the full width at half maximum of the peak of the first comb reflection spectrum by the diffraction grating layer 11ab.
  • the peak of the second comb-like reflection spectrum narrower in full width at half maximum is present in the peaks of the first comb-like reflection spectrum wide in half width, the laser oscillation is generated. It becomes easy to control the wavelength.
  • the distance between the resonator modes of the laser resonator C1 is 25 GHz or less, which is narrower than the full width at half maximum (43 GHz) of the spectral component of the first comb reflection spectrum It is configured to be
  • the distance between the resonator modes is narrowed, but in particular, a plurality of resonators within the full width at half maximum of the first comb-like reflection spectrum If the distance between the modes of the resonator modes becomes narrower as the modes exist, selection of a resonator mode for laser oscillation becomes difficult in the normal case.
  • the laser resonator C1 is a long resonator in which the spacing between the modes of the resonator modes is such that two or more resonator modes are included in the peak of the first comb-like reflection spectrum. Even if it is configured to be long, control to select the resonator mode is facilitated. Furthermore, as shown in FIGS.
  • the peak of the second comb reflection spectrum protrudes higher than the height of the peak of the first comb reflection spectrum, and the reflectance of the peak of the second comb reflection spectrum becomes the first comb shape. It can easily be higher than the reflectance of the peak of the reflection spectrum. Therefore, stable single mode oscillation can be realized more easily.
  • the optical feedback in the laser resonator C1 is obtained from the diffraction grating layer 11ab by the two-branch portion 21 and the ring resonator filter RF1. It is performed in a path that is returned to the diffraction grating layer 11ab via the one of the arm portions 22 and 23, the other of the ring waveguide 24 and the other of the arm portions 22 and 23, and the bifurcated portion 21 one time, and one time Of the ring-shaped waveguide 24 during the optical feedback.
  • the arrowhead of the optical path OP indicates the traveling direction of light, and the optical path OP represents both a clockwise optical path and a counterclockwise optical path.
  • the laser oscillation wavelength is selected using the vernier effect.
  • the FSRs of the first comb reflection spectrum and the second comb reflection spectrum are designed to be slightly different. Note that, by increasing the FSR of the second comb-like reflection spectrum where the peak is sharper, the height of the peak of the overlap (for example, the overlap near 1547 nm) adjacent to 1550 nm where the peak of the spectrum overlap is highest It becomes relatively small. As a result, since the laser oscillation at the wavelength of the overlap peak adjacent to the highest wavelength of the overlap of the spectrum is suppressed, the side mode suppression ratio can be increased.
  • the variable wavelength range in the wavelength tunable laser device 100 is determined by the vernier effect at the least common multiple of FSR.
  • One of the peaks of the first comb-like reflection spectrum and one of the peaks of the second comb-like reflection spectrum are superimposed, and the reflectance becomes maximum at a wavelength where the peaks coincide, and laser oscillation occurs. That is, the rough laser oscillation wavelength is determined by the vernier effect of the diffraction grating layer 11ab and the ring resonator filter RF1 (super mode).
  • the laser oscillation wavelength is from the diffraction grating layer 11ab, the bifurcated portion 21, one of the arm portions 22 and 23 of the ring resonator filter RF1, the ring-shaped waveguide 24, Determined by the overlap of the wavelength of the resonator mode and the super mode defined by the path (resonator length) that is fed back to the diffraction grating layer 11ab via the other of the arm portions 22 and 23 and the 2-branch portion 21 in order Ru.
  • one of the resonator modes of the laser resonator C1 is made to coincide with the overlapping region of the peaks of the first comb-like reflection spectrum and the second comb-like reflection spectrum superimposed, and the corresponding cavity modes are made
  • the laser is oscillated at the wavelength of Therefore, in the tunable laser device 100, the first comb-like reflection spectrum and the second comb-like reflection spectrum are respectively tuned by the microheater 15 for the diffraction grating layer 11ab and the microheater 25 for the ring resonator filter RF1.
  • the microheater 14 By tuning the resonator length by the microheater 14 with respect to the coarse adjustment and the phase adjustment unit 11b, a wavelength variable operation to perform fine adjustment is realized.
  • the first comb reflection spectrum and the second comb reflection spectrum have the largest overlap at a wavelength of 1550 nm (super mode).
  • the laser oscillation wavelength is roughly adjusted to around 1550 nm.
  • the diffraction grating layer 11ab is heated by the microheater 15 with the tuning of the ring resonator filter RF1 fixed. Then, the refractive index of the diffraction grating layer 11ab is increased due to the thermo-optical effect, and the reflection spectrum (first comb-like reflection spectrum) of the diffraction grating layer 11ab is generally shifted to the long wave side as shown by the arrows in FIG. Do.
  • the tuning of the diffraction grating layer 11ab is fixed, only the ring resonator filter RF1 is heated by the microheater 25, and the comb reflection spectrum of the ring resonator filter RF1 is entirely It may be shifted to the long wave side.
  • thermo-optical effect by the micro heater is used to realize the wavelength tunable operation, but the carrier plasma effect by current injection is implemented to realize the wavelength tunable operation. May also be available.
  • the refractive index is lowered by current injection, the comb reflection spectrum is entirely shifted to the short wave side, and an overlap occurs in another spectral component existing on the short wave side from the wavelength at which the super mode was formed. , It is possible to form a new super mode.
  • the reflectance is maximum at a wavelength at which the peaks of the comb reflection spectra generated by the diffraction grating layer 11ab and the ring resonator filter RF1 coincide with each other, and laser oscillation occurs as shown in FIG.
  • the first full comb reflection spectrum of full width at half maximum is shifted, and one of its peaks is matched with one of the peaks of the first comb reflection spectrum of narrow full width half maximum.
  • the tuning of the diffraction grating layer 11ab is fixed, only the ring resonator filter RF1 is heated by the microheater 25, and the comb reflection spectrum of the ring resonator filter RF1 is overall
  • the full width at half maximum of the peak due to the diffraction grating layer 11ab is wide, so the peak of the narrow ring resonator filter RF1 with full width at half maximum is tuned to shift to match the supermode It is easy to realize the transition of
  • the phase adjustment unit 11 b is tuned to perform fine adjustment of the resonator mode.
  • the distance between the resonator modes is narrow and narrower than the full width at half maximum of the peak of the comb-like reflection spectrum of the diffraction grating layer 11ab, a plurality of resonator modes exist among the peaks of the diffraction grating layer 11ab. It is also possible to do.
  • the full width at half maximum of the comb reflection spectrum of the ring resonator filter RF1 is narrower than the full width at half maximum of the comb reflection spectrum of the diffraction grating layer 11ab. Therefore, it is unlikely that a plurality of resonator modes compete with the peak of the comb-like reflection spectrum of the ring resonator filter RF1 so that only one resonator mode matches the peak of the ring resonator filter RF1. It is easy to tune the phase adjustment unit 11b to finely adjust the resonator mode.
  • the wavelength tunable laser device 100 As described above, according to the wavelength tunable laser device 100 according to the first embodiment, it is possible to realize narrowing of the line width of the laser light and stable single mode oscillation.
  • an n-type semiconductor layer 12a (lower cladding layer 22a), an active core layer 11aa, and a spacer are formed on the n-type InP substrate constituting the base B by using metal organic chemical vapor deposition (MOCVD).
  • MOCVD metal organic chemical vapor deposition
  • a layer 12b, a p-type InGaAsP layer to be the diffraction grating layer 11ab, and a p-type InP layer to be a part of the spacer layer 12ea (upper cladding layer 22c) are sequentially deposited.
  • a SiN film is newly deposited to form a pattern corresponding to the optical waveguide layer in the waveguide 11 and the second waveguide 20 in the first waveguide 10. Apply patterning as you like. Then, etching is performed using this SiN film as a mask to form a mesa structure in the first waveguide portion 10 and the second waveguide portion 20, and expose the n-type semiconductor layer 12a (lower cladding layer 22a). At this time, the region corresponding to the bifurcated portion 21, the arm portions 22 and 23, and the ring waveguide 24 is etched in the form of a wide region including them.
  • FIGS. 7AA to 7AC are a sectional view taken along a line AA (a gain portion) cut along a plane parallel to the xy plane of FIG. B line sectional view (phase adjustment unit) and FIG. 7AC respectively show CC sectional view (optical waveguide of the arm unit)
  • FIGS. 7BA to 7BC and FIGS. 7CA to 7CC show CC sectional view (optical waveguide of the arm unit)
  • the mask of the SiN film is removed, and a p-type InP layer and a contact layer 12eb to be the remaining portion of the spacer layer 12ea (upper cladding layer 22c) are sequentially deposited on the entire surface by MOCVD (see FIG. 7AA to 7AC).
  • the step of removing the contact layer 12eb of the optical waveguides of the phase adjustment portion and the arm portion is performed (see FIGS. 7BB and 7BC).
  • a SiN film is deposited on the entire surface, and then a pattern corresponding to a trench for element isolation and a waveguide corresponding to the bifurcated portion 21, the arm portions 22 and 23, and the ring waveguide 24 are patterned.
  • etching is performed using this SiN film as a mask to form a trench structure and a high mesa waveguide in the second waveguide portion 20 (see FIG. 7BC).
  • the depth is reached to the base B.
  • a SiN film is deposited again on the entire surface (see FIGS. 7CA to 7CC), and an opening is formed in a portion corresponding to the diffraction grating loading type gain portion 11a to protect the SiN film.
  • the conductive film is patterned to form the p-side electrode 13 (see FIG. 7CA).
  • an n-side electrode 30 containing AuGeNi is formed on the back surface of the substrate. Furthermore, after the SiN protective film 17 is formed, micro-heaters 14, 15, 25 made of, for example, Ti for changing the refractive index are formed. Finally, the substrate is cleaved into a bar shape in which a plurality of variable wavelength laser elements 100 are arranged, and the end face of the first waveguide 10 on the side of the diffraction grating loaded gain 11a and the end of the arm 22 and 23 where the through port is located. After coating the anti-reflection film, the wavelength tunable laser device 100 is separated to complete the wavelength tunable laser device 100.
  • the arm portions 22 and 23 are optically coupled to the ring waveguide 24 by coming close to the ring waveguide 24. As shown, the arm portions 22 and 23 and the ring waveguide 24 may be optically coupled by the waveguide portions 26 and 27.
  • FIG. 9A is a view for explaining the structure of the waveguide section.
  • FIG. 9A is a view showing a part of a cross section along line AA of FIG.
  • the lower cladding layer 22a made of n-type InP, the optical waveguide layer 22b made of InGaAsP, and the upper cladding layer 22c made of p-type InP are stacked in this order on the base B. It has the high mesa waveguide structure comprised.
  • the arm portion 23 is configured by laminating a lower cladding layer 23a of n-type InP, an optical waveguide layer 23b of InGaAsP, and an upper cladding layer 23c of p-type InP in this order on the base B.
  • the waveguide section 26 is configured by laminating a lower cladding layer 26a of n-type InP, an optical waveguide layer 26b of InGaAsP, and an upper cladding layer 26c of p-type InP in this order on the base B. It is a multi-mode interference (MMI) waveguide of high mesa waveguide structure.
  • the waveguide 27 is also an MMI waveguide having a high mesa waveguide structure having the same structure as the waveguide 26.
  • optical coupling between the arm portions 22 and 23 and the ring waveguide 24 is facilitated by optically coupling the arm portions 22 and 23 and the ring waveguide 24 by the waveguide portions 26 and 27.
  • the coupling coefficient ⁇ can be adjusted more easily.
  • the waveguide section for optically coupling the arm sections 22 and 23 and the ring waveguide 24 is not limited to the MMI waveguide, and may be, for example, a directional coupling type waveguide section 26A as shown in FIG. 9B.
  • the waveguide portion 26A is a high mesa formed by laminating a lower cladding layer 26Aa of n-type InP, an optical waveguide layer 26Ab of InGaAsP, and an upper cladding layer 26Ac of p-type InP in this order on the base B.
  • the upper cladding layer 26Ac is thinner than the upper cladding layer 26c in the waveguide portion 26, it functions as a directional coupling waveguide.
  • the change in the coupling coefficient between the arm and the ring-shaped waveguide due to the change in the width of the waveguide along the arm is a directional coupling waveguide. Is smaller than that of the MMI waveguide. Therefore, when the waveguide portion is formed of the MMI waveguide, the coupling coefficient can be changed more largely by changing the width of the waveguide along the arm portion.
  • the first waveguide unit 10 has the embedded waveguide structure as the first waveguide structure, but the first waveguide unit is the first waveguide structure. It may have a ridge waveguide structure as a waveguide structure.
  • FIG. 10 is a diagram for explaining an example of the first waveguide section having a ridge waveguide structure.
  • FIG. 10 is a cross-sectional view of a portion of the first waveguide unit 10A including the phase adjustment unit 11Ab cut along the xy plane of FIG.
  • the first waveguide portion 10A is a portion including the phase adjustment portion 11Ab, the lower cladding layer 12Aa made of p-type InP, the phase adjustment portion 11Ab being an optical waveguide layer made of InGaAsP, and the upper portion made of n-type InP It has a structure in which the ridge cladding layer 12Ab is sequentially stacked.
  • the first waveguide portion may have a ridge waveguide structure.
  • FIG. 11 is a schematic perspective view of the wavelength tunable laser device according to the second embodiment.
  • the tunable laser device 100A according to the second embodiment includes the tunable laser device 100 according to the first embodiment shown in FIG. 1 and a semiconductor amplifier (SOA) formed on a base B. And 101.
  • the SOA 101 has a buried waveguide structure including an active core layer made of the same material and structure as the first waveguide portion. However, no diffraction grating layer is provided.
  • the tunable laser element 100 and the SOA 101 are optically coupled by a space coupling optical system (not shown).
  • the laser beam L1 output from the wavelength tunable laser device 100 is input to the SOA 101.
  • the SOA 101 optically amplifies the laser beam L1 and outputs it as a laser beam L2.
  • the wavelength tunable laser device 100A according to the second embodiment realizes narrowing of the width of the laser beam and stable single mode oscillation, and further, Since the SOA 101 is provided, laser light can be output at higher power.
  • the tunable laser device 100A In the tunable laser device 100A according to the second embodiment, the tunable laser device 100 and the SOA 101 are optically coupled by a space coupling optical system (not shown). However, the tunable laser device 100 and the SOA 101 May be monolithically formed on the common base B.
  • the third embodiment is different from the first and second embodiments in that the second waveguide portion is formed of a silicon (Si) photonic waveguide.
  • FIG. 12A and 12B are schematic views of a wavelength tunable laser device according to a third embodiment.
  • 12A is a perspective view
  • FIG. 12B is a cross-sectional view to be described later.
  • the wavelength tunable laser device 200 is configured to emit a laser beam by performing laser oscillation in a 1.55 ⁇ m band.
  • the wavelength tunable laser device 200 includes a first waveguide section 210 and a second waveguide section 220.
  • the first waveguide unit 210 includes a waveguide unit 211, a semiconductor laminated unit 212, an n-side electrode 213, and a micro heater 215.
  • the waveguide portion 211 is formed to extend in the z direction in the semiconductor laminated portion 212.
  • a gain portion 211a and a DBR diffraction grating layer 211b are disposed in the first waveguide portion 210.
  • the semiconductor laminated portion 212 is configured by laminating semiconductor layers, and has a function of a cladding portion and the like with respect to the waveguide portion 211.
  • the gain portion 211a has a multiple quantum well structure made of the same material as that of the active core layer 11aa in the first embodiment, and a light confinement layer.
  • the diffraction grating layer 211 b is configured by a sampling diffraction grating made of the same material as the diffraction grating layer 11 ab in the first embodiment.
  • the semiconductor multilayer portion 212 is made of the same material and structure as the portion including the diffraction grating loaded type gain portion 11a of the semiconductor multilayer portion 12 in the first embodiment.
  • the lattice layer 11ab is replaced by a p-type InP layer, and that it has a laminated structure in which the positions of the p-type semiconductor layer and the n-type semiconductor layer are reversed with the gain portion 211a in the y direction.
  • the semiconductor multilayer portion 212 is made of the same material and structure as the portion including the phase adjustment portion 11b of the semiconductor multilayer portion 12 in the first embodiment. It differs in that it has a laminated structure in which the positions of the p-type semiconductor layer and the n-type semiconductor layer are reversed with the phase adjustment portion 11 b interposed therebetween.
  • the first waveguide portion 210 has a buried waveguide structure as a first waveguide structure.
  • the n-side electrode 213 is disposed on the semiconductor multilayer portion 212 along the gain portion 211 a.
  • a SiN protective film is formed on the semiconductor laminated portion 212, and the n-side electrode 213 is in contact with the semiconductor laminated portion 212 through an opening formed in the SiN protective film.
  • the microheater 215 as the first refractive index changer is disposed on the SiN protective film of the semiconductor multilayer portion 212 so as to be along the diffraction grating layer 211b.
  • a p-side electrode (not shown) is formed on the surface of the semiconductor laminate portion 212 opposite to the surface on which the n-side electrode 213 is formed.
  • the second waveguide unit 220 is configured of an SOI (Silicon On Insulator) substrate S.
  • the second waveguide portion 220 includes a bifurcated portion 221, arm portions 222 and 223, a ring-shaped waveguide 224, microheaters 225 and 229, a phase adjusting portion 228, and an overcladding layer 230 made of SiO 2. And have.
  • the bifurcated portion 221 is composed of a 1 ⁇ 2 type branched waveguide including a 1 ⁇ 2 type MMI waveguide 221a, and the 2 port side is connected to each of the two arm portions 222 and 223 and the 1 port side is It is connected to the side of the first waveguide unit 210 via the phase adjustment unit 228.
  • One end of the two arm portions 222 and 223 is integrated by the bifurcated portion 221, and is optically coupled to the diffraction grating layer 211b.
  • a tapered section whose width is narrowed toward the first waveguide section 210 is formed.
  • An overcladding layer having a refractive index higher than that of SiO 2 , for example, made of SiN is formed on the outer periphery of the tapered portion, forming a spot size converter structure.
  • Each of the arm portions 222 and 223 extends in the z direction and is disposed so as to sandwich the ring waveguide 224.
  • the arm portions 222 and 223 are in close proximity to the ring waveguide 224 and both are optically coupled to the ring waveguide 224 with the same coupling coefficient ⁇ .
  • the arm units 222 and 223 and the ring waveguide 224 constitute a ring resonator filter RF2.
  • the ring resonator filter RF2 and the bifurcated portion 221 constitute a reflection mirror M2.
  • the microheater 225 as a second refractive index changer is ring-shaped, and is disposed on the over cladding layer 230 directly above the ring-shaped waveguide 224. Further, the microheater 229 is disposed on the over cladding layer 230 along the phase adjustment unit 228.
  • FIG. 12B is a cross-sectional view of the arm portion 222 of the second waveguide portion 220 taken along a plane parallel to the xy plane of FIG. 12A.
  • the arm portion 222 is composed of a support layer 222aa made of a Si support substrate of the SOI substrate S, and a BOX (Buried OXide) layer 222ab made of SiO 2 located on the support layer 222aa. It has a high mesa waveguide structure comprising a lower layer 222a and a device layer 222b made of Si located in the BOX layer 222ab.
  • the device layer 222 b functions as an optical waveguide layer, and the high mesa waveguide structure is covered with the over cladding layer 230.
  • the other components of the second waveguide 220 that is, the 2-branch 221, the arm 223, the ring waveguide 224, and the phase adjuster 228 also have a high mesa waveguide structure. That is, the second waveguide part 220 has a second waveguide structure different from the first waveguide structure of the first waveguide part 210.
  • the first waveguide section 210 is separately manufactured by a known method as a gain chip, and the device layer, the BOX layer, and part of the support substrate are removed in the SOI substrate S constituting the second waveguide section 220. Mounted in the concave portion CC formed by At this time, the gain portion 211 a of the first waveguide portion 210 and the phase adjustment portion 228 of the second waveguide portion 220 are butt-jointed.
  • the first waveguide section 210 and the second waveguide section 220 constitute a laser resonator C2 configured of a diffraction grating layer 211b optically connected to each other and a reflection mirror M2.
  • the gain unit 211a and the phase adjustment unit 228 are disposed in the laser resonator C2.
  • the diffraction grating layer 211b generates a first comb-like reflection spectrum having substantially periodic reflection characteristics at substantially predetermined wavelength intervals.
  • the ring resonator filter RF2 has a peak with a full width at half maximum narrower than the full width at half maximum of the spectral component of the first comb-like reflection spectrum, and has a substantially different wavelength interval from the wavelength interval of the first comb-like reflection spectrum.
  • a second comb-like reflection spectrum having periodic reflection characteristics is generated.
  • laser oscillation occurs at a wavelength at which the peak of the first comb reflection spectrum, the peak of the second comb reflection spectrum, and one of the resonator modes of the laser resonator C2 coincide with each other.
  • the spacing between the modes of the resonator modes of the laser resonator C2 is narrower than the full width at half maximum of the spectral component of the first comb reflection spectrum.
  • the optical feedback in the laser resonator C2 is from the diffraction grating layer 211b, one of the two branches 221, one of the arms 222 and 223 of the ring resonator filter RF2, the ring waveguide 224, the arm 222, The other of 223 is conducted in a path which is returned to the diffraction grating layer 211 b via the 2-branch portion 221 in order, and is circulated in the ring waveguide 224 during one optical feedback.
  • the optical feedback length becomes long, and therefore it is possible to effectively narrow the line width of the laser beam. Further, as in the first and second embodiments, stable single mode oscillation can be realized.
  • the laser oscillation wavelength is the same as in the first and second embodiments by the microheater 215 for the diffraction grating layer 211b and the microheater 225 for the ring resonator filter RF2. Tuning by adjusting the comb-like reflection spectrum and the second comb-like reflection spectrum by tuning the resonator length with the micro heater 229 for the coarse adjustment by the micro heater 229 for the phase adjustment unit 228. To be realized.
  • the wavelength tunable laser 200 of the third embodiment as in the first and second embodiments, the line width reduction of the laser light and the stable single mode oscillation can be realized. Furthermore, in the wavelength tunable laser device 200, the second waveguide portion 220 is configured of a Si photonics waveguide.
  • the Si photonics waveguide is resistant to bending because the waveguide confinement is strong. Therefore, the ring waveguide 224 with a small diameter can be easily realized. This means that a ring waveguide 224 with a large FSR can be realized, and the design freedom of the ring resonator filter RF2 is improved.
  • the wavelength tunable laser device 200 it is possible to output a laser beam having a small footprint and compact size, and a high side mode suppression ratio.
  • the Si waveguide pattern in the second waveguide portion 220 is transferred onto the SOI substrate using photolithography.
  • the device layer and the BOX layer are etched using, for example, HBr gas to obtain a channel waveguide structure.
  • thermal oxidation without using water vapor may be performed in order to reduce the side roughness of the waveguide generated by the etching.
  • a SiN layer is deposited on the entire surface, and an overcladding layer made of SiN is formed on the portion of the spot size conversion structure described above by photolithography and etching.
  • an SiO 2 layer to be an overcladding layer 230 is deposited on the entire surface.
  • the 1st waveguide part 210 which is a gain chip is not limited to what was mentioned above.
  • it may have a quantum well structure or a quantum dot structure on an InP or GaAs substrate.
  • III-V group compound semiconductors such as InGaAs, InGaAsN, AlInGaAs, InGaAs, etc. can be used.
  • InAs, InGaA, or other III-V compound semiconductor can be used as a compound semiconductor material forming the quantum dot structure.
  • Embodiment 4 Next, the fourth embodiment will be described.
  • the second waveguide portion is made of a silicon Si photonics waveguide, the point that a diffraction grating is provided in the second waveguide portion, and the first waveguide
  • the third embodiment differs from the third embodiment in that the section includes a U-shaped waveguide.
  • FIG. 13 is a schematic perspective view of the wavelength tunable laser device according to the fourth embodiment.
  • the tunable laser device 300 is configured to emit a laser beam by performing laser oscillation in a 1.55 ⁇ m band.
  • the wavelength tunable laser device 300 includes a first waveguide section 310 and a second waveguide section 320.
  • the first waveguide unit 310 includes a waveguide unit 311, a semiconductor multilayer unit 312, and an n-side electrode 313.
  • the waveguide portion 311 is formed in a U-shape in which a part thereof extends in the z direction in the semiconductor laminated portion 312.
  • a gain portion 311a and an optical waveguide layer 311b are disposed in the first waveguide portion 310.
  • the semiconductor laminated portion 312 is configured by laminating semiconductor layers, and has a function of a cladding portion and the like with respect to the waveguide portion 311.
  • Gain portion 311a extends in the z direction, and has a multiple quantum well structure made of the same material as active core layer 11aa in the first embodiment.
  • the optical waveguide layer 311 b is made of the same material as that of the phase adjustment unit 11 b in the first embodiment, and forms a U-shape together with the gain unit 311 a.
  • the semiconductor multilayer portion 312 is made of the same material and structure as the portion including the grating loading type gain portion 11a of the semiconductor multilayer portion 12 in the first embodiment.
  • the lattice layer 11ab is replaced with a p-type InP layer, and that the layer structure has a laminated structure in which the positions of the p-type semiconductor layer and the n-type semiconductor layer are reversed with the gain portion 311a in the y direction.
  • the semiconductor multilayer portion 312 is made of the same material and structure as the portion including the phase adjustment portion 11 b of the semiconductor multilayer portion 12 in the first embodiment. It differs in that it has a stacked structure in which the positions of the p-type semiconductor layer and the n-type semiconductor layer are reversed with the gain portion 311 a interposed therebetween.
  • the first waveguide portion 310 has a buried waveguide structure as a first waveguide structure.
  • the n-side electrode 313 is disposed on the semiconductor multilayer portion 312 along the gain portion 311 a.
  • a SiN protective film is formed on the semiconductor laminated portion 312 so as to cover the semiconductor laminated portion 312, and the n-side electrode 313 is in contact with the semiconductor laminated portion 312 through the opening formed in the SiN protective film.
  • a p-side electrode (not shown) is formed on the surface of the semiconductor lamination portion 312 opposite to the surface on which the n-side electrode 313 is formed.
  • the second waveguide section 320 is configured of an SOI substrate.
  • the second waveguide portion 320 is an overcladding made of a bifurcated portion 321, arm portions 322 and 323, a ring-shaped waveguide 324, microheaters 325, 329 and 333, a phase adjusting portion 328, and SiO 2.
  • a layer 330, a waveguide portion 331, and a diffraction grating portion 332 are provided.
  • the bifurcated portion 321 is composed of a 1 ⁇ 2 type branched waveguide including a 1 ⁇ 2 type MMI waveguide 321a, and the 2 port side is connected to each of the two arm portions 322 and 323 and the 1 port side is It is connected to the gain section 311 a side of the first waveguide section 310.
  • One end of the two arm portions 322 and 323 is integrated by the bifurcated portion 321, and is optically coupled to the diffraction grating portion 332.
  • a tapered portion whose width is narrowed toward the first waveguide portion 310 is formed.
  • An overcladding layer having a refractive index higher than that of SiO 2 , for example, made of SiN is formed on the outer periphery of the tapered portion, forming a spot size converter structure.
  • Each of the arm portions 322 and 323 extends in the z direction, and is disposed to sandwich the ring waveguide 324.
  • the arm portions 322 and 323 are in close proximity to the ring waveguide 324 and both are optically coupled to the ring waveguide 324 with the same coupling coefficient ⁇ .
  • the arm portions 322 and 323 and the ring waveguide 324 constitute a ring resonator filter RF3.
  • the ring resonator filter RF3 and the bifurcated portion 321 constitute a reflection mirror M3.
  • the microheater 325 as a second refractive index changer is ring-shaped, and is disposed on the over cladding layer 330 directly above the ring-shaped waveguide 324.
  • the waveguide portion 331 is a waveguide extending in the z direction, one end of which is connected to the optical waveguide layer 311b side of the first waveguide portion 310, and the other end of which is connected to the diffraction grating portion 332.
  • a phase adjustment unit 328 is provided in the middle of the waveguide unit 331.
  • the micro heater 329 is disposed on the over cladding layer 330 along the phase adjustment unit 328.
  • the microheater 333 as a first refractive index changer is disposed on the over cladding layer 330 along the diffraction grating portion 332.
  • the second waveguide section 320 has a second waveguide structure different from the first waveguide structure of the first waveguide section 310.
  • the diffraction grating section 332 has a configuration in which a sampling diffraction grating is formed along the z direction in a device layer functioning as an optical waveguide layer, and the grooves of the diffraction grating are embedded with SiO 2 of the over cladding layer 330.
  • the first waveguide section 310 is separately manufactured by a known method as a gain chip, and the device layer, the BOX layer, and part of the support substrate are removed in the SOI substrate constituting the second waveguide section 320.
  • the gain section 311 a of the first waveguide section 310 and one port side of the 2-branch section 321 of the second waveguide section 320 are butt-joint connected, and the optical waveguide layer of the first waveguide section 310
  • the butt joint connection 311 b and the waveguide part 331 of the second waveguide part 320 are connected.
  • one port side of the 2-branch portion 321 of the second waveguide portion 320 and the waveguide portion 331 of the second waveguide portion 320 are the first waveguide portion. It is preferable that a tapered portion whose width decreases toward 310 is formed, and an overcladding layer made of, for example, SiN is formed on the outer periphery thereof to form a spot size converter structure.
  • the first waveguide section 310 and the second waveguide section 320 constitute a laser resonator C3 constituted of a diffraction grating section 332 and a reflection mirror M3 optically connected to each other.
  • the gain unit 311a and the phase adjustment unit 328 are disposed in the laser resonator C3.
  • the diffraction grating section 332 generates a first comb-like reflection spectrum having substantially periodic reflection characteristics at substantially predetermined wavelength intervals.
  • the ring resonator filter RF3 has a peak with a full width at half maximum narrower than the full width at half maximum of the peak of the first comb reflection spectrum, and has a substantially periodicity at a wavelength interval different from the wavelength interval of the first comb reflection spectrum. Generating a second comb-like reflection spectrum having a characteristic reflection characteristic.
  • laser oscillation occurs at a wavelength at which the peak of the first comb reflection spectrum, the peak of the second comb reflection spectrum, and one of the resonator modes of the laser resonator C3 coincide.
  • the spacing between the modes of the resonator modes of the laser resonator C3 is narrower than the full width at half maximum of the spectral component of the first comb reflection spectrum.
  • the optical feedback in the laser resonator C3 is from the diffraction grating section 332, one of the two branches 321, one of the arms 322 and 323 of the ring resonator filter RF3, the ring waveguide 324, the arm 322, In the other of H.323, it is performed in the path which returns to the diffraction grating part 332 via the 2-branch part 321 in order, and goes around in the ring waveguide 324 during one optical feedback.
  • the wavelength tunable laser device 300 according to the fourth embodiment can realize narrowing of the line width of laser light and stable single mode oscillation.
  • the laser oscillation wavelength is the same as in the first and second embodiments by the micro heater 333 for the diffraction grating section 332 and the micro heater 325 for the ring resonator filter RF3. Can be tuned by tuning the comb-like reflection spectrum and the second comb-like reflection spectrum separately, and fine tuning by tuning the resonator length with the micro heater 329 for the phase adjustment unit 328. To be realized.
  • the tunable laser device 300 can also be manufactured in the same manner as the tunable laser device 200 according to the third embodiment. That is, a portion related to the second waveguide portion 320 is manufactured using the SOI substrate, and the separately manufactured first waveguide portion 310 is mounted on the concave portion CC by flip chip bonding. Thus, the wavelength tunable laser device 300 is completed.
  • the wavelength tunable laser device 300 as in the first and second embodiments, it is possible to realize narrowing of the line width of the laser light and stable single mode oscillation, and Similarly, it is possible to output a laser beam which has a small footprint and is compact and has a high side mode suppression ratio.
  • FIG. 14 is a schematic view of a laser module according to the fifth embodiment.
  • the laser module 1000 includes the wavelength tunable laser element 100A according to the second embodiment, a collimator lens 1001, an optical isolator 1002, a beam splitter 1003, a condenser lens 1005, an optical fiber 1006, and a power monitor as a light receiving element.
  • a PD (Photo Diode) power monitor PD 1009, an etalon filter 1010, and a power monitor PD 1011 are provided.
  • the wavelength tunable laser device 100A is mounted on an electronic cooling device (not shown) for adjusting the temperature of the wavelength tunable laser device 100A.
  • the wavelength tunable laser device 100A, the power monitors PD 1009 and 1011 and the electronic cooling device are connected to an external control unit.
  • the wavelength tunable laser device 100A is supplied with a drive current from the control unit, and the diffraction grating layer 11ab adjusted by controlling the micro heaters 14, 15, 25 by the control unit, the ring resonator filter RF1, the phase adjustment unit 11b, etc.
  • the laser light of the wavelength determined under the conditions of (1) is amplified to a desired output intensity by the SOA 101 and output as a laser light L2.
  • the collimator lens 1001 converts the laser beam L2 output from the wavelength tunable laser element 100A into a parallel beam.
  • the optical isolator 1002 transmits the laser beam L2 collimated by the collimator lens 1001 only in one direction.
  • the beam splitter 1003 branches a part to the power monitor PD 1009 side while transmitting most of the laser light L 2 transmitted through the optical isolator 1002.
  • the power monitor PD 1009 receives part of the laser beam L2 branched by the beam splitter 1008, and outputs a current having a value according to the light reception intensity.
  • the etalon filter 1010 has a transmission wavelength characteristic having a periodically changing peak according to the order of multiple interference, and the laser light L2 transmitted through the beam splitter 1008 according to the transmission wavelength characteristic at the wavelength of the laser light L2 It penetrates with a high transmittance.
  • the period of the etalon filter 1010 is, for example, 50 GHz at the frequency of light.
  • the power monitor PD1011 receives the laser beam L2 transmitted through the etalon filter 1010, and outputs a current having a value according to the light reception intensity.
  • the condensing lens 1005 condenses the laser beam L2 transmitted through the beam splitter 1003 and couples it to the optical fiber 1006.
  • the optical fiber 1006 propagates the coupled laser light L2 to the outside.
  • the laser light L2 is used, for example, as signal light for optical fiber communication.
  • the etalon filter 1010 uses a bulk filter, a waveguide filter may be used instead.
  • the control unit controls the ratio of the intensity of the laser light monitored by the power monitor PD 1009 to the intensity of the laser light after transmission through the etalon filter 1010 monitored by the power monitor PD 1011 Control is performed to change the drive current and temperature of the wavelength tunable laser element 100A such that the ratio when the wavelength of the laser light L2 becomes a desired wavelength is obtained.
  • the wavelength of the laser beam L2 can be controlled to a desired wavelength (lock wavelength).
  • FIG. 15 is a schematic view of a laser module according to the sixth embodiment.
  • the laser module 1000A includes a wavelength tunable laser element 100B, a collimator lens 1001, an optical isolator 1002, a beam splitter 1003, a power monitor PD 1004, a condenser lens 1005, an optical fiber 1006, a collimator lens 1007, a beam splitter A power monitor PD 1009, an etalon filter 1010, and a power monitor PD 1011 are provided.
  • the wavelength tunable laser device 100B is mounted on an electronic cooling device (not shown) for adjusting the temperature of the wavelength tunable laser device 100B.
  • the wavelength tunable laser device 100B, the power monitors PD 1004, 1009, 1011 and the electronic cooling device are connected to an external control unit.
  • the functions of the collimator lens 1001, the optical isolator 1002, the beam splitter 1003, the power monitor PD 1004, the condenser lens 1005, and the optical fiber 1006 are the same as those of the laser module 1000, and therefore the description thereof is omitted.
  • the wavelength tunable laser device 100B has a coupling coefficient ⁇ 1 between the arm portion 22 and the ring waveguide 24 and a coupling coefficient between the arm portion 23 and the ring waveguide 24. It is designed such that ⁇ 2 has different values. As described above, by setting the coupling coefficients ⁇ 1 and ⁇ 2 to different values, the ring resonator filter RF1 becomes an asymmetric filter, and a part of the oscillated laser light is connected to the two branch parts 21 of the arm parts 22 and 23. It will be outputted from the end face opposite to the other side.
  • the collimator lens 1007 converts the laser beam L3 which is a part of the oscillated laser beam, which is output from the end face of the arm portion 22, into parallel rays.
  • the beam splitter 1008 transmits most of the laser beam L3 that has been made a parallel beam and branches a portion to the power monitor PD 1009 side.
  • the power monitor PD 1009 receives a part of the laser beam L3 branched by the beam splitter 1008, and outputs a current having a value according to the light reception intensity.
  • the etalon filter 1010 has a transmission wavelength characteristic having a periodically changing peak according to the order of multiple interference, and the laser light L3 transmitted through the beam splitter 1008 according to the transmission wavelength characteristic at the wavelength of the laser light L3.
  • the period of the etalon filter 1010 is, for example, 50 GHz at the frequency of light.
  • the power monitor PD1011 receives the laser beam L3 transmitted through the etalon filter 1010, and outputs a current of a value according to the light reception intensity.
  • the laser module 1000A by providing the wavelength tunable laser device 100B, it is possible to realize narrowing of the line width of the laser light L2 and stable single mode oscillation, and to output the laser light L2 with higher power. Furthermore, the received light intensity can be monitored by monitoring the current output from the power monitors PD 1009 and 1011, and wavelength lock control can be performed by the control unit. Furthermore, since the intensity of the laser beam L2 can be monitored by monitoring the current output from the power monitor PD 1004, power feedback control can be performed by the control unit.
  • the control unit controls the ratio of the intensity of the laser light monitored by the power monitor PD 1009 to the intensity of the laser light after transmission through the etalon filter 1010 monitored by the power monitor PD 1011 Control is performed to change the drive current and temperature of the wavelength tunable laser element 100B such that the ratio when the wavelength of the laser beam L2 becomes a desired wavelength is obtained.
  • the wavelength of the laser beam L2 can be controlled to a desired wavelength (lock wavelength).
  • the diffraction grating is a sampling diffraction grating, but the type of diffraction grating is not limited to this, and may be a superstructure diffraction grating or a superimposed diffraction grating.
  • the diffraction grating layer 11ab is provided along and immediately above the active core layer 11aa along the active core layer 11aa, but the present invention is not limited to this.
  • a diffraction grating layer may be provided in the vicinity of the active core layer and directly on the optical waveguide layer.
  • the present invention is not limited by the above embodiment.
  • the present invention also includes those configured by appropriately combining the above-described components. Further, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above embodiment, and various modifications are possible.

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Abstract

Provided is a variable wavelength laser element provided with: a laser resonator constituted of a diffraction grating and a reflective mirror that includes a ring resonator filter; a gain unit; and a phase adjusting unit. The diffraction grating generates a first comb shaped reflection spectrum. The ring resonator filter is provided with a ring-shaped waveguide and two arm parts, and generates a second comb shaped reflection spectrum that differs in wavelength interval from the first comb shaped reflection spectrum at a peak narrower than the full width at half maximum of the first comb shaped reflection spectrum. One peak of the first comb shaped reflection spectrum and one peak of the second comb shaped reflection spectrum are superimposed on the wavelength axis. The interval between modes for resonator mode is a wavelength narrower than the full width at half maximum of the peak for the first comb shaped reflection spectrum.

Description

波長可変レーザ素子およびレーザモジュールWavelength tunable laser device and laser module
　本発明は、波長可変レーザ素子およびこれを用いたレーザモジュールに関するものである。 The present invention relates to a wavelength tunable laser device and a laser module using the same.
　コヒーレント通信の普及に伴い、狭線幅の波長可変レーザ素子の需要が高まっている。波長可変レーザ素子の構成および動作原理は、例えば非特許文献１にて詳細に説明されている。一般に半導体レーザ素子から出力されるレーザ光を狭線幅化するには、共振器を長くする必要がある。波長可変レーザ素子の１つに標本化回折格子（Sampled　Grating）を用いてバーニア効果を利用した分布ブラッグ反射（ＤＢＲ）型波長可変レーザがある（例えば特許文献１）。この波長可変レーザ素子レーザでは、半導体素子内に回折格子の一部が標本化されたＤＢＲを２つ用いる。この２つのＤＢＲミラーの反射スペクトルは、周期が僅かに異なる櫛状の形状をしている。また、ＤＢＲミラーに電流注入もしくは加熱により屈折率変化を起こすことで、その反射波長特性を可変にすることができる。２つのＤＢＲミラーの反射特性を掛け合わせることにより特定の波長領域の反射率を高め、共振器を形成することができる。このとき、共振器長を適切に設計すれば、共振器モードである縦モードの間隔が２つのＤＢＲミラーによる反射帯域と同程度となり、１つの共振器モードだけが選択され、単一モード発振が実現される。 With the spread of coherent communication, the demand for narrow linewidth wavelength tunable laser devices is increasing. The configuration and operation principle of the wavelength tunable laser element are described in detail, for example, in Non-Patent Document 1. Generally, in order to narrow the line width of the laser light output from the semiconductor laser device, it is necessary to make the resonator longer. There is a distributed Bragg reflector (DBR) wavelength tunable laser using a vernier effect using sampled diffraction grating (Sampled Grating) as one of the wavelength tunable laser elements (for example, Patent Document 1). In this wavelength tunable laser device, two DBRs in which a part of the diffraction grating is sampled in the semiconductor device are used. The reflection spectra of the two DBR mirrors have a comb-like shape with a slightly different period. Further, by causing a change in refractive index to the DBR mirror by current injection or heating, it is possible to make its reflection wavelength characteristic variable. By multiplying the reflection characteristics of the two DBR mirrors, the reflectance of a specific wavelength region can be increased to form a resonator. At this time, if the resonator length is properly designed, the distance between the longitudinal modes, which are resonator modes, becomes approximately the same as the reflection band by two DBR mirrors, only one resonator mode is selected, and single mode oscillation is To be realized.
　狭線幅のレーザ光を実現する別の方法として、外部共振器構造を用いて共振長を長尺化し、共振器モードのＱ値を大きくする方法が挙げられる。また、たとえば、２つのリング共振器を用いて共振器を構成した波長可変レーザ素子では（たとえば非特許文献２）、比較的鋭いリング共振器のフィルタ特性（反射波長特性）の重ね合わせを用いることにより、共振器の構成を自由に設計可能である。 As another method for realizing a laser beam with a narrow line width, there is a method of lengthening the resonance length using an external resonator structure to increase the Q value of the resonator mode. In addition, for example, in a tunable laser device in which a resonator is configured using two ring resonators (for example, Non-Patent Document 2), using superposition of filter characteristics (reflected wavelength characteristics) of relatively sharp ring resonators Thus, the configuration of the resonator can be freely designed.
米国特許第６５９０９２４号明細書U.S. Patent No. 6,590,924
　しかし、上述したＤＢＲ型波長可変レーザ素子において、コヒーレント通信で必要となるような狭線幅のレーザ光を得る程度に共振器を長くすると、縦モード間隔が狭くなり、共振器の反射帯域では１つの共振器モードだけの選択を行うことが困難となるので、単一モード発振を得るのが原理上困難である。 However, in the above-mentioned DBR type variable wavelength laser element, if the resonator is made long enough to obtain a laser beam with a narrow line width required for coherent communication, the longitudinal mode spacing becomes narrow, and the reflection band of the resonator Since it is difficult to select only one resonator mode, it is in principle difficult to obtain single mode oscillation.
　また、２つのリング共振器を用いて共振器を構成した波長可変レーザ素子では、２つの鋭い反射波長特性の中心波長がずれた場合、重なり合った部分の反射率変動が大きい。そのため、安定したレーザ発振を実現するには、２つの鋭い反射波長特性のピークとピークが確実に重なり合うようにする必要があるが、そのような制御を行うことは困難である。 Further, in the wavelength tunable laser device in which the resonator is configured using two ring resonators, when the central wavelengths of the two sharp reflection wavelength characteristics are shifted, the reflectance fluctuation of the overlapping portion is large. Therefore, in order to realize stable laser oscillation, it is necessary to ensure that the peaks of the two sharp reflection wavelength characteristics overlap with each other, but such control is difficult.
　本発明は、上記に鑑みてなされたものであって、レーザ光の狭線幅化および安定した単一モード発振を実現できる波長可変レーザ素子およびこれを用いたレーザモジュールを提供することを目的とする。 The present invention has been made in view of the above, and it is an object of the present invention to provide a wavelength tunable laser device which can realize narrowing of the width of laser light and stable single mode oscillation, and a laser module using the same. Do.
　上述した課題を解決し、目的を達成するために、本発明の一態様に係る波長可変レーザ素子は、回折格子と、前記回折格子と光学的に結合されたリング共振器フィルタを含む反射ミラーにより構成されるレーザ共振器と、前記レーザ共振器内に配置された利得部と、前記レーザ共振器内に配置された位相調整部と、を備える波長可変レーザ素子であって、前記回折格子は、第一の櫛状反射スペクトルを生成し、前記リング共振器フィルタは、リング状導波路と、各々が前記リング状導波路と光学的に結合し、それぞれの一端が統合されて前記回折格子と光学的に結合されている２つのアーム部と、を備え、前記第一の櫛状反射スペクトルのピークの半値全幅よりも狭い半値全幅のピークで、前記第一の櫛状反射スペクトルの波長間隔とは異なる波長間隔を有する第二の櫛状反射スペクトルを生成し、前記回折格子と前記リング共振器は前記第一の櫛状反射スペクトルのピークの一つと前記第二の櫛状反射スペクトルのピークの一つとを波長軸上で重ね合わせ可能に構成され、前記レーザ共振器は、共振器モードのモード間の間隔が、前記第一の櫛状反射スペクトルのピークの半値全幅よりも狭くなるように構成されている。 In order to solve the problems described above and achieve the object, a wavelength tunable laser device according to an aspect of the present invention includes a diffraction grating and a reflection mirror including a ring resonator filter optically coupled to the diffraction grating. A tunable laser device comprising: a configured laser resonator; a gain unit disposed in the laser resonator; and a phase adjusting unit disposed in the laser resonator, wherein the diffraction grating is A first comb-like reflection spectrum is generated, and the ring resonator filter is optically coupled to the ring waveguide, each of which is optically coupled to the ring waveguide, and one end thereof is integrated to form the optical grating and the optical grating. Two full-width half-widths narrower than the full-width half-maximum of the peak of the first comb-like reflection spectrum, and the wavelength interval of the first comb-like reflection spectrum Different A second comb-like reflection spectrum having a wavelength interval between the first and second comb-like reflection spectra, and the diffraction grating and the ring resonator produce one of the peaks of the first comb-like reflection spectrum and one of the peaks of the second comb-like reflection spectrum. The laser resonators are configured such that the spacing between the modes of the resonator modes is narrower than the full width at half maximum of the peak of the first comb-like reflection spectrum. ing.
　本発明の一態様に係るレーザモジュールは、本発明の一態様に係る波長可変レーザ素子を備えることを特徴とする。 A laser module according to an aspect of the present invention includes the wavelength tunable laser element according to the aspect of the present invention.
　本発明によれば、レーザ光の狭線幅化および安定した単一モード発振をする波長可変レーザ素子を実現できるという効果を奏する。 According to the present invention, it is possible to realize a wavelength-tunable laser device which performs narrowing of the width of laser light and stable single mode oscillation.
図１は、実施の形態１に係る波長可変レーザ素子の模式的な斜視図である。FIG. 1 is a schematic perspective view of the wavelength tunable laser device according to the first embodiment. 図２Ａは、図１に示す波長可変レーザ素子の模式的な断面図である。FIG. 2A is a schematic cross-sectional view of the wavelength tunable laser device shown in FIG. 図２Ｂは、図１に示す波長可変レーザ素子の模式的な断面図である。FIG. 2B is a schematic cross-sectional view of the wavelength tunable laser device shown in FIG. 図２Ｃは、図１に示す波長可変レーザ素子の模式的な断面図である。FIG. 2C is a schematic cross-sectional view of the wavelength tunable laser device shown in FIG. 図３Ａは、第一の櫛状反射スペクトル、第二の櫛状反射スペクトルを示す図である。FIG. 3A is a diagram showing a first comb-like reflection spectrum and a second comb-like reflection spectrum. 図３Ｂは、第一の櫛状反射スペクトル、第二の櫛状反射スペクトルおよび共振器モードを示す図である。FIG. 3B is a diagram showing a first comb reflection spectrum, a second comb reflection spectrum, and a resonator mode. 図４は、第一の櫛状反射スペクトル、第二の櫛状反射スペクトルおよびその重なりを示す図である。FIG. 4 is a diagram showing a first comb-like reflection spectrum, a second comb-like reflection spectrum and an overlap thereof. 図５は、図１に示す波長可変レーザ素子における光帰還を説明する図である。FIG. 5 is a diagram for explaining the optical feedback in the wavelength tunable laser device shown in FIG. 図６は、図１に示す波長可変レーザ素子におけるレーザ発振波長の選択方法を説明する図である。FIG. 6 is a diagram for explaining a method of selecting a laser oscillation wavelength in the wavelength tunable laser device shown in FIG. 図７ＡＡは、図１に示す波長可変レーザ素子の製造方法の例を示す断面図である。FIG. 7AA is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG. 図７ＡＢは、図１に示す波長可変レーザ素子の製造方法の例を示す断面図である。FIG. 7AB is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG. 図７ＡＣは、図１に示す波長可変レーザ素子の製造方法の例を示す断面図である。FIG. 7AC is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG. 図７ＢＡは、図１に示す波長可変レーザ素子の製造方法の例を示す断面図である。FIG. 7BA is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG. 図７ＢＢは、図１に示す波長可変レーザ素子の製造方法の例を示す断面図である。FIG. 7BB is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG. 図７ＢＣは、図１に示す波長可変レーザ素子の製造方法の例を示す断面図である。FIG. 7BC is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG. 図７ＣＡは、図１に示す波長可変レーザ素子の製造方法の例を示す断面図である。FIG. 7CA is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG. 図７ＣＢは、図１に示す波長可変レーザ素子の製造方法の例を示す断面図である。FIG. 7CB is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG. 図７ＣＣは、図１に示す波長可変レーザ素子の製造方法の例を示す断面図である。FIG. 7CC is a cross-sectional view showing an example of a method of manufacturing the wavelength tunable laser shown in FIG. 図８は、図１に示す波長可変レーザ素子においてリング状導波路と２つのアーム部とを光学的に結合する導波路部を説明する図である。FIG. 8 is a view for explaining a waveguide portion which optically couples the ring waveguide and the two arm portions in the wavelength tunable laser device shown in FIG. 図９Ａは、導波路部の構造を説明する図である。FIG. 9A is a view for explaining the structure of the waveguide section. 図９Ｂは、導波路部の構造を説明する図である。FIG. 9B is a view for explaining the structure of the waveguide section. 図１０は、リッジ導波路構造を有する第１の導波路部の例を説明する図である。FIG. 10 is a diagram for explaining an example of the first waveguide section having a ridge waveguide structure. 図１１は、実施の形態２に係る波長可変レーザ素子の模式的な斜視図である。FIG. 11 is a schematic perspective view of the wavelength tunable laser device according to the second embodiment. 図１２Ａは、実施の形態３に係る波長可変レーザ素子の模式的な斜視図である。FIG. 12A is a schematic perspective view of a wavelength tunable laser device according to a third embodiment. 図１２Ｂは、実施の形態３に係る波長可変レーザ素子の模式的な断面図である。12B is a schematic cross-sectional view of the wavelength tunable laser device according to Embodiment 3. FIG. 図１３は、実施の形態４に係る波長可変レーザ素子の模式的な斜視図である。FIG. 13 is a schematic perspective view of the wavelength tunable laser device according to the fourth embodiment. 図１４は、実施の形態５に係るレーザモジュールの模式図である。FIG. 14 is a schematic view of a laser module according to the fifth embodiment. 図１５は、実施の形態６に係るレーザモジュールの模式図である。FIG. 15 is a schematic view of a laser module according to the sixth embodiment.
　本発明に係る波長可変レーザ素子は、バーニア効果を利用した波長可変レーザ素子において、第一の櫛状反射スペクトルのピークの半値全幅よりも狭い半値全幅のピークで、第一の櫛状反射スペクトルの波長間隔とは異なる波長間隔を有する第二の櫛状反射スペクトルを有し、かつ、共振器モードのモード間の間隔が、第一の櫛状反射スペクトルのピークの半値全幅よりも狭くなるように構成されていることにより、レーザ光の狭線幅化および安定した単一モード発振を実現できる。 The tunable laser device according to the present invention is a tunable laser device using the vernier effect, wherein the peak of the first comb-like reflection spectrum is narrower than the full width at half maximum of the peak of the first comb-like reflection spectrum. Having a second comb-like reflection spectrum having a wavelength spacing different from the wavelength spacing, and the spacing between the modes of the resonator modes being narrower than the full width at half maximum of the first comb-like reflection spectrum By being configured, narrowing of the line width of laser light and stable single mode oscillation can be realized.
　以下に、図面を参照して本発明に係る波長可変レーザ素子およびレーザモジュールの実施の形態を詳細に説明する。なお、この実施の形態によりこの発明が限定されるものではない。また、各図面において、同一または対応する要素には適宜同一の符号を付している。さらに、図面は模式的なものであり、各要素の寸法の関係、各要素の比率などは、現実のものとは異なる場合があることに留意する必要がある。図面の相互間においても、互いの寸法の関係や比率が異なる部分が含まれている場合がある。また、図中で適宜ｘｙｚ座標軸を示し、これにより方向を説明する。 Hereinafter, embodiments of a wavelength tunable laser device and a laser module according to the present invention will be described in detail with reference to the drawings. The present invention is not limited by the embodiment. Further, in the drawings, the same or corresponding elements are appropriately denoted by the same reference numerals. Furthermore, it should be noted that the drawings are schematic, and the relationship of dimensions of each element, the ratio of each element, etc. may be different from the actual one. Even between the drawings, there may be a case where the dimensional relationships and ratios differ from one another. Further, the xyz coordinate axes are appropriately shown in the drawing, and the direction will be described based on this.
（実施の形態１）
　図１は、実施の形態１に係る波長可変レーザ素子の模式的な斜視図である。波長可変レーザ素子１００は、１．５５μｍ帯でレーザ発振し、レーザ光を出力するように構成されている。波長可変レーザ素子１００は、共通の基部Ｂ上に形成された、第１の導波路部１０と第２の導波路部２０とを備えている。基部Ｂはたとえばｎ型ＩｎＰからなる。なお、基部Ｂの裏面にはｎ側電極３０が形成されている。ｎ側電極３０は、たとえばＡｕＧｅＮｉを含んで構成され、基部Ｂとオーミック接触する。 Embodiment 1
FIG. 1 is a schematic perspective view of the wavelength tunable laser device according to the first embodiment. The wavelength tunable laser device 100 is configured to emit a laser beam by performing laser oscillation in a 1.55 μm band. The wavelength tunable laser device 100 includes a first waveguide section 10 and a second waveguide section 20 formed on a common base B. The base B is made of, for example, n-type InP. An n-side electrode 30 is formed on the back surface of the base B. The n-side electrode 30 includes, for example, AuGeNi, and makes ohmic contact with the base B.
　第１の導波路部１０は、導波路部１１と、半導体積層部１２と、ｐ側電極１３と、Ｔｉからなるマイクロヒータ１４、１５とを備えている。導波路部１１は、半導体積層部１２内にｚ方向に延伸するように形成されている。第１の導波路部１０内には、回折格子装荷型利得部１１ａと位相調整部１１ｂが配置されている。半導体積層部１２は、半導体層が積層して構成されており、導波路部１１に対してクラッド部の機能等を備える。導波路部１１、半導体積層部１２の構成については後に詳述する。 The first waveguide unit 10 includes a waveguide unit 11, a semiconductor multilayer unit 12, a p-side electrode 13, and microheaters 14 and 15 made of Ti. The waveguide portion 11 is formed to extend in the z direction in the semiconductor multilayer portion 12. In the first waveguide unit 10, a diffraction grating loading type gain unit 11a and a phase adjustment unit 11b are disposed. The semiconductor multilayer portion 12 is configured by laminating semiconductor layers, and has a function of a cladding portion and the like with respect to the waveguide portion 11. The configurations of the waveguide portion 11 and the semiconductor laminated portion 12 will be described in detail later.
　ｐ側電極１３は、半導体積層部１２上において、回折格子装荷型利得部１１ａに沿うように配置されている。なお、半導体積層部１２には後述するＳｉＮ保護膜が形成されており、ｐ側電極１３はＳｉＮ保護膜に形成された開口部を介して半導体積層部１２に接触している。マイクロヒータ１４は、半導体積層部１２のＳｉＮ保護膜上において、位相調整部１１ｂに沿うように配置されている。第１の屈折率変化器としてのマイクロヒータ１５は、半導体積層部１２のＳｉＮ保護膜上において、ｐ側電極１３に沿うように配置されている。 The p-side electrode 13 is disposed on the semiconductor laminated portion 12 along the diffraction grating loaded gain portion 11 a. In addition, the SiN protective film mentioned later is formed in the semiconductor lamination part 12, and the p side electrode 13 is in contact with the semiconductor lamination part 12 via the opening part formed in the SiN protection film. The micro heater 14 is disposed on the SiN protective film of the semiconductor lamination portion 12 so as to be along the phase adjustment portion 11 b. The microheater 15 as a first refractive index changer is disposed along the p-side electrode 13 on the SiN protective film of the semiconductor multilayer portion 12.
　図２Ａは、第１の導波路部１０のうち回折格子装荷型利得部１１ａが含まれる部分を、図１のｘｙ平面に平行な面に沿って切断したＡ－Ａ線断面図である。図２Ａに示すように、回折格子装荷型利得部１１ａは、活性コア層１１ａａと、活性コア層１１ａａの近傍かつ直上に活性コア層１１ａａに沿って設けられた標本化回折格子からなる回折格子層１１ａｂとを有している。 FIG. 2A is a cross-sectional view taken along the line AA of a portion of the first waveguide section 10 including the diffraction grating loaded gain section 11a, which is cut along a plane parallel to the xy plane of FIG. As shown in FIG. 2A, the diffraction grating loading type gain portion 11a is composed of an active core layer 11aa and a sampling grating provided along the active core layer 11aa in the vicinity of and directly on the active core layer 11aa. And 11ab.
　活性コア層１１ａａは、交互に積層された複数の井戸層と複数のバリア層を含んで構成された多重量子井戸構造と、多重量子井戸構造を上下から下部および上部光閉じ込め層とを有しており、電流注入により発光する。この活性コア層１１ａａの多重量子井戸構造を構成する井戸層及びバリア層は各々組成が異なるＩｎＧａＡｓＰからなり、活性コア層１１ａａからの発光波長帯は、本実施の形態１では１．５５μｍ帯である。下部光閉じ込め層はｎ型ＩｎＧａＡｓＰからなる。上部光閉じ込め層はｐ型ＩｎＧａＡｓＰからなる。下部及び上部光閉じ込め層のバンドギャップ波長は、活性コア層１１ａａのバンドギャップ波長より短い波長に設定されている。回折格子層１１ａｂはｐ型ＩｎＧａＡｓＰ層にｚ方向に沿って標本化回折格子が形成され、回折格子の溝はＩｎＰで埋め込まれた構成を有する。回折格子層１１ａｂにおいて回折格子の格子間隔は一定であるが標本化されており、これにより波長に対し略周期的な反射応答を示す。回折格子層１１ａｂのｐ型ＩｎＧａＡｓＰ層のバンドギャップ波長は活性コア層１１ａａのバンドギャップ波長より短いことが好ましく、たとえば１．２μｍである。 Active core layer 11aa has a multiple quantum well structure including a plurality of well layers and a plurality of barrier layers alternately stacked, and a multiple quantum well structure from the top to the bottom and the upper light confinement layer It emits light by current injection. The well layer and the barrier layer constituting the multiple quantum well structure of the active core layer 11aa are made of InGaAsP different in composition from each other, and the emission wavelength band from the active core layer 11aa is 1.55 μm band in the first embodiment. . The lower optical confinement layer is made of n-type InGaAsP. The upper optical confinement layer is made of p-type InGaAsP. The band gap wavelengths of the lower and upper optical confinement layers are set to be shorter than the band gap wavelength of the active core layer 11aa. In the diffraction grating layer 11ab, a sampling diffraction grating is formed in the p-type InGaAsP layer along the z direction, and the groove of the diffraction grating has a configuration embedded in InP. In the diffraction grating layer 11ab, the grating interval of the diffraction grating is constant but sampled, thereby exhibiting a reflection response that is substantially periodic with respect to the wavelength. The band gap wavelength of the p-type InGaAsP layer of the diffraction grating layer 11ab is preferably shorter than the band gap wavelength of the active core layer 11aa, and is, for example, 1.2 μm.
　回折格子装荷型利得部１１ａが含まれる部分の半導体積層部１２は、たとえば以下のような構成を有する。半導体積層部１２は、基部Ｂを構成するｎ型ＩｎＰ基板上に、ｎ型ＩｎＰからなる、下部クラッド層の機能を有するバッファ層で構成されたｎ型半導体層１２ａを有している。ｎ型半導体層１２ａ上に活性コア層１１ａａが積層されている。さらに活性コア層１１ａａ上には、ｐ型ＩｎＰからなるスペーサ層１２ｂが積層されている。スペーサ層１２ｂ上には回折格子層１１ａｂが積層している。活性コア層１１ａａ、スペーサ層１２ｂ及び回折格子層１１ａｂは、エッチング等により、１．５５μｍ帯の光をシングルモードで光導波するのに適した幅（例えば１．８μｍ）にされたストライプメサ構造とされている。ストライプメサ構造の両脇（紙面左右方向）は、ｐ型ＩｎＰ埋め込み層１２ｃおよびｎ型ＩｎＰ電流ブロッキング層１２ｄからなる電流ブロッキング構造を有した埋込み構造となっている。さらに、回折格子層１１ａｂおよび埋込構造の上には、ｐ型ＩｎＰからなるスペーサ層１２ｅａと、スペーサ層１２ｅａ上に積層したｐ型ＩｎＧａＡｓからなり半導体積層部１２の最上層を形成するコンタクト層１２ｅｂとで構成されたｐ型半導体層１２ｅが積層されている。ｐ型半導体層１２ｅは、少なくとも活性コア層１１ａａの直上からその両脇の埋め込み構造の一部にわたって設けられている。半導体積層部１２には半導体積層部１２を覆うようにＳｉＮ保護膜１６が形成されている。ｐ側電極１３はＡｕＺｎを含んで構成されており、コンタクト層１２ｅｂ上に形成されて、ＳｉＮ保護膜１６の開口部１６ａを介してコンタクト層１２ｅｂとオーミック接触している。以上の構成により、ｎ側電極３０およびｐ側電極１３から活性コア層１１ａａへの電流注入が可能になっている。さらに、マイクロヒータ１５は、ｐ側電極１３とマイクロヒータ１５とを絶縁するために半導体積層部１２に設けられたＳｉＮ保護膜１７上に、ｐ側電極１３に沿うように配置されている。 The semiconductor laminated portion 12 in the portion including the diffraction grating loaded gain portion 11a has, for example, the following configuration. The semiconductor multilayer portion 12 has an n-type semiconductor layer 12a of n-type InP formed of a buffer layer having a function of a lower cladding layer on an n-type InP substrate forming the base B. Active core layer 11aa is stacked on n-type semiconductor layer 12a. Further, on the active core layer 11aa, a spacer layer 12b made of p-type InP is stacked. The diffraction grating layer 11ab is stacked on the spacer layer 12b. Active core layer 11aa, spacer layer 12b and diffraction grating layer 11ab have a stripe mesa structure having a width (for example, 1.8 .mu.m) suitable for single-mode optical waveguide of 1.55 .mu.m band by etching or the like. It is done. Both sides of the stripe mesa structure (in the left-right direction in the drawing) have a buried structure having a current blocking structure including a p-type InP buried layer 12c and an n-type InP current blocking layer 12d. Furthermore, on the diffraction grating layer 11ab and the embedded structure, a spacer layer 12ea made of p-type InP, and a contact layer 12eb made of p-type InGaAs laminated on the spacer layer 12ea and forming the uppermost layer of the semiconductor multilayer portion 12 And the p-type semiconductor layer 12 e is stacked. The p-type semiconductor layer 12e is provided at least from immediately above the active core layer 11aa to a part of the embedded structure on both sides thereof. A SiN protective film 16 is formed on the semiconductor laminated portion 12 so as to cover the semiconductor laminated portion 12. The p-side electrode 13 contains AuZn, is formed on the contact layer 12eb, and is in ohmic contact with the contact layer 12eb via the opening 16a of the SiN protective film 16. With the above configuration, current injection from the n-side electrode 30 and the p-side electrode 13 to the active core layer 11aa is possible. Furthermore, the microheater 15 is disposed along the p-side electrode 13 on the SiN protective film 17 provided in the semiconductor laminated portion 12 in order to insulate the p-side electrode 13 from the microheater 15.
　一方、図２Ｂは、第１の導波路部１０のうち位相調整部１１ｂが含まれる部分を、図１のｘｙ平面に平行な面に沿って切断したＢ－Ｂ線断面図である。図２Ｂに示すように、位相調整部１１ｂを含む第１の導波路部１０の断面構造は、図２Ａに示す構造において活性コア層１１ａａをＩｎＧａＡｓＰからなる光導波層である位相調整部１１ｂに置き換え、回折格子層１１ａｂおよびスペーサ層１２ｂはｐ型ＩｎＰ層１２ｆに置き換え、コンタクト層１２ｅｂを削除した構造を有している。位相調整部１１ｂでの光損失を低減し、光を効果的に閉じ込める為に、位相調整部１１ｂのバンドギャップ波長は活性コア層１１ａａのバンドギャップ波長より短いことが好ましく、たとえば１．３μｍ以下である。 On the other hand, FIG. 2B is a cross-sectional view taken along the line BB taken along a plane parallel to the xy plane in FIG. 1, of a portion of the first waveguide 10 including the phase adjustment portion 11b. As shown in FIG. 2B, the sectional structure of the first waveguide section 10 including the phase adjustment section 11b replaces the active core layer 11aa in the structure shown in FIG. 2A with the phase adjustment section 11b which is an optical waveguide layer made of InGaAsP. The diffraction grating layer 11ab and the spacer layer 12b are replaced by the p-type InP layer 12f, and the contact layer 12eb is eliminated. In order to reduce the optical loss in the phase adjustment part 11b and confine light effectively, the band gap wavelength of the phase adjustment part 11b is preferably shorter than the band gap wavelength of the active core layer 11aa, for example, 1.3 μm or less is there.
　以上のように、第１の導波路部１０は第１の導波路構造としての埋込み導波路構造を有する。 As described above, the first waveguide section 10 has the embedded waveguide structure as the first waveguide structure.
　つぎに、図１に戻って、第２の導波路部２０について説明する。第２の導波路部２０は、２分岐部２１と、２つのアーム部２２、２３と、リング状導波路２４と、Ｔｉからなるマイクロヒータ２５とを備えている。 Next, returning to FIG. 1, the second waveguide section 20 will be described. The second waveguide portion 20 includes a bifurcated portion 21, two arm portions 22 and 23, a ring-shaped waveguide 24, and a micro heater 25 made of Ti.
　２分岐部２１は、１×２型の多モード干渉型（ＭＭＩ）導波路２１ａを含む１×２型の分岐型導波路で構成され、２ポート側が２つのアーム部２２、２３のそれぞれに接続されるとともに１ポート側が第１の導波路部１０側に接続されている。２分岐部２１により、２つのアーム部２２、２３は、その一端が統合され、回折格子層１１ａｂと光学的に結合される。 The bifurcated portion 21 is composed of a 1 × 2 type branched waveguide including a 1 × 2 type multimode interference (MMI) waveguide 21 a, and the two port side is connected to each of the two arm portions 22 and 23. At the same time, one port side is connected to the first waveguide section 10 side. One end of the two arm portions 22 and 23 is integrated by the bifurcated portion 21 and optically coupled to the diffraction grating layer 11ab.
　アーム部２２、２３は、いずれもｚ方向に延伸し、リング状導波路２４を挟むように配置されている。アーム部２２、２３はリング状導波路２４と近接し、いずれも同一の結合係数κでリング状導波路２４と光学的に結合している。κの値はたとえば０．２である。アーム部２２、２３とリング状導波路２４とは、リング共振器フィルタＲＦ１を構成している。また、リング共振器フィルタＲＦ１と２分岐部２１とは、反射ミラーＭ１を構成している。第２の屈折率変化器としてのマイクロヒータ２５はリング状であり、リング状導波路２４を覆うように形成されたＳｉＮ保護膜上に配置されている。 Each of the arm portions 22 and 23 extends in the z direction, and is disposed so as to sandwich the ring waveguide 24. The arm portions 22 and 23 are in close proximity to the ring waveguide 24 and both are optically coupled to the ring waveguide 24 with the same coupling coefficient κ. The value of κ is, for example, 0.2. The arm portions 22 and 23 and the ring waveguide 24 constitute a ring resonator filter RF1. Further, the ring resonator filter RF1 and the bifurcated portion 21 constitute a reflection mirror M1. The microheater 25 as a second refractive index changer is ring-shaped, and is disposed on a SiN protective film formed to cover the ring-shaped waveguide 24.
　図２Ｃは、第２の導波路部２０のうちアーム部２２を、図１のｘｙ平面に平行な面に沿って切断したＣ－Ｃ線断面図である。図２Ｃに示すように、アーム部２２は、基部Ｂ上に、ｎ型ＩｎＰからなる下部クラッド層２２ａ、ＩｎＧａＡｓＰからなる光導波層２２ｂ、およびｐ型ＩｎＰからなる上部クラッド層２２ｃがこの順で積層して構成されたハイメサ導波路構造を有している。ＳｉＮ保護膜２２ｄはアーム部２２を覆うように形成されている。なお、第２の導波路部２０のその他の構成要素である２分岐部２１、アーム部２３、リング状導波路２４も同様にハイメサ導波路構造を有しており、ＳｉＮ保護膜で覆われている。すなわち、第２の導波路部２０は第１の導波路部１０の第１の導波路構造とは異なる第２の導波路構造を有する。 FIG. 2C is a cross-sectional view of the arm portion 22 of the second waveguide portion 20 taken along line CC cut along a plane parallel to the xy plane of FIG. As shown in FIG. 2C, in the arm portion 22, a lower cladding layer 22a of n-type InP, an optical waveguide layer 22b of InGaAsP, and an upper cladding layer 22c of p-type InP are stacked in this order on the base B. The high mesa waveguide structure is configured. The SiN protective film 22 d is formed to cover the arm portion 22. The other components of the second waveguide portion 20, such as the bifurcated portion 21, the arm portion 23, and the ring waveguide 24 also have a high mesa waveguide structure, and are covered with a SiN protective film. There is. That is, the second waveguide section 20 has a second waveguide structure different from the first waveguide structure of the first waveguide section 10.
　第１の導波路部１０と第２の導波路部２０は、互いに光学的に接続された回折格子装荷型利得部１１ａの回折格子層１１ａｂと反射ミラーＭ１とにより構成されるレーザ共振器Ｃ１を構成している。回折格子装荷型利得部１１ａの利得部としての活性コア層１１ａａと位相調整部１１ｂとはレーザ共振器Ｃ１内に配置される。 The first waveguide unit 10 and the second waveguide unit 20 are configured of a laser resonator C1 configured of the diffraction grating layer 11ab of the diffraction grating loading type gain unit 11a optically connected to each other and the reflection mirror M1. Configured. The active core layer 11aa as the gain portion of the diffraction grating loading type gain portion 11a and the phase adjustment portion 11b are disposed in the laser resonator C1.
　つぎに、回折格子層１１ａｂとリング共振器フィルタＲＦ１との反射特性について図３Ａ、３Ｂを用いて説明する。図３Ａ、３Ｂにおいて縦軸は反射率（Reflectance）を示している。回折格子層１１ａｂは、図３Ａに凡例「ＳＧ」で曲線を示すように、略所定の波長間隔で略周期的な反射特性を有する第一の櫛状反射スペクトルを生成する。一方、リング共振器フィルタＲＦ１は、図３Ａに凡例「Ｒｉｎｇ」で曲線を示すように、所定の波長間隔で周期的な反射特性を有する第二の櫛状反射スペクトルを生成する。図３Ｂは図３Ａの反射スペクトルの１５５０ｎｍ近傍を拡大して示した図である。図３Ｂにおいて、凡例「Ｍｏｄｅ」は、レーザ共振器Ｃ１の共振器モードを示している。共振器モードは少なくとも図３Ａに示す１５３０ｎｍ～１５７０ｎｍの波長範囲に亘って存在している。図３Ａ、３Ｂに示すように、第二の櫛状反射スペクトルは、第一の櫛状反射スペクトルのスペクトル成分ＳＣ１の半値全幅よりも狭い半値全幅のピークＳＣ２を有し、第一の櫛状反射スペクトルの波長間隔とは異なる波長間隔で略周期的な反射特性を有する。但し、屈折率の波長分散を考慮すると、スペクトル成分は厳密には等波長間隔になっていないことに注意が必要である。 Next, reflection characteristics of the diffraction grating layer 11ab and the ring resonator filter RF1 will be described with reference to FIGS. 3A and 3B. In FIGS. 3A and 3B, the vertical axis indicates reflectivity. The diffraction grating layer 11ab generates a first comb-like reflection spectrum having substantially periodic reflection characteristics at substantially predetermined wavelength intervals, as shown by a curve in a legend “SG” in FIG. 3A. On the other hand, the ring resonator filter RF1 generates a second comb-like reflection spectrum having periodic reflection characteristics at predetermined wavelength intervals, as shown by a curve in a legend “Ring” in FIG. 3A. FIG. 3B is an enlarged view of around 1550 nm of the reflection spectrum of FIG. 3A. In FIG. 3B, the legend "Mode" indicates the resonator mode of the laser resonator C1. The resonator modes exist over at least the wavelength range of 1530 nm to 1570 nm shown in FIG. 3A. As shown in FIGS. 3A and 3B, the second comb reflection spectrum has a peak SC2 of full width at half maximum narrower than the full width at half maximum of the spectral component SC1 of the first comb reflection spectrum, and the first comb reflection is It has substantially periodic reflection characteristics at wavelength intervals different from the wavelength intervals of the spectrum. However, it should be noted that the spectral components are not strictly equal wavelength intervals in consideration of the wavelength dispersion of the refractive index.
　各櫛状反射スペクトルの特性について例示すると、第一の櫛状反射スペクトルのピーク間の波長間隔（自由スペクトル領域：ＦＳＲ）は光の周波数で表すと３７３ＧＨｚであり、各ピークの半値全幅は光の周波数で表すと４３ＧＨｚである。また、第二の櫛状反射スペクトルのピーク間の波長間隔（ＦＳＲ）は光の周波数で表すと４００ＧＨｚであり、各ピークの半値全幅は光の周波数で表すと２５ＧＨｚである。すなわち、第二の櫛状反射スペクトルのピークの半値全幅（２５ＧＨｚ）は第一の櫛状反射スペクトルのピークの半値全幅（４３ＧＨｚ）より狭い。 To illustrate the characteristics of each comb-like reflection spectrum, the wavelength interval between the peaks of the first comb-like reflection spectrum (free spectral range: FSR) is 373 GHz in terms of light frequency, and the full width at half maximum of each peak is light The frequency is 43 GHz. The wavelength interval (FSR) between the peaks of the second comb-like reflection spectrum is 400 GHz in terms of the light frequency, and the full width at half maximum of each peak is 25 GHz in terms of the light frequency. That is, the full width at half maximum (25 GHz) of the peak of the second comb reflection spectrum is narrower than the full width at half maximum (43 GHz) of the peak of the first comb reflection spectrum.
　また、第二の櫛状反射スペクトルのピークは波長に対して急峻に変化する形状を有しており、波長に対する反射率の２次微分がピークより短波長側及び長波長側で正値をとる波長域がある。第二の櫛状反射スペクトルのピークは例えば二重指数分布（ラプラス分布）型の形状である。一方、第一の櫛状反射スペクトルのピークは、第二の櫛状反射スペクトルのピークに比して、波長に対して緩やかに変化する形状を有しており、波長に対する反射率の２次微分がピークに対して短波長側及び長波長側で負値をとる波長域がある。第一の櫛状反射スペクトルのピークは例えばガウシャン型の形状である。 Also, the peak of the second comb-like reflection spectrum has a shape that changes sharply with respect to the wavelength, and the second derivative of the reflectance with respect to the wavelength takes positive values on the short wavelength side and long wavelength side from the peak There is a wavelength range. The peak of the second comb reflection spectrum is, for example, in the form of a double exponential distribution (Laplace distribution) type. On the other hand, the peak of the first comb-like reflection spectrum has a shape that changes gently with respect to the wavelength, compared to the peak of the second comb-like reflection spectrum, and the second derivative of the reflectance with respect to wavelength There is a wavelength range that takes a negative value on the short wavelength side and the long wavelength side with respect to the peak. The peak of the first comb-like reflection spectrum is, for example, a Gaussian shape.
　波長可変レーザ素子１００において、レーザ発振を実現するために、第一の櫛状反射スペクトルのピークの一つと第二の櫛状反射スペクトルのピークの一つとを波長軸上で重ね合わせ可能に構成されている。図４は、第一の櫛状反射スペクトル、第二の櫛状反射スペクトルおよびその重なりを示す図である。凡例「Ｏｖｅｒｌａｐ」で示す曲線がスペクトルの重なりを示す。図４に示す例では、波長１５５０ｎｍにて重なりがもっとも大きくなる。 In the wavelength tunable laser device 100, in order to realize laser oscillation, one of the peaks of the first comb-like reflection spectrum and one of the peaks of the second comb-like reflection spectrum can be superimposed on the wavelength axis. ing. FIG. 4 is a diagram showing a first comb-like reflection spectrum, a second comb-like reflection spectrum and an overlap thereof. The curve indicated by the legend "Overlap" indicates spectral overlap. In the example shown in FIG. 4, the overlap is largest at a wavelength of 1550 nm.
　なお、このような重ね合わせは、マイクロヒータ１５およびマイクロヒータ２５の少なくともいずれか一つを用いて、マイクロヒータ１５により回折格子層１１ａｂを加熱して熱光学効果によりその屈折率を変化させて第一の櫛状反射スペクトルを波長軸上で全体的に移動させる、および、マイクロヒータ２５によりリング状導波路２４を加熱してその屈折率を変化させて第二の櫛状反射スペクトルを波長軸上で全体的に移動させる、の少なくともいずれか一つを行うことにより、実現することができる。 Note that such superposition is performed by heating the diffraction grating layer 11ab by the microheater 15 using at least one of the microheater 15 and the microheater 25 to change its refractive index by the thermo-optical effect. One comb-like reflection spectrum is moved entirely on the wavelength axis, and the ring-shaped waveguide 24 is heated by the microheater 25 to change its refractive index to make the second comb-like reflection spectrum on the wavelength axis This can be realized by performing at least one of moving the whole in
　一方、波長可変レーザ素子１００において、図３Ｂにその一部を示すように、レーザ共振器Ｃ１による共振器モードが存在する。波長可変レーザ素子１００においては、共振器モードの間隔（縦モード間隔）は２５ＧＨｚ以下となるようにレーザ共振器Ｃ１の共振器長が設定されている。この設定の場合、レーザ共振器Ｃ１の共振器長は１８００μｍ以上となり、発振するレーザ光の狭線幅化が期待できる。 On the other hand, in the wavelength tunable laser device 100, as partially shown in FIG. 3B, a resonator mode by the laser resonator C1 exists. In the wavelength tunable laser device 100, the resonator length of the laser resonator C1 is set such that the distance between the resonator modes (longitudinal mode distance) is 25 GHz or less. In this setting, the resonator length of the laser resonator C1 is 1800 μm or more, and narrowing of the line width of the oscillated laser light can be expected.
　波長可変レーザ素子１００は、ｎ側電極３０およびｐ側電極１３から活性コア層１１ａａへの電流を注入し、活性コア層１１ａａを発光させると、第一の櫛状反射スペクトルのスペクトル成分のピーク、第二の櫛状反射スペクトルのスペクトル成分のピーク、およびレーザ共振器の共振器モードの一つが一致した波長、すなわち１５５０ｎｍでレーザ発振し、レーザ光Ｌ１（図１参照）を出力するように構成されている。なお、レーザ共振器Ｃ１の共振器モードの波長は、マイクロヒータ１４を用いて位相調整部１１ｂを加熱してその屈折率を変化させて、共振器モードの波長を波長軸上で全体的に移動させることにより微調整することができる。すなわち、位相調整部１１ｂは、レーザ共振器Ｃ１の光路長を能動的に制御するための部分である。 When the wavelength tunable laser device 100 injects a current from the n-side electrode 30 and the p-side electrode 13 to the active core layer 11aa to cause the active core layer 11aa to emit light, the peak of the spectral component of the first comb reflection spectrum, The peak of the spectral component of the second comb-like reflection spectrum, and one of the resonator modes of the laser resonator are configured to emit a laser at a coincident wavelength, ie 1550 nm, and to output the laser light L1 (see FIG. 1) ing. The wavelength of the resonator mode of the laser resonator C1 heats the phase adjustment unit 11b using the microheater 14 to change its refractive index, and the wavelength of the resonator mode is moved entirely on the wavelength axis. Fine adjustment can be done by That is, the phase adjustment unit 11b is a portion for actively controlling the optical path length of the laser resonator C1.
　ここで、上述したように、リング共振器フィルタＲＦ１による第二の櫛状反射スペクトルは、回折格子層１１ａｂによる第一の櫛状反射スペクトルのピークの半値全幅よりも狭い半値全幅のピークを有する。これにより、半値全幅の広い第一の櫛状反射スペクトルのピークの中に、これよりも半値全幅の狭い第２の櫛状反射スペクトルのピークを存在させるように重ね合わせることとなるため、レーザ発振波長の制御が容易となる。 Here, as described above, the second comb reflection spectrum by the ring resonator filter RF1 has a full width at half maximum narrower than the full width at half maximum of the peak of the first comb reflection spectrum by the diffraction grating layer 11ab. As a result, since the peak of the second comb-like reflection spectrum narrower in full width at half maximum is present in the peaks of the first comb-like reflection spectrum wide in half width, the laser oscillation is generated. It becomes easy to control the wavelength.
　すなわち、２つのリング共振器を用いて共振器を構成し、鋭い形状のピーク同士で重ね合わせを行う場合と比較して、第二の櫛状反射スペクトルのピークのみが鋭いため、これを、第二の櫛状反射スペクトルのピークよりも鋭くない形状の第一の櫛状反射スペクトルのピーク内に位置するように重ね合わせていくのは容易であり、かつ波長がずれた場合でもその変化は緩やかであり、レーザ発振の波長も安定する。 That is, as compared with the case where a resonator is configured using two ring resonators and superposition is performed between sharp-shaped peaks, only the peak of the second comb-shaped reflection spectrum is sharper, It is easy to overlap so as to be located within the peak of the first comb-like reflection spectrum which is not sharper than the peak of the two comb-like reflection spectra, and the change is gradual even if the wavelength is shifted. And the wavelength of the laser oscillation is also stable.
　さらに、上述したように、波長可変レーザ素子１００は、レーザ共振器Ｃ１の共振器モード間の間隔は２５ＧＨｚ以下であり、第一の櫛状反射スペクトルのスペクトル成分の半値全幅（４３ＧＨｚ）よりも狭くなるように構成されている。
　レーザ光の狭線幅化のために共振器長を長くすると、共振器モード間の間隔が狭くなっていくが、特に、第一の櫛状反射スペクトルのピークの半値全幅内に複数の共振器モードが存在するほどに共振器モードのモード間の間隔が狭くなると、通常の場合はレーザ発振させる共振器モードの選択が困難となってしまう。
　しかし、波長可変レーザ素子１００では、このように共振器モード間の間隔が狭い場合であっても、第一の櫛状反射スペクトルの半値全幅の広いピークの中に、これよりも半値全幅の狭い第二の櫛状反射スペクトルのピークを存在させることとなるため、共振器モードを選択する制御が容易となる。従って、波長可変レーザ素子１００では、レーザ共振器Ｃ１は、共振器モードのモード間の間隔が、第一の櫛状反射スペクトルのピーク内に共振器モードが２本以上含まれるような長い共振器長に構成されていても、共振器モードを選択する制御が容易となる。
　さらに、図３Ａ、３Ｂに示すように、第二の櫛状反射スペクトルのピークの反射率が、第一の櫛状反射スペクトルのピークの反射率よりも高いと、反射ミラーＭ１により反射される光の利得が大きくなり、反射ミラーＭ１による第二の櫛状反射スペクトルのピーク位置で、共振器モードのうち一つだけを安定的に選択することができる。
　さらに、第二の櫛状反射スペクトルのピークが二重指数分布型の形状であれば、第一の櫛状反射スペクトルのピークがガウシャン型の形状の場合に、第一の櫛状反射スペクトルのピークに対するピークの先鋭度を大きくすることができる。これにより、第一の櫛状反射スペクトルのピークの高さよりも第二の櫛状反射スペクトルのピークが突出して高くなり、第二の櫛状反射スペクトルのピークの反射率を、第一の櫛状反射スペクトルのピークの反射率よりも容易に高くできる。したがって、安定した単一モード発振をより容易に実現できる。 Furthermore, as described above, in the wavelength tunable laser device 100, the distance between the resonator modes of the laser resonator C1 is 25 GHz or less, which is narrower than the full width at half maximum (43 GHz) of the spectral component of the first comb reflection spectrum It is configured to be
When the resonator length is increased to narrow the line width of the laser light, the distance between the resonator modes is narrowed, but in particular, a plurality of resonators within the full width at half maximum of the first comb-like reflection spectrum If the distance between the modes of the resonator modes becomes narrower as the modes exist, selection of a resonator mode for laser oscillation becomes difficult in the normal case.
However, in the tunable laser device 100, even if the distance between the resonator modes is narrow like this, the full width at half maximum of the full width at half maximum of the first comb reflection spectrum is narrower than this. The presence of the peak of the second comb-like reflection spectrum facilitates control for selecting the resonator mode. Therefore, in the tunable laser device 100, the laser resonator C1 is a long resonator in which the spacing between the modes of the resonator modes is such that two or more resonator modes are included in the peak of the first comb-like reflection spectrum. Even if it is configured to be long, control to select the resonator mode is facilitated.
Furthermore, as shown in FIGS. 3A and 3B, when the reflectance of the peak of the second comb reflection spectrum is higher than the reflectance of the peak of the first comb reflection spectrum, the light reflected by the reflection mirror M1 Thus, at the peak position of the second comb reflection spectrum by the reflection mirror M1, only one of the resonator modes can be stably selected.
Furthermore, if the peak of the second comb-like reflection spectrum has a double exponential distribution shape, the peak of the first comb-like reflection spectrum if the peak of the first comb-like reflection spectrum has a Gaussian shape The peak sharpness can be increased. As a result, the peak of the second comb reflection spectrum protrudes higher than the height of the peak of the first comb reflection spectrum, and the reflectance of the peak of the second comb reflection spectrum becomes the first comb shape. It can easily be higher than the reflectance of the peak of the reflection spectrum. Therefore, stable single mode oscillation can be realized more easily.
　また、波長可変レーザ素子１００では、その構成により、図５に光路ＯＰで示すように、レーザ共振器Ｃ１内の光帰還は、回折格子層１１ａｂから、２分岐部２１、リング共振器フィルタＲＦ１のアーム部２２、２３のうちの一方、リング状導波路２４、アーム部２２、２３のうちの他方、２分岐部２１を順に経由して回折格子層１１ａｂに帰還する経路で行われ、かつ１回の光帰還中にリング状導波路２４内を周回する。なお、光路ＯＰの矢頭は光の進行方向を示しており、光路ＯＰは時計周りの光路と反時計周りの光路の両方を表している。すなわち、光帰還の光路として、時計周りの光路と反時計周りの光路の２つが存在する。これにより、光帰還長が長くなるので、実効的な共振器長を長くでき、レーザ光Ｌ１の狭線幅化を実現できる。 Further, in the wavelength tunable laser device 100, as shown by the optical path OP in FIG. 5, the optical feedback in the laser resonator C1 is obtained from the diffraction grating layer 11ab by the two-branch portion 21 and the ring resonator filter RF1. It is performed in a path that is returned to the diffraction grating layer 11ab via the one of the arm portions 22 and 23, the other of the ring waveguide 24 and the other of the arm portions 22 and 23, and the bifurcated portion 21 one time, and one time Of the ring-shaped waveguide 24 during the optical feedback. The arrowhead of the optical path OP indicates the traveling direction of light, and the optical path OP represents both a clockwise optical path and a counterclockwise optical path. That is, there are two light paths, a clockwise light path and a counterclockwise light path, as light paths for light feedback. As a result, since the optical feedback length becomes long, the effective resonator length can be made long, and the line width reduction of the laser light L1 can be realized.
　つぎに、図３Ａ、３Ｂ、４、６を用いて、波長可変レーザ素子１００におけるレーザ発振波長の選択方法を説明する。波長可変レーザ素子１００では、バーニア効果を利用してレーザ発振波長の選択を行っている。 Next, a method of selecting a laser oscillation wavelength in the wavelength tunable laser device 100 will be described with reference to FIGS. 3A, 3 B, 4 and 6. In the wavelength tunable laser device 100, the laser oscillation wavelength is selected using the vernier effect.
　図３Ａ、３Ｂ、４にも示すように、第一の櫛状反射スペクトルと第二の櫛状反射スペクトルとのＦＳＲは、わずかに異なるように設計されている。なお、ピークがより鋭い第二の櫛状反射スペクトルのＦＳＲの方を大きくすることで、スペクトルの重なりのピークが最も高い１５５０ｎｍに隣接する重なり（例えば、１５４７ｎｍ付近の重なり）のピークの高さが相対的に小さくなる。その結果、スペクトルの重なりのピークが最も高い波長に隣接する重なりのピークの波長でのレーザ発振が抑制されることとなるので、サイドモード抑圧比を高くできる。 As also shown in FIGS. 3A, 3 B, 4, the FSRs of the first comb reflection spectrum and the second comb reflection spectrum are designed to be slightly different. Note that, by increasing the FSR of the second comb-like reflection spectrum where the peak is sharper, the height of the peak of the overlap (for example, the overlap near 1547 nm) adjacent to 1550 nm where the peak of the spectrum overlap is highest It becomes relatively small. As a result, since the laser oscillation at the wavelength of the overlap peak adjacent to the highest wavelength of the overlap of the spectrum is suppressed, the side mode suppression ratio can be increased.
　波長可変レーザ素子１００における可変波長範囲は、バーニア効果により、ＦＳＲの最小公倍数で決定される。第一の櫛状反射スペクトルのピークの一つと第二の櫛状反射スペクトルのピークの一つが重ね合わせられ、そのピークが一致した波長で反射率が最大となり、レーザ発振が起こる。つまり、回折格子層１１ａｂとリング共振器フィルタＲＦ１のバーニア効果により大まかなレーザ発振波長が決定される（スーパーモード）。より精密には、レーザ発振波長は、レーザ共振器Ｃ１内において、回折格子層１１ａｂから、２分岐部２１、リング共振器フィルタＲＦ１のアーム部２２、２３のうちの一方、リング状導波路２４、アーム部２２、２３のうちの他方、２分岐部２１を順に経由して回折格子層１１ａｂに帰還する経路（共振器長）で定義される共振器モードの波長とスーパーモードとの重なりで決定される。すなわち、重ね合わされた第一の櫛状反射スペクトルのピークと第二の櫛状反射スペクトルのピークの重なり領域に、レーザ共振器Ｃ１の共振器モードの一つを一致させ、その一致した共振器モードの波長でレーザ発振することとなる。したがって、波長可変レーザ素子１００では、回折格子層１１ａｂに対するマイクロヒータ１５とリング共振器フィルタＲＦ１に対するマイクロヒータ２５とにより第一の櫛状反射スペクトルと第二の櫛状反射スペクトルとをそれぞれチューニングすることで粗調、位相調整部１１ｂに対するマイクロヒータ１４により共振器長をチューニングすることで微調を行う波長可変動作が実現される。 The variable wavelength range in the wavelength tunable laser device 100 is determined by the vernier effect at the least common multiple of FSR. One of the peaks of the first comb-like reflection spectrum and one of the peaks of the second comb-like reflection spectrum are superimposed, and the reflectance becomes maximum at a wavelength where the peaks coincide, and laser oscillation occurs. That is, the rough laser oscillation wavelength is determined by the vernier effect of the diffraction grating layer 11ab and the ring resonator filter RF1 (super mode). More precisely, in the laser resonator C1, the laser oscillation wavelength is from the diffraction grating layer 11ab, the bifurcated portion 21, one of the arm portions 22 and 23 of the ring resonator filter RF1, the ring-shaped waveguide 24, Determined by the overlap of the wavelength of the resonator mode and the super mode defined by the path (resonator length) that is fed back to the diffraction grating layer 11ab via the other of the arm portions 22 and 23 and the 2-branch portion 21 in order Ru. That is, one of the resonator modes of the laser resonator C1 is made to coincide with the overlapping region of the peaks of the first comb-like reflection spectrum and the second comb-like reflection spectrum superimposed, and the corresponding cavity modes are made The laser is oscillated at the wavelength of Therefore, in the tunable laser device 100, the first comb-like reflection spectrum and the second comb-like reflection spectrum are respectively tuned by the microheater 15 for the diffraction grating layer 11ab and the microheater 25 for the ring resonator filter RF1. By tuning the resonator length by the microheater 14 with respect to the coarse adjustment and the phase adjustment unit 11b, a wavelength variable operation to perform fine adjustment is realized.
　図３Ａ、３Ｂに示す状態（第１の状態とする）では、第一の櫛状反射スペクトルと第二の櫛状反射スペクトルとは波長１５５０ｎｍで重なりが最も大きい（スーパーモード）。第１の状態ではレーザ発振波長は１５５０ｎｍ付近に粗調されている状態である。第１の状態で位相調整部１１ｂをチューニングすることで共振器モードを微調することで、波長１５５０ｎｍでのレーザ発振を得ることができる。 In the state shown in FIGS. 3A and 3B (referred to as the first state), the first comb reflection spectrum and the second comb reflection spectrum have the largest overlap at a wavelength of 1550 nm (super mode). In the first state, the laser oscillation wavelength is roughly adjusted to around 1550 nm. By finely tuning the resonator mode by tuning the phase adjustment unit 11 b in the first state, it is possible to obtain laser oscillation at a wavelength of 1550 nm.
　つぎに、レーザ発振波長を変更する場合は、リング共振器フィルタＲＦ１のチューニングを固定した状態で、回折格子層１１ａｂのみマイクロヒータ１５で加熱する。すると、熱光学効果により回折格子層１１ａｂの屈折率が上昇し、回折格子層１１ａｂの反射スペクトル（第一の櫛状反射スペクトル）は、図６に矢印で示すように全体的に長波側にシフトする。その結果、１５５０ｎｍ付近のリング共振器フィルタＲＦ１の反射スペクトル（第二の櫛状反射スペクトル）のピークとの重なりが解かれ、長波側に存在する別のピーク（１５５６ｎｍ付近）に重なり、図６に示す第２の状態となる。これにより、別のスーパーモードへの遷移が実現する。さらに、位相調整部１１ｂをチューニングして共振器モードを微調することで、１５５６ｎｍ付近でのレーザ発振を実現できる。なお、レーザ発振波長を短波側に変更する際は、回折格子層１１ａｂのチューニングを固定し、リング共振器フィルタＲＦ１のみマイクロヒータ２５で加熱して、リング共振器フィルタＲＦ１の櫛状反射スペクトルを全体的に長波側にシフトさせればよい。 Next, when the laser oscillation wavelength is changed, only the diffraction grating layer 11ab is heated by the microheater 15 with the tuning of the ring resonator filter RF1 fixed. Then, the refractive index of the diffraction grating layer 11ab is increased due to the thermo-optical effect, and the reflection spectrum (first comb-like reflection spectrum) of the diffraction grating layer 11ab is generally shifted to the long wave side as shown by the arrows in FIG. Do. As a result, the overlap with the peak of the reflection spectrum (second comb-like reflection spectrum) of the ring resonator filter RF1 around 1550 nm is solved, and another peak (about 1556 nm) existing on the long wave side is overlapped. It will be in the second state shown. Thereby, transition to another super mode is realized. Furthermore, by tuning the phase adjustment unit 11 b to finely adjust the resonator mode, laser oscillation around 1556 nm can be realized. When changing the laser oscillation wavelength to the short wave side, the tuning of the diffraction grating layer 11ab is fixed, only the ring resonator filter RF1 is heated by the microheater 25, and the comb reflection spectrum of the ring resonator filter RF1 is entirely It may be shifted to the long wave side.
　本実施の形態１に係る波長可変レーザ素子１００では、波長可変動作を実現するために、マイクロヒータによる熱光学効果を利用しているが、波長可変動作を実現するために電流注入によるキャリアプラズマ効果も利用可能にするようにしてもよい。この場合は電流注入により屈折率が下がるため、櫛状反射スペクトルは全体的に短波側にシフトし、それまでスーパーモードが形成されていた波長より短波側に存在する別のスペクトル成分において重なりが生じ、新たなスーパーモードを形成することが可能である。 In the wavelength tunable laser device 100 according to the first embodiment, the thermo-optical effect by the micro heater is used to realize the wavelength tunable operation, but the carrier plasma effect by current injection is implemented to realize the wavelength tunable operation. May also be available. In this case, since the refractive index is lowered by current injection, the comb reflection spectrum is entirely shifted to the short wave side, and an overlap occurs in another spectral component existing on the short wave side from the wavelength at which the super mode was formed. , It is possible to form a new super mode.
　なお、第１の状態で、回折格子層１１ａｂとリング共振器フィルタＲＦ１とで生成される櫛状反射スペクトルのピークが一致した波長で反射率が最大となりレーザ発振が起こるのは、図６に示すとおり、半値全幅の広い第一の櫛状反射スペクトルをシフトさせて、そのピークの１つを半値全幅の狭い第一の櫛状反射スペクトルのピークの１つに一致させたときである。長波側にチューニングする際、リング共振器フィルタＲＦ１によるピークの半値全幅が狭いので、これに対して回折格子層１１ａｂによる半値全幅の広いピークをチューニングしながらシフトさせて一致させたスーパーモードへの遷移を実現するのは容易である。 Note that, in the first state, the reflectance is maximum at a wavelength at which the peaks of the comb reflection spectra generated by the diffraction grating layer 11ab and the ring resonator filter RF1 coincide with each other, and laser oscillation occurs as shown in FIG. As a result, when the first full comb reflection spectrum of full width at half maximum is shifted, and one of its peaks is matched with one of the peaks of the first comb reflection spectrum of narrow full width half maximum. When tuning to the long wave side, since the full width at half maximum of the peak by the ring resonator filter RF1 is narrow, the transition to the supermode where the broad peak of the full width at half maximum by the grating layer 11ab is tuned and shifted while being tuned Is easy to realize.
　同様の理由により、短波側にチューニングする際は、回折格子層１１ａｂのチューニングを固定し、リング共振器フィルタＲＦ１のみマイクロヒータ２５で加熱して、リング共振器フィルタＲＦ１の櫛状反射スペクトルを全体的に長波側にシフトさせる場合も、回折格子層１１ａｂによるピークの半値全幅が広いので、これに対して半値全幅の狭いリング共振器フィルタＲＦ１のピークをチューニングしながらシフトさせて一致させたスーパーモードへの遷移を実現するのは容易である。 For the same reason, when tuning to the short wave side, the tuning of the diffraction grating layer 11ab is fixed, only the ring resonator filter RF1 is heated by the microheater 25, and the comb reflection spectrum of the ring resonator filter RF1 is overall When shifting to the long wave side, the full width at half maximum of the peak due to the diffraction grating layer 11ab is wide, so the peak of the narrow ring resonator filter RF1 with full width at half maximum is tuned to shift to match the supermode It is easy to realize the transition of
　また、本実施の形態１に係る波長可変レーザ素子１００では、スーパーモードの遷移が行われた後、位相調整部１１ｂをチューニングして共振器モードの微調整を行っている。ここで、共振器モードの間の間隔が狭く、回折格子層１１ａｂの櫛状反射スペクトルのピークの半値全幅よりも狭い場合は、回折格子層１１ａｂのピークの中に複数本の共振器モードが存在することも有りうる。しかし、波長可変レーザ素子１００では、リング共振器フィルタＲＦ１の櫛状反射スペクトルのピークの半値全幅の方が、回折格子層１１ａｂの櫛状反射スペクトルのピークの半値全幅よりも狭い。そのため、リング共振器フィルタＲＦ１の櫛状反射スペクトルのピークに、複数本の共振器モードが競合する可能性は低く、一本のみの共振器モードをリング共振器フィルタＲＦ１のピークに一致するように、位相調整部１１ｂをチューニングして共振器モードの微調整を行うのは容易である。 Further, in the wavelength tunable laser device 100 according to the first embodiment, after the transition of the super mode is performed, the phase adjustment unit 11 b is tuned to perform fine adjustment of the resonator mode. Here, when the distance between the resonator modes is narrow and narrower than the full width at half maximum of the peak of the comb-like reflection spectrum of the diffraction grating layer 11ab, a plurality of resonator modes exist among the peaks of the diffraction grating layer 11ab. It is also possible to do. However, in the tunable laser element 100, the full width at half maximum of the comb reflection spectrum of the ring resonator filter RF1 is narrower than the full width at half maximum of the comb reflection spectrum of the diffraction grating layer 11ab. Therefore, it is unlikely that a plurality of resonator modes compete with the peak of the comb-like reflection spectrum of the ring resonator filter RF1 so that only one resonator mode matches the peak of the ring resonator filter RF1. It is easy to tune the phase adjustment unit 11b to finely adjust the resonator mode.
　以上説明したように、本実施の形態１に係る波長可変レーザ素子１００によれば、レーザ光の狭線幅化および安定した単一モード発振を実現できる。 As described above, according to the wavelength tunable laser device 100 according to the first embodiment, it is possible to realize narrowing of the line width of the laser light and stable single mode oscillation.
　本実施の形態１に係る波長可変レーザ素子１００の製造方法の一例について図７ＡＡ～７ＡＣ、７ＢＡ～７ＢＣ、７ＣＡ～ＣＣで説明する。まず基部Ｂを構成するｎ型ＩｎＰ基板上に、有機金属気相成長（Metal　Organic　Chemical　Vapor　Deposition:ＭＯＣＶＤ）法を用いて、ｎ型半導体層１２ａ（下部クラッド層２２ａ）、活性コア層１１ａａ、スペーサ層１２ｂ、回折格子層１１ａｂとなるｐ型ＩｎＧａＡｓＰ層、スペーサ層１２ｅａ（上部クラッド層２２ｃ）の一部となるｐ型ＩｎＰ層を順次堆積する。 An example of a method of manufacturing the wavelength tunable laser 100 according to the first embodiment will be described with reference to FIGS. 7AA to 7AC, 7BA to 7BC, and 7CA to CC. First, an n-type semiconductor layer 12a (lower cladding layer 22a), an active core layer 11aa, and a spacer are formed on the n-type InP substrate constituting the base B by using metal organic chemical vapor deposition (MOCVD). A layer 12b, a p-type InGaAsP layer to be the diffraction grating layer 11ab, and a p-type InP layer to be a part of the spacer layer 12ea (upper cladding layer 22c) are sequentially deposited.
　つづいて、全面にＳｉＮ膜を堆積した後、回折格子装荷型利得部１１ａを形成する位置のＳｉＮ膜に、回折格子のパターンニングを施す。そして、ＳｉＮ膜をマスクとしてエッチングし、ｐ型ＩｎＧａＡｓＰ層に回折格子となる格子溝を形成するとともに、回折格子装荷型利得部１１ａを形成する位置以外の位置のｐ型ＩｎＧａＡｓＰ層を全て取り除く。つづいて、ＳｉＮ膜のマスクを除去した後に、全面にｐ型ＩｎＰ層を再成長する。つづいて、全面にＳｉＮ膜を堆積した後、回折格子装荷型利得部１１ａよりもやや幅広の形状のパターンになるようにＳｉＮ膜にパターンニングを施す。そして、ＳｉＮ膜をマスクとしてエッチングして、ｎ型半導体層１２ａ（下部クラッド層２２ａ）を露出させる。つづいて、ＳｉＮ膜のマスクをそのまま選択成長マスクとして、ＭＯＣＶＤ法により、位相調整部１１ｂおよび第２の導波路部２０における光導波層となる光導波層を成長する。つづいて、ＳｉＮ膜のマスクを除去した後、新たにＳｉＮ膜を堆積し、第１の導波路部１０における導波路部１１および第２の導波路部２０における光導波層に対応するパターンになるようにパターンニングを施す。そして、このＳｉＮ膜をマスクとしてエッチングして、第１の導波路部１０および第２の導波路部２０におけるメサ構造を形成するとともに、ｎ型半導体層１２ａ（下部クラッド層２２ａ）を露出させる。この時、２分岐部２１、アーム部２２、２３、リング状導波路２４に相当する領域は、それらを含む広い領域の形状でエッチングを行う。 Subsequently, after depositing the SiN film on the entire surface, patterning of the diffraction grating is performed on the SiN film at the position where the diffraction grating loaded gain portion 11 a is to be formed. Then, etching is performed using the SiN film as a mask to form a grating groove serving as a diffraction grating in the p-type InGaAsP layer and remove all p-type InGaAsP layers at positions other than the position where the diffraction grating loading type gain portion 11a is formed. Subsequently, after removing the SiN film mask, a p-type InP layer is regrown on the entire surface. Subsequently, after depositing a SiN film on the entire surface, patterning is performed on the SiN film so as to form a pattern having a shape slightly wider than the diffraction grating loaded gain portion 11 a. Then, etching is performed using the SiN film as a mask to expose the n-type semiconductor layer 12a (lower cladding layer 22a). Subsequently, using the mask of the SiN film as it is as a selective growth mask, an optical waveguide layer to be an optical waveguide layer in the phase adjustment portion 11 b and the second waveguide portion 20 is grown by the MOCVD method. Subsequently, after removing the mask of the SiN film, a SiN film is newly deposited to form a pattern corresponding to the optical waveguide layer in the waveguide 11 and the second waveguide 20 in the first waveguide 10. Apply patterning as you like. Then, etching is performed using this SiN film as a mask to form a mesa structure in the first waveguide portion 10 and the second waveguide portion 20, and expose the n-type semiconductor layer 12a (lower cladding layer 22a). At this time, the region corresponding to the bifurcated portion 21, the arm portions 22 and 23, and the ring waveguide 24 is etched in the form of a wide region including them.
　つづいて、直前の工程で用いたＳｉＮ膜マスクを選択成長マスクとして、ＭＯＣＶＤ法を用いて、露出したｎ型半導体層１２ａ（下部クラッド層２２ａ）上に、ｐ型ＩｎＰ埋め込み層１２ｃ、ｎ型ＩｎＰ電流ブロッキング層１２ｄを順次堆積する（図７ＡＡ～７ＡＣ参照。図７ＡＡは、図１のｘｙ平面に平行な面に沿って切断したＡ－Ａ線断面図（利得部）、図７ＡＢは、Ｂ－Ｂ線断面図（位相調整部）、図７ＡＣは、Ｃ－Ｃ線断面図（アーム部の光導波路）をそれぞれ示す。以下の図７ＢＡ～７ＢＣ、図７ＣＡ～７ＣＣにおいても同じである。）。つづいて、ＳｉＮ膜のマスクを除去した後、ＭＯＣＶＤ法を用いて、全面に、スペーサ層１２ｅａ（上部クラッド層２２ｃ）の残りの部分となるｐ型ＩｎＰ層、コンタクト層１２ｅｂを順次堆積する（図７ＡＡ～７ＡＣ参照）。つづいて、位相調整部とアーム部の光導波路のコンタクト層１２ｅｂを除去する工程を行う（図７ＢＢ、７ＢＣ参照）。つづいて、全面にＳｉＮ膜を堆積した後、素子分離用のトレンチ溝に対応するパターンならびに２分岐部２１、アーム部２２、２３、リング状導波路２４に相当する導波路のパターンニングを施す。そして、このＳｉＮ膜をマスクとしてエッチングを行い、トレンチ構造および第２の導波路部２０におけるハイメサ導波路を形成する（図７ＢＣ参照）。このエッチングでは、たとえば基部Ｂに到る深さまで行う。つづいて、ＳｉＮ膜マスクを除去した後、全面に再びＳｉＮ膜を堆積し（図７ＣＡ～７ＣＣ参照）、回折格子装荷型利得部１１ａに対応する部分に開口部を形成して、ＳｉＮ膜を保護膜とし全面にＡｕＺｎを含む導電膜を堆積した後、導電膜をパターンニングすることによってｐ側電極１３を形成する（図７ＣＡ参照）。一方、基板の裏面にはＡｕＧｅＮｉを含むｎ側電極３０を形成する。さらに、ＳｉＮ保護膜１７を形成した後、たとえばＴｉからなる屈折率変化用のマイクロヒータ１４、１５、２５を形成する。最後に、基板を波長可変レーザ素子１００が複数並んだバー状に劈開し、第１の導波路部１０の回折格子装荷型利得部１１ａ側端面、アーム部２２、２３のスルーポートがある端面に反射防止膜をコートしたのち、各波長可変レーザ素子１００ごとに素子分離することにより、波長可変レーザ素子１００が完成する。 Subsequently, using the SiN film mask used in the previous step as the selective growth mask, the p-type InP buried layer 12c and n-type InP are exposed on the exposed n-type semiconductor layer 12a (lower cladding layer 22a) using the MOCVD method. A current blocking layer 12d is sequentially deposited (see FIGS. 7AA to 7AC. FIG. 7AA is a sectional view taken along a line AA (a gain portion) cut along a plane parallel to the xy plane of FIG. B line sectional view (phase adjustment unit) and FIG. 7AC respectively show CC sectional view (optical waveguide of the arm unit) The same applies to FIGS. 7BA to 7BC and FIGS. 7CA to 7CC below. Subsequently, the mask of the SiN film is removed, and a p-type InP layer and a contact layer 12eb to be the remaining portion of the spacer layer 12ea (upper cladding layer 22c) are sequentially deposited on the entire surface by MOCVD (see FIG. 7AA to 7AC). Subsequently, the step of removing the contact layer 12eb of the optical waveguides of the phase adjustment portion and the arm portion is performed (see FIGS. 7BB and 7BC). Subsequently, a SiN film is deposited on the entire surface, and then a pattern corresponding to a trench for element isolation and a waveguide corresponding to the bifurcated portion 21, the arm portions 22 and 23, and the ring waveguide 24 are patterned. Then, etching is performed using this SiN film as a mask to form a trench structure and a high mesa waveguide in the second waveguide portion 20 (see FIG. 7BC). In this etching, for example, the depth is reached to the base B. Subsequently, after removing the SiN film mask, a SiN film is deposited again on the entire surface (see FIGS. 7CA to 7CC), and an opening is formed in a portion corresponding to the diffraction grating loading type gain portion 11a to protect the SiN film. After depositing a conductive film containing AuZn as a film over the entire surface, the conductive film is patterned to form the p-side electrode 13 (see FIG. 7CA). On the other hand, an n-side electrode 30 containing AuGeNi is formed on the back surface of the substrate. Furthermore, after the SiN protective film 17 is formed, micro-heaters 14, 15, 25 made of, for example, Ti for changing the refractive index are formed. Finally, the substrate is cleaved into a bar shape in which a plurality of variable wavelength laser elements 100 are arranged, and the end face of the first waveguide 10 on the side of the diffraction grating loaded gain 11a and the end of the arm 22 and 23 where the through port is located. After coating the anti-reflection film, the wavelength tunable laser device 100 is separated to complete the wavelength tunable laser device 100.
　なお、上記実施の形態１に係る波長可変レーザ素子１００では、アーム部２２、２３はリング状導波路２４と近接することでリング状導波路２４と光学的に結合しているが、図８に示すようにアーム部２２、２３とリング状導波路２４とを導波路部２６、２７により光学的に結合してもよい。 In the wavelength tunable laser device 100 according to the first embodiment, the arm portions 22 and 23 are optically coupled to the ring waveguide 24 by coming close to the ring waveguide 24. As shown, the arm portions 22 and 23 and the ring waveguide 24 may be optically coupled by the waveguide portions 26 and 27.
　図９Ａは、導波路部の構造を説明する図である。図９Ａは、図８のＡ－Ａ線断面の一部を示す図である。上述したように、アーム部２２は、基部Ｂ上に、ｎ型ＩｎＰからなる下部クラッド層２２ａ、ＩｎＧａＡｓＰからなる光導波層２２ｂ、およびｐ型ＩｎＰからなる上部クラッド層２２ｃがこの順で積層して構成されたハイメサ導波路構造を有している。同様に、アーム部２３は、基部Ｂ上に、ｎ型ＩｎＰからなる下部クラッド層２３ａ、ＩｎＧａＡｓＰからなる光導波層２３ｂ、およびｐ型ＩｎＰからなる上部クラッド層２３ｃがこの順で積層して構成されたハイメサ導波路構造を有している。さらに、導波路部２６は、基部Ｂ上に、ｎ型ＩｎＰからなる下部クラッド層２６ａ、ＩｎＧａＡｓＰからなる光導波層２６ｂ、およびｐ型ＩｎＰからなる上部クラッド層２６ｃがこの順で積層して構成されたハイメサ導波路構造の多モード干渉型（ＭＭＩ）導波路である。なお、導波路部２７も導波路部２６と同じ構造のハイメサ導波路構造のＭＭＩ導波路である。 FIG. 9A is a view for explaining the structure of the waveguide section. FIG. 9A is a view showing a part of a cross section along line AA of FIG. As described above, in the arm portion 22, the lower cladding layer 22a made of n-type InP, the optical waveguide layer 22b made of InGaAsP, and the upper cladding layer 22c made of p-type InP are stacked in this order on the base B. It has the high mesa waveguide structure comprised. Similarly, the arm portion 23 is configured by laminating a lower cladding layer 23a of n-type InP, an optical waveguide layer 23b of InGaAsP, and an upper cladding layer 23c of p-type InP in this order on the base B. Has a high mesa waveguide structure. Further, the waveguide section 26 is configured by laminating a lower cladding layer 26a of n-type InP, an optical waveguide layer 26b of InGaAsP, and an upper cladding layer 26c of p-type InP in this order on the base B. It is a multi-mode interference (MMI) waveguide of high mesa waveguide structure. The waveguide 27 is also an MMI waveguide having a high mesa waveguide structure having the same structure as the waveguide 26.
　このように、アーム部２２、２３とリング状導波路２４とを導波路部２６、２７により光学的に結合することにより、アーム部２２、２３とリング状導波路２４との光学結合をより容易に実現できるとともに、結合係数κの調整をより容易に行うことができる。 Thus, optical coupling between the arm portions 22 and 23 and the ring waveguide 24 is facilitated by optically coupling the arm portions 22 and 23 and the ring waveguide 24 by the waveguide portions 26 and 27. In addition, the coupling coefficient 調整 can be adjusted more easily.
　アーム部２２、２３とリング状導波路２４とを光学的に結合する導波路部はＭＭＩ導波路に限らず、たとえば図９Ｂに示すような方向性結合型の導波路部２６Ａでもよい。導波路部２６Ａは、基部Ｂ上に、ｎ型ＩｎＰからなる下部クラッド層２６Ａａ、ＩｎＧａＡｓＰからなる光導波層２６Ａｂ、およびｐ型ＩｎＰからなる上部クラッド層２６Ａｃがこの順で積層して構成されたハイメサ導波路構造を有するが、上部クラッド層２６Ａｃが導波路部２６における上部クラッド層２６ｃよりも薄く形成されているため、方向性結合型導波路として機能する。 The waveguide section for optically coupling the arm sections 22 and 23 and the ring waveguide 24 is not limited to the MMI waveguide, and may be, for example, a directional coupling type waveguide section 26A as shown in FIG. 9B. The waveguide portion 26A is a high mesa formed by laminating a lower cladding layer 26Aa of n-type InP, an optical waveguide layer 26Ab of InGaAsP, and an upper cladding layer 26Ac of p-type InP in this order on the base B. Although having the waveguide structure, since the upper cladding layer 26Ac is thinner than the upper cladding layer 26c in the waveguide portion 26, it functions as a directional coupling waveguide.
　なお、方向性結合型導波路とＭＭＩ導波路とを比較すると、アーム部に沿った導波路の幅の変化に対するアーム部とリング状導波路との結合係数の変化は、方向性結合型導波路の場合の方がＭＭＩ導波路の場合よりも小さい。したがって、ＭＭＩ導波路で導波路部を形成した場合、アーム部に沿った導波路の幅の変更により結合係数をより大きく変化させることができる。 When comparing the directional coupling waveguide with the MMI waveguide, the change in the coupling coefficient between the arm and the ring-shaped waveguide due to the change in the width of the waveguide along the arm is a directional coupling waveguide. Is smaller than that of the MMI waveguide. Therefore, when the waveguide portion is formed of the MMI waveguide, the coupling coefficient can be changed more largely by changing the width of the waveguide along the arm portion.
　また、上記実施の形態１に係る波長可変レーザ素子１００では、第１の導波路部１０は第１の導波路構造としての埋込み導波路構造を有するが、第１の導波路部は第１の導波路構造としてのリッジ導波路構造を有していてもよい。 In the wavelength tunable laser device 100 according to the first embodiment, the first waveguide unit 10 has the embedded waveguide structure as the first waveguide structure, but the first waveguide unit is the first waveguide structure. It may have a ridge waveguide structure as a waveguide structure.
　図１０は、リッジ導波路構造を有する第１の導波路部の例を説明する図である。図１０は、第１の導波路部１０Ａにおける、位相調整部１１Ａｂが含まれる部分を、図１のｘｙ平面に沿って切断した断面図である。第１の導波路部１０Ａは、位相調整部１１Ａｂが含まれる部分において、ｐ型ＩｎＰからなる下部クラッド層１２Ａａと、ＩｎＧａＡｓＰからなる光導波層である位相調整部１１Ａｂと、ｎ型ＩｎＰからなる上部リッジクラッド層１２Ａｂとが順次積層した構造を有する。このように、第１の導波路部はリッジ導波路構造を有していてもよい。 FIG. 10 is a diagram for explaining an example of the first waveguide section having a ridge waveguide structure. FIG. 10 is a cross-sectional view of a portion of the first waveguide unit 10A including the phase adjustment unit 11Ab cut along the xy plane of FIG. The first waveguide portion 10A is a portion including the phase adjustment portion 11Ab, the lower cladding layer 12Aa made of p-type InP, the phase adjustment portion 11Ab being an optical waveguide layer made of InGaAsP, and the upper portion made of n-type InP It has a structure in which the ridge cladding layer 12Ab is sequentially stacked. Thus, the first waveguide portion may have a ridge waveguide structure.
（実施の形態２）
　図１１は、実施の形態２に係る波長可変レーザ素子の模式的な斜視図である。図１１に示すように、本実施の形態２に係る波長可変レーザ素子１００Ａは、図１に示す実施の形態１に係る波長可変レーザ素子１００と、基部Ｂ上に形成された半導体増幅器（ＳＯＡ）１０１とを備えている。ＳＯＡ１０１は、第１の導波路部と同様の材料、構造からなる活性コア層を備える埋込み導波路構造を有する。ただし、回折格子層は設けられていない。 Second Embodiment
FIG. 11 is a schematic perspective view of the wavelength tunable laser device according to the second embodiment. As shown in FIG. 11, the tunable laser device 100A according to the second embodiment includes the tunable laser device 100 according to the first embodiment shown in FIG. 1 and a semiconductor amplifier (SOA) formed on a base B. And 101. The SOA 101 has a buried waveguide structure including an active core layer made of the same material and structure as the first waveguide portion. However, no diffraction grating layer is provided.
　波長可変レーザ素子１００とＳＯＡ１０１とは、不図示の空間結合光学系で光学的に結合している。波長可変レーザ素子１００から出力されたレーザ光Ｌ１は、ＳＯＡ１０１に入力される。ＳＯＡ１０１はレーザ光Ｌ１を光増幅してレーザ光Ｌ２として出力する。本実施の形態２に係る波長可変レーザ素子１００Ａによれば、実施の形態１に係る波長可変レーザ素子１００と同様に、レーザ光の狭線幅化および安定した単一モード発振を実現し、さらにＳＯＡ１０１を備えているので、レーザ光をより高いパワーで出力できる。 The tunable laser element 100 and the SOA 101 are optically coupled by a space coupling optical system (not shown). The laser beam L1 output from the wavelength tunable laser device 100 is input to the SOA 101. The SOA 101 optically amplifies the laser beam L1 and outputs it as a laser beam L2. Like the wavelength tunable laser device 100 according to the first embodiment, the wavelength tunable laser device 100A according to the second embodiment realizes narrowing of the width of the laser beam and stable single mode oscillation, and further, Since the SOA 101 is provided, laser light can be output at higher power.
　なお、本実施の形態２に係る波長可変レーザ素子１００Ａでは、波長可変レーザ素子１００とＳＯＡ１０１とは不図示の空間結合光学系で光学的に結合しているが、波長可変レーザ素子１００とＳＯＡ１０１とが共通の基部Ｂ上にモノリシックに形成されていてもよい。 In the tunable laser device 100A according to the second embodiment, the tunable laser device 100 and the SOA 101 are optically coupled by a space coupling optical system (not shown). However, the tunable laser device 100 and the SOA 101 May be monolithically formed on the common base B.
（実施の形態３）
　つぎに、実施の形態３について説明する。本実施の形態３では、第２の導波路部がシリコン（Ｓｉ）フォトニクス導波路からなるなど点で実施の形態１、２と異なる。 Third Embodiment
Next, the third embodiment will be described. The third embodiment is different from the first and second embodiments in that the second waveguide portion is formed of a silicon (Si) photonic waveguide.
　図１２Ａ、１２Ｂは、実施の形態３に係る波長可変レーザ素子の模式図である。図１２Ａは斜視図であり、図１２Ｂは後に説明する断面図である。波長可変レーザ素子２００は、１．５５μｍ帯でレーザ発振し、レーザ光を出力するように構成されている。波長可変レーザ素子２００は、第１の導波路部２１０と第２の導波路部２２０とを備えている。 12A and 12B are schematic views of a wavelength tunable laser device according to a third embodiment. 12A is a perspective view, and FIG. 12B is a cross-sectional view to be described later. The wavelength tunable laser device 200 is configured to emit a laser beam by performing laser oscillation in a 1.55 μm band. The wavelength tunable laser device 200 includes a first waveguide section 210 and a second waveguide section 220.
　第１の導波路部２１０は、導波路部２１１と、半導体積層部２１２と、ｎ側電極２１３と、マイクロヒータ２１５とを備えている。導波路部２１１は、半導体積層部２１２内にｚ方向に延伸するように形成されている。第１の導波路部２１０内には、利得部２１１ａとＤＢＲ型の回折格子層２１１ｂが配置されている。半導体積層部２１２は、半導体層が積層して構成されており、導波路部２１１に対してクラッド部の機能等を備える。利得部２１１ａは、実施の形態１における活性コア層１１ａａと同一の材料からなる多重量子井戸構造と光閉じ込め層とを有する。また、回折格子層２１１ｂは、実施の形態１における回折格子層１１ａｂと同一の材料からなる標本化回折格子で構成されている。また、半導体積層部２１２は、利得部２１１ａが含まれる部分においては、実施の形態１における半導体積層部１２の回折格子装荷型利得部１１ａが含まれる部分と同様の材料、構造からなるが、回折格子層１１ａｂがｐ型ＩｎＰ層に置き換えられる点と、ｙ方向において利得部２１１ａを挟んでｐ型半導体層とｎ型半導体層との位置が逆転した積層構造を有する点とで異なる。また、半導体積層部２１２は、回折格子層２１１ｂが含まれる部分においては、実施の形態１における半導体積層部１２の位相調整部１１ｂが含まれる部分と同様の材料、構造からなるが、ｙ方向において位相調整部１１ｂを挟んでｐ型半導体層とｎ型半導体層との位置が逆転した積層構造を有する点とで異なる。第１の導波路部２１０は第１の導波路構造としての埋込み導波路構造を有する。 The first waveguide unit 210 includes a waveguide unit 211, a semiconductor laminated unit 212, an n-side electrode 213, and a micro heater 215. The waveguide portion 211 is formed to extend in the z direction in the semiconductor laminated portion 212. In the first waveguide portion 210, a gain portion 211a and a DBR diffraction grating layer 211b are disposed. The semiconductor laminated portion 212 is configured by laminating semiconductor layers, and has a function of a cladding portion and the like with respect to the waveguide portion 211. The gain portion 211a has a multiple quantum well structure made of the same material as that of the active core layer 11aa in the first embodiment, and a light confinement layer. Further, the diffraction grating layer 211 b is configured by a sampling diffraction grating made of the same material as the diffraction grating layer 11 ab in the first embodiment. In the portion including the gain portion 211a, the semiconductor multilayer portion 212 is made of the same material and structure as the portion including the diffraction grating loaded type gain portion 11a of the semiconductor multilayer portion 12 in the first embodiment. The difference is that the lattice layer 11ab is replaced by a p-type InP layer, and that it has a laminated structure in which the positions of the p-type semiconductor layer and the n-type semiconductor layer are reversed with the gain portion 211a in the y direction. In the portion including the diffraction grating layer 211b, the semiconductor multilayer portion 212 is made of the same material and structure as the portion including the phase adjustment portion 11b of the semiconductor multilayer portion 12 in the first embodiment. It differs in that it has a laminated structure in which the positions of the p-type semiconductor layer and the n-type semiconductor layer are reversed with the phase adjustment portion 11 b interposed therebetween. The first waveguide portion 210 has a buried waveguide structure as a first waveguide structure.
　ｎ側電極２１３は、半導体積層部２１２上において、利得部２１１ａに沿うように配置されている。なお、半導体積層部２１２にはＳｉＮ保護膜が形成されており、ｎ側電極２１３はＳｉＮ保護膜に形成された開口部を介して半導体積層部２１２に接触している。第１の屈折率変化器としてのマイクロヒータ２１５は、半導体積層部２１２のＳｉＮ保護膜上において、回折格子層２１１ｂに沿うように配置されている。また、半導体積層部２１２のｎ側電極２１３が形成された面と反対側の面には、不図示のｐ側電極が形成されている。 The n-side electrode 213 is disposed on the semiconductor multilayer portion 212 along the gain portion 211 a. A SiN protective film is formed on the semiconductor laminated portion 212, and the n-side electrode 213 is in contact with the semiconductor laminated portion 212 through an opening formed in the SiN protective film. The microheater 215 as the first refractive index changer is disposed on the SiN protective film of the semiconductor multilayer portion 212 so as to be along the diffraction grating layer 211b. In addition, a p-side electrode (not shown) is formed on the surface of the semiconductor laminate portion 212 opposite to the surface on which the n-side electrode 213 is formed.
　つぎに、第２の導波路部２２０について説明する。第２の導波路部２２０は、ＳＯＩ（Silicon　On　Insulator）基板Ｓで構成されている。第２の導波路部２２０は、２分岐部２２１と、アーム部２２２、２２３と、リング状導波路２２４と、マイクロヒータ２２５、２２９と、位相調整部２２８と、ＳｉＯ２からなるオーバークラッド層２３０とを備えている。 Next, the second waveguide section 220 will be described. The second waveguide unit 220 is configured of an SOI (Silicon On Insulator) substrate S. The second waveguide portion 220 includes a bifurcated portion 221, arm portions 222 and 223, a ring-shaped waveguide 224, microheaters 225 and 229, a phase adjusting portion 228, and an overcladding layer 230 made of SiO 2. And have.
　２分岐部２２１は、１×２型のＭＭＩ導波路２２１ａを含む１×２型の分岐型導波路で構成され、２ポート側が２つのアーム部２２２、２２３のそれぞれに接続されるとともに１ポート側が位相調整部２２８を介して第１の導波路部２１０側に接続されている。２分岐部２２１により、２つのアーム部２２２、２２３は、その一端が統合され、回折格子層２１１ｂと光学的に結合される。位相調整部２２８の第１の導波路部２１０側には、第１の導波路部２１０に向かって幅が細くなるテーパ部が形成されている。テーパ部の外周には、ＳｉＯ２より屈折率の高い、たとえばＳｉＮからなるオーバークラッド層が形成されており、スポットサイズ変換器構造となっている。 The bifurcated portion 221 is composed of a 1 × 2 type branched waveguide including a 1 × 2 type MMI waveguide 221a, and the 2 port side is connected to each of the two arm portions 222 and 223 and the 1 port side is It is connected to the side of the first waveguide unit 210 via the phase adjustment unit 228. One end of the two arm portions 222 and 223 is integrated by the bifurcated portion 221, and is optically coupled to the diffraction grating layer 211b. On the side of the first waveguide section 210 of the phase adjustment section 228, a tapered section whose width is narrowed toward the first waveguide section 210 is formed. An overcladding layer having a refractive index higher than that of SiO 2 , for example, made of SiN is formed on the outer periphery of the tapered portion, forming a spot size converter structure.
　アーム部２２２、２２３は、いずれもｚ方向に延伸し、リング状導波路２２４を挟むように配置されている。アーム部２２２、２２３はリング状導波路２２４と近接し、いずれも同一の結合係数κでリング状導波路２２４と光学的に結合している。アーム部２２２、２２３とリング状導波路２２４とは、リング共振器フィルタＲＦ２を構成している。また、リング共振器フィルタＲＦ２と２分岐部２２１とは、反射ミラーＭ２を構成している。第２の屈折率変化器としてのマイクロヒータ２２５はリング状であり、オーバークラッド層２３０上でリング状導波路２２４の直上に配置されている。また、マイクロヒータ２２９は、オーバークラッド層２３０上に位相調整部２２８に沿って配置されている。 Each of the arm portions 222 and 223 extends in the z direction and is disposed so as to sandwich the ring waveguide 224. The arm portions 222 and 223 are in close proximity to the ring waveguide 224 and both are optically coupled to the ring waveguide 224 with the same coupling coefficient κ. The arm units 222 and 223 and the ring waveguide 224 constitute a ring resonator filter RF2. The ring resonator filter RF2 and the bifurcated portion 221 constitute a reflection mirror M2. The microheater 225 as a second refractive index changer is ring-shaped, and is disposed on the over cladding layer 230 directly above the ring-shaped waveguide 224. Further, the microheater 229 is disposed on the over cladding layer 230 along the phase adjustment unit 228.
　図１２Ｂは、第２の導波路部２２０のうちアーム部２２２を、図１２Ａのｘｙ平面に平行な平面に沿って切断した断面図である。図１２Ｂに示すように、アーム部２２２は、ＳＯＩ基板ＳのＳｉの支持基板からなる支持層２２２ａａと、支持層２２２ａａ上に位置するＳｉＯ２からなるＢＯＸ（Buried　OXide）層２２２ａｂとで構成された下層２２２ａと、ＢＯＸ層２２２ａｂに位置するＳｉからなるデバイス層２２２ｂと、からなるハイメサ導波路構造を有する。デバイス層２２２ｂが光導波層として機能し、ハイメサ導波路構造はオーバークラッド層２３０で覆われている。なお、第２の導波路部２２０のその他の構成要素である２分岐部２２１、アーム部２２３、リング状導波路２２４、位相調整部２２８も同様にハイメサ導波路構造を有している。すなわち、第２の導波路部２２０は第１の導波路部２１０の第１の導波路構造とは異なる第２の導波路構造を有する。 FIG. 12B is a cross-sectional view of the arm portion 222 of the second waveguide portion 220 taken along a plane parallel to the xy plane of FIG. 12A. As shown in FIG. 12B, the arm portion 222 is composed of a support layer 222aa made of a Si support substrate of the SOI substrate S, and a BOX (Buried OXide) layer 222ab made of SiO 2 located on the support layer 222aa. It has a high mesa waveguide structure comprising a lower layer 222a and a device layer 222b made of Si located in the BOX layer 222ab. The device layer 222 b functions as an optical waveguide layer, and the high mesa waveguide structure is covered with the over cladding layer 230. The other components of the second waveguide 220, that is, the 2-branch 221, the arm 223, the ring waveguide 224, and the phase adjuster 228 also have a high mesa waveguide structure. That is, the second waveguide part 220 has a second waveguide structure different from the first waveguide structure of the first waveguide part 210.
　また、第１の導波路部２１０は、ゲインチップとして公知の方法で別途作製され、第２の導波路部２２０を構成するＳＯＩ基板Ｓにおいてデバイス層とＢＯＸ層と支持基板の一部とが除去されることにより形成された凹部ＣＣに実装されている。このとき、第１の導波路部２１０の利得部２１１ａと、第２の導波路部２２０の位相調整部２２８とはバットジョイント接続されている。 In addition, the first waveguide section 210 is separately manufactured by a known method as a gain chip, and the device layer, the BOX layer, and part of the support substrate are removed in the SOI substrate S constituting the second waveguide section 220. Mounted in the concave portion CC formed by At this time, the gain portion 211 a of the first waveguide portion 210 and the phase adjustment portion 228 of the second waveguide portion 220 are butt-jointed.
　第１の導波路部２１０と第２の導波路部２２０は、互いに光学的に接続された回折格子層２１１ｂと反射ミラーＭ２とにより構成されるレーザ共振器Ｃ２を構成している。利得部２１１ａと位相調整部２２８とはレーザ共振器Ｃ２内に配置される。 The first waveguide section 210 and the second waveguide section 220 constitute a laser resonator C2 configured of a diffraction grating layer 211b optically connected to each other and a reflection mirror M2. The gain unit 211a and the phase adjustment unit 228 are disposed in the laser resonator C2.
　この波長可変レーザ素子２００においても、実施の形態１、２と同様に、回折格子層２１１ｂは、略所定の波長間隔で略周期的な反射特性を有する第一の櫛状反射スペクトルを生成する。また、リング共振器フィルタＲＦ２は、第一の櫛状反射スペクトルのスペクトル成分の半値全幅よりも狭い半値全幅のピークを有し、第一の櫛状反射スペクトルの波長間隔とは異なる波長間隔で略周期的な反射特性を有する第二の櫛状反射スペクトルを生成する。そして、第一の櫛状反射スペクトルのピーク、第二の櫛状反射スペクトルのピーク、およびレーザ共振器Ｃ２の共振器モードの一つが一致した波長でレーザ発振する。また、レーザ共振器Ｃ２の共振器モードのモード間の間隔が、第１の櫛状反射スペクトルのスペクトル成分の半値全幅よりも狭い。さらには、レーザ共振器Ｃ２内の光帰還は、回折格子層２１１ｂから、２分岐部２２１、リング共振器フィルタＲＦ２のアーム部２２２、２２３のうちの一方、リング状導波路２２４、アーム部２２２、２２３のうちの他方、２分岐部２２１を順に経由して回折格子層２１１ｂに帰還する経路で行われ、かつ１回の光帰還中にリング状導波路２２４内を周回する。これにより、本実施の形態３に係る波長可変レーザ素子２００によれば、光帰還長が長くなるので、実効的なレーザ光の狭線幅化が可能となる。また、実施の形態１、２と同様に、安定した単一モード発振を実現できる。 Also in this wavelength tunable laser device 200, as in the first and second embodiments, the diffraction grating layer 211b generates a first comb-like reflection spectrum having substantially periodic reflection characteristics at substantially predetermined wavelength intervals. In addition, the ring resonator filter RF2 has a peak with a full width at half maximum narrower than the full width at half maximum of the spectral component of the first comb-like reflection spectrum, and has a substantially different wavelength interval from the wavelength interval of the first comb-like reflection spectrum. A second comb-like reflection spectrum having periodic reflection characteristics is generated. Then, laser oscillation occurs at a wavelength at which the peak of the first comb reflection spectrum, the peak of the second comb reflection spectrum, and one of the resonator modes of the laser resonator C2 coincide with each other. In addition, the spacing between the modes of the resonator modes of the laser resonator C2 is narrower than the full width at half maximum of the spectral component of the first comb reflection spectrum. Furthermore, the optical feedback in the laser resonator C2 is from the diffraction grating layer 211b, one of the two branches 221, one of the arms 222 and 223 of the ring resonator filter RF2, the ring waveguide 224, the arm 222, The other of 223 is conducted in a path which is returned to the diffraction grating layer 211 b via the 2-branch portion 221 in order, and is circulated in the ring waveguide 224 during one optical feedback. As a result, according to the wavelength tunable laser device 200 according to the third embodiment, the optical feedback length becomes long, and therefore it is possible to effectively narrow the line width of the laser beam. Further, as in the first and second embodiments, stable single mode oscillation can be realized.
　また、波長可変レーザ素子２００においても、レーザ発振波長については、実施の形態１、２の場合と同様に、回折格子層２１１ｂに対するマイクロヒータ２１５とリング共振器フィルタＲＦ２に対するマイクロヒータ２２５とにより第一の櫛状反射スペクトルと第二の櫛状反射スペクトルとをそれぞれチューニングすることで粗調、位相調整部２２８に対するマイクロヒータ２２９により共振器長をチューニングすることで微調を行うことにより、波長可変動作が実現される。 Also in the wavelength tunable laser device 200, the laser oscillation wavelength is the same as in the first and second embodiments by the microheater 215 for the diffraction grating layer 211b and the microheater 225 for the ring resonator filter RF2. Tuning by adjusting the comb-like reflection spectrum and the second comb-like reflection spectrum by tuning the resonator length with the micro heater 229 for the coarse adjustment by the micro heater 229 for the phase adjustment unit 228. To be realized.
　本実施の形態３に係る波長可変レーザ素子２００によれば、実施の形態１、２と同様に、レーザ光の狭線幅化および安定した単一モード発振を実現できる。さらに、波長可変レーザ素子２００は、第２の導波路部２２０がＳｉフォトニクス導波路で構成されている。Ｓｉフォトニクス導波路は、導波路閉じ込めが強いため曲げに強い。したがって、直径の小さなリング状導波路２２４を容易に実現できる。これにより、ＦＳＲの大きいリング状導波路２２４が実現でき、リング共振器フィルタＲＦ２の設計自由度が向上するということを意味する。これにより、波長可変レーザ素子２００によれば、フットプリントが小さくコンパクトであり、且つサイドモード抑圧比の高いレーザ光を出力することができる。 According to the wavelength tunable laser 200 of the third embodiment, as in the first and second embodiments, the line width reduction of the laser light and the stable single mode oscillation can be realized. Furthermore, in the wavelength tunable laser device 200, the second waveguide portion 220 is configured of a Si photonics waveguide. The Si photonics waveguide is resistant to bending because the waveguide confinement is strong. Therefore, the ring waveguide 224 with a small diameter can be easily realized. This means that a ring waveguide 224 with a large FSR can be realized, and the design freedom of the ring resonator filter RF2 is improved. Thus, according to the wavelength tunable laser device 200, it is possible to output a laser beam having a small footprint and compact size, and a high side mode suppression ratio.
　本実施の形態３に係る波長可変レーザ素子２００の製造方法の一例について説明する。まず、ＳＯＩ基板上に、フォトリソグラフィを用いて第２の導波路部２２０におけるＳｉ導波路パターンを転写する。具体的には、例えばＨＢｒガスを用いてデバイス層およびＢＯＸ層をエッチングし、チャネル導波路構造を得る。ここで、エッチングにより生じた導波路の側面粗さを低減する目的で、水蒸気を用いない熱酸化を行っても良い。つづいて、全面にＳｉＮ層を堆積し、フォトリソグラフィとエッチングとにより、上述したスポットサイズ変換構造の部分にＳｉＮからなるオーバークラッド層を形成する。さらに、オーバークラッド層２３０となるＳｉＯ２層を全面に堆積する。 An example of a method of manufacturing the wavelength tunable laser 200 according to the third embodiment will be described. First, the Si waveguide pattern in the second waveguide portion 220 is transferred onto the SOI substrate using photolithography. Specifically, the device layer and the BOX layer are etched using, for example, HBr gas to obtain a channel waveguide structure. Here, thermal oxidation without using water vapor may be performed in order to reduce the side roughness of the waveguide generated by the etching. Subsequently, a SiN layer is deposited on the entire surface, and an overcladding layer made of SiN is formed on the portion of the spot size conversion structure described above by photolithography and etching. Further, an SiO 2 layer to be an overcladding layer 230 is deposited on the entire surface.
　つづいて、リング状導波路２２４上と位相調整部２２８上に、たとえばＴｉからなるマイクロヒータ２２５、２２９を形成する。つづいて、別途作製したゲインチップである第１の導波路部２１０が実装される凹部ＣＣに相当する部分のオーバークラッド層２３０と支持基板の一部をエッチングにより除去し、凹部ＣＣを形成する。この部分に第１の導波路部２１０をフリップチップボンディングにより実装する。これにより波長可変レーザ素子２００が完成する。 Subsequently, micro-heaters 225 and 229 made of Ti, for example, are formed on the ring waveguide 224 and the phase adjustment portion 228. Subsequently, the over cladding layer 230 and a part of the support substrate in a portion corresponding to the concave portion CC on which the first waveguide portion 210 which is a separately manufactured gain chip is mounted is removed by etching to form the concave portion CC. The first waveguide portion 210 is mounted on this portion by flip chip bonding. Thus, the wavelength tunable laser device 200 is completed.
　ところで、ゲインチップである第１の導波路部２１０は、上述したものに限定されない。たとえば、ＩｎＰまたはＧａＡｓ基板上に量子井戸構造または量子ドット構造を有するものであってもよい。量子井戸構造を構成する化合物半導体材料としては、ＩｎＧａＡｓ、ＩｎＧａＡｓＮ、ＡｌＩｎＧａＡｓ、ＩｎＧａＡｓなどのＩＩＩ－Ｖ族化合物半導体を使用できる。また、量子ドット構造を構成する化合物半導体材料としては、ＩｎＡｓ、ＩｎＧａＡ、またはその他のＩＩＩ－Ｖ族化合物半導体を使用できる。 By the way, the 1st waveguide part 210 which is a gain chip is not limited to what was mentioned above. For example, it may have a quantum well structure or a quantum dot structure on an InP or GaAs substrate. As a compound semiconductor material forming the quantum well structure, III-V group compound semiconductors such as InGaAs, InGaAsN, AlInGaAs, InGaAs, etc. can be used. InAs, InGaA, or other III-V compound semiconductor can be used as a compound semiconductor material forming the quantum dot structure.
（実施の形態４）
　つぎに、実施の形態４について説明する。本実施の形態４でも、実施の形態３と同様に第２の導波路部がシリコンＳｉフォトニクス導波路からなるが、第２の導波路部に回折格子が設けられる点と、第１の導波路部がＵ字形状の導波路を備える点などで実施の形態３と異なる。 Embodiment 4
Next, the fourth embodiment will be described. In the fourth embodiment, as in the third embodiment, although the second waveguide portion is made of a silicon Si photonics waveguide, the point that a diffraction grating is provided in the second waveguide portion, and the first waveguide The third embodiment differs from the third embodiment in that the section includes a U-shaped waveguide.
　図１３は、実施の形態４に係る波長可変レーザ素子の模式な斜視図である。波長可変レーザ素子３００は、１．５５μｍ帯でレーザ発振し、レーザ光を出力するように構成されている。波長可変レーザ素子３００は、第１の導波路部３１０と第２の導波路部３２０とを備えている。 FIG. 13 is a schematic perspective view of the wavelength tunable laser device according to the fourth embodiment. The tunable laser device 300 is configured to emit a laser beam by performing laser oscillation in a 1.55 μm band. The wavelength tunable laser device 300 includes a first waveguide section 310 and a second waveguide section 320.
　第１の導波路部３１０は、導波路部３１１と、半導体積層部３１２と、ｎ側電極３１３とを備えている。導波路部３１１は、半導体積層部３１２内においてその一部がｚ方向に延伸するようなＵ字形状に形成されている。第１の導波路部３１０内には、利得部３１１ａと光導波層３１１ｂとが配置されている。半導体積層部３１２は、半導体層が積層して構成されており、導波路部３１１に対してクラッド部の機能等を備える。利得部３１１ａは、ｚ方向に延伸しており、実施の形態１における活性コア層１１ａａと同一の材料からなる多重量子井戸構造を有する。また、光導波層３１１ｂは、実施の形態１における位相調整部１１ｂと同一の材料からなり、利得部３１１ａとともにＵ字形状を形成している。また、半導体積層部３１２は、利得部３１１ａが含まれる部分においては、実施の形態１における半導体積層部１２の回折格子装荷型利得部１１ａが含まれる部分と同様の材料、構造からなるが、回折格子層１１ａｂがｐ型ＩｎＰ層に置き換えられる点と、ｙ方向において利得部３１１ａを挟んでｐ型半導体層とｎ型半導体層との位置が逆転した積層構造を有する点とで異なる。また、半導体積層部３１２は、光導波層３１１ｂが含まれる部分においては、実施の形態１における半導体積層部１２の位相調整部１１ｂが含まれる部分と同様の材料、構造からなるが、ｙ方向において利得部３１１ａを挟んでｐ型半導体層とｎ型半導体層との位置が逆転した積層構造を有する点とで異なる。第１の導波路部３１０は第１の導波路構造としての埋込み導波路構造を有する。 The first waveguide unit 310 includes a waveguide unit 311, a semiconductor multilayer unit 312, and an n-side electrode 313. The waveguide portion 311 is formed in a U-shape in which a part thereof extends in the z direction in the semiconductor laminated portion 312. In the first waveguide portion 310, a gain portion 311a and an optical waveguide layer 311b are disposed. The semiconductor laminated portion 312 is configured by laminating semiconductor layers, and has a function of a cladding portion and the like with respect to the waveguide portion 311. Gain portion 311a extends in the z direction, and has a multiple quantum well structure made of the same material as active core layer 11aa in the first embodiment. The optical waveguide layer 311 b is made of the same material as that of the phase adjustment unit 11 b in the first embodiment, and forms a U-shape together with the gain unit 311 a. In the portion including the gain portion 311a, the semiconductor multilayer portion 312 is made of the same material and structure as the portion including the grating loading type gain portion 11a of the semiconductor multilayer portion 12 in the first embodiment. The difference is that the lattice layer 11ab is replaced with a p-type InP layer, and that the layer structure has a laminated structure in which the positions of the p-type semiconductor layer and the n-type semiconductor layer are reversed with the gain portion 311a in the y direction. In the portion including the optical waveguide layer 311 b, the semiconductor multilayer portion 312 is made of the same material and structure as the portion including the phase adjustment portion 11 b of the semiconductor multilayer portion 12 in the first embodiment. It differs in that it has a stacked structure in which the positions of the p-type semiconductor layer and the n-type semiconductor layer are reversed with the gain portion 311 a interposed therebetween. The first waveguide portion 310 has a buried waveguide structure as a first waveguide structure.
　ｎ側電極３１３は、半導体積層部３１２上において、利得部３１１ａに沿うように配置されている。なお、半導体積層部３１２には半導体積層部３１２を覆うようにＳｉＮ保護膜が形成されており、ｎ側電極３１３はＳｉＮ保護膜に形成された開口部を介して半導体積層部３１２に接触している。また、半導体積層部３１２のｎ側電極３１３が形成された面と反対側の面には、不図示のｐ側電極が形成されている。 The n-side electrode 313 is disposed on the semiconductor multilayer portion 312 along the gain portion 311 a. A SiN protective film is formed on the semiconductor laminated portion 312 so as to cover the semiconductor laminated portion 312, and the n-side electrode 313 is in contact with the semiconductor laminated portion 312 through the opening formed in the SiN protective film. There is. Further, a p-side electrode (not shown) is formed on the surface of the semiconductor lamination portion 312 opposite to the surface on which the n-side electrode 313 is formed.
　つぎに、第２の導波路部３２０について説明する。第２の導波路部３２０は、ＳＯＩ基板で構成されている。第２の導波路部３２０は、２分岐部３２１と、アーム部３２２、３２３と、リング状導波路３２４と、マイクロヒータ３２５、３２９、３３３と、位相調整部３２８と、ＳｉＯ２からなるオーバークラッド層３３０と、導波路部３３１と、回折格子部３３２と、を備えている。 Next, the second waveguide section 320 will be described. The second waveguide section 320 is configured of an SOI substrate. The second waveguide portion 320 is an overcladding made of a bifurcated portion 321, arm portions 322 and 323, a ring-shaped waveguide 324, microheaters 325, 329 and 333, a phase adjusting portion 328, and SiO 2. A layer 330, a waveguide portion 331, and a diffraction grating portion 332 are provided.
　２分岐部３２１は、１×２型のＭＭＩ導波路３２１ａを含む１×２型の分岐型導波路で構成され、２ポート側が２つのアーム部３２２、３２３のそれぞれに接続されるとともに１ポート側が第１の導波路部３１０の利得部３１１ａ側に接続されている。２分岐部３２１により、２つのアーム部３２２、３２３は、その一端が統合され、回折格子部３３２と光学的に結合される。２分岐部３２１の１ポート側には、第１の導波路部３１０に向かって幅が細くなるテーパ部が形成されている。テーパ部の外周には、ＳｉＯ２より屈折率の高い、たとえばＳｉＮからなるオーバークラッド層が形成されており、スポットサイズ変換器構造となっている。 The bifurcated portion 321 is composed of a 1 × 2 type branched waveguide including a 1 × 2 type MMI waveguide 321a, and the 2 port side is connected to each of the two arm portions 322 and 323 and the 1 port side is It is connected to the gain section 311 a side of the first waveguide section 310. One end of the two arm portions 322 and 323 is integrated by the bifurcated portion 321, and is optically coupled to the diffraction grating portion 332. On one port side of the bifurcated portion 321, a tapered portion whose width is narrowed toward the first waveguide portion 310 is formed. An overcladding layer having a refractive index higher than that of SiO 2 , for example, made of SiN is formed on the outer periphery of the tapered portion, forming a spot size converter structure.
　アーム部３２２、３２３は、いずれもｚ方向に延伸し、リング状導波路３２４を挟むように配置されている。アーム部３２２、３２３はリング状導波路３２４と近接し、いずれも同一の結合係数κでリング状導波路３２４と光学的に結合している。アーム部３２２、３２３とリング状導波路３２４とは、リング共振器フィルタＲＦ３を構成している。また、リング共振器フィルタＲＦ３と２分岐部３２１とは、反射ミラーＭ３を構成している。第２の屈折率変化器としてのマイクロヒータ３２５はリング状であり、オーバークラッド層３３０上のリング状導波路３２４の直上に配置されている。 Each of the arm portions 322 and 323 extends in the z direction, and is disposed to sandwich the ring waveguide 324. The arm portions 322 and 323 are in close proximity to the ring waveguide 324 and both are optically coupled to the ring waveguide 324 with the same coupling coefficient κ. The arm portions 322 and 323 and the ring waveguide 324 constitute a ring resonator filter RF3. Further, the ring resonator filter RF3 and the bifurcated portion 321 constitute a reflection mirror M3. The microheater 325 as a second refractive index changer is ring-shaped, and is disposed on the over cladding layer 330 directly above the ring-shaped waveguide 324.
　導波路部３３１は、ｚ方向に延伸する導波路であり、一端が第１の導波路部３１０の光導波層３１１ｂ側に接続されており、他の一端が回折格子部３３２に接続されている。また、導波路部３３１の途中には位相調整部３２８が設けられている。マイクロヒータ３２９は、オーバークラッド層３３０上において位相調整部３２８に沿うように配置されている。第１の屈折率変化器としてのマイクロヒータ３３３は、オーバークラッド層３３０上において回折格子部３３２に沿うように配置されている。 The waveguide portion 331 is a waveguide extending in the z direction, one end of which is connected to the optical waveguide layer 311b side of the first waveguide portion 310, and the other end of which is connected to the diffraction grating portion 332. . In addition, a phase adjustment unit 328 is provided in the middle of the waveguide unit 331. The micro heater 329 is disposed on the over cladding layer 330 along the phase adjustment unit 328. The microheater 333 as a first refractive index changer is disposed on the over cladding layer 330 along the diffraction grating portion 332.
　なお、第２の導波路部３２０の構成要素である２分岐部３２１、アーム部３２２、３２３、リング状導波路３２４、位相調整部３２８、導波路部３３１、回折格子部３３２は、図１２Ｂに示すような実施の形態３と同様のハイメサ導波路構造を有している。すなわち、第２の導波路部３２０は第１の導波路部３１０の第１の導波路構造とは異なる第２の導波路構造を有する。なお、回折格子部３３２は、光導波層として機能するデバイス層にｚ方向に沿って標本化回折格子が形成され、回折格子の溝はオーバークラッド層３３０のＳｉＯ２で埋め込まれた構成を有する。 12B, which are components of the second waveguide 320, the bifurcated part 321, the arms 322 and 323, the ring waveguide 324, the phase adjusting part 328, the waveguide 331, and the diffraction grating 332. It has the same high mesa waveguide structure as that of the third embodiment as shown. That is, the second waveguide section 320 has a second waveguide structure different from the first waveguide structure of the first waveguide section 310. The diffraction grating section 332 has a configuration in which a sampling diffraction grating is formed along the z direction in a device layer functioning as an optical waveguide layer, and the grooves of the diffraction grating are embedded with SiO 2 of the over cladding layer 330.
　また、第１の導波路部３１０は、ゲインチップとして公知の方法で別途作製され、第２の導波路部３２０を構成するＳＯＩ基板においてデバイス層とＢＯＸ層と支持基板の一部とが除去されることにより形成された凹部ＣＣに実装されている。このとき、第１の導波路部３１０の利得部３１１ａと第２の導波路部３２０の２分岐部３２１の１ポート側とがバットジョイント接続され、かつ第１の導波路部３１０の光導波層３１１ｂと第２の導波路部３２０の導波路部３３１とがバットジョイント接続されている。なお、実施の形態３の場合と同様に、第２の導波路部３２０の２分岐部３２１の１ポート側と第２の導波路部３２０の導波路部３３１とは、第１の導波路部３１０に向かって幅が細くなるテーパ部とされ、その外周にたとえばＳｉＮからなるオーバークラッド層が形成され、スポットサイズ変換器構造となっていることが好ましい。 In addition, the first waveguide section 310 is separately manufactured by a known method as a gain chip, and the device layer, the BOX layer, and part of the support substrate are removed in the SOI substrate constituting the second waveguide section 320. Mounted in the concave portion CC formed by At this time, the gain section 311 a of the first waveguide section 310 and one port side of the 2-branch section 321 of the second waveguide section 320 are butt-joint connected, and the optical waveguide layer of the first waveguide section 310 The butt joint connection 311 b and the waveguide part 331 of the second waveguide part 320 are connected. As in the case of the third embodiment, one port side of the 2-branch portion 321 of the second waveguide portion 320 and the waveguide portion 331 of the second waveguide portion 320 are the first waveguide portion. It is preferable that a tapered portion whose width decreases toward 310 is formed, and an overcladding layer made of, for example, SiN is formed on the outer periphery thereof to form a spot size converter structure.
　第１の導波路部３１０と第２の導波路部３２０は、互いに光学的に接続された回折格子部３３２と反射ミラーＭ３とにより構成されるレーザ共振器Ｃ３を構成している。利得部３１１ａと位相調整部３２８とはレーザ共振器Ｃ３内に配置される。 The first waveguide section 310 and the second waveguide section 320 constitute a laser resonator C3 constituted of a diffraction grating section 332 and a reflection mirror M3 optically connected to each other. The gain unit 311a and the phase adjustment unit 328 are disposed in the laser resonator C3.
　この波長可変レーザ素子３００においても、実施の形態１～３と同様に、回折格子部３３２は、略所定の波長間隔で略周期的な反射特性を有する第一の櫛状反射スペクトルを生成する。また、リング共振器フィルタＲＦ３は、第一の櫛状反射スペクトルのピークの半値全幅よりも狭い半値全幅のピークを有し、第一の櫛状反射スペクトルの波長間隔とは異なる波長間隔で略周期的な反射特性を有する第二の櫛状反射スペクトルを生成する。そして、第一の櫛状反射スペクトルのピーク、第二の櫛状反射スペクトルのピーク、およびレーザ共振器Ｃ３の共振器モードの一つが一致した波長でレーザ発振する。また、レーザ共振器Ｃ３の共振器モードのモード間の間隔が、第１の櫛状反射スペクトルのスペクトル成分の半値全幅よりも狭い。さらには、レーザ共振器Ｃ３内の光帰還は、回折格子部３３２から、２分岐部３２１、リング共振器フィルタＲＦ３のアーム部３２２、３２３のうちの一方、リング状導波路３２４、アーム部３２２、３２３のうちの他方、２分岐部３２１を順に経由して回折格子部３３２に帰還する経路で行われ、かつ１回の光帰還中にリング状導波路３２４内を周回する。これにより、実施の形態１～３と同様に、本実施の形態４に係る波長可変レーザ素子３００によれば、レーザ光の狭線幅化および安定した単一モード発振を実現できる。 Also in this wavelength tunable laser device 300, as in the first to third embodiments, the diffraction grating section 332 generates a first comb-like reflection spectrum having substantially periodic reflection characteristics at substantially predetermined wavelength intervals. In addition, the ring resonator filter RF3 has a peak with a full width at half maximum narrower than the full width at half maximum of the peak of the first comb reflection spectrum, and has a substantially periodicity at a wavelength interval different from the wavelength interval of the first comb reflection spectrum. Generating a second comb-like reflection spectrum having a characteristic reflection characteristic. Then, laser oscillation occurs at a wavelength at which the peak of the first comb reflection spectrum, the peak of the second comb reflection spectrum, and one of the resonator modes of the laser resonator C3 coincide. In addition, the spacing between the modes of the resonator modes of the laser resonator C3 is narrower than the full width at half maximum of the spectral component of the first comb reflection spectrum. Furthermore, the optical feedback in the laser resonator C3 is from the diffraction grating section 332, one of the two branches 321, one of the arms 322 and 323 of the ring resonator filter RF3, the ring waveguide 324, the arm 322, In the other of H.323, it is performed in the path which returns to the diffraction grating part 332 via the 2-branch part 321 in order, and goes around in the ring waveguide 324 during one optical feedback. Thus, as in the first to third embodiments, the wavelength tunable laser device 300 according to the fourth embodiment can realize narrowing of the line width of laser light and stable single mode oscillation.
　また、波長可変レーザ素子３００においても、レーザ発振波長については、実施の形態１、２の場合と同様に、回折格子部３３２に対するマイクロヒータ３３３とリング共振器フィルタＲＦ３に対するマイクロヒータ３２５とにより第一の櫛状反射スペクトルと第二の櫛状反射スペクトルとをそれぞれチューニングすることで粗調、位相調整部３２８に対するマイクロヒータ３２９により共振器長をチューニングすることで微調を行うことにより、波長可変動作が実現される。 Also in the wavelength tunable laser device 300, the laser oscillation wavelength is the same as in the first and second embodiments by the micro heater 333 for the diffraction grating section 332 and the micro heater 325 for the ring resonator filter RF3. Can be tuned by tuning the comb-like reflection spectrum and the second comb-like reflection spectrum separately, and fine tuning by tuning the resonator length with the micro heater 329 for the phase adjustment unit 328. To be realized.
　波長可変レーザ素子３００も、実施の形態３に係る波長可変レーザ素子２００と同様にして製造できる。すなわち、ＳＯＩ基板を用いて第２の導波路部３２０に関連する部分を作製し、その凹部ＣＣに、別途作製した第１の導波路部３１０をフリップチップボンディングにより実装する。これにより波長可変レーザ素子３００が完成する。 The tunable laser device 300 can also be manufactured in the same manner as the tunable laser device 200 according to the third embodiment. That is, a portion related to the second waveguide portion 320 is manufactured using the SOI substrate, and the separately manufactured first waveguide portion 310 is mounted on the concave portion CC by flip chip bonding. Thus, the wavelength tunable laser device 300 is completed.
　本実施の形態４に係る波長可変レーザ素子３００によれば、実施の形態１、２と同様に、レーザ光の狭線幅化および安定した単一モード発振を実現できるとともに、実施の形態３と同様に、フットプリントが小さくコンパクトであり、且つサイドモード抑圧比の高いレーザ光を出力することができる。 According to the wavelength tunable laser device 300 according to the fourth embodiment, as in the first and second embodiments, it is possible to realize narrowing of the line width of the laser light and stable single mode oscillation, and Similarly, it is possible to output a laser beam which has a small footprint and is compact and has a high side mode suppression ratio.
（実施の形態５）
　つぎに、実施の形態５に係るレーザモジュールについて説明する。図１４は、本実施の形態５に係るレーザモジュールの模式図である。レーザモジュール１０００は、実施の形態２に係る波長可変レーザ素子１００Ａと、コリメートレンズ１００１と、光アイソレータ１００２と、ビームスプリッタ１００３と、集光レンズ１００５と、光ファイバ１００６と、受光素子としてのパワーモニタＰＤ（Photo　Diode）パワーモニタＰＤ１００９と、エタロンフィルタ１０１０と、パワーモニタＰＤ１０１１と、を備えている。また、波長可変レーザ素子１００Ａは、波長可変レーザ素子１００Ａの温度を調節するための不図示の電子冷却素子に載置されている。波長可変レーザ素子１００Ａ、パワーモニタＰＤ１００９、１０１１および電子冷却素子は外部の制御部に接続されている。 Fifth Embodiment
Next, a laser module according to the fifth embodiment will be described. FIG. 14 is a schematic view of a laser module according to the fifth embodiment. The laser module 1000 includes the wavelength tunable laser element 100A according to the second embodiment, a collimator lens 1001, an optical isolator 1002, a beam splitter 1003, a condenser lens 1005, an optical fiber 1006, and a power monitor as a light receiving element. A PD (Photo Diode) power monitor PD 1009, an etalon filter 1010, and a power monitor PD 1011 are provided. The wavelength tunable laser device 100A is mounted on an electronic cooling device (not shown) for adjusting the temperature of the wavelength tunable laser device 100A. The wavelength tunable laser device 100A, the power monitors PD 1009 and 1011 and the electronic cooling device are connected to an external control unit.
　波長可変レーザ素子１００Ａは、制御部から駆動電流を供給され、制御部によりマイクロヒータ１４、１５、２５を制御することにより調整された回折格子層１１ａｂ、リング共振器フィルタＲＦ１、位相調整部１１ｂなどの条件で決定される波長のレーザ光をＳＯＡ１０１にて所望の出力強度まで増幅してレーザ光Ｌ２として出力する。コリメートレンズ１００１は、波長可変レーザ素子１００Ａから出力されたレーザ光Ｌ２を平行光線とする。光アイソレータ１００２は、コリメートレンズ１００１による平行光線とされたレーザ光Ｌ２を一方向のみに透過する。ビームスプリッタ１００３は、光アイソレータ１００２を透過したレーザ光Ｌ２の大部分を透過しつつ一部をパワーモニタＰＤ１００９側に分岐する。パワーモニタＰＤ１００９は、ビームスプリッタ１００８により分岐されたレーザ光Ｌ２の一部を受光し、その受光強度に応じた値の電流を出力する。エタロンフィルタ１０１０は、多重干渉の次数に応じて周期的に変化するピークを有する透過波長特性を有しており、ビームスプリッタ１００８を透過したレーザ光Ｌ２をレーザ光Ｌ２の波長における透過波長特性に応じた透過率で透過する。エタロンフィルタ１０１０の周期はたとえば光の周波数で５０ＧＨｚである。パワーモニタＰＤ１０１１は、エタロンフィルタ１０１０を透過したレーザ光Ｌ２を受光し、その受光強度に応じた値の電流を出力する。集光レンズ１００５は、ビームスプリッタ１００３を透過したレーザ光Ｌ２を集光して光ファイバ１００６に結合する。光ファイバ１００６は結合されたレーザ光Ｌ２を外部に伝搬する。レーザ光Ｌ２はたとえば光ファイバ通信用の信号光として使用される。エタロンフィルタ１０１０はバルクのものを使用しているが、それに代えて、導波路型のフィルタを用いることもできる。 The wavelength tunable laser device 100A is supplied with a drive current from the control unit, and the diffraction grating layer 11ab adjusted by controlling the micro heaters 14, 15, 25 by the control unit, the ring resonator filter RF1, the phase adjustment unit 11b, etc. The laser light of the wavelength determined under the conditions of (1) is amplified to a desired output intensity by the SOA 101 and output as a laser light L2. The collimator lens 1001 converts the laser beam L2 output from the wavelength tunable laser element 100A into a parallel beam. The optical isolator 1002 transmits the laser beam L2 collimated by the collimator lens 1001 only in one direction. The beam splitter 1003 branches a part to the power monitor PD 1009 side while transmitting most of the laser light L 2 transmitted through the optical isolator 1002. The power monitor PD 1009 receives part of the laser beam L2 branched by the beam splitter 1008, and outputs a current having a value according to the light reception intensity. The etalon filter 1010 has a transmission wavelength characteristic having a periodically changing peak according to the order of multiple interference, and the laser light L2 transmitted through the beam splitter 1008 according to the transmission wavelength characteristic at the wavelength of the laser light L2 It penetrates with a high transmittance. The period of the etalon filter 1010 is, for example, 50 GHz at the frequency of light. The power monitor PD1011 receives the laser beam L2 transmitted through the etalon filter 1010, and outputs a current having a value according to the light reception intensity. The condensing lens 1005 condenses the laser beam L2 transmitted through the beam splitter 1003 and couples it to the optical fiber 1006. The optical fiber 1006 propagates the coupled laser light L2 to the outside. The laser light L2 is used, for example, as signal light for optical fiber communication. Although the etalon filter 1010 uses a bulk filter, a waveguide filter may be used instead.
　このレーザモジュール１０００によれば、波長可変レーザ素子１００Ａを備えることで、レーザ光Ｌ２の狭線幅化および安定した単一モード発振を実現し、さらにレーザ光Ｌ２をより高いパワーで出力できる。さらに、パワーモニタＰＤ１００９、１０１１から出力される電流をモニタすることにより受光強度をモニタし、制御部による波長ロック制御を行うことができる。
　具体的には、波長ロック制御では、制御部は、パワーモニタＰＤ１００９によってモニタされたレーザ光の強度と、パワーモニタＰＤ１０１１によってモニタされた、エタロンフィルタ１０１０透過後のレーザ光の強度との比が、レーザ光Ｌ２の波長が所望の波長になるときの比になるように、波長可変レーザ素子１００Ａの駆動電流と温度とを変化させる制御をする。これにより、レーザ光Ｌ２の波長を所望の波長（ロック波長）に制御することができる。 According to the laser module 1000, by providing the wavelength tunable laser element 100A, the line width reduction of the laser beam L2 and stable single mode oscillation can be realized, and the laser beam L2 can be output with higher power. Furthermore, the received light intensity can be monitored by monitoring the current output from the power monitors PD 1009 and 1011, and wavelength lock control can be performed by the control unit.
Specifically, in wavelength lock control, the control unit controls the ratio of the intensity of the laser light monitored by the power monitor PD 1009 to the intensity of the laser light after transmission through the etalon filter 1010 monitored by the power monitor PD 1011 Control is performed to change the drive current and temperature of the wavelength tunable laser element 100A such that the ratio when the wavelength of the laser light L2 becomes a desired wavelength is obtained. Thereby, the wavelength of the laser beam L2 can be controlled to a desired wavelength (lock wavelength).
（実施の形態６）
　つぎに、実施の形態６に係るレーザモジュールについて説明する。図１５は、本実施の形態６に係るレーザモジュールの模式図である。レーザモジュール１０００Ａは、波長可変レーザ素子１００Ｂと、コリメートレンズ１００１と、光アイソレータ１００２と、ビームスプリッタ１００３と、パワーモニタＰＤ１００４と、集光レンズ１００５と、光ファイバ１００６と、コリメートレンズ１００７と、ビームスプリッタ１００８と、パワーモニタＰＤ１００９と、エタロンフィルタ１０１０と、パワーモニタＰＤ１０１１とを備えている。また、波長可変レーザ素子１００Ｂは、波長可変レーザ素子１００Ｂの温度を調節するための不図示の電子冷却素子に載置されている。波長可変レーザ素子１００Ｂ、パワーモニタＰＤ１００４、１００９、１０１１、および電子冷却素子は外部の制御部に接続されている。 Sixth Embodiment
Next, a laser module according to the sixth embodiment will be described. FIG. 15 is a schematic view of a laser module according to the sixth embodiment. The laser module 1000A includes a wavelength tunable laser element 100B, a collimator lens 1001, an optical isolator 1002, a beam splitter 1003, a power monitor PD 1004, a condenser lens 1005, an optical fiber 1006, a collimator lens 1007, a beam splitter A power monitor PD 1009, an etalon filter 1010, and a power monitor PD 1011 are provided. The wavelength tunable laser device 100B is mounted on an electronic cooling device (not shown) for adjusting the temperature of the wavelength tunable laser device 100B. The wavelength tunable laser device 100B, the power monitors PD 1004, 1009, 1011 and the electronic cooling device are connected to an external control unit.
　コリメートレンズ１００１、光アイソレータ１００２、ビームスプリッタ１００３、パワーモニタＰＤ１００４、集光レンズ１００５、光ファイバ１００６の機能はレーザモジュール１０００の場合と同じなので説明を省略する。 The functions of the collimator lens 1001, the optical isolator 1002, the beam splitter 1003, the power monitor PD 1004, the condenser lens 1005, and the optical fiber 1006 are the same as those of the laser module 1000, and therefore the description thereof is omitted.
　波長可変レーザ素子１００Ｂは、波長可変レーザ素子１００Ａの備える波長可変レーザ素子１００において、アーム部２２とリング状導波路２４との結合係数κ１と、アーム部２３とリング状導波路２４との結合係数κ２とが互いに異なる値となるように設計したものである。このように、結合係数κ１とκ２を互いに異なる値とすることにより、リング共振器フィルタＲＦ１は非対称フィルタとなり、発振したレーザ光の一部が、アーム部２２、２３の２分岐部２１と接続された側とは反対の端面からそれぞれ出力されることとなる。 In the wavelength tunable laser device 100 provided in the wavelength tunable laser device 100A, the wavelength tunable laser device 100B has a coupling coefficient κ1 between the arm portion 22 and the ring waveguide 24 and a coupling coefficient between the arm portion 23 and the ring waveguide 24. It is designed such that κ2 has different values. As described above, by setting the coupling coefficients κ1 and κ2 to different values, the ring resonator filter RF1 becomes an asymmetric filter, and a part of the oscillated laser light is connected to the two branch parts 21 of the arm parts 22 and 23. It will be outputted from the end face opposite to the other side.
　コリメートレンズ１００７は、アーム部２２の端面から出力された、発振したレーザ光の一部であるレーザ光Ｌ３を平行光線とする。ビームスプリッタ１００８は、平行光線とされたレーザ光Ｌ３の大部分を透過しつつ一部をパワーモニタＰＤ１００９側に分岐する。パワーモニタＰＤ１００９は、ビームスプリッタ１００８により分岐されたレーザ光Ｌ３の一部を受光し、その受光強度に応じた値の電流を出力する。エタロンフィルタ１０１０は、多重干渉の次数に応じて周期的に変化するピークを有する透過波長特性を有しており、ビームスプリッタ１００８を透過したレーザ光Ｌ３をレーザ光Ｌ３の波長における透過波長特性に応じた透過率で透過する。エタロンフィルタ１０１０の周期はたとえば光の周波数で５０ＧＨｚである。パワーモニタＰＤ１０１１は、エタロンフィルタ１０１０を透過したレーザ光Ｌ３を受光し、その受光強度に応じた値の電流を出力する。 The collimator lens 1007 converts the laser beam L3 which is a part of the oscillated laser beam, which is output from the end face of the arm portion 22, into parallel rays. The beam splitter 1008 transmits most of the laser beam L3 that has been made a parallel beam and branches a portion to the power monitor PD 1009 side. The power monitor PD 1009 receives a part of the laser beam L3 branched by the beam splitter 1008, and outputs a current having a value according to the light reception intensity. The etalon filter 1010 has a transmission wavelength characteristic having a periodically changing peak according to the order of multiple interference, and the laser light L3 transmitted through the beam splitter 1008 according to the transmission wavelength characteristic at the wavelength of the laser light L3. It penetrates with a high transmittance. The period of the etalon filter 1010 is, for example, 50 GHz at the frequency of light. The power monitor PD1011 receives the laser beam L3 transmitted through the etalon filter 1010, and outputs a current of a value according to the light reception intensity.
　このレーザモジュール１０００Ａによれば、波長可変レーザ素子１００Ｂを備えることで、レーザ光Ｌ２の狭線幅化および安定した単一モード発振を実現し、さらにレーザ光Ｌ２をより高いパワーで出力できる。さらに、パワーモニタＰＤ１００９、１０１１から出力される電流をモニタすることにより受光強度をモニタし、制御部による波長ロック制御を行うことができる。さらに、パワーモニタＰＤ１００４から出力される電流をモニタすることによりレーザ光Ｌ２の強度をモニタすることができるので、制御部によりパワーフィードバック制御を行うことができる。 According to the laser module 1000A, by providing the wavelength tunable laser device 100B, it is possible to realize narrowing of the line width of the laser light L2 and stable single mode oscillation, and to output the laser light L2 with higher power. Furthermore, the received light intensity can be monitored by monitoring the current output from the power monitors PD 1009 and 1011, and wavelength lock control can be performed by the control unit. Furthermore, since the intensity of the laser beam L2 can be monitored by monitoring the current output from the power monitor PD 1004, power feedback control can be performed by the control unit.
　具体的には、波長ロック制御では、制御部は、パワーモニタＰＤ１００９によってモニタされたレーザ光の強度と、パワーモニタＰＤ１０１１によってモニタされた、エタロンフィルタ１０１０透過後のレーザ光の強度との比が、レーザ光Ｌ２の波長が所望の波長になるときの比になるように、波長可変レーザ素子１００Ｂの駆動電流と温度とを変化させる制御をする。これにより、レーザ光Ｌ２の波長を所望の波長（ロック波長）に制御することができる。 Specifically, in wavelength lock control, the control unit controls the ratio of the intensity of the laser light monitored by the power monitor PD 1009 to the intensity of the laser light after transmission through the etalon filter 1010 monitored by the power monitor PD 1011 Control is performed to change the drive current and temperature of the wavelength tunable laser element 100B such that the ratio when the wavelength of the laser beam L2 becomes a desired wavelength is obtained. Thereby, the wavelength of the laser beam L2 can be controlled to a desired wavelength (lock wavelength).
　なお、上記実施の形態では、回折格子は標本化回折格子であるが、回折格子の種類はこれに限られず、超構造回折格子（Superstructure　Grating）や重畳回折格子（Superimposed　Grating）でもよい。
　また、実施の形態１では、回折格子層１１ａｂは、活性コア層１１ａａの近傍かつ直上に、活性コア層１１ａａに沿って設けられているが、本発明はこれに限られない。たとえば、位相調整部とは反対側において活性コア層と接続する光導波層が設けられている場合、活性コア層の近傍かつ当該光導波層の直上に回折格子層が設けられていてもよい。 In the above embodiment, the diffraction grating is a sampling diffraction grating, but the type of diffraction grating is not limited to this, and may be a superstructure diffraction grating or a superimposed diffraction grating.
Further, in the first embodiment, the diffraction grating layer 11ab is provided along and immediately above the active core layer 11aa along the active core layer 11aa, but the present invention is not limited to this. For example, in the case where an optical waveguide layer connected to the active core layer is provided on the opposite side to the phase adjustment portion, a diffraction grating layer may be provided in the vicinity of the active core layer and directly on the optical waveguide layer.
　また、上記実施の形態により本発明が限定されるものではない。上述した各構成要素を適宜組み合わせて構成したものも本発明に含まれる。また、さらなる効果や変形例は、当業者によって容易に導き出すことができる。よって、本発明のより広範な態様は、上記の実施の形態に限定されるものではなく、様々な変更が可能である。 Further, the present invention is not limited by the above embodiment. The present invention also includes those configured by appropriately combining the above-described components. Further, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above embodiment, and various modifications are possible.
　１０、１０Ａ、２１０、３１０　第１の導波路部
　１１、２１１、３１１　導波路部
　１１ａ　回折格子装荷型利得部
　１１ａａ　活性コア層
　１１ａｂ、２１１ｂ　回折格子層
　１１ｂ、１１Ａｂ、２２８、３２８　位相調整部
　１２、２１２、３１２　半導体積層部
　１２Ａａ、２６Ａａ　下部クラッド層
　１２Ａｂ　上部リッジクラッド層
　１３　ｐ側電極
　１４、１５、２５、２１５、２２５、２２９、３２５、３２９、３３３　マイクロヒータ
　２０、２２０、３２０　第２の導波路部
　２１　２分岐部
　２１ａ、２２１ａ、３２１ａ　ＭＭＩ導波路
　２２、２３、２２２、２２３、３２２、３２３　アーム部
　２２ａ、２３ａ、２６ａ　下部クラッド層
　２２ｂ、２３ｂ、２６ｂ、２６Ａｂ、３１１ｂ　光導波層
　２２ｃ、２３ｃ、２６ｃ、２６Ａｃ　上部クラッド層
　２４、２２４、３２４　リング状導波路
　２６、２６Ａ、２７、３３１　導波路部
　３０、２１３、３１３　ｎ側電極
　１００、１００Ａ、１００Ｂ、２００、３００　波長可変レーザ素子
　２１１ａ、３１１ａ　利得部
　２２２ａ　下層
　２２２ａａ　支持層
　２２２ａｂ　ＢＯＸ層
　２２２ｂ　デバイス層
　２３０、３３０　オーバークラッド層
　３３２　回折格子部
　１０００、１０００Ａ　レーザモジュール
　１００１、１００７　コリメートレンズ
　１００２　光アイソレータ
　１００３、１００８　ビームスプリッタ
　１００４、１００９、１０１１　パワーモニタＰＤ
　１００５　集光レンズ
　１００６　光ファイバ
　１０１０　エタロンフィルタ
　Ｂ　基部
　Ｃ１、Ｃ２、Ｃ３　レーザ共振器
　ＣＣ　凹部
　Ｌ１、Ｌ２、Ｌ３　レーザ光
　Ｍ１、Ｍ２、Ｍ３　反射ミラー
　ＯＰ　光路
　ＲＦ１、ＲＦ２、ＲＦ３　リング共振器フィルタ
　ＳＣ１、ＳＣ２　スペクトル成分 10, 10A, 210, 310 1st waveguide part 11, 211, 311 Waveguide part 11a Diffraction grating loading type gain part 11aa Active core layer 11ab, 211b Diffraction grating layer 11b, 11Ab, 228, 328 Phase adjustment part 12, 212, 312 semiconductor laminated part 12Aa, 26Aa lower clad layer 12Ab upper ridge clad layer 13p side electrode 14, 15, 25, 215, 225, 229, 325, 329, 333 micro heater 20, 220, 320 second waveguide Part 21 2 branch part 21a, 221a, 321a MMI waveguide 22, 23, 222, 223, 322, 323 arm part 22a, 23a, 26a lower clad layer 22b, 23b, 26b, 26Ab, 311b optical waveguide layer 22c, 23c, 26c, 26Ac upper cladding layer 24, 22 , 324 ring-shaped waveguide 26, 26A, 27, 331 waveguide part 30, 213, 313 n- side electrode 100, 100A, 100B, 200, 300 wavelength tunable laser element 211a, 311a gain part 222a lower layer 222aa support layer 222ab BOX layer 222b Device Layer 230, 330 Overcladding Layer 332 Diffraction grating section 1000, 1000A Laser module 1001, 1007 Collimator lens 1002 Optical isolator 1003, 1008 Beam splitter 1004, 1009, 1011 Power monitor PD
1005 Condenser Lens 1006 Optical Fiber 1010 Etalon Filter B Base C1, C2, C3 Laser Resonator CC Concave L1, L2, L3 Laser Light M1, M2, M3 Reflecting Mirror OP Optical Path RF1, RF2, RF3 Ring Resonator Filter SC1, SC2 Spectral component

Claims (21)

  1. 　回折格子と、前記回折格子と光学的に結合されたリング共振器フィルタを含む反射ミラーにより構成されるレーザ共振器と、
    　前記レーザ共振器内に配置された利得部と、
    　前記レーザ共振器内に配置された位相調整部と、
    　を備える波長可変レーザ素子であって、
    　前記回折格子は、第一の櫛状反射スペクトルを生成し、
    　前記リング共振器フィルタは、
    　　　　リング状導波路と、
    　　　　各々が前記リング状導波路と光学的に結合し、それぞれの一端が統合されて前記回折格子と光学的に結合されている２つのアーム部と、
    　　　　を備え、
    　　　　前記第一の櫛状反射スペクトルのピークの半値全幅よりも狭い半値全幅のピークで、前記第一の櫛状反射スペクトルの波長間隔とは異なる波長間隔を有する第二の櫛状反射スペクトルを生成し、
    　前記回折格子と前記リング共振器は前記第一の櫛状反射スペクトルのピークの一つと前記第二の櫛状反射スペクトルのピークの一つとを波長軸上で重ね合わせ可能に構成され、
    　　前記レーザ共振器は、共振器モードのモード間の間隔が、前記第一の櫛状反射スペクトルのピークの半値全幅よりも狭くなるように構成されている波長可変レーザ素子。     A laser resonator comprising: a diffraction grating; and a reflection mirror including a ring resonator filter optically coupled to the diffraction grating;
    A gain unit disposed in the laser resonator;
    A phase adjustment unit disposed in the laser resonator;
    A tunable laser device comprising:
    The diffraction grating produces a first comb-like reflection spectrum,
    The ring resonator filter is
    Ring-shaped waveguide,
    Two arms, each optically coupled to the ring waveguide, one end of each of which is integrated and optically coupled to the diffraction grating;
    Equipped with
    Generating a second comb-like reflection spectrum having a wavelength interval different from the wavelength interval of the first comb-like reflection spectrum at a peak of a full width half maximum narrower than the full width half maximum of the peak of the first comb-like reflection spectrum ,
    The diffraction grating and the ring resonator are configured such that one of the peaks of the first comb reflection spectrum and one of the peaks of the second comb reflection spectrum can be superimposed on a wavelength axis,
    The wavelength tunable laser device, wherein the laser resonator is configured such that the spacing between modes of the resonator modes is narrower than the full width at half maximum of the peak of the first comb reflection spectrum.
  2. 　さらに前記位相調整部の屈折率を調整することで、重ね合わされた前記第一の櫛状反射スペクトルの前記ピークと前記第二の櫛状反射スペクトルの前記ピークの重なり領域に、前記レーザ共振器の前記共振器モードの一つを一致させ、その一致した前記共振器モードの波長でレーザ発振するように構成されていることを特徴とする請求項１に記載の波長可変レーザ素子。 Furthermore, by adjusting the refractive index of the phase adjustment unit, the laser resonator is provided in an overlapping region of the peak of the first comb reflection spectrum and the peak of the second comb reflection spectrum which are superimposed. The wavelength tunable laser device according to claim 1, wherein one of the resonator modes is matched, and laser oscillation is performed at the wavelength of the matched resonator mode.
  3. 　前記レーザ共振器内の光帰還の経路は、前記回折格子から、前記２つのアーム部のうち一方、前記リング状導波路、前記２つのアーム部のうち他方を経由して前記回折格子に帰還する経路であることを特徴とする請求項１または２に記載の波長可変レーザ素子。 The optical feedback path in the laser resonator is returned from the diffraction grating to the diffraction grating via one of the two arm portions, the ring waveguide, and the other of the two arm portions. The wavelength tunable laser device according to claim 1, which is a path.
  4. 　前記回折格子の屈折率を変化させる第１の屈折率変化器と、前記リング共振器の屈折率を変化させる第２の屈折率変化器とを備え、前記第１の屈折率変化器および前記第２の屈折率変化器の少なくともいずれか一つを用いて、前記第一の櫛状反射スペクトルのピークの一つと前記第二の櫛状反射スペクトルのピークの一つとを波長軸上で重ね合わせることを特徴とする請求項１～３のいずれか一つに記載の波長可変レーザ素子。 A first refractive index changer that changes a refractive index of the diffraction grating; and a second refractive index changer that changes a refractive index of the ring resonator, the first refractive index changer and the first refractive index changer Superimposing one of the peaks of the first comb-like reflection spectrum and one of the peaks of the second comb-like reflection spectrum on a wavelength axis using at least one of the two refractive index changers The wavelength tunable laser device according to any one of claims 1 to 3, characterized in that
  5. 　前記回折格子は標本化回折格子であることを特徴とする請求項１～４のいずれか一つに記載の波長可変レーザ素子。 The wavelength tunable laser device according to any one of claims 1 to 4, wherein the diffraction grating is a sampling diffraction grating.
  6. 　前記回折格子は超構造回折格子であることを特徴とする請求項１～４のいずれか一つに記載の波長可変レーザ素子。 The wavelength tunable laser device according to any one of claims 1 to 4, wherein the diffraction grating is a superstructure diffraction grating.
  7. 　前記回折格子は重畳回折格子であることを特徴とする請求項１～４のいずれか一つに記載の波長可変レーザ素子。 The wavelength tunable laser device according to any one of claims 1 to 4, wherein the diffraction grating is a superposition diffraction grating.
  8. 　前記回折格子は前記利得部の近傍に設けられていることを特徴とする請求項１～７のいずれか一つに記載の波長可変レーザ素子。 The wavelength tunable laser device according to any one of claims 1 to 7, wherein the diffraction grating is provided in the vicinity of the gain section.
  9. 　前記回折格子は前記利得部に沿って設けられていることを特徴とする請求項１～８のいずれか一つに記載の波長可変レーザ素子。 The wavelength tunable laser device according to any one of claims 1 to 8, wherein the diffraction grating is provided along the gain section.
  10. 　前記利得部は埋込み導波路構造内に配置され、前記リング共振器フィルタはハイメサ導波路構造を有することを特徴とする請求項１～９のいずれか一つに記載の波長可変レーザ素子。 The wavelength tunable laser device according to any one of claims 1 to 9, wherein the gain section is disposed in a buried waveguide structure, and the ring resonator filter has a high mesa waveguide structure.
  11. 　前記利得部はリッジ導波路構造内に配置され、前記リング共振器フィルタはハイメサ導波路構造を有することを特徴とする請求項１～９のいずれか一つに記載の波長可変レーザ素子。 The wavelength tunable laser device according to any one of claims 1 to 9, wherein the gain section is disposed in a ridge waveguide structure, and the ring resonator filter has a high mesa waveguide structure.
  12. 　前記リング共振器フィルタにおいて、前記リング状導波路と、前記２つのアーム部とは、多モード干渉型導波路部により光学的に結合していることを特徴とする請求項１～１１のいずれか一つに記載の波長可変レーザ素子。 12. The ring resonator filter according to any one of claims 1 to 11, wherein the ring waveguide and the two arm portions are optically coupled by a multimode interference waveguide portion. The wavelength tunable laser device according to one of the aspects.
  13. 　前記リング共振器フィルタにおいて、前記リング状導波路と、前記２つのアーム部とは、方向性結合型導波路部により光学的に結合していることを特徴とする請求項１～１１のいずれか一つに記載の波長可変レーザ素子。 12. The ring resonator filter according to any one of claims 1 to 11, wherein the ring waveguide and the two arm portions are optically coupled by a directional coupling waveguide portion. The wavelength tunable laser device according to one of the aspects.
  14. 　前記レーザ発振により出力したレーザ光を光増幅する半導体光増幅器をさらに備えることを特徴とする請求項１～１３のいずれか一つに記載の波長可変レーザ素子。 The wavelength tunable laser device according to any one of claims 1 to 13, further comprising a semiconductor optical amplifier that optically amplifies the laser light output by the laser oscillation.
  15. 　前記レーザ共振器は、前記共振器モードのモード間の間隔が、前記第一の櫛状反射スペクトルのピーク内に、前記共振器モードが２本以上含まれるように構成されていることを特徴とする請求項１～１４のいずれか一つに記載の波長可変レーザ素子。 The laser resonator is characterized in that an interval between modes of the resonator modes is such that two or more of the resonator modes are included in a peak of the first comb-like reflection spectrum. The wavelength tunable laser device according to any one of claims 1 to 14.
  16. 　前記第一の櫛状反射スペクトルのピークはガウシャン型の形状であり、前記第二の櫛状反射スペクトルのピークは二重指数分布型の形状であることを特徴とする請求項１～１５のいずれか一つに記載の波長可変レーザ素子。 The peak of the first comb-like reflection spectrum has a Gaussian shape, and the peak of the second comb-like reflection spectrum has a double exponential distribution shape, any one of claims 1 to 15. The tunable laser device according to any one of the preceding claims.
  17. 　前記リング共振器フィルタにおいて前記リング共振器と光学的に結合する前記２つのアーム部の結合係数が互いに異なるように構成されている
    　ことを特徴とする請求項１～１６のいずれか一つに記載の波長可変レーザ素子。     The coupling coefficient of the two arm portions optically coupled to the ring resonator in the ring resonator filter is configured to be different from each other. Tunable laser element.
  18. 　前記位相調整部の屈折率を調整する第３の屈折率変化器をさらに備えることを特徴とする請求項３に記載の波長可変レーザ素子。 The wavelength tunable laser device according to claim 3, further comprising a third refractive index changer that adjusts the refractive index of the phase adjustment unit.
  19. 　前記第１、第２、及び第３の屈折率変化器はそれぞれ、前記回格子、前記リング共振器、及び前記位相調整部のそれぞれの近傍に設けられ、それぞれの屈折率を熱的に変化させる抵抗ヒータであることを特徴とする請求項１８に記載の波長可変レーザ素子。 The first, second, and third refractive index changers are respectively provided in the vicinity of the turn grating, the ring resonator, and the phase adjustment unit, and thermally change the respective refractive indexes. The wavelength tunable laser device according to claim 18, which is a resistance heater.
  20. 　請求項１～１９のいずれか一つに記載の波長可変レーザ素子を備えることを特徴とするレーザモジュール。 A laser module comprising the wavelength tunable laser device according to any one of claims 1 to 19.
  21. 　請求項１７に記載の波長可変レーザ素子と、
    　前記波長可変レーザ素子の前記２つのアーム部の中の一つのアーム部の端部のうち統合されていない端部の端面から出力するレーザ光の一部を受光する受光素子と、
    　を備えることを特徴とするレーザモジュール。     A wavelength tunable laser device according to claim 17;
    A light receiving element for receiving a part of laser light output from an end face of an unintegrated end of an end of one of the two arms of the wavelength tunable laser element;
    A laser module comprising:
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