Laser Module

Abstract

To provide a laser module capable of preventing damages while improving productivity.SOLUTION: A laser module 1 comprises a QCL element 21 and a support member 24. The QCL element 21 includes: an end surface 21a that is positioned at a first side S1 in a direction D2 orthogonal to a direction D1 as a lamination direction; and an end surface 21b that is positioned at a second side S2 of the side opposite to the first side S1 in the direction D2. A substrate 22 includes end surfaces 22a to 22d. The support member 24 includes: a first part P1 having a surface 24a opposite to at least one part of the end surface 22d; and a second part P2 including a surface 24b opposite to at least one part of the end surface 22a and a surface 24c positioned to the side opposite to the surface 24b in the direction D2. At least one part of a terahertz wave L1 generated by an active layer 232 is entered into the surface 24b of the support member 24 via the substrate 22, and is injected from the surface 24c via an inner part of the second part P2.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Conventionally, a difference frequency generation type terahertz quantum cascade laser (DFG-THz-QCL: Difference Frequency Generation THz-Quantum Cascade Laser) has been known. For example, Patent Document 1 discloses that in order to prevent terahertz waves from being totally reflected at an end face (a surface on the terahertz wave emission side) of a substrate constituting a terahertz quantum cascade laser, the end face is polished so as to be inclined with respect to an end face of an active layer. [Prior art documents] [Patent documents]

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

[0004] However, polishing the substrate end face as described above is relatively difficult, which can reduce the productivity of terahertz quantum cascade lasers. Furthermore, to improve the extraction efficiency of terahertz waves, it is possible to adopt a configuration in which the polished substrate end face is brought into contact with the lens surface of a lens for outputting terahertz waves. In this case, there is a risk of the substrate being damaged when the end face of the substrate is positioned and pressed against the lens surface.

[0005] Therefore, an object of one aspect of the present disclosure is to provide a laser module that can prevent damage while improving productivity. [Means for solving the problem]

[0006] A laser module according to one aspect of the present disclosure includes a quantum cascade laser element having a substrate, a first cladding layer provided on the substrate, an active layer provided on the side of the first cladding layer opposite the substrate, the active layer generating terahertz waves at a difference frequency between a first frequency and a second frequency, and a second cladding layer provided on the side of the active layer opposite the first cladding layer, and a support member that supports the substrate of the quantum cascade laser element and propagates the terahertz waves, wherein the quantum cascade laser element has a first end face located on a first side in a second direction orthogonal to a first direction that is a stacking direction of the substrate, the first cladding layer, the active layer, and the second cladding layer, and a second end face located on a second side opposite to the first side in the second direction, and the substrate forms a part of the first end face and has a first end face extending along the first direction and a third direction orthogonal to the first direction and the second direction. the active layer has a first active layer end face that forms a part of the first end face and that configures a resonator for oscillating light of the first frequency and light of the second frequency, and a second active layer end face that forms a part of the second end face; the support member has a first portion having a first surface that faces at least a part of the fourth substrate end face, and a second portion having a second surface that is connected to the first surface and faces at least a part of the first substrate end face, and a third surface that is located on the opposite side of the second surface in the second direction; and at least a part of the terahertz waves generated in the active layer are incident on the second surface of the support member through the substrate, pass through the inside of the second portion, and emerge from the third surface.

[0007] The laser module includes a support member that supports the substrate of the quantum cascade laser device. At least a portion of the terahertz waves generated in the active layer pass through the second portion of the support member and are emitted from the third surface. If a configuration is adopted in which terahertz waves are output directly from the first substrate end surface of the substrate toward the outside (e.g., a lens), a polished surface inclined with respect to the plane along the first and third directions must be formed on the first substrate end surface to improve the extraction efficiency of the terahertz waves. The process of forming such a polished surface is relatively difficult, which may reduce the productivity of the quantum cascade laser device. Furthermore, the substrate may be damaged when the polished surface thus formed is brought into contact with a lens. On the other hand, in the laser module, the terahertz waves are output to the outside via the support member (second portion), so there is no need to form a polished surface on the first substrate end surface. Furthermore, by pressing the first substrate end surface against the second surface of the support member, the substrate can be stably fixed to the support member while appropriately protecting the first substrate end surface. Therefore, the aforementioned reduction in productivity and damage to the substrate can be prevented.

[0008] The third surface may be inclined with respect to the second surface so as to approach the second surface as it moves from the third substrate end surface side to the fourth substrate end surface side along the first direction. With this configuration, the angle of incidence of the terahertz wave with respect to the third surface (the interface between the third surface and the outside) can be made smaller than when the third surface is not inclined. This makes it possible to suppress total reflection and surface reflection of the terahertz wave at the third surface, and to increase the efficiency of extracting the terahertz wave to the outside.

[0009] The first active layer end face may be located closer to the second side than the first substrate end face so as to be spaced apart from the second surface in the second direction. This configuration prevents contact between the first active layer end face and the second surface of the support member, thereby preventing a decrease in the oscillation efficiency of the first frequency light and the second frequency light due to such contact. As a result, the output of terahertz waves generated by the difference frequency between the first frequency and the second frequency can be increased.

[0010] The laser module may further include a reflective film provided to cover an end face of the first active layer for improving the reflectance of the light of the first frequency and the light of the second frequency. With this configuration, the oscillation efficiency of the light of the first frequency and the light of the second frequency in the active layer can be improved. As a result, the output of the terahertz wave generated by the difference frequency between the first frequency and the second frequency can be increased.

[0011] The first and second portions may be integrally formed. According to the above configuration, by using an integrally formed support member, it is possible to improve the support stability of the quantum cascade laser element.

[0012] The support member may have a first member including a first portion and a second member including a second portion and separate from the first member. According to the above configuration, the first and second portions are separated into separate members (the first and second members), which facilitates the manufacture of the support member. For example, if it is difficult to process the portion where the first and second surfaces intersect with sufficient precision in an integrally formed support member, combining the first and second members makes it easier to achieve precision in the portion, thereby reducing the difficulty of manufacturing the support member.

[0013] The support member may be divided into a first member and a second member with a plane along the first surface as a boundary surface. Alternatively, the support member may be divided into a first member and a second member with a plane along the second surface as a boundary surface. According to the above configuration, the support member can be easily manufactured by combining two substantially rectangular parallelepiped members (the first member and the second member).

[0014] The first member may be made of a material having a higher thermal conductivity than the second member. According to the above configuration, the first member of the support member that comes into contact with the bottom surface of the substrate (the fourth substrate end surface opposite to the active layer side) is made of a material having a higher thermal conductivity than the second member. As a result, it is possible to improve the efficiency of dissipating heat generated in the quantum cascade laser element, and to improve the operational reliability of the quantum cascade laser element.

[0015] The first portion may have a fourth surface connected to the first surface and facing the second side in the second direction, and the second substrate end surface, the second active layer end surface, and the fourth surface may be flush with each other. According to the above configuration, when light of the first frequency is oscillated using an external resonator positioned opposite the second active layer end surface, interference between the light emitted from the second active layer end surface toward the external resonator and the support member can be prevented. As a result, a decrease in the coupling efficiency between the quantum cascade laser element and the external resonator can be avoided. Furthermore, since the entire fourth substrate end surface can be in surface contact with the support member (first portion), the efficiency of dissipating heat generated in the quantum cascade laser element can be improved.

[0016] The first portion may have a fourth surface connected to the first surface and facing the second side in the second direction, and the second substrate end surface and the second active layer end surface may protrude toward the second side beyond the fourth surface. According to the above configuration, when light of the first frequency is oscillated using an external resonator positioned opposite the second active layer end surface, interference between the light emitted from the second active layer end surface toward the external resonator and the support member can be more reliably prevented. As a result, a decrease in the coupling efficiency between the quantum cascade laser element and the external resonator can be more reliably avoided.

[0017] The first surface may be bonded to the end face of the fourth substrate via an adhesive layer, and the second surface may not be bonded to the end face of the first substrate. According to the above configuration, by bonding the first surface and the end face of the fourth substrate with an adhesive layer, the quantum cascade laser element can be appropriately fixed to the support member. Furthermore, loss of terahertz waves caused by the presence of an adhesive layer having a refractive index different from that of the support member between the end face of the first substrate and the second surface can be suppressed.

[0018] The first surface may be bonded to the end surface of the fourth substrate via a first adhesive layer, and the second surface may be bonded to the end surface of the first substrate via a second adhesive layer, which may have substantially the same refractive index as the second portion of the support member. This configuration allows the substrate to be more stably fixed to the support member compared to when no adhesive layer (second adhesive layer) is provided between the end surface of the first substrate and the second surface. Furthermore, by providing a second adhesive layer between the second surface and the end surface of the first substrate, which has substantially the same refractive index as the second portion, terahertz wave loss can be reduced, which may occur when an adhesive layer with a refractive index significantly different from that of the second portion is provided between the second surface and the end surface of the first substrate. Furthermore, since an air gap between the end surface of the first substrate and the second surface can be reduced, terahertz wave loss due to the air gap can also be reduced.

[0019] The second portion may have substantially the same refractive index as the substrate. According to the above configuration, reflection of the terahertz wave traveling from the substrate to the support member toward the substrate can be suppressed at the interface between the support member and the substrate, thereby improving the propagation efficiency of the terahertz wave from the substrate to the support member.

[0020] The laser module may further include a first lens disposed opposite the third surface and configured to pass the terahertz wave propagated through the support member. According to the above configuration, the terahertz wave emitted from the third surface is guided to the first lens, thereby increasing the extraction efficiency of the terahertz wave.

[0021] The lens surface of the first lens facing the support member may be in contact with the third surface, and the first lens may have substantially the same refractive index as the second portion. With this configuration, reflection of the terahertz wave at the interface between the third surface of the support member and the lens surface of the first lens can be suppressed, and the extraction efficiency of the terahertz wave can be further improved.

[0022] When viewed from the third direction, the support member does not have to overlap with the quantum cascade laser element. According to the above configuration, it is possible to ensure a degree of freedom in the arrangement of the quantum cascade laser element relative to the support member in the third direction.

[0023] The support member may have a wall portion erected on the first surface on one side of the quantum cascade laser element in the third direction so as to face at least a part of the substrate. According to the above configuration, when fixing the quantum cascade laser element to the support member, the substrate of the quantum cascade laser element can be pressed against the wall portion, thereby easily positioning the quantum cascade laser element in the third direction. Furthermore, since the contact area between the substrate and the support member can be increased by the area where the wall portion contacts the substrate compared to when the wall portion is not provided, the efficiency of dissipating heat generated in the quantum cascade laser element can be improved.

[0024] The laser module may further include a holder for holding the quantum cascade laser element and the support member, and a package for accommodating the quantum cascade laser element, the support member, and the holder. According to the above configuration, by accommodating the unit consisting of the quantum cascade laser element and the support member in the package, damage to the unit can be prevented, and a highly reliable laser module can be obtained.

[0025] The laser module may further include a first lens arranged opposite to the third surface and passing the terahertz wave propagated inside the support member, a movable diffraction grating constituting an external resonator for light of the first frequency, and a second lens arranged between the quantum cascade laser element and the movable diffraction grating and passing the light emitted from the second active layer end face and the light returning from the movable diffraction grating to the quantum cascade laser element, and the package may further accommodate the movable diffraction grating and the second lens, and an optical path between the first lens and the movable diffraction grating may be arranged within the package. According to the above configuration, in a configuration in which light of the first frequency is oscillated using an external resonator, a highly reliable laser module can be obtained by also accommodating the external resonator within the package. [Effects of the Invention]

[0026] According to one aspect of the present disclosure, it is possible to provide a laser module that can improve productivity and prevent damage. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a perspective view of a laser module according to an 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 side view of the QCL unit. [Figure 5] FIG. 5 is a plan view of the QCL unit. [Figure 6] FIG. 6 is a cross-sectional view of the QCL unit taken along line VI-VI in FIG. [Figure 7] FIG. 7 is a cross-sectional view of a QCL device. [Figure 8] FIG. 8 is a plan view showing the arrangement of the components housed in the package. [Figure 9] 9A is a side view of a QCL unit according to a first modified example, and FIG. 9B is a side view of a QCL unit according to a second modified example. [Figure 10] Fig. 10(A) is a side view of a QCL unit according to a third modified example, and Fig. 10(B) is a side view of a QCL unit according to a fourth modified example. [Figure 11] Fig. 11A is a plan view of a QCL unit according to a fifth modification, and Fig. 11B is a schematic cross-sectional view of the QCL unit taken along line BB in Fig. 11A. [Figure 12] FIG. 12 is a side view of a QCL unit according to the sixth modification. [Figure 13] FIG. 13 is a cross-sectional view of the QCL unit taken along line XIII-XIII in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0028] An embodiment of the present disclosure will be described in detail below with reference to the drawings. In the following description, identical or equivalent elements will be designated by the same reference numerals, and redundant description will be omitted. Terms such as "upper" and "lower" are used for convenience based on the state shown in the drawings. Some of the drawings may be exaggerated to clearly illustrate the characteristics of the embodiment. Therefore, the dimensional ratios of the various parts in the drawings may differ from the actual dimensional ratios.

[0029] A laser module 1 according to this embodiment will be described with reference to FIGS. 1 to 8. The laser module 1 is a small terahertz light source module, for example, the size of a handheld device or less. As an example, the laser module 1 is configured to be capable of operating at room temperature with single mode and wavelength tunability using a quantum cascade laser element 21 (hereinafter referred to as "QCL element 21"), which is a difference frequency generation type terahertz quantum cascade laser (DFG-THz-QCL). The laser module 1 includes a QCL unit 2 including the QCL element 21 and a support member 24, a diffraction grating unit 3, a lens 4 (second lens), a lens holder 5, a lens 6 (first lens), a holder 7, and a package 8.

[0030] The package 8 is a housing that airtightly houses the QCL unit 2, the diffraction grating unit 3, the lens 4, the lens holder 5, and the holder 7. An optical path between the light incident surface 61 of the 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.

[0031] 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.

[0032] 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 holder 7 is mounted. In this embodiment, the holder 7 is placed directly on the bottom wall 81, but a separate member such as a heat dissipation member (e.g., a Peltier element) may be disposed between the bottom wall 81 and the holder 7. In other words, the 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.

[0033] The side wall 82 stands 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 unit 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.

[0034] 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.

[0035] 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 21 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.

[0036] 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.

[0037] The portions of the lead terminals 9 located outside the package 8 are electrically connected to the driving power supply for the QCL element 21, the driving power supply for the movable diffraction grating 31, etc. Meanwhile, 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 21, the movable diffraction grating 31, etc.). That is, the electrode terminals and the components inside the package 8 are electrically connected via conductive wires (not shown), so that power is supplied to the components from an external power source via the lead terminals 9 and the wires. Furthermore, if the above-mentioned temperature sensor, temperature control element, etc. are disposed inside the package 8, these components are also electrically connected to the electrode terminals.

[0038] 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 21a of the QCL element 21 has a through-hole 85 penetrating in a direction perpendicular to the side wall 822 (i.e., in the X-axis direction). A lens 6 is attached to the through-hole 85.

[0039] [QCL unit configuration] As shown in FIGS. 3 to 7, the QCL unit 2 includes a QCL element 21 and a support member 24. The QCL element 21 includes a substrate 22 and a semiconductor layer 23. In FIGS. 3 to 7, direction D1 (first direction) is the stacking direction of the QCL element 21 (the stacking direction of the substrate 22, lower cladding layer 231, active layer 232, and upper cladding layer 233, which will be described later). That is, direction D1 is the height direction of the QCL element 21. Direction D2 (second direction) is a direction perpendicular to direction D1 and is the longitudinal direction of the QCL element 21 (the direction in which end faces 21a and 21b, which will be described later, face each other). Direction D3 (third direction) is a direction perpendicular to directions D1 and D2 and is the width direction of the QCL element 21.

[0040] The QCL device 21 is a terahertz light source capable of outputting terahertz waves in a room temperature environment. The QCL device 21 is rod-shaped. The QCL device 21 has an end face 21a (first end face) and an end face 21b (second end face) facing each other in direction D2. As shown in FIG. 4, the end face 21a is formed by an end face 22a of the substrate 22 and an end face 23a of the semiconductor layer 23. The end face 21b is formed by an end face 22b of the substrate 22 and an end face 23b of the semiconductor layer 23. As shown in FIG. 6, the QCL device 21 can be formed as a ridge-stripe laser device by a typical semiconductor process. The QCL device 21 can be obtained, for example, by forming InGaAs / InAlAs on an InP substrate (substrate 22) by epitaxial growth.

[0041] The substrate 22 is, for example, a rectangular plate-shaped InP single crystal substrate (semi-insulating substrate: a high-resistance semiconductor substrate not doped with impurities). The length (length in direction D2), width (length in direction D3), and thickness (length in direction D1) of the substrate 22 are approximately several hundred μm to several mm, several hundred μm to several mm, and several hundred μm, respectively. In this embodiment, as an example, the length of the substrate 22 is approximately 3 mm, the width of the substrate 22 is approximately 1 mm, and the thickness of the substrate 22 is approximately 500 μm. The terahertz waves generated by difference frequency generation inside the active layer 232 are mainly propagated to the support member 24 via the substrate 22. From the viewpoint of increasing the extraction efficiency of the terahertz waves from the substrate 22 to the support member 24, the substrate 22 is a semi-insulating substrate as described above, or a 1×10 17 cm -3 The substrate preferably has the following carrier density:

[0042] As shown in FIGS. 4 and 5, the substrate 22 has end faces 22a to 22e.

[0043] End face 22a (first substrate end face) is a surface that constitutes part of end face 21a of QCL element 21 and extends along directions D1 and D3. That is, end face 22a is a surface perpendicular to direction D2. End face 22a is in surface contact with surface 24b (second surface) of support member 24, which will be described later.

[0044] End face 22b (second substrate end face) is a surface that constitutes part of end face 21b of QCL element 21. That is, end face 22b is located on the opposite side to end face 22a in direction D2. Like end face 22a, end face 22b is a surface perpendicular to direction D2.

[0045] The end face 22c (third substrate end face) is a face facing the semiconductor layer 23 including the active layer 232 in the direction D1. The end face 22c extends along the directions D2 and D3. That is, the end face 22c is a face perpendicular to the direction D1.

[0046] End face 22d (fourth substrate end face) is a face located on the opposite side to end face 22c in direction D1. Like end face 22c, end face 22d is a face perpendicular to direction D1. End face 22d is bonded to face 24a (first face) of support member 24 (described later) via adhesive layer 26.

[0047] The pair of end faces 22e are side faces of the substrate 22 (faces facing the direction D3).

[0048] The semiconductor layer 23 is provided on the end surface 22c of the substrate 22. The thickness (length in the direction D1) of the semiconductor layer 23 is approximately 10 μm to 20 μm. The semiconductor layer 23 has an end surface 23a that constitutes a part of the end surface 21a of the QCL element 21 and an end surface 23b that constitutes a part of the end surface 21b of the QCL element 21. The semiconductor layer 23 emits light in a wide band in the mid-infrared region (e.g., 3 μm to 20 μm) from each of the end surfaces 23a and 23b. The end surfaces 23a and 23b are surfaces perpendicular to the direction D2. The end surfaces 23a and 23b are, for example, cleavage planes formed by cleavage. The end surface 23a is located on a first side S1 in the direction D2 and faces the lens 6. The end surface 23b is located on a second side S2 opposite the first side S1 in the direction D2 and faces the lens 4. End face 23b 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 QCL device 21. To emit light over such a wide bandwidth as described above, QCL device 21 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.

[0049] 6 and 7, the semiconductor layer 23 has a lower cladding layer 231 (first cladding layer), an active layer 232, and an upper cladding layer 233 (second cladding layer). In this embodiment, the semiconductor layer 23 also has an upper guide layer 234, a lower guide layer 235, an upper contact layer 236, and a lower contact layer 237.

[0050] Starting from the end face 22c side of the substrate 22, a lower contact layer 237, a lower cladding layer 231, a lower guide layer 235, an active layer 232, an upper guide layer 234, an upper cladding layer 233, and an upper contact layer 236 are stacked in this order. Support layers 238 are provided between the lower cladding layer 231 and the upper cladding layer 233 on both sides (both sides in the direction D3) of the active layer 232, the upper guide layer 234, and the lower guide layer 235, which are formed in a ridge stripe shape. The lower contact layer 237 has a portion that extends outward (outside in the direction D3) than the lower cladding layer 231. In this embodiment, an end of the lower contact layer 237 in the direction D3 coincides with an end of the substrate 22 in the direction D3 (i.e., the position of the end face 22e).

[0051] The lower contact layer 237 is, for example, a highly Si-doped InGaAs layer (Si: 1.0×10 18 / cm 3 ) and is provided on the end surface 22c of the substrate 22.

[0052] The lower cladding layer 231 is, for example, a Si-doped InP layer (Si: 1.5×10 16 / cm 3 ) and is provided on the lower contact layer 237. That is, the lower cladding layer 231 is provided on the end face 22c of the substrate 22 with the lower contact layer 237 interposed therebetween.

[0053] The lower guide layer 235 is, for example, a Si-doped InGaAs layer (Si: 1.5×10 16 / cm 3 ) and is provided on the lower cladding layer 231.

[0054] The active layer 232 is a layer in which a quantum cascade structure is formed, and is provided on the lower guide layer 235. That is, the active layer 232 is provided on the side of the lower cladding layer 231 opposite the substrate 22. As shown in FIG. 7 , the active layer 232 has an end face 232a (first active layer end face) and an end face 232b (second active layer end face) that face each other in direction D2. The end face 232a is part of the end face 23a of the semiconductor layer 23. That is, the end face 232a is part of the end face 21a of the QCL device 21. The end face 232b is part of the end face 23b of the semiconductor layer 23. That is, the end face 232b is part of the end face 21b of the QCL device 21. As an example, the active layer 232 has a structure in which InGaAs layers and InAlAs layers are alternately stacked along direction D1.

[0055] The upper guide layer 234 is, for example, a Si-doped InGaAs layer (Si: 1.5×10 16 / cm 3 ) and is provided on the active layer 232.

[0056] The upper cladding layer 233 is, for example, a Si-doped InP layer (Si: 1.5×10 16 / cm 3 ) and is provided on the upper guiding layer 234. That is, the upper cladding layer 233 is provided on the opposite side of the active layer 232 from the lower cladding layer 231.

[0057] The upper contact layer 236 is, for example, a highly Si-doped InP layer (Si: 1.5×10 18 / cm 3 ) and is provided on the upper cladding layer 233.

[0058] The support layer 238 is, for example, an Fe-doped InP layer.

[0059] As shown in FIG. 6 , the insulating film 27 is formed to cover the upper surface 236a of the upper contact layer 236, the side surface 23c of the semiconductor layer 23 intersecting the direction D3, and a portion of the lower contact layer 237. The insulating film 27 is formed of, for example, SiN. A contact hole 27a is formed in the insulating film 27 to expose a portion of the upper surface 236a of the upper contact layer 236. The contact hole 27a extends along the direction D2 to expose a central portion of the upper surface 236a in the direction D3. In addition, in the direction D3, an end 27b of the insulating film 27 on the lower contact layer 237 is located inside the end of the lower contact layer 237. That is, the upper surface of the lower contact layer 237 is exposed outside the end 27b of the insulating film 27.

[0060] The first electrode 28 is formed on the upper surface 236a of the upper contact layer 236. The first electrode 28 is electrically connected to a part of the upper surface 236a of the upper contact layer 236 through the contact hole 27a.

[0061] The second electrode 29 is formed on the lower contact layer 237 so as to be in contact with a portion of the lower contact layer 237 that is exposed outside the end 27b of the insulating film 27. In this embodiment, the second electrode 29 is formed so as to cover part of the side surface and the top surface of the semiconductor layer 23, but this is not necessarily the case. That is, the second electrode 29 only needs to be electrically connected to at least the lower contact layer 237 and spaced apart from the first electrode 28. With the above configuration, the QCL element 21 can be driven by passing a current from the second electrode 29 to the first electrode 28.

[0062] To obtain a single-mode terahertz wave, it is necessary to simultaneously oscillate two single-mode wavelengths (both mid-infrared light) inside the QCL element 21. In this embodiment, as an example, a single-mode wavelength of one wavelength (a wavelength corresponding to the second frequency ω2) is oscillated by a diffraction grating (described in detail below) provided inside the QCL element 21, and a single-mode wavelength of the other wavelength (a wavelength corresponding to a first frequency ω1 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 234 is formed with a diffraction grating layer 234a (see FIG. 7 ) that functions as a distributed feedback (DFB) structure along the direction D2 (i.e., the resonance direction) in which the end face 232a and the end face 232b face each other. The diffraction grating layer 234a oscillates light of a wavelength (a wavelength corresponding to the second frequency ω2) that is outside the wavelength at which the gain peak of the QCL element 21 occurs in a single mode. The QCL element 21 is in a state where both the DFB single mode and the Fabry-Perot mode have gain simultaneously. Note that 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.

[0063] End facets 232a and 232b of the active layer 232 form a resonator that oscillates the second light. Meanwhile, end facet 232a of the active layer 232 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, the active layer 232 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.

[0064] As shown in FIG. 7, the radiation direction A1 of the terahertz waves generated in this manner is oriented at a radiation angle θ with respect to the direction from end face 232b toward end face 232a (the right direction in FIG. 7) along the resonance direction (direction D2). C More specifically, the terahertz wave generated in the active layer 232 is inclined downward (toward the substrate 22) by a radiation angle θ (Cherenkov radiation angle) given by the following formula (1):C propagates as a plane wave (i.e., in phase) within the substrate 22. In the following formula (1), n MIR is the group refractive index of the substrate 22 for mid-infrared light, and n THz is the refractive index of the substrate 22 for the terahertz wave.

[0065] θ C =cos -1 (n MIR / n THz )…(1)

[0066] The support member 24 is a member that supports the substrate 22 of the QCL device 21 and propagates terahertz waves. The support member 24 is made of, for example, silicon (e.g., HRFZ-Si (High Resistivity Float Zone Silicon)). However, the support member 24 is not limited to silicon. From the viewpoint of suppressing the reflection of terahertz waves toward the substrate 22 at the interface between the support member 24 and the substrate 22, the support member 24 is preferably made of a material having substantially the same refractive index as the substrate 22.

[0067] 4 to 6, in this embodiment, the support member 24 has a width greater than that of the QCL element 21 in the direction D3. When viewed from the direction D3, the support member 24 is formed in a substantially L-shape so as to support the end faces 22a and 22d of the substrate. The support member 24 has surfaces 24a to 24g.

[0068] The surface 24a (first surface) is a surface facing at least a portion of the end surface 22d of the substrate 22. The surface 24a is a surface perpendicular to the direction D1. As shown in FIGS. 4 and 5, in this embodiment, the surface 24a faces the entire end surface 22d. More specifically, the width of the surface 24a (length in the direction D3) is greater than the width of the end surface 22d, and the substrate 22 is disposed at the center of the surface 24a in the direction D3. The width of the surface 24a is, for example, about 3 mm. The length of the surface 24a (length in the direction D2) is the same as the length of the end surface 22d, for example, about 3 mm.

[0069] The surface 24b (second surface) is connected to the surface 24a and faces at least a portion of the end surface 22a of the substrate 22. More specifically, the surface 24b is connected to an end of the surface 24a on the first side S1 in the direction D2 and extends perpendicular to the surface 24a. That is, the surface 24b is perpendicular to the direction D2.

[0070] Surface 24c (third surface) is a surface located on the opposite side of surface 24b in direction D2. As shown in Fig. 4, surface 24c is inclined at an inclination angle θ with respect to surface 24b so as to approach surface 24b as it moves from end surface 22c to end surface 22d along direction D1 (i.e., downward in Fig. 4).

[0071] Surface 24d (fourth surface) is connected to surface 24a and faces the second side S2 in direction D2. More specifically, surface 24d is connected to an end of surface 24a on the second side S2 in direction D2 and extends perpendicular to surface 24a. That is, surface 24d is perpendicular to direction D2.

[0072] Surface 24e is a surface that connects the upper end of surface 24b and the upper end of surface 24c. Surface 24e is a surface that is perpendicular to direction D1. In the present embodiment, as an example, surface 24e is formed to be substantially flush with end surface 22c of substrate 22 that is placed on surface 24a.

[0073] Surface 24f is a surface located on the opposite side of surfaces 24a and 24e in direction D1. Surface 24f connects the lower end of surface 24c to the lower end of surface 24d. Surface 24f is a surface perpendicular to direction D1.

[0074] The pair of surfaces 24g are side surfaces of the support member 24 (surfaces facing the direction D3).

[0075] The length of the support member 24 in direction D2 (i.e., the distance from surface 24c to surface 24d along direction D2) is, for example, about 4 mm to 5 mm. The length of the support member 24 in direction D1 (i.e., the distance from surface 24e to surface 24f along direction D1) is, for example, about 1 mm. The length of the support member 24 in direction D3 (i.e., the distance between a pair of surfaces 24g along direction D3) is, for example, about 3 mm.

[0076] As described above, the support member 24 has a first portion P1 facing the end face 22d of the substrate 22 in the direction D1 and a second portion P2 facing the end face 22a of the substrate 22 in the direction D2. The first portion P1 has a surface 24a and overlaps with the QCL element 21 in the direction D1. The second portion P2 has a surface 24b and a surface 24c and overlaps with the QCL element 21 in the direction D2.

[0077] As shown in FIG. 4, the terahertz wave L1 generated in the active layer 232 (semiconductor layer 23) is emitted at an angle θ C Therefore, at least a part of the terahertz waves L1 generated in the active layer 232 (semiconductor layer 23) is incident on the surface 24b of the support member 24 through the substrate 22, passes through the inside of the second portion P2, and is emitted from the surface 24c. As described above, the surface 24c is inclined at the inclination angle θ. The inclination angle θ may be set so that the angle of incidence of the terahertz waves L1 on the surface 24c is smaller than when the surface 24c is not inclined (i.e., when the inclination angle θ is 0 degrees). By configuring the surface 24c as described above, the terahertz waves L1 are incident in a direction inclined with respect to the direction from the second side S2 to the first side S1 in the direction D2 (i.e., when the radiation angle θ C ) to the surface 24c (the interface between the surface 24c and the outside) can be made smaller than when the surface 24c is not tilted. This makes it possible to suppress total reflection and surface reflection of the terahertz wave L1 at the surface 24c, thereby increasing the efficiency of extracting the terahertz wave L1 to the outside. For example, when the tilt angle θ is set to the radiation angle θ of the terahertz wave L1, CBy setting the angle of incidence of the terahertz wave L1 with respect to the surface 24c to approximately coincide with the angle of incidence of the terahertz wave L1, the angle of incidence of the terahertz wave L1 with respect to the surface 24c can be brought close to 0 degrees, and reflection of the terahertz wave at the surface 24c can be effectively suppressed. Here, because the substrate 22 is very thin, it is very difficult to polish the end surface 22a of the substrate 22 to form an inclined surface similar to the above-described surface 24c without damaging the substrate 22. On the other hand, forming the above-described inclined surface (surface 24c) on the support member 24, which is thicker than the substrate 22, is relatively easy compared to polishing the end surface 22a of the substrate 22. In this way, the configuration in which the substrate 22 is fixed to the support member 24 eliminates the need for the difficult polishing of the end surface 22a of the substrate 22. Furthermore, by making the surface 24c the inclined surface described above, it is possible to obtain the same effect as that conventionally obtained by making the end surface 22a of the substrate 22 an inclined surface (i.e., suppression of reflection of the terahertz wave).

[0078] When the surface 24c of the support member 24 is brought into contact with the lens 6 as in this embodiment, the surface 24c does not necessarily have to be an inclined surface as described above (i.e., the inclination angle θ may be 0 degrees). On the other hand, when the terahertz wave L1 is output directly to the outside from the surface 24c without using the lens 6, it is preferable to make the surface 24c an inclined surface as described above from the viewpoint of increasing the extraction efficiency of the terahertz wave.

[0079] In this embodiment, the end face 22c of the substrate 22 is formed to be substantially flush with the face 24e of the support member 24, and therefore even if the end face 232a (end face 23a) were flush with the end face 22a of the substrate 22, the end face 232a would not come into contact with the face 24b of the support member 24. According to the above configuration, it is possible to prevent the end face 232a (end face 23a) from coming into contact with the face 24b of the support member 24, and therefore it is possible to prevent a decrease in the oscillation efficiency of the first light and the second light due to the contact (i.e., a decrease in the function of the end face 232a as a resonator).

[0080] 4 and 5, the end face 232a of the active layer 232 (in this embodiment, the end face 23a of the semiconductor layer 23) is located on the second side S2 of the end face 22a of the substrate 22 so as to be spaced apart from the face 24b of the support member 24 in the direction D2. This configuration can prevent contact between the end face 232a (end face 23a) and the face 24b of the support member 24, thereby preventing a decrease in the oscillation efficiency of the first light and the second light due to the contact (i.e., a decrease in the function of the end face 232a as a resonator). As a result, the output of the terahertz wave L1 generated by the difference frequency between the first frequency ω1 and the second frequency ω2 can be increased. As described above, in this embodiment, the end surface 22c of the substrate 22 is formed substantially flush with the surface 24e of the support member 24. Therefore, even if the end surface 232a (end surface 23a) were flush with the end surface 22a of the substrate 22, the end surface 232a would not come into contact with the surface 24b of the support member 24. However, due to manufacturing errors or the like, the surface 24e may be located slightly above the end surface 22c. Furthermore, in order to more firmly support the substrate 22 by the support member 24, the support member 24 may be formed so that the surface 24e is located above the end surface 22c. According to the above-described configuration in which the end surface 232a (end surface 23a) is set back toward the second side S2 from the end surface 22a of the substrate 22, contact between the end surface 232a and the surface 24b can be reliably prevented even in the above-described case. Furthermore, when a reflective film 25 (described later) is provided on the end face 232a as in this embodiment, interference between the reflective film 25 and the surface 24b can be prevented by setting back the end face 232a toward the second side S2 from the end face 22a.

[0081] As shown in FIGS. 4, 5, and 7, the laser module 1 includes a reflective film 25 provided to cover the end face 232a of the active layer 232 (the end face 23a of the semiconductor layer 23 in this embodiment) to improve the reflectivity of the first light and the second light. The reflective film 25 is formed of, for example, gold (Au). That is, an HR coating is applied to the end face 232a of the active layer 232. With this configuration, the amount of mid-infrared light (the first light and the second light) incident on the end face 232a from the end face 232b side that is reflected toward the end face 232b can be increased, thereby improving the oscillation efficiency of the first light and the second light in the active layer 232. As a result, the output of the terahertz wave L1 generated by the difference frequency between the first frequency ω1 and the second frequency ω2 can be increased.

[0082] 4, the first portion P1 and the second portion P2 are integrally formed. According to the above configuration, the support member 24 formed integrally therewith can be used to improve the support stability of the QCL element 21.

[0083] As shown in FIG. 4 , the first portion P1 has a surface 24d, and the end surface 22b of the substrate 22, the end surface 232b of the active layer 232 (the end surface 23b of the semiconductor layer 23 in this embodiment), and the surface 24d are flush with each other. With this configuration, when the first light is oscillated using an external resonator (a movable diffraction grating 31, described later) positioned opposite the end surface 232b, interference between the light emitted from the end surface 232b toward the external resonator (light emitted with a relatively large divergence angle) and the support member 24 can be prevented. As a result, a decrease in the coupling efficiency between the QCL element 21 and the external resonator can be avoided. Furthermore, since the entire end surface 22d of the substrate 22 can be in surface contact with the support member 24 (first portion P1), the heat dissipation efficiency of the heat generated by the QCL element 21 can be improved. That is, the heat generated by the QCL element 21 can be appropriately dissipated from the substrate 22 to the support member 24.

[0084] As shown in FIG. 4, the surface 24a of the support member 24 is bonded to the end surface 22d of the substrate 22 via an adhesive layer 26. The adhesive layer 26 is, for example, solder, resin, or the like. On the other hand, the surface 24b of the support member 24 is not bonded to the end surface 22a of the substrate 22. For example, the surface 24b is in direct surface contact with the end surface 22a without an adhesive layer. According to the above configuration, by bonding the surface 24a and the end surface 22d with the adhesive layer 26, the QCL element 21 can be appropriately fixed to the support member 24. Furthermore, the loss of the terahertz wave L1 caused by the presence of an adhesive layer having a refractive index different from that of the support member 24 (second portion P2) between the end surface 22a and the surface 24b can be suppressed.

[0085] The second portion P2 has substantially the same refractive index as the substrate 22. In this embodiment, the support member 24 is formed integrally, and therefore the entire support member 24 has substantially the same refractive index as the substrate 22. According to the above configuration, reflection of the terahertz wave L1 traveling from the substrate 22 to the support member 24 toward the substrate 22 at the interface between the support member 24 and the substrate 22 can be suppressed, and the propagation efficiency of the terahertz wave L1 from the substrate 22 to the support member 24 can be improved. Note that "substantially the same refractive index" means that the difference in refractive index is within a range of 0.3.

[0086] 4 and 6, when viewed from direction D3, support member 24 does not overlap with QCL element 21. That is, on surface 24a of support member 24, no portion (e.g., wall portion) overlapping with QCL element 21 is provided on either side of QCL element 21 in direction D3. This configuration ensures flexibility in the arrangement of QCL element 21 relative to support member 24 in direction D3.

[0087] [Configuration of the terahertz wave output lens (lens 6)] Lens 6 is a lens for outputting the terahertz waves generated by QCL element 21 to the outside. As shown in Fig. 3, lens 6 is disposed at a position facing surface 24c of support member 24, and passes terahertz waves L1 (see Fig. 4) that have propagated inside support member 24. According to the above configuration, by guiding terahertz waves L1 emitted from surface 24c of support member 24 to lens 6, the extraction efficiency of terahertz waves L1 can be improved.

[0088] The lens 6 has a flat light incident surface 61 (lens surface) facing the surface 24c of the support member 24 and a curved light exit surface 62 that emits terahertz waves L1, which are output light, to the outside of the package 8. The light incident surface 61 is in contact with the surface 24c of the support member 24. The lens 6 is formed of a material having substantially the same refractive index as the second portion P2 of the support member 24. This configuration can suppress reflection of the terahertz waves L1 at the interface between the surface 24c of the support member 24 and the light incident surface 61 of the lens 6, thereby further improving the extraction efficiency of the terahertz waves. Note that, although the light incident surface 61 is in surface contact with the surface 24c in this embodiment, the light incident surface 61 may also be in line contact with the surface 24c. This configuration can also achieve the same effect as when the light incident surface 61 is in surface contact. That is, the terahertz waves L1 can be efficiently propagated from the support member 24 to the lens 6 through the contact portion between the light incident surface 61 and the surface 24c.

[0089] The lens 6 is, for example, a silicon lens formed in a hemispherical or hyperhemispherical shape. Silicon lenses are scratch-resistant. Even if scratches or dirt occur, the terahertz waves L1, which have longer wavelengths than visible light, near-infrared light, and the like, are less likely to be affected. This allows the lens 6 to be arranged so that it is exposed to the outside of the package 8. However, the material of the lens 6 is not limited to silicon. For example, the lens 6 may be formed from other materials that transmit the terahertz waves L1, such as Tsurupica. Furthermore, a low-reflection coating may be provided on the light exit surface 62 of the lens 6 to reduce the reflectance of the terahertz waves L1 in order to increase the extraction efficiency of the terahertz waves L1.

[0090] The lens 6 is attached to a through-hole 85 provided in a side wall 822 of the package 8. The structure for attaching the lens 6 to the through-hole 85 will be described in detail below.

[0091] 3, the through hole 85 has a small diameter hole 85a, a large diameter hole 85b, and a counterbore surface 85c. The small diameter hole 85a opens toward the inside of the package 8 in the optical axis direction of the 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 axis of the small diameter hole 85a and the central axis of the large diameter hole 85b approximately coincide with the optical axis of the lens 6.

[0092] 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.

[0093] The outer edge of the light incident surface 61 of the lens 6 is inserted through 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 using, for example, a fixing resin or an adhesive. The 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 21 via the support member 24 at the light incident surface 61, collimate the terahertz waves L1 into a beam, and extract the terahertz waves L1 from the light exit surface 62 to the outside of the package 8. The lens 6 also functions to maintain the interior of the package 8 airtight. According to the above configuration, the 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 lens 6. The 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 lens 6) caused by providing a window material other than the 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 lens 6, it is possible to easily and accurately fix a hemispherical or hyperhemispherical lens 6 that does not have a thick edge to hold the lens from the side.

[0094] [External cavity configuration] An external resonator that oscillates the above-mentioned first light (light of the first frequency ω1) is configured by the lens 4 and the movable diffraction grating 31. That is, the first light travels back and forth between the end face 232a of the active layer 232 and the movable diffraction grating 31 (specifically, the diffraction grating portion 314, which will be described later) via the lens 4, thereby amplifying the first light.

[0095] (Configuration of external cavity lens (lens 4)) Lens 4 is a lens for an external resonator and transmits mid-infrared light. Lens 4 may be made of, for example, zinc selenide (ZnSe). Lens 4 is disposed between QCL element 21 and movable diffraction grating 31 and transmits light (mid-infrared light) emitted from end face 232b and light (mid-infrared light) returning from movable diffraction grating 31 to QCL element 21 (active layer 232).

[0096] Lens 4 has first lens surface 41 and second lens surface 42. Lens 4 is, for example, an aspherical lens. First lens surface 41 is a surface facing end surface 21b of QCL element 21 (end surface 232b of active layer 232). First lens surface 41 may be a flat surface or a non-flat surface (for example, a curved surface convex toward QCL element 21). Second lens surface 42 is a curved surface facing movable diffraction grating 31 on the opposite side to first lens surface 41. First lens surface 41 and second lens surface 42 may be provided with a low-reflection coating that has a reflectance of 5% or less at the wavelength at which QCL element 21 has a gain peak. Lens 4 may be made of a material that transmits mid-infrared light, such as Ge or CaF2.

[0097] The lens 4 is fixed to the lens holder 5 so that the optical axis of the lens 4 and the resonance axis of the QCL element 21 (i.e., the axis parallel to the direction D2 passing through the end faces 232a and 232b of the active layer 232, and the optical axis of the mid-infrared light emitted by the QCL element 21) substantially coincide with each other. That is, the 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 21.

[0098] The 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 21 in the optical axis direction (direction D2) of the 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 approximately coincide with the optical axis of the 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 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, for example, with a bonding resin, adhesive, or the like.

[0099] (Structure of the diffraction grating unit) As shown in FIGS. 3 and 8 , the diffraction grating unit 3 is disposed on the opposite side of the lens 4 (lens holder 5) from the side on which the QCL element 21 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 21. 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.

[0100] The light collimated by the 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 232b of the active layer 232 via the lens 4. In this embodiment, the movable diffraction grating 31 and the end face 232b form a Littrow-type external resonator.

[0101] Furthermore, the movable diffraction grating 31 can rapidly change the orientation of the diffraction grating portion 314 that diffracts and reflects incident light. This allows the wavelength of the light that returns from the movable diffraction grating 31 to the end face 232b of the active layer 232 (i.e., the wavelength corresponding to the first frequency ω1) 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 21.

[0102] 8, 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.

[0103] 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.

[0104] 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.

[0105] A diffraction grating section 314 is provided on the surface (mirror surface) of the movable section 313 facing the QCL element 21. The diffraction grating section 314 has a plurality of grating grooves (not shown) and diffracts and reflects the light emitted from the QCL element 21. The diffraction grating unit 3 is arranged so that the optical axis of the lens 4 (i.e., the optical axis of the mid-infrared light collimated by the lens 4) substantially coincides with the center of the diffraction grating section 314, and light incident on the diffraction grating section 314 is diffracted on the optical axis in the direction opposite to the incident direction.

[0106] 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 along 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 21. 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.

[0107] 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).

[0108] 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.

[0109] 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.

[0110] Inclined surface 33a is inclined with respect to end surface 21b of QCL element 21. 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 21b. The inclination angle of inclined surface 33a (the angle with respect to end surface 21b of QCL element 21) is set depending on the oscillation wavelength of QCL element 21, the number of grating grooves in diffraction grating portion 314, the blazed angle, etc.

[0111] 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.

[0112] 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).

[0113] [Holder configuration] Next, the configuration of the holder 7 will be described with reference to Fig. 3. The holder 7 is a member that holds (supports) the QCL unit 2 within the package 8. The holder 7 also functions as a heat sink to suppress heat generation from the QCL unit 2 when the QCL element 21 is driven. The holder 7 can be made of, for example, a material that has good thermal conductivity, can be precisely machined, and has sufficient hardness and rigidity to maintain its shape. The holder 7 can be made of, for example, the same metal material as the bottom wall 81, such as copper-tungsten.

[0114] In this embodiment, in addition to the QCL unit 2, the lens 4 (lens holder 5) and the diffraction grating unit 3 are also fixed to the holder 7. That is, the holder 7 supports all of the components required to form an external resonator for oscillating the first light. With the above configuration, before housing the QCL unit 2, the lens 4 (lens holder 5), and the diffraction grating unit 3 in the package 8, these components can be fixed to the holder 7 and their positions can be adjusted (positioned) relative to each other. That is, the QCL unit 2, the lens 4 (lens holder 5), and the diffraction grating unit 3 can be mounted on the holder 7 while performing the above-described position adjustment, and then the 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.

[0115] The holder 7 is fixed on the bottom wall 81 inside the package 8. For example, the bottom surface 7b of the 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 holder 7 and the bottom wall 81. Furthermore, the holder 7 may be attached to a portion other than the bottom wall 81 (for example, the side wall 82).

[0116] The holder 7 has, in order from the side where the lens 6 is arranged, a support surface 7a on which the QCL unit 2 is placed, a support surface 7c on which the lens holder 5 is placed, and a support surface 7d on which the diffraction grating unit 3 is placed 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 unit 2, the lens holder 5, and the diffraction grating unit 3) on each of the inclined support surfaces 7a, 7c, and 7d, the positional relationship between the components constituting the external resonator can be appropriately determined. With the top surface of the bottom wall 81 as a reference, the support surface 7a is located higher than the support surface 7c, which is located higher than the support surface 7d. Steps are formed between the support surfaces 7a and 7c and between the support surfaces 7c and 7d.

[0117] The holder 7 has a side surface 7e 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 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.

[0118] The QCL unit 2 is fixed to the support surface 7a by fixing the surface 24f of the support member 24 to the support surface 7a of the holder 7. 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 of the lens 4 and the resonance axis of the QCL element 21 (the optical axis of the mid-infrared light emitted from the end surface 232b) coincide with each other. For example, the height position of the lens holder 5 relative to the support surface 7c can be fine-tuned 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.

[0119] The laser module 1 is manufactured, for example, as follows. First, the lens 6 is attached to the through-hole 85 of the package 8 before the top wall 83 is attached. Next, the QCL unit 2, the lens 4 (lens holder 5), and the diffraction grating unit 3 are attached to the holder 7 outside the package 8. At this time, the positions of the QCL unit 2, the lens 4 (lens holder 5), and the diffraction grating unit 3 are adjusted so that the resonance axis of the QCL element 21 and the optical axis of the lens 4 coincide with each other and the optical axis passes through the center of the diffraction grating portion 314. Next, the holder 7 on which the components are mounted as described above is housed in the package 8. The holder 7 is fixed in the package 8 so that the surface 24c of the support member 24 of the QCL unit 2 contacts (or is close to) the approximate center of the light incident surface 61 of the lens 6. Next, the components housed in the package 8 that require an electrical supply (such as the QCL element 21) are electrically connected to electrode terminals (lead terminals 9) by wires or the like (not shown). After the arrangement of each component and the wiring process inside the package 8 are completed, the inside of the package 8 is evacuated or replaced with nitrogen, and the top wall 83 is airtightly joined to the end 82a of the side wall 82 opposite to the bottom wall 81. In this way, the above-described laser module 1 is obtained.

[0120] [Action and effect] The laser module 1 described above includes a support member 24 that supports the substrate 22 of the QCL element 21. As shown in FIG. 4, at least a portion of the terahertz wave L1 generated in the active layer 232 passes through the second portion P2 of the support member 24 and is emitted from the surface 24c. If a configuration is adopted in which the terahertz wave is output directly from the end surface 22a of the substrate 22 toward the outside (e.g., a lens), a polished surface inclined with respect to the plane along the directions D1 and D3 (i.e., the plane perpendicular to the direction D2) must be formed on the end surface 22a to enhance the extraction efficiency of the terahertz wave. The process of forming such a polished surface is relatively difficult, which may reduce the productivity of the QCL element 21. Furthermore, the substrate may be damaged when the polished surface thus formed is brought into contact with a lens. In contrast, in the laser module 1, the terahertz wave L1 is output to the outside via the support member 24 (the second portion P2), so there is no need to form a polished surface on the end surface 22a of the substrate 22. Furthermore, by pressing the end face 22a against the face 24b of the support member 24, the end face 22a can be appropriately protected while the substrate 22 can be stably fixed to the support member 24. Therefore, the aforementioned decrease in productivity and damage to the substrate can be prevented. As described above, the laser module 1 can improve productivity while preventing damage.

[0121] Furthermore, since the support member 24 has not only the second portion P2 but also the first portion P1 facing the end face 22d of the substrate 22, the heat dissipation of the QCL element 21 and ease of handling during manufacturing can be improved. More specifically, heat generated in the QCL element 21 can be appropriately dissipated from the substrate 22 to the support member 24 via the contact portion between the end face 22d and the surface 24a. Furthermore, by attaching the QCL element 21 to the support member 24 having the first portion P1 and the second portion P2, a QCL unit 2 can be obtained that is larger in both directions D1 and D2 than the QCL element 21 alone. Note that in this embodiment, the width of the support member 24 in direction D3 (e.g., 3 mm) is larger than the width of the QCL element 21 (e.g., 1 mm), and therefore the QCL unit 2 is also larger in direction D3 than the QCL element 21 alone. Gripping the support member 24 of the enlarged QCL unit 2 is easier than gripping the QCL element 21 alone (for example, the substrate 22 portion), which improves the handleability (for example, portability) of the QCL element 21. Furthermore, providing a base, that is, the support member 24, improves the ease of pressing the QCL unit 2 against the lens 6. As a result, damage to the QCL element 21 during manufacturing and operation can be effectively prevented, and reliability can be improved.

[0122] The laser module 1 also includes a holder 7 that holds the QCL unit 2 (i.e., the QCL element 21 and the support member 24), and a package 8 that houses the QCL unit 2 and the holder 7. According to the above configuration, by housing the QCL unit 2, which is made up of the QCL element 21 and the support member 24, in the package 8, damage to the QCL unit 2 can be prevented, and a highly reliable laser module 1 can be obtained.

[0123] Moreover, the package 8 further houses a movable diffraction grating 31 and a lens 4, and an optical path between the lens 4 and the movable diffraction grating 31 is arranged inside the package 8. According to the above configuration, in a configuration in which the first light is oscillated using the movable diffraction grating 31, which is an external resonator, by also housing the external resonator inside the package 8, a highly reliable laser module 1 can be obtained.

[0124] The configuration of the QCL unit is not limited to the above embodiment (QCL unit 2). Below, several modified examples of the QCL unit will be described with reference to FIGS.

[0125] [First Modification] 9A, the QCL unit 2A according to the first modification differs from the QCL unit 2 in that it has an adhesive layer 26a in addition to the adhesive layer 26. More specifically, in the QCL unit 2A, the surface 24a of the support member 24 is adhered to the end surface 22d of the substrate 22 via the adhesive layer 26 (first adhesive layer), and the surface 24b of the support member 24 is also adhered to the end surface 22a of the substrate 22 via the adhesive layer 26a (second adhesive layer). The adhesive layer 26a has substantially the same refractive index as the second portion P2 of the support member 24.

[0126] According to the QCL unit 2A, the substrate 22 can be fixed to the support member 24 more stably than when no adhesive layer 26a is provided between the end face 22a of the substrate 22 and the face 24b of the support member 24 (i.e., QCL unit 2). Furthermore, by providing the adhesive layer 26a, which has substantially the same refractive index as the second portion P2, between the face 24b and the end face 22a, it is possible to suppress the loss of the terahertz wave that may occur when an adhesive layer with a refractive index relatively different from that of the second portion P2 is disposed between the face 24b and the end face 22a. Furthermore, since it is possible to prevent an air layer from being interposed between the end face 22a and the face 24b, it is also possible to suppress the loss of the terahertz wave due to the air layer.

[0127] [Second Modification] 9B, the QCL unit 2B according to the second modification differs from the QCL unit 2 in that the end face 22b of the substrate 22 and the end face 232b of the active layer 232 (in this embodiment, the entire end face 23b of the semiconductor layer 23 including the end face 232b) protrude toward the second side S2 beyond the surface 24d of the support member 24. The end face 22b and the end face 23b are formed flush with each other.

[0128] According to the QCL unit 2B, when the first light is oscillated using an external resonator (movable diffraction grating 31) disposed at a position facing the end face 232b of the active layer 232, interference between the light emitted from the end face 232b toward the external resonator and the support member 24 (i.e., the portion including the surface 24d) can be more reliably prevented. As a result, a decrease in the coupling efficiency between the QCL element 21 and the external resonator can be more reliably avoided.

[0129] [Third and Fourth Modifications] As shown in FIGS. 10A and 10B, QCL units 2C and 2D according to the third and fourth modifications differ from the QCL unit 2 in that the support member 24 is composed of a first member 24A including a first portion P1 and a second member 24B including a second portion P2. The second member 24B is a separate member from the first member 24A. The first member 24A and the second member 24B are fixed to each other so that their relative positions do not shift. The method for fixing the first member 24A and the second member 24B to each other is not limited to a specific method. For example, the first member 24A and the second member 24B may be bonded (joined) using an adhesive or the like, or the first member 24A and the second member 24B may be fixed to each other via a member that sandwiches the first member 24A and the second member 24B.

[0130] In this embodiment, surface 24a (first surface) and surface 24b (second surface) are connected to each other, but "surface 24a and surface 24b are connected" means either a configuration in which the first part P1 including surface 24a and the second part P2 including surface 24b are integrally formed (i.e., a configuration in which the first member 24A and the second member 24B are not separated but are integrally formed), or a configuration in which the first member 24A and the second member 24B are fixed to each other so that the relative positional relationship between the first member 24A and the second member 24B does not change, as in the present modified example (third modified example and fourth modified example).

[0131] According to the above configuration, by separating the first portion P1 and the second portion P2 into separate members (first member 24A and second member 24B), it is possible to facilitate the manufacture of the support member 24. For example, if it is difficult to process with sufficient precision the portion where the surface 24a and the surface 24b intersect in the integrally formed support member 24, combining the first member 24A and the second member 24B makes it easier to achieve precision in the above portion, thereby making it easier to manufacture the support member 24.

[0132] 10A, in the QCL unit 2C, the support member 24 is divided into a first member 24A and a second member 24B by a boundary B, which is a plane along the surface 24a. That is, the support member 24 is divided into a portion (first member 24A) below the boundary B (the side opposite the side where the QCL element 21 is located with respect to the boundary B) and a portion (second member 24B) above the boundary B (the side where the QCL element 21 is located with respect to the boundary B). In the QCL unit 2C, the surface 24c of the support member 24 is formed by continuously connecting a surface 24c1 of the first member 24A and a surface 24c2 of the second member 24B. Similarly, the surface 24g of the support member 24 is formed by continuously connecting a surface 24g1 of the first member 24A and a surface 24g2 of the second member 24B.

[0133] 10B, in the QCL unit 2D, the support member 24 is divided into a first member 24A and a second member 24B with a plane along the surface 24b as a boundary surface B. That is, the support member 24 is divided into a portion (first member 24A) on the second side S2 of the boundary surface B (the side on which the QCL element 21 is located with respect to the boundary surface B) and a portion (second member 24B) on the first side S1 of the boundary surface B (the side opposite the side on which the QCL element 21 is located with respect to the boundary surface B). In the QCL unit 2D, the surface 24f of the support member 24 is formed by continuously connecting the surface 24f1 of the first member 24A and the surface 24f2 of the second member 24B. Similarly, the surface 24g of the support member 24 is formed by continuously connecting the surface 24g1 of the first member 24A and the surface 24g2 of the second member 24B.

[0134] In either configuration of the QCL unit 2C or 2D, the support member 24 can be easily manufactured by combining two substantially rectangular parallelepiped members (the first member 24A and the second member 24B).

[0135] When the support member 24 is divided into a first member 24A including the first portion P1 and a second member 24B including the second portion P2, as in the third and fourth modifications, the first member 24A may be formed of a material with higher thermal conductivity than the second member 24B. The support member 24 has a role of emitting the terahertz wave L1 propagated through the substrate 22 from the surface 24c, but this role is mainly performed by the second portion P2 rather than the first portion P1. For this reason, the material of the first portion P1 may be a material with lower transmittance of the terahertz wave L1 than the second portion P2 but with higher thermal conductivity than the second portion P2. For example, the second portion P2 may be formed of the material of the support member 24 described above (HRFZ-Si), while the first portion P1 may be formed of a metal (Cu, Mo, etc.), a diamond-based material, ceramics (SiC, AlN, Al2O3, etc.), etc. According to the above configuration, the first member 24A of the support member 24, which is in contact with the bottom surface of the substrate 22 (the end surface 22d opposite to the active layer 232 side), is made of a material with higher thermal conductivity than the second member 24B. As a result, it is possible to improve the efficiency of dissipating heat generated in the QCL element 21, and to improve the operational reliability of the QCL element 21.

[0136] [Fifth Modification] As shown in FIG. 11 , a QCL unit 2E according to the fifth modification differs from the QCL unit 2 in that it includes a support member 240 instead of the support member 24. (B) of FIG. 11 is a schematic cross-sectional view of the QCL unit 2E taken along the line BB in (A) of FIG. 11 . The support member 240 includes a wall portion 241 standing on the surface 24a of the support member 240 on one side of the QCL element 21 in the direction D3, facing at least a portion of the substrate 22. In the example of FIG. 11 , the wall portion 241 is arranged to overlap the entire end surface 22e of the substrate 22 when viewed from the direction D3. That is, the upper surface of the wall portion 241 is flush with and continuous with the surface 24e. Furthermore, a side surface 241a of the wall portion 241 facing the end surface 22e of the substrate 22 abuts against the end surface 22e. That is, the wall portion 241 functions as a member for positioning the substrate 22 in the direction D3.

[0137] According to the QCL unit 2E, when fixing the QCL element 21 to the support member 240, the substrate 22 of the QCL element 21 is pressed against the wall 241, thereby facilitating the positioning of the QCL element 21 in the direction D3. Furthermore, compared to when the wall 241 is not provided, the contact area between the substrate 22 and the support member 240 can be increased by the area where the side surface 241a of the wall 241 contacts the end surface 22e of the substrate 22, thereby improving the efficiency of dissipating heat generated by the QCL element 21.

[0138] [Sixth Modification] The above-described QCL units 2, 2A to 2E are used in a configuration in which a member (holder 7 in this embodiment) supporting the QCL units 2, 2A to 2E is provided on the side of the substrate 22 opposite the semiconductor layer 23 (a so-called epi-side up state). On the other hand, as shown in Figures 12 and 13, a QCL unit 2F according to a sixth modification is used in a configuration in which a member (submount 30 in this example) supporting the QCL unit 2F is provided on the side of the substrate 22 where the semiconductor layer 23 is located (a so-called epi-side down state). That is, the QCL unit 2F is fixed not by attaching the support member 24 to another member (for example, holder 7), but by attaching the semiconductor layer 23 to another member (submount 30 in this case).

[0139] As shown in FIG. 13 , the QCL unit 2F is suitable for such epi-side-down assembly by having peripheral portions 101 and 102, each having a layer structure similar to that of the semiconductor layer 23, on both sides of the semiconductor layer 23 (ridge portion) in the direction D3. Grooves 201 and 202 are formed by etching between the semiconductor layer 23 and the peripheral portions 101 and 102. The first electrode 28 and the second electrode 29 are provided on the surface of the submount 30. The first electrode 28 is disposed between the submount 30 and the upper contact layer 236 of the semiconductor layer 23 and is electrically connected to the upper contact layer 236 via a contact hole 27a in the insulating film 27. The second electrode 29 is electrically connected to the lower contact layer 237 via contact holes 27c and 27d in the insulating film 27. The contact hole 27c is an opening provided in a portion of the insulating film 27 formed across the semiconductor layer 23 and the peripheral portion 101, corresponding to the groove 201. The contact hole 27d is an opening provided in a portion of the insulating film 27 formed across the semiconductor layer 23 and the peripheral edge portion 102, corresponding to the groove portion 202.

[0140] As described above, the QCL unit including the QCL element 21 and the support member 24 may be configured in the epi-side up configuration (QCL units 2, 2A to 2E) or the epi-side down configuration (QCL unit 2F).

[0141] [Other variations] Although one embodiment of the present disclosure and several modified examples of the QCL unit (Modifications 1 to 6) have been described above, the present disclosure is not limited to the above embodiment. The materials and shapes of each component are not limited to the specific materials and shapes described above, and various materials and shapes other than those described above can be used. Furthermore, some components included in the above embodiment and each modified example (QCL units 2A to 2F) may be omitted or modified as appropriate, and can be combined in any manner.

[0142] For example, in the laser module 1 of the above embodiment, the QCL unit 2 is housed in the package 8. However, the QCL unit 2 may be used without being housed in the package 8. Furthermore, when the QCL element 21 is configured to be able to emit the first light and the second light by itself (i.e., when the end faces 232a and 232b of the active layer 232 form resonators for both the first light and the second light), the movable diffraction grating 31 as the external resonator may be omitted. That is, the laser module according to the present disclosure may be configured only with the QCL unit. Furthermore, when the laser module 1 includes the package 8, the size of the package 8 is not particularly limited. That is, the laser module 1 is not necessarily limited to one that is miniaturized to a size equal to or smaller than a handheld device. Furthermore, the type of package 8 is not limited to a butterfly package. Furthermore, in the above embodiment, the lens 6 also serves as a light entrance window (window material) of the package 8. However, the lens 6 may be housed inside the package 8. In this case, a window material other than the lens 6 may be provided in the through-hole 85 of the side wall 822 of the package 8. [Explanation of symbols]

[0143] 1...laser module, 4...lens (second lens), 6...lens (first lens), 7...holder, 8...package, 21...quantum cascade laser element, 22...substrate, 21a...end face (first end face), 21b...end face (second end face), 22a...end face (first substrate end face), 22b...end face (second substrate end face), 22c...end face (third substrate end face), 22d...end face (fourth substrate end face), 24, 240...support member, 24A...first member, 24B...second member, 24a...surface (first surface), 24b...surface (second surface), 24c...surface (third surface), 24d...surface (fourth surface), 25...reflective film, 26...adhesive layer (first adhesive layer), 26a...adhesive layer (second adhesive layer), 31...movable diffraction grating, 61...light incident surface (lens surface), 231...lower cladding layer (first cladding layer), 232...active layer, 232a...end surface (first active layer end surface), 232b...end surface (second active layer end surface), 233...upper cladding layer (second cladding layer), 241...wall portion, B...boundary surface, D1...direction (first direction), D2...direction (second direction), D3...direction (third direction), L1...terahertz wave, P1...first portion, P2...second portion, S1...first side, S2...second side, ω1...first frequency, ω2...second frequency, ω3...difference frequency.

Claims

1. a quantum cascade laser element including: a substrate; a first clad layer provided on the substrate; an active layer provided on the first clad layer opposite to the substrate, the active layer generating a terahertz wave having a difference frequency between a first frequency and a second frequency; and a second clad layer provided on the active layer opposite to the first clad layer; a support member that supports the substrate of the quantum cascade laser element and propagates the terahertz wave; Equipped with The quantum cascade laser device is a first end face located on a first side 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; a second end surface located on a second side opposite to the first side in the second direction; and The substrate is a first substrate end surface that forms a part of the first end surface and extends along the first direction and a third direction that is perpendicular to the first direction and the second direction; a second substrate end surface constituting a part of the second end surface; a third substrate end surface facing the active layer in the first direction; a fourth substrate end surface located on the opposite side to the third substrate end surface in the first direction; and The active layer is a first active layer end face that constitutes a part of the first end face and that constitutes a resonator for oscillating the light of the first frequency and the light of the second frequency; a second active layer end surface constituting a part of the second end surface; and The support member is a first portion having a first surface facing at least a portion of the fourth substrate end surface; a second portion having a second surface connected to the first surface and facing at least a portion of the first substrate end surface, and a third surface located on the opposite side to the second surface in the second direction; and at least a portion of the terahertz waves generated in the active layer is incident on the second surface of the support member through the substrate, passes through an inside of the second portion, and is emitted from the third surface; the third surface is inclined with respect to the second surface so as to approach the second surface from the third substrate end surface side toward the fourth substrate end surface side along the first direction; Laser module.

2. A quantum cascade laser element having a substrate, a first clad layer provided on the substrate, an active layer provided on the opposite side of the first clad layer from the substrate, the active layer generating terahertz waves at a difference frequency between a first frequency and a second frequency, and a second clad layer provided on the opposite side of the active layer from the first clad layer; a support member that supports the substrate of the quantum cascade laser element and propagates the terahertz wave; Equipped with The quantum cascade laser device is a first end face located on a first side 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; a second end surface located on a second side opposite to the first side in the second direction; and The substrate is a first substrate end surface that forms a part of the first end surface and extends along the first direction and a third direction that is perpendicular to the first direction and the second direction; a second substrate end surface constituting a part of the second end surface; a third substrate end surface facing the active layer in the first direction; a fourth substrate end surface located on the opposite side to the third substrate end surface in the first direction; and The active layer is a first active layer end face that constitutes a part of the first end face and that constitutes a resonator for oscillating the light of the first frequency and the light of the second frequency; a second active layer end surface constituting a part of the second end surface; and The support member is a first portion having a first surface facing at least a portion of the fourth substrate end surface; a second portion having a second surface connected to the first surface and facing at least a portion of the first substrate end surface, and a third surface located on the opposite side to the second surface in the second direction; and at least a portion of the terahertz waves generated in the active layer is incident on the second surface of the support member through the substrate, passes through an inside of the second portion, and is emitted from the third surface; the first active layer end face is located on the second side of the first substrate end face so as to be spaced apart from the second surface in the second direction; Laser module.

3. a reflective film provided to cover an end face of the first active layer and configured to improve reflectance of the light of the first frequency and the light of the second frequency; 3. The laser module according to claim 1.

4. A quantum cascade laser element having a substrate, a first clad layer provided on the substrate, an active layer provided on the opposite side of the first clad layer from the substrate, the active layer generating terahertz waves at a difference frequency between a first frequency and a second frequency, and a second clad layer provided on the opposite side of the active layer from the first clad layer; a support member that supports the substrate of the quantum cascade laser element and propagates the terahertz wave; Equipped with The quantum cascade laser device is a first end face located on a first side 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; a second end surface located on a second side opposite to the first side in the second direction; and The substrate is a first substrate end surface that forms a part of the first end surface and extends along the first direction and a third direction that is perpendicular to the first direction and the second direction; a second substrate end surface constituting a part of the second end surface; a third substrate end surface facing the active layer in the first direction; a fourth substrate end surface located on the opposite side to the third substrate end surface in the first direction; and The active layer is a first active layer end face that constitutes a part of the first end face and that constitutes a resonator for oscillating the light of the first frequency and the light of the second frequency; a second active layer end surface constituting a part of the second end surface; and The support member is a first portion having a first surface facing at least a portion of the fourth substrate end surface; a second portion having a second surface connected to the first surface and facing at least a portion of the first substrate end surface, and a third surface located on the opposite side to the second surface in the second direction; and at least a portion of the terahertz waves generated in the active layer is incident on the second surface of the support member through the substrate, passes through an inside of the second portion, and is emitted from the third surface; The first portion and the second portion are integrally formed. Laser module.

5. The support member has a first member including the first portion and a second member including the second portion and being a separate member from the first member. The laser module according to any one of claims 1 to 3.

6. A quantum cascade laser element having a substrate, a first clad layer provided on the substrate, an active layer provided on the opposite side of the first clad layer from the substrate, the active layer generating terahertz waves at a difference frequency between a first frequency and a second frequency, and a second clad layer provided on the opposite side of the active layer from the first clad layer; a support member that supports the substrate of the quantum cascade laser element and propagates the terahertz wave; Equipped with The quantum cascade laser device is a first end face located on a first side 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; a second end surface located on a second side opposite to the first side in the second direction; and The substrate is a first substrate end surface that forms a part of the first end surface and extends along the first direction and a third direction that is perpendicular to the first direction and the second direction; a second substrate end surface constituting a part of the second end surface; a third substrate end surface facing the active layer in the first direction; a fourth substrate end surface located on the opposite side to the third substrate end surface in the first direction; and The active layer is a first active layer end face that constitutes a part of the first end face and that constitutes a resonator for oscillating the light of the first frequency and the light of the second frequency; a second active layer end surface constituting a part of the second end surface; and The support member is a first portion having a first surface facing at least a portion of the fourth substrate end surface; a second portion having a second surface connected to the first surface and facing at least a portion of the first substrate end surface, and a third surface located on the opposite side to the second surface in the second direction; and at least a portion of the terahertz waves generated in the active layer is incident on the second surface of the support member through the substrate, passes through an inside of the second portion, and is emitted from the third surface; the support member has a first member including the first portion and a second member including the second portion and being a separate member from the first member, The support member is divided into the first member and the second member by a plane along the first surface as a boundary surface. Laser module.

7. The support member is divided into the first member and the second member by a plane along the second surface as a boundary surface.

6. The laser module according to claim 5.

8. The first member is formed of a material having a higher thermal conductivity than the second member. The laser module according to any one of claims 5 to 7.

9. A quantum cascade laser element having a substrate, a first clad layer provided on the substrate, an active layer provided on the opposite side of the first clad layer from the substrate, the active layer generating terahertz waves at a difference frequency between a first frequency and a second frequency, and a second clad layer provided on the opposite side of the active layer from the first clad layer; a support member that supports the substrate of the quantum cascade laser element and propagates the terahertz wave; Equipped with The quantum cascade laser device is a first end face located on a first side 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; a second end surface located on a second side opposite to the first side in the second direction; and The substrate is a first substrate end surface that forms a part of the first end surface and extends along the first direction and a third direction that is perpendicular to the first direction and the second direction; a second substrate end surface constituting a part of the second end surface; a third substrate end surface facing the active layer in the first direction; a fourth substrate end surface located on the opposite side to the third substrate end surface in the first direction; and The active layer is a first active layer end face that constitutes a part of the first end face and that constitutes a resonator for oscillating the light of the first frequency and the light of the second frequency; a second active layer end surface constituting a part of the second end surface; and The support member is a first portion having a first surface facing at least a portion of the fourth substrate end surface; a second portion having a second surface connected to the first surface and facing at least a portion of the first substrate end surface, and a third surface located on the opposite side to the second surface in the second direction; and at least a portion of the terahertz waves generated in the active layer is incident on the second surface of the support member through the substrate, passes through an inside of the second portion, and is emitted from the third surface; the first portion has a fourth surface connected to the first surface and facing the second side in the second direction; the second substrate end surface, the second active layer end surface, and the fourth surface are formed flush with each other. Laser module.

10. A quantum cascade laser element having a substrate, a first clad layer provided on the substrate, an active layer provided on the opposite side of the first clad layer from the substrate, the active layer generating terahertz waves at a difference frequency between a first frequency and a second frequency, and a second clad layer provided on the opposite side of the active layer from the first clad layer; a support member that supports the substrate of the quantum cascade laser element and propagates the terahertz wave; Equipped with The quantum cascade laser device is a first end face located on a first side 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; a second end surface located on a second side opposite to the first side in the second direction; and The substrate is a first substrate end surface that forms a part of the first end surface and extends along the first direction and a third direction that is perpendicular to the first direction and the second direction; a second substrate end surface constituting a part of the second end surface; a third substrate end surface facing the active layer in the first direction; a fourth substrate end surface located on the opposite side to the third substrate end surface in the first direction; and The active layer is a first active layer end face that constitutes a part of the first end face and that constitutes a resonator for oscillating the light of the first frequency and the light of the second frequency; a second active layer end surface constituting a part of the second end surface; and The support member is a first portion having a first surface facing at least a portion of the fourth substrate end surface; a second portion having a second surface connected to the first surface and facing at least a portion of the first substrate end surface, and a third surface located on the opposite side to the second surface in the second direction; and at least a portion of the terahertz waves generated in the active layer is incident on the second surface of the support member through the substrate, passes through an inside of the second portion, and is emitted from the third surface; the first portion has a fourth surface connected to the first surface and facing the second side in the second direction; the second substrate end surface and the second active layer end surface protrude toward the second side beyond the fourth surface; Laser module.

11. the first surface is bonded to an end surface of the fourth substrate via an adhesive layer; the second surface is not bonded to the end surface of the first substrate; The laser module according to any one of claims 1 to 10.

12. A quantum cascade laser element having a substrate, a first clad layer provided on the substrate, an active layer provided on the opposite side of the first clad layer from the substrate, the active layer generating terahertz waves at a difference frequency between a first frequency and a second frequency, and a second clad layer provided on the opposite side of the active layer from the first clad layer; a support member that supports the substrate of the quantum cascade laser element and propagates the terahertz wave; Equipped with The quantum cascade laser device is a first end face located on a first side 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; a second end surface located on a second side opposite to the first side in the second direction; and The substrate is a first substrate end surface that forms a part of the first end surface and extends along the first direction and a third direction that is perpendicular to the first direction and the second direction; a second substrate end surface constituting a part of the second end surface; a third substrate end surface facing the active layer in the first direction; a fourth substrate end surface located on the opposite side to the third substrate end surface in the first direction; and The active layer is a first active layer end face that constitutes a part of the first end face and that constitutes a resonator for oscillating the light of the first frequency and the light of the second frequency; a second active layer end surface constituting a part of the second end surface; and The support member is a first portion having a first surface facing at least a portion of the fourth substrate end surface; a second portion having a second surface connected to the first surface and facing at least a portion of the first substrate end surface, and a third surface located on the opposite side to the second surface in the second direction; and at least a portion of the terahertz waves generated in the active layer is incident on the second surface of the support member through the substrate, passes through an inside of the second portion, and is emitted from the third surface; the first surface is bonded to an end surface of the fourth substrate via a first adhesive layer; the second surface is bonded to the end surface of the first substrate via a second adhesive layer; the second adhesive layer has substantially the same refractive index as the second portion of the support member; Laser module.

13. the second portion has substantially the same refractive index as the substrate; The laser module according to any one of claims 1 to 12.

14. a first lens disposed at a position facing the third surface and configured to pass the terahertz wave propagated inside the support member; The laser module according to any one of claims 1 to 13.

15. a lens surface of the first lens facing the support member is in contact with the third surface, The first lens has substantially the same refractive index as the second portion. The laser module according to claim 14.

16. When viewed from the third direction, the support member does not overlap the quantum cascade laser element. The laser module according to any one of claims 1 to 15.

17. A quantum cascade laser element having a substrate, a first clad layer provided on the substrate, an active layer provided on the opposite side of the first clad layer from the substrate, the active layer generating terahertz waves at a difference frequency between a first frequency and a second frequency, and a second clad layer provided on the opposite side of the active layer from the first clad layer; a support member that supports the substrate of the quantum cascade laser element and propagates the terahertz wave; Equipped with The quantum cascade laser device is a first end face located on a first side 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; a second end surface located on a second side opposite to the first side in the second direction; and The substrate is a first substrate end surface that forms a part of the first end surface and extends along the first direction and a third direction that is perpendicular to the first direction and the second direction; a second substrate end surface constituting a part of the second end surface; a third substrate end surface facing the active layer in the first direction; a fourth substrate end surface located on the opposite side to the third substrate end surface in the first direction; and The active layer is a first active layer end face that constitutes a part of the first end face and that constitutes a resonator for oscillating the light of the first frequency and the light of the second frequency; a second active layer end surface constituting a part of the second end surface; and The support member is a first portion having a first surface facing at least a portion of the fourth substrate end surface; a second portion having a second surface connected to the first surface and facing at least a portion of the first substrate end surface, and a third surface located on the opposite side to the second surface in the second direction; and at least a portion of the terahertz waves generated in the active layer is incident on the second surface of the support member through the substrate, passes through an inside of the second portion, and is emitted from the third surface; the support member has a wall portion erected on the first surface so as to face at least a part of the substrate on one side of the quantum cascade laser element in the third direction; Laser module.

18. a holder that holds the quantum cascade laser element and the support member; a package that accommodates the quantum cascade laser element, the support member, and the holder; The laser module according to any one of claims 1 to 17.

19. a first lens disposed at a position facing the third surface and configured to pass the terahertz wave propagated inside the support member; a movable diffraction grating that forms an external resonator for light of the first frequency; a second lens disposed between the quantum cascade laser element and the movable diffraction grating, for transmitting light emitted from the second active layer end face and light returning from the movable diffraction grating to the quantum cascade laser element; the package further houses the movable diffraction grating and the second lens; an optical path between the first lens and the movable diffraction grating is disposed within the package; 20. The laser module of claim 18.

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