Semiconductor laser device

Abstract

To provide a semiconductor laser device capable of securing high airtightness of a package while suppressing damages of an anti-reflection coating provided to a light emission window.SOLUTION: A quantum cascade laser device 1 comprises: a QCL element 2; and a package 3. On a side wall 32 of the package 3, a light emission window 11 passing through a laser beam L emitted from the QCL element 2 is provided. The light emission window 11 is structured by: a small diameter hole 12; a large diameter hole 13 larger than the small diameter hole 12; an annular counterbore face 14 connecting the small diameter hole 12 and the large diameter hole 13; and a window member 15 arranged inside of the large diameter hole 13. An incidence face 15a of the window member 15 includes: a first region A1 providing an anti-reflection coating 151; and a second region A2 which is annularly formed so as to circumference the first region A1 so as to be separated from the first region A1, and is metalized. The second region A2 is bonded to the annular counterbore face 14 via a solder member 16.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] Conventionally, a semiconductor laser device (semiconductor laser module) in which a semiconductor laser element is housed in a package is known (for example, Patent Document 1). In the semiconductor laser device, a light emission window for extracting laser light emitted from the semiconductor laser element to the outside of the package is provided in a side wall of the package. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-315633 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned semiconductor laser device, an anti-reflection film may be formed on the light exit window to improve the efficiency of laser light extraction. If the heat resistance of the anti-reflection film is relatively low, the anti-reflection film may be damaged by the heat generated during brazing when the light exit window is brazed to the package using a brazing material with a relatively high melting point. In addition, in the above-mentioned semiconductor laser device, the inside of the package needs to be in a vacuum state or an inert gas atmosphere, so the package needs to be airtight.

[0005] In view of the above, an object of the present disclosure is to provide a semiconductor laser device that can suppress damage to an anti-reflection film provided on a light exit window and ensure high airtightness of the package. [Means for solving the problem]

[0006] A semiconductor laser device according to one aspect of the present disclosure includes a semiconductor laser element and a package that hermetically houses the semiconductor laser element, the package having a bottom wall, a side wall erected on the bottom wall and formed in an annular shape so as to surround an area in which the semiconductor laser element is housed when viewed from a direction perpendicular to the bottom wall, and a top wall that closes an opening of the side wall on the opposite side to the bottom wall, the side wall being provided with a light exit window through which laser light emitted from the semiconductor laser element passes, the light exit window having a first hole portion that opens toward the inside of the package in an optical axis direction along the optical axis of the laser light, and a second hole portion that opens toward the outside of the package, includes the first hole portion when viewed from the optical axis direction and is larger than the first hole portion. The package is composed of two holes, an annular countersunk surface that connects the first hole and the second hole and extends along a plane that intersects with the optical axis direction, and a window member arranged inside the second hole, the window member having an incident surface into which the laser light is incident, an exit surface that is the surface opposite to the incident surface and that emits the laser light that has passed through the window member to the outside of the package, and a side that connects the incident surface and the exit surface and extends along the optical axis direction, the incident surface includes a central portion of the incident surface and has a first region where a first anti-reflection film is provided, and a metallized second region that is spaced apart from the first region and formed in an annular shape to surround the first region, and the second region is joined to the countersunk surface via a solder member.

[0007] In the semiconductor laser device, the light exit window is joined to the side wall of the package by a solder member having a melting point lower than that of the brazing material. This makes it possible to closely contact the window member and the countersink surface while suppressing damage to the window member (particularly the antireflection film) due to heat, as compared to the case where the brazing material is used. In addition, on the entrance surface of the window member, the first region where the antireflection film (first antireflection film) is provided and the second region where the solder member is bonded are separated from each other. This makes it possible to suppress the stress when the solder member in the second region melts or solidifies from being transmitted to the antireflection film on the first region. As a result, damage (cracks, peeling, etc.) of the antireflection film caused by the above stress is suppressed. As described above, according to the semiconductor laser device, damage to the antireflection film provided on the light exit window can be suppressed and high airtightness of the package can be ensured.

[0008] The side surface may have a third region that is metallized so as to be continuous with the second region, and at least a part of the side surface may be joined to at least a part of the inner surface of the second hole portion via a solder member. According to the above configuration, since the region that is continuous from the second region to the side surface (third region) of the window member is metallized, a part of the solder member can be suitably wetted and spread toward the third region during solder joining. As a result, the solder member can be interposed between the side surface of the window member and the inner surface of the second hole portion, and the airtightness of the package can be suitably improved.

[0009] The length of the first hole along the optical axis direction may be shorter than the length of the second hole along the optical axis direction. With the above configuration, the light exit window can be brought closer to the semiconductor laser element compared to when the length of the first hole is equal to or longer than the length of the second hole. This makes it possible to make the laser light enter the light exit window while the spread of the laser light is still small, even when the beam radiation angle of the laser light emitted from the semiconductor laser element is large. As a result, the light exit window can be made smaller, and the package can be made smaller.

[0010] The exit surface may have a fourth region provided with a second anti-reflection film, and the fourth region may include the first region and be larger than the first region when viewed from the optical axis direction. When a laser beam, which is a diverging beam, enters the window member, the region through which the laser beam passes on the entrance surface of the window member is smaller than the region through which the laser beam passes on the exit surface of the window member. Therefore, as in the above configuration, by making the first anti-reflection film on the entrance surface side smaller than the second anti-reflection film on the exit surface side (i.e., by making the first region smaller than the fourth region), a region corresponding to the difference between the fourth region and the first region can be secured as the second region. In this way, by designing the sizes of the first region, the second region, and the fourth region in consideration of the beam radiation angle of the laser beam, the window member can be made smaller, and thus the package can be made smaller.

[0011] The semiconductor laser device may further include a lens disposed outside the package for focusing or collimating the laser light transmitted through the light exit window. According to the above configuration, the lens is an external member disposed outside the package, which makes it possible to flexibly arrange and replace the lens.

[0012] The wavelength of the laser light may be in the range of 4 μm to 12 μm. Generally, an anti-reflection film compatible with light of 4 μm to 12 μm has a low heat resistance temperature, but in the semiconductor laser device, a solder member having a relatively low melting point is used as a joining material, so that the window member provided with the anti-reflection film can be attached to the side wall by solder joining while suppressing damage to the anti-reflection film due to heat.

[0013] The light exit surface of the window member may protrude beyond the outer surface of the package of the side wall on which the light exit window is provided. This configuration can improve the workability when joining the window member to the side wall from the outside of the package. In addition, when an external lens is attached to the light exit surface of the window member, the workability of attaching the lens can also be improved. Effect of the Invention

[0014] According to the present disclosure, it is possible to provide a semiconductor laser device that can suppress damage to an anti-reflection film provided on a light exit window and ensure high airtightness of the package. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view of a quantum cascade laser device according to one embodiment. [Diagram 2] FIG. 2 is a cross-sectional side view of the quantum cascade laser device shown in FIG. [Diagram 3] FIG. 3 is a plan view of the quantum cascade laser device shown in FIG. [Figure 4] FIG. 4 is a diagram showing a typical example of the relationship between the radiation angle (horizontal axis) and the radiation intensity (vertical axis) of laser light emitted by a quantum cascade laser. [Diagram 5] FIG. 5 is a partially enlarged view of the quantum cascade laser device shown in FIG. [Figure 6] FIG. 6 is a front view of a portion of the side wall including the small diameter hole and the large diameter hole. [Figure 7] In FIG. 7, (A) is a diagram showing the entrance surface of the window member, (B) is a cross-sectional view of the window member, and (C) is a diagram showing the exit surface of the window member. [Figure 8] In FIG. 8, (A) is a top view of the Peltier module, and (B) is a side view of the Peltier module. [Figure 9] In FIG. 9, (A) is a top view of the heat spreader, (B) is a side view of the heat spreader, and (C) is a bottom view of the heat spreader. [Figure 10] In FIG. 10, (A) is a top view of a heat sink on which each element is mounted, and (B) is a side view of the heat sink on which each element is mounted. [Figure 11] FIG. 11 is a perspective view of the lens holder. [Figure 12] FIG. 12 is a front view of the lens holder. [Figure 13] In FIG. 13, (A) is a top view of the lens holder, (B) is a bottom view of the lens holder, and (C) is a side cross-sectional view of the lens holder. [Figure 14] FIG. 14 is a diagram illustrating a cross section taken along line XIV-XIV in FIG. [Figure 15] FIG. 15 is a diagram showing a schematic positional relationship between a lens and a lens holder when a lens holder according to a comparative example is used. [Figure 16] FIG. 16 is a diagram showing a part of an assembly procedure of the quantum cascade laser device shown in FIG. [Figure 17] In FIG. 17, (A) is a front view of the lens holder of the first modified example, and (B) is a cross-sectional view of the lens holder taken along line BB in (A). [Figure 18]In FIG. 18, (A) is a front view of the lens holder of the second modified example, and (B) is a cross-sectional view of the lens holder taken along line BB in (A). [Figure 19] In FIG. 19, (A) is a front view of a lens holder of a third modified example, and (B) is a cross-sectional view of the lens holder taken along line BB in (A). [Figure 20] FIG. 20 is a side cross-sectional view of a modified quantum cascade laser device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding parts are given the same reference numerals, and duplicated explanations will be omitted. Note that in the drawings, some parts are exaggerated to easily explain the configuration according to the embodiment, and may differ from the actual dimensions. In the following description, the terms "upper", "lower", etc. are used for convenience based on the state shown in the drawings.

[0017] As shown in FIGS. 1 to 3, a quantum cascade laser device 1 (semiconductor laser device) includes a quantum cascade laser element (hereinafter, “QCL ​​element”) 2 and a package 3 that accommodates the QCL element 2 airtightly.

[0018] The QCL element 2 is a type of semiconductor laser element. The QCL element 2 has an end face 2a (emission face) intersecting in one direction (the X-axis direction in this embodiment), and is configured to emit laser light L of a wide band wavelength (for example, 4 μm to 12 μm) in the mid-infrared region from the end face 2a. In this embodiment, the optical axis of the laser light L emitted from the QCL element 2 is along the X-axis direction. The QCL element 2 has a structure in which, for example, a plurality of active layers having different central wavelengths are stacked in a stacked shape, and can emit the above-mentioned wide band light. However, the QCL element 2 may have a structure consisting of a single active layer, and can also emit the above-mentioned wide band light. As shown in FIG. 4, the laser light L emitted from the QCL element 2 has a beam radiation angle (divergence angle) that is very large compared to a laser diode or the like, based on the principle of the quantum cascade laser.

[0019] The package 3 is a so-called butterfly package. The package 3 has a bottom wall 31, a side wall 32, and a top wall 33. In Fig. 3, the top wall 33 of the package 3 is not shown.

[0020] The bottom wall 31 is a rectangular plate-shaped member. The bottom wall 31 is formed of a metal material such as copper tungsten. The bottom wall 31 is a base member on which various members such as the Peltier module 4 described later are mounted. For convenience, in this specification, the longitudinal direction of the bottom wall 31 is represented as the X-axis direction, the lateral direction of the bottom wall 31 is represented as the Y-axis direction, and the direction perpendicular to the bottom wall 31 (i.e., the direction perpendicular to the X-axis direction and the Y-axis direction) is represented as the Z-axis direction. As described above, the X-axis direction is also the direction along the optical axis of the laser light L emitted from the QCL element 2 (optical axis direction).

[0021] The side wall 32 is erected on the bottom wall 31. When viewed from the Z-axis direction, the side wall 32 is formed in an annular shape so as to surround an area (internal space S) in which the QCL element 2 and the like are housed. In this embodiment, the side wall 32 is a rectangular tubular member surrounding the internal space S. The side wall 32 is formed of a metal material such as Kovar. The side wall 32 is, for example, a Kovar frame plated with Ni / Au. In this embodiment, the side wall 32 is provided in the center of the bottom wall 31 in the longitudinal direction (X-axis direction). The width of the side wall 32 in the short-side direction (Y-axis direction) is the same as the width of the bottom wall 31 in the short-side direction, and the width of the side wall 32 in the long-side direction (X-axis direction) is shorter than the width of the bottom wall 31 in the long-side direction. That is, on both sides of the bottom wall 31 in the long-side direction, protruding parts 31a are formed so as to protrude outward from the side wall 32. At portions of the protruding portion 31a corresponding to the four corners of the bottom wall 31, screw holes 31b are provided for attaching the package 3 (bottom wall 31) to another member.

[0022] The top wall 33 is a member that closes an opening of the side wall 32 on the opposite side to the bottom wall 31. The top wall 33 has a rectangular plate shape. The outer shape (lengthwise and widthwise) of the top wall 33 as viewed from the Z-axis direction approximately matches the outer shape of the side wall 32. The top wall 33 is formed, for example, from the same metal material (e.g., Kovar) as the side wall 32.

[0023] A plurality of lead pins 10 (14 in total, seven on each side in the short-side direction) are inserted into a portion 321 of the side wall 32 extending along the longitudinal direction (X-axis direction) (i.e., the portion intersecting the short-side direction (Y-axis direction)) for passing current through components such as the QCL element 2 housed in the package 3.

[0024] A light emission window 11 is provided on one of the portions 322 of the side wall 32 extending along the short side direction (Y-axis direction) (i.e., the portion intersecting the long side direction (X-axis direction)) to pass the laser light L emitted from one end face 2a of the QCL element 2.

[0025] 5 and 6, the light exit window 11 is composed of a small diameter hole 12 (first hole portion), a large diameter hole 13 (second hole portion), and a countersunk surface 14, which are formed by a side wall 32 (portion 322), and a window member 15. The window member 15 is provided with anti-reflection films 151, 152 and a metal film 153, which will be described later (see FIG. 7). These members are very thin compared to the main body of the window member 15, and therefore are not shown in the drawings other than FIG. 7.

[0026] The small diameter hole 12 opens to the inside of the package 3 (i.e., the internal space S) in the optical axis direction (i.e., the X-axis direction) along the optical axis of the laser light L. The large diameter hole 13 opens to the outside of the package 3. When viewed from the X-axis direction, the large diameter hole 13 has a shape that includes the small diameter hole 12 and is larger than the small diameter hole 12. The small diameter hole 12 and the large diameter hole 13 each extend in the X-axis direction. The small diameter hole 12 and the large diameter hole 13 connected by the countersink surface 14 form a through hole penetrating in the X-axis direction. In this embodiment, each of the small diameter hole 12 and the large diameter hole 13 is formed in a circular shape, and the diameter d2 of the large diameter hole 13 is larger than the diameter d1 of the small diameter hole 12 (d2>d1). In addition, the central axis of the small diameter hole 12 and the central axis of the large diameter hole 13 may coincide with the optical axis of the laser light L emitted from the QCL element 2. The countersunk surface 14 is an annular surface that connects the small diameter hole 12 and the large diameter hole 13 and extends along a plane (YZ plane) that intersects with the X-axis direction. More specifically, the countersunk surface 14 connects the end of the small diameter hole 12 on the large diameter hole 13 side to the end of the large diameter hole 13 on the small diameter hole 12 side. The large diameter hole 13 and the countersunk surface 14 can be formed by performing a countersunk process from the outside of the package 3. In this embodiment, the countersunk surface 14 is formed in a continuous annular shape, but the countersunk surface 14 may be formed in a discontinuous annular shape. For example, a notch may be formed in a part of the inner wall surface of the small diameter hole 12, and the countersunk surface 14 may be divided at the part where the notch is formed.

[0027] In this embodiment, the diameter d1 of the small diameter hole 12 is 3.8 mm, the diameter d2 of the large diameter hole 13 is 5.7 mm, and the radial width ((d2-d1) / 2) of the countersunk surface 14 is 0.95 mm. The length w1 of the small diameter hole 12 along the X-axis direction is shorter than the length w2 of the large diameter hole 13 along the X-axis direction. In this embodiment, the thickness t (length along the X-axis direction) of the side wall 32 is 1 mm, the length w1 of the small diameter hole 12 is 0.23 mm, and the length w2 of the large diameter hole 13 is 0.77 mm.

[0028] The window member 15 is formed of a material (e.g., germanium, etc.) that transmits the laser light L having a wavelength in the mid-infrared region. The window member 15 is formed in a disk shape and is disposed inside the large diameter hole 13. The window member 15 has an incident surface 15a, an exit surface 15b, and a side surface 15c. The incident surface 15a and the exit surface 15b are surfaces that intersect with the X-axis direction and are formed in a circular shape. The incident surface 15a is a surface on the side of the internal space S, and is a surface on which the laser light L (in this embodiment, the laser light L collimated by the lens 8) is incident. The exit surface 15b is a surface on the opposite side to the incident surface 15a (i.e., a surface on the outer side of the package 3), and is a surface that emits the laser light L that has passed through the window member 15 to the outside of the package 3. The side surface 15c is a surface that connects the incident surface 15a and the exit surface 15b and extends along the X-axis direction. In this embodiment, the diameter of the window member 15 (the entrance surface 15a or the exit surface 15b) is 5.4 mm, and the thickness of the window member 15 (the length along the X-axis direction) is 0.7 mm.

[0029] As shown in (A) and (B) of FIG. 7, the incident surface 15a has a first region A1 and a second region A2. The first region A1 includes a central portion of the incident surface 15a, and is an area where an antireflection film 151 (first antireflection film) is provided. The antireflection film 151 is a film member having a function of suppressing reflection of the laser light L having a wavelength in the mid-infrared region on the incident surface 15a. The antireflection film 151 is formed of, for example, a high refractive index material such as germanium (Ge) or silicon (Si), an intermediate refractive index material such as zinc sulfide (ZnS) or zinc selenide (ZnSe), a low refractive index material such as yttrium fluoride (YF3), or a dielectric multilayer film in which a plurality of substances having different refractive indices that transmit mid-infrared light are alternately laminated. The antireflection film 151 is formed in a circular shape. The thickness (length along the X-axis direction) of the antireflection film 151 is determined according to the design of the transmission wavelength (the wavelength of the laser light L to be transmitted) of the antireflection film 151. The thickness of the antireflection film 151 is, for example, 1.0 μm or more and 3.0 μm or less. For example, when the design value of the transmission wavelength is 5.2 μm, the thickness of the antireflection film 151 is set to, for example, 1.4 μm. In this embodiment, the diameter of the antireflection film 151 (i.e., the diameter of the first region A1) is 4.2 mm.

[0030] The second region A2 is an annular region spaced apart from the first region A1 and surrounding the first region A1. The second region A2 is metallized with a metal film 153. The metal film 153 is made of a material suitable for solder bonding (i.e., a material having good affinity with the solder member 16 described later). The metal film 153 is made of, for example, Cr / Ni / Au (0.2 μm / 0.5 μm / 0.5 μm). In this embodiment, the inner diameter of the metal film 153 formed on the incident surface 15a (i.e., the inner diameter of the second region A2) is 4.5 mm. That is, in this embodiment, a 0.15 mm wide annular region in which the incident surface 15a (germanium base) is exposed is formed between the outer edge of the first region A1 and the inner edge of the second region A2.

[0031] 7B, the side surface 15c has a third region A3 that is metallized so as to be continuous with the second region A2. That is, the metal film 153 is provided continuously from the second region A2 to the side surface 15c.

[0032] 7B and 7C, the emission surface 15b has a fourth region A4 in which an antireflection film 152 (second antireflection film) is provided. The antireflection film 152 is a film member having a function of suppressing reflection of the laser light L having a wavelength in the mid-infrared region on the emission surface 15b. The antireflection film 152 is formed in a circular shape from the same material as the antireflection film 151. In this embodiment, the diameter of the antireflection film 152 (i.e., the diameter of the fourth region A4) is 4.6 mm. That is, the fourth region A4 is a region that includes the first region A1 and is larger than the first region A1 when viewed from the X-axis direction.

[0033] The window member 15 is directly bonded to the side wall 32 (portion 322). Specifically, the second region A2 of the incident surface 15a (i.e., the region metallized by the metal film 153) is bonded to the countersunk surface 14 via the solder member 16 formed in an annular shape. The solder member is a bonding material having a melting point of 450°C or less. The solder member 16 is formed, for example, from a SnAgCu-based solder material having a melting point of 220°C. The solder member 16 is originally a sheet-like member formed in an annular shape (see FIG. 16).

[0034] In this embodiment, the thickness of the solder member 16 before soldering (i.e., in the state of a circular ring-shaped sheet) is 0.1 mm, the outer diameter is 5.5 mm, and the inner diameter is 4.2 mm. That is, in this embodiment, the inner diameter (4.2 mm) of the solder member 16 is the same as the diameter (4.2 mm) of the first region A1, and the first region A1 and the solder member 16 do not overlap each other. In addition, the first region A1 where the anti-reflection film 151 is formed and the second region A2 where the metal film 153 is formed are separated from each other. In this way, the first region A1 and the second region A2 are completely separated, and there is a region between the first region A1 and the second region A2 where the base material of the window member 15 (germanium base material in this embodiment) is exposed, so that the solder member 16 is less likely to flow onto the first region A1 (on the anti-reflection film 151) during soldering. On the other hand, the solder member 16 easily wets and spreads over the metal film 153, which has high affinity with the solder member 16. This makes it difficult for stress generated when the solder member 16 melts or solidifies during soldering to be transmitted to the anti-reflection film 151 on the first region A1.

[0035] As described above, the solder member 16 spreads over the metal film 153, so that a portion of the solder member 16 also extends over the third region A3 (see FIG. 5). That is, a portion of the solder member 16 enters between the side surface 15c and the inner surface of the large diameter hole 13. That is, at least a portion of the side surface 15c of the window member 15 is joined to at least a portion of the inner surface of the large diameter hole 13 via the solder member 16. This effectively enhances the airtightness of the package 3 at the attachment portion of the window member 15.

[0036] In this embodiment, the emission surface 15b of the window member 15 is substantially flush with an outer surface 32a (the outer surface of the package 3) of the sidewall 32 on which the light emission window 11 is provided. That is, the length w2 of the large diameter hole 13 (i.e., the depth of the countersinking) is adjusted so that the emission surface 15b and the outer surface 32a of the sidewall 32 are substantially flush with each other.

[0037] Next, a description will be given of each member housed in the package 3. In addition to the QCL element 2, the internal space S formed by the package 3 mainly houses a Peltier module 4, a heat spreader 5, a heat sink 6, a submount 7, a lens 8, a lens holder 9, and a temperature sensor T (see FIG. 10).

[0038] The Peltier module 4 is a temperature control element for adjusting the temperature of the QCL element 2. Specifically, the Peltier module 4 has a cooling / heating function for maintaining the temperature of the QCL element 2 at a temperature corresponding to the oscillation wavelength of the QCL element 2. The temperature control by the Peltier module 4 is performed based on the temperature of the QCL element 2 measured by a temperature sensor T (see FIG. 10) mounted on the heat sink 6.

[0039] As shown in FIG. 8, the Peltier module 4 has a plurality of Peltier elements 41, which are thermoelectric semiconductor elements, and a pair of ceramic substrates 42, 43 that sandwich the plurality of Peltier elements 41 from above and below. The ceramic substrate 42 is provided on the top wall 33 side of the Peltier elements 41, and the ceramic substrate 43 is provided on the bottom wall 31 side of the Peltier elements 41. Each of the ceramic substrates 42, 43 is formed of, for example, alumina. The outer surface of each of the ceramic substrates 42, 43 (the surface opposite to the Peltier element 41 side) is a metallized surface on which a metal film 44 such as Cu / Ni / Au is formed by plating. The outer surfaces of the ceramic substrates 42, 43 are provided with an In foil 45, which is a solder member, via the metal film 44. The ceramic substrate 42 is solder-joined to the heat spreader 5 via the In foil 45. On the other hand, the ceramic substrate 43 is solder-joined to an upper surface 31c (the surface facing the top wall 33) of the bottom wall 31 of the package 3 via an In foil 45. Two lead wires 20 for passing a direct current to the Peltier module 4 are electrically connected to one of the ceramic substrates (the ceramic substrate 43 in this embodiment). The two lead wires 20 are each connected to a different lead pin 10.

[0040] The heat spreader 5 is a member mounted on the Peltier module 4, and dissipates heat generated in the QCL element 2 to the Peltier module 4. The heat spreader 5 is formed of a material with excellent thermal conductivity, such as copper. As shown in Fig. 9, the heat spreader 5 has a bottom surface 51 soldered to the Peltier module 4 via an In foil 45 (see Fig. 8) provided on a ceramic substrate 42, a first top surface 52 on which the heat sink 6 and the submount 7 are mounted, and a second top surface 53 (second mounting surface) on which the lens holder 9 is mounted.

[0041] Here, the thermal expansion coefficient of copper (approximately 17×10 -6 / K) is the thermal expansion coefficient of alumina (approximately 7×10 -6 / K). For this reason, in the case where the ceramic substrate 42 of the Peltier module 4 is made of alumina and the heat spreader 5 is made of copper, if the entire bottom surface 51 of the heat spreader 5 is joined to the ceramic substrate 42 via the In foil 45, there is a risk that a crack will occur in the Peltier element 41 due to long-term use of the quantum cascade laser device 1 or due to a large temperature difference that occurs between the upper and lower surfaces of the Peltier element 41 during temperature control.

[0042] Therefore, in this embodiment, grooves 51a are formed on the bottom surface 51 of the heat spreader 5 to divide the joint surface with the Peltier module 4 into multiple parts. In this embodiment, as an example, two grooves 51a extend along the short-side direction (Y-axis direction) at positions that divide the bottom surface 51 into three parts in the long-side direction (X-axis direction). The two grooves 51a divide the joint surface with the Peltier module 4 into three parts approximately equally. By dividing the joint surface with the Peltier module 4 into multiple parts (three in this case), stress caused by the difference in thermal expansion coefficient between the material (alumina) of the ceramic substrate 42 and the material (copper) of the heat spreader 5 is reduced, and the occurrence of cracks in the Peltier element 41 described above is suppressed.

[0043] Furthermore, the four corners (corners) of the Peltier module 4 are particularly weak in mechanical strength. Therefore, in this embodiment, notched grooves 51b are formed in the four corners of the bottom surface 51 of the heat spreader 5. This makes it possible to avoid bonding between the ceramic substrate 42 and the bottom surface 51 of the heat spreader 5 in the portions corresponding to the four corners of the Peltier module 4, and effectively reduces the stress on the four corners of the Peltier module 4 caused by the difference in the thermal expansion coefficients.

[0044] The groove portion 51a and the notched groove 51b described above also function as an escape route for air layers (voids) that are mixed in when the ceramic substrate 42 and the bottom surface 51 are solder-joined via the In foil 45. This makes it possible to improve the bonding quality and thermal conductivity between the Peltier module 4 (ceramic substrate 42) and the heat spreader 5.

[0045] Furthermore, by using a soft solder material such as In or InSn (In in this embodiment) as the solder material joining the Peltier module 4 (ceramic substrate 42) and the heat spreader 5, the stress of expansion or contraction due to heat can be suitably absorbed, thereby improving the reliability of the quantum cascade laser device 1.

[0046] The first upper surface 52 is located at a higher position (top wall 33 side) than the second upper surface 53. In the present embodiment, as an example, the first upper surface 52 is provided with two screw holes 52a for screwing the heat sink 6 and a protrusion 52b protruding upward (top wall 33 side). The protrusion 52b extends along the short direction (Y axis direction) at an end (end opposite to the second upper surface 53 side) in the longitudinal direction (X axis direction) of the first upper surface 52. The protrusion 52b is a portion for abutting against the end of the heat sink 6 for positioning.

[0047] A plurality of (four in this embodiment) convex portions 53a (second convex portions) formed in an island shape are provided on the second upper surface 53. The four convex portions 53a are portions to be bonded to a lens holder 9, which will be described later.

[0048] The heat sink 6 is a member mounted on the first upper surface 52 of the heat spreader 5. The heat sink 6 is formed of a material having excellent thermal conductivity, such as copper, similar to the heat spreader 5. The heat sink 6 is formed in a substantially rectangular parallelepiped shape. For example, the width of the heat sink 6 along the X-axis direction is 5 mm, and the width of the heat sink 6 along the Y-axis direction is 6 mm. As shown in FIG. 10, the upper surface 6a (surface on the top wall 33 side) of the heat sink 6 is mounted with a submount 7 on which the QCL element 2 is mounted, a temperature sensor T for measuring the temperature of the QCL element 2, and a ceramic pattern SP for wiring. The lower surface 6b of the heat sink 6 abuts against the first upper surface 52 of the heat spreader 5. In order to make it possible to easily replace the QCL element 2 when a defect occurs in the QCL element 2, the heat sink 6 is fixed to the heat spreader 5 by screws. In order to secure the screw, the heat sink 6 is provided with a screw hole 6c penetrating in the Z-axis direction and a countersunk groove 6d formed around the screw hole 6c. The screw hole 6c is provided at a position corresponding to the screw hole 52a (see FIG. 9) of the heat spreader 5 described above. For example, a screw member (not shown) having a screw locking agent (adhesive for preventing the screw from loosening) applied to its tip is inserted into the screw hole 6c and the screw hole 52a, thereby fixing the heat sink 6 to the heat spreader 5. The countersunk groove 6d is a groove portion provided to accommodate the head of the screw member. Note that, as the screw locking agent, a thermosetting resin adhesive (e.g., epoxy resin, etc.) that does not generate outgas is preferably used.

[0049] The temperature sensor T and the ceramic pattern SP are electrically connected to a predetermined lead pin 10 via a wire (not shown). The QCL element 2 is also electrically connected to a predetermined lead pin 10 via the ceramic pattern SP and a wire (not shown). This allows power to be supplied to the QCL element 2 and the temperature sensor T from an external power supply device via the lead pin 10.

[0050] The submount 7 is a rectangular plate-like member on which the QCL element 2 is mounted. The QCL element 2 is mounted on the submount 7 so that the optical axis of the laser light L emitted from the end face 2a coincides with the center of the light emission window 11 (i.e., the central axis of the small diameter hole 12 and the large diameter hole 13). The submount 7 is made of a material (e.g., aluminum nitride, etc.) having a thermal expansion coefficient close to that of the QCL element 2. The QCL element 2 and the submount 7 are joined via, for example, an AnSn-based solder material. The submount 7 and the heat sink 6 are joined via, for example, an SnAgCuNiGe-based solder material.

[0051] Next, the lens 8 and the lens holder 9 will be described with reference to Figs. 11 to 15. As described above, the laser light L has a relatively large beam radiation angle due to the principle of the quantum cascade laser (see Fig. 4). Therefore, in order to effectively use the laser light L, it is necessary to perform beam shaping (focusing, collimation, etc.) of the laser light L using optical elements such as lenses. On the other hand, since the laser light L having an oscillation wavelength in the mid-infrared region is invisible, an expensive beam monitor or detector having sensitivity in the mid-infrared region is required to perform alignment (positioning) of the lens for the above beam shaping. Therefore, in this embodiment, the lens 8 for performing the above beam shaping is built in advance inside the package 3. This configuration has the advantage that the user does not need to align the lens (external lens).

[0052] The lens 8 is a member for collecting or collimating the laser light L emitted from the QCL element 2. The lens holder 9 is a member for holding the lens 8. The lens 8 is disposed opposite to an end face 2a, which is the emission surface of the QCL element 2 from which the laser light L is emitted.

[0053] The lens 8 is, for example, an aspheric lens made of ZnSe. As shown in FIG. 11 and FIG. 14, the lens 8 has an incident surface 8a, a side surface 8b, and an exit surface 8c. The incident surface 8a is a surface on which the laser light L is incident. In this embodiment, the incident surface 8a is a flat surface. The side surface 8b is a surface extending from the edge of the incident surface 8a along the optical axis direction (i.e., the X-axis direction) of the laser light L. The exit surface 8c is a surface from which the laser light L that has passed through the lens 8 is exited. In this embodiment, the exit surface 8c is formed in an aspheric curved shape. In this embodiment, the diameter of the lens 8 (the diameter of the incident surface 8a) is 5 mm, and the effective diameter of the lens 8 is 4.5 mm. The effective diameter of lens 8 is the diameter of an incident beam that can satisfy the optical characteristics of the lens on a plane (incident plane 8a) perpendicular to the optical axis direction (X-axis direction) of laser light L (if lens 8 is a collimating lens, the diameter of incident light that can be transmitted and collimated as a lens specification). The area within the effective diameter of lens 8 is called the effective area.

[0054] As shown in FIG. 11, the lens holder 9 is a member having an approximately rectangular parallelepiped shape. The lens holder 9 is formed of, for example, aluminum with a black alumite surface treatment. A through hole penetrating along the X-axis direction is provided in the center of the lens holder 9 as viewed from the X-axis direction. The lens holder 9 has a small diameter hole 9a and a large diameter hole 9b constituting the through hole. The small diameter hole 9a and the large diameter hole 9b each extend in the X-axis direction. The large diameter hole 9b is provided at a position farther away from the QCL element 2 than the small diameter hole 9a. That is, the small diameter hole 9a is provided closer to the QCL element 2 than the large diameter hole 9b. The large diameter hole 9b has a shape including the small diameter hole 9a and larger than the small diameter hole 9a when viewed from the X-axis direction. The large diameter hole 9b is formed to a size larger than the outer shape of the lens 8 so that the lens 8 can be accommodated inside it. In this embodiment, each of the small diameter hole 9a and the large diameter hole 9b is formed in a circular shape. The small diameter hole 9a and the large diameter hole 9b are connected by an annular countersunk surface 9c extending along a plane (YZ plane) intersecting the X-axis direction. More specifically, the countersunk surface 9c connects the end of the small diameter hole 9a on the large diameter hole 9b side to the end of the large diameter hole 9b on the small diameter hole 9a side. In this embodiment, the countersunk surface 9c is formed in a continuous annular shape, but the countersunk surface 9c may be formed in a discontinuous annular shape. For example, a notch may be formed in a part of the inner wall surface of the small diameter hole 9a, and the countersunk surface 9c may be divided at the part where the notch is formed.

[0055] 11 and 12, a groove 9d (recess) is formed on the inner surface of the large diameter hole 9b along the X-axis direction, extending from the end of the lens holder 9 opposite the QCL element 2 side to the countersunk surface 9c. In this embodiment, a pair of grooves 9d facing each other are formed along one diagonal of the rectangular lens holder 9 when viewed from the X-axis direction.

[0056] As shown in Fig. 12 and Fig. 14, the central axis AX1 of the small diameter hole 9a does not coincide with the central axis AX2 of the large diameter hole 9b. That is, the central axis AX1 of the small diameter hole 9a is eccentric from the central axis AX2 of the large diameter hole 9b. In Fig. 14, the pair of grooves 9d is ignored for ease of understanding. That is, Fig. 14 shows a schematic cross-sectional structure taken along line XIV-XIV in Fig. 12, assuming that the pair of grooves 9d is not provided in the large diameter hole 9b.

[0057] In this embodiment, the central axis AX1 of the small diameter hole 9a is shifted in a direction D with respect to the central axis AX2 of the large diameter hole 9b. The direction D is a direction from one groove portion 9d to the other groove portion 9d as viewed from the X-axis direction. The diameter d3 of the small diameter hole 9a is 4.5 mm, which is the same as the effective diameter of the lens 8, and the diameter d4 of the large diameter hole 9b is 5.15 mm. As described above, since the central axis AX1 is decentered with respect to the central axis AX2, as shown in Figs. 12 and 14, the width of the countersunk surface 9c (here, the portion excluding the groove portion 9d) on the central axis AX1 side on a straight line passing through the central axis AX1 and the central axis AX2 is the minimum width wmin of the countersunk surface 9c. The width of the countersunk surface 9c (here, the portion excluding the groove portion 9d) on the central axis AX2 side on a straight line passing through the central axis AX1 and the central axis AX2 is the maximum width wmax of the countersunk surface 9c. In this embodiment, the minimum width wmin is 0.25 mm, the maximum width wmax is 0.4 mm, and the distance d between the central axis AX1 and the central axis AX2 is 0.075 mm.

[0058] The edge of the entrance surface 8a of the lens 8 abuts against the countersunk surface 9c. In addition, the side surface 8b of the lens 8 is positioned relative to the inner surface of the large diameter hole 9b along the direction D from the central axis AX2 of the large diameter hole 9b toward the central axis AX1 of the small diameter hole 9a. Specifically, the side surface 8b of the lens 8 abuts against the inner surface of the large diameter hole 9b along the direction D. As a result, the central axis AX3 of the lens 8 is disposed closer to the central axis AX1 of the small diameter hole 9a than the central axis AX2 of the large diameter hole 9b. In this embodiment, as described above, the diameter (5 mm) and effective diameter (4.5 mm) of the lens 8, the diameter d3 (4.5 mm) of the small diameter hole 9a, the diameter d4 (5.15 mm) of the large diameter hole 9b, and the distance d (0.075 mm) between the central axis AX1 and the central axis AX2 are set. As a result, the central axis AX3 of the lens 8 is approximately aligned with the central axis AX1 of the small diameter hole 9a. That is, when viewed from the X-axis direction, the entire effective area of ​​lens 8 overlaps with small diameter hole 9a. In other words, the entire effective area of ​​lens 8 is exposed to the QCL element 2 side through small diameter hole 9a. This makes it possible to make maximum use of the effective area of ​​lens 8.

[0059] Next, a method of fixing the lens 8 to the lens holder 9 will be described. As shown in FIG. 14, at least a part of the side surface 8b of the lens 8 is fixed to the inner surface of the large diameter hole 9b via the resin adhesive B1 in a state where the lens 8 is positioned relative to the lens holder 9 as described above. The resin adhesive B1 is formed of, for example, a thermosetting resin such as an epoxy resin. For example, by pouring the resin adhesive B1 into the groove 9d, the resin adhesive B1 that has entered the groove 9d flows between the side surface 8b of the lens 8 and the inner surface of the large diameter hole 9b even around the groove 9d due to capillary action. The resin adhesive B1 also flows between the entrance surface 8a and the countersunk surface 9c of the lens 8 due to capillary action. In this state, the lens holder 9 is baked, whereby the resin adhesive B1 is hardened and the lens 8 is fixed to the lens holder 9. The process of pouring the resin adhesive B1 into the groove 9d is performed, for example, by inserting a needle member for applying the resin adhesive B1 into the groove 9d and injecting the resin adhesive B1 from the tip of the needle member toward the countersunk surface 9c in the groove 9d. In this case, the groove 9d may be formed to a size that allows the needle member to be inserted.

[0060] With reference to FIG. 15, the effect obtained by the structure (hereinafter referred to as "eccentric structure") in which the center axis AX1 of the small diameter hole 9a is eccentric in the direction D with respect to the center axis AX2 of the large diameter hole 9b as described above and the lens 8 is positioned along the direction D will be described in detail. FIG. 15 is a diagram showing a schematic diagram of the positional relationship between the lens 8 and the lens holder 900 when the lens holder 900 according to the comparative example is used. In the lens holder 900, the center axis AX1 of the small diameter hole 9a is not eccentric with respect to the center axis AX2 of the large diameter hole 9b. That is, the center axis AX1 coincides with the center axis AX2. In this case, in order to make the most of the effective diameter of the lens 8, it is necessary to coincide the center axis AX3 of the lens 8 with the center axis of the lens holder 900 (that is, the center axes AX1 and AX2) as shown in the left part of FIG. 15. If such a positional relationship between the lens 8 and the lens holder 900 is maintained, no problem occurs. However, in reality, when the lens 8 is placed at the center of the lens holder 900 and the side surface 8b of the lens 8 and the inner surface of the large diameter hole 9b are bonded via the resin adhesive B1, as shown in the right part of Fig. 15, the surface tension of the resin adhesive B1 may cause the central axis AX3 of the lens 8 to deviate from the central axis (central axes AX1, AX2) of the lens holder 9 during baking. Specifically, the amount of the resin adhesive B1 filled between the side surface 8b of the lens 8 and the large diameter hole 9b is not necessarily uniform, so that the lens 8 may move in the direction in which the surface tension of the resin adhesive B1 is stronger. When such a movement (displacement) of the lens 8 occurs, a part of the effective area of ​​the lens 8 overlaps with the countersunk surface 9c, and the effective area cannot be utilized to the maximum extent. That is, as shown in the right part of FIG. 15, when the central axis AX3 of the lens 8 and the optical axis of the laser light L emitted from the QCL element 2 are aligned, the luminous flux of the laser light L cannot be captured in the part of the effective area of ​​the lens 8 that overlaps with the countersink surface 9c.

[0061] On the other hand, according to the decentering structure shown in FIG. 12 and FIG. 14, the side surface 8b of the lens 8 can be intimately attached to the inner surface of the large diameter hole 9b, which is the installation end of the lens 8, along the direction D. The closer the distance between the side surface 8b of the lens 8 and the inner surface of the large diameter hole 9b is (i.e., the attached portion and its periphery), the stronger the surface tension of the resin adhesive B1 acts. Therefore, even if the baking process is performed, the lens 8 is not pulled back to the opposite side of the direction D with respect to the lens holder 9. That is, before and after the baking process, the state (see FIG. 12 and FIG. 14) in which the side surface 8b of the lens 8 is abutted against the inner surface of the large diameter hole 9b along the direction D is maintained. Therefore, according to the decentering structure, it is possible to make the most of the effective area of ​​the lens 8 by adjusting the dimensions so that the effective area of ​​the lens 8 coincides with the small diameter hole 9a while the lens 8 is positioned as described above.

[0062] It is not necessary that the portion of the side surface 8b of the lens 8 that abuts against the inner surface of the large diameter hole 9b and the inner surface of the large diameter hole 9b are in direct contact with each other. That is, as shown in Fig. 14, a small amount of resin adhesive B1 that has seeped in by capillary action may be present between the portion of the side surface 8b of the lens 8 that abuts against the inner surface of the large diameter hole 9b and the inner surface of the large diameter hole 9b.

[0063] As shown in FIG. 11, FIG. 12, and FIG. 13B, a wall portion 90 (i.e., a cylindrical portion extending along the X-axis direction) constituting the large diameter hole 9b of the lens holder 9 has a bottom wall portion 92 (first wall portion) facing the second upper surface 53 of the heat spreader 5. The bottom wall portion 92 has a lower surface 92a (first mounting surface) facing the second upper surface 53. The lower surface 92a is formed with a plurality of (four in this embodiment) protruding portions 92b (first protruding portions) protruding toward the heat spreader 5 side. The four protruding portions 92b are provided at positions corresponding to the four protruding portions 53a (see FIG. 9A) provided on the second upper surface 53 of the heat spreader 5. Each protruding portion 92b is bonded to each protruding portion 53a via an adhesive layer B2 (see FIG. 2) made of a UV-curable resin (photo-curable resin).

[0064] In this embodiment, the four convex portions 92b are arranged in a well-balanced manner at the four corners of the bottom wall portion 92. That is, the four convex portions 92b are arranged such that the centers of the four convex portions 92b coincide with approximately the center of the bottom wall portion 92 when viewed from the Z-axis direction. This allows the lens holder 9 to be stably fixed onto the second upper surface 53 of the heat spreader 5, and realizes a structure that is resistant to impacts, vibrations, and the like.

[0065] As shown in FIG. 11 and FIG. 13A, the wall portion 90 has a top wall portion 91 (second wall portion) facing the top wall 33 of the package 3. The top wall portion 91 faces the bottom wall portion 92 via the large diameter hole 9b. A notch 91a is formed at the end of the top wall portion 91 opposite to the small diameter hole 9a side. A notch 92c is also formed at the end of the bottom wall portion 92 opposite to the small diameter hole 9a side. When viewed from the Z-axis direction, the notch 91a and the notch 92c have portions that overlap with each other. That is, the top wall portion 91 is formed so as not to overlap at least a portion of the notch 92c of the bottom wall portion 92 when viewed from the direction in which the bottom wall portion 92 and the top wall portion 91 face each other (the Z-axis direction). A part of the second upper surface 53 of the heat spreader 5 can be viewed from above the top wall 91 through the overlapping portion between the notch 91a and the notch 92c. That is, light can be irradiated from above the top wall 91 to the second upper surface 53 of the heat spreader 5 through the above portion. According to this structure, the lens holder 9 is placed on the second upper surface 53 of the heat spreader 5 so that the positions of the four convex portions 53a and the positions of the four convex portions 92b are aligned, and then UV light is irradiated from above the lens holder 9, so that the UV light can be suitably guided to the space between the lower surface 92a of the lens holder 9 and the second upper surface 53 of the heat spreader 5. This allows the adhesive layer B2 provided between each convex portion 92b and each convex portion 53a to be appropriately cured.

[0066] In addition, since the location where the adhesive layer B2 is applied is defined by the island-shaped convex portions 92b and the island-shaped convex portions 53a, the location where the adhesive layer B2 is applied and the amount of the adhesive layer B2 applied can be standardized among a plurality of products (quantum cascade laser devices 1). In addition, there is a limit to the depth to which UV light penetrates into the UV curable resin. For this reason, if the UV curable resin is applied to the entire lower surface 92a without providing the convex portions 92b and the convex portions 53a, a problem may occur in which the UV light does not reach the inside (center side) of the UV curable resin and the UV curable resin cannot be completely cured. By defining the location where the adhesive layer B2 is applied in an island shape as described above, such a problem can be avoided. In addition, by providing the island-shaped convex portions 92b and the convex portions 53a, a sufficient space for passing UV light can be formed between the lower surface 92a and the second upper surface 53 at a position where the convex portions 92b and the convex portions 53a do not overlap. This makes it possible for the UV light that enters the space to be reflected by the valley portions (areas where convex portions 92b and convex portions 53a are not formed) of the lower surface 92a and the second upper surface 53, allowing the UV light to be irradiated onto the adhesive layer B2 on each convex portion 53a.

[0067] Next, a manufacturing method (assembly method) of the quantum cascade laser device 1 will be described. As shown in FIG. 16, first, the package 3 is prepared before the top wall 33 is bonded to the side wall 32. Then, the window member 15 (the window member 15 on which the anti-reflection films 151, 152 and the metal film 153 are provided in advance (see FIG. 7)) is bonded to the side wall 32. Specifically, the solder member 16, which is a circular sheet member formed into a washer shape, is sandwiched between the countersunk surface 14 and the window member 15. Then, a load is applied to the window member 15 from the outside of the package 3 so as to press the window member 15 against the countersunk surface 14. In this state, the window member 15 and the countersunk surface 14 are bonded via the solder member 16 by using, for example, a vacuum soldering device (vacuum soldering furnace). At this time, a jig may be used to align the center of the window member 15 with the central axis of the countersunk opening (the small diameter hole 12 and the large diameter hole 13).

[0068] Next, the heat spreader 5 is placed on the Peltier module 4 with the In foil 45, which is a solder member, attached on the top and bottom, and these members are arranged at a predetermined position on the bottom wall 31 using a jig. Then, a load is applied from above the heat spreader 5 so as to press these members against the bottom wall 31. In this state, the bottom wall 31, the Peltier module 4, and the heat spreader 5 are joined via the In foil 45 arranged between the respective members by using, for example, a vacuum soldering device. Next, as shown in FIG. 2, the lead wires 20 of the Peltier module 4 are soldered to the lead pins 10.

[0069] Next, the heat sink 6, on which elements such as the QCL element 2, submount 7, temperature sensor T, and ceramic pattern SP are previously mounted, is fixed to the first upper surface 52 of the heat spreader 5. Specifically, the heat sink 6 is screwed to the heat spreader 5 by inserting screw members (not shown) into the screw holes 6c (see FIG. 10) of the heat sink 6 and the screw holes 52a of the heat spreader 5. In addition, the temperature sensor T and the ceramic pattern SP are electrically connected to predetermined lead pins 10 by wires (not shown).

[0070] Next, the lens holder 9 on which the lens 8 is mounted as described above is fixed to the second upper surface 53 of the heat spreader 5. Specifically, a UV-curable resin (adhesive layer B2) is applied in advance onto each of the convex portions 53a formed on the second upper surface 53 of the heat spreader 5. Then, the lens holder 9 is vacuum-chucked using, for example, a Convum (vacuum generator) and moved into the package 3. Then, the QCL element 2 is driven to emit the laser light L, and active alignment is performed to align the optical axis of the laser light L with the central axis of the lens 8 while observing the laser light L with a beam monitor.

[0071] Next, with the optical axis of the laser light L aligned with the central axis of the lens 8, the lens holder 9 is fixed to the heat spreader 5. Specifically, with the optical axis of the laser light L aligned with the central axis of the lens 8, UV light is irradiated from above the lens holder 9 through the notches 91a and 92c of the lens holder 9 toward the second upper surface 53 of the heat spreader 5. As a result, each convex portion 92b of the lens holder 9 and each convex portion 53a of the heat spreader 5 are bonded to each other via the adhesive layer B2.

[0072] Here, the position of each convex portion 92b is designed to overlap with each convex portion 53a of the heat spreader 5 when the optical axis of the laser light L is aligned with the central axis of the lens 8. In addition, the height dimension (length along the Z-axis direction) of each convex portion 53a and each convex portion 92b is designed so that a gap of about several hundred μm smaller than the thickness of the UV curing resin (adhesive layer B2) previously applied on each convex portion 53a is formed between each convex portion 53a of the heat spreader 5 and each convex portion 92b of the lens holder 9 when the optical axis of the laser light L is aligned with the central axis of the lens 8. As a result, when the lens holder 9 is moved relative to the heat spreader 5 so that the optical axis of the laser light L is aligned with the central axis of the lens 8, the convex portions 92b of the lens holder 9 are adjusted to come into contact with the adhesive layer B2 on each convex portion 53a of the heat spreader 5. In other words, the height dimensions of each convex portion 53a and each convex portion 92b and the thickness of the adhesive layer B2 are designed so that when the lens holder 9 is pressed into the UV-curable resin (adhesive layer B2) pre-applied on the heat spreader 5, the optical axis of the laser light L and the central axis of the lens 8 are aligned.

[0073] Next, the top wall 33 is joined to the upper end (the end opposite to the bottom wall 31) of the side wall 32 of the package 3. In this manner, the quantum cascade laser device 1 shown in FIG.

[0074] In the quantum cascade laser device 1 described above, the light output window 11 is joined to the side wall 32 of the package 3 by the solder member 16 (in this embodiment, a SnAgCu-based solder material with a melting point of 220° C.) having a lower melting point than the brazing material (having a melting point of 450° C. or higher). This makes it possible to closely contact the window member 15 and the countersunk surface 14 while suppressing damage to the window member 15 and the like (particularly the antireflection films 151 and 152) caused by heat, as compared to the case where a brazing material is used. In addition, on the entrance surface 15a of the window member 15, the first region A1 where the antireflection film 151 is provided and the second region A2 where the solder member 16 is joined are separated from each other (see FIG. 7). This prevents the stress generated when the solder member 16 in the second region A2 melts or solidifies from being transmitted to the antireflection film 151 on the first region A1. As a result, damage (such as cracking or peeling) of the antireflection film 151 caused by the above stress is suppressed. As described above, according to the quantum cascade laser device 1, damage to the anti-reflection film 151 provided on the light exit window 11 can be suppressed, and high airtightness of the package 3 can be ensured.

[0075] Moreover, the side surface 15c of the window member 15 has a third region A3 that is metalized so as to be continuous with the second region A2, and at least a part of the side surface 15c is joined to at least a part of the inner surface of the large diameter hole 13 via the solder member 16 (see FIG. 5). According to the above configuration, the continuous region from the second region A2 to the side surface 15c (third region A3) of the window member 15 is metalized, so that a part of the solder member 16 can be suitably wetted and spread toward the third region A3 during solder joining. As a result, the solder member 16 can be interposed between the side surface 15c of the window member 15 and the inner surface of the large diameter hole 13, and the airtightness of the package 3 can be suitably improved.

[0076] The wavelength of the laser light L emitted from the QCL element 2 is in the range of 4 μm to 12 μm. As an example, the heat resistance temperature of the antireflection films 151, 152 is about 260° C. Meanwhile, in the quantum cascade laser device 1, the solder member 16 having a relatively low melting point is used as a bonding material, so that the window member 15 provided with the antireflection films 151, 152 can be attached to the side wall 32 by solder bonding while suppressing damage to the antireflection films 151, 152 due to heat.

[0077] In the quantum cascade laser device 1, the lens holder 9 has a small diameter hole 9a and a large diameter hole 9b whose central axes AX1 and AX2 are eccentric to each other. The side surface 8b of the lens 8 is positioned relative to the inner side surface of the large diameter hole 9b along a direction D from the central axis AX2 of the large diameter hole 9b toward the central axis AX1 of the small diameter hole 9a. This makes it possible to suitably suppress the positional deviation of the lens 8 (movement of the lens 8 relative to the lens holder 9) caused by the surface tension of the resin adhesive B1 arranged around the lens 8 when the lens 8 is arranged in the center of the large diameter hole 9b (for example, see the left part of FIG. 15). Furthermore, with the lens 8 positioned in this way, the central axis AX3 of the lens 8 is arranged in a position close to the central axis AX1 of the small diameter hole 9a (the central axis AX3 and the central axis AX1 are coincident in this embodiment). This makes it possible to reduce the area of ​​the region where the effective region of the lens 8 (the region within the effective diameter centered on the central axis AX3 of the lens) and the countersunk surface 9c interfere (overlap). As a result, it is possible to efficiently utilize the effective area of ​​the lens 8. Furthermore, by efficiently utilizing the effective area of ​​the lens 8, the lens 8 can be made smaller, and therefore the package 3 can be made smaller.

[0078] In this embodiment, the central axis AX3 of the lens 8 is approximately aligned with the central axis AX1 of the small diameter hole 9a, and the effective diameter of the lens 8 is approximately aligned with the diameter d3 of the small diameter hole 9a. According to the above configuration, the entire effective area of ​​the lens 8 (area within the effective diameter) can be exposed through the small diameter hole 9a. This makes it possible to maximize the effective area of ​​the lens 8 while appropriately supporting the edge of the entrance surface 8a of the lens 8 by minimizing the size of the small diameter hole 9a and ensuring the area of ​​the countersunk surface 9c.

[0079] Further, a groove 9d is formed on the inner side surface of the large diameter hole 9b along the X-axis direction and reaches the countersunk surface 9c, and the resin adhesive B1 fills the groove 9d. According to the above configuration, the resin adhesive B1 can be easily injected between the side surface 8b of the lens 8 and the inner side surface of the large diameter hole 9b through the groove 9d.

[0080] Further, the lens holder 9 has a lower surface 92a on which a plurality of (four in this embodiment) convex portions 92b protruding toward the heat spreader 5 are formed, and the plurality of convex portions 92b are bonded to the second upper surface 53 of the heat spreader 5 via an adhesive layer B2 made of a UV-curable resin. In this embodiment, the second upper surface 53 has a plurality of convex portions 53a protruding toward the lens holder 9 at positions corresponding to the plurality of convex portions 92b, and the plurality of convex portions 92b are bonded to the plurality of convex portions 53a via the adhesive layer B2. According to the above configuration, the locations where the adhesive layer B2 is provided can be dispersed on the plurality of convex portions 92b, so that the adhesive layer B2 on each convex portion 92b can be easily and appropriately cured compared to the case where the adhesive layer B2 is provided over a wide range over the entire surface. Furthermore, in this embodiment, the adhesive layer B2 is disposed in the center of the space formed between the lower surface 92a and the second upper surface 53 (between the convex portion 92b and the convex portion 53a). This allows the adhesive layer B2 to be appropriately irradiated with UV light reflected by the lower surface 92a and the second upper surface 53 in the space. As a result, the adhesive layer B2 can be more appropriately cured, and the lens holder 9 can be stably fixed to the heat spreader 5.

[0081] Furthermore, the bottom wall portion 92 of the lens holder 9 is provided with a notch 92c for guiding light to the second upper surface 53 of the heat spreader 5. According to the above configuration, UV light can be irradiated onto the second upper surface 53 of the heat spreader 5 from the side opposite to the side where the heat spreader 5 is disposed with respect to the lens holder 9 (i.e., from above the lens holder 9) through the notch 92c provided in the bottom wall portion 92. This makes it possible to easily perform light irradiation for curing the adhesive layer B2 between the lower surface 92a and the second upper surface 53.

[0082] The lens holder 9 also has a top wall 91 that faces the bottom wall 92 via the large diameter hole 9b. The top wall 91 is formed so as not to overlap at least a part of the notch 92c provided in the bottom wall 92 when viewed from the direction in which the bottom wall 92 and the top wall 91 face each other (Z-axis direction). According to the above configuration, the bottom wall 92 and the top wall 91 can appropriately protect the lens 8 placed in the large diameter hole 9b from the outside. Since the top wall 91 is formed so as not to overlap at least a part of the notch 92c provided in the bottom wall 92, the lens holder 9 can be irradiated with light from the outside of the lens holder 9 (the side opposite the bottom wall 92 across the top wall 91), and the light can be irradiated to the second upper surface 53 of the heat spreader 5.

[0083] Note that, instead of the notch 92c, a through hole penetrating in the Z-axis direction may be formed in the bottom wall portion 92. Similarly, instead of the notch 91a, a through hole penetrating in the Z-axis direction and having a portion overlapping with the notch 92c or through hole provided in the bottom wall portion 92 may be formed in the top wall portion 91. Even with this configuration, it is possible to direct light to the second upper surface 53 of the heat spreader 5 by irradiating the lens holder 9 from above.

[0084] Furthermore, the QCL element 2 and the lens holder 9 are mounted on the same heat spreader 5. The QCL element 2 is mounted on the heat spreader 5 via a submount 7 and a heat sink 6. According to the above configuration, by sharing a base (heat spreader 5) on which the QCL element 2 and the lens holder 9 are mounted, it is possible to suppress relative movement of the lens holder 9 with respect to the QCL element 2 when the heat spreader 5 expands or contracts due to heat. As a result, it is possible to suppress the occurrence of optical axis deviation (deviation of the central axis AX3 of the lens 8 with respect to the optical axis of the laser light L) caused by temperature changes in the package 3.

[0085] Moreover, the package 3 airtightly accommodates the above-mentioned QCL element 2, lens 8, and lens holder 9. According to the above configuration, it is possible to efficiently utilize the effective area of ​​the lens 8 arranged in the package 3, so that it is possible to reduce the size of the lens 8 and the package 3 as well.

[0086] [Variations] Although one embodiment of the present disclosure has been described above, the present disclosure is not limited to the above-mentioned embodiment. For example, the materials and shapes of each component are not limited to the above-mentioned materials and shapes, and various materials and shapes can be adopted. In addition, some of the components included in the above embodiment may be appropriately changed or omitted.

[0087] The shape of the lens holder is not limited to the shape of the above-mentioned lens holder 9. For example, instead of the above-mentioned lens holder 9, lens holders 9A to 9C shown in Figures 17 to 19 may be used.

[0088] As shown in FIG. 17, the lens holder 9A of the first modification is different from the lens holder 9 in that a rectangular large diameter hole 9Ab is formed instead of the circular large diameter hole 9b, and the groove 9d is not formed (the large diameter hole 9Ab is formed to a size including a portion corresponding to the groove 9d). In this way, the large diameter hole 9Ab is not necessarily formed to be circular as long as it is formed to a size that can accommodate the lens 8. With such a large diameter hole 9Ab, it is possible to ensure sufficient space for filling the resin adhesive B1 at the four corners of the large diameter hole 9Ab without providing the groove 9d. From another perspective, in the lens holder 9A, the portions corresponding to the four corners of the large diameter hole 9Ab each function as a recess corresponding to the groove 9d of the lens holder 9. Note that the small diameter hole 9a may also be formed to a shape other than a circle (for example, a rectangular shape similar to the large diameter hole 9Ab, which is one size smaller than the large diameter hole 9Ab).

[0089] As shown in FIG. 18, the lens holder 9B of the second modification is different from the lens holder 9 in that it has a top wall 91B with a circular (curved) upper surface instead of the top wall 91. In addition, the lens holder 9B employs the top wall 91B, so that there is no space for forming the groove 9d that was provided on the top wall 91 side of the lens holder 9. For this reason, in the lens holder 9B, a pair of grooves 9d is formed on each of both sides in the Y-axis direction on the bottom wall 92 side. Thus, the position where the groove 9d is formed in the lens holder is not particularly limited. In addition, the number of grooves 9d is also not particularly limited. In addition, in the lens holder 9B, the length along the X-axis direction of the part of the wall forming the large diameter hole 9b, excluding the bottom wall 92, is shorter than the wall 90 of the lens holder 9. Specifically, the length along the X-axis direction of the above part is slightly shorter than the length along the X-axis direction of the lens 8. According to such a configuration, the portion that blocks the UV light from above the lens holder 9B can be reduced, so that the UV light for curing the adhesive layer B2 can be guided to the heat spreader 5 side more suitably.

[0090] As shown in FIG. 19, the lens holder 9C of the third modification is different from the lens holder 9 in that it has a top wall portion 91C, which is shorter in length along the X-axis direction than the top wall portion 91, instead of the top wall portion 91. The length of the top wall portion 91C along the X-axis direction is about half the length of the lens 8 along the X-axis direction. In addition, in the lens holder 9C, the length along the X-axis direction of the wall portion forming the large diameter hole 9b, except for the bottom wall portion 92, is the same as that of the top wall portion 91C. That is, the lens holder 9C is formed in a substantially L-shape when viewed from the Y-axis direction. In the lens holder 9C, there are fewer portions that block the UV light from above the lens holder 9C than in the lens holder 9B, so that the UV light for curing the adhesive layer B2 can be more suitably guided to the heat spreader 5 side. Furthermore, like lens holder 9C, the wall portion constituting the large diameter hole 9b of the lens holder does not need to surround the entire side surface 8b of the lens 8, but may be configured to surround only a portion of the side surface 8b of the lens 8 on the incident surface 8a side.

[0091] Also, as in the quantum cascade laser device 1A according to the modified example shown in FIG. 20, the lens does not necessarily have to be accommodated in the package 3. The quantum cascade laser device 1A is different from the quantum cascade laser device 1 in that it does not include the lens 8 and the lens holder 9 in the package 3, but includes a lens 8A attached to the outside of the package 3. That is, the quantum cascade laser device 1A includes a lens 8A that is arranged outside the package 3 and collects or collimates the laser light L that has passed through the light output window 11. Also, due to this difference, the quantum cascade laser device 1A is different from the quantum cascade laser device 1 in that it includes a heat spreader 5A configured to be able to arrange the QCL element 2 in a position close to the light output window 11, instead of the heat spreader 5. As described above, the beam radiation angle of the laser light L is very large. Therefore, in order to make the light exit window 11 as small as possible while allowing all of the luminous flux of the laser light L to pass outside the package 3 through the light exit window 11, it is preferable to place the light exit window 11 as close as possible to the exit surface (end surface 2a) of the QCL element 2 from which the laser light L is emitted. For this reason, the quantum cascade laser device 1A that does not include a lens inside the package 3 includes the above-mentioned heat spreader 5A.

[0092] According to the quantum cascade laser device 1A, the lens 8A is an external member disposed outside the package 3, so that the lens 8 can be flexibly disposed and replaced. Furthermore, as described above, the length w1 of the small diameter hole 12 along the optical axis direction (X-axis direction) of the laser light L is shorter than the length w2 of the large diameter hole 13 (see FIG. 5). According to the above configuration, the light exit window 11 can be brought closer to the QCL element 2 compared to the case where the length w1 of the small diameter hole 12 is equal to or longer than the length w2 of the large diameter hole 13. This makes it possible to make the laser light L enter the light exit window 11 while the spread of the laser light L is small, even if the beam radiation angle of the laser light L emitted from the QCL element 2 is large. As a result, the light exit window 11 can be made smaller, and the package 3 can be made smaller.

[0093] As described above, the exit surface 15b of the window member 15 has the fourth region A4 in which the antireflection film 152 is provided, and the fourth region A4 includes the first region A1 and is larger than the first region A1 when viewed from the X-axis direction. When a lens is not provided in the package 3 as in the quantum cascade laser device 1A and the laser light L, which is divergent light, enters the window member 15, the region through which the laser light L passes on the entrance surface 15a of the window member 15 is smaller than the region through which the laser light L passes on the exit surface 15b of the window member 15. Therefore, as in the above configuration, by making the antireflection film 151 on the entrance surface 15a side smaller than the antireflection film 152 on the exit surface 15b side (i.e., by making the first region A1 smaller than the fourth region A4), a region corresponding to the difference between the fourth region A4 and the first region A1 can be secured as the second region A2. In this way, by designing the sizes of the first region A1, the second region A2, and the fourth region A4 taking into account the beam radiation angle of the laser light L, the window member 15 can be made smaller, and ultimately the package 3 can be made smaller.

[0094] In the above embodiment, the exit surface 15b of the window member 15 is substantially flush with the outer surface of the side wall 32. However, the exit surface 15b of the window member 15 may protrude beyond the outer surface of the side wall 32 to the outside of the package 3. That is, the thickness of the window member 15 may be greater than the length w2 of the large diameter hole 13. In this case, the workability of bonding the window member 15 to the side wall 32 from the outside of the package 3 can be improved. In addition, when an external lens 8A is attached to the exit surface 15b of the window member 15 as in the quantum cascade laser device 1A, the workability of attaching the lens can also be improved. In addition, by thinning the side wall 32, the package 3 can be made smaller in size, and the lens 8A can be reliably arranged close to the window member 15.

[0095] In the above embodiment, a quantum cascade laser element (QCL element 2) is illustrated as an example of a semiconductor laser element, but a laser element other than a quantum cascade laser element may be used as the semiconductor laser element housed in the package 3. In addition, the semiconductor laser element may be a distributed feedback (DFB) semiconductor laser element having a diffraction grating structure provided on an upper portion of an active layer.

[0096] In the above embodiment, the package 3 is a butterfly package, but the package form is not limited to this. For example, the package may be a CAN package. [Explanation of symbols]

[0097] 1, 1A... quantum cascade laser device (semiconductor laser device), 2... quantum cascade laser element (semiconductor laser element), 2a... end face (emission surface), 3... package, 5, 5A... heat spreader, 8, 8A... lens, 8a... incident surface, 8b... side, 8c... emission surface, 9, 9A, 9B, 9C... lens holder, 9a... small diameter hole, 9b... large diameter hole, 9c... counterbore surface, 9d... groove (recess), 11... light exit window, 12... small diameter hole (first hole portion), 13... large diameter hole (second hole portion), 14... counterbore surface, 15... window member, 15a... incident surface, 15b... emission surface, 15c... side, 16...solder member, 31...bottom wall, 32...side wall, 33...top wall, 53...second upper surface (second mounting surface), 53a...convex portion (second convex portion), 91...top wall portion (second wall portion), 92...bottom wall portion (first wall portion), 92a...lower surface (first mounting surface), 92b...convex portion (first convex portion), 92c...notch, 151...anti-reflection film (first anti-reflection film), 152...anti-reflection film (second anti-reflection film), 153...metal film, A1...first region, A2...second region, A3...third region, A4...fourth region, AX1, AX2, AX3...central axis, B1...resin adhesive, B2...adhesive layer, D...direction, L...laser light.

Claims

1. A semiconductor laser element; a package that houses the semiconductor laser element; The package comprises: The bottom wall and a side wall provided upright on the bottom wall and formed in an annular shape so as to surround a region in which the semiconductor laser element is housed when viewed from a direction perpendicular to the bottom wall; a top wall that closes an opening on the side wall opposite to the bottom wall side, a light exit window for passing a laser beam emitted from the semiconductor laser element is provided on the side wall; The light exit window is A first hole portion extending in an optical axis direction along an optical axis of the laser light; a second hole portion extending in the optical axis direction and including the first hole portion when viewed in the optical axis direction and larger than the first hole portion; an annular countersunk surface that connects the first hole portion and the second hole portion and extends along a plane that intersects with the optical axis direction; a window member disposed inside the second hole; It is composed of The surface of the window member facing the countersink surface is a first region including a central portion of a surface of the window member facing the countersink surface, the first region being provided with a first antireflection film; a second region that is metallized and is formed in an annular shape so as to surround the first region and is spaced apart from the first region; The second region is joined to the countersunk surface via a solder member.

2. the window member has a side surface extending along the optical axis direction, the side surface has a third region that is metallized so as to be continuous with the second region; The semiconductor laser device according to claim 1 , wherein at least a part of the side surface is joined to at least a part of an inner surface of the second hole portion via the solder member.

3. 3. The semiconductor laser device according to claim 1, wherein a length of the first hole along the optical axis direction is shorter than a length of the second hole along the optical axis direction.

4. the window member has an emission surface through which the laser light transmitted through the window member is emitted to the outside of the package, the exit surface has a fourth region provided with a second antireflection film; 4. The semiconductor laser device according to claim 1, wherein the fourth region includes the first region when viewed from the optical axis direction and is larger than the first region.

5. 5. The semiconductor laser device according to claim 1, further comprising a lens arranged outside the package for focusing or collimating the laser light transmitted through the light exit window.

6. 6. The semiconductor laser device according to claim 1, wherein the wavelength of the laser light is within a range of 4 μm to 12 μm.

7. the window member has an emission surface through which the laser light transmitted through the window member is emitted to the outside of the package, 7. The semiconductor laser device according to claim 1, wherein the emission surface protrudes outward from the package beyond an outer surface of the package of the sidewall on which the light emission window is provided.

Images