Laser module

Abstract

To provide a laser module which is miniaturized and is packaged in such an embodiment that loss of light contributing to the generation of a terahertz wave can be suppressed.SOLUTION: A laser module 1A comprises: a QCL element 2; a diffraction lattice unit 3 including a movable diffraction lattice 31; a first lens 4 which allows light pass through, wherein the light is outgoing light from an end surface 12b of the QCL element 2 and the light feedbacking from the movable diffraction lattice 31 to the QCL element 2; a second lens 6 which allows terahertz wave pass through, wherein the terahertz wave is exited from the QCL element 2; a first holder 7; and a package 8. The first holder 7 includes: a support surface 7a on which the QCL element 2 is mounted; and a side surface 7e which is connected to the support surface 7a, and is opposite to the first lens 4 in a resonance direction. A distance d1 from a cross point 7i in which the side surface 7e along the resonance direction and the support surface 7a intersect each other to the end surface 12b is shorter than a distance d2 of a cross point 7i along the resonance direction and the first lens 4.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] BACKGROUND ART Difference frequency generation terahertz quantum cascade lasers (DFG-THz-QCLs) have been known (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6893591 [Patent Document 2] US Patent Application Publication No. 2015 / 0311665 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned terahertz quantum cascade laser, from the viewpoint of user convenience, there is a demand for a product that can be miniaturized and packaged in a manner that can suppress loss of light that contributes to the generation of terahertz waves. However, the above-mentioned Patent Documents 1 and 2 do not disclose a method for realizing such packaging.

[0005] Therefore, an object of one aspect of the present disclosure is to provide a laser module that is packaged in a manner that allows for miniaturization and suppresses loss of light that contributes to generation of terahertz waves. [Means for solving the problem]

[0006] A laser module according to one aspect of the present disclosure is a quantum cascade laser element having a substrate having a main surface and a back surface opposite to the main surface, a first cladding layer provided on the main surface, an active layer provided on the first cladding layer on the side opposite to the substrate, and a second cladding layer provided on the active layer on the side opposite to the first cladding layer, wherein the active layer has a first end face and a second end face facing each other in a second direction perpendicular to a first direction which is a stacking direction of the substrate, the first cladding layer, the active layer, and the second cladding layer, the first end face forming a resonator for oscillating light of a first frequency and light of a second frequency, and the active layer generating terahertz waves of a difference frequency between the first frequency and the second frequency; a diffraction grating unit including a movable diffraction grating which forms an external resonator for the light of the first frequency; and a diffraction grating unit disposed between the quantum cascade laser element and the movable diffraction grating, and configured to receive light emitted from the second end face and light emitted from the movable diffraction grating. the first holder has a support surface on which the quantum cascade laser element is placed, and a first side surface connected to the support surface and facing the first lens in the second direction, and when viewed from a direction orthogonal to the first direction and the second direction, a first distance from an intersection of the first side surface and the support surface along the second direction to the second end surface is smaller than a second distance between the intersection and the first lens in the second direction.

[0007] The laser module includes a packaged configuration for oscillating light of a first frequency and light of a second frequency required for generating terahertz waves by difference frequency generation, namely, a quantum cascade laser element, a first holder for holding the quantum cascade laser element, a movable diffraction grating (diffraction grating unit), and a first lens disposed between the quantum cascade laser element and the movable diffraction grating. Furthermore, when the direction from the first lens toward the quantum cascade laser element along a second direction (i.e., resonance direction) in which both end faces (first end face and second end face) of the quantum cascade laser element face each other is defined as a positive direction, a first distance from an intersection point between the first side surface and the support surface of the first holder along the second direction to the second end face is smaller than a second distance along the second direction between the intersection point and the first lens. By arranging the quantum cascade laser element and the first holder in this manner, the quantum cascade laser element (second end face) can be brought as close as possible to the first lens. This prevents the first lens and the movable diffraction grating from becoming larger, thereby enabling the overall package to be more compact. Furthermore, by setting the first distance to a small value as described above, it is possible to suppress interference between the light emitted from the second end face and the first holder (i.e., a portion of the emitted light is blocked by the first holder and does not reach the first lens). This reduces the loss of light that contributes to the generation of terahertz waves. As a result, it is possible to obtain a laser module that is packaged in a manner that allows for miniaturization and suppresses the loss of light that contributes to the generation of terahertz waves.

[0008] The first distance may be equal to or less than 0. According to the above configuration, that is, the configuration in which the second end face is flush with the first side face or the configuration in which the second end face protrudes further toward the first lens than the first side face, interference between the light emitted from the second end face and the first holder can be more reliably prevented, and therefore the loss of light that contributes to the generation of terahertz waves can be more effectively reduced.

[0009] The first distance may be 0. According to the above configuration, i.e., the configuration in which the second end face is flush with the first side face, the entire portion of the quantum cascade laser element extending to the second end face can be brought into contact with the first holder (support surface), thereby improving the efficiency of heat dissipation from the quantum cascade laser element to the first holder.

[0010] A resonance axis passing through the first end face and the second end face of the quantum cascade laser element may intersect with the optical axis of the second lens by tilting the support surface so as to intersect with the optical axis of the second lens, and the first end face may be spaced from the light incident surface of the second lens. With the above configuration, it is possible to bring the quantum cascade laser element (e.g., a side surface of a substrate continuous with the first end face) into contact with or close to the light incident surface of the second lens while spacing the first end face constituting the resonator for light of the first frequency and light of the second frequency for generating terahertz waves from the light incident surface of the second lens. This prevents the reflectivity of the first end face, which is important for oscillation of light of the first frequency and light of the second frequency, from being affected by the second lens, and ensures the extraction efficiency of terahertz waves from the quantum cascade laser element to the second lens.

[0011] The first lens and the diffraction grating unit may be fixed to the first holder. According to the above configuration, before the quantum cascade laser element, the first lens, and the diffraction grating unit are housed in the package, these components can be fixed to the first holder and their positions can be adjusted. This improves work efficiency compared to when the positions of the components are adjusted inside the package.

[0012] The second lens may be a silicon lens formed in a hemispherical or hyperhemispherical shape. Silicon lenses are scratch-resistant. Even if the silicon lens is scratched or soiled, it is less susceptible to terahertz waves, which have longer wavelengths than visible light and near-infrared light. Therefore, the second lens can be placed so that it is exposed to the outside of the package.

[0013] The first holder may have a second side surface connected to the support surface and facing the second lens in the second direction, and the first end surface may be located closer to the second lens than the second side surface in the second direction. According to the above configuration, by making the first end surface of the quantum cascade laser element protrude closer to the second lens than the second side surface of the first holder, it is possible to bring the first end surface of the quantum cascade laser element into contact with or close to the second lens for outputting terahertz waves while suppressing interference between the first holder and the second lens.

[0014] The package may have a sidewall facing the first end face, and the sidewall may have a through-hole penetrating in a third direction perpendicular to the sidewall. The through-hole may have a first hole opening to the inside of the package, a second hole including the first hole when viewed from the third direction and larger than the first hole, and opening to the outside of the package, and an annular counterbore surface connecting the first hole and the second hole and extending along a plane intersecting the third direction. The outer edge of the light incident surface of the second lens may be inserted through the second hole from the outside of the package and fixed in surface contact with the counterbore surface. According to the above configuration, the second lens for outputting terahertz waves can be attached to the sidewall from the outside of the package, facilitating the installation of the second lens. Furthermore, the second lens can be used as a window material for closing the through-hole provided in the sidewall. As a result, the number of parts can be reduced, thereby reducing manufacturing costs and miniaturizing the entire package. Furthermore, since optical loss (attenuation of the terahertz waves, which are output light) caused by providing a window material separate from the second lens can be avoided, it is also possible to achieve high output of the terahertz waves.

[0015] The first end face may be located inside the first hole. According to the above configuration, the first end face of the quantum cascade laser element can be extended into the first hole, so that the substrate of the quantum cascade laser element can be in contact with or close to the light incident surface of the second lens. This improves the extraction efficiency of the terahertz wave and reduces the size of the entire package.

[0016] The first holder may have a main body including a portion of the support surface facing the first lens and the first side surface, and a protrusion connected to the main body including a portion of the support surface facing the second lens, at least a portion of the protrusion being located inside the first hole. According to the above configuration, by extending the first holder (protrusion) into the first hole, the contact area between the quantum cascade laser element and the first holder (support surface) can be increased. As a result, the efficiency of heat dissipation from the quantum cascade laser element to the first holder can be improved.

[0017] The laser module may further include a second holder that holds the second lens, and the second lens and the second holder may be housed in a package, and the package may have a sidewall facing the first end face, and the sidewall may be provided with a light exit window for passing light that is emitted from the first end face and passes through the second lens. According to the above configuration, the second lens for outputting terahertz waves can be housed in the package in the same way as the first lens, thereby preventing damage and contamination of the second lens.

[0018] The second holder may be fixed to the package independently of the first holder. According to the above configuration, since the first holder and the second holder are independent, the quantum cascade laser element can be attached to the first holder and the second lens can be attached to the second holder in parallel before the components are housed in the package. This improves the efficiency of the laser module assembly.

[0019] The first lens and the diffraction grating unit may be fixed to the first holder, and the second holder may be formed integrally with the first holder or fixed to the first holder. According to the above configuration, the integrated structure of the first holder and the second holder can be prepared outside the package, so that the positions of the quantum cascade laser element, the first lens, the diffraction grating unit, and the second lens can be adjusted outside the package. This improves work efficiency compared to when the position adjustments are performed inside the package.

[0020] The second holder may have a through hole penetrating in a third direction perpendicular to the side wall, the through hole having a first hole portion opening toward the quantum cascade laser element, a second hole portion including the first hole portion when viewed from the third direction and opening toward the side wall to be larger than the first hole portion, and an annular counterbore surface connecting the first hole portion and the second hole portion and extending along a plane intersecting the second direction, and the outer edge of the light incident surface of the second lens may be inserted through the second hole portion from the side wall side and fixed in surface contact with the counterbore surface. According to the above configuration, the second lens for outputting terahertz waves can be attached to the second holder from the outside (the side opposite to the side where the quantum cascade laser element is arranged), thereby facilitating the attachment of the second lens.

[0021] The first end face may be located inside the first hole. According to the above configuration, the first end face of the quantum cascade laser element can be extended into the first hole, so that the substrate of the quantum cascade laser element can be in contact with or close to the light incident surface of the second lens. This improves the extraction efficiency of the terahertz wave and reduces the size of the entire package.

[0022] The first holder may have a main body including a portion of the support surface facing the first lens and the first side surface, and a protrusion connected to the main body and including a portion of the support surface facing the second lens, and at least a portion of the protrusion may be located inside the first hole. According to the above configuration, by extending the first holder (protrusion) into the first hole, the contact area between the quantum cascade laser element and the first holder (support surface) can be increased. As a result, the efficiency of heat dissipation from the quantum cascade laser element to the first holder can be improved.

[0023] The width of the protrusion in a fourth direction perpendicular to the first and second directions may be smaller than the width of the main body in the fourth direction. According to the above configuration, by making the width of the protrusion smaller than the width of the main body, interference between the first holder and the package or the second holder can be prevented while ensuring the volume of the first holder that functions as a heat bath.

[0024] The protrusion may be formed in a shape such that the width of the protrusion gradually decreases as it approaches the second lens along the second direction. According to the above configuration, when the first holder on which the quantum cascade laser is mounted is housed and positioned within the package, the risk of interference (contact) between the protrusion and the side wall (mainly the inner surface of the first hole) can be effectively reduced, and the volume of the first holder that functions as a heat bath can be sufficiently increased. [Effects of the Invention]

[0025] According to one aspect of the present disclosure, it is possible to provide a laser module that is packaged in a manner that allows for miniaturization and suppresses loss of light that contributes to generation of terahertz waves. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a perspective view of a laser module according to a first embodiment. [Figure 2] FIG. 2 is a perspective view of the laser module as seen from an angle different from that of 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 a quantum cascade laser device. [Figure 5] FIG. 5 is a diagram showing the positional relationship between the quantum cascade laser device and the second lens. [Figure 6] FIG. 6 is a side view showing the arrangement of the first lens, the second lens, the quantum cascade laser element, the first holder, and the diffraction grating unit housed in the package. [Figure 7] FIG. 7 is a plan view showing the arrangement of the first lens, lens holder, second lens, quantum cascade laser element, first holder, and diffraction grating unit housed in a package. [Figure 8] FIG. 8 is a cross-sectional view of the laser module according to the second embodiment. [Figure 9] FIG. 9 is a schematic perspective view of the laser module according to the second embodiment. [Figure 10] FIG. 10 is a cross-sectional view of the laser module according to the third embodiment. [Figure 11] FIG. 11 is a schematic perspective view of the laser module according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, an embodiment 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.

[0028] [First embodiment] A laser module 1A according to a first embodiment will be described with reference to FIGS. 1 to 7. The laser module 1A is a small terahertz light source module that is handheld size or smaller. As an example, the laser module 1A is configured to be single-mode, wavelength-tunable, and operable at room temperature using a quantum cascade laser element 2 (hereinafter referred to as "QCL element 2") that is a difference frequency generation type terahertz quantum cascade laser (DFG-THz-QCL). The laser module 1A includes the QCL element 2, a diffraction grating unit 3, a first lens 4 (a lens for an external resonator), a lens holder 5, a second lens 6 (a lens for outputting terahertz waves), a first holder 7, and a package 8.

[0029] The package 8 is a housing that airtightly houses the QCL element 2, the diffraction grating unit 3, the first lens 4, the lens holder 5, and the first holder 7. An optical path between the light incident surface 61 of the second lens 6 and the movable diffraction grating 31 (diffraction grating unit 3) is also arranged inside the package 8. Note that components other than those described above (for example, a temperature sensor for measuring the temperature inside the package 8, a temperature control element such as a Peltier element, etc.) may also be arranged inside the package 8.

[0030] In this embodiment, as an example, the package 8 is a butterfly package. The package 8 has a bottom wall 81, a side wall 82, and a top wall 83. Note that the top wall 83 is not shown in FIG. 2.

[0031] The bottom wall 81 is a rectangular plate-shaped member. The bottom wall 81 is formed of a metal material such as copper tungsten. The bottom wall 81 is a base member on which the first holder 7 is mounted. In this embodiment, the first holder 7 is placed directly on the bottom wall 81; however, a separate member such as a heat dissipation member (e.g., a Peltier element) may be disposed between the bottom wall 81 and the first holder 7. That is, the first holder 7 may be disposed on the bottom wall 81 via a separate member. For convenience, in this specification, the longitudinal direction of the bottom wall 81 is referred to as the X-axis direction, the lateral direction of the bottom wall 81 is referred to as the Y-axis direction, and the direction perpendicular to the bottom wall 81 (i.e., the direction perpendicular to the X-axis and Y-axis directions) is referred to as the Z-axis direction.

[0032] The side wall 82 is erected on the bottom wall 81. When viewed from the Z-axis direction, the side wall 82 is formed in an annular shape so as to surround the internal space in which the QCL element 2 and the like are housed. In this embodiment, the side wall 82 is formed in a rectangular cylindrical shape. The side wall 82 is formed of a metal material such as Kovar. The side wall 82 is, for example, a Kovar frame plated with Ni / Au. In this embodiment, the side wall 82 is provided in the center of the bottom wall 81 in the longitudinal direction (X-axis direction). The width of the side wall 82 in the lateral direction (Y-axis direction) is the same as the width of the bottom wall 81 in the lateral direction, and the width of the side wall 82 in the longitudinal direction (X-axis direction) is shorter than the width of the bottom wall 81 in the longitudinal direction. In other words, protrusions 81a are formed on both sides of the bottom wall 81 in the longitudinal direction, protruding outward beyond the side walls 82. At the portions of the protruding portion 81a corresponding to the four corners of the bottom wall 81, screw holes 81b are provided for attaching the package 8 (bottom wall 81) to another member.

[0033] The top wall 83 is a member that closes the opening of the side wall 82 on the opposite side from the bottom wall 81. The top wall 83 has a rectangular plate shape. The outer shape (lengthwise and widthwise) of the top wall 83 when viewed from the Z-axis direction approximately matches the outer shape of the side wall 82. The top wall 83 is formed, for example, from the same metal material (e.g., Kovar) as the side wall 82. The top wall 83 is airtightly joined, for example, by seam welding or the like, to the end 82a of the side wall 82 on the opposite side from the bottom wall 81, with the inside of the package 8 being evacuated or replaced with nitrogen.

[0034] A plurality of lead terminals 9 (14 in total, seven on each side in the short-side direction) for passing current to components such as the QCL element 2 housed in the package 8 are inserted into a pair of side walls 821 (i.e., portions intersecting in the short-side direction (Y-axis direction)) of the side walls 82 that extend along the longitudinal direction (X-axis direction). Each lead terminal 9 is a flat conductive member extending in the Y-axis direction.

[0035] Each of the pair of side walls 821 is provided with protruding walls 84 that protrude from both the outer surface (the outer surface of the package 8) and inner surface (the inner surface of the package 8) of the side wall 821. The protruding walls 84 are eave-shaped members that extend along the X-axis direction above (toward the top wall 83) the center position of the side wall 821 in the Z-axis direction. The lead terminals 9 are arranged on the upper surfaces of the protruding walls 84 at approximately equal intervals along the X-axis direction.

[0036] The portions of the lead terminals 9 located outside the package 8 are electrically connected to the driving power supply for the QCL element 2, the driving power supply for the movable diffraction grating 31 (a power supply for passing current through the coil 315, which will be described later), and the like. On the other hand, the portions of the lead terminals 9 located inside the package 8 function as electrode terminals for supplying power to the components inside the package 8 (e.g., the QCL element 2, the movable diffraction grating 31, and the like). That is, the electrode terminals and the components inside the package 8 are electrically connected via conductive wires (not shown), and thus power is supplied to the components from an external power supply via the lead terminals 9 and the wires. Furthermore, if the above-mentioned temperature sensor, temperature control element, and the like are disposed inside the package 8, these components are also electrically connected to the electrode terminals.

[0037] Of the pair of side walls 822 extending along the short-side direction (Y-axis direction) of the side wall 82 (i.e., portions intersecting in the longitudinal direction (X-axis direction)), the side wall 822 facing one end face (end face 2a) of the QCL element 2 has a through-hole 85 penetrating in a direction perpendicular to the side wall 822 (i.e., X-axis direction) (third direction). A second lens 6 is attached to the through-hole 85.

[0038] Next, the configuration of each part housed in the package 8 will be described.

[0039] [Quantum cascade laser device configuration] The QCL 2 is a terahertz light source configured to be able to output terahertz waves in a room temperature environment. A configuration example of the QCL 2 will be described in detail mainly with reference to FIGS. 3 and 4. FIG. 4 shows a cross-sectional structure of the QCL 2 along a plane passing through the center of the QCL 2 in the Y-axis direction and parallel to the Z-axis direction. The QCL 2 has a rod shape. The QCL 2 can be formed as a ridge-stripe laser element by a typical semiconductor process. The QCL 2 can be obtained, for example, by forming InGaAs / InAlAs by epitaxial growth on an InP substrate (substrate 21, described later).

[0040] The QCL 2 has end faces 2a and 2b facing each other along the longitudinal direction, and emits light in a wide band in the mid-infrared region (e.g., 3 μm to 20 μm) from each of the end faces 2a and 2b. The end faces 2a and 2b are, for example, cleaved surface formed by cleavage. The end face 2a faces the second lens 6. The end face 2b faces the first lens 4. The end face 2b may be provided with a low-reflection coating that provides a reflectance of 5% or less at the wavelength corresponding to the gain peak of the QCL 2. In order to emit light in the wide band described above, the QCL 2 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.

[0041] 4, the QCL device 2 includes a substrate 21 and a semiconductor layer 10. The semiconductor layer 10 includes a lower cladding layer 11 (first cladding layer), an active layer 12, and an upper cladding layer 13 (second cladding layer). In this embodiment, the semiconductor layer 10 also includes an upper guide layer 14, a lower guide layer 15, an upper contact layer 16, and a lower contact layer 17.

[0042] The substrate 21 has a principal surface 21a and a back surface 21b opposite to the principal surface 21a. The principal surface 21a is the surface on which the active layer 12 is disposed. The back surface 21b is the surface facing the support surface 7a of the first holder 7 (see FIGS. 2 and 3). The substrate 21 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, width, and thickness of the substrate 21 are approximately several hundred μm to several mm, several hundred μm to several mm, and several hundred μm, respectively. The terahertz waves generated by difference frequency generation inside the active layer 12 are extracted to the outside (second lens 6) mainly via the substrate 21. From the viewpoint of increasing the extraction efficiency of the terahertz waves from the substrate 21 to the outside, the substrate 21 is preferably a semi-insulating substrate as described above, or a 1×10 17 cm -3 The substrate preferably has the following carrier density:

[0043] The substrate 21 has a side surface 21c connecting the principal surface 21a and the back surface 21b. The side surface 21c faces the light incident surface 61 of the second lens 6. In order to prevent the terahertz waves propagating inside the substrate 21 from being totally reflected at the cleaved substrate end surface (side surface 21c) and to increase the efficiency of extracting the terahertz waves to the outside, the side surface 21c is polished so as to be inclined at an angle θ1 shown in FIG. 4. Furthermore, in order to avoid deterioration of the oscillation characteristics of mid-infrared light, the polished inclined surface is configured so as not to reach the epitaxial growth layer (i.e., the semiconductor layer 10) including the active layer 12. More specifically, the side surface 21c has a first surface 21d, which is an inclined surface formed by polishing, and a second surface 21e, which remains unpolished.

[0044] The first surface 21d is connected to the back surface 21b and extends from the back surface 21b toward the main surface 21a. The first surface 21d is inclined with respect to the main surface 21a and the back surface 21b. The first surface 21d is inclined so as to move away from the end surface 2b as it moves from the back surface 21b toward the main surface 21a. The angle θ1 formed between the first surface 21d and the main surface 21a is, for example, approximately 30° to 80°. The first surface 21d is, for example, a polished surface formed by polishing a rectangular plate-shaped semiconductor substrate. A corner 21f connecting the first surface 21d and the back surface 21b is formed between the first surface 21d and the back surface 21b.

[0045] The second surface 21e is connected to the end of the first surface 21d on the principal surface 21a side and to the principal surface 21a. The second surface 21e is inclined with respect to the first surface 21d. The second surface 21e is approximately perpendicular to the principal surface 21a and the back surface 21b. A corner 21g connecting the second surface 21e and the principal surface 21a is formed between the second surface 21e and the principal surface 21a. A corner 21h connecting the first surface 21d and the second surface 21e is formed between the first surface 21d and the second surface 21e. Because the first surface 21d is an inclined surface as described above, the corner 21f is located closer to the end surface 2b than the corner 21h.

[0046] The semiconductor layer 10 is provided on the major surface 21a of the substrate 21. The semiconductor layer 10 has a side surface 10a. The side surface 10a is part of the end surface 2a of the QCL device 2. The side surface 10a is a flat surface. The side surface 10a is approximately perpendicular to the major surface 21a and the back surface 21b of the substrate 21. That is, in this embodiment, the side surface 10a is located on the same plane as the second surface 21e of the substrate 21. The thickness of the semiconductor layer 10 is approximately 10 μm to 20 μm.

[0047] The lower contact layer 17 is, for example, an InGaAs layer (Si doped: 1.5×10 18 cm -3 ) and is provided on the main surface 21a of the substrate 21. The lower cladding layer 11 is, for example, an InP layer (Si doped: 1.5×10 16 cm -3 ) and is provided on the surface of the lower contact layer 17. That is, the lower cladding layer 11 is provided on the main surface 21a of the substrate 21 via the lower contact layer 17. The lower guide layer 15 is, for example, an InGaAs layer (Si doped: 1.5×10 16 cm -3 ) and is provided on the surface of the lower clad layer 11 .

[0048] The active layer 12 has a quantum cascade structure and is provided on the surface of the lower guide layer 15. That is, the active layer 12 is provided on the side of the lower cladding layer 11 opposite to the substrate 21. The active layer 12 has end faces 12a (first end face) and 12b (second end face) that face each other in a direction D2 (second direction) perpendicular to a direction D1 (first direction) that is the stacking direction of the substrate 21 and the semiconductor layer 10. The end face 12a of the active layer 12 is part of the end face 2a of the QCL device 2 and the side face 10a of the semiconductor layer 10. The end face 12b of the active layer 12 is part of the end face 2b of the QCL device 2. As an example, the active layer 12 has a structure in which InGaAs layers and InAlAs layers are alternately stacked along the direction D1.

[0049] The upper guide layer 14 is, for example, an InGaAs layer (Si doped: 1.5×10 16 cm -3 ) and is provided on the surface of the active layer 12. The upper cladding layer 13 is, for example, an InP layer (Si doped: 1.5×10 16 cm -3 ) and is provided on the surface of the upper guide layer 14. In other words, the upper cladding layer 13 is provided on the opposite side of the active layer 12 from the lower cladding layer 11. The upper contact layer 16 is, for example, an InP layer (Si doped: 1.5×10 18 cm -3 ) and is provided on the surface of the upper clad layer 13 .

[0050] To generate a single-mode terahertz wave, it is necessary to simultaneously oscillate two single-mode wavelengths (both mid-infrared light) inside the QCL device 2. In this embodiment, the single-mode wavelength of one wavelength (corresponding to the second frequency ω2) is oscillated by a diffraction grating (described in detail below) provided inside the QCL device 2, and the single-mode wavelength of the other wavelength (corresponding to the first frequency ω1, which is different from the second frequency ω2) is oscillated by an external resonator (described in detail below). To oscillate the single-mode wavelength, the upper guide layer 14 is provided with a diffraction grating layer 14a that functions as a distributed feedback (DFB) structure along the direction D2 (i.e., the resonance direction) in which the end face 12a and the end face 12b face each other. The diffraction grating layer 14a oscillates in a single mode light of a wavelength (corresponding to the second frequency ω2) that is outside the wavelength at which the gain peak of the QCL device 2 occurs. The QCL device 2 is set in a state in which both the single-mode light due to the DFB and the Fabry-Perot mode have gain simultaneously. The light of the first frequency ω1 (hereinafter referred to as "first light") and the light of the second frequency ω2 (hereinafter referred to as "second light") are both mid-infrared light.

[0051] End facets 12a and 12b of active layer 12 form a resonator that oscillates the second light. Meanwhile, end facet 12a of active layer 12 and movable diffraction grating 31, which is an external resonator, form a resonator that oscillates the first light. As a result of oscillating the first light and the second light with this configuration, active layer 12 generates a terahertz wave 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 through Cherenkov phase matching.

[0052] The radiation direction A1 of the terahertz waves generated in this way is at a radiation angle θ with respect to the direction from end face 12b toward end face 12a along the resonance direction (direction D2) (the right direction in FIG. 4). C More specifically, the terahertz wave generated in the active layer 12 is inclined downward (toward the substrate 21) by a radiation angle θ (Cherenkov radiation angle) given by the following equation (1): C propagates as a plane wave (i.e., in phase) within the substrate 21. In the following formula (1), n MIR is the 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.

[0053] θ C =cos -1 (n MIR / n THz )…(1)

[0054] [Configuration of the terahertz wave output lens (second lens)] The second lens 6 is a lens for outputting the terahertz waves generated by the QCL element 2 to the outside. The second lens 6 passes the light emitted from the QCL element 2 (terahertz waves L1). The second lens 6 is, for example, a silicon lens formed in a hemispherical or hyperhemispherical shape. Silicon lenses are scratch-resistant. Even if the lens is scratched or soiled, terahertz waves, which have longer wavelengths than visible light and near-infrared light, are less susceptible to such damage. Therefore, the second lens 6 can be disposed so that it is exposed to the outside of the package 8.

[0055] In this embodiment, the second lens 6 is a hyper-hemispherical lens. The second lens 6 has a flat light incident surface 61 facing the end surface 2a of the QCL device 2 and a curved light exit surface 62 that emits the terahertz wave L1, which is output light, to the outside of the package 8. The lens diameter (diameter) of the second lens 6 is not limited to a specific range. However, if the second lens 6 is a hemispherical or hyper-hemispherical lens, the lens diameter is directly reflected in the lens thickness. Therefore, from the viewpoint of realizing a compact laser module 1A, the lens diameter of the second lens 6 is preferably 20 mm or less. The material of the second lens 6 is not limited to silicon. For example, the second lens 6 may be formed of other materials that transmit terahertz waves, such as Tsurupica. The light exit surface 62 of the second lens 6 may be provided with a low-reflection coating to reduce the reflectance of terahertz waves and increase the extraction efficiency of terahertz waves.

[0056] The second lens 6 is attached to a through-hole 85 provided in a side wall 822 of the package 8. The structure for attaching the second lens 6 to the through-hole 85 will be described in detail below.

[0057] As shown in FIG. 3, the through-hole 85 has a small-diameter hole 85a (first hole portion), a large-diameter hole 85b (second hole portion), and a countersunk surface 85c. The small-diameter hole 85a opens toward the inside of the package 8 in the optical axis direction of the second lens 6 (i.e., the X-axis direction). The large-diameter hole 85b opens toward the outside of the package 8 in the X-axis direction. When viewed from the X-axis direction, the large-diameter hole 85b includes the small-diameter hole 85a and has a shape larger than that of the small-diameter hole 85a. The small-diameter hole 85a and the large-diameter hole 85b each extend in the X-axis direction. In this embodiment, the small-diameter hole 85a and the large-diameter hole 85b are each formed in a circular shape, and the diameter of the large-diameter hole 85b is larger than the diameter of the small-diameter hole 85a. As an example, the central axes of the small-diameter hole 85a and the large-diameter hole 85b substantially coincide with the optical axis AX2 of the second lens 6 (see FIG. 6).

[0058] The counterbore surface 85c is an annular surface that connects the small diameter hole 85a and the large diameter hole 85b and extends along a plane (YZ plane) that intersects with the X-axis direction. More specifically, the counterbore surface 85c connects the end of the small diameter hole 85a facing the large diameter hole 85b with the end of the large diameter hole 85b facing the small diameter hole 85a. The large diameter hole 85b and the counterbore surface 85c can be formed by counterbore processing the side wall 822 from the outside of the package 8. Note that in this embodiment, the counterbore surface 85c is formed in a continuous annular shape, but the counterbore surface 85c may also be formed in a discontinuous annular shape. For example, a notch may be formed in a portion of the inner wall surface of the small diameter hole 85a, thereby dividing the counterbore surface 85c at the portion where the notch is formed. The small diameter hole 85a and the large diameter hole 85b connected by the counterbore surface 85c form a through hole 85 that penetrates in the X-axis direction.

[0059] The outer edge of the light incident surface 61 of the second lens 6 is inserted into the large-diameter hole 85b from the outside of the package 8 and is fixed in surface contact with the counterbore surface 85c. The outer edge of the light incident surface 61 is fixed to the counterbore surface 85c, for example, with a fixing resin, an adhesive, or the like. The second lens 6 attached to the through-hole 85 of the sidewall 822 in this manner functions to receive the terahertz waves L1 output from the QCL element 2 at the light incident surface 61, collimate the terahertz waves L1 into a beam, and extract the waves L1 to the outside of the package 8 from the light exit surface 62. The second lens 6 also functions to maintain the airtightness of the inside of the package 8. According to the above configuration, the second lens 6 for outputting terahertz waves can be attached to the sidewall 822 from the outside of the package 8, facilitating the attachment of the second lens 6. The second lens 6 can also be used as a window material for covering the through-hole 85 provided in the package 8 (sidewall 822). As a result, the number of parts can be reduced, thereby reducing manufacturing costs and miniaturizing the entire package. Furthermore, since optical loss (i.e., attenuation of the terahertz waves L1 due to passing through a window material other than the second lens 6) caused by providing a window material other than the second lens 6 can be avoided, it is also possible to achieve high output of the terahertz waves L1. Furthermore, according to the above-described method for attaching the second lens 6, it is possible to easily and accurately fix the hemispherical or hyperhemispherical second lens 6, which does not have a thick edge to hold the lens from the side.

[0060] [Positional relationship between the QCL element and the second lens] Next, the positional relationship between the QCL 2 and the second lens 6 will be described. As shown in FIGS. 3 and 5, the QCL 2 and the second lens 6 are arranged so that a portion of the side surface 21c of the substrate 21 of the QCL 2 is in contact with approximately the center of the light incident surface 61 of the second lens 6. For this reason, the QCL 2 is arranged at an angle with respect to the optical axis direction (X-axis direction) of the second lens 6. As a result, the QCL 2 and the second lens 6 are arranged so that the end surface 12a of the active layer 12 and the light incident surface 61 are spaced apart, and only a portion of the side surface 21c of the substrate 21 is in contact with the light incident surface 61. As an example, as shown in FIG. 5, a corner 21h of the side surface 21c is in line contact with the light incident surface 61. Alternatively, a first surface 21d, which is an inclined surface of the side surface 21c, may be in surface contact with the light incident surface 61. By separating the end surface 12a of the active layer 12 from the light incident surface 61 in this manner, it is possible to prevent the oscillation characteristics of mid-infrared light at the end surface 12a from being affected. The inclination angle θ of the QCL element 2 with respect to the optical axis direction (X-axis direction) of the second lens 6 Q (See FIG. 5) is, for example, the radiation angle θ of the terahertz wave L1 generated inside the QCL element 2. C (see FIG. 4) For example, the QCL element 2 may be tilted with respect to the second lens 6 so that the radiation direction A1 (see FIG. 4) of the terahertz wave L1 generated inside the QCL element 2 and the optical axis direction (X-axis direction) of the second lens 6 roughly coincide with each other.

[0061] The resonance axis (axis along the resonance direction (direction D2)) passing through end face 12a and end face 12b of QCL element 2 intersects with the optical axis AX2 of second lens 6 because support surface 7a is inclined so as to intersect with optical axis AX2 of second lens 6 (i.e., because QCL element 2 is placed on inclined support surface 7a). End face 12a is spaced apart from light incident surface 61 of second lens 6, and first lens 4 is disposed so that the optical axis AX1 of first lens 4 substantially coincides with the resonance axis. With the above configuration, end face 12a constituting the resonator of the first light and the second light for generating terahertz wave L1 can be spaced apart from light incident surface 61 of second lens 6, while QCL element 2 (for example, side surface 21c of substrate 21 continuous with end face 12a) can be brought into contact with or close to light incident surface 61 of second lens 6. This prevents the reflectivity of the end face 12a, which is important in oscillating the first light and the second light, from being affected by the second lens 6 (i.e., the reflection characteristics of the end face 12a are changed due to the end face 12a coming into contact with the light incident surface 61 of the second lens 6), while ensuring the extraction efficiency of the terahertz wave L1 from the QCL element 2 to the second lens 6.

[0062] From the viewpoint of efficiently introducing the terahertz wave L1 into the second lens 6, it is preferable that the focal point of the second lens 6 is located inside the QCL device 2. By partially contacting the second lens 6 and the QCL device 2 (substrate 21) in this manner, the influence of the refractive index of the air present between them (i.e., optical loss due to reflection at the interface with air) is reduced. As a result, the terahertz wave L1 emitted from the QCL device 2 can be efficiently introduced into the second lens 6, and the output of the terahertz wave L1 can be increased. Furthermore, the spread of the terahertz wave L1 emitted by the second lens 6 can be suppressed, and an output with an appropriate beam shape can be obtained.

[0063] [External cavity configuration] The first lens 4 and the movable diffraction grating 31 (diffraction grating unit) form an external resonator that oscillates the above-mentioned first light (light of the first frequency ω1). That is, the first light travels back and forth between the end surface 12a of the active layer 12 and the movable diffraction grating 31 (specifically, the diffraction grating section 314, which will be described later) via the first lens 4, thereby amplifying the first light. From the viewpoint of miniaturizing the laser module 1A and reducing light loss, it is preferable that the first lens 4 and the movable diffraction grating 31 be disposed as close as possible to each other within the package 8 without causing interference between the components.

[0064] (Configuration of the external cavity lens (first lens)) The first lens 4 is a lens for an external resonator and transmits mid-infrared light. The first lens 4 may be formed of, for example, zinc selenide (ZnSe). The first lens 4 is, for example, an aspherical lens with a working distance of 3 mm or less. From the viewpoint of increasing the efficiency as an external resonator, the first lens 4 is preferably configured with a working distance of 1 mm or less and a numerical aperture of 0.6 or more. The first lens 4 is disposed between the QCL element 2 and the movable diffraction grating 31, and transmits light (mid-infrared light) emitted from the end face 12b and light (mid-infrared light) returning from the movable diffraction grating 31 to the QCL element 2.

[0065] The first lens 4 has a first lens surface 41 and a second lens surface 42. The first lens 4 is, for example, an aspherical lens. The first lens surface 41 faces the end surface 2b of the QCL 2 (the end surface 12b of the active layer 12). The first lens surface 41 may be a flat surface or a non-flat surface (for example, a curved surface convex toward the QCL 2). The second lens surface 42 is a curved surface facing the movable diffraction grating 31 on the opposite side to the first lens surface 41. The first lens surface 41 and the second lens surface 42 may be provided with a low-reflection coating that has a reflectance of 5% or less at the wavelength corresponding to the gain peak of the QCL 2. The first lens 4 may be made of a material that transmits mid-infrared light, such as Ge or CaF2.

[0066] The first lens 4 is fixed to the lens holder 5 so that the optical axis AX1 (see FIG. 6) of the first lens 4 and the resonance axis of the QCL element 2 (i.e., the axis parallel to the direction D2 passing through the end faces 12a and 12b of the active layer 12, and the optical axis of the mid-infrared light emitted by the QCL element 2) substantially coincide with each other. That is, the first lens 4 and the movable diffraction grating 31 are arranged so as to be inclined with respect to the horizontal plane (XY plane) in the same manner as the QCL element 2. That is, the radiation direction A1 of the terahertz wave L1 and the resonance direction (direction D2) of the external resonator are not collinear but intersect with each other.

[0067] The first lens 4 is held by a lens holder 5. As an example, the lens holder 5 has a substantially rectangular parallelepiped outer shape. The lens holder 5 has a small diameter hole 5a, a large diameter hole 5b, and a counterbore surface 5c. The small diameter hole 5a opens toward the QCL element 2 in the optical axis direction (direction D2) of the first lens 4. The large diameter hole 5b opens toward the movable diffraction grating 31 in direction D2. When viewed from direction D2, the large diameter hole 5b has a shape that includes the small diameter hole 5a and is larger than the small diameter hole 5a. The small diameter hole 5a and the large diameter hole 5b each extend in direction D2. The small diameter hole 5a and the large diameter hole 5b are each formed in a circular shape, and the diameter of the large diameter hole 5b is larger than the diameter of the small diameter hole 5a. As an example, the central axis of the small diameter hole 5a and the central axis of the large diameter hole 5b substantially coincide with the optical axis AX1 of the first lens 4. Counterbore surface 5c is an annular surface that connects small diameter hole 5a and large diameter hole 85b and extends along a plane that intersects with direction D2. More specifically, counterbore surface 5c connects the end of small diameter hole 5a facing large diameter hole 5b with the end of large diameter hole 5b facing small diameter hole 5a. The outer edge of first lens surface 41 of first lens 4 is inserted into large diameter hole 5b and is fixed in surface contact with counterbore surface 5c. The outer edge of first lens surface 41 is fixed to counterbore surface 5c with, for example, an adhesive resin, an adhesive, or the like.

[0068] (Structure of the diffraction grating unit) The diffraction grating unit 3 is disposed on the opposite side of the first lens 4 (lens holder 5) from the side on which the QCL element 2 is disposed. The diffraction grating unit 3 includes a movable diffraction grating 31, a magnet 32, and a yoke 33. The movable diffraction grating 31 is formed in a substantially plate shape. The movable diffraction grating 31 is, for example, a MEMS diffraction grating fabricated using an MEMS process. The movable diffraction grating 31 is not limited to a specific configuration. For example, the movable diffraction grating 31 may be an electrostatically driven type that can fix the diffraction grating angle at any angle, or an electromagnetically driven type that can perform high-frequency angle modulation at a resonant frequency. The magnet 32 ​​is disposed on the opposite side of the movable diffraction grating 31 from the QCL element 2. The movable diffraction grating 31 is fixed to the yoke 33, and the magnet 32 ​​is housed within the yoke 33. In this way, the movable diffraction grating 31, the magnet 32, and the yoke 33 are integrated and form a single unit.

[0069] The light collimated by the first lens 4 is incident on the movable diffraction grating 31. The movable diffraction grating 31 diffracts and reflects the incident light, thereby feeding back light of a specific wavelength from the incident light to the end face 2b (end face 12b of the active layer 12) of the QCL device 2 via the first lens 4. In this embodiment, the movable diffraction grating 31 and the end face 2b form a Littrow-type external resonator.

[0070] Furthermore, the movable diffraction grating 31 can rapidly change the orientation of the diffraction grating portion 314 (see FIG. 7) that diffracts and reflects incident light. This allows the wavelength of the light (i.e., the wavelength corresponding to the first frequency ω1) that is fed back from the movable diffraction grating 31 to the end face 12b of the QCL element 2 to be variable. In other words, it is possible to change the wavelength of the terahertz wave L1 generated by difference frequency generation between the first frequency ω1 and the second frequency ω2. This allows wavelength sweeping within the gain band of the QCL element 2.

[0071] 7, the movable diffraction grating 31 includes a support portion 311, a pair of connecting portions 312, a movable portion 313, a diffraction grating portion 314, and a coil 315. The movable diffraction grating 31 is configured as an MEMS device that oscillates the movable portion 313 around an axis A that passes through the pair of connecting portions 312. The axis A is an axis parallel to the Y-axis direction.

[0072] The support part 311 is a flat frame body having a rectangular shape in a plan view. The support part 311 supports the movable part 313 via a pair of connecting parts 312. Each connecting part 312 is a flat member having a rectangular rod shape in a plan view, and extends straight along the axis A. Each connecting part 312 connects the movable part 313 to the support part 311 on the axis A so that the movable part 313 can swing freely around the axis A.

[0073] The movable portion 313 is located inside the support portion 311. As described above, the movable portion 313 is capable of swinging around the axis A. The movable portion 313 is a flat plate-like member that is substantially rectangular in plan view. The support portion 311, the connecting portion 312, and the movable portion 313 are integrally formed by being built into, for example, a single SOI (Silicon on Insulator) substrate.

[0074] A diffraction grating section 314 is provided on the surface (mirror surface) of the movable section 313 facing the QCL element 2. The diffraction grating section 314 has a plurality of grating grooves (not shown) and diffracts and reflects the light emitted from the QCL element 2. The diffraction grating unit 3 is arranged so that the optical axis AX1 of the first lens 4 (i.e., the optical axis of the mid-infrared light collimated by the first lens 4) substantially coincides with the center of the diffraction grating section 314, and light incident on the diffraction grating section 314 is diffracted along the same optical axis AX1 in the direction opposite to the incident direction.

[0075] The diffraction grating unit 314 includes, for example, a resin layer on the surface of the movable unit 313 on which a diffraction grating pattern is formed and a metal layer provided on the surface of the resin layer so as to follow the diffraction grating pattern. Alternatively, the diffraction grating unit 314 may be formed only by a metal layer provided on the movable unit 313 and on which a diffraction grating pattern is formed. Examples of the diffraction grating pattern that can be used include a blazed grating with a sawtooth cross section, a binary grating with a rectangular cross section, and a holographic grating with a sinusoidal cross section. The diffraction grating pattern is formed on the resin layer by, for example, nanoimprint lithography. The metal layer is, for example, a metal reflective film made of gold and formed by vapor deposition. The period and depth of the grating grooves in the diffraction grating unit 314 are configured, for example, to maximize the diffraction efficiency for the wavelength corresponding to the gain peak of the QCL device 2. Here, the diffraction efficiency refers to the efficiency when light incident on the diffraction grating unit 314 is diffracted in opposite directions along the same optical axis. From the viewpoint of realizing a compact laser module 1A, the size of the diffraction grating section 314 (mirror surface) is preferably large enough to include a circular area with a diameter of 1 mm to 15 mm.

[0076] Coil 315 is made of a metal material such as copper, and has a damascene structure embedded in a groove formed in the surface of movable part 313. Coil 315 is a drive coil that passes a current to drive movable diffraction grating 31 (i.e., to oscillate movable part 313).

[0077] The magnet 32 ​​generates a magnetic field (magnetic force) that acts on the coil 315. The magnet 32 ​​is a neodymium magnet (permanent magnet) formed in a substantially rectangular parallelepiped shape.

[0078] The yoke 33 amplifies the magnetic force of the magnet 32 ​​and forms a magnetic circuit together with the magnet 32. The surface of the yoke 33 is blackened, for example, by zinc plating. The yoke 33 has an inclined surface 33a, a lower surface 33b, and a protrusion 33c.

[0079] Inclined surface 33a is inclined with respect to end surface 2b of QCL element 2. By fixing movable diffraction grating 31 on such inclined surface 33a, the normal direction of diffraction grating portion 314 of movable diffraction grating 31 can be inclined with respect to end surface 2b. The inclination angle of inclined surface 33a (the angle with respect to end surface 2b of QCL element 2) is set depending on the oscillation wavelength of QCL element 2, the number of grating grooves in diffraction grating portion 314, the blazed angle, etc.

[0080] The yoke 33 is formed in a generally U-shape (inverted C-shape) when viewed from the Y-axis direction, and defines an arrangement space SP that opens to an inclined surface 33a. The magnet 32 ​​is arranged in this arrangement space SP, and the magnet 32 ​​is housed within the yoke 33. The movable diffraction grating 31 is fixed to the inclined surface 33a at the edge of the support portion 311 so as to cover the opening of the arrangement space SP.

[0081] In the movable diffraction grating 31, when a current flows through the coil 315, a Lorentz force is generated in a predetermined direction on electrons flowing through the coil 315 due to the magnetic field formed by the magnet 32 ​​and the yoke 33. As a result, the coil 315 is subjected to a force in the predetermined direction. Therefore, by controlling the direction or magnitude of the current flowing through the coil 315, the movable part 313 (diffraction grating part 314) can be oscillated around the axis A. Furthermore, by passing a current of a frequency corresponding to the resonant frequency of the movable part 313 through the coil 315, the movable part 313 can be oscillated at high speed at the resonant frequency level (for example, at a frequency of 1 kHz or higher).

[0082] [Configuration of the first holder] Next, the configuration of the first holder 7 will be described, mainly with reference to FIGS. 3 and 6. The first holder 7 is a member that holds (supports) the QCL element 2 within the package 8. The first holder 7 also functions as a heat sink to suppress heat generation from the QCL element 2 when the QCL element 2 is driven. The first holder 7 can be formed, for example, from a material that has good thermal conductivity, can be precisely machined, and has sufficient hardness and rigidity to maintain its shape. The first holder 7 can be formed, for example, from the same metal material as the bottom wall 81, such as copper-tungsten.

[0083] In this embodiment, in addition to the QCL element 2, the first lens 4 (lens holder 5) and the diffraction grating unit 3 are also fixed to the first holder 7. That is, the first holder 7 supports all components required to configure an external resonator for oscillating the first light. With the above configuration, before housing the QCL element 2, the first lens 4 (lens holder 5), and the diffraction grating unit 3 in the package 8, these components can be fixed to the first holder 7 and their positions can be adjusted (positioned) relative to each other. That is, the QCL element 2, the first lens 4 (lens holder 5), and the diffraction grating unit 3 can be mounted on the first holder 7 while performing the above-described position adjustment, and then the first holder 7 can be housed in the package 8. This improves work efficiency compared to when the positions of the components are adjusted within the package 8.

[0084] The first holder 7 is fixed onto the bottom wall 81 inside the package 8. For example, the bottom surface 7b of the first holder 7 is fixed to the bottom wall 81 with an adhesive or the like. However, as described above, another member such as a Peltier element may be interposed between the first holder 7 and the bottom wall 81. Furthermore, the first holder 7 may be attached to a portion other than the bottom wall 81 (for example, the side wall 82).

[0085] The first holder 7 has, in order from the side where the second lens 6 is disposed, a support surface 7a on which the QCL element 2 is mounted, a support surface 7c on which the lens holder 5 is mounted, and a support surface 7d on which the diffraction grating unit 3 is mounted along the direction D2. These support surfaces 7a, 7c, and 7d are inclined so as to be parallel to the resonance direction (direction D2) of the external resonator. By arranging each component (the QCL element 2, the lens holder 5, and the diffraction grating unit 3) on each of the inclined support surfaces 7a, 7c, and 7d in this manner, the positional relationship between each component constituting the external resonator can be appropriately determined. With the upper surface of the bottom wall 81 as a reference, the support surface 7a is positioned higher than the support surface 7c, which is positioned higher than the support surface 7d. Steps are formed between the support surfaces 7a and 7c and between the support surfaces 7c and 7d.

[0086] The first holder 7 has a side surface 7e (first side surface) connecting the support surface 7a and the support surface 7c, and a side surface 7f connecting the support surface 7c and the support surface 7d. The side surfaces 7e and 7f are perpendicular to the direction D2. The side surface 7e faces the first lens 4 (lens holder 5) in the direction D2. The lens holder 5 is placed on the support surface 7c so as to be spaced apart from the side surface 7e. The side surface 7f abuts against the side surface of the yoke 33 facing the lens holder 5, and serves to position the yoke 33. The support surface 7d is formed with a recess 7g into which a protrusion 33c provided on the lower surface 33b of the yoke 33 is inserted. The diffraction grating unit 3 is fixed to the support surface 7d by fitting the protrusion 33c into the recess 7g.

[0087] The bottom surface 5d of the lens holder 5 is fixed to the support surface 7c via an adhesive layer B1. The adhesive layer B1 is, for example, a photocurable resin. The lens holder 5 is fixed to the support surface 7c so that the optical axis AX1 of the first lens 4 and the resonance axis of the QCL element 2 (the optical axis of the mid-infrared light emitted from the end surface 12b) coincide with each other. For example, the height position of the lens holder 5 relative to the support surface 7c can be finely adjusted by adjusting the amount of the adhesive layer B1, the strength with which the lens holder 5 is pressed against the adhesive layer B1, and the like. However, the method of fixing the lens holder 5 to the support surface 7c is not limited to the above. For example, the lens holder 5 may be fixed to the support surface 7c by screws or the like.

[0088] Mid-infrared light having a relatively large divergence angle is emitted from the end face (end face 12b) of the QCL element 2 on the first lens 4 side. Therefore, from the viewpoint of preventing such mid-infrared light from being blocked by the first holder 7 (mainly the support surface 7a) and avoiding a decrease in the coupling efficiency of the external cavity, the laser module 1A is configured as follows. That is, when viewed from the Y-axis direction (a direction orthogonal to the directions D1 and D2), if the direction from the first lens 4 toward the QCL element 2 along the direction D2 is defined as the positive direction, a distance d1 (first distance) from an intersection 7i of the side face 7e and the support surface 7a along the direction D2 to the end face 12b is smaller than a distance d2 (second distance) between the intersection 7i along the direction D2 and the first lens 4 (first lens surface 41). In this embodiment, the end face 2b of the QCL element 2, including the end face 12b of the active layer 12, is flush with the side face 7e. That is, the distance d1 is zero. When end face 2b is located closer to second lens 6 than intersection point 7i in direction D2, distance d1 is greater than 0, and when end face 2b protrudes closer to first lens 4 than intersection point 7i in direction D2, distance d1 is less than 0. Note that when first lens surface 41 is a non-flat surface (i.e., when the distance between intersection point 7i and first lens surface 41 varies along the Y-axis direction), distance d2 is the minimum value of the distance between intersection point 7i and first lens surface 41 (i.e., the distance between intersection point 7i and the portion of first lens surface 41 that is closest to intersection point 7i along direction D2).

[0089] The first holder 7 has a side surface 7h (second side surface) that is connected to the support surface 7a and faces the light incident surface 61 of the second lens 6 in the direction D2. The end surface 2a of the QCL element 2 facing the second lens 6 (the end surface including the end surface 12a of the active layer 12) is located closer to the second lens 6 than the side surface 7h in the direction D2. According to the above configuration, by making the end surface 12a of the QCL element 2 protrude toward the second lens 6 beyond the side surface 7h of the first holder 7, it is possible to bring the end surface 12a of the QCL element 2 into contact with or close to the second lens 6 for outputting terahertz waves while suppressing interference between the first holder 7 and the second lens 6.

[0090] In this embodiment, the first holder 7 has a main body 71 including a portion 71a (see FIG. 7) of the support surface 7a facing the first lens 4 and a side surface 7e, and a protrusion 72 connected to the main body 71. In this embodiment, the protrusion 72 is a portion formed in a tapered shape toward the second lens 6 in a plan view, as shown in FIG. 7. The protrusion 72 includes a portion 72a of the support surface 7a facing the second lens 6, and also includes the above-mentioned side surface 7h.

[0091] As shown in FIG. 3 , the end face 12a of the active layer 12 of the QCL element 2 is located inside the small-diameter hole 85a in the sidewall 822. With the above configuration, the end face 12a of the QCL element 2 can be extended into the small-diameter hole 85a, allowing the substrate 21 of the QCL element 2 to contact or be close to (in this embodiment, in contact with) the light incident surface 61 of the second lens 6. This improves the extraction efficiency of the terahertz wave L1 and reduces the overall size of the package. More specifically, by bringing the QCL element 2 and the second lens 6 closer together, the size of the second lens 6 required to collimate the terahertz wave L1 can be reduced, thereby reducing the overall size of the laser module 1A.

[0092] Furthermore, at least a portion of the protrusion 72 is located inside the small-diameter hole 85a. That is, the protrusion 72 is partially inserted into the small-diameter hole 85a. According to the above configuration, by extending the first holder 7 (protrusion 72) into the small-diameter hole 85a, the contact area between the QCL element 2 and the first holder 7 (support surface 7a) can be increased. As a result, the efficiency of heat dissipation from the QCL element 2 to the first holder 7 can be improved.

[0093] Furthermore, the first width of the protrusion 72 in a width direction (i.e., the Y-axis direction) (fourth direction) perpendicular to the directions D1 and D2 is smaller than the width of the main body 71 in the width direction. As shown in FIG. 7, the protrusion 72 is formed in a shape such that the width of the protrusion 72 gradually decreases as it approaches the second lens 6 along the direction D2. In the present embodiment, as an example, the protrusion 72 is formed in a tapered shape that narrows in a plan view. According to the above configuration, by making the width of the protrusion 72 smaller than the width of the main body 71, it is possible to prevent interference between the first holder 7 and the package 8 (side wall 822) while ensuring the volume of the first holder 7 that functions as a heat bath. Furthermore, by forming the protrusion 72 in a tapered shape as described above, the risk of interference (contact) between the protrusion 72 and the side wall 822 (mainly the inner surface of the small diameter hole 85a) can be effectively reduced when the first holder 7 carrying the QCL element 2 is accommodated and positioned within the package 8, and the volume of the first holder 7 that functions as a heat bath (the volume of the portion of the first holder 7 that is close to the QCL element 2) can be made sufficiently large.

[0094] The laser module 1A is manufactured, for example, as follows. First, the second lens 6 is attached to the through-hole 85 of the package 8 before the top wall 83 is attached. Next, the QCL element 2, the first lens 4 (lens holder 5), and the diffraction grating unit 3 are attached to the first holder 7 outside the package 8. At this time, the positions of the QCL element 2, the first lens 4 (lens holder 5), and the diffraction grating unit 3 are adjusted so that the resonance axis of the QCL element 2 and the optical axis AX1 of the first lens 4 coincide with each other and the optical axis AX1 passes through the center of the diffraction grating portion 314. Next, the first holder 7 on which the components are mounted as described above is housed in the package 8. The first holder 7 is fixed in the package 8 so that a portion of the side surface 21c of the substrate 21 of the QCL element 2 contacts (or is close to) the approximate center of the light incident surface 61 of the second lens 6. Next, among the components housed in the package 8, those that require an electrode supply (such as the QCL element 2) are electrically connected to the electrode terminals (lead terminals 9) by wires or the like (not shown). After the arrangement and wiring of the components inside the package 8 are completed, the inside of the package 8 is purged with a vacuum or nitrogen, and a top wall 83 is airtightly joined to an end 82a of the side wall 82 opposite to the bottom wall 81. In this way, the above-described laser module 1A is obtained.

[0095] The laser module 1A described above packages a configuration for oscillating the first light and the second light required to generate the terahertz wave L1 by difference frequency generation, namely, the QCL element 2, the first holder 7 that holds the QCL element 2, the movable diffraction grating 31 (diffraction grating unit 3), and the first lens 4. When viewed from the Y-axis direction, the direction from the first lens 4 to the QCL element 2 along direction D2 (i.e., resonance direction) in which both end faces (end faces 12a and 12b) of the QCL element 2 face each other is defined as the positive direction. In this case, the distance d1 (zero in this embodiment) along direction D2 from an intersection 7i of a side surface 7e of the first holder 7 and the support surface 7a to end face 12b is smaller than the distance d2 between the intersection 7i and the first lens 4 (first lens surface 41) along direction D2 (see FIG. 6 ). Here, as the distance from the end face 12b, from which the mid-infrared light is emitted, to the first lens 4 (first lens surface 41) increases, the size of the first lens 4 (first lens surface 41) required to allow a sufficient amount of mid-infrared light having a divergence angle to enter increases. Furthermore, since the range of mid-infrared light collimated by the first lens 4 also increases, the area of ​​the movable diffraction grating 31 (diffraction grating portion 314) that receives the collimated mid-infrared light must be increased accordingly. As a result, the size of the movable diffraction grating 31 also increases. On the other hand, by arranging the QCL element 2 and the first holder 7 in this manner, the QCL element 2 (end face 12b) can be brought as close as possible to the first lens 4. This prevents the first lens 4 and the movable diffraction grating 31 from becoming larger, thereby enabling the overall package 8 to be made smaller. Furthermore, by setting the distance d1 to a small value as described above, it is possible to suppress interference between the light (mid-infrared light) emitted from the end face 12b and the first holder 7 (i.e., a part of the emitted light is blocked by the first holder 7 and does not reach the first lens 4). This reduces the loss of light that contributes to the generation of terahertz waves. As a result, it is possible to obtain a laser module 1A that is packaged in a manner that allows miniaturization and suppresses the loss of light that contributes to the generation of terahertz waves. For example, if the laser module 1A is packaged in a manner that allows miniaturization and suppresses the loss of light that contributes to the generation of terahertz waves, the laser module 1A can be packaged in a manner that allows miniaturization and suppresses the loss of light that contributes to the generation of terahertz waves. 3In the laser module 1A, a current equal to or greater than the threshold is injected into the QCL element 2, and the angle of the movable diffraction grating 31 is changed by external control, thereby generating a single-mode terahertz wave L1 with a variable wavelength.

[0096] Furthermore, in laser module 1A, distance d1 may be equal to or less than 0. According to the above configuration, that is, the configuration in which end face 12b is flush with side face 7h (the configuration of this embodiment) or the configuration in which end face 12b protrudes further toward first lens 4 than side face 7h, interference between the light emitted from end face 12b and first holder 7 can be more reliably prevented, and therefore loss of light that contributes to generation of terahertz waves can be more effectively reduced.

[0097] Furthermore, in the configuration of this embodiment where the distance d1 is equal to 0 (i.e., the end face 12b and the side face 7h are flush), the entire portion extending to the end face 12b of the QCL element 2 can be brought into contact with the first holder 7 (support surface 7a), thereby improving the heat dissipation efficiency from the QCL element 2 to the first holder 7.

[0098] [Second embodiment] A laser module 1B according to the second embodiment will be described with reference to Figures 8 and 9. In Figure 9, in order to clearly show the positional relationship of the main components housed in the package 8, the top wall 83, the protruding wall 84, and the lead terminals 9 are not shown.

[0099] The laser module 1B differs from the laser module 1A mainly in that a terahertz wave output lens (second lens 6) is housed inside the package 8. The laser module 1B includes a second holder 100 that holds the second lens 6 inside the package 8. That is, in the laser module 1B, the second lens 6 and the second holder 100 are housed inside the package 8. Furthermore, in place of the second lens 6, a light exit window 200, which is a window material separate from the second lens 6, is provided in the through hole 85 of the side wall 822.

[0100] The second holder 100 has a substantially rectangular parallelepiped outer shape. The second holder 100 is fixed to the bottom wall 81 between the first holder 7 and a side wall 822 having a through-hole 85 formed therein by means of adhesive resin, adhesive, screws, or the like. However, the shape and fixing method of the second holder 100 are not limited to those described above. For example, the second holder 100 may be fixed to a side wall 82 (e.g., a pair of side walls 821 located on both sides of the second holder 100) instead of the bottom wall 81. The second holder 100 may be formed, for example, from a material that can be precisely machined and has sufficient hardness and rigidity to maintain its shape. The second holder 100 may be formed, for example, from a metal such as aluminum, stainless steel, or copper, or from a hard plastic.

[0101] The second holder 100 is provided with a through-hole 101 that penetrates in a direction perpendicular to the sidewall 822 (i.e., the X-axis direction) (third direction). The second lens 6 is attached to the through-hole 101. The through-hole 101 has a small-diameter hole 101a (first hole portion), a large-diameter hole 101b (second hole portion), and a counterbore surface 101c. The small-diameter hole 101a opens toward the QCL element 2 in the optical axis direction of the second lens 6 (i.e., the X-axis direction). The large-diameter hole 101b opens toward the sidewall 822 in which the through-hole 85 is provided in the X-axis direction. When viewed from the X-axis direction, the large-diameter hole 101b includes the small-diameter hole 101a and has a shape that is larger than the small-diameter hole 101a. The small-diameter hole 101a and the large-diameter hole 101b each extend in the X-axis direction. In this embodiment, each of the small diameter hole 101a and the large diameter hole 101b is formed in a circular shape, and the diameter of the large diameter hole 101b is larger than the diameter of the small diameter hole 101a. As an example, the central axis of the small diameter hole 101a and the central axis of the large diameter hole 101b substantially coincide with the optical axis AX2 of the second lens 6 (see FIG. 6).

[0102] The counterbore surface 101c is an annular surface that connects the small diameter hole 101a and the large diameter hole 101b and extends along a plane (YZ plane) that intersects with the X-axis direction. More specifically, the counterbore surface 101c connects the end of the small diameter hole 101a facing the large diameter hole 101b with the end of the large diameter hole 101b facing the small diameter hole 101a. The large diameter hole 101b and the counterbore surface 101c can be formed by counterbore processing the second holder 100 from the side opposite the QCL element 2 side of the second holder 100. In this embodiment, the counterbore surface 101c is formed as a continuous annular surface, but the counterbore surface 101c may also be formed as a discontinuous annular surface. For example, a notch may be formed in a portion of the inner wall surface of the small diameter hole 101a, thereby dividing the counterbore surface 101c at the portion where the notch is formed. The small diameter hole 101a and the large diameter hole 101b connected by the counterbore surface 101c form a through hole 101 that penetrates in the X-axis direction.

[0103] The outer edge of the light incident surface 61 of the second lens 6 is inserted into the large diameter hole 101b from the side of the sidewall 822 where the through hole 85 is provided, and is fixed in surface contact with the countersunk surface 101c. The outer edge of the light incident surface 61 is fixed to the countersunk surface 101c with, for example, a fixing resin, an adhesive, or the like. With the above configuration, the second lens 6 for outputting terahertz waves can be attached to the second holder 100 from the outside of the second holder 100 (the side opposite to the side where the QCL element 2 is arranged), which makes it easy to attach the second lens 6.

[0104] The height position of the through hole 101 in the second holder 100 is set so that the optical axis AX2 of the second lens 6 attached to the through hole 101 and the center of the light exit window 200 provided in the through hole 85 approximately coincide (i.e., coincide within the range of mechanical accuracy).

[0105] 8 and 9, the height (length in the Z-axis direction) and width (length in the Y-axis direction) of the second holder 100 are smaller than the internal dimensions (height, width) of the package 8. However, the height and width of the second holder 100 may be set to be approximately equal to the internal dimensions of the package 8. That is, the second holder 100 may be configured to separate, within the package 8, a first space on the side of the sidewall 822 where the through-hole 85 is provided, from a second space on the side of the second holder 100 on the QCL element 2 side. This allows the second holder 100 to prevent scattered components of mid-infrared light (components that do not contribute to external resonance) generated in the second space from entering the first space due to reflection, etc., within the package 8. As a result, it is possible to suppress the generation of the scattered components (stray light) emitted to the outside of the package 8 through the light exit window 200.

[0106] The light exit window 200 is formed in, for example, a disk shape. The light exit window 200 is attached to the through-hole 85, for example, similar to the second lens 6 in the first embodiment. That is, the outer edge of the surface of the light exit window 200 facing the sidewall 822 is inserted into the large-diameter hole 85b from the outside of the package 8 and is fixed in surface contact with the counterbore surface 85c. The light exit window 200 is sealed to the counterbore surface 85c to maintain airtightness inside the package 8. The light exit window 200 is made of any material that transmits terahertz waves, such as silicon, Tsurupica, or polyethylene. A low-reflection coating may be provided on both surfaces (outer and inner surfaces) of the light exit window 200 to reduce reflection of terahertz waves.

[0107] According to the laser module 1B described above, the second lens 6 for outputting the terahertz wave can be housed in the package in the same way as the first lens 4, so that the second lens 6 can be prevented from being damaged or contaminated.

[0108] Furthermore, in the laser module 1B, the second holder 100 is a separate member from the first holder 7 and is fixed to the package 8 independently of the first holder 7. According to the above configuration, since the first holder 7 and the second holder 100 are independent, the work of attaching the QCL element 2 and the like to the first holder 7 and the work of attaching the second lens 6 to the second holder 100 can be performed in parallel before the respective members are housed in the package 8. This improves the efficiency of the assembly of the laser module 1B.

[0109] Furthermore, in laser module 1B, similar to laser module 1A, end face 12a of active layer 12 of QCL element 2 is located inside small diameter hole 101a of second holder 100. According to the above configuration, end face 12a of QCL element 2 can be advanced into small diameter hole 101a, and substrate 21 of QCL element 2 can be brought into contact with or close to (contact in this embodiment) light incident surface 61 of second lens 6. This improves the extraction efficiency of terahertz wave L1 and reduces the size of the entire package.

[0110] Furthermore, at least a portion of the protrusion 72 of the first holder 7 is located inside the small diameter hole 101a of the second holder 100. According to the above configuration, by extending the first holder 7 (protrusion 72) into the small diameter hole 101a, the contact area between the QCL element 2 and the first holder 7 (support surface 7a) can be increased. As a result, the efficiency of heat dissipation from the QCL element 2 to the first holder 7 can be improved.

[0111] [Third embodiment] A laser module 1C according to the third embodiment will be described with reference to Figures 10 and 11. In Figure 11, in order to clearly illustrate the positional relationship of the main components housed in the package 8, the top wall 83, the protruding wall 84, and the lead terminals 9 are not shown.

[0112] The laser module 1C differs from the laser module 1B mainly in that the second holder 100 is fixed to the first holder. The laser module 1C has a first holder 7A instead of the first holder 7. The first holder 7A differs from the first holder 7 in that it has an extension portion 73 that extends along the bottom wall 81 from the lower part of the main body portion 71 of the first holder 7 toward the side wall 822 where the through hole 85 is provided. The second holder 100 is fixed onto the extension portion 73 by adhesive, adhesive resin, screw fastening, or the like. In this embodiment, as an example, the second holder 100 is fixed to the upper surface of the extension portion 73 via an adhesive layer B2. The adhesive layer B2 is, for example, a photocurable resin similar to the adhesive layer B1.

[0113] In the laser module 1C, in addition to the QCL element 2, the first lens 4 (lens holder 5) and the diffraction grating unit 3 are fixed to the first holder 7A, as in the first and second embodiments. The second holder 100 is fixed to the first holder 7A (extension 73). According to the above configuration, the first holder 7A and the second holder 100 can be integrated into a structure outside the package 8. Therefore, the positions of the QCL element 2, the first lens 4 (lens holder 5), the diffraction grating unit 3, and the second lens 6 can be adjusted outside the package 8. This improves work efficiency compared to when the positions are adjusted inside the package 8. More specifically, the adjustment of the external resonator and the subsequent positioning of the holder (a member combining the first holder 7A and the second holder 100) for emitting the terahertz wave L1 in a desired direction while bringing the end face of the QCL element 2 (a part of the side surface 21c of the substrate 21) into contact with (or close to) the light incident surface 61 of the terahertz wave output lens (second lens 6) can be performed outside the package 8. This eliminates the constraints of workspace when aligning the components housed in the package 8, thereby improving the efficiency and accuracy of the alignment work. Note that the second holder 100 may be formed integrally with the first holder 7A. In this case, a member (adhesive layer B2 in this embodiment) for attaching the second holder 100 to the first holder 7A is not required.

[0114] Furthermore, in the laser module 1C, when a temperature control element such as a Peltier element is placed between the first holder 7A and the bottom wall 81, the contact area between the first holder 7A and the temperature control element can be increased by the amount of the extension portion 73, thereby improving the heat dissipation efficiency compared to when the first holder 7 is used.

[0115] [Variations] Although one embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment. The materials and shapes of each component are not limited to those described above, and various materials and shapes can be used. Furthermore, some components included in the laser modules 1A, 1B, and 1C according to the above embodiment may be omitted or modified as appropriate. For example, while the above embodiment allows the laser modules 1A, 1B, and 1C to be miniaturized as described above, the laser modules 1A, 1B, and 1C are not necessarily limited to those miniaturized to handtop size or smaller. Furthermore, the type of package 8 is not limited to a butterfly package. [Explanation of symbols]

[0116] DESCRIPTION OF SYMBOLS 1A, 1B, 1C...laser module, 2...quantum cascade laser element, 3...diffraction grating unit, 4...first lens, 6...second lens, 7, 7A...first holder, 7a...support surface, 7e...side surface (first side surface), 7h...side surface (second side surface), 7i...intersection, 8...package, 11...lower cladding layer (first cladding layer), 12...active layer, 12a...end surface (first end surface), 12b...end surface (second end surface), 13...upper cladding layer (second cladding layer), 21...substrate, 21a...main surface, 21b...rear surface, 31...movable Diffraction grating, 61...light incident surface, 71...main body, 72...protrusion, 71a, 72a...portion, 82, 822...side wall, 85, 101...through hole, 85a, 101a...small diameter hole (first hole portion), 85b, 101b...large diameter hole (second hole portion), 85c, 101c...countersunk surface, 100...second holder, 200...light exit window, D1...direction (first direction), d1...distance (first distance), D2...direction (second direction), d2...distance (second distance), L1...terahertz wave, ω1...first frequency, ω2...second frequency, ω3...difference frequency.

Claims

1. A quantum cascade laser device comprising: a substrate having a main surface and a back surface opposite to the main surface; a first clad layer provided on the main surface; an active layer provided on the first clad layer on the side opposite to the substrate; and a second clad layer provided on the active layer on the side opposite to the first clad layer, the active layer has a first end face and a second end face facing each other in a second direction perpendicular to a first direction that is a stacking direction of the substrate, the first cladding layer, the active layer, and the second cladding layer, the first end facet constitutes a resonator for oscillating light of a first frequency and light of a second frequency, the active layer generates a terahertz wave having a difference frequency between the first frequency and the second frequency. The quantum cascade laser element; a diffraction grating unit including a movable diffraction grating that forms an external resonator for light of the first frequency; a first lens disposed between the quantum cascade laser element and the movable diffraction grating, the first lens passing light emitted from the second end face and light returning from the movable diffraction grating to the quantum cascade laser element; a second lens disposed at a position opposite to the first end face and configured to pass the terahertz wave emitted from the quantum cascade laser element; a first holder for holding the quantum cascade laser element; a package that houses the quantum cascade laser element, the diffraction grating unit, the first lens, and the first holder, and in which an optical path is disposed between a light incident surface of the second lens and the movable diffraction grating, The first holder includes: a support surface on which the back surface of the substrate of the quantum cascade laser element is placed; a first side surface connected to the support surface and facing the first lens in the second direction; In the second direction, the second end surface protrudes toward the first lens side beyond an intersection point between the first side surface and the support surface. Laser module.

2. a resonance axis passing through the first end face and the second end face of the quantum cascade laser element intersects with the optical axis of the second lens by inclining the support surface so as to intersect with the optical axis of the second lens; the first end surface is spaced from the light incident surface of the second lens; 2. The laser module according to claim 1.

3. the first lens and the diffraction grating unit are fixed to the first holder; 3. The laser module according to claim 1.

4. The second lens is a silicon lens formed into a hemisphere or a hyperhemispheric shape. The laser module according to any one of claims 1 to 3.

5. a second holder for holding the second lens; the second lens and the second holder are housed in the package; the package has a sidewall facing the first end face, a light exit window is provided on the side wall to allow light that has been emitted from the first end surface and passed through the second lens to pass therethrough; The laser module according to any one of claims 1 to 4.

6. the second holder is fixed to the package independently of the first holder; 6. The laser module according to claim 5.

7. the first lens and the diffraction grating unit are fixed to the first holder, The second holder is integrally formed with the first holder or fixed to the first holder.

6. The laser module according to claim 5.

8. the second holder has a through-hole that penetrates in a third direction perpendicular to the side wall, The through hole is a first hole portion that opens to the quantum cascade laser element side; a second hole portion that includes the first hole portion when viewed from the third direction and that opens toward the sidewall to a larger extent than the first hole portion; an annular counterbore surface that connects the first hole portion and the second hole portion and extends along a plane that intersects with the second direction, an outer edge portion of the light incident surface of the second lens is inserted from the side wall side through the second hole portion and fixed in surface contact with the counterbore surface; The laser module according to any one of claims 5 to 7.

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