Laser module

Abstract

To provide a laser module capable of improving productivity and improving extraction efficiency of a terahertz wave to the outside.SOLUTION: A laser module 1A comprises a support substrate 10, a QCL element 20, a resin layer 30, and an emission direction defining portion 40. The QCL element 20 has a substrate 21 having a front surface 21c that emits a terahertz wave L, and a semiconductor laminate 22 including an active layer 222 that generates the terahertz wave L. The emission direction defining portion 40 is provided on an upper surface 30a of the resin layer 30, and is configured to emit the terahertz wave L emitted from the front surface 21c of the substrate 21 to the outside from the upper surface 30a. The resin layer 30 contacts the front surface 21c of the substrate 21 and extends in a front-rear direction X when viewed from an up-down direction Z. A height position of the upper surface 30a of the resin layer 30 with respect to a support surface 10a of the support substrate 10 reaches at least a height position of an upper surface 21b of the substrate 21 with respect to the support surface 10a.SELECTED DRAWING: Figure 2

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: Difference Frequency Generation THz-Quantum Cascade Laser) has been known. For example, Patent Document 1 discloses that in order to prevent terahertz waves from being totally reflected at an end face (a surface on the terahertz wave emission side) of a substrate constituting a terahertz quantum cascade laser, the end face is polished so as to be inclined with respect to an end face of an active layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2015 / 0311665 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a need to efficiently extract terahertz waves from DFG-THz-QCLs to the outside, but as described in Patent Document 1 above, the process of polishing the end faces of the substrate is relatively difficult, which can be a factor in reducing the productivity of DFG-THz-QCLs.

[0005] Therefore, an object of one aspect of the present disclosure is to provide a laser module that can improve productivity and improve the efficiency of extracting terahertz waves to the outside. [Means for solving the problem]

[0006] The present disclosure includes the following laser modules [1] to

[16] .

[0007] [1] A support having a support surface; a quantum cascade laser device disposed on the support surface; a resin layer disposed on the support surface; an emission direction regulating portion disposed on the resin layer, The quantum cascade laser device is a substrate having a first surface facing the support surface, a second surface opposite to the first surface, and a third surface connecting the first surface and the second surface and emitting terahertz waves; a semiconductor laminate including an active layer provided on the second surface of the substrate, the active layer generating first pump light of a first frequency and second pump light of a second frequency, and generating a terahertz wave of a difference frequency between the first frequency and the second frequency by difference frequency generation between the first pump light and the second pump light; the resin layer has a fourth surface facing the support surface and a fifth surface opposite the fourth surface, the emission direction defining portion is provided on the fifth surface and configured to emit the terahertz waves emitted from the third surface of the substrate to the outside from the fifth surface in a direction facing the fifth surface, the resin layer is in contact with a third surface of the substrate and extends in a second direction along an emission direction of the terahertz wave from the third surface when viewed from a first direction in which the first surface and the second surface face each other; a height position of the fifth surface of the resin layer relative to the support surface at least reaches a height position of the second surface of the substrate relative to the support surface.

[0008] The laser module described in [1] above is configured as a DFG-THz-QCL that generates terahertz waves by difference frequency generation. According to the laser module, by abutting a resin layer having a refractive index smaller than that of air on the third surface of the substrate, total reflection of terahertz waves at the end face of the substrate (i.e., the interface between the third surface and air), which is a problem when emitting terahertz waves into air, can be suppressed. This allows terahertz waves to be efficiently propagated from the substrate of the quantum cascade laser element to the resin layer, and the terahertz waves passing through the resin layer can be emitted in a direction determined by the emission direction defining portion (i.e., a direction facing the fifth surface). Therefore, according to the laser module, the laser module can be configured relatively simply, thereby improving productivity (yield) and improving the extraction efficiency of terahertz waves to the outside.

[0009] [2] The laser module of [1] further comprising a reflective layer disposed between the support surface of the support body and the first surface of the substrate and the fourth surface of the resin layer, and which reflects the terahertz waves.

[0010] According to the configuration [2] above, the terahertz waves emitted from the third surface of the substrate in an oblique direction inclined downward (toward the support surface) with respect to the second direction in the quantum cascade laser element are reflected by the reflective layer toward the resin layer without escaping to the support, thereby further improving the extraction efficiency of the terahertz waves.

[0011] [3] The laser module of [1] or [2], further comprising a reflective layer provided on an end surface of the substrate opposite the third surface in the second direction, which reflects the terahertz wave.

[0012] According to the configuration [3] above, the terahertz waves are reflected by the reflective layer at the end face of the substrate opposite to the third face, thereby increasing the amount of terahertz waves traveling from the end face toward the third face, thereby more effectively improving the extraction efficiency of terahertz waves.

[0013] [4] The laser module of any one of [1] to [3], further comprising a reflective layer provided on a side surface of the substrate that intersects with a third direction perpendicular to both the first direction and the second direction, and that reflects the terahertz wave.

[0014] According to the configuration [4] above, the terahertz waves that attempt to escape from the side surface of the substrate can be reflected by the reflective layer and returned to the inside of the substrate, thereby increasing the amount of terahertz waves emitted from the third surface, thereby further effectively improving the extraction efficiency of terahertz waves.

[0015] [5] The laser module according to any one of [1] to [4], wherein the emission direction determining unit is a planar antenna provided on the fifth surface.

[0016] According to the configuration [5] above, it is possible to freely design the beam profile of the output light by adjusting the arrangement, shape, or number of planar antennas.

[0017] [6] The laser module according to any one of [1] to [5], further comprising a reflective film provided on an end face of the semiconductor laminate that intersects with the first direction at least in a portion including the active layer, and that reflects the first pump light and the second pump light.

[0018] According to the configuration [6] above, oscillation of the first pump light and the second pump light in the semiconductor laminate (active layer) is promoted, and terahertz waves can be generated with high efficiency.

[0019] [7] The laser module according to any one of [1] to [6], wherein the third surface of the substrate is a surface perpendicular to the first surface and the second surface.

[0020] In the past, in order to prevent total reflection of the terahertz waves at the terahertz wave exit surface (third surface), polishing was sometimes performed to make the exit surface an inclined surface. In contrast, according to the configuration [7] above, the terahertz waves are preferably propagated from the substrate to the resin layer by abutting the exit surface (third surface) against the resin layer, so that such an inclined surface (polished surface) can be omitted. As a result, the productivity of laser modules can be effectively improved.

[0021] [8] The laser module of any one of [1] to [7], further comprising a reflection suppression structure provided in a portion of the substrate including the third surface or in a position facing the third surface, which suppresses the terahertz waves traveling from the substrate to the resin layer from being reflected toward the substrate.

[0022] According to the configuration of [8] above, it is possible to improve the propagation efficiency of the terahertz wave from the quantum cascade laser element (substrate) to the resin layer.

[0023] [9] The laser module of [8], wherein the anti-reflection structure is constituted by a portion of the substrate including the third surface, and is formed so that, when viewed from the first direction, the area occupied by the substrate in a plane perpendicular to the second direction gradually decreases along the second direction toward the side where the output direction determining portion is provided.

[0024] In the configuration [9] above, the anti-reflection structure including the third surface of the substrate functions as an impedance matching layer. More specifically, the area occupied by the substrate can be gradually reduced along the emission direction of the terahertz waves (in other words, the area occupied by the resin layer can be gradually increased). This allows the refractive index experienced by the terahertz waves passing through the region where the substrate and the resin layer coexist to be gradually changed from that of the substrate to that of the resin layer. In this way, by gradually changing the refractive index experienced by the terahertz waves rather than abruptly, it is possible to effectively prevent the terahertz waves that attempt to enter the resin layer from being returned to the quantum cascade laser element side.

[0025]

[10] The laser module of [8], wherein the anti-reflection structure is provided at a position facing the third surface of the substrate, and is formed by a structure in which a plurality of high-refractive-index material layers made of a high-refractive-index material having a higher refractive index than the resin layer are spaced apart from each other along the second direction, and a portion of the resin layer is inserted between adjacent high-refractive-index material layers.

[0026] According to the configuration

[10] above, by providing a reflection suppression structure that functions as a broadband anti-reflection (AR) coating, it is possible to effectively prevent terahertz waves that attempt to enter the resin layer from being returned to the quantum cascade laser element side.

[0027]

[11] The laser module according to

[10] , wherein the plurality of high refractive index material layers are formed from the same material as the substrate.

[0028] According to the configuration of

[11] above, by forming a plurality of grooves spaced apart in the second direction at the tip of the substrate that was originally formed integrally, the part of the substrate remaining between the grooves can be used as a high-refractive-index material layer. This makes it possible to easily form a high-refractive-index material layer, thereby improving the productivity of laser modules having the effect of

[10] above.

[0029]

[12] The laser module of

[10] or

[11] , wherein the plurality of high refractive index material layers are connected to the substrate.

[0030] According to the above-mentioned configuration

[12] , it is possible to improve the support stability of the multiple high-refractive-index material layers. Furthermore, for example, by performing an operation such as digging grooves in a single rectangular plate-shaped substrate member, it is possible to easily form a structure in which the substrate and the multiple high-refractive-index material layers are connected, thereby improving the productivity of the substrate and the anti-reflection structure (multiple high-refractive-index material layers).

[0031]

[13] The antireflection structure is formed by an inclined surface provided on the third surface of the substrate, The laser module according to [8], wherein the inclined surface is inclined with respect to the second direction when viewed from the first direction in order to suppress total reflection of the terahertz wave.

[0032] According to the configuration of

[13] above, the inclined surface (reflection suppressing structure) provided on the third surface can suppress total reflection of the terahertz wave, which effectively prevents the terahertz wave radiated outward in the second direction from being totally reflected by the third surface and returned to the quantum cascade laser element side when viewed from the first direction.

[0033]

[14] The antireflection structure is formed by a subwavelength periodic structure provided at a position facing the third surface of the substrate; the subwavelength periodic structure is formed by a plurality of unit regions that are two-dimensionally arranged at a period shorter than the wavelength of the terahertz wave when viewed from the first direction, each of the plurality of unit areas is configured by a part of the substrate and a part of the resin layer; [8] A laser module configured such that the proportion of the resin layer in each of the plurality of unit regions gradually increases along the second direction toward the side where the emission direction determining portion is provided.

[0034] According to the configuration of

[14] above, by providing a subwavelength periodic structure in which the proportion of the resin layer gradually increases along the emission direction of the terahertz waves, it is possible to obtain the same effect as the impedance matching layer of [9] above. Furthermore, by forming a metalens with a subwavelength periodic structure, it is also possible to control the phase of the terahertz waves.

[0035]

[15] The laser module according to any one of [1] to

[14] , wherein the thickness of the substrate in the first direction is equal to or greater than half the wavelength of the terahertz wave.

[0036] According to the configuration of

[15] above, the thickness of the substrate having the terahertz wave emission surface (third surface) is set to at least half the wavelength of the terahertz wave, thereby improving the extraction efficiency of the terahertz wave. Furthermore, as described above, the resin layer is provided up to a position that reaches at least the upper surface (second surface) of the substrate, so the thicker the substrate, the thicker the resin layer. This makes it easier to manufacture the resin layer disposed on the support. As a result, when mass-producing laser modules, manufacturing variations between products are suppressed, and yields can be improved.

[0037]

[16] The laser module of any one of [1] to

[15] , wherein the resin layer is provided so as to cover a side surface of the substrate that intersects with a third direction that is perpendicular to both the first direction and the second direction.

[0038] According to the configuration

[16] above, the resin layer can improve the stability of supporting the quantum cascade laser element in the third direction, and can also appropriately protect the quantum cascade laser element. [Effects of the Invention]

[0039] According to one aspect of the present disclosure, it is possible to provide a laser module that can improve productivity and improve the efficiency of extracting terahertz waves to the outside. [Brief explanation of the drawings]

[0040] [Figure 1] FIG. 1 is a plan view of the laser module of the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the laser module taken along line II-II in FIG. [Figure 3] FIG. 3 is a cross-sectional view of the laser module taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view of the laser module taken along line IV-IV in FIG. [Figure 5] FIG. 5 is a plan view of the laser module according to the second embodiment. [Figure 6] FIG. 6 is a cross-sectional view of the laser module taken along line VI-VI in FIG. [Figure 7] FIG. 7 is a plan view of the laser module according to the third embodiment. [Figure 8] FIG. 8 is a cross-sectional view of the laser module taken along line VIII-VIII in FIG. [Figure 9] FIG. 9 is a plan view of the laser module according to the fourth embodiment. [Figure 10] FIG. 10 is a plan view of the laser module according to the fifth embodiment. [Figure 11] FIG. 11 is a cross-sectional view of the laser module taken along line XI-XI in FIG. [Figure 12] FIG. 12 is a plan view of the laser module according to the sixth embodiment. [Figure 13] FIG. 13 is a cross-sectional view of the laser module taken along line XIII-XIII in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0041] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be designated by the same reference numerals, and duplicate explanations will be omitted. Furthermore, terms such as "upper" and "lower" are used for convenience based on the state shown in the drawings. Furthermore, some parts in the drawings are exaggerated to clearly explain the characteristics of the embodiments. Therefore, the dimensional ratios of the various parts in the drawings may differ from the actual dimensional ratios.

[0042] [First embodiment] A laser module 1A according to the first embodiment will be described with reference to Figures 1 to 4. The laser module 1A includes a support substrate 10 (support), a QCL element 20 (quantum cascade laser element), a resin layer 30, and an emission direction defining section 40. The QCL element 20 is a difference frequency generation terahertz quantum cascade laser (DFG-THz-QCL). The laser module 1A is configured to include such a QCL element 20, and is therefore capable of emitting single-mode, wavelength-tunable terahertz waves and operating at room temperature.

[0043] (support substrate) The support substrate 10 is a member having a flat support surface 10a on which the QCL element 20 and the resin layer 30 are disposed. As an example, the support substrate 10 is formed in a rectangular parallelepiped shape. The support substrate 10 is, for example, an InP substrate. When the support substrate 10 is formed of a material that transmits the terahertz waves L, a metal layer 51 (reflective layer) made of a metal such as gold, platinum, silver, copper, aluminum, titanium, or nickel may be provided on the support surface 10a. That is, the QCL element 20 and the resin layer 30 may be disposed on the support surface 10a via the metal layer 51. The metal layer 51 is a member that prevents the terahertz waves L emitted from the QCL element 20 to the resin layer 30 from escaping into the support substrate 10. Note that when the support substrate 10 is formed of a material that does not transmit the terahertz waves L, such as a metal, the metal layer 51 may be omitted.

[0044] (QCL element) The QCL element 20 is disposed on the support surface 10a of the support substrate 10 via a metal layer 51. The QCL element 20 is a terahertz light source configured to be able to output terahertz waves L in a room temperature environment. The QCL element 20 is formed in a rod shape. The QCL element 20 includes a substrate 21 and a semiconductor stack 22. In this embodiment, the QCL element 20 is formed as a ridge-stripe laser element by a general semiconductor process. The QCL element 20 is obtained, for example, by forming InGaAs / InAlAs on the substrate 21 by epitaxial growth.

[0045] The substrate 21 is, for example, a rectangular parallelepiped InP single crystal substrate (semi-insulating substrate: a high-resistance semiconductor substrate that is not doped with impurities). The substrate 21 has a lower surface 21a (first surface), an upper surface 21b (second surface), a front surface 21c (third surface), a rear surface 21d (end surface), and a pair of side surfaces 21e. In this specification, the direction in which the lower surface 21a and the upper surface 21b face each other is referred to as the up-down direction Z (first direction). Furthermore, the direction perpendicular to the up-down direction Z and in which the front surface 21c and the rear surface 21d face each other is referred to as the front-back direction X (second direction), and the direction perpendicular to both the up-down direction Z and the front-back direction X and in which the pair of side surfaces 21e face each other is referred to as the width direction Y (third direction). In the following description, the positional relationship of each member will be described with the side where the upper surface 21b is located relative to the lower surface 21a as the upper side, and the side where the front surface 21c is located relative to the rear surface 21d as the front side.

[0046] The lower surface 21a is a surface facing the support surface 10a (in this embodiment, a surface supported by the support surface 10a via the metal layer 51). The upper surface 21b is a surface located opposite the lower surface 21a in the vertical direction Z. The front surface 21c is a surface that connects the lower surface 21a and the upper surface 21b and emits the terahertz waves L. As shown in FIG. 2, the front surface 21c is in contact with the resin layer 30, and the terahertz waves L output forward from the front surface 21c are propagated into the resin layer 30. The rear surface 21d is a surface located opposite the front surface 21c in the front-rear direction X. The pair of side surfaces 21e are surfaces that intersect with the width direction Y.

[0047] The length in the front-rear direction X, the width in the width direction Y, and the thickness in the up-down direction Z of the substrate 21 are approximately several hundred μm to several mm, several hundred μm to several mm, and several hundred μm, respectively. As an example, the length of the substrate 21 is approximately 3 mm, the width is approximately 1 mm, and the thickness is approximately 500 μm. The terahertz waves L generated by difference frequency generation inside the active layer 222 of the semiconductor laminate 22, which will be described later, are propagated to the resin layer 30 via the substrate 21. From the viewpoint of increasing the extraction efficiency of the terahertz waves L via the substrate 21, the substrate 21 is preferably a semi-insulating substrate as described above, or a 1×10 17 cm -3 The substrate preferably has a carrier density of:

[0048] The semiconductor laminate 22 is provided on the upper surface 21b of the substrate 21. The thickness of the semiconductor laminate 22 in the up-down direction Z is approximately 10 μm to 20 μm. The semiconductor laminate 22 has end faces 22a and 22b that intersect with the front-rear direction X. The end faces 22a and 22b are surfaces perpendicular to the front-rear direction X. The end faces 22a and 22b are, for example, cleavage surfaces formed by cleavage. The end face 22a is a surface facing the front side (the side on which the resin layer 30 is arranged). The end face 22b is a surface located on the opposite side (rear side) from the end face 22a. The end faces 22a and 22b form a resonator. That is, the light (the first pump light of the first frequency ω1 and the second pump light of the second frequency ω2 described later) in a wide band in the mid-infrared region (for example, 3 μm or more and 20 μm or less) generated in the active layer 222 is amplified by the resonance between the end faces 22a and 22b.

[0049] 3 and 4, the semiconductor laminate 22 has a lower cladding layer 221 (first cladding layer), an active layer 222, and an upper cladding layer 223 (second cladding layer). In this embodiment, the semiconductor laminate 22 also has an upper guide layer 224, a lower guide layer 225, an upper contact layer 226, and a lower contact layer 227.

[0050] 3, the support layers 228 are provided between the lower cladding layer 221 and the upper cladding layer 223 on both sides in the width direction Y of the active layer 222, the upper guide layer 224, and the lower guide layer 225, which are formed in a ridge stripe shape. The lower contact layer 227 has a portion that extends outward (outward in the width direction Y) from the lower cladding layer 221.

[0051] The lower contact layer 227 is, for example, a highly Si-doped InGaAs layer (Si: 1.0×10 18 / cm 3 ) and is provided on the upper surface 21b of the substrate 21. The lower cladding layer 221 is, for example, a Si-doped InP layer (Si: 1.5×10 16 / cm 3 ) and is provided on the lower contact layer 227. The lower guide layer 225 is, for example, a Si-doped InGaAs layer (Si: 1.5×10 16 / cm 3 ) and is provided on the lower cladding layer 221.

[0052] The active layer 222 is a layer in which a quantum cascade structure is formed, and is provided on the lower guide layer 225. The active layer 222 has a cascade structure in which quantum well light-emitting layers (light-emitting layers) used to generate light and electron injection layers (injection layers) used to inject electrons (carriers) into the light-emitting layers are alternately stacked in multiple stages. Specifically, a semiconductor stack structure consisting of a light-emitting layer and an injection layer is defined as a unit stack body for one period, and the active layer 222 having the cascade structure is configured by stacking these unit stack bodies in multiple stages. Each of the light-emitting layer and the injection layer has a structure in which, for example, a plurality of InGaAs layers (well layers) and InAlAs layers (barrier layers) are alternately stacked.

[0053] The upper guide layer 224 is, for example, a Si-doped InGaAs layer (Si: 1.5×10 16 / cm 3 ) and is provided on the active layer 222. The upper cladding layer 223 is, for example, a Si-doped InP layer (Si: 1.5×10 16 / cm 3 ) and is provided on the upper guide layer 224 and the support layer 228. The upper contact layer 226 is, for example, a highly Si-doped InP layer (Si: 1.5×10 18 / cm 3 ) and is provided on the upper cladding layer 223. The support layer 228 is, for example, an Fe-doped InP layer.

[0054] 3, the insulating film 23 is formed to cover the upper surface 226a of the upper contact layer 226, the side surface 22c of the semiconductor laminate 22 intersecting the width direction Y, and a portion of the lower contact layer 227. The insulating film 23 is formed of, for example, SiN. An opening 23a is formed in the insulating film 23 to expose a portion of the upper surface 226a of the upper contact layer 226. The opening 23a extends along the front-rear direction X so as to expose a central portion of the upper surface 226a in the width direction Y. In addition, in the width direction Y, the end 23b of the insulating film 23 on the lower contact layer 227 is located more inward than the end of the lower contact layer 227. That is, the upper surface of the lower contact layer 227 is exposed outside the end 23b of the insulating film 23.

[0055] The first electrode 24 is formed on the upper surface 226a of the upper contact layer 226. The first electrode 24 is formed of a metal such as Ti / Au. The first electrode 24 is electrically connected to a portion of the upper surface 226a of the upper contact layer 226 through the opening 23a. As shown in FIGS. 1 and 2, the first electrode 24 extends in the front-rear direction X. A front end 24a of the first electrode 24 is located rearward of the end surface 22a of the semiconductor laminate 22. A rear end 24b of the first electrode 24 is located forward of the end surface 22b of the semiconductor laminate 22. This prevents the first electrode 24 from contacting (conducting to) metal films 52 and 53, which will be described later, with the metal films 52 and 53.

[0056] The second electrode 25 is formed on the lower contact layer 227 so as to be in contact with an exposed portion of the lower contact layer 227 outside the end 23b of the insulating film 23. The second electrode 25 is formed of a metal such as Ti / Au. In this embodiment, the second electrode 25 is formed so as to cover a portion of the side and upper surface of the semiconductor laminate 22, but this is not necessarily required. That is, the second electrode 25 only needs to be electrically connected to at least the lower contact layer 227 and spaced apart from the first electrode 24. As shown in FIG. 1 , the second electrode 25 extends in the front-rear direction X, similar to the first electrode 24. The front end 25a and the rear end 25b of the second electrode 25 are located inside the end faces 22a and 22b of the semiconductor laminate 22 in the front-rear direction X, similar to the front end 24a and the rear end 24b of the first electrode 24. That is, the front end 25a of the second electrode 25 is located rearward of the end face 22a of the semiconductor laminate 22. The rear end 25b of the second electrode 25 is located forward of the end surface 22b of the semiconductor laminate 22. This prevents the second electrode 25 from contacting (conducting between) metal films 52 and 53 (described later) with the second electrode 25. With this configuration, the QCL device 20 can be driven by passing a current from the second electrode 25 to the first electrode 24.

[0057] As an example, in the QCL device 20, two types of diffraction grating layers 224a and 224b that function as a distributed feedback (DFB) structure are provided in the upper guiding layer 224. This allows the QCL device 20 to generate a first pump light with a first frequency ω1 and a second pump light with a second frequency ω2, as well as a terahertz wave L with a difference frequency ω3 between these. The diffraction grating layers 224a and 224b may be provided inside a cladding layer (e.g., the upper cladding layer 223). Both the first pump light and the second pump light are mid-infrared light.

[0058] As described above, the end faces 22a and 22b of the semiconductor laminate 22 form a resonator that oscillates the first pump light and the second pump light. The active layer 222 generates the terahertz wave L with the difference frequency ω3 (=|ω1-ω2|) between the first frequency ω1 of the first pump light and the second frequency ω2 of the second pump light by difference frequency generation using Cherenkov phase matching.

[0059] As shown in FIG. 4, the radiation direction (output direction) of the generated terahertz wave L is at a radiation angle θ with respect to the direction (direction from end face 22b to end face 22a) going forward along the resonance direction (front-rear direction X). C More specifically, the terahertz wave L generated in the active layer 222 is inclined downward (toward the substrate 21) by a radiation angle θ C propagates as a plane wave (i.e., in phase) within the substrate 21. In the following formula (1), n MIR is the group refractive index of the substrate 21 for mid-infrared light, and n THz is the refractive index of the substrate 21 for the terahertz wave. C depends on the material of the substrate 21 (i.e., the refractive index corresponding to the material) and the frequency of the terahertz wave L, but is, for example, 5 degrees to 30 degrees. In this embodiment, as an example, the radiation angle θ C is 20 degrees.

[0060] θ C =cos -1 (n MIR / nTHz )…(1)

[0061] 1, 2, and 4, a metal film 52 (reflective film) for reflecting the first pump light and the second pump light is provided on the end face 22a of the semiconductor laminate 22. Furthermore, a metal film 53 (reflective film, reflective layer) for reflecting the first pump light and the second pump light is provided on the end face 22b of the semiconductor laminate 22. The metal films 52, 53 are, for example, metal films made of the same material (e.g., metal such as Ti / Au) as the first electrode 24 and the second electrode 25. Although the metal films 52, 53 may be omitted, providing the metal films 52, 53 can promote laser oscillation of the first pump light and the second pump light between the end faces 22a, 22b, and ultimately improve the generation efficiency of the terahertz wave L by difference frequency generation.

[0062] 4, the metal film 52 is provided only on the end face 22a of the semiconductor laminate 22 so as not to inhibit the propagation of the terahertz wave L from the front face 21c to the resin layer 30, and is not provided on the front face 21c of the substrate 21. In contrast, the metal film 53 is provided continuously not only on the end face 22b of the semiconductor laminate 22 but also on the rear face 21d of the substrate 21 so as to prevent the terahertz wave from escaping backward from the rear face 21d.

[0063] 2 and 3, a pair of side surfaces 21e of the substrate 21 are provided with metal films 54 (reflective layers) for reflecting the terahertz waves L. The metal films 54 are made of, for example, the same material as the first electrode 24 and the second electrode 25 (for example, a metal such as Ti / Au).

[0064] (resin layer) The resin layer 30 is disposed on the support surface 10a of the support substrate 10 via the metal layer 51. In this embodiment, the resin layer 30 is disposed on the entire support surface 10a (metal layer 51) where the QCL element 20 (substrate 21) is not provided. That is, the resin layer 30 is disposed in front of the QCL element 20 as shown in FIGS. 1 and 2, and is also disposed on both sides of the QCL element 20 in the width direction Y (i.e., in the side regions facing the pair of side surfaces 21e) as shown in FIGS. 1 and 3. That is, as shown in FIG. 3, a portion of the resin layer 30 covers the side surface 21e of the substrate 21 via the metal film 54. The resin layer 30 in the side region (i.e., the portion covering the side surface 21e of the substrate 21 via the metal film 54) may be omitted. However, providing the resin layer 30 in the side region improves the support stability of the QCL element 20 in the width direction Y and provides appropriate protection for the QCL element 20.

[0065] The resin layer 30 has an upper surface 30a (fifth surface) and a lower surface 30b (fourth surface). The lower surface 30b is a surface facing the support surface 10a (in this embodiment, a surface supported by the support surface 10a via the metal layer 51). The upper surface 30a is a surface located opposite the lower surface 30b in the vertical direction Z. The resin layer 30 abuts at least against the front surface 21c of the substrate 21. As shown in FIGS. 1 and 2, the resin layer 30 extends in the front-rear direction X (i.e., the direction along the emission direction of the terahertz waves L from the front surface 21c when viewed from the vertical direction Z). More specifically, the resin layer 30 extends forward from the portion abutting against the front surface 21c to have a certain length or more (a length sufficient to ensure an area in which a planar antenna 41, described later, is disposed). 2, the height position of the upper surface 30a of the resin layer 30 relative to the support surface 10a reaches at least the height position of the upper surface 21b of the substrate 21 relative to the support surface 10a. In this embodiment, the upper surface 30a of the resin layer 30 is at approximately the same height as the upper surface 21b of the substrate 21, but the resin layer 30 may be provided so that the upper surface 30a of the resin layer 30 reaches a position higher than the upper surface 21b of the substrate 21.

[0066] (Emission direction determining part) The emission direction regulating unit 40 is provided on the upper surface 30a of the resin layer 30. The emission direction regulating unit 40 is configured to emit the terahertz waves L emitted from the front surface 21c of the substrate 21 to the outside from the upper surface 30a of the resin layer 30 in a direction facing the upper surface 30a (i.e., upward). In other words, the emission direction regulating unit 40 converts the terahertz waves L propagating inside the resin layer 30 into output light Lout having upward directivity that is emitted from the upper surface 30a of the resin layer 30.

[0067] The emission direction determining unit 40 may be configured with, for example, one or more planar antennas 41. In the present embodiment, as an example, the emission direction determining unit 40 is configured as an antenna array consisting of 12 planar antennas 41 arranged in a 3×4 matrix. For example, by adjusting the arrangement (pitch, etc.), size, shape, etc. of the multiple planar antennas 41 with respect to the wavelength of the terahertz waves L propagating inside the resin layer 30, the emission direction of the terahertz waves L can be made to have directionality (upward in the present embodiment). Examples of the planar antenna 41 that can be used include a patch antenna, a bowtie antenna, a dipole antenna, a slot antenna, and a radial line slot antenna. The terahertz waves L emitted from the front surface 21c of the substrate 21 are radiated so as to also spread in the width direction Y. For this reason, as shown in FIG. 1 , the width (length in the width direction Y) of the formation region of the emission direction determining unit 40 (in the present embodiment, the smallest rectangular region including all of the multiple planar antennas 41 when viewed from the up-down direction Z) is preferably set to be larger than the width of the substrate 21. By configuring the emission direction defining portion 40 to be wider than the QCL element 20 (substrate 21) in this way, it becomes possible to efficiently extract the radiation component of the terahertz wave L spreading in the width direction Y as the output light Lout.

[0068] (Operation and effect of the first embodiment) The laser module 1A is configured as a DFG-THz-QCL that generates terahertz waves L by difference frequency generation. According to the laser module 1A, by abutting the resin layer 30, which has a refractive index difference with the substrate 21 of the QCL element 20 smaller than that of air, on the front surface 21c of the substrate 21, total reflection of the terahertz waves L at the end face of the substrate 21 (i.e., the interface between the front surface 21c and air), which is a problem when emitting the terahertz waves L into air, can be suppressed. This allows the terahertz waves L to be efficiently propagated from the substrate 21 of the QCL element 20 to the resin layer 30, and the terahertz waves L passing through the inside of the resin layer 30 can be emitted in a direction determined by the emission direction defining unit 40 (i.e., a direction facing the upper surface 30a (upward in this embodiment)). Therefore, according to the laser module 1A, the relatively simple configuration of the laser module 1A can improve productivity (yield) and the extraction efficiency of the terahertz waves L to the outside.

[0069] As shown in FIG. 2, a metal layer 51 that reflects terahertz waves L is disposed between the support surface 10a of the support substrate 10 and the lower surface 21a of the substrate 21 and the lower surface 30b of the resin layer 30. According to the above configuration, the terahertz waves L emitted from the front surface 21c of the substrate 21 in a diagonal direction (the direction indicated by the arrow in FIGS. 2 and 4 ) that is inclined downward (toward the support surface 10a) with respect to the front-rear direction X in the QCL device 20 are reflected by the metal layer 51 toward the resin layer 30 without escaping to the support substrate 10. This further improves the extraction efficiency of the terahertz waves L. That is, when a member that transmits terahertz waves L (for example, an InP substrate similar to the substrate 21) is used as the support substrate 10 as in this embodiment, the metal layer 51 can appropriately prevent the terahertz waves L from passing through the inside of the support substrate 10 and exiting downward. As a result, the output light Lout that is ultimately extracted upward can be increased. In this embodiment, the metal layer 51 is provided over the entire surface of the support surface 10a, including the side regions between the support surface 10a and the lower surface 30b of the resin layer 30 disposed on both sides of the QCL element 20 in the width direction Y. However, it is not necessary to provide the metal layer 51 over the entire surface of the support surface 10a. For example, the metal layer 51 may be omitted from the side regions.

[0070] As shown in FIG. 4 , a metal film 53 functioning as a reflective layer that reflects the terahertz waves L is provided on the end face (rear face 21d) of the substrate 21 located opposite the front face 21c in the front-rear direction X. As described above, in this embodiment, the metal film 53 serves to increase the reflectivity of the first pump light and the second pump light in the semiconductor laminate 22 (active layer 222) at a portion overlapping the end face 22b of the semiconductor laminate 22 to thereby increase the oscillation efficiency, and also serves to prevent the terahertz waves L from escaping backward at a portion overlapping the rear face 21d of the substrate 21. According to the above configuration, the terahertz waves L are reflected forward by the metal film 53 on the rear face 21d of the substrate 21, thereby increasing the amount of terahertz waves L traveling from the rear face 21d toward the front face 21c (i.e., terahertz waves that ultimately propagate to the resin layer 30 and contribute to an increase in the output light Lout). This makes it possible to more effectively improve the extraction efficiency of the terahertz waves L.

[0071] 1 and 3, a metal film 54 that functions as a reflective layer that reflects terahertz waves L is provided on the side surface 21e of the substrate 21 that intersects with the width direction Y. According to the above configuration, the terahertz waves L that attempt to escape from the side surface 21e of the substrate 21 to the outside (outside in the width direction Y) can be reflected by the metal film 54 and returned to the inside of the substrate 21, thereby increasing the amount of terahertz waves L emitted from the front surface 21c. This makes it possible to more effectively improve the extraction efficiency of the terahertz waves L.

[0072] Each of the metal layer 51 and the metal films 53 and 55 may be made of a material other than metal (for example, a semiconductor material doped at a relatively high concentration (e.g., InP, InGaAs, GaAs, Si, etc.)) as long as it is capable of reflecting the terahertz wave L.

[0073] The emission direction defining portion 40 is a planar antenna 41 (in this embodiment, an antenna array consisting of a plurality of planar antennas 41) provided on the upper surface 30a of the resin layer 30. According to the above configuration, by adjusting the arrangement, shape, number, etc. of the planar antennas 41, it is possible to freely design the beam profile of the output light Lout.

[0074] 1, 2, and 4, metal films 52, 53 functioning as reflective films for reflecting the first pump light and the second pump light are provided on end faces (in this embodiment, the entire end faces 22a, 22b) of a portion of the semiconductor stack 22 including at least the active layer 222, the end faces intersecting with the front-rear direction X. According to the above configuration, oscillation of the first pump light and the second pump light in the semiconductor stack 22 (active layer 222) can be promoted, and terahertz waves L can be generated with high efficiency. The metal films 52, 53 may be made of a material other than metal (for example, a semiconductor material (e.g., InP, InGaAs, GaAs, Si, etc.) doped at a relatively high concentration) as long as they are capable of reflecting the first pump light and the second pump light (mid-infrared light).

[0075] As shown in FIGS. 2 and 4 , the front surface 21c of the substrate 21 is a surface perpendicular to the bottom surface 21a and the top surface 21b. That is, the front surface 21c is a surface perpendicular to the front-rear direction X and parallel to the width direction Y and the up-down direction Z. Conventionally, in order to prevent total reflection of the terahertz waves L at the emission surface (front surface 21c) of the terahertz waves L, polishing may be performed to make the emission surface (front surface 21c) an inclined surface inclined with respect to the up-down direction Z when viewed from the width direction Y. In contrast, in this embodiment, the emission surface (front surface 21c) is abutted against the resin layer 30, thereby allowing the terahertz waves L to be suitably propagated from the substrate 21 to the resin layer 30, thereby eliminating the need for such an inclined surface (polished surface). As a result, the productivity of the laser module 1A can be effectively improved. In the laser module 1A, a conventional inclined surface may be provided on the front surface 21c, but since the angle requirement for total reflection can be relaxed by contacting the resin layer 30, it is possible to obtain a sufficient effect even if the inclination angle is smaller than that of a conventional inclined surface. Therefore, even when a conventional inclined surface is provided on the front surface 21c, the polishing time and polishing amount of the conventional polishing process can be reduced, thereby improving the productivity of the laser module 1A.

[0076] The thickness of the substrate 21 in the vertical direction Z (500 μm in this embodiment) is preferably set to at least half the wavelength of the terahertz waves L. According to the above configuration, the thickness of the substrate 21 having the exit surface (front surface 21 c) of the terahertz waves L is set to at least half the wavelength of the terahertz waves L, thereby improving the extraction efficiency of the terahertz waves L. As described above, the resin layer 30 is provided up to a position at least reaching the upper surface 21 b of the substrate 21. Therefore, the thicker the substrate 21, the thicker the resin layer 30. This facilitates the manufacturing of the resin layer 30 disposed on the support substrate 10. In other words, by ensuring a certain thickness or more of the resin layer 30, it becomes easier to form the resin layer 30 compared to a process of forming a very thin resin layer 30. As a result, in mass-producing the laser module 1A, manufacturing variations among products are suppressed, and yields can be improved.

[0077] [Second embodiment] A laser module 1B of the second embodiment will be described with reference to Figures 5 and 6. The laser module 1B differs from the laser module 1A in that it includes a reflection suppression structure 61 that suppresses the terahertz wave L traveling from the substrate 21 to the resin layer 30 from being reflected toward the substrate 21. The following mainly describes the configuration of the laser module 1B that differs from that of the laser module 1A, and omits a description of the configuration that is the same as that of the laser module 1A.

[0078] The reflection suppression structure 61 is configured by a portion (tip portion) including the front surface 21c of the substrate 21. As shown in FIG. 5, the reflection suppression structure 61 is formed so that, when viewed from the up-down direction Z, the area occupied by the substrate 21 in a plane (YZ plane) perpendicular to the front-rear direction X gradually decreases along the front-rear direction X toward the side where the emission direction regulating unit 40 is provided (i.e., forward). In the present embodiment, as an example, the reflection suppression structure 61 is formed in a triangular prism shape tapering forward when viewed from the up-down direction Z. That is, while the entire front surface 21c of the laser module 1A is a plane perpendicular to the front-rear direction X, the laser module 1B has a structure in which a triangular prism-shaped tip portion (reflection suppression structure 61) is added.

[0079] In the laser module 1B, the antireflection structure 61, including the front surface 21c of the substrate 21, functions as an impedance matching layer. More specifically, the area occupied by the substrate 21 can be gradually reduced (in other words, the area occupied by the resin layer 30 can be gradually increased) along the emission direction of the terahertz waves L (the forward direction as viewed from the vertical direction Z). This allows the refractive index experienced by the terahertz waves L passing through a region where the substrate 21 and the resin layer 30 coexist to be gradually changed from that of the substrate 21 to that of the resin layer 30. By gradually changing the refractive index experienced by the terahertz waves L in this way, it is possible to effectively prevent the terahertz waves L attempting to enter the resin layer 30 from being returned to the QCL element 20. This improves the propagation efficiency of the terahertz waves L from the QCL element 20 (substrate 21) to the resin layer 30, thereby effectively increasing the output light Lout.

[0080] The shape of the reflection suppression structure 61, which functions as an impedance matching layer for gradually changing the refractive index as described above, is not limited to the triangular prism shape shown in FIG. 5. In the above-described triangular prism-shaped reflection suppression structure 61, the area occupied by the substrate 21 in a plane perpendicular to the front-rear direction X (the YZ plane) is configured to decrease linearly toward the front. However, the reflection suppression structure 61 may be formed to taper nonlinearly (e.g., curvedly) toward the front when viewed from the up-down direction Z, or may be formed to decrease in a stepped manner the width of the substrate 21 in the width direction Y toward the front. However, by forming the reflection suppression structure 61 into a triangular prism shape, the area occupied by the substrate 21 in the YZ plane decreases linearly, thereby enabling a smooth change in the refractive index. Furthermore, the reflection suppression structure 61 can be easily manufactured by obliquely cutting off both sides of the tip of the substrate 21 in the width direction Y.

[0081] [Third embodiment] 7 and 8, a laser module 1C according to a third embodiment will be described. The laser module 1C differs from the laser module 1A in that it includes a reflection suppression structure 62 that suppresses the terahertz wave L traveling from the substrate 21 to the resin layer 30 from being reflected toward the substrate 21. The following mainly describes the configuration of the laser module 1C that differs from that of the laser module 1A, and omits a description of the configuration that is the same as that of the laser module 1A.

[0082] In the laser module 1C, the front surface 21c is configured as a surface perpendicular to the front-rear direction X, similar to the laser module 1A. The reflection anti-reflection structure 62 is provided at a position facing the front surface 21c of the substrate 21. The reflection anti-reflection structure 62 is formed by a structure in which a plurality of high-refractive index material layers 62a made of a high-refractive index material having a higher refractive index than the resin layer 30 are provided at intervals along the front-rear direction X, and parts of the resin layer 30 are inserted between adjacent high-refractive index material layers 62a. In the present embodiment, as an example, three rectangular plate-shaped high-refractive index material layers 62a are arranged at positions facing the front surface 21c.

[0083] In the laser module 1C, portions of the resin layer 30 sandwiched between the multiple high-refractive-index material layers 62a function as low-refractive-index layers. By alternately arranging the high-refractive-index layers (high-refractive-index material layers 62a) and the low-refractive-index layers (portions of the resin layers 30) in this manner, a reflection-suppressing structure 62 that functions as a broadband anti-reflection (AR) coating is obtained. More specifically, by adjusting the thickness and number of the high-refractive-index layers and the low-refractive-index layers and arranging them in a multilayer structure, the reflection-suppressing structure 62 can function as an AR coating. The thickness and number of the high-refractive-index layers and the low-refractive-index layers may be appropriately designed to provide sufficient low-reflection performance for the terahertz waves L.

[0084] According to the laser module 1C, by providing the antireflection structure 62 that functions as an AR coating, it is possible to effectively prevent the terahertz waves L that are about to enter the resin layer 30 from being returned to the QCL element 20 side.

[0085] Furthermore, the plurality of high-refractive-index material layers 62a are formed from the same material as the substrate 21. According to the above configuration, by forming a plurality of grooves spaced apart in the front-rear direction X at the tip of the rectangular parallelepiped substrate 21 that was originally formed integrally, the portions of the substrate 21 remaining between the grooves can be used as the high-refractive-index material layers 62a. In this case, the high-refractive-index material layers 62a can be easily formed, thereby improving the productivity of the laser module 1C.

[0086] Furthermore, as shown in FIG. 8 , in the laser module 1C, the multiple high-refractive-index material layers 62a are connected to the substrate 21. As an example, the grooves (portions into which the resin layer 30 is embedded) provided in the antireflection structure 62 open to the upper surface 21b and a pair of side surfaces 21e of the substrate 21, but do not open to the lower surface 21a. That is, the bottoms of the grooves do not reach the lower surface 21a of the substrate 21. As a result, the high-refractive-index material layers 62a provided between adjacent grooves are connected to the plate-shaped portion 62b including the lower surface 21a of the substrate 21, forward of the front surface 21c. This configuration can improve the support stability of the multiple high-refractive-index material layers 62a. Furthermore, for example, by performing an operation such as digging grooves in a single rectangular plate-shaped substrate member so that the grooves do not penetrate all the way to the bottom, a structure in which the substrate 21 and the multiple high-refractive-index material layers 62a are connected via the portions 62b can be easily formed. This improves the productivity of the substrate 21 and the antireflection structure 62 (the multiple high-refractive-index material layers 62a).

[0087] The plurality of high-refractive-index material layers 62a do not have to be connected to the substrate 21. For example, if the above-described grooves are formed so as to penetrate from the upper surface 21b to the lower surface 21a of the substrate 21, the plurality of high-refractive-index material layers 62a will be separated from each other and from the substrate 21. In such a case, the plurality of high-refractive-index material layers 62a may be bonded to, for example, the metal layer 51 (or to the support surface 10a when the metal layer 51 is omitted). Furthermore, the high-refractive-index material layers 62a may be made of a member different from that of the substrate 21. In such a case, the high-refractive-index material layers 62a may be connected to the substrate 21 via the portions 62b, or may be separated from the substrate 21.

[0088] [Fourth embodiment] A laser module 1D of the fourth embodiment will be described with reference to Fig. 9. The laser module 1D differs from the laser module 1A in that it includes an inclined surface 21f that functions as a reflection suppressing structure that suppresses the terahertz wave L traveling from the substrate 21 to the resin layer 30 from being reflected (total reflection) toward the substrate 21. The following mainly describes the configuration of the laser module 1D that differs from the laser module 1A, and omits a description of the configuration that is the same as that of the laser module 1A.

[0089] As shown in FIG. 9, the terahertz wave L generated in the semiconductor laminate 22 (active layer 222) has the above-mentioned radiation angle θ C (Cherenkov radiation angle) in such a manner that the terahertz waves L are spread in the width direction Y. If the terahertz waves L thus emitted can be prevented from being totally reflected at the front surface 21c and propagated to the resin layer 30, the output light Lout can be increased accordingly.

[0090] Therefore, in the laser module 1D, both side portions in the width direction Y of the front surface 21c (portions onto which the terahertz waves L, which are emitted so as to spread in the width direction Y as described above, are incident) are cut off obliquely along the up-down direction Z (so as to be inclined in the width direction Y). As a result, an inclined surface 21f is formed in a part of the front surface 21c. The inclined surface 21f is inclined with respect to the width direction Y when viewed from the up-down direction Z in order to suppress total reflection of the terahertz waves L. That is, the inclined surface 21f is inclined so that the angle of incidence of the terahertz waves L with respect to the inclined surface 21f when viewed from the up-down direction Z is smaller than the angle of incidence of the terahertz waves L with respect to the front surface 21c (i.e., the YZ plane) when the inclined surface 21f is not formed. More specifically, the inclined surface 21f is inclined backward (away from the emission direction defining portion 40) as it extends from the center of the QCL element 20 outward in the width direction Y.

[0091] As an example, the inclination angle θ of the inclined surface 21f with respect to the width direction Y is set to the above-mentioned radiation angle θ C The angle is set to match or be close to the Cherenkov radiation angle. Such an inclined surface 21f can be easily formed compared to a conventional polished surface (an inclined surface that is inclined with respect to the vertical direction Z when viewed from the width direction Y). Specifically, it can be easily formed by cutting off the semiconductor laminate 22 straight in the vertical direction Z at a position that does not overlap with the semiconductor laminate 22 in the vertical direction Z.

[0092] According to the laser module 1D, the inclined surface 21f (reflection suppressing structure) provided on the front surface 21c can suppress total reflection of the terahertz wave L. This effectively prevents the terahertz wave L radiated outward in the width direction Y from being totally reflected by the front surface 21c and returned to the QCL element 20 when viewed from the up-down direction Z. As a result, the propagation efficiency of the terahertz wave L to the resin layer 30 can be improved, and the output light Lout can be increased.

[0093] [Fifth embodiment] 10 and 11, a laser module 1E of the fifth embodiment will be described. The laser module 1E differs from the laser module 1A in that it includes a reflection suppression structure 63 that suppresses the terahertz wave L traveling from the substrate 21 to the resin layer 30 from being reflected toward the substrate 21. The following mainly describes the configuration of the laser module 1E that differs from the laser module 1A, and omits a description of the configuration that is the same as that of the laser module 1A.

[0094] The reflection suppression structure 63 is configured by a sub-wavelength periodic structure provided at a position facing the front surface 21c of the substrate 21. The reflection suppression structure 63 (sub-wavelength periodic structure) is formed by a plurality of unit areas A that are two-dimensionally arranged at a period shorter than the wavelength of the terahertz waves L when viewed from the up-down direction Z. That is, the distance (period) between the centers of adjacent unit areas A is shorter than the wavelength of the terahertz waves L. As an example, the plurality of unit areas A are square regions when viewed from the up-down direction Z and are arranged in a square lattice pattern. Each of the plurality of unit areas A is configured by a part of the substrate 21 and a part of the resin layer 30. That is, each unit area A is a region where the substrate 21 and the resin layer 30 are mixed. The proportion of the resin layer 30 in each of the plurality of unit areas A is configured to gradually increase toward the side where the emission direction regulating section 40 is provided (i.e., forward) along the front-rear direction X.

[0095] In the laser module 1E, each unit area A is provided with a cylindrical hole H extending in the vertical direction Z at the center of the unit area A. The portion of the unit area A where no hole H is provided is formed by the substrate 21. That is, one hole H is provided at the center of one unit area A by removing a part of the substrate 21. A part of the resin layer 30 is embedded inside the hole H.

[0096] As an example, the reflection suppressing structure 63 is formed integrally with the substrate 21. That is, the tip of a substrate member formed integrally with the substrate 21 serves as the reflection suppressing structure 63. In this case, the portion of the reflection suppressing structure 63 along the rear end surface of the first-stage unit area A located furthest to the rear (the portion indicated by the dashed line in FIG. 10) can be regarded as the front surface 21c of the substrate 21.

[0097] The depth of the holes H is constant in the multiple unit regions A. The bottoms of the holes H do not reach the lower surface 21a of the substrate 21. As a result, the reflection suppression structure 63 has a plate-shaped bottom 63a that is continuously connected to the lower surface 21a of the substrate 21. Meanwhile, in the multiple unit regions A, the diameter Ha of the holes H is configured to gradually increase toward the front. This achieves a structure in which the proportion of the resin layer 30 in each of the multiple unit regions A gradually increases toward the front. However, this structure may be achieved by a configuration in which the depth of the holes H becomes deeper toward the front, or by a configuration in which both the diameter Ha and the depth of the holes H change.

[0098] The laser module 1E can obtain the same effect as the impedance matching layer (reflection anti-structure 61) of the laser module 1B by providing a sub-wavelength periodic structure (reflection anti-structure 63) configured so that the proportion of the resin layer 30 gradually increases along the emission direction (the direction traveling forward as viewed from the up-down direction Z) of the terahertz waves L. Furthermore, by forming a metalens using the sub-wavelength periodic structure (reflection anti-structure 63), it is also possible to control the phase of the terahertz waves L (output light Lout).

[0099] [Sixth embodiment] A laser module 1F of the sixth embodiment will be described with reference to Figures 12 and 13. The laser module 1F differs from the laser module 1E in that the laser module 1F includes a reflection suppression structure 64 (pillar structure) in which a plurality of pillars P are periodically arranged, instead of a reflection suppression structure 63 (hole structure) in which a plurality of holes H, each filled with a part of the resin layer 30, are periodically arranged.

[0100] In the laser module 1F, each unit area A is provided with a cylindrical pillar P extending in the vertical direction Z at the center of the unit area A. In the unit area A, the pillar P is formed of a substrate 21. Meanwhile, a resin layer 30 is filled in the portion of the unit area A where the pillar P is not provided.

[0101] The height of the pillars P is constant in the multiple unit regions A. The reflection antireflection structure 64 has a plate-shaped bottom 64a that is continuously connected to the lower surface 21a of the substrate 21. The multiple pillars P are erected on the bottom 64a. Meanwhile, in the multiple unit regions A, the diameter Pa of the pillars P is configured to gradually increase toward the front. This achieves a structure in which the proportion of the resin layer 30 in each of the multiple unit regions A gradually increases toward the front. However, such a structure may be realized by a configuration in which the height of the pillars P decreases toward the front, or by a configuration in which both the diameter Pa and the height of the pillars P change.

[0102] The laser module 1F having such an anti-reflection structure 64 (pillar structure) can also provide the same effects as the laser module 1E having the above-mentioned anti-reflection structure 63 (hole structure).

[0103] [Variations] Although several embodiments (first to sixth embodiments) of the laser module have been described above, the present disclosure is not limited to these embodiments. The materials and shapes of each component are not limited to the specific materials and shapes described above, and various materials and shapes other than those described above can be used. Furthermore, some components included in one embodiment may be omitted or modified as appropriate, and can be arbitrarily combined with components included in other embodiments.

[0104] For example, in the above embodiment, the QCL device 20 is configured to oscillate the first pump light and the second pump light by itself, but a Littrow-type resonator may be configured between the QCL device 20 and an external resonator (e.g., a movable diffraction grating disposed opposite the end face 22 b). In this case, the metal film 53 covering the end face 22 b is omitted.

[0105] In the above embodiment, an antenna array consisting of a plurality of planar antennas 41 is used as the emission direction determining unit 40, but the emission direction determining unit 40 may be configured by a single antenna or may be realized by a structure other than an antenna. For example, the emission direction determining unit 40 may be realized by a grating structure provided on the upper surface 30a of the resin layer 30.

[0106] Furthermore, in the above embodiment, the width (length in the width direction Y) of the support substrate 10 is made larger than the width of the QCL element 20 (substrate 21), and the resin layer 30 is also provided on both sides of the QCL element 20 in the width direction Y (i.e., the side regions facing the pair of side surfaces 21e). However, the width of the support substrate 10 may be made substantially the same as the width of the QCL element 20. In this case, since the support surface 10a extending to the side regions is not formed, the resin layer 30 in the side regions may be omitted. In this way, by limiting the width of the support substrate 10 to the minimum width necessary to support the QCL element 20 (substrate 21), the width size of the entire laser module can be made compact. [Explanation of symbols]

[0107] 1A, 1B, 1C, 1D, 1E, 1F... laser module, 10... support substrate (support), 10a... support surface, 20... QCL element (quantum cascade laser element), 21... substrate, 21a... lower surface (first surface), 21b... upper surface (second surface), 21c... front surface (third surface), 21d... rear surface (end surface), 21e... side surface, 21f... inclined surface (reflection suppression structure), 22... semiconductor laminate, 22a, 22b... end surface, 30... resin layer, 30a... upper surface (fifth surface), 30 b...bottom surface (fourth surface), 40...emission direction determining portion, 41...planar antenna, 51...metal layer (reflective layer), 52...metal film (reflective film), 53...metal film (reflective film, reflective layer), 54...metal film (reflective layer), 61, 62, 63, 64...reflection suppression structure, 222...active layer, A...unit area, L...terahertz wave, X...front-back direction (second direction), Y...width direction (third direction), Z...up-down direction (first direction), ω1...first frequency, ω2...second frequency, ω3...difference frequency.

Claims

1. a support having a support surface; a quantum cascade laser device disposed on the support surface; a resin layer disposed on the support surface; an emission direction regulating portion disposed on the resin layer, The quantum cascade laser device is a substrate having a first surface facing the support surface, a second surface opposite to the first surface, and a third surface connecting the first surface and the second surface and emitting terahertz waves; a semiconductor laminate including an active layer provided on the second surface of the substrate, the active layer generating first pump light of a first frequency and second pump light of a second frequency, and generating a terahertz wave of a difference frequency between the first frequency and the second frequency by difference frequency generation between the first pump light and the second pump light; the resin layer has a fourth surface facing the support surface and a fifth surface opposite to the fourth surface, the emission direction defining portion is provided on the fifth surface and configured to emit the terahertz waves emitted from the third surface of the substrate to the outside from the fifth surface in a direction facing the fifth surface, the resin layer is in contact with a third surface of the substrate and extends in a second direction along an emission direction of the terahertz wave from the third surface when viewed from a first direction in which the first surface and the second surface face each other; a height position of the fifth surface of the resin layer relative to the support surface at least reaches a height position of the second surface of the substrate relative to the support surface; Laser module.

2. The laser module according to claim 1 , further comprising a reflective layer arranged between the support surface of the support body and the first surface of the substrate and the fourth surface of the resin layer, and configured to reflect the terahertz waves.

3. The laser module according to claim 1 , further comprising a reflective layer provided on an end surface of the substrate opposite to the third surface in the second direction, the reflective layer reflecting the terahertz wave.

4. The laser module according to claim 1 , further comprising a reflective layer provided on a side surface of the substrate that intersects with a third direction perpendicular to both the first direction and the second direction, and that reflects the terahertz wave.

5. The laser module according to claim 1 , wherein the emission direction determining portion is a planar antenna provided on the fifth surface.

6. 2. The laser module according to claim 1, further comprising a reflective film provided on an end surface of the semiconductor laminate that intersects with the first direction at least in a portion including the active layer, and that reflects the first pump light and the second pump light.

7. The laser module according to claim 1 , wherein the third surface of the substrate is a surface perpendicular to the first surface and the second surface.

8. 2. The laser module of claim 1, further comprising a reflection suppression structure provided in a portion of the substrate including the third surface or in a position facing the third surface, the reflection suppression structure suppressing the terahertz waves traveling from the substrate to the resin layer from being reflected toward the substrate.

9. 9. The laser module of claim 8, wherein the anti-reflection structure is formed by a portion of the substrate that includes the third surface, and is formed so that, when viewed from the first direction, the area occupied by the substrate in a plane perpendicular to the second direction gradually decreases along the second direction toward the side where the emission direction determining portion is provided.

10. 9. The laser module of claim 8, wherein the anti-reflection structure is provided at a position facing the third surface of the substrate, and is formed by a structure in which a plurality of high-refractive-index material layers made of a high-refractive-index material having a refractive index higher than that of the resin layer are spaced apart from each other along the second direction, and a portion of the resin layer is inserted between adjacent high-refractive-index material layers.

11. The laser module according to claim 10 , wherein the plurality of high refractive index material layers are formed of the same material as the substrate.

12. The laser module of claim 11 , wherein the plurality of high refractive index material layers are coupled to the substrate.

13. the antireflection structure is formed by an inclined surface provided on the third surface of the substrate, The laser module according to claim 8 , wherein the inclined surface is inclined with respect to the second direction when viewed from the first direction in order to suppress total reflection of the terahertz wave.

14. the antireflection structure is formed by a subwavelength periodic structure provided at a position facing the third surface of the substrate, the subwavelength periodic structure is formed by a plurality of unit regions that are two-dimensionally arranged at a period shorter than the wavelength of the terahertz wave when viewed from the first direction, each of the plurality of unit areas is configured by a part of the substrate and a part of the resin layer; 9. The laser module according to claim 8, wherein the proportion of the resin layer in each of the plurality of unit regions gradually increases along the second direction toward the side where the emission direction determining portion is provided.

15. The laser module according to claim 1 , wherein the thickness of the substrate in the first direction is equal to or greater than half the wavelength of the terahertz wave.

16. The laser module according to claim 1 , wherein the resin layer is provided so as to cover a side surface of the substrate that intersects with a third direction that is perpendicular to both the first direction and the second direction.

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