Laser Module

Abstract

To allow an improvement of an amplification of a terahertz wave and an efficiency of a wavelength conversion.SOLUTION: A laser module 1A comprises a QCL element 2A and a light source 5. The QCL element 2A includes: a substrate 3; a lower clad layer 41 that is provided onto the substrate; an active layer 42 that is provided to the side opposite to the substrate 3 of the lower clad layer 41, and generates a terahertz wave T1; an upper clad layer 43 that is provided to the side opposite to the lower clad layer 41 of the active layer 42; and a first electrode 6 that is provided to the side opposite to the active layer 42 of the upper clad layer 43. A terahertz wave T2 from the light source 5 is entered into the active layer 42 via the substrate 3, and is reflected by the first electrode 6 as well as being amplified and converting a wavelength. A terahertz wave T3 after the amplification and the conversion of the wavelength by the active layer 42 is injected to an external part via the substrate 3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a laser module. [Background technology]

[0002] Conventionally, a difference frequency generation type terahertz quantum cascade laser (DFG-THz-QCL) has been known. For example, Non-Patent Document 1 discloses a method of amplifying terahertz waves by irradiating the terahertz waves (pulse waves) onto an end face of an active layer of such a terahertz quantum cascade laser. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Dominic Bachmann, Norbert Leder, Markus Rosch, Giacomo Scalari, Mattias Beck, Holger Arthaber, Jerome Faist, Karl Unterrainer, and Juraj Darmo, “Broadband terahertz amplification in a heterogeneous quantum cascade laser”, Feb 2015, Vol. 23, No. 3, OPTICS EXPRESS, pp. 3117-3125. Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the thickness of the active layer is usually only a few micrometers to a few tens of micrometers, it is not easy to make a sufficient amount of terahertz waves incident on the end facets of the active layer. Furthermore, when terahertz waves are incident on the end facets of the active layer along the resonance direction (the direction in which the pair of end faces of the active layer face each other), the amount of terahertz waves absorbed by the active layer becomes relatively large, which reduces the efficiency of terahertz wave amplification (or wavelength conversion).

[0005] Therefore, an object of one aspect of the present disclosure is to provide a laser module that can improve the efficiency of amplification or wavelength conversion of terahertz waves. [Means for solving the problem]

[0006] A laser module according to one aspect of the present disclosure includes a quantum cascade laser element that generates a first terahertz wave having a difference frequency between a first frequency and a second frequency, and a light source that emits a second terahertz wave different from the first terahertz wave to the quantum cascade laser element, wherein the quantum cascade laser element has a substrate, a first clad layer provided on the substrate, and a resonator that is provided on the opposite side of the first clad layer from the substrate and forms a resonator that oscillates light of the first frequency and light of the second frequency, an active layer that generates the first terahertz wave, a second clad layer provided on the active layer on the opposite side of the first clad layer, and a metal electrode provided on the second clad layer on the opposite side of the active layer, wherein the second terahertz wave enters the active layer through the substrate and is reflected and amplified or wavelength-converted by the metal electrode, and the second terahertz wave that has been amplified or wavelength-converted in the active layer is emitted to the outside through the substrate.

[0007] The laser module described above uses a quantum cascade laser element that generates terahertz waves (first terahertz waves) by difference frequency generation to amplify or wavelength-convert a second terahertz wave emitted from a light source. In the laser module described above, the second terahertz wave emitted from the light source is incident on the substrate rather than on the end face of the active layer. That is, the second terahertz wave is incident on the active layer (i.e., the surface of the active layer facing the substrate) via the inside of the substrate. This method allows the second terahertz wave to be easily incident on the active layer and suppresses absorption of the second terahertz wave by the active layer, compared to a method in which the second terahertz wave is incident on the end face of the active layer. Furthermore, by reflecting the second terahertz wave at a metal electrode located on the opposite side of the active layer from the substrate, the second terahertz wave (i.e., third terahertz wave) amplified or wavelength-converted in the active layer can be easily extracted to the outside via the substrate again. As a result, the laser module described above can improve the efficiency of terahertz wave amplification or wavelength conversion.

[0008] The substrate may be made of InP or Si. According to the above configuration, by forming the substrate from a material (InP or Si) having a small absorption coefficient of terahertz waves, loss (attenuation) of the terahertz waves passing through the substrate can be suppressed, and the amount of light of the third terahertz waves extracted to the outside can be increased.

[0009] The length of the active layer in the first direction, which is the resonance direction of the quantum cascade laser element, may be 100 μm to 3 mm. According to the above configuration, it is possible to preferably realize a configuration in which the third terahertz wave can be extracted to the outside by reflecting the second terahertz wave once at the metal electrode. In other words, it is possible to prevent the second terahertz wave from being reflected multiple times within the quantum cascade laser element. This reduces the loss of the second terahertz wave within the quantum cascade laser element due to multiple reflections, and as a result, it is possible to improve the light intensity of the third terahertz wave.

[0010] The substrate may be made of Si, and may have a first main surface facing the first cladding layer and a second main surface located opposite the first main surface. The second terahertz wave may be reflected at least once by the second main surface of the substrate and re-enter the active layer after being initially reflected by the metal electrode and before being emitted to the outside as a third terahertz wave. According to the above configuration, by multiple-reflecting the second terahertz wave within the quantum cascade laser element, the second terahertz wave can be incident on the active layer multiple times. This increases the number of times the second terahertz wave is amplified or wavelength-converted, thereby effectively improving the efficiency of amplification or wavelength conversion. Note that when the second terahertz wave is multiple-reflected within the quantum cascade laser element, loss of the second terahertz wave within the quantum cascade laser element is greater than when the second terahertz wave is not multiple-reflected. However, by forming the substrate from Si, loss of the second terahertz wave (absorption by the substrate) can be effectively suppressed. That is, with the above configuration, it is possible to obtain the advantage of multiple reflections (improved efficiency of amplification or wavelength conversion of the second terahertz wave) while suppressing the disadvantage of multiple reflections (loss of the second terahertz wave).

[0011] The substrate may have a first end face located on a first side in a first direction that is a resonance direction of the quantum cascade laser element and a second end face located on a second side opposite to the first side in the first direction, the active layer may have a third end face located on the first side in the first direction and a fourth end face located on the second side in the first direction, and the second terahertz wave may be incident on the first end face along a direction that is inclined with respect to the first direction so as to approach the active layer as it moves from the first side to the second side in the first direction. With the above configuration, the second terahertz wave can be incident from the first end face of the substrate and reliably guided to the active layer, and can also be reliably reflected by the metal electrode and extracted to the outside.

[0012] The third terahertz wave may be emitted from the second end facet along a direction inclined with respect to the first direction so as to move away from the active layer in the first direction from the first side to the second side. With the above configuration, it is possible to extract output light (third terahertz wave) from the second end facet opposite to the first end facet which is the incident surface of the second terahertz wave, and therefore it is possible to easily avoid interference between the light source which outputs the second terahertz wave and the member which captures the third terahertz wave, and it is possible to improve the degree of freedom in design regarding the arrangement of each member.

[0013] The substrate may have a first main surface facing the first cladding layer and a second main surface located on the opposite side to the first main surface, and the first end surface may be inclined with respect to the second direction perpendicular to the first main surface so as to approach the second end surface as it extends from the first main surface to the second main surface along the second direction. With the above configuration, the angle of incidence of the second terahertz wave with respect to the first end surface can be reduced, and reflection (loss) of the second terahertz wave at the first end surface can be suppressed.

[0014] The inclination angle of the first end face with respect to a plane orthogonal to the first direction may be approximately equal to the angle at which the emission direction of the first terahertz wave is inclined with respect to the first direction. According to the above configuration, by making the second terahertz wave approximately perpendicularly incident on the first end face, the propagation direction of the third terahertz wave and the propagation direction of the first terahertz wave can be approximately equalized. As a result, phase matching between the third terahertz wave and the first terahertz wave can be achieved, and the interaction between the third terahertz wave and the first terahertz wave can effectively improve the efficiency of amplification or wavelength conversion of the third terahertz wave.

[0015] The substrate may have a first main surface facing the first cladding layer and a second main surface located on the opposite side to the first main surface, and the second end surface may be inclined with respect to the second direction perpendicular to the first main surface so as to approach the first end surface as it extends from the first main surface to the second main surface along the second direction. With the above configuration, the angle of incidence of the third terahertz wave with respect to the second end surface can be reduced, and reflection (loss) of the third terahertz wave at the second end surface can be suppressed.

[0016] The inclination angle of the second end face with respect to a plane perpendicular to the first direction may be approximately equal to the angle at which the emission direction of the first terahertz wave is inclined with respect to the first direction. According to the above configuration, when the propagation direction of the third terahertz wave and the propagation direction of the first terahertz wave are approximately equal to each other, phase matching between the third terahertz wave and the first terahertz wave can be achieved, and the efficiency of amplification or wavelength conversion of the third terahertz wave can be effectively improved by the interaction between the third terahertz wave and the first terahertz wave. Furthermore, in this case, the incident angle of the third terahertz wave with respect to the second end face can be made close to 0 degrees, thereby effectively suppressing reflection (loss) of the third terahertz wave at the second end face.

[0017] The laser module may further include an incident lens having an incident surface on which the second terahertz wave is incident and an opposing surface opposing the first end surface, and the opposing surface of the incident lens may be in direct or indirect contact with the first end surface. According to the above configuration, by making the second terahertz wave incident on the first end surface via the incident lens, it is possible to suppress interfacial reflection of the second terahertz wave at the first end surface, and by concentrating the second terahertz wave, it is possible to improve the incidence efficiency of the second terahertz wave on the active layer.

[0018] The incident lens may be made of Si. By making the incident lens from Si, which has an extremely small absorption coefficient for terahertz waves, attenuation of the second terahertz wave at the incident lens can be suppressed.

[0019] The incident lens may be a metalens having a concave-convex structure formed on the incident surface. By configuring the incident lens as a metalens, it is possible to reduce the size of the incident lens (reduce its thickness).

[0020] The laser module may further include an output lens having an output surface that outputs the third terahertz wave and an opposing surface that faces the second end surface, and the opposing surface of the output lens may be in direct or indirect contact with the second end surface. According to the above configuration, the third terahertz wave is extracted to the outside from the second end surface via the output lens, thereby improving the extraction efficiency of the third terahertz wave.

[0021] The output lens may be made of Si. By making the output lens of Si, which has an extremely small absorption coefficient for terahertz waves, attenuation of the third terahertz wave at the output lens can be suppressed.

[0022] The output lens may be a metalens having a concave-convex structure formed on the output surface. By configuring the output lens as a metalens, it is possible to reduce the size of the output lens (reduce its thickness).

[0023] The first end face of the substrate may protrude further toward the first side than the third end face of the active layer in the first direction. According to the above configuration, processing (e.g., polishing) of the first end face into an inclined surface can be easily performed.

[0024] The second end face of the substrate may protrude further toward the second side than the fourth end face of the active layer in the first direction. According to the above configuration, the second end face can be easily processed into an inclined surface (e.g., polished).

[0025] the active layer may have a third end face located on the first side in the first direction and a fourth end face located on the second side in the first direction; the substrate may have a first main surface facing the first cladding layer and a second main surface located on the opposite side from the first main surface; the first end face may be inclined with respect to the second direction orthogonal to the first main surface so as to approach the second end face as it extends from the first main surface to the second main surface along the second direction; the first end face of the substrate may protrude toward the first side in the first direction beyond the third end face of the active layer; and the second terahertz wave may be incident on the first main surface along the second direction, pass through the inside of the substrate, and be reflected by the first end face and the second main surface, thereby being incident on the active layer. According to the above configuration, the entrance surface for the second terahertz wave and the exit surface for the third terahertz wave can be separated by a large distance, thereby easily avoiding interference between the light source that outputs the second terahertz wave and the component that captures the third terahertz wave, and improving the design freedom regarding the placement of each component.

[0026] the substrate may have a first end face located on a first side in a first direction that is a resonance direction of the quantum cascade laser element, and a second end face located on a second side opposite to the first side in the first direction; the active layer may have a third end face located on the first side in the first direction, and a fourth end face located on the second side in the first direction; the substrate may have a first main surface facing the first cladding layer, and a second main surface located on the opposite side to the first main surface; the first end face may be inclined with respect to the second direction orthogonal to the first main surface so as to approach the second end face as it extends from the second main surface to the first main surface along the second direction; the first end face of the substrate may protrude toward the first side in the first direction beyond the third end face of the active layer; and the second terahertz wave may be incident on the second main surface along the second direction, pass through the inside of the substrate, and be reflected by the first end face, thereby entering the active layer. According to the above configuration, the entrance surface for the second terahertz wave and the exit surface for the third terahertz wave can be separated by a large distance, thereby easily avoiding interference between the light source that outputs the second terahertz wave and the component that captures the third terahertz wave, and improving the design freedom regarding the placement of each component. [Effects of the Invention]

[0027] According to one aspect of the present disclosure, it is possible to provide a laser module that can improve the efficiency of amplification or wavelength conversion of terahertz waves. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a schematic diagram of a laser module according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the QCL device of FIG. [Figure 3] FIG. 3 is a schematic cross-sectional view of the QCL device taken along line III-III in FIG. [Figure 4] FIG. 4 is a schematic diagram of the laser module according to the second embodiment. [Figure 5] FIG. 5 is a schematic diagram of a laser module according to the third embodiment. [Figure 6]FIG. 6 is a schematic diagram of a laser module according to the fourth embodiment. [Figure 7] FIG. 7 is a schematic configuration diagram of a laser module according to the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0029] An embodiment of the present disclosure will be described in detail below with reference to the drawings. In the following description, identical or equivalent elements will be designated by the same reference numerals, and redundant description will be omitted. Terms such as "upper" and "lower" are used for convenience based on the state shown in the drawings. Some features of the embodiment are exaggerated in the drawings to clearly illustrate them. Therefore, the dimensional ratios of the various parts in the drawings may differ from the actual dimensional ratios.

[0030] [First embodiment] A laser module 1A according to a first embodiment will be described with reference to FIGS. 1 to 3. As shown in FIG. 1, the laser module 1A includes a quantum cascade laser device 2A (hereinafter referred to as "QCL device 2A") and a light source 5. The QCL device 2A generates a terahertz wave T1 (first terahertz wave) having a difference frequency ω3 (=|ω1-ω2|) between a first frequency ω1 and a second frequency ω2. The light source 5 emits a terahertz wave T2 (second terahertz wave) different from the terahertz wave T1 to the QCL device 2A. The laser module 1A is configured to amplify or wavelength convert the terahertz wave T2 emitted from the light source 5 using the QCL device 2A, which is a difference frequency generation terahertz quantum cascade laser (DFG-THz-QCL).

[0031] Fig. 2 shows a cross section along a plane perpendicular to the resonance direction of the QCL element 2A. Fig. 3 shows a cross section along line III-III in Fig. 2. An upper contact layer 44 and a lower contact layer 45, which will be described later, are omitted from Figs. 1 and 3. Direction D1 (first direction) is the resonance direction of the QCL element 2A, direction D2 (second direction) is the stacking direction of the QCL element 2A (the stacking direction of a substrate 3, a lower cladding layer 41, an active layer 42, and an upper cladding layer 43, which will be described later), and direction D3 is perpendicular to directions D1 and D2.

[0032] The QCL device 2A is a terahertz light source configured to be able to output terahertz waves T1 in a room temperature environment, for example. The QCL device 2A has a substrate 3, a semiconductor layer 4, a first electrode 6 (metal electrode), and a second electrode 7. The QCL device 2A can be formed as a ridge-stripe laser device using a typical semiconductor process. The QCL device 2A can be obtained, for example, by forming InGaAs / InAlAs by epitaxial growth on an InP substrate (substrate 3).

[0033] The substrate 3 is, for example, a rectangular plate-shaped InP single crystal substrate (semi-insulating substrate: a high-resistance semiconductor substrate not doped with impurities). The length (length in direction D1), width (length in direction D3), and thickness (length in direction D2) of the substrate 3 are approximately several hundred μm to several mm, several hundred μm to several mm, and several hundred μm, respectively. In this embodiment, as an example, the length of the substrate 3 is approximately 3 mm, the width of the substrate 3 is approximately 1 mm, and the thickness of the substrate 3 is approximately 300 μm.

[0034] The substrate 3 has an upper surface 3a (first main surface) facing the semiconductor layer 4, and a lower surface 3b (second main surface) located on the opposite side to the upper surface 3a. The substrate 3 also has an end surface 3c (first end surface) located on a first side S1 (the right side in FIG. 3) in the direction D1, and an end surface 3d (second end surface) located on a second side S2 (the left side in FIG. 3) opposite to the first side S1 in the direction D1.

[0035] The semiconductor layer 4 is provided on the upper surface 3a of the substrate 3. The thickness (length in the direction D2) of the semiconductor layer 4 is approximately 10 μm to 20 μm (e.g., 15 μm). The semiconductor layer 4 has an end surface 4a located on a first side S1 in the direction D1 and an end surface 4b located on a second side S2 in the direction D1. The semiconductor layer 4 emits light in a wide band in the mid-infrared region (e.g., 3 μm to 20 μm) from each of the end surfaces 4a and 4b (more specifically, the end surfaces 42a and 42b of the active layer 42). The end surfaces 4a and 4b are surfaces perpendicular to the direction D1. The end surfaces 4a and 4b are, for example, cleavage planes formed by cleavage. In order to emit light in the wide band described above, the QCL device 2A may have a structure in which multiple active layers having different center wavelengths are stacked, or may have a structure consisting of a single active layer.

[0036] The semiconductor layer 4 has a lower cladding layer 41 (first cladding layer), an active layer 42, an upper cladding layer 43 (second cladding layer), an upper guide layer (not shown), a lower guide layer (not shown), an upper contact layer 44, a lower contact layer 45, and a support layer 46.

[0037] A lower contact layer 45, a lower cladding layer 41, a lower guide layer, an active layer 42, an upper guide layer, an upper cladding layer 43, and an upper contact layer 44 are stacked in this order from the upper surface 3a of the substrate 3. The upper guide layer is disposed between the active layer 42 and the upper cladding layer 43. The lower guide layer is disposed between the active layer 42 and the lower cladding layer 41. Support layers 46 are provided between the lower cladding layer 41 and the upper cladding layer 43 on both sides (on both sides in the direction D3) of the active layer 42, the upper guide layer, and the lower guide layer, which are formed in a ridge stripe shape. The lower contact layer 45 has a portion that extends outward (outside in the direction D3) beyond the lower cladding layer 41. In this embodiment, an end of the lower contact layer 45 in the direction D3 coincides with an end of the substrate 3 in the direction D3.

[0038] The lower contact layer 45 is, for example, a highly Si-doped InGaAs layer (Si: 1.0×1018 / cm 3 ) and is provided on the upper surface 3 a of the substrate 3 .

[0039] The lower cladding layer 41 is, for example, a Si-doped InP layer (Si: 1.5×10 16 / cm 3 ) and is provided on the lower contact layer 45. That is, the lower cladding layer 41 is provided on the upper surface 3a of the substrate 3 with the lower contact layer 45 interposed therebetween.

[0040] The lower guide layer is, for example, a Si-doped InGaAs layer (Si: 1.5 × 10 16 / cm 3 ) and is provided on the lower cladding layer 41 .

[0041] The active layer 42 is a layer in which a quantum cascade structure is formed, and is provided on the lower guide layer. That is, the active layer 42 is provided on the side of the lower cladding layer 41 opposite the substrate 3. As shown in FIG. 3, the active layer 42 has an end face 42a (third end face) located on the first side S1 in the direction D1 and an end face 42b (fourth end face) located on the second side S2 in the direction D1. The end face 42a is a part of the end face 4a of the semiconductor layer 4. The end face 42b is a part of the end face 4b of the semiconductor layer 4. As an example, the active layer 42 has a structure in which InGaAs layers and InAlAs layers are alternately stacked along the direction D2.

[0042] The upper guide layer is, for example, a Si-doped InGaAs layer (Si: 1.5 × 10 16 / cm 3 ) and is provided on the active layer 42.

[0043] The upper cladding layer 43 is, for example, a Si-doped InP layer (Si: 1.5×10 16 / cm 3 ) and is provided on the upper guide layer. That is, the upper cladding layer 43 is provided on the opposite side of the active layer 42 from the lower cladding layer 41.

[0044] The upper contact layer 44 is, for example, a highly Si-doped InP layer (Si: 1.5×10 18 / cm 3 ) and is provided on the upper cladding layer 43 .

[0045] The support layer 46 is, for example, an Fe-doped InP layer.

[0046] As shown in FIG. 2, an insulating film 47 is formed to cover the upper surface 44a of the upper contact layer 44, the side surface 4c of the semiconductor layer 4 intersecting the direction D3, and a portion of the lower contact layer 45. The insulating film 47 is formed of, for example, SiN. A contact hole 47a is formed in the insulating film 47 to expose a portion of the upper surface 44a of the upper contact layer 44. The contact hole 47a extends along the direction D1 (see FIG. 3) so as to expose a central portion of the upper surface 44a in the direction D3. In addition, in the direction D3, an end 47b of the insulating film 47 on the lower contact layer 45 is located inside the end of the lower contact layer 45. That is, the upper surface of the lower contact layer 45 is exposed outside the end 47b of the insulating film 47.

[0047] The first electrode 6 is formed on the upper surface 44a of the upper contact layer 44. The first electrode 6 is formed of a metal such as Ti / Au. That is, the first electrode 6 is provided on the upper cladding layer 43 on the opposite side to the active layer 42. The first electrode 6 is electrically connected to a part of the upper surface 44a of the upper contact layer 44 through a contact hole 47a.

[0048] The second electrode 7 is formed on the lower contact layer 45 so as to be in contact with a portion of the lower contact layer 45 that is exposed outside the end 47b of the insulating film 47. The second electrode 7 is formed of a metal such as Ti / Au. In this embodiment, the second electrode 7 is formed so as to cover part of the side and upper surfaces of the semiconductor layer 4, but this is not essential. That is, the second electrode 7 only needs to be electrically connected to at least the lower contact layer 45 and spaced apart from the first electrode 6. With the above configuration, the QCL device 2A can be driven by passing a current from the second electrode 7 to the first electrode 6.

[0049] As an example, in the QCL device 2A, by providing two types of diffraction grating layers that function as a distributed feedback (DFB) structure in the upper guide layer, it is possible to generate a first pump light with a first frequency ω1 and a second pump light with a second frequency ω2, and to generate a terahertz wave T1 with a difference frequency ω3. Note that the diffraction grating layers may be provided inside a cladding layer (e.g., upper cladding layer 43). The light with the first frequency ω1 (hereinafter referred to as "first light") and the light with the second frequency ω2 (hereinafter referred to as "second light") are both mid-infrared light.

[0050] The active layer 42 forms a resonator that oscillates the first light and the second light. As an example, the end faces 42a and 42b of the active layer 42 function as reflective surfaces that reflect the first light and the second light toward the inside of the active layer 42 so as to confine the first light and the second light within the active layer 42. However, the end faces 42a and 42b do not necessarily function as the reflective surfaces. For example, when an external resonator (e.g., a diffraction grating) other than the QCL device 2A is disposed opposite the end face 42a, at least one of the first light and the second light may be emitted from the end face 42a to the external resonator, and the light diffracted and reflected by the external resonator may be fed back to the end face 42a. The active layer 42 generates a terahertz wave T1 with a difference frequency ω3 (=|ω1-ω2|) between the first frequency ω1 of the first light and the second frequency ω2 of the second light by difference frequency generation using Cherenkov phase matching.

[0051] As shown in FIG. 3, the radiation direction of the terahertz wave T1 thus generated is oriented along the resonance direction (direction D1) from the first side S1 to the second side S2 (leftward in FIG. 3) at a radiation angle θ C More specifically, the terahertz wave T1 generated in the active layer 42 is inclined downward (toward the substrate 3) by a radiation angle θ C propagates as a plane wave (i.e., in phase) within the substrate 3. In the following formula (1), n MIR is the group refractive index of the substrate 3 for mid-infrared light, and n THz is the refractive index of the substrate 3 for the terahertz wave. C depends on the material of the substrate 3 (i.e., the refractive index corresponding to the material) and the frequency of the terahertz wave T1, but is, for example, 5 degrees to 30 degrees. In this embodiment, as an example, the radiation angle θ C is 20 degrees.

[0052] θ C =cos -1 (n MIR / n THz )…(1)

[0053] 3, the end face 3c of the substrate 3 is inclined with respect to the direction D2 so as to approach the end face 3d (i.e., move toward the second side S2) as it moves from the upper face 3a to the lower face 3b along the direction D2. Meanwhile, the end face 3d of the substrate 3 is inclined with respect to the direction D2 so as to approach the end face 3c (i.e., move toward the first side S1) as it moves from the upper face 3a to the lower face 3b along the direction D2. That is, in this embodiment, when viewed from the direction D3, the substrate 3 is formed in a tapered shape that narrows from the upper face 3a to the lower face 3b.

[0054] The inclination angle θ1 of the end face 3c with respect to the plane perpendicular to the direction D1 is the angle at which the emission direction of the terahertz wave T1 from the active layer 42 is inclined with respect to the direction D1 (i.e., the above-mentioned radiation angle θ CSimilarly, the inclination angle θ2 of the end face 3d with respect to the plane perpendicular to the direction D1 is also approximately equal to the radiation angle θ C It roughly coincides with.

[0055] As shown in FIG. 1 , in this embodiment, the light source 5 is disposed at a position opposite the end face 3c. The terahertz waves T2 emitted by the light source 5 are incident on the active layer 42 through the substrate 3. That is, the terahertz waves T2 pass through the inside of the substrate 3, are transmitted through the lower cladding layer 41, and are incident on the lower surface of the active layer 42 (the surface facing the lower cladding layer 41). The terahertz waves T2 incident on the active layer 42 are transmitted through the upper cladding layer 43 and reflected by the first electrode 6. Furthermore, the interaction between the terahertz waves T2 and the active layer 42 causes amplification or wavelength conversion of the terahertz waves T2 passing through the active layer 42. The terahertz waves T3 (third terahertz waves) thus reflected by the first electrode 6 and amplified or wavelength-converted by the interaction with the active layer 42 are emitted to the outside through the substrate 3.

[0056] Here, amplification of the terahertz waves T2 means that the light amount (light intensity) of the terahertz waves T3 emitted from the substrate 3 becomes greater than the light amount (light intensity) of the terahertz waves T2 emitted from the light source 5. Furthermore, wavelength conversion of the terahertz waves T2 means that the wavelength of the terahertz waves T3 emitted from the substrate 3 changes from the wavelength of the terahertz waves T2 emitted from the light source 5. The interaction between the terahertz waves T2 incident on the active layer 42 and the active layer 42 may cause both the amplification and wavelength conversion described above, or may cause only one of the amplification and wavelength conversion.

[0057] 1, in this embodiment, the terahertz waves T2 emitted from the light source 5 are incident on the end surface 3c of the substrate 3 along a direction inclined with respect to the direction D1 so as to approach the active layer 42 as they move from the first side S1 to the second side S2 in the direction D1. The angle θt at which the emission direction of the terahertz waves T2 is inclined with respect to the direction D1 is adjusted to be approximately equal to the inclination angle θ1, for example. In this case, the angle of incidence of the terahertz waves T2 with respect to the end surface 3c can be brought close to 0 degrees, thereby suppressing reflection of the terahertz waves T2 at the end surface 3c. As a result, the terahertz waves T2 can be efficiently introduced into the substrate 3.

[0058] Meanwhile, the terahertz waves T3 are emitted from the end face 3d of the substrate 3 along a direction inclined with respect to the direction D1 so as to move away from the active layer 42 as they move from the first side S1 to the second side S2 in the direction D1. In this embodiment, the inclination angle θ2 is equal to the inclination angle θ1. Therefore, when the angle θt is adjusted to be substantially equal to the inclination angle θ1, the angle of incidence of the terahertz waves T3 with respect to the end face 3d can be made close to 0 degrees, thereby suppressing reflection of the terahertz waves T3 at the end face 3d. As a result, the terahertz waves T3 can be efficiently extracted to the outside.

[0059] According to the laser module 1A described above, the terahertz waves T2 emitted from the light source 5 can be amplified or wavelength-converted using the QCL element 2A that generates the terahertz waves T1 by difference frequency generation. In the laser module 1A, the terahertz waves T2 emitted from the light source 5 are incident on the substrate 3 rather than on the end faces 42a and 42b of the active layer 42. That is, the terahertz waves T2 are incident on the active layer 42 (i.e., the surface of the active layer 42 facing the substrate 3) via the inside of the substrate 3. According to this method, compared to a method in which the terahertz waves T2 are incident on the end faces 42a and 42b of the active layer 42, it is possible to easily incident the terahertz waves T2 into the active layer 42 and to suppress absorption of the terahertz waves T2 by the active layer 42. That is, if the terahertz waves T2 are incident on the active layer 42 in a direction parallel to the resonance direction (direction D1), the distance the terahertz waves T2 travel within the active layer 42 becomes long, resulting in a large amount of absorption of the terahertz waves T2 in the active layer 42. On the other hand, by incidenting the terahertz waves T2 on the active layer 42 via the substrate 3 as in the present embodiment, the incident direction of the terahertz waves T2 with respect to the active layer 42 can be tilted with respect to the resonance direction (direction D1). As a result, the distance the terahertz waves T2 travel within the active layer 42 can be shortened compared to the above case, thereby reducing the amount of absorption of the terahertz waves T2 in the active layer 42. Furthermore, by reflecting the terahertz waves T2 at the first electrode 6 located on the opposite side of the active layer 42 from the substrate 3, the terahertz waves T2 amplified or wavelength-converted in the active layer 42 (i.e., the terahertz waves T3) can be easily extracted to the outside via the substrate 3 again. As described above, the laser module 1A can improve the efficiency of amplification or wavelength conversion of the terahertz wave T2.

[0060] Furthermore, the substrate 3 is made of InP. According to the above configuration, by forming the substrate 3 from a material with a small absorption coefficient of the terahertz waves T2, it is possible to suppress loss (attenuation) of the terahertz waves T2 and T3 passing through the substrate 3 and improve the amount of terahertz waves T3 extracted to the outside. From a similar perspective, the substrate 3 may be made of Si (silicon). Since Si has a smaller absorption coefficient of the terahertz waves T2 than InP, the above effect can be further enhanced.

[0061] The length L (see FIG. 3) of the active layer 42 in the resonance direction (direction D1) of the QCL device 2A is 100 μm to 3 mm. The length L can be preferably set to 100 μm to 1 mm. The length L is more preferably set to a length (e.g., 300 μm) approximately equal to the wavelength of the terahertz wave T2. According to the above configuration, a configuration (see FIG. 1) that allows the terahertz wave T2 to be reflected once by the first electrode 6 and the terahertz wave T3 to be extracted to the outside can be preferably realized. That is, multiple reflections of the terahertz wave T2 within the QCL device 2A (see the second embodiment (FIG. 4) described later) can be prevented. This reduces the loss of the terahertz wave T2 within the QCL device 2A due to multiple reflections, and as a result, the light intensity of the terahertz wave T3 can be improved.

[0062] Moreover, the terahertz waves T2 are incident on the end face 3c along a direction inclined with respect to the direction D1 so as to approach the active layer 42 as they move from the first side S1 to the second side S2 in the direction D1. According to the above configuration, the terahertz waves T2 can be made to enter from the end face 3c of the substrate 3 and reliably guided to the active layer 42, and can also be reliably reflected by the first electrode 6 and extracted to the outside.

[0063] Furthermore, the end face 3c is inclined with respect to the direction D2 so as to approach the end face 3d from the upper face 3a toward the lower face 3b along the direction D2. According to the above configuration, the incident angle of the terahertz wave T2 with respect to the end face 3c can be reduced, and the reflection (loss) of the terahertz wave T2 at the end face 3c can be suppressed.

[0064] The inclination angle θ1 of the end face 3c is equal to the radiation angle θ of the terahertz wave T1. C According to the above configuration, by making the terahertz waves T2 incident on the end face 3c substantially perpendicularly, the traveling direction of the terahertz waves T3 and T1 can be made to substantially coincide with each other. As a result, phase matching between the terahertz waves T3 and T1 can be achieved, and the interaction between the terahertz waves T3 and T1 can effectively improve the efficiency of amplification or wavelength conversion of the terahertz waves T3.

[0065] Furthermore, the terahertz waves T3 are emitted from the end face 3d along a direction inclined with respect to the direction D1 so as to move away from the active layer 42 as they move from the first side S1 to the second side S2 in the direction D1. According to the above configuration, output light (terahertz waves T3) can be extracted from the end face 3d opposite the end face 3c, which is the incident surface of the terahertz waves T2. This makes it possible to easily avoid interference between the light source 5 that outputs the terahertz waves T2 and a member (not shown) that captures the terahertz waves T3, thereby improving the design flexibility regarding the arrangement of each member. The terahertz waves T2 emitted from the light source 5 may be incident on the end face 3c via a separate member such as a mirror member; the light source 5 itself does not necessarily need to be positioned opposite the end face 3c. Even in such a case, the above configuration provides the effect of avoiding interference between the separate member positioned opposite the end face 3c and the complementary member.

[0066] Furthermore, the end face 3d is inclined with respect to the direction D2 so as to approach the end face 3c from the upper face 3a toward the lower face 3b along the direction D2. According to the above configuration, the angle of incidence of the terahertz wave T3 with respect to the end face 3d can be reduced, and the reflection (loss) of the terahertz wave T3 at the end face 3d can be suppressed.

[0067] The inclination angle θ2 of the end face 3d is equal to the radiation angle θ of the terahertz wave T1. CAccording to the above configuration, when the traveling direction of the terahertz waves T3 and T1 is made to substantially coincide with each other, phase matching between the terahertz waves T3 and T1 can be achieved, and the efficiency of amplification or wavelength conversion of the terahertz waves T3 can be effectively improved by the interaction between the terahertz waves T3 and T1. Furthermore, in this case, the incident angle of the terahertz waves T3 with respect to the end face 3d can be made close to 0 degrees, so that reflection (loss) of the terahertz waves T3 at the end face 3d can be effectively suppressed.

[0068] [Second embodiment] A laser module 1B according to the second embodiment will be described with reference to Fig. 4. The laser module 1B differs from the laser module 1A in that the laser module 1B includes a QCL element 2B that is longer in the direction D1 than the QCL element 2A. The substrate 3 of the QCL element 2B is made of Si.

[0069] In the laser module 1B, the terahertz waves T2 emitted from the light source 5 are reflected at least once (only once in this embodiment, as an example) by the lower surface 3b of the substrate 3 and re-enter the active layer 42 after being first reflected by the first electrode 6 and before being emitted to the outside as terahertz waves T3. That is, in the laser module 1B, the terahertz waves T2 are multiple-reflected inside the QCL device 2B. In this embodiment, the terahertz waves T3 after being reflected a second time by the first electrode 6 are emitted from the end face 3d. Note that the number of times the terahertz waves T2 are reflected by the lower surface 3b of the substrate 3 may be one, as in this embodiment, or may be two or more. The number of times the terahertz waves T2 are reflected by the lower surface 3b depends on the incident angle of the terahertz waves T2 (angle θt in FIG. 1 ) and the device length of the QCL device 2B (length in direction D1).

[0070] According to the second embodiment, by multiple-reflecting the terahertz wave T2 within the QCL element 2B, the terahertz wave T2 can be incident on the active layer 42 multiple times (twice in this embodiment). This increases the number of times the terahertz wave T2 is amplified or wavelength-converted, thereby effectively improving the efficiency of amplification or wavelength conversion. Note that, as described in the first embodiment, when the terahertz wave T2 is multiple-reflected within the QCL element 2B, the loss of the terahertz wave T2 within the QCL element 2B is greater than when multiple reflection is not performed. However, by forming the substrate 3 from Si, the loss of the terahertz wave T2 (absorption into the substrate 3) can be effectively suppressed. That is, according to the second embodiment, the advantage of multiple reflection (improved efficiency of amplification or wavelength conversion of the terahertz wave T2) can be obtained while suppressing the disadvantage of multiple reflection (loss of the terahertz wave T2).

[0071] [Third embodiment] A laser module 1C of the third embodiment will be described with reference to Fig. 5. The laser module 1C differs from the laser module 1A in that it includes a lens 8 (entrance lens) and a lens 9 (exit lens).

[0072] The lens 8 has an incident surface 8a onto which the terahertz waves T2 are incident and an opposing surface 8b opposing the end face 3c. The opposing surface 8b of the lens 8 is in direct or indirect contact with the end face 3c. In the example of FIG. 5, the opposing surface 8b is in direct contact with the end face 3c, but a spacer member having a refractive index substantially equal to that of the lens 8 may be interposed between the opposing surface 8b and the end face 3c. That is, the opposing surface 8b may be in indirect contact with the end face 3c via the spacer member. By making the terahertz waves T2 incident on the end face 3c via the lens 8, it is possible to suppress interfacial reflection of the terahertz waves T2 at the end face 3c, and by concentrating the terahertz waves T2, it is possible to improve the incidence efficiency of the terahertz waves T2 on the active layer 42.

[0073] The lens 9 has an emission surface 9a that emits the terahertz wave T3 and an opposing surface 9b that faces the end face 3d. The opposing surface 9b of the lens 9 is in direct or indirect contact with the end face 3d. In the example of FIG. 5, the opposing surface 9b is in direct contact with the end face 3d, but a spacer member having a refractive index substantially equal to that of the lens 9 may be interposed between the opposing surface 9b and the end face 3d. In other words, the opposing surface 9b may be in indirect contact with the end face 3d via the spacer member. By extracting the terahertz wave T3 from the end face 3d via the lens 9, the extraction efficiency of the terahertz wave T3 can be improved.

[0074] The lenses 8 and 9 may be made of Si. That is, the lenses 8 and 9 may be silicon lenses. By making the lenses 8 and 9 of Si, which has an extremely small absorption coefficient of terahertz waves, it is possible to suppress attenuation of the terahertz waves T2 and T3 in the lenses 8 and 9.

[0075] Alternatively, lenses 8 and 9 may be metalenses in which a concave-convex structure is formed on the incident surface 8a or the exit surface 9a. For example, the optical element for terahertz waves disclosed in JP 2021-099399 A or JP 2021-099400 A can be used as such a metalense. By configuring lenses 8 and 9 as metalenses, it is possible to reduce the size of lenses 8 and 9 (reduce their thickness).

[0076] [Fourth embodiment] A laser module 1D of the fourth embodiment will be described with reference to Fig. 6. The laser module 1D differs from the laser module 1A in that it includes a QCL element 2D instead of the QCL element 2A. The laser module 1D also differs from the laser module 1A in the direction in which the terahertz wave T2 is incident on the QCL element 2D. The QCL element 2D differs from the QCL element 2A in that it includes a substrate 3D instead of the substrate 3.

[0077] The end face 3c of the substrate 3D protrudes toward the first side S1 in the direction D1 further than the end face 42a of the active layer 42. According to the above configuration, a process (e.g., a polishing process) for processing the end face 3c into an inclined surface can be easily performed. That is, a process for forming an inclined surface (end face 3c) can be easily performed by polishing the end face of the substrate 3D that is originally formed as a surface parallel to the direction D2. More specifically, it is possible to reduce the possibility of contact with the semiconductor layer 4 and damaging the semiconductor layer 4 during the polishing process.

[0078] The end face 3d of the substrate 3D protrudes toward the second side S2 in the direction D1 further than the end face 42b of the active layer 42. According to the above configuration, a process (e.g., a polishing process) for processing the end face 3d into an inclined surface can be easily performed. That is, a process for forming an inclined surface (end face 3d) can be easily performed by polishing the end face of the substrate 3D that is originally formed as a surface parallel to the direction D2. More specifically, it is possible to reduce the possibility of contact with the semiconductor layer 4 and damaging the semiconductor layer 4 during the polishing process.

[0079] In the laser module 1D, the upper surface 3a of the substrate 3D protrudes toward the first side S1 further than the end surface 42a of the active layer 42 in the direction D1, and the light source 5 is disposed at a position facing the portion of the upper surface 3a protruding toward the first side S1 further than the end surface 42a. The terahertz waves T2 emitted from the light source 5 are incident on the upper surface 3a along the direction D2 (a direction perpendicular to the upper surface 3a), pass through the inside of the substrate 3D, and are reflected by the end surface 3c and the lower surface 3b, thereby being incident on the active layer 42.

[0080] That is, the terahertz waves T2 incident on the substrate 3D from the upper surface 3a are reflected by the end surface 3c, then further reflected by the lower surface 3b, and travel through the interior of the substrate 3D to the active layer 42. The terahertz waves T2 are then reflected by the first electrode 6, becoming terahertz waves T3 and emitting them to the outside from the end surface 3d. With the above configuration, the incidence surface of the terahertz waves T2 (the portion of the upper surface 3a closer to the first side S1 than the end surface 42a) and the emission surface of the terahertz waves T3 (end surface 3d) can be separated by a large distance. This makes it easy to avoid interference between the light source 5 that outputs the terahertz waves T2 and a component (not shown) that captures the terahertz waves T3, improving the design flexibility regarding the arrangement of each component.

[0081] [Fifth embodiment] A laser module 1E of the fifth embodiment will be described with reference to Fig. 7. The laser module 1E differs from the laser module 1A in that it includes a QCL element 2E instead of the QCL element 2A. The laser module 1E also differs from the laser module 1A in the direction in which the terahertz wave T2 is incident on the QCL element 2E. The QCL element 2E differs from the QCL element 2A in that it includes a substrate 3E instead of the substrate 3.

[0082] The end face 3c of the substrate 3E is inclined with respect to the direction D2 so as to approach the end face 3d as it moves from the lower face 3b to the upper face 3a along the direction D2. The end face 3c of the substrate 3E protrudes toward the first side S1 more than the end face 42a of the active layer 42 in the direction D1. More specifically, in the direction D1, the end on the first side S1 of the upper face 3a of the substrate 3E is located at the same position as the end face 42a of the active layer 42, but the end on the first side S1 of the lower face 3b of the substrate 3E is located closer to the first side S1 than the end face 42a of the active layer 42. Note that in this embodiment, the end on the second side S2 of the upper face 3a of the substrate 3E is located at the same position as the end face 42b of the active layer 42, and the end on the second side S2 of the lower face 3b of the substrate 3E is located closer to the second side S2 than the end face 42b of the active layer 42. The light source 5 is disposed at a position facing a portion of the lower surface 3b that protrudes further toward the first side S1 than the end surface 42a. The terahertz waves T2 emitted from the light source 5 are incident on the lower surface 3b along direction D2 (a direction perpendicular to the lower surface 3b), pass through the inside of the substrate 3E, and are reflected by the end surface 3c, thereby entering the active layer 42.

[0083] That is, the terahertz waves T2 incident on the substrate 3E from the lower surface 3b are reflected by the end surface 3c, and then travel through the inside of the substrate 3E to reach the active layer 42. The terahertz waves T2 are then reflected by the first electrode 6. In the example of FIG. 7, the terahertz waves T3 reflected by the first electrode 6 are reflected by the lower surface 3b of the substrate 3E and emitted to the outside from the end surface 3d. With the above configuration, the incident surface of the terahertz waves T2 (the portion of the lower surface 3b closer to the first side S1 than the end surface 42a) and the emission surface of the terahertz waves T3 (the end surface 3d) can be separated by a large distance. Therefore, as in the fourth embodiment, interference between the light source 5 that outputs the terahertz waves T2 and a component (not shown) that captures the terahertz waves T3 can be easily avoided, and the design flexibility regarding the arrangement of each component can be improved.

[0084] [Other variations] Although several embodiments (first to fifth embodiments) of the present disclosure have been described above, the present disclosure is not limited to the above embodiments. The materials and shapes of the components of the laser modules 1A to 1E are not limited to the specific materials and shapes described above, and various materials and shapes other than those described above can be adopted.

[0085] Furthermore, some of the configurations included in each of the above embodiments (first to fifth embodiments) may be omitted or modified as appropriate, and can be arbitrarily combined. Below, several examples of the above-mentioned arbitrary combinations are given. For example, in the laser module 1B of the second embodiment, both the lens 8 and the lens 9 (or one of the lens 8 and the lens 9) in the third embodiment may be added. In addition, in the laser module 1C of the third embodiment, one of the lens 8 and the lens 9 may be omitted. In addition, in the fifth embodiment (FIG. 7), the end face 3d may be configured as a surface that is inclined in the same direction as in the other embodiments. The terahertz wave T3 reflected by the first electrode 6 may be directly emitted from the end face 3d without being reflected by the lower surface 3b.

[0086] In the above embodiment, the inclination angle θ1 of the end face 3c and the inclination angle θ2 of the end face 3d are set to the Cherenkov angle (the radiation angle θ of the terahertz wave T1). C ), but the magnitudes of the tilt angles θ1 and θ2 are not particularly limited. In addition, when the wavelength of the terahertz wave T1 can be swept (scanned) within a certain range by using an external resonator in the QCL element, the radiation angle θ calculated by the above formula (1) according to the wavelength of the terahertz wave T1 can be C In this case, the radiation angle θ C may be calculated assuming a terahertz wave T1 having an arbitrary wavelength included in the above sweepable range. For example, the radiation angle θ C may be calculated assuming the terahertz wave T1 has a central wavelength in the sweepable range. Furthermore, the end faces 3c and 3d do not necessarily have to be configured as inclined surfaces. That is, at least one of the end faces 3c and 3d may be configured as a surface parallel to the direction D2. [Explanation of symbols]

[0087] DESCRIPTION OF SYMBOLS 1A, 1B, 1C, 1D, 1E...laser module, 2A, 2B, 2D, 2E...quantum cascade laser element, 3, 3D, 3E...substrate, 3a...upper surface (first main surface), 3b...lower surface (second main surface), 3c...end surface (first end surface), 3d...end surface (second end surface), 5...light source, 6...first electrode (metal electrode), 8...lens (incident lens), 8a...incident surface, 8b...opposing surface, 9...lens (output lens), 9a...output surface, 9b...opposing surface, 41...lower clamp clad layer (first clad layer), 42...active layer, 43...upper clad layer (second clad layer), 42a...end face (third end face), 42b...end face (fourth end face), D1...direction (first direction), D2...direction (second direction), T1...terahertz wave (first terahertz wave), T2...terahertz wave (second terahertz wave), T3...terahertz wave (third terahertz wave), S1...first side, S2...second side, ω1...first frequency, ω2...second frequency, ω3...difference frequency.

Claims

1. a quantum cascade laser element that generates a first terahertz wave having a difference frequency between the first frequency and the second frequency; a light source that emits a second terahertz wave different from the first terahertz wave to the quantum cascade laser element; Equipped with The quantum cascade laser device is A substrate; a first cladding layer provided on the substrate; an active layer that is provided on the opposite side of the first clad layer from the substrate, that constitutes a resonator that oscillates light of the first frequency and light of the second frequency, and that generates the first terahertz wave; a second cladding layer provided on the active layer on the opposite side to the first cladding layer; a metal electrode provided on the second clad layer on the opposite side to the active layer, the second terahertz wave is incident on the active layer through the substrate, and is reflected by the metal electrode and amplified or wavelength-converted; a third terahertz wave, which is the second terahertz wave after being amplified or wavelength-converted in the active layer, being emitted to the outside through the substrate; Laser module.

2. the substrate is formed of InP or Si; 2. The laser module according to claim 1.

3. The length of the active layer in a first direction, which is a resonance direction of the quantum cascade laser element, is 100 μm to 3 mm.

3. The laser module according to claim 1.

4. the substrate is made of Si, the substrate has a first main surface facing the first cladding layer and a second main surface located on the opposite side to the first main surface; the second terahertz wave is reflected by the second main surface of the substrate at least once and re-enters the active layer before being emitted to the outside as the third terahertz wave after being first reflected by the metal electrode.

2. The laser module according to claim 1.

5. the substrate has a first end face located on a first side in a first direction that is a resonance direction of the quantum cascade laser element, and a second end face located on a second side opposite to the first side in the first direction, the active layer has a third end face located on the first side in the first direction and a fourth end face located on the second side in the first direction, the second terahertz wave is incident on the first end face along a direction inclined with respect to the first direction so as to approach the active layer as it moves from the first side to the second side in the first direction. The laser module according to any one of claims 1 to 4.

6. the third terahertz wave is emitted from the second end face along a direction inclined with respect to the first direction so as to move away from the active layer as it travels from the first side to the second side in the first direction.

6. The laser module according to claim 5.

7. the substrate has a first main surface facing the first cladding layer and a second main surface located on the opposite side to the first main surface; the first end surface is inclined with respect to a second direction perpendicular to the first main surface so as to approach the second end surface as the first end surface moves from the first main surface to the second main surface along the second direction; 7. The laser module according to claim 5 or 6.

8. an inclination angle of the first end face with respect to a plane orthogonal to the first direction substantially coincides with an angle at which the emission direction of the first terahertz wave is inclined with respect to the first direction; 8. The laser module according to claim 7.

9. the substrate has a first main surface facing the first cladding layer and a second main surface located on the opposite side to the first main surface; the second end surface is inclined with respect to a second direction perpendicular to the first main surface so as to approach the first end surface as the second end surface moves from the first main surface to the second main surface along the second direction, The laser module according to any one of claims 5 to 8.

10. an inclination angle of the second end face with respect to a plane orthogonal to the first direction substantially coincides with an inclination angle of the emission direction of the first terahertz wave with respect to the first direction; The laser module according to claim 9 .

11. an incident lens having an incident surface onto which the second terahertz wave is incident and an opposing surface opposing the first end surface, the opposing surface of the entrance lens is in direct or indirect contact with the first end surface; The laser module according to any one of claims 5 to 10.

12. The entrance lens is made of Si. The laser module according to claim 11.

13. The incident lens is a metalens having a concave-convex structure formed on the incident surface. The laser module according to claim 11.

14. an emission lens having an emission surface that emits the third terahertz wave and an opposing surface that faces the second end surface, the opposing surface of the emission lens is in direct or indirect contact with the second end surface; The laser module according to any one of claims 5 to 13.

15. The output lens is made of Si. The laser module according to claim 14.

16. The output lens is a metalens having a concave-convex structure formed on the output surface. The laser module according to claim 14.

17. the first end face of the substrate protrudes further toward the first side than the third end face of the active layer in the first direction; 9. The laser module according to claim 7 or 8.

18. the second end face of the substrate protrudes further toward the second side than the fourth end face of the active layer in the first direction; 11. The laser module according to claim 9 or 10.

19. the substrate has a first end face located on a first side in a first direction that is a resonance direction of the quantum cascade laser element, and a second end face located on a second side opposite to the first side in the first direction, the active layer has a third end face located on the first side in the first direction and a fourth end face located on the second side in the first direction, the substrate has a first main surface facing the first cladding layer and a second main surface located on the opposite side to the first main surface; the first end surface is inclined with respect to a second direction perpendicular to the first main surface so as to approach the second end surface as the first end surface moves from the first main surface to the second main surface along the second direction, the first end face of the substrate protrudes further toward the first side than the third end face of the active layer in the first direction; the second terahertz wave is incident on the first principal surface along the second direction, passes through the inside of the substrate, and is reflected by the first end face and the second principal surface, thereby being incident on the active layer. The laser module according to any one of claims 1 to 4.

20. the substrate has a first end face located on a first side in a first direction that is a resonance direction of the quantum cascade laser element, and a second end face located on a second side opposite to the first side in the first direction, the active layer has a third end face located on the first side in the first direction and a fourth end face located on the second side in the first direction, the substrate has a first main surface facing the first cladding layer and a second main surface located on the opposite side to the first main surface; the first end surface is inclined with respect to a second direction perpendicular to the first main surface so as to approach the second end surface as the first end surface moves from the second main surface to the first main surface along the second direction, the first end face of the substrate protrudes further toward the first side than the third end face of the active layer in the first direction; the second terahertz wave is incident on the second principal surface along the second direction, passes through the inside of the substrate, and is reflected by the first end surface, thereby being incident on the active layer. The laser module according to any one of claims 1 to 4.

Images