Semiconductor lasers and module elements

Abstract

A semiconductor laser (10) according to the present invention comprises a first clad layer (102), an active layer (104), and a second clad layer (106) in order on a substrate (101), a ridge part disposed in the waveguide direction in the second clad layer and a heater (113) disposed near the ridge part are provided, and the oscillation wavelength is 1.6-2.4 µm. Between the first clad layer and the active layer, and the active layer and the second clad layer, respectively, a first guide layer (103), a second guide layer (105), a diffraction grating (112) at the boundary between the first clad layer and the first guide layer or the boundary between the second clad layer and the second guide layer, and an insulating film (111) on the surface of the second guide layer other than the ridge part are provided, and the heater is disposed on the insulating film.　As a result, the present invention can provide a semiconductor laser that performs wavelength sweeps at fast speed and over a wide wavelength range.

Description

[Technical Field]

[0001] The present invention relates to a semiconductor laser and a module element that can sweep wavelengths over a wide range at high speed. [Background technology]

[0002] Optical gas measurement systems are capable of measuring concentrations with high accuracy in real time, and are used in a variety of fields, such as analyzing the components of gases emitted from factories and gases in the atmosphere, inspecting for gas leaks from equipment and pipes, and testing for Helicobacter pylori in medical care.

[0003] Optical gas measurement systems basically utilize the phenomenon in which gas molecules absorb light at wavelengths specific to each gas species. Gas absorption lines can be broadly divided into fundamental tones, which involve only one vibrational energy, and overtones and combination tones, which involve multiple vibrational energies. For many gas species, fundamental tones exhibit significant light absorption in the wavelength range of 4 μm or longer, while overtones and combination tones exhibit significant light absorption in the wavelength range of 3 μm or shorter.

[0004] Figure 4 shows the wavelength range and intensity of absorption lines for gas species that exhibit significant optical absorption in the wavelength range from 1.6 μm to 2.4 μm (hereinafter referred to as the "wavelength range around 2 μm"). The wavelength range around 2 μm contains many absorption lines for gas species related to the greenhouse effect and environmental pollution, such as methane, carbon dioxide, nitrous oxide, carbon monoxide, hydrochloric acid, water, and ammonia. In the figure, gas species surrounded by dashed lines are related to the greenhouse effect, while gas species surrounded by dotted lines are related to environmental pollution. The shaded areas indicate the optical communication wavelength band.

[0005] Gas absorption lines have narrow linewidths, with multiple absorption lines clustered in a narrow wavelength range for each gas species. Since normal gas measurement uses a single absorption line, it is desirable that the light from the light source used in gas measurement has a narrow linewidth and a single wavelength. Semiconductor lasers are widely used as light sources for gas measurement because it is relatively easy to obtain emission at a single wavelength, they are compact, and they consume less power than gas lasers or solid-state lasers.

[0006] In order to apply semiconductor lasers used in gas measurement to the wavelength region around 2 μm, semiconductor lasers on InP substrates that oscillate at a single wavelength (hereinafter referred to as "lasers around 2 μm wavelength") have been researched and developed, and some of these lasers have already been put into practical use and are commercially available (for example, Non-Patent Documents 1, 2, and 4).

[0007] In lasers in the wavelength band around 2 μm, a multiple quantum well structure (MQW) with compressively strained InGaAs or InGaAsP well layers on an InP substrate is used as the active layer, making it possible to oscillate in a wavelength band longer than the optical fiber communication band.Furthermore, by applying the structures of DFB lasers and DBR lasers that have a proven track record in optical fiber communication lasers, oscillation at a single wavelength is possible.

[0008] Furthermore, by using InAs for the well layer, it is possible to fabricate a laser with an oscillation wavelength of 2.3 μm (for example, Non-Patent Document 3). Furthermore, by using a structure with an InGaAsSb well layer, it is possible to cover the wavelength range from 2.2 μm to 2.4 μm. Details are explained below.

[0009] As shown in FIG. 5 , a conventional semiconductor laser 30 on an InP substrate, which oscillates at a wavelength of around 2 μm, includes an n-type InP substrate 301, an n-type InP cladding layer 302, InGaAsP guide layers 303_1 and 303_2, an active layer 304, InGaAsP guide layers 305_2 and 305_1, a p-type InP cladding layer 306, a p-type InGaAs contact layer 307, an n-type electrode 308, and a p-type electrode 309.

[0010] The active layer 304 uses MQW, with well and barrier layers made of InGaAs or InGaAsSb, and a large compressive strain is applied to the well layer. The layer structure other than the MQW is substantially the same as that of lasers used in optical fiber communications, so a 2 μm band laser on an InP substrate can be fabricated in the same way as a laser for optical fiber communications.

[0011] As described above, the semiconductor laser 30 uses an MQW having a well layer to which a large compressive strain is applied, thereby lengthening the emission wavelength. The emission wavelength of the MQW is basically close to the bandgap wavelength of the well layer.

[0012] Figure 6 shows the change in bandgap wavelength when the thickness of the MQW well layer of a 2 μm band laser on an InP substrate is changed. Here, InGaAs or InGaAsSb (Sb molar composition ratio = 0.1, 0.2, 0.3) is used for the well layer and barrier layer, respectively, and the compressive strain of the well layer is set to 2%. Furthermore, the barrier layer is lattice-matched to InP, and the Sb molar composition ratio of the barrier layer is equal to that of the well layer.

[0013] As shown in Figure 6, by using InGaAsSb for the well layer, a bandgap wavelength of 2.2 μm to 2.4 μm can be obtained. By using an MQW including this InGaAsSb well layer as the active layer and providing a diffraction grating that will produce an oscillation wavelength near the bandgap wavelength, it is possible to fabricate a DFB laser or DBR laser that oscillates at a single wavelength in the wavelength range from 2.2 μm to 2.4 μm.

[0014] Figure 7 shows the oscillation spectrum of a DFB laser with an InGaAs / InGaAs MQW active layer fabricated on an InP substrate (injection current: 60 mA). The linewidth of the oscillation peak is approximately 0.1 to 0.2 nm, and the side mode suppression ratio (SMSR) is 30 dB.

[0015] On the other hand, as shown in FIG. 8, the gas species to be measured, for example, carbon dioxide ( 12 C 16 O2) absorption line (dotted line in the figure) and water ( 1 H2 16The absorption lines of carbon dioxide (CO) (solid lines in the figure) have a narrow linewidth around a wavelength of 2.05 μm, and many absorption lines are observed densely in a narrow wavelength range. The absorption lines were obtained using HITRAN (High-resolution transmission molecular absorption database). The spacing between absorption lines is approximately 0.5 nm for carbon dioxide and 2-3 nm for water.

[0016] In this way, in gas measurement, the linewidth of the semiconductor laser's oscillation spectrum is narrower than the wavelength interval of this absorption line, so in gas measurement using a semiconductor laser, one of the absorption lines is targeted, and the laser's oscillation wavelength is swept (changed) near the absorption line of the gas to analyze the change in light transmittance.

[0017] The oscillation wavelength of a semiconductor laser changes depending on the temperature of the heat sink on which the semiconductor laser is mounted and the current injected into the semiconductor laser. The time response of the laser wavelength change is faster with the injected current than with the heat sink temperature. Therefore, in gas measurement, the laser wavelength is usually swept by changing the injected current.

[0018] Figure 9 shows the change in oscillation wavelength due to the heat sink temperature and injection current of a DFB laser. Here, the DFB laser has a cavity length of 900 μm, an InGaAs / InGaAs MQW active layer on an InP substrate, and an oscillation wavelength set to around 2.05 μm. At each heat sink temperature (15°C, 25°C, 35°C, 45°C), increasing the injection current to the laser from 50 mA to 150 mA shifts the oscillation wavelength by about 0.2 nm toward the longer wavelength side.

[0019] Because both the linewidth of the gas absorption line and the linewidth of the laser oscillation spectrum are narrow, a wavelength sweep for one gas absorption line is possible with a shift of about 0.2 nm of the semiconductor laser, and this change in transmittance allows for the selection and measurement of just one absorption line of the target gas.

[0020] This change in oscillation wavelength due to the injection current is mainly caused by Joule heat generated by the current, which increases the temperature near the active layer and changes the effective refractive index. In this case, since the heat capacity of the laser itself is small, the laser oscillation wavelength changes in a shorter time than when the temperature of the heat sink is changed. Furthermore, when measuring trace gas concentrations, methods such as f-detection and 2f-detection can be used, in which the light source is modulated at a constant frequency and the signal from the detector is phase-sensitively detected at a frequency that is an integer multiple of that frequency.

[0021] On the other hand, changing the temperature of the heat sink allows for a wider range of temperature changes than changing the injection current. Figure 10 shows the change in oscillation wavelength when the injection current to the DFB laser is kept constant and the heat sink temperature is changed. The laser's oscillation wavelength changes by about 2 nm when the heat sink temperature is changed by 20°C, and the rate of change in oscillation wavelength is about 0.1 nm / °C.

[0022] This change in oscillation wavelength due to temperature is mainly due to the change in the effective refractive index, and is comparable for materials that can be fabricated on an InP substrate. Therefore, even for lasers with different oscillation wavelengths, the rate of change in oscillation wavelength due to the heat sink temperature is comparable to that of lasers oscillating at a wavelength around 2.05 μm.

[0023] As shown in Figure 11, by changing the temperature of the heat sink, it is possible to measure not only the absorption lines of one gas, but also multiple gas absorption lines. Here, the temperature of the heat sink was changed and light was incident from a DFB laser into a gas cell filled with carbon dioxide, and the change in transmittance was observed (solid line in the figure). When compared with the spectrum of the gas absorption line (dotted line in the figure), it is clear that the transmittance changes depending on the wavelength and intensity of the gas absorption line, making it possible to measure multiple gas absorption lines.

[0024] In this way, by sweeping the laser light over a wide wavelength range, it is possible to measure multiple absorption lines for a single gas species, improving the accuracy of gas measurement. Furthermore, by expanding the wavelength range that can be swept, it is possible to measure multiple gas species with a single laser. For example, by setting the DFB laser's oscillation wavelength to around 2.047 μm when the heat sink temperature is 15°C, and changing the oscillation wavelength with the heat sink temperature, it is possible to measure the absorption lines of both carbon dioxide and water gases (Figure 8).

[0025] As described above, in gas measurement using a semiconductor laser, it is useful to expand the wavelength range that can be swept. [Prior art documents] [Non-patent literature]

[0026] [Non-Patent Document 1] M. Mitsuhara and M. Oishi, “Chapter2: 2 μm wavelength lasers employing InP-based strained-layer quantum wells,” in “Long-wavelength infrared semiconductor lasers (ed. HK Choi,),” Wiley, New Jersey, 2004. [Non-patent document 2] T. Sato, M. Mitsuhara, T. Watanabe, K. Kasaya, T. Takeshita and Y. Kondo, “2.1-μm-wavelength InGaAs multiple-quantum-well distributed feedback lasers grown by MOVPE,” IEEE Journal of Selected Topics in QUuantum Electronics, VOL. 13, NO. 5, 2007, 1079-1082. [Non-patent document 3] T. Sato, M. Mitsuhara, N. Nunoya, T. Fujisawa, K. Kasaya, F. Kano and Y. Kondo, “2.33-μm-wavelength distributed feedback lasers with InAs-In0.53Ga0.47As multiple-quantum wells on InP substrates,” IEEE Photonics Technology Letters, VOL. 20, NO. 12, 2008, 1045-1047. [Non-patent document 4] https: / / www.ntt-electronics.com / product / gas_sensing / gas_sensing.html Summary of the Invention [Problem to be solved by the invention]

[0027] However, in a gas measurement system, when wavelength sweeping is performed by changing the temperature of the heat sink, it becomes difficult to perform measurement at high speed, as will be explained in detail below.

[0028] In a typical laser module, a semiconductor laser, a heat sink, a submount, and a Peltier element are mounted in that order. The temperature of the semiconductor laser is measured by a thermistor placed on the heat sink. When the temperature of the heat sink is changed, the temperature change of the semiconductor laser is affected not only by the heat capacity of the semiconductor laser, but also by the heat capacity of the heat sink, submount, and Peltier element. As a result, the total heat capacity from the semiconductor laser to the Peltier element becomes large, making it difficult to change the temperature of the laser in a short time. This is a problem because it takes a long time to measure the gas.

[0029] Furthermore, when using the f-detection method or 2f-detection method to measure gas concentration, it takes time to change the temperature of the heat sink and stabilize the temperature of the semiconductor laser (active layer), making it difficult to measure by modulating the light source at a high frequency.

[0030] In this way, in measurements where wavelength sweeping is performed by changing the temperature of the heat sink, the wavelength range that can be swept by the laser can be expanded, but on the other hand, high-speed measurements and high-frequency modulation measurements become difficult.

[0031] As described above, in measurements where wavelength sweep is performed by current injection, high speed measurements are possible, but it is difficult to expand the wavelength range.

[0032] As described above, in gas measurement using semiconductor lasers, high speed measurement over a wide wavelength range is an issue. [Means for solving the problem]

[0033] In order to solve the above-mentioned problems, the semiconductor laser according to the present invention comprises a first cladding layer, an active layer, and a second cladding layer, which are arranged in this order on a substrate, and a ridge portion disposed in the second cladding layer in a waveguiding direction; At a distance of 0.1 μm to 5 μm The heater to be placed a semiconductor optical amplifier disposed in the waveguiding direction; and a groove disposed between the heater and the semiconductor optical amplifier for suppressing a temperature increase in the semiconductor optical amplifier due to the heater. The oscillation wavelength is 1.6 μm to 2.4 μm. [Effects of the Invention]

[0034] According to the present invention, it is possible to provide a semiconductor laser and a module element that can sweep wavelengths at high speed over a wide wavelength range. [Brief explanation of the drawings]

[0035] [Figure 1A] FIG. 1A is a schematic perspective view showing the configuration of a semiconductor laser according to a first embodiment of the present invention. [Figure 1B] FIG. 1B is a cross-sectional view taken along line IB-IB' showing the configuration of the semiconductor laser according to the first embodiment of the present invention. [Figure 1C] FIG. 1C is a schematic top view showing the configuration of the semiconductor laser according to the first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram for explaining the operation of the semiconductor laser according to the first embodiment of the present invention. [Figure 3A] FIG. 3A is a schematic perspective view showing the configuration of an optical semiconductor element according to a second embodiment of the present invention. [Figure 3B] FIG. 3B is a schematic top view showing the configuration of the optical semiconductor element according to the second embodiment of the present invention. [Figure 4] FIG. 4 is a diagram for explaining gas measurement using a conventional semiconductor laser. [Figure 5] FIG. 5 is a cross-sectional view showing the configuration of a conventional semiconductor laser for gas measurement. [Figure 6] FIG. 6 is a diagram for explaining a conventional semiconductor laser for gas measurement. [Figure 7] FIG. 7 is a diagram for explaining a conventional semiconductor laser for gas measurement. [Figure 8] FIG. 8 is a diagram for explaining a conventional semiconductor laser for gas measurement. [Figure 9] FIG. 9 is a diagram for explaining a conventional semiconductor laser for gas measurement. [Figure 10] FIG. 10 is a diagram for explaining a conventional semiconductor laser for gas measurement. [Figure 11] FIG. 11 is a diagram for explaining a conventional semiconductor laser for gas measurement. DETAILED DESCRIPTION OF THE INVENTION

[0036] First Embodiment A semiconductor laser according to a first embodiment of the present invention will be described with reference to FIGS. 1A to 2. FIG.

[0037] <Configuration of semiconductor laser> As shown in FIGS. 1A to 1C, the semiconductor laser 10 according to this embodiment has a ridge waveguide structure having a ridge portion, and includes, in order, a substrate 101, a first cladding layer 102, a first guide layer 103, an active layer 104, a second guide layer 105, and a second cladding layer 106.

[0038] In addition, a diffraction grating 112 is provided at the boundary between the second guide layer 105 and the second cladding layer 106. The Bragg wavelength of the diffraction grating 112 is 2.33 μm.

[0039] An n-type InP substrate is used as the substrate 101, and an n-type electrode 108 made of, for example, AuGeNi or Au is provided on the back surface.

[0040] The first cladding layer 102 is n-type InP, and the first guide layer 103 is InGaAsP (having a bandgap wavelength of 1.15 μm and a film thickness of 0.1 μm).

[0041] The active layer 104 is a multiple quantum well (MQW) consisting of a compressively strained InGaAsSb well layer and a tensilely strained InGaAsSb barrier layer, with a layer thickness of 6 to 7 nm over four periods. The photoluminescence wavelength of the MQW is about 2.33 μm, and the carbon monoxide ( 12 C 16 O2) absorption line (Figure 2, see below).

[0042] The second guide layer 105 is made of InGaAsP (having a bandgap wavelength of 1.15 μm and a film thickness of 0.1 μm).

[0043] The second cladding layer 106 is made of p-type InP and has a protrusion that extends in the waveguide direction (Y direction in the drawing) and forms a ridge.

[0044] On the second cladding layer 106, a p-type electrode 109 such as AuZnNi or Au, and a pad electrode (for example, Au) 110 are provided in this order via a contact layer 107 such as p-type InGaAs.

[0045] On the surface of the semiconductor laser 10, an insulating film (for example, SiO2) 111 is formed on the portion other than the portion where the p-type electrode 109 is to be formed.

[0046] Furthermore, a heater 113 is disposed on the surface of the insulating film 111 on the second guide layer 105, near the ridge portion and parallel to the ridge portion. A pad electrode (e.g., Au) 114 is provided to electrically connect to the heater 113, and is connected to an external power supply (not shown) to apply voltage. The heater 113 is made of Pt, has a film thickness of 0.6 μm, and a width of 15 μm. Here, the distance between the heater 113 and the ridge portion is 0.2 μm.

[0047] Here, an example has been shown in which the heater 113 is arranged parallel to the ridge portion, but it does not have to be arranged parallel, and it is sufficient if it is arranged in the vicinity of the ridge portion.

[0048] <Semiconductor laser operation> The semiconductor laser 10 according to this embodiment is mounted in a semiconductor laser module. The semiconductor laser module includes, in order, the semiconductor laser 10 according to this embodiment, a heat sink, a submount, and a Peltier element.

[0049] In gas measurement, the wavelength of the gas absorption line is determined by the gas species, so the oscillation wavelength of the semiconductor laser must be matched to the wavelength of the gas absorption line to be measured and stabilized by temperature control. In this embodiment, the oscillation wavelength is changed by locally changing the temperature around the active layer 104 of the laser using heater 113 while the temperature of the heat sink is kept constant by a Peltier element.

[0050] In semiconductor lasers, the change in the oscillation wavelength of a DFB laser due to temperature is mainly due to the temperature change in the effective refractive index around the active layer, i.e., around the diffraction grating (resonator structure). Therefore, the longer the area through which the temperature propagates from a heat source such as a heat sink or heater, the longer it takes for the temperature around the active layer of the semiconductor laser to stabilize.

[0051] When wavelength sweeping is performed by changing the temperature of the heat sink in a conventional semiconductor laser, the temperature change and stabilization around the active layer is affected not only by the heat capacity of the semiconductor laser, but also by the heat capacity of the heat sink, submount, and Peltier element, so wavelength sweeping takes a long time.

[0052] On the other hand, in this embodiment, a heater 113 is provided in the semiconductor laser 10, which makes it possible to relatively reduce the dependency of temperature changes around the active layer 104 on the heat capacity of the heat sink, submount, and Peltier element compared to conventional semiconductor lasers, and to increase the dependency on the heat capacity of the main body of the semiconductor laser 10. As a result, it is possible to shorten the time for temperature change and stabilization around the active layer 104 and shorten the time required for wavelength sweeping, thereby enabling high-speed gas measurement.

[0053] Furthermore, if a heater is used in a buried-structure laser, which is conventionally used in semiconductor lasers on InP substrates, the heater is placed near the surface of the second cladding layer, which increases the distance between the heater and the active layer and the area through which the heater temperature propagates, resulting in a long time until the temperature around the active layer of the semiconductor laser stabilizes.

[0054] On the other hand, in the semiconductor laser 10 according to the present embodiment, the heater 113 can be disposed near the surface of the second guide layer 105 in the ridge waveguide structure, so that the distance between the heater 113 and the active layer 104 can be reduced, and the area through which the temperature of the heater 113 propagates can be reduced. As a result, the time required for the temperature around the active layer 104 of the semiconductor laser to stabilize can be shortened, and the time required for wavelength sweep can be shortened, enabling high-speed gas measurement.

[0055] Furthermore, in the semiconductor laser 10 according to this embodiment, in the second guide layer (InGaAsP) 105 exposed in a region other than the ridge portion, a part of the first cladding layer (n-type InP) 102 or the n-type InP substrate 101 may be removed in a region outside the region where the pad electrodes 110 and 114 are to be disposed. As a result, the region outside the region where the pad electrodes 110 and 114 are to be disposed does not have the second guide layer 105, the active layer 104, and the first guide layer 103. Here, "outside the region where the pad electrodes are to be disposed" refers to the side opposite the ridge portion with respect to each of the pad electrodes 110 and 114.

[0056] This reduces the volume of the semiconductor laser 10, reducing its heat capacity and preventing the heat from the heater 113 from propagating outside the laser region that becomes the active layer. As a result, heat conduction from the heater 113 to the laser region that becomes the active layer is improved, shortening the time required for wavelength sweeping and enabling high-speed gas measurement.

[0057] <Effects of semiconductor lasers> The effects of the semiconductor laser 10 according to this embodiment will be described. For comparison, a conventional semiconductor laser that changes (sweeps) the wavelength with a change in the temperature of the heat sink, i.e., the semiconductor laser 10, will also be described in which no current flows through the heater.

[0058] First, in the semiconductor laser 10, the oscillation threshold current is 30 mA when the heat sink temperature is 20° C., and the oscillation wavelength is 2.330 μm when the injection current is 100 mA.

[0059] Assuming a conventional case where wavelength is changed by changing the temperature of a heat sink, the injection current to the semiconductor laser 10 is kept constant at 100 mA, and the temperature of the heat sink is increased from 20°C to 50°C. As a result, the oscillation wavelength changes from 2.330 μm to 2.333 μm in approximately 500 milliseconds.

[0060] On the other hand, in the semiconductor laser 10 according to this embodiment, with the current injected into the laser held at 100 mA and the heat sink temperature held at 20° C., the oscillation wavelength is changed solely by the current flowing through the heater 113. By increasing the current flowing through the heater 113 from 0 mA to 210 mA, the oscillation wavelength changes from 2.330 μm to 2.333 μm in approximately 5 milliseconds.

[0061] For example, as shown in Figure 2, 12 C 16 The absorption spectrum of carbon monoxide (O2) has many absorption lines in the wavelength range of 2.325 to 2.345. 12 C 16When measuring carbon monoxide (O2), the oscillation wavelength of the semiconductor laser 10 is swept from 2.330 μm to 2.333 μm as described above. 12 C 16 It is possible to sweep at least one of the absorption lines of O2, and the gas concentration can be obtained by analyzing the change in light transmittance due to the light absorption.

[0062] As described above, the semiconductor laser according to the present embodiment can sweep the wavelength in a shorter time by arranging a heater near the active layer, compared to the conventional method of controlling the temperature of a heat sink, thereby enabling gas measurement by sweeping the wavelength over a wide wavelength range at high speed.

[0063] Therefore, the semiconductor laser according to this embodiment can significantly reduce the time required for gas measurement. Furthermore, the light source can be modulated at a high frequency during gas measurement, and high-sensitivity and high-accuracy measurements can be performed using the f detection method or 2f detection method.

[0064] When the temperature of the laser is changed using a heater, the temperature of the heat sink also has an effect, and the oscillation wavelength stabilizes when the laser, or more specifically, the area around the active layer, reaches thermal equilibrium. The time required to reach this thermal equilibrium can be shortened by adjusting the relative positions of the ridge of the semiconductor laser and the heater, the heater shape, and the isolation grooves to suppress heat conduction.

[0065] For example, in this embodiment, the spacing (distance) between the Pt heater and the ridge portion is set to 0.2 μm, but this is not limitative. The spacing (distance) between the heater and the ridge portion can be narrowed to approximately 0.1 μm by shortening the wavelength of the exposure light source, improving the positioning accuracy of the photomask and wafer, improving etching technology, etc.

[0066] Furthermore, if the gap (distance) between the heater and the ridge portion is long, the heat conduction from the heater to the waveguide decreases, so it is desirable to set this gap (distance) to about 5 μm or less.

[0067] <Method of manufacturing semiconductor laser> An example of a method for manufacturing the semiconductor laser 10 according to this embodiment will be described below.

[0068] First, a first cladding layer (n-type InP) 102, a first guide layer (InGaAsP) 103, an active layer (MQW) 104, a second guide layer (InGaAsP) 105, and an InP protective layer are grown on an n-type InP substrate 101 by metalorganic molecular beam epitaxy.

[0069] Next, after removing the InP protective layer, a diffraction grating 112 having a Bragg wavelength of 2.33 μm at room temperature is formed on the upper surface of the second guide layer (InGaAsP) 105 by etching.

[0070] Next, the second cladding layer (p-type InP) 106, the contact layer (p-type InGaAs) 107, and the InP protective layer are regrown on the diffraction grating 112 by metalorganic vapor phase epitaxy.

[0071] Next, the second cladding layer (p-type InP) 106, the contact layer (p-type InGaAs) 107, and the InP protective layer are processed by dry etching and wet etching to form a ridge portion.

[0072] Next, in the second guide layer (InGaAsP) 105 exposed in the area other than the ridge portion, the area outside the area where the pad electrode will be placed in the process described below is removed down to the first cladding layer (n-type InP) 102 or a part of the n-type InP substrate 101.

[0073] Next, an insulating film is deposited over the entire upper surface of the wafer, and then the insulating film and the InP protective layer on the contact layer (p-type InGaAs) 107 are removed.

[0074] Next, metal (AuZnNi, Au) that will become p-type electrode 109 is evaporated on contact layer (p-type InGaAs) 107 by resistance heating.

[0075] Next, a heater 113 made of Pt is formed on the insulating film 111 near the ridge portion by lithography and electron beam evaporation.

[0076] Next, a p-type electrode 109 and pad electrodes 110 and 114 of a heater 113 made of Au are formed.

[0077] Next, after polishing the rear surface of the n-type InP substrate 101, metal (AuGeNi, Au) that will become the n-type electrode 108 is evaporated and annealed to form the electrode.

[0078] Next, a ridge waveguide structure with a cavity length of 450 μm is formed by cleavage.

[0079] Finally, a highly reflective film is deposited on one cleaved surface, and an anti-reflective film is deposited on the other cleaved surface.

[0080] In this manner, the semiconductor laser 10 is manufactured.

[0081] Although the present embodiment has been described as an example using a DFB laser configuration, a DBR laser configuration may also be used, which uses a change in refractive index to control the oscillation wavelength in the same way as a DFB laser.

[0082] In this embodiment, an example in which Pt is used for the heater has been shown, but the metal used for the heater may be any conductor with high resistance, and for example, a metal such as a titanium tungsten alloy (TiW) may be used.

[0083] <Second embodiment> An optical semiconductor device according to a second embodiment of the present invention will be described with reference to FIGS. 3A and 3B.

[0084] <Configuration of optical semiconductor element> As shown in FIGS. 3A and 3B, the optical semiconductor device 20 according to this embodiment has a ridge waveguide structure having a ridge portion, and includes a semiconductor laser 20_1 and a semiconductor optical amplifier (SOA) 20_2.

[0085] Similar to the first embodiment, the semiconductor laser 20_1 includes, in this order, a substrate 201, a first cladding layer 202, a first guide layer 203_1, an active layer 204_1, a second guide layer 205_1, and a second cladding layer 206, and the first cladding layer 202 to the second cladding layer 206 form a ridge waveguide. Here, the second cladding layer 206 has a convex portion that forms a ridge portion.

[0086] An n-type electrode 208 is provided on the rear surface of the substrate 201, and a p-type electrode 209_1 and a pad electrode 210_1 are provided in this order on the second cladding layer 206 via a contact layer 207_1.

[0087] A diffraction grating 212 is provided at the boundary between the second guide layer 205_1 and the second cladding layer 206, and a heater 213 and a pad electrode 214 are provided near the second cladding layer 206.

[0088] The active layer 204_1 is a multiple quantum well (MQW) and is made up of four periods of compressively strained InGaAs well layers and InGaAsP barrier layers that are nearly lattice-matched to InP. The photoluminescence wavelength of the MQW is about 1.80 μm, and the photoluminescence wavelength of the hydrogen chloride ( 1 H 28 Cl) and water ( 1 H2 16 O) absorption line.

[0089] Moreover, the diffraction grating 212 of the semiconductor laser 20_1 has a Bragg wavelength of 1.80 μm at room temperature.

[0090] Other configurations of the semiconductor laser 20_1 are substantially the same as those of the first embodiment.

[0091] The semiconductor optical amplifier (SOA) 20_2 includes, in order, a substrate 201, a first cladding layer 202, a third guide layer 203_2, an SOA active layer 204_2, a fourth guide layer 205_2, and a second cladding layer 206, and the first cladding layer 202 to the second cladding layer 206 form a ridge waveguide. An n-type electrode 208 is provided on the back surface of the substrate 201, and a p-type electrode 209_2 and a pad electrode 210_2 are provided on the second cladding layer 206 via a contact layer 207_2, in order.

[0092] Here, in order to narrow the injection current to the semiconductor laser 20_1 and the injection current to the SOA 20_2, the contact layers 207_1 and 207_2, the p-type electrodes 209_1 and 209_2, and the pad electrodes 210_1 and 210_2 are separated, and a portion near the upper surface of the second cladding layer 206 is removed.

[0093] Moreover, the substrate 201, the first cladding layer 202, the second cladding layer 206, and the n-type electrode 208 are common to the semiconductor laser 20_1.

[0094] In the SOA 20_2, the SOA active layer 204_2 is a multiple quantum well (MQW) that is made up of four periods of compressively strained InGaAs well layers and InGaAsP barrier layers that are nearly lattice-matched to InP. The photoluminescence wavelength of the MQW4 is about 1.85 μm.

[0095] In the optical semiconductor element 20, the ridge waveguide of the semiconductor laser 20_1 and the ridge waveguide of the SOA 20_2 are optically coupled and connected in the waveguiding direction (Y direction in the drawing).

[0096] <Effects of optical semiconductor elements> The optical semiconductor element 20 according to this embodiment is mounted in an optical semiconductor module. The optical semiconductor module includes, in order, the optical semiconductor element 20 according to this embodiment, a heat sink, a submount, and a Peltier element.

[0097] First, the temperature of the heat sink of the optical semiconductor module is set to 20°C, the injection current to the semiconductor laser 20_1 is set to 100 mA, and the injection current to the semiconductor optical amplifier is set to 250 mA. Next, by increasing the heater current from 0 mA to 180 mA, the wavelength emitted from the semiconductor optical amplifier changes from 1.800 μm to 1.804 μm in about 5 milliseconds.

[0098] At this time, the optical output power decreases from 12 mW to 10 mW. In this way, the decrease in optical output power during wavelength sweeping can be suppressed to about 2 mW.

[0099] For example, hydrogen chloride ( 1 H 28 Cl) and water ( 1 H2 16 When measuring hydrogen chloride (O), the oscillation wavelength of the optical semiconductor element 20 is swept from 1.800 μm to 1.804 μm as described above. 1 H 28 Cl) and water ( 1 H2 16 It is possible to sweep at least one absorption line for each of the 2000 mW and 1000 mW of fluorine-containing gases, and obtain the gas concentration by analyzing the change in light transmittance due to the light absorption. In this way, multiple gas species can be measured with a single laser.

[0100] In a semiconductor laser for gas measurement, it is desirable that the change in optical output power due to the change in wavelength be small. However, in the semiconductor laser 10 according to the first embodiment, when the temperature around the active layer increases, not only the oscillation wavelength but also the optical output power decreases.

[0101] On the other hand, in the optical semiconductor device 20 according to this embodiment, the decrease in optical output during wavelength sweeping due to an increase in temperature around the active layer of the semiconductor laser 20_1 can be compensated for by the SOA, thereby suppressing changes in optical output.

[0102] The optical semiconductor element according to this embodiment has the same effects as the first embodiment, and is capable of sweeping wavelengths over a wide wavelength range at high speed, while suppressing changes in optical output, enabling highly accurate gas measurement.

[0103] In addition, in this embodiment, as shown in Figures 3A and 3B, in order to suppress heat conduction from the heater of the semiconductor laser to the SOA, a part of the first cladding layer other than the ridge waveguide, the first and / or third guide layer, the active layer and / or SOA active layer, and the second and / or fourth guide layer may be removed between the vicinity of the heater of the semiconductor laser and the SOA, and a configuration may be formed in which a groove 215 is provided.

[0104] This makes the SOA less susceptible to temperature increases caused by the heater, making it easier to control the heat sink temperature. This allows the output of the semiconductor laser to be efficiently amplified and changes in optical output to be suppressed, enabling highly accurate gas measurement.

[0105] <Method of manufacturing optical semiconductor element> An example of a method for manufacturing the optical semiconductor element 20 according to this embodiment will be described below.

[0106] First, as a layer structure constituting the semiconductor laser 20_1, a first cladding layer (n-type InP) 202, a first guide layer (InGaAsP) 203_1, an active layer (MQW) 204_1, a second guide layer (InGaAsP) 205_1, a second cladding layer (n-type InP) 206, and an InP protective layer are crystal-grown in this order on an n-type InP substrate 201 by metal organic vapor phase epitaxy, as in the first embodiment.

[0107] Next, the first guide layer (InGaAsP) to the InP protective layer in the region other than the portion constituting the semiconductor laser 20_1 are removed by etching.

[0108] Next, using metal organic vapor phase epitaxy, the following layers are regrown in the etched region in this order as a layer structure constituting the semiconductor optical amplifier (SOA) 20_2: a third guide layer (InGaAsP) 203_2, an SOA active layer (MQW) 204_2, a fourth guide layer (InGaAsP) 205_2, and a portion of the second cladding layer (p-type InP).

[0109] Next, after removing the InP protective layer from the portion constituting the semiconductor laser 20_1, a diffraction grating 212 is formed by etching on the upper surface of the second guide layer (InGaAsP) 205_1 in this portion.

[0110] Next, a second cladding layer (p-type InP) 206, a contact layer (p-type InGaAs), and an InP protective layer are regrown on the entire surface of the wafer by metal organic vapor phase epitaxy.

[0111] Next, the second cladding layer (p-type InP) 206, the contact layer (p-type InGaAs), and the InP protective layer are processed by dry etching and wet etching to form ridge portions in the semiconductor laser 20_1 and the SOA 20_2.

[0112] Next, in the second guide layer (InGaAsP) 205_1 exposed in the area other than the ridge portion, the area outside the area where the pad electrode will be placed in the process described later is removed down to the first cladding layer (n-type InP) 202 or a part of the n-type InP substrate 201.

[0113] Next, in the region between the vicinity of the heater 213 of the semiconductor laser 20_1 and the SOA 20_2, a part of the first cladding layer 202 other than the ridge waveguide, the first and / or third guide layers 203_1, 203_2, the active layer and / or SOA active layer 204_1, 204_2, and the second and / or fourth guide layers 205_1, 205_2 are removed to form a groove 215.

[0114] Next, in order to electrically isolate the semiconductor laser 20_1 and the SOA 20_2 during current injection, a part of the second cladding layer (p-type InP) 206, the contact layer (p-type InGaAs), and the InP protective layer near (around) the boundary between the semiconductor laser 20_1 and the SOA 20_2 are removed, resulting in the separation of regions that will become the contact layer (p-type InGaAs) 207_1 of the semiconductor laser 20_1 and the contact layer (p-type InGaAs) 207_2 of the SOA.

[0115] Next, an insulating film 211 is deposited over the entire upper surface of the wafer, and then the insulating film 211 and the InP protective layer on the contact layers (p-type InGaAs) 207_1 and 207_2 of the semiconductor laser 20_1 and the SOA 20_2 are removed.

[0116] Next, metals (AuZnNi, Au) to become p-type electrodes 209_1 and 209_2 are evaporated on the contact layers (p-type InGaAs) 207_1 and 207_2 by resistance heating.

[0117] Next, a heater 213 made of Pt is formed on the insulating film 211 near the ridge portion by lithography and electron beam evaporation.

[0118] Next, pad electrodes 210_1 and 210_2 of the p-type electrode 209 and a pad electrode 214 of the heater 213 are formed, each made of Au.

[0119] Next, after polishing the rear surface of the n-type InP substrate 201, an n-type electrode 208 is vapor-deposited and annealed to form the electrode.

[0120] Next, a ridge waveguide structure is formed by cleavage, with the semiconductor laser 20_1 having a cavity length of 450 μm and the SOA 20_2 having a length of 600 μm.

[0121] Finally, a high reflection film is deposited on the cleavage plane on the semiconductor laser 20_1 side, and an anti-reflection film is deposited on the cleavage plane on the SOA 20_2 side.

[0122] In this manner, the optical semiconductor element 20 is manufactured.

[0123] In the embodiment of the present invention, an example has been shown in which only the current flowing through the heater is changed, but the oscillation wavelength may be changed by changing both the current flowing through the heater and the injection current.

[0124] In an embodiment of the present invention, carbon monoxide ( 12 C 16O2) as the measurement target, and an MQW active layer with a photoluminescence wavelength of about 2.33 μm is used to change the oscillation wavelength from 2.330 μm to 2.333 μm. 1 H 28 Cl) and water ( 1 H2 16 In the example shown, the measurement target is a gas (O) and an MQW active layer with a photoluminescence wavelength of about 1.80 μm is used, with the emission (oscillation) wavelength being 1.800 μm to 1.804 μm, but the present invention is not limited to this. Other gases may be measured, and the oscillation wavelength of the semiconductor laser may be set to another wavelength band between 1.6 and 2.4 μm.

[0125] In addition, in the MQW, the well layer can be made of InGaAs, InAs, or InGaAsSb, and the barrier layer can be made of InGaAs, InGaAsP, or InGaAsSb, as long as it can accommodate a laser oscillation wavelength of 1.6 to 2.4 μm. The layer thickness and period can also be within a range that does not cause lattice relaxation.

[0126] The cladding and guiding layers may be made of materials that are approximately lattice-matched to InP and have the functions of both the cladding and guiding layers. Here, "approximately lattice-matched to InP" refers to a state in which lattice relaxation does not occur on InP.

[0127] Furthermore, the substrate is not limited to an InP substrate, but may be a dielectric substrate such as SiO2, a Si substrate, an SOI substrate, or the like, using wafer bonding or the like.

[0128] Although the example in which the diffraction grating is disposed at the boundary between the second cladding layer and the second guide layer has been shown, it may also be disposed at the boundary between the first cladding layer and the first guide layer. The configuration of the diffraction grating (depth, period, etc.) may be set in accordance with the oscillation wavelength of the semiconductor laser.

[0129] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the configuration and manufacturing method of the semiconductor laser are shown, but the present invention is not limited to these examples. Anything that can exhibit the functions and effects of the semiconductor laser can be used. [Industrial Applicability]

[0130] The present invention relates to a wavelength-swept semiconductor laser and a module element, and can be applied to gas measurement. [Explanation of symbols]

[0131] 10 Semiconductor laser 101 Substrate 102 First cladding layer 104 Active layer 106 Second cladding layer 113 Heater

Claims

1. a first cladding layer, an active layer, and a second cladding layer disposed in this order on a substrate; a ridge portion disposed in the second cladding layer in a waveguide direction; a heater disposed at a distance of 0.1 μm to 5 μm from the ridge portion; a semiconductor optical amplifier disposed in the waveguiding direction; a groove disposed between the heater and the semiconductor optical amplifier for suppressing a temperature increase in the semiconductor optical amplifier due to the heater; Equipped with The oscillation wavelength is 1.6 μm to 2.4 μm. A semiconductor laser characterized by:

2. a first guide layer disposed between the first cladding layer and the active layer; a second guide layer disposed between the active layer and the second cladding layer; a diffraction grating disposed at either the boundary between the first cladding layer and the first guide layer or the boundary between the second cladding layer and the second guide layer; an insulating film disposed on a surface of the second guide layer other than the ridge portion, The heater is disposed on the insulating film on the surface of the second guide layer.

2. The semiconductor laser according to claim 1.

3. a pad electrode electrically connected to the heater and disposed on the surface of the second guide layer via the insulating film; The second guide layer, the active layer, and the first guide layer are not included in the region outside the pad electrode.

3. The semiconductor laser according to claim 2.

4. the active layer has a multiple quantum well structure, In the multiple quantum well structure, the well layer is made of any one of InGaAs, InAs, and InGaAsSb, and the barrier layer is made of any one of InGaAs, InGaAsP, and InGaAsSb.

4. The semiconductor laser according to claim 2 or 3.

5. The heater is disposed parallel to the ridge.

5. The semiconductor laser according to claim 1, wherein the first and second electrodes are arranged parallel to each other.

6. A semiconductor laser according to any one of claims 1 to 5; A heat sink; Peltier element and A modular element comprising:

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