Optical semiconductor element and integrated semiconductor laser
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-12-24
- Publication Date
- 2026-08-13
Smart Images
Figure JP2025045239_13082026_PF_FP_ABST
Abstract
Description
Optical semiconductor device, and integrated semiconductor laser
[0001] The present invention relates to an optical semiconductor device and an integrated semiconductor laser.
[0002] As an invention of an optical semiconductor device that outputs laser light, for example, there is an optical semiconductor device disclosed in Patent Document 1. In this optical semiconductor device, a clad layer, an insulating layer, and a thin film resistor are laminated on an optical waveguide, and a comb-shaped power electrode and a comb-shaped ground electrode are connected to the thin film resistor. The teeth of the power electrode are connected to the thin film resistor between the teeth of the ground electrode, and the teeth of the power electrode and the teeth of the ground electrode are alternately connected in the length direction of the thin film resistor, so the thin film resistor is substantially divided.
[0003] When a voltage is applied to the thin film resistor by the power electrode and the ground electrode, current flows from the teeth of the power electrode through the thin film resistor to the teeth of the ground electrode, and the thin film resistor between the teeth generates heat. Since the refractive index of the optical waveguide changes due to this heat generation, the wavelength of the output laser light is controlled by controlling the heat generation of the thin film resistor.
[0004] Japanese Patent Application Laid-Open No. 2007-273650
[0005] In the optical semiconductor device disclosed in Patent Document 1, current flows through the thin film resistor between the teeth of the power electrode and the teeth of the ground electrode, but no current flows in the portion of the thin film resistor directly under the teeth. Therefore, this portion does not generate heat, and since the heat of the thin film resistor is dissipated from the teeth of each electrode, the temperature of the portion of the optical waveguide directly under the teeth is lower than the temperature directly under the space between the teeth. When the temperature directly under the space between the teeth becomes low, the optical waveguide is not uniformly heated, so the refractive index of the optical waveguide becomes non-uniform in the length direction.
[0006] The present invention has been made in view of the above, and an object thereof is to provide a technique capable of suppressing non-uniform heating of an optical waveguide.
[0007] To solve the above-mentioned problems and achieve the objective, the optical semiconductor element according to the present invention comprises a base, a first cladding layer located on the base, an optical waveguide layer located on the first cladding layer, a second cladding layer located on the optical waveguide layer, a metal film located on the second cladding layer above the optical waveguide layer, a dielectric protective film covering the metal film, a heater located on the protective film above the metal film, a first wiring connected to the heater, and a second wiring connected to the heater.
[0008] In the optical semiconductor device according to the present invention, the first cladding layer may include a diffraction grating layer in which a low refractive index portion and a high refractive index portion having a higher refractive index than the low refractive index portion are periodically arranged along the direction in which the optical waveguide layer extends.
[0009] Furthermore, in the optical semiconductor device according to the present invention, the metal film may be provided in a portion of the region above the diffraction grating layer, and the heater may be provided above the portion of the region.
[0010] Furthermore, the optical semiconductor element according to the present invention may have a plurality of the first wiring and the second wiring, and the first wiring and the second wiring may be connected to the heater alternately at intervals in the longitudinal direction of the heater.
[0011] Furthermore, the optical semiconductor element according to the present invention may have a plurality of heaters, with the first wiring connected from one first electrode to each of the plurality of heaters, and the second wiring connected from one second electrode to each of the plurality of heaters.
[0012] Furthermore, the optical semiconductor device according to the present invention may have a plurality of first electrodes and a plurality of second electrodes, wherein the first wiring is connected from each of the first electrodes to the heater, and the second wiring is connected from each of the second electrodes to the heater.
[0013] Furthermore, the optical semiconductor device according to the present invention may include a thermal resistance layer below the optical waveguide layer, the thermal conductivity of which is lower than that of the first cladding layer.
[0014] Furthermore, in the optical semiconductor device according to the present invention, the waveguide having the first cladding layer, the optical waveguide layer, and the second cladding layer may be an embedded waveguide structure.
[0015] Furthermore, in the optical semiconductor device according to the present invention, the waveguide having the first cladding layer, the optical waveguide layer, and the second cladding layer may have a high mesa waveguide structure.
[0016] Furthermore, in the optical semiconductor element according to the present invention, the upper surface of the heater, excluding the connection points with the first wiring and the connection points with the second wiring, may be covered with a dielectric protective film.
[0017] Furthermore, the integrated semiconductor laser according to the present invention comprises any one of the aforementioned optical semiconductor elements.
[0018] According to the present invention, it is possible to suppress the uneven heating of the optical waveguide.
[0019] Figure 1 is a schematic diagram of a tunable laser device according to an embodiment. Figure 2 is a diagram showing the configuration of an integrated semiconductor laser. Figure 3 is a cross-sectional view taken along line A-A in Figure 1. Figure 4 is a cross-sectional view taken along line B-B in Figure 1. Figure 5 is a cross-sectional view taken along line C-C in Figure 1. Figure 6 is a cross-sectional view taken along line D-D in Figure 1. Figure 7 is a schematic diagram of a tunable laser device according to a modified example. Figure 8 is a diagram showing a modified arrangement of a microheater for heating the diffraction grating and a metal film arranged on the +Z side of the diffraction grating. Figure 9 is a cross-sectional view taken along line E-E in Figure 8. Figure 10 is a view from the +Z direction of a modified arrangement of a microheater for heating the diffraction grating and a metal film arranged on the -Z side of the microheater. Figure 11 is a cross-sectional view of the first waveguide according to a modified example. Figure 12 is a cross-sectional view of the first waveguide with a high mesa structure. Figure 13 is a schematic diagram showing a modified configuration for heating a ring-shaped waveguide. Figure 14 is a cross-sectional view of the first waveguide according to a modified example.
[0020] Embodiments of the present invention will be described in detail below with reference to the attached drawings. However, the present invention is not limited to the embodiments described below. Furthermore, in the drawings, the same or corresponding elements are appropriately denoted by the same reference numerals. It should also be noted that the drawings are schematic, and the dimensional relationships of each element may differ from those in reality. Even between drawings, there may be parts where the dimensional relationships and ratios differ.
[0021] Furthermore, the Cartesian coordinate system of the X, Y, and Z axes is shown in the diagram as appropriate, and directions are explained using this system. In the space represented by the Cartesian coordinate system, the direction in which the X component increases is called the +X direction, and the direction in which the X component decreases is called the -X direction. Similarly, the Y and Z components are defined as the +Y direction, -Y direction, +Z direction, and -Z direction. For the sake of explanation, the +Z direction may be referred to as the upward direction (upward), and the -Z direction as the downward direction (downward), and the Z axis direction may be referred to as the up and down direction.
[0022] Figure 1 is a schematic diagram of a tunable laser device 1 according to an embodiment of the present invention. The tunable laser device 1 comprises a modularized integrated semiconductor laser 10 and a control device 100 that controls the operation of the integrated semiconductor laser 10. In Figure 1, the integrated semiconductor laser 10 and the control device 100 are configured as separate components, but they may be integrated into a single module.
[0023] The integrated semiconductor laser 10 has three microheaters 221 to 223 that generate heat in response to power supplied from the control device 100, and by locally heating the first waveguide section 21 and the second waveguide section 22, it changes the wavelength of the laser light L1 output from the integrated semiconductor laser 10.
[0024] Figure 2 shows the configuration of the integrated semiconductor laser 10. The integrated semiconductor laser 10 is a tunable laser that utilizes the Vernier effect, for example, and under the control of the control device 100, the wavelength of the output laser light L1 is variable to one of several wavelengths, and the laser light L1 of that one wavelength is output.
[0025] The integrated semiconductor laser 10 comprises a first waveguide portion 21 and a second waveguide portion 22, respectively, formed on a common base portion 11. Here, the base portion 11 is made of, for example, n-type InP. On the back surface of the base portion 11, an n-side electrode 12 is formed, which is made of, for example, AuGeNi and makes ohmic contact with the base portion 11.
[0026] A first waveguide section 21, which is an example of an optical semiconductor device, has an embedded waveguide structure. This first waveguide section 21 comprises a waveguide section 211, a semiconductor laminated section 212, and a p-side electrode 213. The waveguide section 211 is formed to extend in the X direction within the semiconductor laminated section 212. The first waveguide section 21 also includes a gain section 211a, a phase adjustment section 211c, and a DBR (Distributed Bragg Reflector) type diffraction grating section 211b. Here, the gain section 211a is an active layer having a multiple quantum well structure made of InGaAsP and an optical confinement layer. The diffraction grating section 211b, which is an example of a diffraction grating layer, is composed of a sampling diffraction grating made of InGaAsP and InP. The phase adjustment section 211c has a structure in which an optical waveguide layer made of InGaAsP is sandwiched between cladding layers made of InP.
[0027] The semiconductor laminate 212 is constructed by stacking InP-based semiconductor layers and has the function of a cladding portion relative to the waveguide portion 211. A protective film 214 made of SiN, which is a dielectric, is formed on the semiconductor laminate 212. The p-side electrode 213 is positioned on the semiconductor laminate 212 along the gain portion 211a. The p-side electrode 213 is in contact with the semiconductor laminate 212 through an opening (not shown) formed in the protective film 214.
[0028] Furthermore, microheaters 221, 222, and electrode pads 231a, 231b, 232a, and 232b are provided on the protective film 214. Here, the strip-shaped microheater 221, made of Ti or the like, is arranged on the protective film 214 along the diffraction grating portion 211b. The conductive electrode pad 231a is positioned on the protective film 214 on the +Y direction side of the microheater 221. The electrode pad 231a is formed in a strip shape and has a plurality of wires 231a1 aligned in the Y direction and spaced apart in the X direction, and the plurality of wires 231a1 are comb-shaped. Each of these plurality of wires 231a1 is electrically connected to the microheater 221. The conductive electrode pad 231b is positioned on the protective film 214 on the -Y direction side of the microheater 221. The electrode pad 231b is formed in a strip shape and has multiple wires 231b1 aligned in the Y direction and spaced apart in the X direction, with the multiple wires 231b1 arranged in a comb-like pattern. Each of these multiple wires 231b1 is electrically connected to the microheater 221, adjacent to the wire 231a1 in the X direction and spaced apart from the wire 231a1. Electrode pad 231a is an example of a first electrode, and electrode pad 231b is an example of a second electrode. Wiring 231a1 is an example of a first wiring, and wiring 231b1 is an example of a second wiring.
[0029] A microheater 222 made of Ti or the like is arranged on the protective film 214 along the phase adjustment section 211c. A conductive electrode pad 232a is arranged on the protective film 214 on the +Y side of the microheater 222 and is provided with a strip-shaped wiring 232a1. The wiring 232a1 is electrically connected to the microheater 222 at its +X side end. A conductive electrode pad 232b is arranged on the protective film 214 on the -Y side of the microheater 222 and is provided with a strip-shaped wiring 232b1. The wiring 232b1 is electrically connected to the microheater 222 at its -X side end. Electrode pad 232a is an example of a first electrode, and electrode pad 232b is an example of a second electrode. Wiring 232a1 is an example of a first wiring, and wiring 232b1 is an example of a second wiring.
[0030] Figure 3 is a cross-sectional view taken along line A-A in Figure 1. Figure 4 is a cross-sectional view taken along line B-B in Figure 1, and Figure 5 is a cross-sectional view taken along line C-C in Figure 1. The first cladding layer 216a is a semiconductor layer made of n-type InP. The second cladding layer 216b is a semiconductor layer made of p-type InP. The embedded layer 217 is a semiconductor layer made of n-type InP.
[0031] The active core layer 211a1, which constitutes the gain section 211a, is interposed between the first cladding layer 216a and the second cladding layer 216b. The active core layer 211a1 emits light when current is injected.
[0032] The diffraction grating section 211b is composed of an optical waveguide layer 211b1, a high refractive index section 211b2, and a low refractive index section 211b3. The optical waveguide layer 211b1 is made of InGaAsP and is interposed between the first cladding layer 216a and the second cladding layer 216b. The optical waveguide layer 211b1 is arranged in series with the active core layer 211a1 along the X direction. The diffraction grating section 211b has a configuration in which the high refractive index section 211b2 and the low refractive index section 211b3 are periodically arranged along the direction in which the optical waveguide layer 211b1 extends, i.e., the X direction. The high refractive index section 211b2 is made of, for example, InGaAsP. The low refractive index section 211b3 is made of, for example, n-type InP. The period of the arrangement of the high refractive index section 211b2 and the low refractive index section 211b3 is determined and set depending on the desired laser oscillation wavelength. The high refractive index portion 211b2 has a higher refractive index than the low refractive index portion 211b3. A metal film 215a is provided on the second cladding layer 216b on the +Z direction side of the optical waveguide layer 211b1. The metal film 215a is made of, for example, Au. The metal film 215a may also be a laminated structure of Ti, Pt, and Au. The metal film 215a is arranged along the diffraction grating portion 211b and is interposed in a strip shape between the protective film 214 and the second cladding layer 216b. A microheater 221 is provided on the +Z direction side of the metal film 215a. When viewed in the Z-axis direction, the region of the microheater 221 and the metal film 215a is not limited to a configuration that includes the region of the optical waveguide layer 211b1, but may also be a configuration that extends over the region of the optical waveguide layer 211b1 when viewed in the Z-axis direction.
[0033] The electrode pad 231b becomes the negative electrode. The electrode pad 231a becomes the positive electrode and is supplied with power from the control device 100. When power is supplied to the electrode pad 231a, current flows through the microheater 221 between adjacent wirings 231a1 and 231b1, causing the microheater 221 to heat up. When the microheater 221 heats up, the metal film 215a is heated, and this heated metal film 215a heats the diffraction grating portion 211b. In addition, the temperature of the microheater 221 changes as the control device 100 controls the power supplied to the microheater 221, which changes the temperature of the diffraction grating portion 211b and thus changes its refractive index. The metal film 215a between the microheater 221 and the diffraction grating portion 211b makes the temperature distribution on the -Z direction side of the metal film 215a uniform, thus suppressing uneven temperature distribution of the diffraction grating portion 211b. Furthermore, compared to a configuration in which current flows between one end and the other end of the microheater 222, the current path is shorter and the resistance is lower because the wiring 231a1 and wiring 231b1 are comb-shaped, allowing heating to be performed by supplying high power at a low voltage.
[0034] The optical waveguide layer 211c1, which constitutes the phase adjustment section 211c, is interposed between the first cladding layer 216a and the second cladding layer 216b. The optical waveguide layer 211c1 is arranged in series with the active core layer 211a1 along the X direction. The optical waveguide layer 211c1 is made of InGaAsP. A metal film 215b is provided on the second cladding layer 216b on the +Z direction side of the optical waveguide layer 211c1. The metal film 215b is made of, for example, Au. The metal film 215b may also have a laminated structure of Ti, Pt, and Au. The metal film 215b is arranged along the phase adjustment section 211c and is interposed between the protective film 214 and the second cladding layer 216b. A microheater 222 is provided on the +Z direction side of the metal film 215b. When viewed in the Z-axis direction, the region of the microheater 222 and the metal film 215b is not limited to a configuration that includes the region of the optical waveguide layer 211c1, but may also be a configuration that extends over the region of the optical waveguide layer 211c1 when viewed in the Z-axis direction.
[0035] The electrode pad 232b acts as the negative electrode. The electrode pad 232a acts as the positive electrode and is supplied with power from the control device 100. Since the power supplied to the microheater 222 is relatively low, the voltage restrictions are relaxed. Therefore, to create a structure that is easier to manufacture within the range of known processes, the electrode pad 232a has one wiring 232a1 and the electrode pad 232b has one wiring 232b1. When power is supplied to the electrode pad 232a, current flows from the wiring 232a1 through the microheater 222 to the wiring 232b1, causing the microheater 222 to heat up. When the microheater 222 heats up, the metal film 215b is heated, and this heated metal film 215b heats the phase adjustment unit 211c. Also, because the control device 100 controls the power supplied to the microheater 222, the temperature of the microheater 222 changes, which in turn changes the temperature of the phase adjustment unit 211c and thus its refractive index. The metal film 215b located between the microheater 222 and the phase adjustment unit 211c helps to make the temperature distribution on the -Z side of the metal film 215b uniform, thereby suppressing temperature unevenness in the phase adjustment unit 211c. The number of wires 232a1 and 232b1 are not limited to one each, but can be selected as appropriate.
[0036] Returning to Figure 2, the second waveguide section 22 comprises a two-branch section 241, two arm sections 242 and 243, and a ring-shaped waveguide 244. The two-branch section 241 is composed of a 1x2 type branched waveguide including a 1x2 type multimode interference (MMI) waveguide 241a, with the two-port side connected to the two arm sections 242 and 243 respectively, and the one-port side connected to the first waveguide section 21. In other words, the two-branch section 241 integrates one end of the two arm sections 242 and 243, and optically couples them with the diffraction grating section 211b.
[0037] The two-branch section 241, the arm sections 242 and 243, and the ring-shaped waveguide 244 described above all have a high-mesa waveguide structure in which an optical waveguide layer 242a made of InGaAsP is sandwiched between a first cladding layer 244b and a second cladding layer 244c made of InP.
[0038] The arm portions 242 and 243 both extend in the X direction and are positioned to sandwich the ring-shaped waveguide 244. A protective film 245 made of SiN is formed on the arm portions 242 and 243. These arm portions 242 and 243 are optically coupled to the ring-shaped waveguide 244 with the same coupling coefficient κ. The arm portions 242 and 243 and the ring-shaped waveguide 244 constitute a ring resonator filter RF1. The ring resonator filter RF1 and the two-branch portion 241 constitute a reflective mirror M1.
[0039] Figure 6 is a cross-sectional view taken along line D-D in Figure 1. The ring-shaped waveguide 244 has a high-mesa structure in which an optical waveguide layer 244a made of InGaAsP is sandwiched between a first cladding layer 244b and a second cladding layer 244c. On the ring-shaped waveguide 244, a metal film 215c is provided on the second cladding layer 244c. The metal film 215c is made of, for example, Au. The metal film 215c may also have a laminated structure of Ti, Pt, and Au. On the ring-shaped waveguide 244, a protective film 244d made of SiN is formed so as to cover the metal film 215c. The metal film 215c is arranged along the ring-shaped waveguide 244 and is interposed between the protective film 244d and the second cladding layer 244c. A microheater 223 is also arranged on the protective film 244d. The microheater 223 is ring-shaped and positioned along the protective film 244d.
[0040] A laminated portion 24a is formed on the +Y direction side of the arm portion 242, and a laminated portion 24b is formed on the -Y direction side of the arm portion 243. The laminated portions 24a and 24b protrude in the +Z direction on the base portion 11. The laminated portions 24a and 24b can be manufactured by known semiconductor manufacturing processes. An electrode pad 233a is provided on the laminated portion 24a, and an electrode pad 233b is provided on the laminated portion 24b. The conductive electrode pad 233a has wiring 233a1 along the Y direction. The wiring 233a1 is electrically connected to the microheater 223. The conductive electrode pad 233b also has wiring 233b1 along the Y direction. The wiring 233b1 is electrically connected to the microheater 223.
[0041] Electrode pad 233b becomes the negative electrode. Electrode pad 233a becomes the positive electrode and is supplied with power from the control device 100. When power is supplied to electrode pad 233a, current flows from wiring 233a1 through microheater 223 to wiring 233b1, causing microheater 223 to heat up. When microheater 223 heats up, the metal film 215c is heated, and this heated metal film 215c heats the ring-shaped waveguide 244. Furthermore, because the control device 100 controls the power supplied to microheater 223, the temperature of microheater 223 changes, which in turn changes the temperature of ring-shaped waveguide 244 and its refractive index. The metal film 215c between microheater 223 and the second cladding layer 244c makes the temperature distribution on the -Z side of the metal film 215c uniform, thus suppressing uneven temperature distribution in ring-shaped waveguide 244.
[0042] The first waveguide section 21 and the second waveguide section 22 described above constitute an optical resonator C1, which is composed of a diffraction grating section 211b and a reflection mirror M1 that are optically connected to each other. The gain section 211a and the phase adjustment section 211c are located inside the optical resonator C1.
[0043] The diffraction grating 211b generates a first comb-shaped reflection spectrum having substantially periodic reflection characteristics at substantially predetermined wavelength intervals. On the other hand, the ring resonator filter RF1 generates a second comb-shaped reflection spectrum having substantially periodic reflection characteristics at substantially predetermined wavelength intervals. Here, the second comb-shaped reflection spectrum has a peak with a full width at half maximum that is narrower than the peak of the first comb-shaped reflection spectrum, and has substantially periodic reflection characteristics at wavelength intervals different from those of the first comb-shaped reflection spectrum. However, it should be noted that, considering the wavelength dispersion of the refractive index, the spectral components are not strictly at equiwavelength intervals.
[0044] To illustrate the characteristics of each comb-shaped reflection spectrum, the wavelength interval between peaks (free spectral region: FSR) of the first comb-shaped reflection spectrum is 840 GHz when expressed in terms of light frequency. On the other hand, the wavelength interval between peaks (FSR) of the second comb-shaped reflection spectrum is 730 GHz when expressed in terms of light frequency.
[0045] In the integrated semiconductor laser 10, in order to realize laser oscillation, one peak of the first comb-shaped reflection spectrum and one peak of the second comb-shaped reflection spectrum are configured to be overlapped on the wavelength axis. Such overlapping can be achieved by using at least one of the microheaters 221 and 223. By heating the diffraction grating portion 211b with the microheater 221 to change its refractive index by the thermo-optical effect and thereby changing the first comb-shaped reflection spectrum by moving it entirely on the wavelength axis, and / or by heating the ring waveguide 244 with the microheater 223 to change its refractive index and thereby changing the second comb-shaped reflection spectrum by moving it entirely on the wavelength axis.
[0046] On the other hand, in the integrated semiconductor laser 10, there are resonator modes by the optical resonator C1. And in the integrated semiconductor laser 10, the resonator length of the optical resonator C1 is set so that the interval between resonator modes (vertical mode interval) is 25 GHz or less. In this case, the resonator length of the optical resonator C1 is 1800 μm or more, and narrowing of the linewidth of the oscillating laser light can be expected. Note that the wavelength of the resonator mode of the optical resonator C1 can be finely adjusted by heating the phase adjustment portion 211c with the microheater 222 to change its refractive index and thereby moving the wavelength of the resonator mode entirely on the wavelength axis. That is, the phase adjustment portion 211c is a part for actively controlling the optical path length of the optical resonator C1.
[0047] The integrated semiconductor laser 10 is configured such that when the control device 100 injects current from the n-side electrode 12 and the p-side electrode 213 into the gain portion 211a to cause the gain portion 211a to emit light, laser oscillation occurs at a wavelength, for example, 1550 nm, where one peak of the spectral components of the first comb-shaped reflection spectrum, one peak of the spectral components of the second comb-shaped reflection spectrum, and one of the resonator modes of the optical resonator C1 coincide, and the laser light L1 is output.
[0048] In addition, in the integrated semiconductor laser 10, the wavelength of the laser beam L1 can be changed by utilizing the Vernier effect. For example, when the diffraction grating portion 211b is heated by the micro heater 221, the refractive index of the diffraction grating portion 211b increases due to the thermo-optical effect, and the first comb-shaped reflection spectrum of the diffraction grating portion 211b shifts entirely toward the longer wavelength side. As a result, the peak of the first comb-shaped reflection spectrum near 1550 nm is disengaged from the peak of the second comb-shaped reflection spectrum of the ring resonator filter RF1 and overlaps with another peak of the second comb-shaped reflection spectrum existing on the longer wavelength side (for example, near 1556 nm). Further, by controlling the temperature of the phase adjustment portion 211c to finely tune the resonator mode and overlapping one of the resonator modes with the two comb-shaped reflection spectra, laser oscillation near 1556 nm can be realized. That is, in the integrated semiconductor laser 10, the first comb-shaped reflection spectrum and the second comb-shaped reflection spectrum are respectively tuned by the micro heater 221 for the diffraction grating portion 211b and the micro heater 223 for the ring resonator filter RF1 to perform coarse tuning, and fine tuning is performed by tuning the resonator length by the micro heater 222 for the phase adjustment portion 211c, thereby realizing a wavelength variable operation.
[0049] [Modification Example] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be implemented in various other forms. For example, the present invention may be implemented by modifying the above-described embodiments as follows. Note that the above-described embodiments and the following modification examples may be combined with each other. The present invention also includes those configured by appropriately combining the components of the above-described embodiments and each modification example. Further, additional effects and modification examples can be easily derived by those skilled in the art. Therefore, a broader aspect of the present invention is not limited to the above-described embodiments and modification examples, and various changes are possible.
[0050] Figure 7 is a schematic diagram of a modified tunable laser device 1. The tunable laser device 1 does not have a microheater 222, a metal film 215b, or electrode pads 232a and 232b, but instead has a microheater 224, a metal film 215d, and electrode pads 234a and 234b. The microheater 224 is positioned on a protective film 245 of the arm portion 243. The region of the arm portion 243 below the microheater 224 functions as a phase adjustment unit 243c that changes the phase of light.
[0051] The metal film 215d is provided on the second cladding layer 244c. The metal film 215d is made of, for example, Au. The metal film 215d may also have a laminated structure of Ti, Pt, and Au. The metal film 215d is positioned along the phase adjustment section 243c and is interposed between the protective film 245 and the second cladding layer 244c.
[0052] A laminated portion 24c is formed near the phase adjustment portion 243c. The laminated portion 24c protrudes in the +Z direction on the base portion 11. The laminated portion 24c can be manufactured by a known semiconductor manufacturing process. Electrode pads 234a and 234b are provided on the laminated portion 24c. The conductive electrode pad 234a is electrically connected to the microheater 224. The conductive electrode pad 234b is also electrically connected to the microheater 224.
[0053] Electrode pad 234b becomes the negative electrode. Electrode pad 234a becomes the positive electrode and is supplied with power from the control device 100. When power is supplied to electrode pad 234a, current flows to electrode pad 234b via microheater 224, causing microheater 224 to heat up. When microheater 224 heats up, the metal film 215d is heated, and this heated metal film 215d heats the phase adjustment unit 243c. Furthermore, because the control device 100 controls the power supplied to microheater 224, the temperature of microheater 224 changes, which in turn changes the temperature of the phase adjustment unit 243c and thus its refractive index. The metal film 215d between microheater 224 and phase adjustment unit 243c helps to make the temperature distribution on the -Z side of the metal film 215d uniform, thus preventing the temperature of the phase adjustment unit 243c from becoming uneven.
[0054] Figure 8 is a modified view from the +Z direction of a microheater that heats the diffraction grating portion 211b and a metal film positioned on the +Z side of the diffraction grating portion 211b, and Figure 9 is a cross-sectional view taken along line E-E in Figure 8. In this modified view, strip-shaped microheaters 221a and 221b are provided on the protective film 214 instead of the microheater 221. The microheaters 221a and 221b, made of Ti, are positioned on the protective film 214 along the diffraction grating portion 211b.
[0055] Microheaters 221a and 221b are arranged with an interval between them in the X direction. The conductive electrode pad 231a has wiring 231a1 connected to microheaters 221a and 221b. The conductive electrode pad 231b also has wiring 231b1 connected to microheaters 221a and 221b.
[0056] Metal films 215a1 and 215a2 are provided on the second cladding layer 216b on the +Z direction side of the optical waveguide layer 211b1. The metal films 215a1 and 215a2 are made of, for example, Au. The metal film 215a may have a laminated structure of Ti, Pt, and Au. The metal films 215a1 and 215a2 are arranged along the diffraction grating portion 211b and are interposed in a strip shape between the protective film 214 and the second cladding layer 216b. The metal films 215a1 and 215a2 are spaced apart in the X direction. A microheater 221a is provided on the +Z direction side of the metal film 215a1, and a microheater 221b is provided on the +Z direction side of the metal film 215a2.
[0057] When power is supplied to the electrode pad 231a, current flows through the microheater 221a between the wiring 231a1 and 231b1 connected to the microheater 221a, causing the microheater 221a to heat up. Similarly, when power is supplied to the electrode pad 231a, current flows through the microheater 221b between the wiring 231a1 and 231b1 connected to the microheater 221b, causing the microheater 221b to heat up. When the microheaters 221a and 221b heat up, the metal films 215a1 and 215a2 are heated, and the diffraction grating portion 211b is heated by these heated metal films 215a1 and 215a2. The metal films 215a1 and 215a2 make the temperature distribution on the -Z direction side of the metal films 215a and 215a2 uniform, thus suppressing uneven temperature distribution of the diffraction grating portion 211b.
[0058] Figure 10 is a view from the +Z direction of a modified arrangement of a microheater that heats the diffraction grating portion 211b and a metal film positioned on the -Z side of the microheater. In this modified arrangement, microheaters 221a and 221b are provided on the protective film 214 instead of microheater 221. Also in this modified arrangement, conductive electrode pads 231ab, 231ac, 231bb, and 231bc are provided on the protective film 214 instead of electrode pads 231a and 231b. The wiring 231a1 of electrode pad 231ab is connected to microheater 221a, and the wiring 231a1 of electrode pad 231ac is connected to microheater 221b. Furthermore, the wiring 231b1 of the electrode pad 231bb is connected to the microheater 221a, and the wiring 231b1 of the electrode pad 231bc is connected to the microheater 221b.
[0059] On the +Z direction side of the optical waveguide layer 211b1, metal films 215a1 and 215a2 are provided on the second cladding layer 216b. The metal films 215a1 and 215a2 are arranged along the diffraction grating portion 211b and are interposed in a strip shape between the protective film 214 and the second cladding layer 216b. The metal films 215a1 and 215a2 are spaced apart in the X direction. A microheater 221a is provided on the +Z direction side of the metal film 215a1, and a microheater 221b is provided on the +Z direction side of the metal film 215a2.
[0060] When power is supplied to the electrode pad 231ab, current flows through the microheater 221a between the wiring 231a1 and 231b1 connected to the microheater 221a, causing the microheater 221a to heat up. Similarly, when power is supplied to the electrode pad 231ac, current flows through the microheater 221b between the wiring 231a1 and 231b1 connected to the microheater 221b, causing the microheater 221b to heat up. When the microheaters 221a and 221b heat up, the metal films 215a1 and 215a2 are heated, and the diffraction grating portion 211b is heated by these heated metal films 215a1 and 215a2. The metal films 215a1 and 215a2 make the temperature distribution on the -Z direction side of the metal films 215a and 215a2 uniform, thus suppressing uneven temperature distribution of the diffraction grating portion 211b.
[0061] Figure 11 is a cross-sectional view of the first waveguide section 21 according to a modified example. In this modified example, a high thermal resistance layer 218 is provided between the first waveguide section 21 and the base 11 on the -Z direction side of the first waveguide section 21. The high thermal resistance layer 218 is made of a semiconductor material with a lower thermal conductivity than the first cladding layer 216a, that is, a semiconductor material having a higher thermal resistance than the semiconductor material constituting the first cladding layer 216a. In this modified example, the thermal resistance is higher compared to a configuration without the high thermal resistance layer 218, making it possible to suppress heat from escaping from the first waveguide section 21 to the base 11.
[0062] The first waveguide section 21 is not limited to an embedded waveguide structure, but may also be a high mesa structure. Figure 12 is a cross-sectional view of the first waveguide section 21A of a high mesa structure at the same position as the line C-C in Figure 1. The first cladding layer 216aa is a semiconductor layer made of n-type InP. The second cladding layer 216ba is a semiconductor layer made of p-type InP.
[0063] A metal film 215a is provided on the second cladding layer 216b. The first cladding layer 216aa, the second cladding layer 216ba, the optical waveguide layer 211b1, the high refractive index portion 211b2, the low refractive index portion 211b3 (not shown), and the metal film 215a are covered with a protective film 214. A microheater 221 is positioned on the protective film 214 on the +Z direction side of the metal film 215a. An electrode pad 232a is provided on the protective film 214 on the +Y direction side of the first waveguide portion 21A, and an electrode pad 232b is provided on the protective film 214 on the -Y direction side of the first waveguide portion 21A.
[0064] Similar to the embodiment, the microheater 221 is connected to the electrode pad 232a by a wire 231a1 and to the electrode pad 232b by a wire 231b1 (not shown). In this configuration as well, when the microheater 221 generates heat, the metal film 215a is heated, and the diffraction grating portion 211b is heated by this heated metal film 215a. The metal film 215a makes the temperature distribution on the -Z direction side of the metal film 215a uniform, thereby suppressing uneven temperature distribution of the diffraction grating portion 211b in the high mesa structure.
[0065] Figure 13 is a schematic diagram showing a modified configuration for heating the ring-shaped waveguide 244. In this modified configuration, the second waveguide section 22 does not have the laminated section 24b, electrode pads 233a, 233b, and microheater 223, but does have a microheater 223a and electrode pads 233aa, 233ba.
[0066] The microheater 223a is formed in a C-shape with a portion of a ring cut off. Electrode pads 233aa and 233ba are provided on the laminated portion 24a. The conductive electrode pad 233aa has wiring 233a1 aligned in the Y direction. The wiring 233a1 is electrically connected to one end of the microheater 223a. The conductive electrode pad 233ba also has wiring 233b1 aligned in the Y direction. The wiring 233b1 is electrically connected to the other end of the microheater 223a.
[0067] Electrode pad 233ba becomes the negative electrode. Electrode pad 233aa becomes the positive electrode and is supplied with power from the control device 100. When power is supplied to electrode pad 233aa, current flows from wiring 233a1 through microheater 223a to wiring 233b1, causing microheater 223a to heat up. When microheater 223a heats up, the metal film 215c is heated, and this heated metal film 215c heats the ring-shaped waveguide 244. The metal film 215c between microheater 223a and the second cladding layer 244c helps to make the temperature distribution on the -Z side of the metal film 215c uniform, thereby suppressing uneven temperature distribution in the ring-shaped waveguide 244.
[0068] Figure 14 is a cross-sectional view of the first waveguide section 21 according to a modified example. In this modified example, the upper surfaces of the microheaters 221 and 222 are covered with a protective film 214a made of SiN. According to this modified example, a short circuit between the wiring 231a1 and the wiring 231b1 can be suppressed.
[0069] This invention can be used in optical semiconductor devices and integrated semiconductor lasers.
[0070] 1 Wavelength-tunable laser device 10 Integrated semiconductor laser 11 Base 12 n-side electrodes 21, 21A First waveguide section 22 Second waveguide section 24a, 24b, 24c Laminated section 100 Control device 211 Waveguide section 211a Gain section 211a1 Active core layer 211b Diffraction grating section 211b1 Optical waveguide layer 211b2 High refractive index section 211b3 Low refractive index section 211c Phase adjustment section 211c1 Optical waveguide layer 212 Semiconductor laminated section 213 p-side electrode 214 Protective film 215a, 215a1, 215a2, 215b, 215c, 215d Metal film 216a, 216aa First cladding layer 216b, 216ba Second cladding layer 217 Embedding layer 218 High thermal resistance layer 221-224, 221a, 221b, 223a Microheater 231a, 231b, 231ab, 231ac, 231bb, 231bc, 232a, 232b, 233a, 233aa, 233b, 233ba, 234a, 234b Electrode pad 231a1, 231b1, 232a1, 232b1, 233a1, 233b1 Wiring 241 Two-way branch 241a Multimode interference waveguide 242, 243 Arm section 242a Optical waveguide layer 243c Phase adjustment section 244 Ring-shaped waveguide 244a Optical waveguide layer 244b First cladding layer 244c Second cladding layer 244d, 245 Protective film C1 Optical resonator L1 Laser beam M1 Reflection mirror RF1 Ring resonator filter
Claims
1. An optical semiconductor element comprising: a base; a first cladding layer located on the base; an optical waveguide layer located on the first cladding layer; a second cladding layer located on the optical waveguide layer; a metal film located on the second cladding layer above the optical waveguide layer; a dielectric protective film covering the metal film; a heater located on the protective film above the metal film; a first wiring connected to the heater; and a second wiring connected to the heater.
2. The optical semiconductor device according to claim 1, wherein the first cladding layer includes a diffraction grating layer in which a low refractive index portion and a high refractive index portion having a higher refractive index than the low refractive index portion are periodically arranged along the direction in which the optical waveguide layer extends, the first cladding layer being located below the optical waveguide layer.
3. The optical semiconductor element according to claim 2, wherein the metal film is provided in a portion of the region above the diffraction grating layer, and the heater is provided above the portion of the region.
4. The optical semiconductor element according to claim 1, wherein the element has a plurality of first wirings and second wirings, and the first wirings and second wirings are connected to the heater alternately at intervals in the longitudinal direction of the heater.
5. The optical semiconductor element according to claim 4, wherein the element has a plurality of heaters, the first wiring is connected from one first electrode to each of the plurality of heaters, and the second wiring is connected from one second electrode to each of the plurality of heaters.
6. The optical semiconductor element according to claim 1, comprising a plurality of first electrodes and a plurality of second electrodes, wherein a first wiring is connected from each of the first electrodes to the heater, and a second wiring is connected from each of the second electrodes to the heater.
7. The optical semiconductor device according to claim 1, further comprising a thermal resistance layer having a thermal conductivity lower than that of the first cladding layer, located below the optical waveguide layer.
8. The optical semiconductor element according to claim 1, wherein the waveguide having the first cladding layer, the optical waveguide layer, and the second cladding layer is an embedded waveguide structure.
9. The optical semiconductor device according to claim 1, wherein the waveguide having the first cladding layer, the optical waveguide layer, and the second cladding layer has a high mesa waveguide structure.
10. The optical semiconductor element according to claim 1, wherein the upper surface of the heater, excluding the connection points with the first wiring and the connection points with the second wiring, is covered with a dielectric protective film.
11. An integrated semiconductor laser comprising an optical semiconductor element according to any one of claims 1 to 10.