Semiconductor laser element, semiconductor laser device, manufacturing method for semiconductor laser device, and gas analyzer

Abstract

The present invention is a distributed feedback semiconductor laser element (3) that increases the intensity of a single-mode light while stably outputting the same, and has a diffraction grating (3M) formed on a waveguide (3L), wherein: the waveguide (3L) comprises a diffraction grating section (301) having the diffraction grating (3M) formed therein, and a flat section (302) having a region that does not have the diffraction grating (301) formed therein and is wider than the diffraction grating section (301); the flat section (302) has a connecting section (303) having a region that has a width that changes continuously approaching the site of connection with the diffraction grating section (301); and a highly reflective film (HR) is provided to an end surface on the opposite side of the flat section (302) from the connecting section (303), and an anti-reflective film (AR) is provided to an end surface on the opposite side of the diffraction grating section (301) from the connecting section (303).

Description

[Technical Field]

[0001] The present invention relates to a semiconductor laser element, a semiconductor laser device, a method for manufacturing a semiconductor laser element, and a gas analyzer. [Background technology]

[0002] Conventionally, mid-infrared laser absorption spectroscopy (QCL-IR) is one of the gas analysis methods using quantum cascade lasers (QCLs) that oscillate in the mid-infrared region.

[0003] This QCL-IR gas analyzer irradiates a sample containing a component to be measured with laser light from a quantum cascade laser, detects the intensity of the laser light transmitted through the sample with a photodetector, and analyzes the component to be measured using the detection signal. Here, the quantum cascade laser must control the oscillation wavelength to a wavelength suitable for the component to be measured and efficiently extract a single light beam at the desired oscillation wavelength; for example, a quantum cascade laser such as that shown in Patent Document 1 is used.

[0004] In this quantum cascade laser, a periodic diffraction grating corresponding to the oscillation wavelength is formed in the waveguide in order to extract a single light beam with a desired oscillation wavelength. In the quantum cascade laser, in order to improve the single mode of the laser beam, it is desirable to reduce the width dimension of the waveguide, and in order to increase the output (gain) of the laser beam, it is desirable to increase the width dimension and length dimension of the waveguide.

[0005] However, if the width of the waveguide is reduced (to approximately twice the oscillation wavelength or less) in order to improve the single-mode characteristics of the laser light, the output power (gain) of the laser light will decrease. On the other hand, if the width or longitudinal direction of the waveguide is increased in order to increase the intensity of the laser light, the single-mode characteristics of the laser light will decrease. In other words, there is a trade-off between the single-mode characteristics of the laser light and the optical output power (gain) in terms of the width of the waveguide.

[0006] Furthermore, increasing the width or length of the waveguide to increase the intensity of the laser beam increases the power consumption required for laser oscillation, which in turn increases the temperature rise of the semiconductor laser element, increases the chirp rate of the laser oscillation wavelength, and reduces the resolution in gas analysis. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 8-107253 Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above problems, the inventors of the present application have considered forming a diffraction grating portion in which a diffraction grating is formed and a flat portion in which no diffraction grating is formed in a waveguide having a diffraction grating, as shown in FIG. 9, thereby improving single mode characteristics by reducing the width of the diffraction grating portion and increasing the width of the flat portion to increase the output (gain) of the laser light.

[0009] However, it has been found that in the above configuration, unintended reflection occurs at the corner formed between the diffraction grating portion and the flat portion, hindering single mode characteristics.

[0010] The present invention has been made to solve the above-mentioned problems, and its main object is to increase the optical output (gain) of a semiconductor laser element while stably outputting single-mode light. [Means for solving the problem]

[0011] That is, the semiconductor laser element according to the present invention is a semiconductor laser element having a diffraction grating formed on a waveguide, wherein the waveguide comprises a diffraction grating portion in which the diffraction grating is formed, and a flat portion having a region in which the diffraction grating is not formed and which is wider than the diffraction grating portion, the flat portion has a connection portion having a region whose width continuously changes toward the connection point with the diffraction grating portion, and a high-reflection film is provided on an end face of the flat portion opposite to the connection portion, and a low-reflection film is provided on an end face of the diffraction grating portion opposite to the connection portion.

[0012] Such a semiconductor laser element has a narrow diffraction grating portion and a wide flat portion, thereby improving single-mode characteristics while increasing the output (gain) of laser light. Furthermore, the flat portion has a connection portion whose width continuously changes toward the connection point with the diffraction grating portion, thereby reducing unintended reflections and enabling stable output of single-mode light. Furthermore, a high-reflection film is provided on the end face of the flat portion opposite the connection portion, and a low-reflection film is provided on the end face of the diffraction grating portion opposite the connection portion, enabling stable output of single-mode light from the end face of the diffraction grating portion. Since the end face of the diffraction grating portion opposite the connection portion serves as a light exit surface, single-mode characteristics can be further improved.

[0013] As a specific embodiment, the width of the connection portion may be gradually narrowed toward the connection point with the diffraction grating portion.

[0014] It is also considered that the maximum width of the connection portion is equal to or smaller than the maximum width of the portion of the flat portion other than the connection portion, and the minimum width of the connection portion is equal to or larger than the maximum width of the diffraction grating portion.

[0015] It is desirable that the flat portion have a rectangular portion having a rectangular shape and the connection portion.

[0016] Specifically, in order to reduce unintentional reflection between the diffraction grating portion and the connecting portion, or between the flat portion and the connecting portion, it is desirable that the connecting portion between the diffraction grating portion and the connecting portion and / or the connecting portion between the flat portion and the connecting portion be R-shaped.

[0017] As a specific embodiment of the connection portion, the connection portion may have a tapered portion whose width continuously narrows toward the connection point with the diffraction grating portion, and a narrow portion connecting the tapered portion and the diffraction grating portion.

[0018] In order to suppress oscillation in transverse modes and emit single-mode light, it is desirable that the width of the light-emitting end of the waveguide be 1 to 2 times the oscillation wavelength.

[0019] In order to reasonably achieve both stabilization of single-mode light and increase in optical output (gain), it is desirable that the area of ​​the region where the diffraction grating is not formed be equal to or larger than the area of ​​the region where the diffraction grating is formed.

[0020] It is desirable to have a first electrode for supplying a current to the diffraction grating portion, and a second electrode provided separately from the first electrode for supplying a current to the flat portion. This configuration allows the current flowing through the diffraction grating section and the current flowing through the flat section to be controlled independently, thereby reducing the current flowing through the grating section and reducing the chirp rate, which is the rate at which the oscillation wavelength changes when a pulsed current is applied, and improving the resolution when used in a gas analyzer.

[0021] If a diffraction grating is formed at the connection portion, the width of the region where the diffraction grating is formed may change, which may cause instability of the single-mode light. For this reason, it is desirable that the connection portion be a region where the diffraction grating is not formed. With this configuration, the single-mode characteristics can be further improved.

[0022] Furthermore, a manufacturing method of a semiconductor laser element according to the present invention is a manufacturing method of a semiconductor laser element having a diffraction grating formed on a waveguide, and is characterized by comprising: a structure forming step of forming a laminated structure on a substrate, the laminated structure having a diffraction grating region where the diffraction grating is formed and a flat region where the diffraction grating is not formed; and a waveguide forming step of etching the laminated structure to form a waveguide having a diffraction grating portion where the diffraction grating is formed and a flat portion where the diffraction grating is not formed and has a region wider than the diffraction grating portion, the flat portion having a region where the width continuously changes toward the connection point with the diffraction grating portion.

[0023] Furthermore, a semiconductor laser device according to the present invention is a semiconductor laser device comprising a substrate and a semiconductor laser element provided on the substrate, wherein the semiconductor laser element is a distributed feedback type having a diffraction grating formed on a waveguide, the waveguide comprising a diffraction grating portion where the diffraction grating is formed, and a flat portion having a region where the diffraction grating is not formed and which is wider than the diffraction grating portion, and the flat portion has a connection portion having a region whose width continuously changes toward a connection point with the diffraction grating portion.

[0024] Furthermore, the present invention provides a gas analyzer for analyzing a component to be measured contained in a gas, comprising: a measurement cell into which the gas is introduced; the semiconductor laser device for irradiating the measurement cell with laser light; a photodetector for detecting the laser light that has passed through the measurement cell; and an analysis unit for analyzing the component to be measured using a detection signal from the photodetector. [Effects of the Invention]

[0025] According to the present invention configured as described above, the semiconductor laser element can stably output single-mode light while increasing the optical output (gain). [Brief explanation of the drawings]

[0026] [Figure 1]1 is an overall schematic diagram of an exhaust gas analyzer in which a semiconductor laser device according to an embodiment of the present invention is used. [Figure 2] FIG. 2 is an overall schematic diagram of the semiconductor laser device according to the embodiment. [Figure 3] FIG. 2 is a cross-sectional view perpendicular to the waveguide direction of the semiconductor laser element of the embodiment. [Figure 4] FIG. 2 is a cross-sectional view of the semiconductor laser element of the embodiment taken along line AA. [Figure 5] FIG. 2 is a plan view showing a waveguide of the semiconductor laser element according to the embodiment. [Figure 6] 3A to 3C are schematic diagrams illustrating a method for manufacturing the semiconductor laser device according to the embodiment. [Figure 7] FIG. 10 is a plan view showing a waveguide of a semiconductor laser device according to a modified embodiment. [Figure 8] FIG. 10 is a plan view showing a waveguide of a semiconductor laser device according to a modified embodiment. [Figure 9] FIG. 10 is a plan view showing a waveguide of a semiconductor laser device as a comparative example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a semiconductor laser device according to the present invention will now be described with reference to the drawings.

[0028] <1.Device configuration> 1, the semiconductor laser device 100 of this embodiment is used in a gas analyzer 10 that analyzes measurement target components in exhaust gas emitted from an internal combustion engine, for example. Here, the gas analyzer 10 has a multi-reflection type measurement cell 11 into which exhaust gas is introduced, a semiconductor laser device 100 that irradiates laser light onto the measurement cell 11, a photodetector 12 that detects the laser light that has passed through the measurement cell 11, and an analysis unit 13 that analyzes the measurement target components using the detection signal of the photodetector 12.

[0029] Specifically, the semiconductor laser device 100 has a wavelength range of ±1 cm relative to the absorption wavelength of the component to be measured. -1As shown in FIGS. 2 and 3, the laser diode has a semiconductor substrate 2 such as an InP substrate and a semiconductor laser element 3 formed on the semiconductor substrate 2.

[0030] The semiconductor substrate 2 on which the semiconductor laser element 3 is provided is housed in an airtight container 5 such as a butterfly package. A light guiding section 51 for guiding the laser light to the outside is formed in a portion of the airtight container 5 facing the light emission surface 3x of the semiconductor laser element 3. An optical window member 6 is provided in the light guiding section 51, and the optical window member 6 is slightly inclined (for example, by 2 degrees) so that the laser light reflected by the optical window member 6 does not return to the semiconductor laser element 3. In addition, a cooling module 7 for cooling the semiconductor laser element 3 and the like are also housed in the airtight container 5.

[0031] 3 and 4, the semiconductor laser element 3 is of a distributed feedback (DFB) type, and includes a waveguide 3L composed of a cladding layer and a core layer provided on a semiconductor substrate 2. In this waveguide 3L, light passes through the core layer due to the difference in refractive index between the cladding layer and the core layer.

[0032] Specifically, the semiconductor laser device 3 is formed by forming a buffer layer 31, a core layer 32, an upper cladding layer 33, and a cap layer 34 in this order on the upper surface of a semiconductor substrate 2. These layers 31 to 34 all extend in the same direction. These layers 31 to 34 also all extend in the same direction, and their widthwise side surfaces are covered with a protective film 35 to form a waveguide 3L extending in one direction. The protective film 35 is an inorganic film, and may be, for example, SiO2 or a combination of SiO2 and Si3N4.

[0033] The buffer layer 31 and the upper cladding layer 33 are both layers made of InP. A lower cladding layer made of InP may be provided between the buffer layer 31 and the core layer 32, or the buffer layer 31 may function as a cladding layer.

[0034] The cap layer 34 is a layer made of InGaAs, and a part of its upper surface (the central part in the width direction) is covered with an upper electrode 91.

[0035] The core layer 32 has a lower guide layer 321 made of InGaAs, an active layer 322 that emits light when a current is injected therein, and an upper guide layer 323 made of InGaAs.

[0036] The active layer 322 has a multiple quantum well structure having multiple well layers, and is configured by alternately stacking a predetermined number of semiconductor layers that form the light-emitting region and semiconductor layers that form the injection region. The semiconductor layers that form the light-emitting region are configured by alternately stacking InGaAs and InAlAs, and the semiconductor layers that form the injection region are configured by alternately stacking InGaAs and InAlAs.

[0037] The semiconductor laser device 3 configured in this manner is a quantum cascade laser in which a plurality of well layers are connected in multiple stages, as shown in FIG. 6, and emits light due to optical transitions between subbands formed in the quantum wells.

[0038] In this semiconductor laser device 3, a diffraction grating 3M is formed between the core layer 32 and the upper cladding layer 33, i.e., on the upper guide layer 323 (see FIG. 4). This diffraction grating 3M is composed of concave and convex portions alternately formed on the upper guide layer 323, and the concave and convex portions extend in the width direction of the upper guide layer 323. This diffraction grating 3M constructively amplifies light of a predetermined oscillation wavelength. The predetermined oscillation wavelength is determined by the pitch of the diffraction grating 3M.

[0039] A lower electrode 92 is provided on the lower surface of the semiconductor substrate 2 in a portion located below the semiconductor laser element 3. A current (or voltage) for laser oscillation is applied to the upper electrode 91 and the lower electrode 92, thereby emitting a predetermined oscillation wavelength defined by the diffraction grating 3M. A current source (or voltage source) is connected to the upper electrode 91 and the lower electrode 92 for laser oscillation, and the laser control device 8 controls the current source (or voltage source) (see FIG. 2).

[0040] 2. Characteristic Configuration of Semiconductor Laser Element 3 Therefore, in the semiconductor laser device 3 of this embodiment, the waveguide 3L has a diffraction grating portion 301 in which the diffraction grating 3M is formed, and a flat portion 302 in which the diffraction grating 3M is not formed, as shown in Figures 4 and 5.

[0041] The diffraction grating section 301 is for obtaining the predetermined oscillation wavelength, extends linearly along the longitudinal direction in a plan view, and has substantially the same width in the width direction perpendicular to the longitudinal direction. As described above, the diffraction grating 3M formed in this diffraction grating section 301 is composed of concave and convex portions alternately formed between the core layer 32 and the upper cladding layer 33, i.e., in the upper guide layer 323. The width of the diffraction grating section 301 is configured to be 1 to 2 times the predetermined oscillation wavelength. With this configuration, the width of the light-emitting end of the waveguide 3L is 1 to 2 times the oscillation wavelength, and single-mode light can be efficiently emitted while suppressing transverse mode oscillation.

[0042] The flat portion 302 is intended to increase the optical output (gain), is an area where the above-mentioned diffraction grating 3M is not formed, and is wider than the diffraction grating portion 301. The flat portion 302 of this embodiment has a rectangular portion 302m that is substantially rectangular in plan view, and a connection portion 303 whose width continuously changes toward the connection point CP1 with the diffraction grating portion 301. This flat portion 302 is formed between the core layer 32 and the upper cladding layer 33 by not forming any recessed or protruding portions in the upper guide layer 323.

[0043] The flat portion 302 also has a connecting portion 303 whose width continuously changes toward the connection point with the diffraction grating portion 301. The connecting portion 303 has a portion whose width gradually increases from the diffraction grating portion 301 toward the rectangular portion 302m. In this embodiment, the entire connecting portion 303 is configured so that its width gradually increases from the diffraction grating portion 301 toward the rectangular portion 302m. That is, the connecting portion 303 is tapered from the rectangular portion 302m toward the diffraction grating portion 301. In other words, the connecting portion 303 is configured so that its width continuously decreases toward the connection point with the diffraction grating portion 301. The width dimension of the connecting portion 303 on the diffraction grating portion 301 side is the same as the width dimension of the diffraction grating portion 301, and sides 303a at both ends of the connecting portion 303 in the width direction are continuous with both sides of the rectangular portion 302m in the width direction. On the other hand, the width dimension of the connecting portion 303 on the rectangular portion 302m side is the same as the width dimension of the rectangular portion 302m, and sides 303a on both ends of the connecting portion 303 in the width direction are continuous with both sides of the diffraction grating portion 301 in the width direction. With this configuration, the maximum width of the connecting portion 303 is equal to or less than the maximum width of the portion of the flat portion 302 other than the connecting portion 303, and the minimum width of the connecting portion 303 is equal to or greater than the maximum width of the diffraction grating portion 301. Furthermore, sides 303a on both ends of the connecting portion 303 in the width direction are linear. In addition, the connecting portion 303 in this embodiment is a region where the diffraction grating 3M is not formed.

[0044] In this embodiment, the connection point CP1 between the diffraction grating portion 301 and the connecting portion 303 and / or the connection point CP2 between the rectangular portion 302m and the connecting portion 303 may be rounded. Specifically, in a plan view, both widthwise sides of the diffraction grating 301 and both widthwise sides 303a of the connecting portion 303 are connected in an arc shape, and both widthwise sides of the rectangular portion 302m and both widthwise sides 303a of the connecting portion 303 are connected in an arc shape. In other words, there is no angular shape between the diffraction grating portion 301 and the rectangular portion 302m. This makes it possible to reduce unintended reflection between the diffraction grating portion 301 and the connecting portion 303 or between the rectangular portion 302m and the connecting portion 303.

[0045] Here, in the waveguide 3L of the semiconductor laser device 3 of this embodiment, the area of ​​the region where the diffraction grating 3M is not formed may be configured to be equal to or larger than the area of ​​the region where the diffraction grating 3M is formed.

[0046] In the semiconductor laser device 3 configured in this manner, the end face of the diffraction grating portion 301 opposite to the connecting portion 303 serves as a light exit surface 3x. A high-reflection film HR is provided on the end face of the flat portion 302 (rectangular portion 302m) opposite to the connecting portion 303, and a low-reflection film AR is provided on the end face of the diffraction grating portion 301 opposite to the connecting portion 303. The light exit surface 3x is formed by providing the low-reflection film AR on the end face of the diffraction grating portion 301 opposite to the connecting portion 303.

[0047] 4, the upper electrode 91 of the semiconductor laser device 3 has a first electrode 91a for supplying a current to the diffraction grating portion 301, and a second electrode 91b provided separately from the first electrode 91a for supplying a current to the flat portion 302. With this configuration, the current I flat and the current I flowing through the region where the diffraction grating 3M is provided (DFB region) DFB The control unit 100 may be configured so that the above-mentioned control signals can be controlled individually.

[0048] 3. Manufacturing Method of Semiconductor Laser Device 100 Next, a method for manufacturing the semiconductor laser device 100 will be described with reference to FIG.

[0049] On the upper surface of the semiconductor substrate 2, an InP layer to be the buffer layer 31, an InGaAs layer to be the lower guide layer 321, an InGaAs layer and an InAlAs layer to be the active layer 322, and an InGaAs layer to be the upper guide layer 323 are stacked by metal organic chemical vapor deposition (MOVPE).

[0050] A diffraction grating region 323x in which the diffraction grating 3M is formed by photolithography and wet etching, and a flat region 323y in which the diffraction grating 3M is not formed, are formed on the upper surface of the upper guide layer 323. Then, an InP layer to become the upper cladding layer 33 and an InGaAs layer to become the cap layer 34 are stacked on the upper part of the upper guide layer 323 by metal organic chemical vapor deposition (MOVPE). This forms a stacked structure on the semiconductor substrate 2, which has the diffraction grating region 323x in which the diffraction grating 3M is formed and the flat region 323y in which the diffraction grating 3M is not formed (structure forming step).

[0051] The laminated structure thus formed is etched to form waveguide 3L. Specifically, the laminated structure is etched to form waveguide 3L, which includes diffraction grating portion 301 on which diffraction grating 3M is formed, and flat portion 302, which is an area on which diffraction grating 3M is not formed and has a width wider than diffraction grating portion 301, and flat portion 302 has connecting portion 303 whose width continuously changes toward the connecting portion with diffraction grating portion 301 (waveguide forming step).

[0052] Further, a protective film 35 made of, for example, SiO2 is formed so as to cover both sides of the waveguide 3L in the width direction. The semiconductor laser element 3 is formed. It is possible to form a plurality of semiconductor laser elements 3 on one semiconductor substrate 2.

[0053] Then, an upper electrode 91 (91a, 91b) and a lower electrode 92 for laser oscillation are formed on the semiconductor laser element 3. A low-reflection film AR is formed on one end surface of the diffraction grating portion 301, and a high-reflection film HR is formed on one end surface of the flat portion. Thereafter, the semiconductor substrate 2 is cut into regions each having a semiconductor laser element 3, thereby forming semiconductor laser chips. This semiconductor laser chip is mounted on a cooling module 7 and provided in an airtight container 5.

[0054] <4. Effects of this embodiment> Such a semiconductor laser device 100 has a narrow diffraction grating portion 301 and a wide flat portion 302, thereby improving single-mode characteristics and increasing the optical output (gain) of the laser light. Furthermore, the flat portion 302 has a connecting portion 303 whose width continuously changes toward the connecting portion with the diffraction grating portion 301. This reduces unintended reflections and enables stable output of single-mode light. Furthermore, a high-reflection film HR is provided on the end surface of the flat portion 302 opposite the connecting portion 303, and a low-reflection film AR is provided on the end surface of the diffraction grating portion 301 opposite the connecting portion 303. Since the end surface of the diffraction grating portion 301 opposite the connecting portion 303 serves as a light exit surface, single-mode light can be stably output from the end surface of the diffraction grating portion 301.

[0055] In addition, in a configuration in which the area of ​​the region where the diffraction grating 3M is not formed is equal to or larger than the area of ​​the region where the diffraction grating 3M is formed, the first electrode 91a for supplying current to the diffraction grating portion 301 and the second electrode 91b for supplying current to the flat portion 302 are provided, so that the total current (I flat +I DBF ) increases, the current I DBF This makes it possible to suppress a rise in temperature of the diffraction grating portion 301, reduce the chirp rate, and improve the resolution when used in the gas analyzer 10.

[0056] <5. Other embodiments> The present invention is not limited to the above-described embodiment.

[0057] For example, the planar shape of the semiconductor laser device 3 is not limited to the above-described embodiment, and may be configured such that both widthwise sides of the connecting portion 303 are not continuous with both widthwise sides of the rectangular portion 302s, as shown in Fig. 7. Specifically, both widthwise sides of the connecting portion 303 are continuous with the end side 302a of the rectangular portion 302s on the diffraction grating portion side. Even in this case, it is desirable that the connection point CP1 between the diffraction grating portion 301 and the connecting portion 303 and / or the connection point CP2 between the rectangular portion 302s and the connecting portion 303 be rounded.

[0058] The shape of connecting portion 303 is not limited to one in which both sides in the width direction are linear, but may be one in which both sides are curved. In this case, connecting portion 303 may have a portion in which the width gradually increases from diffraction grating portion 301 to flat portion 302, such as a constricted shape, where the width temporarily decreases from diffraction grating portion 301 to flat portion 302.

[0059] Furthermore, as shown in FIG. 8, the connection portion 303 may be configured to have a tapered portion 303m whose width continuously narrows toward the connection point CP1 with the diffraction grating portion 301, and a narrow portion 303n that connects the tapered portion 303m and the diffraction grating portion 301.

[0060] Furthermore, in the above embodiment, the upper electrode 91 has a two-electrode configuration of an electrode 91a for the diffraction grating portion and an electrode 91b for the flat portion, but it may also be a single electrode common to the diffraction grating portion 301 and the flat portion 302.

[0061] Additionally, in the above embodiment, the diffraction grating portion 301 and the flat portion 302 have the same width, but the width of at least one of the diffraction grating portion 301 and the flat portion 302 may vary in the longitudinal direction. For example, the flat portion 302 may not have the rectangular portion 302s, and in this case, the flat portion 302 may have a tapered shape, for example, in which the width varies continuously from one end to the other.

[0062] The driving method of the semiconductor laser element 3 may be a continuous wave (CW) method, a quasi-continuous wave (quasi-CW) method, or a pulse oscillation method.

[0063] In the above embodiment, a distributed feedback (DFB) semiconductor laser device has been described, but the present invention is also applicable to a distributed Bragg reflector (DBR) semiconductor laser device.

[0064] In the above embodiment, an example has been described in which the semiconductor laser device 100 is applied to the gas analyzer 10, but it may also be applied to other optical analyzers, or may be used for optical communications.

[0065] Furthermore, the subject of analysis is not limited to exhaust gas, but may be various gases such as gases generated in semiconductor manufacturing processes, by-product gases in material production plants, exhaled breath, gases generated from batteries, and the atmosphere, or even liquids.

[0066] Furthermore, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0067] 10. Gas analyzer 11. Measuring cell 12. Photodetector 13...Analysis Department 100 Semiconductor laser device 3L...Waveguide 3M diffraction grating 2. Semiconductor substrate 3. Semiconductor laser element 301 Diffraction grating section 302...Flat area 302s...Rectangular part 303···Connection 303m Tapered section 303n...Narrow part CP1: Connection point between the diffraction grating and the connection section CP2: Connection point between flat section and connection section 3x...Light exit surface HR...High reflective coating AR...Low reflection film 91a...1st electrode 91b...Second electrode [Industrial Applicability]

[0068] According to the present invention, it is possible to provide a semiconductor laser device that stably outputs single-mode light with increased intensity.

Claims

1. A quantum cascade laser having a diffraction grating formed on a waveguide, The waveguide is a diffraction grating portion in which the diffraction grating is formed; a flat portion having a region where the diffraction grating is not formed and a width greater than that of the diffraction grating portion, the flat portion has a connection portion having a region whose width continuously changes toward a connection point with the diffraction grating portion, a high-reflection film is provided on an end surface of the flat portion opposite to the connection portion, and a low-reflection film is provided on an end surface of the diffraction grating portion opposite to the connection portion, the flat portion has a rectangular portion having a rectangular shape and the connection portion, A quantum cascade laser, wherein a connection portion between the diffraction grating portion and the connection portion and / or a connection portion between the rectangular portion and the connection portion is rounded.

2. The quantum cascade laser according to claim 1 , wherein the width of the connection portion continuously narrows toward the connection point with the diffraction grating portion.

3. 3. The quantum cascade laser according to claim 1, wherein the maximum width of the connection portion is equal to or less than the maximum width of the portion of the flat portion other than the connection portion, and the minimum width of the connection portion is equal to or greater than the maximum width of the diffraction grating portion.

4. 4. The quantum cascade laser according to claim 1, wherein the connection portion has a tapered portion whose width continuously narrows toward the connection point with the diffraction grating portion, and a narrow portion connecting the tapered portion and the diffraction grating portion.

5. 5. The quantum cascade laser according to claim 1, wherein the width of the light-emitting end of the waveguide is 1 to 2 times the oscillation wavelength.

6. 6. The quantum cascade laser according to claim 1, wherein an area of ​​the region where the diffraction grating is not formed is equal to or greater than an area of ​​the region where the diffraction grating is formed.

7. a first electrode for supplying a current to the diffraction grating portion; 7. The quantum cascade laser according to claim 1, further comprising: a second electrode provided separately from the first electrode for supplying a current to the flat portion.

8. A semiconductor laser device comprising a substrate and a quantum cascade laser provided on the substrate, 8. A semiconductor laser device, wherein the quantum cascade laser is one according to claim 1.

9. A method for manufacturing a quantum cascade laser having a diffraction grating formed on a waveguide, comprising: a structure forming step of forming a laminated structure on a substrate, the laminated structure having a diffraction grating region where the diffraction grating is formed and a flat region where the diffraction grating is not formed; a waveguide forming step of etching the laminated structure to form a waveguide having a diffraction grating portion in which the diffraction grating is formed and a flat portion in which the diffraction grating is not formed and which has a region wider than the diffraction grating portion, the flat portion having a connection portion whose width continuously changes toward a connection point with the diffraction grating portion.

10. An analytical device for analyzing a measurement target component contained in a sample, a measuring cell into which the sample is introduced; a semiconductor laser device according to claim 8, which irradiates the measurement cell with laser light; a photodetector that detects laser light that has passed through the measurement cell; and an analysis unit that analyzes the component to be measured using the detection signal from the photodetector.

Images