Quantum cascade laser device and method for manufacturing quantum cascade laser device

Abstract

A quantum cascade laser device according to the present disclosure comprises: a semiconductor substrate; a cascade laser region and a difference frequency waveguide laminated on the semiconductor substrate; and a grating coupling region. The grating coupling region is configured to couple, to a waveguide mode of the difference frequency waveguide, light emitted from the cascade laser region in a direction inclined with respect to an upper surface of the semiconductor substrate.

Description

Quantum cascade laser device and method for manufacturing quantum cascade laser device

[0001] The present disclosure relates to quantum cascade laser devices and methods for manufacturing quantum cascade laser devices.

[0002] Patent Document 1 discloses a terahertz nonlinear quantum cascade laser (THz-nonlinear-QCL) device. This quantum cascade laser includes a semiconductor substrate and an optical waveguide formed on a first surface of the semiconductor substrate. The optical waveguide has a first region and a second region located on one side of the first region in the optical waveguiding direction. The first region generates first light of a first wavelength, and the second region generates second light of a second wavelength. The optical waveguide generates output light having a frequency corresponding to the difference between the first wavelength and the second wavelength by difference frequency generation. In the quantum cascade laser, the output light is emitted from an inclined surface.

[0003] Japanese Patent Application Laid-Open No. 2022-153286

[0004] In the quantum cascade laser device described in Patent Document 1, the nonlinear optical effect of crystals such as InP and GaAs is utilized to generate a frequency f １ and frequency f ２ The difference frequency f of the absolute value of the difference Ｔ The difference frequency f Ｔ are terahertz (THz) waves, which are emitted by Cherenkov radiation. The quantum cascade laser device of Patent Document 1 requires oblique grinding of the substrate after wafer processing is complete. This makes manufacturing difficult. Furthermore, the emission direction of the THz waves depends on the angle at which the substrate is obliquely ground. This requires precise processing accuracy.

[0005] An object of the present disclosure is to provide a quantum cascade laser device that can be easily manufactured and a method for manufacturing the quantum cascade laser device.

[0006] a first cladding layer provided on the first cladding layer, a first core layer provided on the third cladding layer, and a fourth cladding layer provided on the first core layer; and a first grating coupling region configured to couple light emitted from the cascade laser region in a direction tilted with respect to an upper surface of the semiconductor substrate to a waveguide mode of the first difference frequency waveguide.

[0007] a first cladding layer provided on the first cladding layer, a second cladding layer provided on the first cladding layer, and a third cladding layer provided on the first cladding layer; a first core layer provided on the third cladding layer, and a fourth cladding layer provided on the first core layer; and the grating coupling region couples light emitted from the cascade laser region in a direction tilted with respect to an upper surface of the semiconductor substrate to a waveguide mode of the difference frequency waveguide.

[0008] In the quantum cascade laser device and the method for manufacturing the quantum cascade laser device according to the present disclosure, the grating coupling region couples light emitted from the cascade laser region in a direction oblique to the upper surface of the semiconductor substrate with the guided mode of the difference frequency waveguide. This allows light to be emitted from the difference frequency waveguide, eliminating the need for oblique grinding of the substrate. This makes it possible to easily manufacture the quantum cascade laser device.

[0009] 1 is a perspective view of a quantum cascade laser device according to a first embodiment; FIG. 2 is a cross-sectional view of the quantum cascade laser device according to the first embodiment; FIG. 3 is a diagram illustrating a band structure of a conduction band of one stage according to the first embodiment; FIG. 4 is a diagram illustrating a quantum well structure of one stage according to the first embodiment and the square of a wave function at each energy level; FIG. 5 is a diagram illustrating an example of wavelength dependence of gain according to the first embodiment; FIG. 6 is a perspective view of a quantum cascade laser device according to a modification of the first embodiment; FIG. 7 is a diagram illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment; FIG. 8 is a diagram illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment; FIG. 9 is a diagram illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment; FIG. 10 is a diagram illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment; FIG. 11 is a diagram illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment; FIG. 12 is a diagram illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment; FIG. 1 is a cross-sectional view of a quantum cascade laser device according to a third embodiment. FIG. 2 is a perspective view of a quantum cascade laser device according to a fourth embodiment. FIG. 3 is a cross-sectional view of a quantum cascade laser device according to the fourth embodiment. FIG. 4 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to the fourth embodiment. FIG. 5 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to the fourth embodiment. FIG. 6 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to the fourth embodiment. FIG. 7 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to the fourth embodiment. FIG. 8 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to the fourth embodiment. FIG. 9 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to the fourth embodiment. FIG. 10 is a perspective view of a quantum cascade laser device according to a fifth embodiment.10 is a cross-sectional view of a quantum cascade laser device according to a fifth embodiment. FIG. 11 is a perspective view of a quantum cascade laser device according to a sixth embodiment. FIG. 12 is a cross-sectional view of a quantum cascade laser device according to a sixth embodiment. FIG. 13 is a cross-sectional view of a quantum cascade laser device according to a seventh embodiment. FIG. 14 is a cross-sectional view of a quantum cascade laser device according to a seventh embodiment. FIG. 15 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to a seventh embodiment. FIG. 16 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to a seventh embodiment. FIG. 17 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to a seventh embodiment. FIG. 18 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to a seventh embodiment. FIG. 19 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to a seventh embodiment. FIG. 19 is a cross-sectional view of a quantum cascade laser device according to a tenth embodiment. FIG. 19 is a cross-sectional view of a quantum cascade laser device according to a tenth embodiment. 13 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to a tenth embodiment. FIG. 14 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to a tenth embodiment. FIG. 15 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to a tenth embodiment. FIG. 16 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to a tenth embodiment. FIG. 17 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to a tenth embodiment. FIG. 18 is a diagram illustrating a method for manufacturing a quantum cascade laser device according to a twelfth embodiment. FIG. 19 is a perspective view of a quantum cascade laser device according to an eleventh embodiment. FIG. 20 is a cross-sectional view of a quantum cascade laser device according to an eleventh embodiment. FIG. 21 is a perspective view of a quantum cascade laser device according to a twelfth embodiment.13. A cross-sectional view of a quantum cascade laser device according to a twelfth embodiment. A perspective view of a quantum cascade laser device according to a thirteenth embodiment. A perspective view of a quantum cascade laser device according to a modification of the thirteenth embodiment. A diagram illustrating the arrangement of a diffraction grating according to a fourteenth embodiment. A cross-sectional view of a quantum cascade laser device according to a fifteenth embodiment. A perspective view of a quantum cascade laser device according to the fifteenth embodiment. A cross-sectional view of a quantum cascade laser device according to a sixteenth embodiment. A perspective view of a quantum cascade laser device according to the sixteenth embodiment. A cross-sectional view of a quantum cascade laser device according to a seventeenth embodiment. A perspective view of a quantum cascade laser device according to the seventeenth embodiment. A diagram illustrating a method for manufacturing a quantum cascade laser device according to the seventeenth embodiment. A diagram illustrating a method for manufacturing a quantum cascade laser device according to the seventeenth embodiment. A diagram illustrating a method for manufacturing a quantum cascade laser device according to the seventeenth embodiment. A diagram illustrating a method for manufacturing a quantum cascade laser device according to the seventeenth embodiment. A diagram illustrating a method for manufacturing a quantum cascade laser device according to the seventeenth embodiment. A diagram illustrating a method for manufacturing a quantum cascade laser device according to the seventeenth embodiment. 16A to 16C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventeenth embodiment.FIGS. ...

[0010] A quantum cascade laser device and a method for manufacturing a quantum cascade laser device according to each embodiment will be described with reference to the drawings. The same or corresponding components are designated by the same reference numerals, and repeated description may be omitted.

[0011] First Embodiment Fig. 1 is a perspective view of a quantum cascade laser device 100 according to a first embodiment. The quantum cascade laser device 100 is a buried ridge type THz nonlinear QCL device having a cavity length L and a ridge width W. Hereinafter, the difference frequency between the first fundamental wave and the second fundamental wave, which will be described later, may be referred to as a THz wave or THz light. In addition, the wavelength λ of the difference frequency Ｔis sometimes referred to as the THz wave wavelength or the difference frequency wavelength. Quantum cascade laser device 100 includes substrate 2, which is a semiconductor substrate made of, for example, n-type InP. An n-type electrode 1 is provided on the back surface of substrate 2, and an n-type electrode 14 is provided on the top surface of substrate 2.

[0012] On the substrate 2, a layer having a thickness of 3.5 μm and a difference frequency wavelength λ Ｔ The refractive index at n ｃ１Ｑ Ｔ The cladding layer 3 is made of n-type InP. On the cladding layer 3, a layer having a thickness of 225 nm and made of n-type Ga ０．４７ In ０．５３ The guide layer 5 is made of As. ｘ In １－ｘ Furthermore, current blocking layers 4 made of InP doped with Fe are provided on both sides of the guide layer 5 on the cladding layer 3 .

[0013] A plurality of stages, ie, 35 stages 6, are provided on the guide layer 5. The 35 stages 6 will be described later. A guide layer 7 having a layer thickness of 230 nm and made of n-type GaInAs is provided on the guide layer 7. A layer having a layer thickness of 3.5 μm and a difference frequency wavelength λ Ｔ The refractive index at n ｃ２Ｑ Ｔ A cladding layer 8 made of n-type InP is provided on the cladding layer 8. A grating coupling region 9 having a thickness of 1.0 μm and made of n-type GaInAs is provided on the cladding layer 8.

[0014] Above the grating coupling region 9, a layer having a thickness of d ｃ１ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ｃ１Ｔ Ｔ The cladding layer 10 is made of n-type InP. ａ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ａＴ ＴOn the core layer 11, a layer having a thickness of d ｃ２ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ｃ２Ｔ Ｔ A cladding layer 12 made of n-type InP is provided on the cladding layer 12. A contact layer 13 having a thickness of 300 nm and made of n-type GaInAs is provided on the cladding layer 12.

[0015] The cladding layer 3, the guide layers 5, 35, stages 6, the guide layer 7, and the cladding layer 8 are collectively referred to as a QCL waveguide or a cascade laser region. The cladding layer 10, the core layer 11, and the cladding layer 12 are collectively referred to as a THz waveguide or a difference frequency waveguide. That is, a cascade laser region and a difference frequency waveguide are stacked on the substrate 2. In this embodiment, the cascade laser region is provided on the substrate 2, and the difference frequency waveguide is provided on the cascade laser region. The cascade laser region includes the cladding layer 3, a plurality of stages 6 provided on the cladding layer 3, and a cladding layer 8 provided on the plurality of stages 6. The difference frequency waveguide includes the cladding layer 10, a core layer 11 provided on the cladding layer 10, and a cladding layer 12 provided on the core layer 11.

[0016] 2 is a cross-sectional view of the quantum cascade laser device 100 according to the first embodiment. ａ -z ｂ The cross section is obtained by cutting along a straight line. １ Ｑ and the period is Λ １ Ｑ The guide layer 7 further includes a diffraction grating 15 having a length L ２ Ｑ and the period is Λ ２ Ｑ A diffraction grating 16 is provided.

[0017] In FIG. 2, the wavelength λ １ Ｑ , frequency f １ Ｑ , propagation constant β １Ｑ QCL guided mode 17 propagating in the cascade laser region at wavelength λ ２ Ｑ , frequency f ２ Ｑ , propagation constant β ２ Ｑ A QCL guided mode 18 is shown schematically propagating through the cascade laser region at wavelength λ. １ Ｑ The QCL guided mode 17 is the first fundamental wave, with a wavelength λ ２ Ｑ The QCL waveguide mode 18 of frequency f is sometimes called the second fundamental wave. That is, the cascade laser region is irradiated with the diffraction gratings 15 and 16 at a frequency f １ Ｑ The first fundamental wave and frequency f ２ Ｑ The wavelength λ can be expressed as λ=c / f when the speed of light c is used.

[0018] 2 also shows THz light 19, 20 emitted from the cascade laser region in a direction tilted with respect to the upper surface of the substrate 2. The THz light 19 is inclined at an angle −θ ｃｍ Cherenkov radiation occurs in an inclined direction, and f １ Ｑ -f ２ Ｑ The absolute value of frequency f Ｔ The THz light 20 is incident on the xz plane in the y direction at an angle θ ｃｐ Cherenkov radiation occurs in an inclined direction, with a frequency of f Ｔ Hereafter, −θ ｃｍ Absolute value of and θ ｃｐ When the values ​​are the same, they are −θ ｃ and θ ｃ Furthermore, in Figure 2, the wavelength λ Ｔ , frequency f Ｔ , propagation constant β Ｔ The THz guided mode 21 propagating through the difference frequency waveguide at a frequency f １ Ｑ and frequency f ２ Ｑ The waveguide mode corresponds to the difference frequency of

[0019] The grating coupling region 9 is provided between the cascade laser region and the difference frequency waveguide. The grating coupling region 9 has a length L Ｔ and the period is Λ Ｔ A diffraction grating 22 having a THz waveguide mode 21 is provided. A THz waveguide mode 21 from the difference frequency waveguide is emitted as THz light 24 from an emission end face 23, which is the front end face of the quantum cascade laser device 100. The emission end face 23 of the difference frequency waveguide is perpendicular to the upper surface of the substrate 2. A rear end face 25 is provided on the side of the substrate 2 opposite to the emission end face 23.

[0020] 3 is a diagram showing the band structure of the conduction band of one stage 50 according to the first embodiment. As an example, FIG. 3 shows a band structure of 5.0×10 ６ 1 shows the band structure of the conduction band of one stage 50 of 35 stages 6 when an electric field of 1000 V / m is applied. This structure is disclosed in Non-Patent Document 1 "J. Kim et al., "Theoretical and experimental study of optical gain and linewidth enhancement factor of type-I quantum-cascade lasers," IEEE J. Quantum. Electron., vol. 40, no. 12, pp. 1663-1674, December 2004."

[0021] Each of the multiple stages 6 has an active region 48 and an injector region 49 configured to inject carriers into the active region 48. Each of the active region 48 and the injector region 49 has alternating barrier layers and well layers.

[0022] In the active region 48, a barrier layer 31, a well layer 32, a barrier layer 33, a well layer 34, a barrier layer 35, a well layer 36, and a barrier layer 37 are stacked in this order. In the injector region 49, a barrier layer 37, a well layer 38, a barrier layer 39, a well layer 40, a barrier layer 41, a well layer 42, a barrier layer 43, a well layer 44, a barrier layer 45, a well layer 46, and a barrier layer 47 are stacked in this order.

[0023] The barrier layer 31 has a thickness of 2.4 nm and is made of undoped Al ０．４８ In ０．５２ It is formed from As. ｘ In １－ｘ As may be abbreviated as AlInAs. The well layer 32 has a thickness of 6.5 nm and is made of undoped GaInAs. The barrier layer 33 has a thickness of 0.9 nm and is made of undoped AlInAs. The well layer 34 has a thickness of 6.6 nm and is made of undoped GaInAs. The barrier layer 35 has a thickness of 1.5 nm and is made of undoped AlInAs. The well layer 36 has a thickness of 3.2 nm and is made of undoped GaInAs.

[0024] The barrier layer 37 has a thickness of 4.0 nm and is made of undoped AlInAs. The well layer 38 has a thickness of 4.1 nm and is made of undoped GaInAs. The barrier layer 39 has a thickness of 1.7 nm and is made of undoped AlInAs. The well layer 40 has a thickness of 3.7 nm and is made of undoped GaInAs. The barrier layer 41 has a thickness of 1.2 nm and is made of undoped AlInAs.

[0025] The well layer 42 is made of n-type doped GaInAs with a thickness of 3.4 nm. The barrier layer 43 is made of n-type doped AlInAs with a thickness of 1.1 nm. The well layer 44 is made of n-type doped GaInAs with a thickness of 3.4 nm. The barrier layer 45 is made of undoped AlInAs with a thickness of 1.1 nm. The well layer 46 is made of undoped GaInAs with a thickness of 2.9 nm. The barrier layer 47 is made of undoped AlInAs with a thickness of 2.4 nm.

[0026] The active region 48 is a region that emits light by electrons transitioning between subbands formed in the active region 48. The injector region 49 is a region that injects electrons into the active region 48. In this embodiment, the active region 48 is configured with three wells. The doping amounts of the well layer 42, the barrier layer 43, and the well layer 44 in this embodiment are, for example, 2.5×10１７ cm －３ In this embodiment, as an example, 35 stages 6 are configured by connecting 35 stages 50 vertically.

[0027] 4 is a diagram showing the quantum well structure of one stage 50 according to the first embodiment and the square of the wave function at each energy level. The square of the wave function represents the probability of electrons being present. There are 10 energy levels allowed in one stage 50. In FIG. 4, the levels where electrons are present mainly in the active region 48 are indicated by solid lines, and the levels where electrons are present mainly in the injector region 49 are indicated by dashed lines. The five levels where electrons are present mainly in the active region 48 are #1, #2, #4, #7, and #9, and the five levels where electrons are present mainly in the injector region 49 are #3, #5, #6, #8, and #10.

[0028] Calculation of the electron density revealed that, among the levels where electrons exist mainly in the active region 48, the electron density at energy level #4 is higher than the electron density at energy level #2. In other words, it was found that a population inversion necessary for laser oscillation was achieved.

[0029] 5 is a diagram showing an example of the wavelength dependence of gain according to the first embodiment. Fig. 5 shows the wavelength dependence of gain when an electric field is applied from electrode 14 to electrode 1 and a current of 360 mA is injected in quantum cascade laser device 100 having a cavity length L = 2.0 mm and a ridge width W = 10 μm. Wavelength λ ｐ = 9.47 μm, maximum gain g ｐ = 21.86 cm －１ and there is a gain over the range from 8.0 μm to 12.0 μm.

[0030] Suppose the wavelength λ of the first fundamental wave is １ Ｑ and the wavelength λ of the second fundamental wave ２ Ｑ are set to 8.80 μm and 10.46 μm, respectively. In this case, the corresponding frequency f １ Ｑ and f ２ Ｑ are 3.407 x 10 respectively. １３ Hz and 2.866 x 10 １３Hz. Therefore, the wavelength of the difference frequency is λ Ｔ and frequency f Ｔ = (f １ Ｑ -f ２ Ｑ ) are 55.45 μm and 5.406 × 10, respectively. １２ Hz = 5.406 THz.

[0031] The refractive indices of InP, AlAs, GaAs, and InAs in the first fundamental wave and the second fundamental wave are given in Non-Patent Document 2 "S. H. Wemple et al., "Behavior of the Electronic Dielectric Constant in Covalent and Ionic Materials," Phys. Rev. B, vol. 3, no. 4, pp. 1338-1351, February 1971," Non-Patent Document 3 "Iga, ed., "Semiconductor Lasers," pp. 36, Ohmsha (October 25, 1994)," and Non-Patent Document 4 "M. A. Afromowitz, "Refractive Index of The refractive indexes of GaInAs and AlInAs, which are ternary mixed crystals, were calculated using Non-Patent Document 5, "S. Adachi, 'Material parameters of In1-xGaxAsyP1-y,' J. Appl. Phys., vol. 53, No. 12, pp. 8775-8792, 1982." The wavelength λ Ｔ The refractive indices of InP, GaAs, and InAs for THz waves at .tbd.=55.45 μm were calculated with reference to Non-Patent Document 6, "E. D. Palik, "Handbook of Optical Constants of Solids III," 1998," and the refractive index of GaInAs was calculated using Non-Patent Document 5. The results are shown in Table 1.

[0032]

[0033] Using the refractive indices shown in Table 1, the propagation constant β for the first fundamental wave in the cascade laser region is １ Ｑand the effective refractive index n ｅｆ１ Ｑ = β １ Ｑ / [2π / λ １ Ｑ ] are 2.27131 x 10 ６ m －１ Similarly, the propagation constant β for the second fundamental wave is ２ Ｑ and the effective refractive index n ｅｆ２ Ｑ = β ２ Ｑ / [2π / λ ２ Ｑ ] are 1.89965 x 10 ６ m －１ and 3.16246.

[0034] The diffraction gratings 15 and 16 provided in the guide layer 7 may be higher-order diffraction gratings, but first-order is preferable from the viewpoint of providing high feedback. １ Ｑ is the wavelength λ in the waveguide １ Ｑ / n ｅｆ１ Ｑ Similarly, the period Λ of the first-order diffraction grating 16 for the second fundamental wave is ２ Ｑ is the wavelength λ in the waveguide ２ Ｑ / n ｅｆ２ Ｑ In this embodiment, as an example, the period Λ is set in the guide layer 7. １ Ｑ = 1.305 μm and length L １ Ｑ = 800 μm, and a diffraction grating 15 with a period Λ ２ Ｑ = 1.657 μm and length L ２ Ｑ A diffraction grating 16 having a wavelength λ = 800 μm is provided. １ Ｑ = 8.80 μm and wavelength λ ２ ＱIt is possible to obtain two wavelengths of 10.46 μm. The ratio of the convex portions to the concave portions of each diffraction grating is preferably 1:1, but can be selected arbitrarily.

[0035] THz wave wavelength λ Ｔ Refractive index n of cladding layer 3 at 55.45 μm ｃ１Ｑ Ｔ and the refractive index n of the cladding layer 8 ｃ２Ｑ Ｔ is 3.6300, and the effective refractive index of the first fundamental wave, n ｅｆ１ Ｑ = 3.18111 and the effective refractive index of the second fundamental wave n ｅｆ２ Ｑ = 3.16246. Therefore, Cherenkov radiation occurs in the cladding layers 3 and 8. That is, from the cascade laser region, the resonance direction and the angle θ ｃｐ and angle -θ ｃｍ The light is emitted in the direction of the arrow.

[0036] Cherenkov radiation angle from cladding layer 3 -θ ｃｍ and the Cherenkov radiation angle θ from the cladding layer 8 ｃｐ can be expressed by the formulas (1) and (2) according to Non-Patent Document 7 "Z.-S. Suh, "Simple analytical solution of Cerenkov-type Terahertz wave generation via difference frequency generation in dielectric waveguides," J. Lightw. Technol., vol. 37, No. 17, pp. 4236-4243, 2019." ０ Ｔ is expressed by equation (3).

[0037]

[0038]

[0039]

[0040] Here, since both the cladding layer 3 and the cladding layer 8 are made of InP, the refractive index n ｃ１Ｑ Ｔ = nｃ２Ｑ Ｔ = 3.6300. Therefore, the Cherenkov radiation angle is θ ｃｍ = θ ｃｐ = θ ｃ = 25.37°.

[0041] Also, as can be seen from Table 1, the difference frequency wavelength λ Ｔ The refractive index of GaInAs at λ = 55.45 μm is higher than that of InP. Therefore, if GaInAs is used as the core and InP is used as the cladding, a THz waveguide, which is a waveguide for difference frequencies, can be formed. The waveguide may be multimode, but a simple mode is desirable from the perspective of using the emitted light.

[0042] Therefore, in this embodiment, the thickness d of the cladding layer 10 ｃ１ Ｔ and the thickness d of the cladding layer 12 ｃ２ Ｔ 20 μm, and the thickness d of the core layer 11 ａ Ｔ In this case, the wavelength λ Ｔ = 55.45 μm THz wave propagation constant β of the difference frequency waveguide Ｔ and the effective refractive index n ｅｆ Ｔ are 4.58629x10 respectively. ５ m －１ and 4.04751. From Non-Patent Document 8 "A. Yariv et. al., "Periodic structures for integrated optics," IEEE J. Quantum. Electron., vol. QE-13, no. 4, pp. 233-253, April 1977," the angle θ ｃ The light incident at and propagating through the waveguide with a propagation constant β Ｔ In order for light propagating at the grating coupling region 9 to be coupled, the period Λ of the diffraction grating 22 in the grating coupling region 9 must be Ｔ must satisfy equation (4).

[0043]

[0044] m is an integer other than 0. When formula (4) is applied to this embodiment with m=1, the period Λ of the diffraction grating 22 isＴ The period Λ is 72.25 μm. Ｔ The ratio of the convex portions to the concave portions of the diffraction grating 22 is preferably 1:1, but is not limited to this and can be selected arbitrarily.

[0045] In view of the above, in this embodiment, as an example, a period Λ is formed in the grating coupling region 9. Ｔ = 72.25 μm and length L Ｔ A diffraction grating 22 having an angle θ = 1000 μm is provided. ｃ＝ θ ｃｐ The THz light 20 that emits Cherenkov radiation at Ｔ This allows the THz light 24 to be coupled to the THz guided mode 21 propagating in the difference frequency waveguide. As a result, the THz light 24 is emitted perpendicularly to the emission end face 23 of the quantum cascade laser device 100.

[0046] Also, -θ ｃｍ A portion of the THz light 19 that emits Cherenkov radiation at -θ is absorbed inside the quantum cascade laser device 100. The other portion of the THz light 19 is totally reflected by the electrodes 1, 14, the output end face 23, and the rear end face 25, and is ultimately coupled to the THz guided mode 21 of the difference frequency waveguide by the diffraction grating 22 in the grating coupling region 9, and extracted as THz light 24. Although the description may be omitted in the following embodiments, -θ ｃｍ The THz light 19 emitted by the Cerenkov radiation can also be extracted to the outside of the device.

[0047] As described above, the grating coupling region 9 is configured to couple the THz light 19, 20 to the THz guided mode 21 of the difference frequency waveguide. Specifically, the grating coupling region 9 has a diffraction grating 22 configured to couple the THz light 19, 20 to the THz guided mode 21 of the difference frequency waveguide. This allows the THz light 24 to be emitted from the difference frequency waveguide, thereby eliminating the need for, for example, oblique grinding of the substrate 2 after the wafer process is completed. Therefore, the quantum cascade laser device 100 can be easily manufactured.

[0048] The difference frequency waveguide of this embodiment can be considered as a three-layer slab waveguide in which the core layer 11 is sandwiched between the cladding layers 10 and 12. Therefore, the optical intensity distribution of the difference frequency waveguide is a Lorentz type, the same as that of a normal optical waveguide. Therefore, the THz light 24 can be coupled with an external optical system with high efficiency.

[0049] 6 is a perspective view of a quantum cascade laser device 200 according to a modification of the first embodiment. The quantum cascade laser device 200 differs from the quantum cascade laser device 100 in that an insulating film 26 made of, for example, SiON is provided between the current blocking layer 4 and the electrode 14. The other structures are similar to those of the quantum cascade laser device 100. By inserting the insulating film 26, it is possible to further suppress the current flowing outside the ridge of width W. The insulating film 26 may also be provided in the following embodiments.

[0050] Next, a method for manufacturing the quantum cascade laser device 100 will be described. Figures 7A to 7H are diagrams for explaining a method for manufacturing the quantum cascade laser device 100 according to the first embodiment. First, as shown in Figure 7A, a cladding layer 3, a guide layer 5, a stage 6, and a guide layer 7 are crystal-grown in this order on a substrate 2. For the crystal growth, a molecular beam epitaxy (MBE) method, a metal organic chemical vapor deposition (MOCVD) method, or the like can be used.

[0051] Next, as shown in FIG. 7B, a period Λ is formed in the guide layer 7 by photolithography and etching. １ Ｑ and a period Λ ２ Ｑ The diffraction grating 15 has a length L １ Ｑ , width is W ｇ >W, depth d ｇ Ｑ is 0<d ｇ Ｑ The length of the diffraction grating 16 is L ２ Ｑ , width is W ｇ >W, depth d ｇＱ is 0<d ｇ Ｑ ≦230 nm.

[0052] 7C, a cladding layer 8 and a grating coupling region 9 are grown in this order on the guide layer 7 by MBE, MOCVD, or the like. Next, as shown in FIG. 7D, a period Λ is formed in the grating coupling region 9 by photolithography and etching. Ｔ The diffraction grating 22 has a length L Ｔ , width is W ｇ Ｔ >W, depth d ｇ Ｔ is 0<d ｇ Ｔ ≦1.0 μm.

[0053] Next, as shown in Fig. 7E, crystal growth is performed in this order on the grating coupling region 9 by MBE, MOCVD, or the like to form the cladding layer 10, core layer 11, cladding layer 12, and contact layer 13. As a result, the cascade laser region and difference frequency waveguide are stacked on the substrate 2, and the grating coupling region 9 is formed between the cascade laser region and the difference frequency waveguide. Next, as shown in Fig. 7F, photolithography and etching are used to etch away both sides of the ridge with width W to the middle of the cladding layer 3.

[0054] 7G, current blocking layers 4 are grown on both sides of the ridge by MBE, MOCVD, etc. to cover both sides of the core layer 11. Next, as shown in FIG. 7H, an electrode 1 is formed on the back surface of the substrate 2, and an electrode 14 is formed on the contact layer 13 and the current blocking layer 4.

[0055] The dimensions, materials, concentrations, and the like of each layer described above are merely examples and may be changed. In addition, the present embodiment illustrates an example in which the number of stages is 35. The number of stages is not limited to this, and can be selected as needed. The structure of the active region 48 and injector region 49 constituting one stage 50 is not limited to the structure illustrated in this embodiment. In addition, the present embodiment illustrates a GaInAs / AlInAs-based QCL device using an InP substrate. This embodiment is not limited to this, but can also be applied to GaAs / AlGaAs-based QCL devices using a GaAs substrate and InGaN / AlGaN-based QCL devices using a GaN substrate. Furthermore, the QCL device of this embodiment is lattice-matched to the substrate. This embodiment is also applicable to lattice-mismatched systems, i.e., strain-introduced systems, in which the lattice constant is larger or smaller than that of the substrate.

[0056] The above-described modifications can be applied as appropriate to the quantum cascade laser devices and methods for manufacturing quantum cascade laser devices according to the following embodiments. Note that the quantum cascade laser devices and methods for manufacturing quantum cascade laser devices according to the following embodiments have many points in common with the first embodiment, so the following description will focus on the differences from the first embodiment.

[0057] Second Embodiment Fig. 8 is a perspective view of a quantum cascade laser device 300 according to a second embodiment. Fig. 9 is a cross-sectional view of the quantum cascade laser device 300 according to the second embodiment. Fig. 9 is a cross-sectional view of Fig. 8. ａ -z ｂ The cross section is shown by cutting along a straight line. In this embodiment, the grating coupling region 9 is provided inside the cladding layer below the core layer 11 of the difference frequency waveguide. The grating coupling region 9 is separated from the cascade laser region. The other configurations are the same as those of the first embodiment.

[0058] Specifically, in the quantum cascade laser device 300, a layer having a thickness of d ｃ１Ａ Ｔ A cladding layer 51 made of n-type InP is provided on the cladding layer 51. A grating coupling region 9 is provided on the cladding layer 51. A layer having a thickness of dｃ１Ｂ Ｔ and a cladding layer 52 made of n-type InP is provided. ｃ１Ａ Ｔ +d ｃ１Ｂ Ｔ = d ｃ１ Ｔ is.

[0059] By providing the grating coupling region 9 in the cladding layer of the difference frequency waveguide, the THz light 20 can be more easily coupled to the difference frequency waveguide, and the output of the THz light 24 can be increased.

[0060] Third Embodiment Fig. 10 is a perspective view of a quantum cascade laser device 400 according to a third embodiment. Fig. 11 is a cross-sectional view of the quantum cascade laser device 400 according to the third embodiment. Fig. 11 is a cross-sectional view of Fig. 10 . ａ -z ｂ The cross section is shown by cutting along a straight line. In this embodiment, the grating coupling region is provided at the interface between the core layer 11 and the cladding layer 10 below the core layer 11 in the difference frequency waveguide. Specifically, the grating coupling region is formed by providing a diffraction grating 22 on the upper surface of the cladding layer 10 and burying the diffraction grating 22 in the core layer 11. The other configurations are the same as those of the first embodiment.

[0061] With this configuration, it is possible to more easily couple the THz light 20 to the difference frequency waveguide, thereby increasing the power of the THz light 24. Furthermore, since there is no need to add a layer as a grating coupling region, the manufacturing process of the quantum cascade laser device 400 can be simplified.

[0062] Fourth Embodiment Fig. 12 is a perspective view of a quantum cascade laser device 500 according to a fourth embodiment. Fig. 13 is a cross-sectional view of the quantum cascade laser device 500 according to the fourth embodiment. Fig. 13 shows a cross-sectional view of Fig. 12. ａ -z ｂ The cross section obtained by cutting along a straight line is shown. This embodiment differs from the first embodiment in that a difference frequency waveguide is provided on a substrate 2 and a cascade laser region is provided on the difference frequency waveguide. Other concepts are similar to the structure of the first embodiment.

[0063] Specifically, a cladding layer 10, a core layer 11, and a cladding layer 12 are stacked in this order on a substrate 2. A grating coupling region 9, a cladding layer 3, guide layers 5, 35, a stage 6, a guide layer 7, and a cladding layer 8 are stacked in this order on the cladding layer 12. The grating coupling region 9 is provided between the cascade laser region and the difference frequency waveguide.

[0064] In this embodiment, as in the first embodiment, the resonance direction and the angle θ ｃｐ and angle -θ ｃｍ The THz light 19 and 20 are emitted in the direction of the angle θ ｃｐ and angle -θ ｃｍ respectively satisfy the formula (5) and the formula (6).

[0065]

[0066]

[0067] the period Λ of the diffraction grating 22 in the grating coupling region 9 Ｔ satisfies the formula (7), where m is an integer other than zero.

[0068]

[0069] In this embodiment as well, the grating coupling region 9 allows the THz light 19, 20 to be coupled to the THz guided mode 21 of the difference frequency waveguide. Furthermore, the difference frequency waveguide may have a relatively rough control of its layer thickness. Therefore, it is possible to use a liquid phase epitaxial (LPE) device, which has a high growth rate. In other words, in this embodiment, in which the difference frequency waveguide is first formed on the substrate 2, the quantum cascade laser device 500 can be manufactured easily and inexpensively.

[0070] Next, a method for manufacturing the quantum cascade laser device 500 will be described. Figures 14A to 14H are diagrams for explaining a method for manufacturing the quantum cascade laser device 500 according to the fourth embodiment. First, as shown in Figure 14A, a cladding layer 10, a core layer 11, a cladding layer 12, and a grating coupling region 9 are crystal-grown in this order on a substrate 2. For the crystal growth, LPE, MBE, MOCVD, or the like can be used. Next, as shown in Figure 14B, a pattern with a period Λ is formed in the grating coupling region 9 by photolithography and etching. Ｔ The diffraction grating 22 has a length L Ｔ , width is W ｇ Ｔ >W, depth d ｇ Ｔ is 0<d ｇ Ｔ ≦1.0 μm.

[0071] 14C, the cladding layer 3, the guide layer 5, the stage 6, and the guide layer 7 are crystal-grown in this order by MBE, MOCVD, or the like on the grating coupling region 9. Next, as shown in FIG. 14D, a period Λ is formed in the guide layer 7 by photolithography and etching. １ Ｑ and a period Λ ２ Ｑ The diffraction grating 15 has a length L １ Ｑ , width is W ｇ >W, depth d ｇ Ｑ is 0<d ｇ Ｑ The length of the diffraction grating 16 is L ２ Ｑ , width is W ｇ >W, depth d ｇ Ｑ is 0<d ｇ Ｑ ≦230 nm.

[0072] 14E, crystal growth of cladding layer 8 and contact layer 13 is performed in this order on guide layer 7 by MBE, MOCVD, or the like. Next, as shown in FIG. 14F, photolithography and etching are used to etch away both sides of the ridge having width W to the middle of cladding layer 10.

[0073] 14G, current blocking layers 4 are grown on both sides of the ridge by MBE, MOCVD, etc. Next, as shown in FIG. 14H, an electrode 1 is formed on the back surface of the substrate 2, and an electrode 14 is formed on the contact layer 13 and the current blocking layer 4.

[0074] Fifth Embodiment Fig. 15 is a perspective view of a quantum cascade laser device 600 according to a fifth embodiment. Fig. 16 is a cross-sectional view of the quantum cascade laser device 600 according to the fifth embodiment. Fig. 16 shows a cross-sectional view of Fig. 15. ａ -z ｂ The cross section obtained by cutting along a straight line is shown. In this embodiment, the grating coupling region 9 is provided inside the cladding layer above the core layer 11 of the difference frequency waveguide. The grating coupling region 9 is separated from the cascade laser region. The other structures are the same as those of the fourth embodiment.

[0075] Specifically, a layer having a thickness of d on the core layer 11 ｃ２Ａ Ｔ A cladding layer 61 made of n-type InP is provided on the cladding layer 61. A grating coupling region 9 is provided on the cladding layer 61. A layer having a thickness of d ｃ２Ｂ Ｔ and a cladding layer 62 made of n-type InP is provided. ｃ２Ａ Ｔ +d ｃ２Ｂ Ｔ = d ｃ２ Ｔ The cladding layer 3 is provided on the cladding layer 62 .

[0076] In this embodiment, by providing the grating coupling region 9 in the cladding layer of the difference frequency waveguide, it is possible to easily couple the THz light 19 to the difference frequency waveguide, and the output of the THz light 24 can be increased.

[0077] Sixth Embodiment Fig. 17 is a perspective view of a quantum cascade laser device 700 according to a sixth embodiment. Fig. 18 is a cross-sectional view of the quantum cascade laser device 700 according to the sixth embodiment. Fig. 18 shows a cross-sectional view of Fig. 17. ａ -z ｂ The cross section obtained by cutting along a straight line is shown. In this embodiment, the grating coupling region is provided at the interface between the core layer 11 and the cladding layer 12 above the core layer 11 in the difference frequency waveguide. Specifically, the grating coupling region can be formed by providing a diffraction grating 22 on the top surface of the core layer 11 and burying it in the cladding layer 12. The other structures are the same as those in the fourth embodiment.

[0078] In this embodiment, by providing a grating coupling region at the interface between the core layer 11 and the cladding layer 12, it is possible to further facilitate coupling of the THz light 19 to the difference frequency waveguide, thereby increasing the output of the THz light 24. Furthermore, since there is no need to add a layer as the grating coupling region, the manufacturing process of the quantum cascade laser device 700 can be simplified.

[0079] Seventh Embodiment Fig. 19 is a perspective view of a quantum cascade laser device 800 according to a seventh embodiment. Fig. 20 is a cross-sectional view of the quantum cascade laser device 800 according to the seventh embodiment. Fig. 20 shows a cross-sectional view of Fig. 19. ａ -z ｂ In this embodiment, the wavelength λ of the first fundamental wave is １ Ｑ and the wavelength λ of the second fundamental wave ２ Ｑ The corresponding frequencies f １ Ｑ and f ２ Ｑ are 3.612 x 10 respectively １３ Hz and 2.861 x 10 １３ Hz. Difference frequency wavelength λ Ｔ and the difference frequency f Ｔ = f １ Ｑ -f ２ Ｑare 39.90 μm and 7.513×10, respectively. １２ Hz = 7.513 THz.

[0080] In the quantum cascade laser device 800, a guide layer 71 having a thickness of 230 nm and made of n-type GaInAs is provided on the stage 6. A cladding layer 8 having a thickness of d ｃ１ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ｃ１Ｔ Ｔ On the cladding layer 72, a layer having a thickness of d ａ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ａＴ Ｔ The core layer 73 is made of n-type InP. ｃ２ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ｃ２Ｔ Ｔ and a cladding layer 74 made of n-type GaInAs is provided.

[0081] The current blocking layer 4 covers both sides of the cascade laser region from the cladding layer 3 to the cladding layer 8. The difference frequency waveguide including the cladding layer 72, the core layer 73 and the cladding layer 74 is exposed from the current blocking layer 4.

[0082] The guide layer 71 has a length L １ Ｑ , the period is Λ １ Ｑ and a diffraction grating 75 having a length L ２ Ｑ , the period is Λ ２ Ｑ 20, a diffraction grating 76 having a wavelength λ １ Ｑ , frequency f １ Ｑ , propagation constant β １ Ｑ QCL guided mode 77 propagating through the cascade laser region at wavelength λ２ Ｑ , frequency f ２ Ｑ , propagation constant β ２ Ｑ Schematically shows a QCL waveguide mode 78 propagating in the cascade laser region. In this embodiment, the QCL waveguide mode 77 is the first fundamental wave, and the QCL waveguide mode 78 is the second fundamental wave.

[0083] 20 also shows THz light 79, 80 emitted from the cascade laser region in a direction tilted with respect to the upper surface of the substrate 2. The THz light 79 is inclined at an angle −θ ｃｍ Cherenkov radiation occurs in an inclined direction, with a frequency of f Ｔ = f １ Ｑ -f ２ Ｑ The THz light 80 is incident on the xz plane in the y direction at an angle θ ｃｐ Cherenkov radiation occurs in an inclined direction, with a frequency of f Ｔ It has.

[0084] Furthermore, in FIG. Ｔ , frequency f Ｔ , propagation constant β Ｔ The THz guided mode 81 propagating through the difference frequency waveguide is shown schematically. Ｔ , the period is Λ Ｔ The diffraction grating 82 is formed by etching away the cladding layer 8 to a depth of about 1 μm from the top surface and burying it with the cladding layer 72. In this way, the grating coupling region of this embodiment is provided between the cascade laser region and the difference frequency waveguide. The period of the diffraction grating 82 will be described later. THz light 83 is emitted from the emission end face 23.

[0085] As in the first embodiment, the refractive indices of InP, AlAs, GaAs, and InAs in the first fundamental wave and the second fundamental wave were obtained from Non-Patent Documents 2, 3, and 4. The refractive indices of GaInAs and AlInAs, which are ternary mixed crystals, were calculated using Non-Patent Document 5. ＴThe refractive indices of InP, GaAs, and InAs for THz waves at λ=39.90 μm were calculated with reference to Non-Patent Document 6, and the refractive index of GaInAs was calculated using Non-Patent Document 5. The results are shown in Table 2.

[0086]

[0087] From the refractive indices shown in Table 2, the propagation constant β for the first fundamental wave in the cascade laser region is １ Ｑ and the effective refractive index n ｅｆ１ Ｑ = β １ Ｑ / [2π / λ １ Ｑ ] are 2.41324 x 10 ６ m －１ Similarly, the propagation constant β for the second fundamental wave is ２ Ｑ and the effective refractive index n ｅｆ２ Ｑ = β ２ Ｑ / [2π / λ ２ Ｑ ] are 1.89592 x 10 ６ m －１ and 3.16228.

[0088] The diffraction gratings 75 and 76 may be higher-order diffraction gratings, but first-order diffraction gratings are preferable from the viewpoint of providing high feedback. １ Ｑ is the wavelength in the waveguide, λ １ Ｑ / n ｅｆ１ Ｑ Similarly, the period Λ of the first-order diffraction grating for the second fundamental wave is ２ Ｑ is the wavelength in the waveguide, λ ２ Ｑ / n ｅｆ２ Ｑ Therefore, for example, the period Λ is set to 1.657 μm, which is half of the period Λ in the guide layer 71. １ Ｑ = 1.302 μm and length L １ Ｑ = 800 μm, and a diffraction grating 75 with a period Λ２ Ｑ = 1.657 μm and length L ２ Ｑ If a diffraction grating 76 with a wavelength of λ = 800 μm is provided, １ Ｑ = 8.30 μm and wavelength λ ２ Ｑ Two wavelengths of 10.48 μm can be obtained.

[0089] In addition, the difference frequency wavelength λ Ｔ Refractive index n of cladding layer 3 at 39.90 μm ｃ１Ｑ Ｔ and the refractive index n of the cladding layer 8 ｃ２Ｑ Ｔ is 4.2000, and the effective refractive index of the first fundamental wave n ｅｆ１ Ｑ = 3.18785 and the effective refractive index of the second fundamental wave n ｅｆ２ Ｑ = 3.16228. Therefore, Cherenkov radiation occurs in the cladding layers 3 and 8. As in the first embodiment, from equations (1) to (3), the Cherenkov radiation angle −θ ｃｍ and the Cherenkov radiation angle θ in the cladding layer 8 ｃｐ In this embodiment, θ ｃｍ = θ ｃｐ = θ ｃ = 38.54°.

[0090] Also, as can be seen from Table 2, the difference frequency wavelength λ Ｔ The refractive index of InP at λ = 39.90 μm is higher than that of GaInAs. Therefore, if InP is used as the core and GaInAs as the cladding, a waveguide at the difference frequency, that is, a difference frequency waveguide, can be formed. The waveguide may be multimode, but from the viewpoint of using the emitted light, a simple mode is preferable. Therefore, in this embodiment, the thickness d of the cladding layer 72 is ｃ１ Ｔ and the thickness d of the cladding layer 74 ｃ２ Ｔ The thickness of the core layer 73 is d ａ Ｔ In this case, the wavelength λ Ｔ= 39. Propagation constant β of the difference frequency waveguide for THz waves of 90 μm Ｔ and the effective refractive index n ｅｆ Ｔ are 6.13845x10 respectively. ５ m －１ and the result is 3.89818.

[0091] Using equation (4) as in the first embodiment, the angle θ ｃ The light incident at and propagating through the waveguide with a propagation constant β Ｔ To couple light propagating at Ｔ That is, for example, the period Λ is set to 65.09 μm at the interface between the cladding layers 8 and 72. Ｔ = 65.09 μm and length L Ｔ If a diffraction grating of 1000 μm is provided, the angle θ ｃ = θ ｃｐ The THz light emitted by Cherenkov radiation at Ｔ As a result, the THz light 83 is emitted perpendicularly to the emission end face 23.

[0092] In this embodiment, the current blocking layer 4 buries the cladding layers 3 to 8 on both sides of the ridge, but does not bury the difference frequency waveguide. This is because if the ridge portion of the difference frequency waveguide were buried with Fe-doped InP, which has a high refractive index, the THz waves would not be confined in the ridge portion, and there is a possibility that it would become an anti-waveguide. Furthermore, although not shown, both sides of the ridge of the difference frequency waveguide and the top of the current blocking layer 4 may be covered with an insulating film such as SiON.

[0093] Next, a method for manufacturing quantum cascade laser device 800 will be described. Figures 21A to 21H are diagrams for explaining a method for manufacturing quantum cascade laser device 800 according to the seventh embodiment. First, as shown in Figure 21A, crystal growth is performed in this order on substrate 2 using MBE, MOCVD, or the like to form cladding layer 3, guide layer 5, stage 6, and guide layer 71. Next, as shown in Figure 21B, photolithography and etching are performed to form a periodic structure Λ in guide layer 71. １ Ｑ , length is L １Ｑ , width is W ｇ >W, depth d ｇ Ｑ is 0<d ｇ Ｑ Similarly, a diffraction grating 75 having a period Λ≦230 nm is formed in the guide layer 71. ２ Ｑ , length is L ２ Ｑ , width is W ｇ >W, depth d ｇ Ｑ is 0<d ｇ Ｑ A diffraction grating 76 of ≦230 nm is formed.

[0094] 21C, the cladding layer 8 is grown on the guide layer 71 by MBE, MOCVD, or the like. Next, as shown in FIG. 21D, a periodic Λ is formed in the cladding layer 8 by photolithography and etching. Ｔ , length is L Ｔ , width is W ｇ Ｔ >W, depth d ｇ Ｔ is 0<d ｇ Ｔ 21E, a diffraction grating 82 of ≦1.0 μm is formed. Next, as shown in FIG. 21E, a cladding layer 72, a core layer 73, a cladding layer 74, and a contact layer 13 are crystal-grown in this order on the cladding layer 8 by MBE, MOCVD, or the like.

[0095] Next, as shown in Fig. 21F, photolithography and etching are used to etch away both sides of the ridge to a point halfway through the cladding layer 3. Next, as shown in Fig. 21G, a current blocking layer 4 is grown by MBE, MOCVD, or the like to a height that buries the cladding layer 8 on both sides of the ridge. Next, as shown in Fig. 21H, an electrode 1 is formed on the back surface of the substrate 2, and an electrode 14 is formed on the contact layer 13.

[0096] Eighth Embodiment Fig. 22 is a perspective view of a quantum cascade laser device 900 according to an eighth embodiment. Fig. 23 is a cross-sectional view of the quantum cascade laser device 900 according to the eighth embodiment. Fig. 23 is a cross-sectional view of Fig. 22. ａ -z ｂThe cross section is shown by cutting along a straight line. This embodiment differs from the seventh embodiment in that the grating coupling region is provided inside the cladding layer below the core layer 73 of the difference frequency waveguide. The other configurations are the same as those of the seventh embodiment.

[0097] In the quantum cascade laser device 900, a layer having a thickness of d is provided on the cladding layer 8. ｃ１Ａ Ｔ A cladding layer 91 made of n-type GaInAs is provided on the cladding layer 91. A grating coupling region 92 made of n-type InP and having a thickness of 1.0 μm is provided on the cladding layer 91. A grating coupling region 92 made of n-type InP and having a thickness of d ｃ１Ｂ Ｔ and a cladding layer 93 made of n-type GaInAs is provided. ｃ１Ａ Ｔ +d ｃ１Ｂ Ｔ = d ｃ１ Ｔ is.

[0098] If the grating coupling region 92 is provided in the cladding layer of the difference frequency waveguide, it becomes easier to couple the THz light 80 to the difference frequency waveguide, and the output of the THz light 83 can be increased.

[0099] Ninth Embodiment Fig. 24 is a perspective view of a quantum cascade laser device 1000 according to a ninth embodiment. Fig. 25 is a cross-sectional view of the quantum cascade laser device 1000 according to the ninth embodiment. Fig. 25 is a cross-sectional view of Fig. 24. ａ -z ｂ In this embodiment, the grating coupling region is provided at the interface between the cladding layer 72 and the core layer 73 of the difference frequency waveguide. The grating coupling region is formed on the upper surface of the cladding layer 72 and has a length L Ｔ and the period is Λ Ｔ The diffraction grating 94 is provided and buried in the core layer 73. The other configurations are the same as those of the seventh embodiment.

[0100] By providing the grating coupling region at the interface between the cladding layer 72 and the core layer 73, it is possible to easily couple the THz light 80 to the difference frequency waveguide, thereby increasing the output of the THz light 83. Furthermore, since there is no need to add a layer as the grating coupling region, the manufacturing process can be simplified.

[0101] Tenth Embodiment Fig. 26 is a perspective view of a quantum cascade laser device 1100 according to a tenth embodiment. Fig. 27 is a cross-sectional view of the quantum cascade laser device 1100 according to the tenth embodiment. Fig. 27 is a cross-sectional view of Fig. 26. ａ -z ｂ The cross section obtained by cutting along a straight line is shown. This embodiment differs from the seventh embodiment in that a difference frequency waveguide is provided on a substrate 2, and a cascade laser region is provided on the difference frequency waveguide.

[0102] That is, cladding layer 72, core layer 73, and cladding layer 74 are stacked in this order on substrate 2. Cladding layer 3, guide layers 5 and 35, stage 6, guide layer 71, and cladding layer 8 are stacked in this order on cladding layer 74. Diffraction grating 94, which constitutes the grating coupling region, is formed by etching away cladding layer 74 to a depth of approximately 1 μm from the top surface and burying it with cladding layer 3.

[0103] The quantum cascade laser device 1100 also includes a current blocking layer 4 that covers both sides of the cascade laser region. The current blocking layer 4 is provided on the upper surface of the cladding layer 74. The side surfaces of the core layer 73 of the difference frequency waveguide are exposed from the current blocking layer 4.

[0104] The difference frequency waveguide can be formed with relatively rough control of the layer thickness. Therefore, it is possible to form the difference frequency waveguide using an LPE apparatus with a high growth rate. Therefore, according to this embodiment, in which the difference frequency waveguide is first formed on the substrate 2, the quantum cascade laser device 1100 can be manufactured easily and at low cost.

[0105] Next, a method for manufacturing quantum cascade laser device 1100 will be described. Figures 28A to 28H are diagrams for explaining a method for manufacturing quantum cascade laser device 1100 according to embodiment 10. First, as shown in Figure 28A, cladding layer 72, core layer 73, and cladding layer 74 are crystal-grown in this order on substrate 2 by LPE, MBE, MOCVD, or the like. Next, as shown in Figure 28B, a periodic structure having a period of Λ is formed in cladding layer 74 by photolithography and etching. Ｔ , length is L Ｔ , width is W ｇ Ｔ >W, depth d ｇ Ｔ is 0<d ｇ Ｔ A diffraction grating 94 of ≦1.0 μm is formed.

[0106] 28C, the cladding layer 3, the guide layers 5, 35, the stage 6, and the guide layer 71 are crystal-grown in this order on the cladding layer 74 by MBE, MOCVD, or the like. Next, as shown in FIG. 28D, a periodic pattern having a period of Λ is formed in the guide layer 71 by photolithography and etching. １ Ｑ , length is L １ Ｑ , width is W ｇ >W, depth d ｇ Ｑ is 0<d ｇ Ｑ Similarly, a diffraction grating 75 having a period Λ≦230 nm is formed in the guide layer 71. ２ Ｑ , length is L ２ Ｑ , width is W ｇ >W, depth d ｇ Ｑ is 0<d ｇ Ｑ A diffraction grating 76 of ≦230 nm is formed.

[0107] Next, as shown in Fig. 28E, cladding layer 8 and contact layer 13 are crystal-grown in this order on guide layer 71 by MBE, MOCVD, or the like. Next, as shown in Fig. 28F, both sides of the ridge are etched away down to cladding layer 74 by photolithography and etching. Next, as shown in Fig. 28G, current blocking layers 4 are grown and embedded on both sides of the ridge by MBE, MOCVD, or the like. Next, as shown in Fig. 28H, electrode 1 is formed on the back surface of substrate 2, and electrode 14 is formed on contact layer 13 and current blocking layer 4.

[0108] Eleventh Embodiment Fig. 29 is a perspective view of a quantum cascade laser device 1200 according to an eleventh embodiment, and Fig. 30 is a cross-sectional view of the quantum cascade laser device 1200 according to the eleventh embodiment. ａ -z ｂ The present embodiment differs from the tenth embodiment in that the grating coupling region 92 is provided inside the cladding layer above the core layer 73 of the difference frequency waveguide. Ｔ and the period is Λ Ｔ The other configurations are the same as those of the tenth embodiment.

[0109] In this embodiment, by providing the grating coupling region 92 in the cladding layer of the difference frequency waveguide, it is possible to easily couple the THz light 79 to the difference frequency waveguide, and the output of the THz light 83 can be increased.

[0110] 31 is a perspective view of a quantum cascade laser device 1300 according to a twelfth embodiment. FIG. 32 is a cross-sectional view of the quantum cascade laser device 1300 according to the twelfth embodiment. FIG. 32 is a cross-sectional view of FIG. 31. ａ -z ｂ The present embodiment differs from the tenth embodiment in that a diffraction grating 94 constituting the grating coupling region is provided at the interface between the cladding layer 74 and the core layer 73. Ｔ , the period is Λ ＴThe diffraction grating 94 is formed by removing a depth of about 1 μm from the upper surface of the core layer 73 by etching and burying it with the cladding layer 74. The other configurations are the same as those of the tenth embodiment.

[0111] According to this embodiment, there is no need to add a layer as a grating coupling region, and therefore the manufacturing process can be simplified.

[0112] 33 is a perspective view of a quantum cascade laser device 1400 according to a thirteenth embodiment. The quantum cascade laser device 1400 differs from the first embodiment in that it includes a highly reflective film 102 that covers the rear facet 25 opposite to the emission facet 23. The other configurations are the same as those of the first embodiment.

[0113] As the high reflection film 102, for example, alumina (Al ２ O ３ The high-reflection film 102 is formed on the rear facet of the optical fiber 100. The high-reflection film 102 can eliminate or reduce the first and second fundamental waves emitted from the rear facet. This can increase the THz wave output.

[0114] 34 is a perspective view of a quantum cascade laser device 1500 according to a modification of the thirteenth embodiment. The quantum cascade laser device 1500 differs from the quantum cascade laser device 1400 in that the portion of the output end face 23 corresponding to the difference frequency waveguide is exposed, and a highly reflective film 102 is further provided to cover the portion corresponding to the cascade laser region. This causes the first fundamental wave and the second fundamental wave to remain within the resonator and not be emitted outside the device. This allows the output of the THz waves to be further increased.

[0115] The highly reflective film 102 is expected to have high reflectivity not only for the first fundamental wave and the second fundamental wave but also for the THz light 24. The highly reflective film 102 is not limited to the quantum cascade laser device of the first embodiment, and may be applied to devices of other embodiments.

[0116] Fourteenth Embodiment Fig. 35 is a diagram illustrating the arrangement of diffraction gratings 15 and 16 according to a fourteenth embodiment. Up until now, the diffraction gratings corresponding to the first fundamental wave and the second fundamental wave have been arranged in cascade in the resonator direction. In other words, the diffraction gratings corresponding to the first fundamental wave and the second fundamental wave have been provided at the same height. In this embodiment, the diffraction grating 15 corresponding to the first fundamental wave and the diffraction grating 16 corresponding to the second fundamental wave are provided at positions offset in the direction perpendicular to the top surface of the substrate 2. In the example of Fig. 35, the diffraction grating 15 and the diffraction grating 16 are provided on the top and bottom surfaces of the guide layer 7, respectively. The other configurations are the same as those of any of the first to thirteenth embodiments.

[0117] According to this embodiment, the lengths L1 and L2 of the diffraction gratings 15 and 16 can be freely set within the range of the resonator length L. In other words, the lengths L1 and L2 can be set so that the diffraction gratings 15 and 16 partially overlap in a planar view. Here, as the length of the diffraction grating increases, the spectral linewidth can be narrowed. Therefore, according to this embodiment, it is possible to narrow the linewidths of the wavelengths of the first fundamental wave and the second fundamental wave.

[0118] Fifteenth embodiment Fig. 36 is a perspective view of a quantum cascade laser device 1600 according to a fifteenth embodiment. Fig. 37 is a cross-sectional view of the quantum cascade laser device according to the fifteenth embodiment. Fig. 37 is a cross-sectional view of Fig. 36. ａ -z ｂ The cross section obtained by cutting along a straight line is shown. In the embodiments up to now, the diffraction grating corresponding to the first fundamental wave and the diffraction grating corresponding to the second fundamental wave are provided above the 35 stage 6 in the cascade laser region, that is, in the guide layer 7. In contrast, in this embodiment, the diffraction grating 15 corresponding to the first fundamental wave and the diffraction grating 16 corresponding to the second fundamental wave are provided below the 35 stage 6 in the cascade laser region, that is, in the guide layer 5.

[0119] In this case, it is possible to obtain the THz lights 19 and 20 in the same manner as in the previous embodiments. The arrangement of the diffraction gratings 15 and 16 in this embodiment may be applied to any of the embodiments.

[0120] Sixteenth embodiment Fig. 38 is a perspective view of a quantum cascade laser device 1700 according to a sixteenth embodiment. Fig. 39 is a cross-sectional view of the quantum cascade laser device 1700 according to the sixteenth embodiment. Fig. 39 is a cross-sectional view of Fig. 38. ａ -z ｂ The cross section obtained by cutting along a straight line is shown. This embodiment differs from the first embodiment in that difference frequency waveguides are provided in two locations, between the electrode 1 and the cascade laser region, and between the cascade laser region and the electrode 14. In other words, it can be said that the quantum cascade laser device 100 of the first embodiment further includes a difference frequency waveguide and a grating coupling region provided between the substrate 2 and the cascade laser region.

[0121] In the quantum cascade laser device 1700, a layer having a thickness of d ｃ１ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ｃ１Ｔ Ｔ The cladding layer 201 is made of n-type InP. ａ１ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ａ１Ｔ Ｔ The core layer 202 is made of n-type GaInAs. ｃ２ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ｃ２Ｔ Ｔ and a cladding layer 203 made of n-type InP is provided. The cladding layer 201, the core layer 202 and the cladding layer 203 constitute a first difference frequency waveguide.

[0122] A grating coupling region 204 having a thickness of 1.0 μm and made of n-type GaInAs is provided on the cladding layer 203. A cascade laser region is provided on the grating coupling region 204. The structure of the cascade laser region is the same as that of the first embodiment. A grating coupling region 205 having a thickness of 1.0 μm and made of n-type GaInAs is provided on the cascade laser region.

[0123] Above the grating coupling region 205, a layer having a thickness of d ｃ３ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ｃ３Ｔ Ｔ The cladding layer 206 is made of n-type InP. ａ２ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ａ２Ｔ Ｔ On the core layer 207, a layer having a thickness of d ｃ４ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ｃ４Ｔ Ｔ and a cladding layer 208 made of n-type InP is provided. The cladding layer 206, the core layer 207 and the cladding layer 208 form a second difference frequency waveguide.

[0124] In FIG. 39, the wavelength λ Ｔ , frequency f Ｔ , propagation constant β Ｔ 39 also shows a THz guided mode 209 propagating through the first difference frequency waveguide at a wavelength λ Ｔ , frequency f Ｔ , propagation constant β Ｔ The grating coupling region 204 is shown with a THz guided mode 210 propagating in the second difference frequency waveguide at a length L １ Ｔ , the period is Λ １ Ｔ The grating coupling region 205 has a diffraction grating 211 with a length of L ２ Ｔ , the period is Λ ２ Ｔ A diffraction grating 212 having the above structure is formed. THz light 213 is emitted from the first difference frequency waveguide. THz light 214 is emitted from the second difference frequency waveguide.

[0125] Cherenkov radiation angle in cladding layer 3 -θ ｃｍand the Cherenkov radiation angle θ in the cladding layer 8 ｃｐ can be calculated using the formulas (1) to (3) in the same way as in the first embodiment. On the other hand, the period Λ of the diffraction grating 211 in the grating coupling region 204 １ Ｔ is obtained from equation (8) using an integer m excluding zero.

[0126]

[0127] Also, the period Λ of the diffraction grating 212 in the grating coupling region 205 ２ Ｔ is obtained from equation (9) using an integer j excluding zero.

[0128]

[0129] In this embodiment, since both the cladding layer 3 and the cladding layer 8 are made of InP, the Cherenkov radiation angle is θ ｃｍ = θ ｃｐ = θ ｃ = 25.37°. In addition, since both the grating coupling region 204 and the grating coupling region 205 are made of GaInAs, the period of the diffraction gratings 211 and 212 is Λ １ Ｔ =Λ ２ Ｔ =Λ Ｔ = 72.25 mm.

[0130] From the above, the grating coupling region 204 allows the THz light 19 emitted from the cascade laser region in a direction tilted with respect to the upper surface of the substrate 2 to be coupled to the THz waveguide mode 209 of the first difference frequency waveguide. Furthermore, the grating coupling region 205 allows the THz light 20 emitted from the cascade laser region in a direction tilted with respect to the upper surface of the substrate 2 to be coupled to the THz waveguide mode 210 of the second difference frequency waveguide.

[0131] In this embodiment, difference frequency waveguides are provided at two locations, above and below the cascade laser region, so that the THz light 213, 214 emitted from the emission end face 23 can be approximately twice as large as in Embodiment 1. The structure of this embodiment in which difference frequency waveguides are provided at two locations may be applied to any of the embodiments.

[0132] Seventeenth embodiment Fig. 40 is a cross-sectional view of a quantum cascade laser device 1800 according to a seventeenth embodiment. Fig. 41 is a perspective view of the quantum cascade laser device 1800 according to the seventeenth embodiment. Fig. 41 is a cross-sectional view of Fig. 40. ａ -z ｂ The cross section is shown by cutting along a straight line. In this embodiment, the grating coupling region 221 and the cladding layers 222, 224 and core layer 223 of the difference frequency waveguide are intentionally undoped. Furthermore, voltage is applied only to the cascade laser region. This reduces the operating voltage and increases the THz output.

[0133] In the quantum cascade laser device 1800, a contact layer 13 is provided on the cladding layer 8. A grating coupling region 221 and a difference frequency waveguide are provided on the contact layer 13. Specifically, a grating coupling region 221 having a layer thickness of 1.0 μm and made of undoped GaInAs is provided on the contact layer 13. A grating coupling region 221 having a layer thickness of d ｃ１ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ｃ１Ｔ Ｔ On the cladding layer 222, a cladding layer 222 having a thickness of d ａ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ａＴ Ｔ On the core layer 223, a layer having a thickness of d ｃ２ Ｔ , difference frequency wavelength λ Ｔ The refractive index at n ｃ２Ｔ Ｔ and a cladding layer 224 made of undoped InP is provided.

[0134] In this embodiment, the ridge width W of the cascade laser region Ｑ and the ridge width W of the difference frequency waveguide ＴHowever, the present invention is not limited to this, and both may have the same width, as in the other embodiments.

[0135] The electrode 14 is provided on the contact layer 13, avoiding the difference frequency waveguide. A voltage is applied only to the electrode 1, substrate 2, cladding layer 3, guide layers 5 and 35, stage 6, guide layer 7, cladding layer 8, contact layer 13, and electrode 14. In other words, no voltage is applied to the grating coupling region 221, cladding layer 222, core layer 223, or cladding layer 224. This allows for a reduction in operating voltage.

[0136] Furthermore, the grating coupling region 221, the cladding layer 222, the core layer 223, and the cladding layer 224 are undoped layers that are not intentionally doped. This reduces the optical absorption of THz light, thereby increasing the output of THz light 24.

[0137] Next, a method for manufacturing the quantum cascade laser device 1800 will be described. Figures 42A to 42J are diagrams for explaining a method for manufacturing the quantum cascade laser device 1800 according to the seventeenth embodiment. First, as shown in Figure 42A, crystal growth is performed in this order on the substrate 2 using MBE, MOCVD, or the like to form the cladding layer 3, guide layer 5, stage 6, and guide layer 7. Next, as shown in Figure 42B, photolithography and etching are used to form a layer with a period Λ in the guide layer 7. １ Ｑ , length is L １ Ｑ , width is W ｇ >W Ｑ , depth d ｇ Ｑ is 0<d ｇ Ｑ Similarly, a diffraction grating 15 having a period Λ≦230 nm is formed in the guide layer 7. ２ Ｑ , length is L ２ Ｑ , width is W ｇ >W Ｑ , depth d ｇ Ｑ is 0<d ｇ Ｑ A diffraction grating 16 of ≦230 nm is formed.

[0138] 42C, a cladding layer 8 is grown on the guide layer 7 by MBE, MOCVD, or the like. Next, as shown in FIG. 42D, the cladding layer 3 is partially removed by photolithography and etching to form a cladding layer 8 having a width W Ｑ 42E, a current blocking layer 4 is grown on both sides of the ridge by MBE, MOCVD or the like.

[0139] 42F, the contact layer 13 and the grating coupling region 221 are grown by crystal growth using MBE, MOCVD, or the like on the cladding layer 8 and the current blocking layer 4. Next, as shown in FIG. 42G, a pattern having a period Λ is formed in the grating coupling region 221 by photolithography and etching. Ｔ , length is L Ｔ , width is W ｇ Ｔ >W Ｔ , depth d ｇ Ｔ is 0<d ｇ Ｔ The diffraction grating 22 is formed to be ≦1.0 μm.

[0140] Next, as shown in Fig. 42H, crystal growth of cladding layer 222, core layer 223, and cladding layer 224 is performed in this order on grating coupling region 221 by MBE, MOCVD, etc. Next, as shown in Fig. 42I, photolithography and etching are used to remove the cladding layer up to grating coupling region 221, resulting in a width W Ｔ 42J, an electrode 1 is formed on the rear surface of the substrate 2, and an electrode 14 is formed on the contact layer 13.

[0141] The above-mentioned difference frequency values ​​of 5.406 THz (wavelength 55.45 μm) and 7.513 THz (wavelength 39.90 μm) are merely examples, and each embodiment can be applied to any THz wave.

[0142] The technical features described in each embodiment may be used in appropriate combination.

[0143] REFERENCE SIGNS LIST 1 Electrode, 2 Substrate, 3 Cladding layer, 4 Current blocking layer, 5 Guide layer, 6 35 stage, 7 Guide layer, 8 Cladding layer, 9 Grating coupling region, 10 Cladding layer, 11 Core layer, 12 Cladding layer, 13 Contact layer, 14 Electrode, 15 Diffraction grating, 16 Diffraction grating, 17 QCL waveguide mode, 18 QCL waveguide mode, 19 THz light, 20 THz light, 21 THz waveguide mode, 22 Diffraction grating, 23 Emission end face, 24 THz light, 25 Rear end face, 26 Insulating film, 31 Barrier layer, 32 Well layer, 33 Barrier layer, 34 Well layer, 35 Barrier layer, 36 Well layer, 37 Barrier layer, 38 Well layer, 39 Barrier layer, 40 Well layer, 41 Barrier layer, 42 Well layer, 43 Barrier layer, 44 Well layer, 45 Barrier layer, 46 Well layer, 47 Barrier layer, 48 Active region, 49 Injector region, 50 Stage, 51 Cladding layer, 52 Cladding layer, 61 Cladding layer, 62 Cladding layer, 71 Guide layer, 72 Cladding layer, 73 Core layer, 74 Cladding layer, 75 Diffraction grating, 76 Diffraction grating, 77 QCL guided mode, 78 QCL guided mode, 79 THz light, 80 THz light, 81 THz guided mode, 82 Diffraction grating, 83 THz light, 91 Cladding layer, 92 Grating coupling region, 93 Cladding layer, 94 Diffraction grating, 100 Quantum cascade laser device, 101 Diffraction grating, 102 Highly reflective film, 200 Quantum cascade laser device, 201 Cladding layer, 202 Core layer, 203 Cladding layer, 204 Grating coupling region, 205 Grating coupling region, 206 Cladding layer, 207 Core layer, 208 Cladding layer, 209 THz guided mode, 210 THz guided mode, 211 Diffraction grating, 212 Diffraction grating, 213 THz light, 214 THz light, 221 Grating coupling region, 222 Cladding layer, 223 Core layer, 224 Cladding layer, 300 Quantum cascade laser device, 400 Quantum cascade laser device, 500 Quantum cascade laser device, 600 Quantum cascade laser device, 700 Quantum cascade laser device, 800 Quantum cascade laser device, 900 Quantum cascade laser device, 1000 Quantum cascade laser device, 1100 Quantum cascade laser device, 1200 Quantum cascade laser device,1300 quantum cascade laser device, 1400 quantum cascade laser device, 1500 quantum cascade laser device, 1600 quantum cascade laser device, 1700 quantum cascade laser device, 1800 quantum cascade laser device,

Claims

1. A quantum cascade laser device comprising: a semiconductor substrate; a cascade laser region and a first difference frequency waveguide stacked on the semiconductor substrate; and a first grating coupling region, wherein the cascade laser region has a first cladding layer, a plurality of stages provided on the first cladding layer, and a second cladding layer provided on the plurality of stages, each of the plurality of stages having an active region and an injector region configured to inject carriers into the active region, each of the active region and the injector region having alternating barrier layers and well layers, wherein the first difference frequency waveguide has a third cladding layer, a first core layer provided on the third cladding layer, and a fourth cladding layer provided on the first core layer, and wherein the first grating coupling region is configured to couple light emitted from the cascade laser region in a direction oblique to the top surface of the semiconductor substrate to a waveguide mode of the first difference frequency waveguide.

2. The quantum cascade laser device according to claim 1, wherein the output end face of said first difference frequency waveguide is perpendicular to the upper surface of said semiconductor substrate.

3. The quantum cascade laser device according to claim 1 or 2, characterized in that the cascade laser region is configured so that oscillation occurs at a first fundamental wave of a first frequency and a second fundamental wave of a second frequency, the first difference frequency waveguide has the waveguide mode corresponding to the difference frequency between the first frequency and the second frequency, and the first grating coupling region has a diffraction grating configured to couple light emitted from the cascade laser region in a direction tilted with respect to the upper surface of the semiconductor substrate to the waveguide mode of the first difference frequency waveguide.

4. The quantum cascade laser device according to claim 3, wherein the cascade laser region is provided on the semiconductor substrate, and the first difference frequency waveguide is provided on the cascade laser region.

5. From the cascade laser region, the resonance direction and angle θ ｃｐ and angle -θ ｃｍ The light is emitted in a direction that forms an angle θ ｃｐ and angle -θ ｃｍ are respectively and and the period Λ of the diffraction grating in the first grating coupling region is satisfied. Ｔ teeth, and β １ Ｑ is the propagation constant of the cascade laser region for the first fundamental wave, and β ２ Ｑ is the propagation constant of the cascade laser region for the second fundamental wave, and β Ｔ is the propagation constant of the first difference frequency waveguide for the difference frequency between the first fundamental wave and the second fundamental wave, and λ Ｔ is the wavelength of the difference frequency, and n ｃ１Ｑ Ｔ is the wavelength λ of the first cladding layer Ｔ is the refractive index at n ｃ２Ｑ Ｔ is the wavelength λ of the second cladding layer Ｔ is the refractive index at n ｃ１Ｔ Ｔ is the wavelength λ of the third cladding layer Ｔ 5. The quantum cascade laser device according to claim 4, wherein m is a refractive index at m, and m is an integer other than zero.

6. The quantum cascade laser device according to claim 4 or 5, wherein the first grating coupling region is provided between the cascade laser region and the first difference frequency waveguide.

7. The quantum cascade laser device according to claim 4 or 5, wherein the first grating coupling region is provided inside the third cladding layer and is separated from the cascade laser region.

8. The quantum cascade laser device according to claim 4 or 5, wherein the first grating coupling region is provided at the interface between the third cladding layer and the first core layer.

9. The quantum cascade laser device according to any one of claims 4 to 8, further comprising current blocking layers covering both sides of the first core layer.

10. A quantum cascade laser device according to any one of claims 4 to 8, further comprising current blocking layers covering both sides of the cascade laser region, the first core layer being exposed from the current blocking layers.

11. The quantum cascade laser device according to claim 3, wherein the first difference frequency waveguide is provided on the semiconductor substrate, and the cascade laser region is provided on the first difference frequency waveguide.

12. From the cascade laser region, the resonance direction and angle θ ｃｐ and angle -θ ｃｍ The light is emitted in the direction of the angle θ ｃｐ and angle -θ ｃｍ are respectively and and the period Λ of the diffraction grating in the first grating coupling region is satisfied. Ｔ teeth, and β １ Ｑ is the propagation constant of the cascade laser region for the first fundamental wave, and β ２ Ｑ is the propagation constant of the cascade laser region for the second fundamental wave, and β Ｔ is the propagation constant of the first difference frequency waveguide for the difference frequency, and λ Ｔ is the wavelength of the difference frequency between the first fundamental wave and the second fundamental wave, and n ｃ１Ｑ Ｔ is the wavelength λ of the first cladding layer Ｔ is the refractive index at n ｃ２Ｑ Ｔ is the wavelength λ of the second cladding layer Ｔ is the refractive index at n ｃ２Ｔ Ｔ is the wavelength λ of the fourth cladding layer Ｔ 12. The quantum cascade laser device according to claim 11, wherein m is a refractive index at m, and m is an integer other than zero.

13. The quantum cascade laser device according to claim 11 or 12, wherein the first grating coupling region is provided between the cascade laser region and the first difference frequency waveguide.

14. The quantum cascade laser device according to claim 11 or 12, wherein the first grating coupling region is provided inside the fourth cladding layer and is separated from the cascade laser region.

15. The quantum cascade laser device according to claim 11 or 12, wherein the first grating coupling region is provided at the interface between the fourth cladding layer and the first core layer.

16. The quantum cascade laser device according to any one of claims 11 to 15, further comprising current blocking layers covering both sides of the first core layer.

17. The quantum cascade laser device according to any one of claims 11 to 15, further comprising current blocking layers covering both sides of the cascade laser region, the first core layer being exposed from the current blocking layers.

18. The quantum cascade laser device according to any one of claims 1 to 17, further comprising a first highly reflective film covering a rear end facet opposite to an output end facet of the quantum cascade laser device.

19. A quantum cascade laser device as described in any one of claims 1 to 18, characterized in that a portion of the output end face of the quantum cascade laser device corresponding to the first difference frequency waveguide is exposed, and a second highly reflective film is provided to cover a portion corresponding to the cascade laser region.

20. A quantum cascade laser device as described in any one of claims 3 to 17, characterized in that the cascade laser region has a diffraction grating corresponding to the first fundamental wave and a diffraction grating corresponding to the second fundamental wave, and the diffraction grating corresponding to the first fundamental wave and the diffraction grating corresponding to the second fundamental wave are provided at positions offset in a direction perpendicular to the upper surface of the semiconductor substrate.

21. A quantum cascade laser device as described in any one of claims 3 to 17, characterized in that the cascade laser region has a diffraction grating corresponding to the first fundamental wave and a diffraction grating corresponding to the second fundamental wave, and the diffraction grating corresponding to the first fundamental wave and the diffraction grating corresponding to the second fundamental wave are provided on the plurality of stages in the cascade laser region.

22. A quantum cascade laser device as described in any one of claims 3 to 17, characterized in that the cascade laser region has a diffraction grating corresponding to the first fundamental wave and a diffraction grating corresponding to the second fundamental wave, and the diffraction grating corresponding to the first fundamental wave and the diffraction grating corresponding to the second fundamental wave are provided below the plurality of stages in the cascade laser region.

23. A quantum cascade laser device as described in any one of claims 4 to 10, comprising: a second difference frequency waveguide provided between the semiconductor substrate and the cascade laser region; and a second grating coupling region, wherein the second difference frequency waveguide has a fifth cladding layer, a second core layer provided on the fifth cladding layer, and a sixth cladding layer provided on the second core layer, and the second grating coupling region is configured to couple light emitted from the cascade laser region in a direction tilted with respect to the upper surface of the semiconductor substrate to a guided mode of the second difference frequency waveguide.

24. A quantum cascade laser device as described in any one of claims 4 to 10, characterized in that the cascade laser region has a contact layer provided on the second cladding layer, the first difference frequency waveguide is provided on the contact layer, and an upper electrode of the quantum cascade laser device is provided on the contact layer, avoiding the first difference frequency waveguide.

25. The quantum cascade laser device of claim 24, wherein the third cladding layer, the first core layer, the fourth cladding layer, and the first grating coupling region are undoped.

26. A cascade laser region and a difference frequency waveguide are stacked on a semiconductor substrate, and the grating coupling region is formed between the cascade laser region and the difference frequency waveguide or inside the difference frequency waveguide, the cascade laser region having a first cladding layer, a plurality of stages provided on the first cladding layer, and a second cladding layer provided on the plurality of stages, each of the plurality of stages having an active region and an injector region configured to inject carriers into the active region, each of the active region and the injector region having alternating barrier layers and well layers, and the difference frequency waveguide having a third cladding layer, a first core layer provided on the third cladding layer, and a fourth cladding layer provided on the first core layer, A method for manufacturing a quantum cascade laser device, characterized in that the grating coupling region couples light emitted from the cascade laser region in a direction tilted with respect to the top surface of the semiconductor substrate to a guided mode of the difference frequency waveguide.

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