Light source unit

Abstract

This invention provides a light source unit that can suppress light loss while avoiding variations in product quality. [Solution] The laser element 10 has a substrate 11 and a semiconductor laminate 12 formed on the substrate 11 including an active layer 122, and the optical integrated circuit element 20 has a substrate 22 and a unit circuit 30 provided on the substrate 22. The unit circuit 30 has an optical input / output end face 31a facing the first end face 10a of the laser element 10 across a space S, an input / output waveguide 31 extending from the optical input / output end face 31a, and an optical feedback section 40 configured to transmit light of a predetermined wavelength incident from the laser element 10 and return light of a predetermined wavelength to the laser element 10, thereby changing the wavelength of the output light Lo1 within a predetermined wavelength range. The size of the space S in the resonance direction X is smaller than the thickness tL of the active layer 122 and the thickness tW of the input / output waveguide 31 at the optical input / output end face 31a in the thickness direction of the substrate 22.

Description

Technical Field

[0001] The present disclosure relates to a light source unit.

Background Art

[0002] Conventionally, a light source unit including a laser element and an optical integrated circuit (PIC) element including a unit circuit has been known (for example, Patent Document 1). In such a light source unit, light is emitted from the laser element to the unit circuit. Among the light incident on the unit circuit, light having a predetermined wavelength is incident on the laser element again by the optical feedback unit of the unit circuit and amplified inside the laser element. The light amplified in this way is output to the outside of the device as output light.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the light source unit as described above, it is necessary to optically connect the laser element and the input / output waveguide of the unit circuit. The end face of the laser element and the optical input / output end face, which is the end of the input / output waveguide, are preferably as close as possible to suppress light loss. For example, in the light source unit described in Patent Document 1, the end face of the laser element and the optical input / output end face are arranged to be in contact with each other. However, in the design where the end face of the laser element and the optical input / output end face are in contact as described above, due to the influence of burrs that may occur on the end face of the laser element or the optical input / output end face, the end face of the laser element and the optical input / output end face cannot be properly abutted, and there is a risk of variation in product quality. On the other hand, in a configuration where the end face of the laser element and the optical input / output end face are arranged apart from each other, light loss may occur due to divergence of light in the space between the end face of the laser element and the optical input / output end face.

[0005] Therefore, one aspect of this disclosure aims to provide a light source unit that can suppress light loss while avoiding variations in product quality. [Means for solving the problem]

[0006] [1] A laser element comprising a first substrate and a quantum cascade laser element or an interband cascade laser element having a semiconductor laminate formed on the first substrate and including at least an active layer, The system comprises a second substrate and an optical integrated circuit element having a unit circuit provided on the second substrate, The laser element has a first end face and a second end face that face each other in the resonance direction of the laser element, The aforementioned unit circuit is The first end face of the laser element and the optical input / output end face facing each other across space, An input / output waveguide extending from the aforementioned optical input / output end face, The system includes an optical feedback unit that is optically connected to the input / output waveguide and configured to guide light of a predetermined wavelength incident from the first end face of the laser element and return the light of the predetermined wavelength to the laser element, thereby changing the wavelength of the output light within a predetermined wavelength range. A light source unit in which the size of the space in the resonance direction is smaller than the thickness of the active layer in the stacking direction of the semiconductor laminate and the thickness of the input / output waveguide at the optical input / output end face in the thickness direction of the second substrate.

[0007] In the light source unit described in [1] above, the unit circuit includes an input / output waveguide into which light emitted from the laser element is incident, and an optical feedback section. The optical feedback section returns light of a predetermined wavelength from the light emitted by the laser element back to the laser element. This amplifies the light of the predetermined wavelength in the laser element. Here, a space is provided between the first end face on the unit circuit side of the laser element and the optical input / output end face of the unit circuit. With the above configuration, the laser element and the input / output end face can be optically connected without contact between them. As a result, variations in product quality caused by burrs etc. that may occur on the first end face or the optical input / output end face can be avoided. Furthermore, the size of the above space is configured to be smaller than the thickness of the active layer and the thickness of the input / output waveguide at the optical input / output end face. Generally, the divergence angle of light in quantum cascade laser elements and interband cascade laser elements is larger than that of other laser elements, but by making the distance between the first end face and the optical input / output end face sufficiently small as in the above configuration, the loss of light in the above space can be suppressed.

[0008] [2] The light source unit according to [1], wherein the size of the space in the resonance direction is 1 μm or less.

[0009] According to the configuration described in [2] above, by bringing the first end face of the laser element and the optical input / output end face of the unit circuit close together, the loss of light in the space can be suppressed more effectively.

[0010] [3] The light source unit according to [1], wherein the size of the space in the resonance direction is one-quarter or less of the shortest wavelength in the predetermined wavelength range.

[0011] According to the configuration described in [3] above, by making the distance between the first end face of the laser element and the optical input / output end face of the unit circuit sufficiently small relative to the shortest wavelength in the wavelength tuning range, the loss of light in the above space can be suppressed.

[0012] [4] Having a plurality of the laser elements, Each of the plurality of laser elements has a plurality of unit circuits provided in correspondence with each of the plurality of laser elements, The plurality of unit circuits are arranged along an array direction perpendicular to the resonance direction and the thickness direction, as described in any one of [1] to [3], in the light source unit.

[0013] According to the configuration described in [4] above, for example, if the wavelength ranges of the light emitted from multiple laser elements are the same, the output power of the output light can be increased compared to a light source unit consisting of a single laser element. Also, if the wavelength ranges of the light emitted from multiple laser elements are different, the wavelength tuning range of the output light can be widened compared to a light source unit consisting of a single laser element.

[0014] [5] The light source unit according to [4] wherein at least one of the plurality of laser elements outputs the output light from the second end face.

[0015] In the configuration described in [5] above, in the unit circuit corresponding to the laser element configured to output output light from the second end face, it is not necessary to provide some optical circuits (such as output waveguides) that are required when outputting light from an optical integrated circuit element. This simplifies the circuit on the substrate and allows for miniaturization of the optical integrated circuit element. Furthermore, with the above configuration, the output light from the laser element is output directly to the outside from the second end face of the laser element without passing through optical circuits such as output waveguides. This suppresses the loss of light due to the output light passing through the optical circuits.

[0016] [6] The second substrate has an extended portion that extends in the resonance direction toward the side where the laser element is provided, rather than toward the optical input / output end face. The laser element is a light source unit according to any one of [1] to [5], which is mounted on the extended portion.

[0017] In the configuration of [6] above, the laser element is placed on the same substrate as the substrate provided with the unit circuit. By arranging the laser element in this way, the heights of the laser element and the optical input / output end face in the thickness direction of the substrate can be easily and accurately aligned.

[0018] [7] The optical integrated circuit element has a third end face that faces the first end face and includes the optical input / output end face. When viewed from the arrangement direction orthogonal to the resonance direction and the thickness direction, the third end face has a first portion provided with the optical input / output end face and a second portion that is farther from the first end face than the first portion in the resonance direction, and the light source unit according to any one of [1] to [6].

[0019] According to the configuration of [7] above, the laser element and the optical input / output end face are separated via a space of a suitable size. Further, the second portion of the third end face where the optical input / output end face is not provided is configured such that the distance from the laser element is larger than that of the first portion provided with the optical input / output end face. That is, in the case of viewing from the arrangement direction, for the first portion that affects the coupling of light between the laser element and the input / output waveguide, the distance between the laser element and the optical input / output end face is set to a size that can suppress optical loss, and for the second portion, the distance between the laser element and the optical integrated circuit element (third end face) is made large. Thereby, even if burrs or the like occur in the second portion, it is possible to suppress the proximity arrangement of the laser element and the optical input / output end face (first portion) from being hindered by the influence of the burrs or the like.

[0020] [8] The optical integrated circuit element has a third end face that faces the first end face and includes the optical input / output end face. When viewed from the thickness direction, the third end face has a third portion provided with the optical input / output end face and a fourth portion that is farther from the first end face than the third portion in the resonance direction, and the light source unit according to any one of [1] to [7].

[0021] According to the configuration of [8] above, the laser element and the optical input / output end face are separated via a space of a suitable size. Further, the fourth portion of the third end face where the optical input / output end face is not provided is configured such that the distance from the laser element is greater than that of the third portion where the optical input / output end face is provided. That is, when viewed from the thickness direction, for the third portion that affects the coupling of light between the laser element and the input / output waveguide, the distance between the laser element and the optical input / output end face is set to a size that can suppress optical loss, while for the fourth portion, the distance between the laser element and the optical integrated circuit element (third end face) is made large. Thereby, even if burrs or the like occur in the fourth portion, it is possible to suppress the proximity arrangement of the laser element and the optical input / output end face (third portion) from being hindered by the influence of the burrs or the like.

[0022] [9] The width of the active layer in the arrangement direction orthogonal to the resonance direction and the thickness direction is larger than the width in the arrangement direction of the input / output waveguide at the optical input / output end face, the light source unit according to any one of [1] to [8].

[0023] According to the configuration of [9] above, compared with a configuration in which the width of the active layer in the arrangement direction is smaller than the width in the arrangement direction of the input / output waveguide at the optical input / output end face, the output of the laser element can be increased. As a result, the output of the output light can be increased.

[0024]

[10] The width of the active layer in the arrangement direction orthogonal to the resonance direction and the thickness direction is smaller than the width in the arrangement direction of the input / output waveguide at the optical input / output end face, the light source unit according to any one of [1] to [8].

[0025] According to the configuration of

[10] above, since the width of the input / output waveguide is larger than the width of the active layer, light can be sufficiently propagated from the laser element to the input / output waveguide. Thereby the law of nature, Compared with the configuration of [9] above, the mode matching efficiency between the laser element and the input / output waveguide can be improved, and the coupling loss can be reduced.

[0026]

[11] The light source unit according to any one of [1] to

[10] , further comprising a cooling element on which the laser element and the optical integrated circuit element are mounted.

[0027] According to the configuration described in

[11] above, the temperature of the laser element and the optical integrated circuit element can be kept uniform. As a result, variations in the performance of the light source unit caused by temperature changes can be suppressed.

[0028]

[12] A lens portion that transmits the output light, A light source unit according to any one of [1] to

[11] , further comprising a package that houses the laser element and the optical integrated circuit element and also houses or holds the lens portion.

[0029] According to the configuration described in

[12] above, each component constituting the light source unit (laser element and optical integrated circuit element) can be appropriately protected by the package, and external influences on each component can be suppressed. In addition, the output light can be appropriately extracted to the outside through the lens portion housed or held in the package.

[0030]

[13] The light source unit according to

[12] , wherein the width of the package in the arrangement direction perpendicular to the resonance direction and the thickness direction is greater than the height of the package in the thickness direction.

[0031] According to the configuration described in

[13] above, the package height can be reduced. As a result, the device can be made smaller. [Effects of the Invention]

[0032] According to one aspect of this disclosure, it is possible to provide a light source unit that can suppress light loss while avoiding variations in product quality. [Brief explanation of the drawing]

[0033] [Figure 1] Figure 1 shows the cross-sectional structure of the light source unit according to the first embodiment. [Figure 2] Figure 2 shows the cross-sectional structure of the light source unit along the line II-II in Figure 1. [Figure 3] Figure 3 shows an example configuration of a laser element and a corresponding unit circuit. [Figure 4] Figure 4 shows an example of a waveguide configuration. [Figure 5] Figure 5 shows the cross-sectional structure of the area where the laser element and the optical integrated circuit element face each other. [Figure 6] Figure 6 shows an example of the placement of the power monitor. [Figure 7] Figure 7 shows an example of the control configuration of a light source unit. [Figure 8] Figure 8 shows an example of pulse timing. [Figure 9] Figure 9 shows another example of pulse timing. [Figure 10] Figure 10 shows an example of the output waveguide configuration. [Figure 11] Figure 11 shows a first modified example of the third end face. [Figure 12] Figure 12 shows a second modified example of the third end face. [Figure 13] Figure 13 shows the cross-sectional structure of the light source unit according to the second embodiment. [Figure 14] Figure 14 is a plan view showing the configuration of an optical integrated circuit element in the second embodiment. [Figure 15] Figure 15 shows an example configuration of a laser element and a corresponding unit circuit in the second embodiment. [Figure 16] Figure 16 shows a first modified example of the wavelength adjustment section. [Figure 17] Figure 17 shows a second modified example of the wavelength adjustment section. [Figure 18] Figure 18 shows a first modified example of a loop-type optical feedback section. [Figure 19] Figure 19 shows a second modified example of a loop-type optical feedback section. [Figure 20]Figure 20 shows a modified example of the optical integrated circuit element in the second embodiment. [Figure 21] Figure 21 shows a modified example of a waveguide. [Modes for carrying out the invention]

[0034] Hereinafter, one embodiment of the present disclosure will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant explanations will be omitted. The drawings may be simplified or exaggerated in part for ease of understanding. Therefore, the dimensional ratios of the embodiment are not limited to those shown in the drawings. [First Embodiment]

[0035] As shown in Figures 1 and 2, the light source unit 1 of the first embodiment comprises a plurality of laser elements 10 and an optical integrated circuit element 20. As shown in Figure 2, the optical integrated circuit element 20 has a substrate 22 (second substrate) and a plurality of unit circuits 30 (301 to 304) provided on the substrate 22 (Ge layer 25 described later). As shown in Figure 3, the unit circuit 30 is composed of various optical elements including waveguides provided on the substrate 22 (Ge layer 25). In this embodiment, one unit circuit 30 is provided corresponding to one laser element 10.

[0036] Hereinafter, the thickness direction of the substrate 22 will be referred to as the thickness direction Z, the resonance direction common to the multiple laser elements 10 will be referred to as the resonance direction X, and the direction perpendicular to the thickness direction Z and the resonance direction X (in this embodiment, the direction in which the multiple laser elements 10 are arranged) will be referred to as the arrangement direction Y.

[0037] Multiple laser elements 10 and optical integrated circuit elements 20 are housed within a package 2. In the light source unit 1, a cooling element 3, a carrier substrate 4, a lens section 5, an output window 6, and a temperature sensor 7 are further housed within the package 2.

[0038] Package 2 has a bottom wall 2a, a side wall 2b, and a top wall 2c. The bottom wall 2a is a rectangular plate-shaped member whose resonance direction X is the longitudinal direction and whose arrangement direction Y is the short direction. The side wall 2b is connected to the edge of the bottom wall 2a when viewed from the thickness direction Z and extends in the thickness direction Z. That is, when viewed from the thickness direction Z, the side wall 2b is formed in an annular shape (rectangular in this embodiment) so as to surround the internal space in which the optical integrated circuit element 20 etc. is housed. In other words, in this embodiment, the side wall 2b is formed in a rectangular cylindrical shape. The top wall 2c is a member that closes the opening on the side of the side wall 2b opposite to the side connected to the bottom wall 2a. The top wall 2c is a rectangular plate-shaped member. In this embodiment, the outer shapes of the bottom wall 2a and the top wall 2c when viewed from the thickness direction Z are substantially the same as the outer shape of the side wall 2b. An opening 2b1 is provided in the portion of the side wall 2b that extends along the arrangement direction Y to allow the output light Lo of the light source unit 1 to pass through. The opening 2b1 is formed, for example, in a circular shape. For example, the height HP in the thickness direction Z of package 2 is approximately 10 mm to 30 mm, and the width BP in the arrangement direction Y is approximately 20 mm to 40 mm.

[0039] The output window 6 is fixed to the inside of the side wall 2b so as to close the opening 2b1. The output window 6 is made of a material that transmits output light Lo, and is made of materials such as germanium (Ge), zinc selenide (ZnSe), zinc sulfide (ZnS), calcium fluoride (CaF2), or chalcogenide (chalcogenide glass). In this embodiment, as an example, the output window 6 is formed in the shape of a disc. The output window 6 may be fixed to the outside of the side wall 2b so as to close the opening 2b1, or it may be provided inside the opening 2b1 so as to close the opening 2b1.

[0040] The cooling element 3 is located on the bottom wall 2a of the package 2. Multiple laser elements 10 and optical integrated circuit elements 20 are mounted on the cooling element 3. In this embodiment, a carrier substrate 4 on which multiple laser elements 10 and optical integrated circuit elements 20 are mounted is mounted on the cooling element 3. The carrier substrate 4 is formed from a material such as copper (Cu), aluminum (Al), silicon (Si), or aluminum nitride (AlN). Multiple laser elements 10, optical integrated circuit elements 20, a lens portion 5, and a temperature sensor 7 are mounted on the carrier substrate 4. With this configuration, the multiple laser elements 10 and optical integrated circuit elements 20 are cooled by the cooling element 3 via the carrier substrate 4. The cooling element 3 is a thermoelectric cooler (TEC) using, for example, a Peltier element.

[0041] The lens section 5 is positioned on the carrier substrate 4 between the optical integrated circuit element 20 and the output window 6. The lens section 5 includes a lens holder 5a and a lens 5b. The lens holder 5a has, for example, a roughly rectangular parallelepiped shape and holds the lens 5b. The lens 5b collimates the light (output light Lo2, described later) output from the optical integrated circuit element 20. As another example of the arrangement of the lens 5b, it may be fixed to the inside or outside of the side wall 2b so as to close the opening 2b1 of the package 2, or it may be provided inside the opening 2b1 so as to close the opening 2b1. According to the above other arrangement examples, the lens holder 5a can be omitted, and the output window 6 can also be omitted by having the lens 5b also serve as the output window 6.

[0042] The temperature sensor 7 is located on the carrier substrate 4. The temperature sensor 7 is used for detecting the temperature inside the package 2, etc. The temperature sensor 7 is, for example, a thermistor. The position of the temperature sensor 7 is not particularly limited, but as shown in Figure 2, the temperature sensor 7 is preferably located near the multiple laser elements 10, which are heat sources (in this embodiment, on the opposite side of the lens portion 5, with the optical integrated circuit element 20 in between).

[0043] The optical integrated circuit element 20 is placed on the cooling element 3 via a carrier substrate 4. The optical integrated circuit element 20 has a substrate 22 and a plurality of unit circuits 30 (301 to 304). As shown in Figure 4, the optical integrated circuit element 20 is constructed by stacking a plurality of layers on the substrate 22. The substrate 22 is formed of silicon (Si) as an example. For example, in this embodiment, the optical integrated circuit element 20 is constructed by stacking an SiO2 layer 23 made of silicon oxide (SiO2), a Si layer 24 made of silicon (Si), and a Ge layer 25 made of germanium (Ge) on the substrate 22 in this order. The thickness of the substrate 22 is, for example, about 200 μm to 650 μm, and in this embodiment it is 625 μm. Also, as an example, the thickness of the SiO2 layer 23 is 2.5 μm, the thickness of the Si layer 24 is 3.0 μm, and the thickness of the Ge layer 25 is 3.0 μm.

[0044] The SiO2 layer 23 plays a role in efficiently heating the waveguide 25a formed in the Ge layer 25 with heat generated from the phase shifter 49, which will be described later. Generally, Si has high thermal conductivity. Therefore, in a configuration without the SiO2 layer 23, some of the heat generated from the phase shifter 49 would be transferred to the substrate 22, making it difficult to efficiently heat the waveguide 25a. The presence of the SiO2 layer 23 suppresses the transfer of heat generated from the phase shifter 49 to the substrate 22, making it possible to efficiently heat the waveguide 25a.

[0045] A waveguide 25a is formed in the Ge layer 25. In this embodiment, the waveguide 25a is formed by providing a pair of recesses 25b on the surface of the Ge layer 25. More specifically, the waveguide 25a is a so-called rib-type waveguide formed by a rib-like portion between the pair of recesses 25b. In this embodiment, the thickness tW of the waveguide 25a is the same as the thickness of the Ge layer 25 (the portion where the recesses 25b are not provided). In addition, a pair of trenches T are provided on the outside of the pair of recesses 25b. Each trench T extends from the surface of the Ge layer 25 to the surface of the SiO2 layer 23 on the Ge layer 25 side. The pair of trenches T play a role in efficiently heating the waveguide 25a by confining the heat generated from the phase shifter 49 to the region sandwiched between the pair of trenches T. Figure 4 schematically shows an example of a partial cross-sectional structure of the waveguide provided in the Ge layer 25. Therefore, in the cross-section of waveguide 25a, there may be portions where the phase shifter 49 and the pair of trenches T are not present. Waveguide 25a in Figure 4 shows a configuration common to various waveguides such as the input / output waveguide 31, waveguide 42, ring waveguide 43, and output waveguide 60, which will be described later.

[0046] As shown in Figures 1 and 5, the substrate 22 has an extended portion 22a that extends in the resonance direction X toward the side where the laser element 10 is provided. In this embodiment, the extended portion 22a is the part of the substrate 22 that extends in the resonance direction X more than each of the layers 23, 24, and 25 when viewed from the thickness direction Z. That is, the SiO2 layer 23, Si layer 24, and Ge layer 25 are not laminated on the extended portion 22a (part of the substrate 22). The extended portion 22a is formed to have a smaller thickness in the thickness direction Z compared to other parts of the substrate 22.

[0047] The extended portion 22a is provided with a plurality of support portions 22b extending in the thickness direction Z. Each support portion 22b is, for example, a columnar member (pedestal) with the thickness direction Z as its axial direction. Each support portion 22b may be formed integrally with the extended portion 22a, or it may be formed as a separate member from the extended portion 22a. The plurality of support portions 22b support the laser element 10. As an example, one laser element 10 is supported by four support portions 22b. The four support portions 22b are arranged to support the four corners of the face of the laser element 10 on the extended portion 22a side. Each laser element 10 is mechanically stable when mounted on the optical integrated circuit element 20 by being supported at its four corners by the four support portions 22b.

[0048] Furthermore, a connecting material 21 is provided in the space between each laser element 10 and the extended portion 22a. The connecting material 21 is, for example, solder. The connecting material 21 connects the substrate 22 and each laser element 10. As shown in Figure 2, as an example, the connecting material 21 is provided in the area inside the four support portions 22b when viewed from the thickness direction Z. The laser element 10 and the substrate 22 (extended portion 22a) face each other with an air gap in the portion that does not overlap with the multiple support portions 22b and the connecting material 21 when viewed from the thickness direction Z (the stacking direction of the semiconductor laminate 12). That is, at least a part of the surface of the laser element 10 (semiconductor laminate 12) that faces the extended portion 22a is exposed to the air. In this way, by supporting the four corners of each laser element 10 with four support portions 22b and making the area inside the four support portions 22b the mounting area for the connecting material 21, the heat dissipation of each laser element 10 can be improved. Note that the support portion 22b and the connecting member 21 are not shown in Figure 1.

[0049] As shown in Figure 5, the optical integrated circuit element 20 has a third end face 20a that faces the first end face 10a, which is one end face of each laser element 10 in the resonance direction X. In this embodiment, the third end face 20a is a flat surface perpendicular to the resonance direction X. The third end face 20a also has a first portion 20a1 and a second portion 20a2. The first portion 20a1 is the portion on which the optical input / output end face 31a, described later, is provided. The second portion 20a2 is the portion that, when viewed from the array direction Y, is further away from the first end face 10a of the laser element 10 than the first portion 20a1. In this embodiment, the third end face 20a of the SiO2 layer 23 is located further from the first end face 10a than the third end faces 20a of the other layers constituting the optical integrated circuit element 20. In other words, of the third end face 20a, the portion formed by the Ge layer 25 and the Si layer 24 corresponds to the first portion 20a1, and the portion formed by the SiO2 layer 23 corresponds to the second portion 20a2.

[0050] As shown in Figure 2, in this embodiment, four laser elements 10 (laser elements 101 to 104) are arranged along the alignment direction Y. Here, "multiple laser elements 10 are arranged along the alignment direction Y" is not limited to a configuration in which multiple laser elements 10 are provided at the same position in the resonance direction X (for example, a configuration in which the position of the first end face 10a of each laser element 10 in the resonance direction X is the same). For example, multiple laser elements 10 may be provided so as to be offset from each other in the resonance direction X. The laser elements 10 are composed of quantum cascade laser elements or interband cascade laser elements. The output wavelength of a quantum cascade laser element is about 4 μm to 15 μm, and the output wavelength of an interband cascade laser element is about 3 μm to 6 μm. In this embodiment, all of the multiple laser elements 10 are composed of quantum cascade laser elements.

[0051] As shown in Figure 5, each laser element 10 comprises a substrate 11 (first substrate) and a semiconductor laminate 12. As an example, the semiconductor laminate 12 includes a lower cladding layer 121, an active layer 122, and an upper cladding layer 123. Each laser element 10 is constructed by stacking the substrate 11, lower cladding layer 121, active layer 122, and upper cladding layer 123 in this order in the thickness direction Z. The substrate 11 is made of, for example, an S-doped InP single crystal substrate. The active layer 122 has, for example, an InGaAs / InAlAs multiple quantum well structure (quantum cascade structure). The thickness tL of the active layer 122 in the thickness direction Z is, for example, 2 μm or more. Note that various semiconductor material systems such as GaAs / AlGaAs, InAs / AlSb, GaN / AlGaN, SiGe / Si, etc. can be applied to the semiconductor material system of the active layer 122.

[0052] The lower cladding layer 121 is, for example, a Si-doped InP layer. The thickness of the lower cladding layer 121 is, for example, 5 μm or more. As an example, the thickness of the lower cladding layer 121 is about 5 μm. The upper cladding layer 123 is, for example, a Si-doped InP layer. The thickness of the upper cladding layer 123 is, for example, 5 μm or more. As an example, the thickness of the upper cladding layer 123 is about 5 μm. Note that the semiconductor laminate 12 may include layers other than the lower cladding layer 121, the active layer 122, and the upper cladding layer 123.

[0053] When the laser element 10 is composed of an interband cascade laser element, the substrate 11 is made of, for example, InP, GaSb, or GaAs. The lower cladding layer 121 and the upper cladding layer 123 are made of, for example, InAs / AlSb. The active layer 122 is made of, for example, III-V / Si. The thickness tL of the active layer 122 of the interband cascade laser element is, for example, about 0.5 μm to 5 μm.

[0054] In this embodiment, the stacking direction of the semiconductor laminate 12 coincides with the thickness direction Z (thickness direction of the substrate 22). In this embodiment, the upper cladding layer 123 is placed on the support portion 22b. This reduces the area in which the laser element 10 and the optical integrated circuit element 20 (third end face 20a) face each other, compared to the first modified example described later (see Figure 11). As a result, the risk of contact between the laser element 10 and the optical integrated circuit element 20 (third end face 20a) due to burrs, etc., can be reduced. Each laser element 10 has, for example, a roughly rectangular parallelepiped shape. The width BL1 (see Figure 2) of each laser element 10 in the arrangement direction Y is, for example, about 100 μm to 500 μm. Also, the length LL (see Figure 2) of each laser element in the resonance direction X is, for example, about 1 mm to 5 mm.

[0055] Each laser element 10 has a first end face 10a, which is one end face in the resonance direction X, and a second end face 10b, which is opposite to the first end face 10a. Each laser element 10 is configured to emit light in the fingerprint region (i.e., the mid-infrared region, which is suitable for identifying molecular structures and materials) from each of the first end face 10a and the second end face 10b. In this embodiment, each laser element 10 emits light from the active layer 122 on the first end face 10a. The first end face 10a and the second end face 10b are flat surfaces perpendicular to the resonance direction X, and the optical axis of the light emitted from each laser element 10 is aligned with the resonance direction X.

[0056] The thickness of the upper cladding layer 123 may be adjusted so that when each laser element 10 is placed on the support portion 22b, the positions of the active layer 122 and the Ge layer 25 coincide in the thickness direction Z (so that at least a portion of the optical input / output end face 31a and the active layer 122 overlap each other when viewed from the resonance direction X). Alternatively, the height of the support portion 22b may be adjusted to ensure that the positions of the active layer 122 and the Ge layer 25 coincide in the thickness direction Z.

[0057] As shown in Figure 2, in this embodiment, a plurality of unit circuits 30 (301 to 304) corresponding to each of the plurality of laser elements 10 are provided on the substrate 22 (Ge layer 25). Each of the plurality of unit circuits 30 (at least the portion including the optical input / output end face 31a described later) is arranged along the array direction Y so as to face the resonance direction X with respect to each of the plurality of laser elements 10. Here, "a plurality of unit circuits 30 are arranged along the array direction Y" is not limited to a configuration in which the plurality of unit circuits 30 are provided at the same position in the resonance direction X (for example, a configuration in which the positions of each optical input / output end face 31a in the resonance direction X are the same). That is, the plurality of unit circuits 30 may be provided so as to be offset from each other in the resonance direction X.

[0058] Referring to Figure 3, the configuration of each unit circuit 30 will be explained. Here, we will focus on one unit circuit 30 out of several unit circuits 30 (301 to 304). Figure 3 schematically illustrates an example of the configuration of one unit circuit 30. As an example, the unit circuit 30 has an optical input / output end face 31a, an input / output waveguide 31, an optical feedback section 40, and an output waveguide 60. For example, the waveguide constituting the unit circuit 30 is formed by a waveguide 25a, which is part of the Ge layer 25, as described above. The input / output waveguide 31 extends from the optical input / output end face 31a on the third end face 20a of the optical integrated circuit element 20. The optical input / output end face 31a faces the first end face 10a of the corresponding laser element 10 in the resonance direction X. As a result, the unit circuit 30 (optical input / output end face 31a) is optically connected to the corresponding laser element 10. The unit circuit 30 only needs to have at least an optical input / output end face 31a, an input / output waveguide 31, and an optical feedback section 40. The unit circuit 30 does not need to include an output waveguide 60 and a monitor waveguide 85, which will be described later. The output waveguide 60 and the monitor waveguide 85 may be provided as separate elements from the unit circuit 30 in the optical integrated circuit element 20 (Ge layer 25).

[0059] As shown in Figures 1 to 3 and Figure 5, the optical input / output end face 31a and the first end face 10a of the laser element 10 are separated by a space S. That is, the first end face 10a and the optical input / output end face 31a are optically connected via the space S. The size of the space S in the resonance direction X is configured to be one-quarter or less of the shortest wavelength λ1 in a predetermined wavelength range (for example, the range of λ1 to λ2) that can be adjusted by the optical feedback unit 40 (wavelength adjustment unit 41 described later).

[0060] The optical feedback section 40 includes a wavelength adjustment section 41 and a mirror section 50. The wavelength adjustment section 41 is optically connected to the input / output waveguide 31. For example, the wavelength adjustment section 41 is configured as a vernier filter consisting of a plurality (three for example) ring resonators. The wavelength adjustment section 41 has a plurality of waveguides (waveguides 42, 44, 46, 48 and ring waveguides 43, 45, 47).

[0061] Waveguide 42 is optically connected to input / output waveguide 31. Waveguide 44 is optically connected to waveguide 42 via ring waveguide 43. Specifically, when an integer multiple of the wavelength of light passing through waveguide 42 in the direction of arrow A in Figure 3 is equal to the circumference of ring waveguide 43, light passing through waveguide 44 in the direction of arrow B in Figure 3 is generated.

[0062] Waveguide 46 is optically connected to waveguide 44 via ring waveguide 45. Specifically, when an integer multiple of the wavelength of light passing through waveguide 44 in the direction of arrow B in Figure 3 is equal to the circumference of ring waveguide 45, light passing through waveguide 46 in the direction of arrow C in Figure 3 is generated.

[0063] Waveguide 48 is optically connected to waveguide 46 via ring waveguide 47. Specifically, when an integer multiple of the wavelength of light passing through waveguide 46 in the direction of arrow C in Figure 3 is equal to the circumference of ring waveguide 47, light passing through waveguide 48 in the direction of arrow D in Figure 3 is generated. With the multiple waveguides configured as described above, light of a predetermined wavelength corresponding to the circumference of ring waveguides 43, 45, and 47 passes (guides) from waveguide 42 to waveguide 48. The end of waveguide 48 in the direction of arrow D is optically connected to mirror section 50.

[0064] The mirror section 50 is configured as a Sagnac loop mirror using, for example, a 2x2 coupler. In the 2x2 coupler that constitutes the mirror section 50, the port on the side other than the side to which the waveguide 48 is connected is optically connected to the output waveguide 60. The mirror section 50 is configured to branch off a portion of the light incident from the wavelength adjustment section 41 as output light Lo1 to the output waveguide 60, and to return the remaining light to the input / output waveguide 31. In this way, the wavelength adjustment section 41 and Mirror section 50 In the optical feedback section 40 (so-called series type) which is constructed by arranging the two in series, the light emitted from the laser element 10 travels back and forth through the wavelength adjustment section 41 and returns to the laser element 10, thus providing higher wavelength selectivity compared to the loop-type optical feedback sections 40A and 40B described later.

[0065] The mirror section 50 may have a highly reflective film provided on the side surface of the optical integrated circuit element 20. In this case, the mirror section 50 may have a 1x2 coupler instead of the 2x2 coupler described above. That is, instead of the waveguide formed in a loop in the example of Figure 3, a single waveguide connecting the 1x2 coupler and the highly reflective film may be provided. Furthermore, when light is output from the second end face 10b side of the laser element 10 (i.e., when the output waveguide 60 is not required), as in the second embodiment described later, the waveguide 48 may extend to the highly reflective film.

[0066] In this embodiment, a phase shifter 49 (not shown in figures other than Figures 4 and 21) is provided along each of the ring waveguides 43, 45, and 47. The phase shifter 49 is, for example, a thermal phase shifter that generates heat when power is supplied. The phase shifter 49 is constructed as a thin-film heater using a high-resistance material such as Ti, W, or TiN. By generating heat, the phase shifter 49 changes (increases) the refractive index of the portion of each of the ring waveguides 43, 45, and 47 that is aligned with the phase shifter 49. This makes it possible to shift the phase of the light circulating through each of the ring waveguides 43, 45, and 47. In other words, by controlling the power supplied to the phase shifter 49, the amount of phase adjustment (phase shift amount) of the wavelength adjustment unit 41 can be controlled. This makes it possible to adjust the wavelength of the output light Lo1 passing through the wavelength adjustment unit 41.

[0067] Furthermore, a phase shifter 49 may be provided as a phase shifter for longitudinal mode control, positioned along the waveguides such as the input / output waveguide 31 and waveguide 48. In this case, the refractive index of the waveguide along the phase shifter 49 can be changed by generating heat. As a result, the longitudinal modes of the resonator formed by the laser element 10 and the optical feedback unit 40 can be shifted. This allows for fine-tuning of the wavelength of the output light Lo1.

[0068] Next, we will explain the amplification and monitoring of light between a pair of laser elements 10 and a unit circuit 30. Here, we will focus on one pair of laser elements 10 and unit circuits 30 from among the multiple pairs of laser elements 10 and unit circuits 30.

[0069] Light emitted from the first end face 10a of the laser element 10 is incident into the input / output waveguide 31 as input light Lin. Of the input light Lin, light with a wavelength that can pass through the wavelength adjustment unit 41 (resonance peak wavelength) (intermediate light Lmid) is input from the wavelength adjustment unit 41 to the mirror unit 50. A portion of the intermediate light Lmid is reflected by the mirror unit 50 and returned to the laser element 10 via the wavelength adjustment unit 41 as return light Lr. When the return light Lr is incident on the laser element 10, the light with the resonance peak wavelength is amplified inside the laser element 10.

[0070] A portion of the light amplified inside the laser element 10 is emitted again from the first end face 10a to the input / output waveguide 31, and similarly, the reflected light Lr is returned to the laser element 10, further amplifying the light at the resonant peak wavelength inside the laser element 10. In other words, the laser element 10, the input / output waveguide 31, and the optical feedback section 40 form an external resonator. In this process of light amplification, a portion of the intermediate light Lmid passing through the mirror section 50 is output to the output waveguide 60 as output light Lo1.

[0071] As shown in Figure 2, the light source unit 1 has a wavelength monitor 71 optically connected to each unit circuit 30. The wavelength monitor 71 is configured to measure the wavelength of light amplified in each unit circuit 30. In this embodiment, a portion of the output light Lo1 passing through the output waveguide 60 is branched by a coupler 72 and guided to the wavelength monitor 71. For example, the coupler 72 branches the output light Lo1 to the output waveguide 60 downstream of the coupler 72 and to a waveguide 73 for guiding the light to the wavelength monitor 71 at a predetermined branching ratio (e.g., 99:1). The light branched to the waveguide 73 may be configured to pass through, for example, a wavelength-dependent (selective) element (e.g., a ring resonator or a Mach-Zehnder interferometer) configured to selectively pass light of a specific wavelength before being incident on the wavelength monitor 71. For example, the wavelength monitor 71 is flip-chip mounted on the Ge layer 25. The wavelength monitor 71 and the waveguide 73 are optically connected, for example, via a grating coupler. The grating coupler is installed in the Ge layer 25 and directs the incident light out of the plane of the Ge layer 25, thereby directing the light onto the wavelength monitor 71.

[0072] The light source unit 1 has a power monitor 81 that is optically connected to each unit circuit 30. The power monitor 81 is configured to measure the output of the light amplified in each unit circuit 30. In this embodiment, a portion of the output light Lo1 passing through the output waveguide 60 is branched by a coupler 82 and guided to the power monitor 81. For example, the coupler 82 branches the light that has passed through the coupler 72 to the output waveguide 60 downstream of the coupler 82 and to a waveguide 83 for guiding the light to the power monitor 81 at a predetermined branching ratio (e.g., 99:1). For example, the power monitor 81 is flip-chip mounted on the Ge layer 25. The power monitor 81 and the waveguide 83 are optically connected, for example, via a grating coupler. The grating coupler is provided on the Ge layer 25 and causes the incident light to be directed to the power monitor 81 by emitting the incident light in the out-of-plane direction of the Ge layer 25.

[0073] In the example shown in Figure 2, all wavelength monitors 71 and power monitors 81 are grating-coupled to waveguides 73 and 83, but the connection configuration of the wavelength monitors 71 and power monitors 81 is not limited to the above example. For example, the wavelength monitors 71 and power monitors 81 may be edge-coupled to waveguides 73 and 83. That is, the wavelength monitors 71 and power monitors 81 may be positioned facing the side surface of the optical integrated circuit element 20. In this case, the light incident on the wavelength monitors 71 and power monitors 81 is emitted from the side surface of the optical integrated circuit element 20 along the in-plane direction of the Ge layer 25.

[0074] Furthermore, one of the wavelength monitor 71 and power monitor 81 may be grating-coupled, while the other is edge-coupled. Also, the wavelength monitor 71 and power monitor 81 may be arranged in different configurations depending on the unit circuit 30 to which they are connected. For example, the wavelength monitor 71 and power monitor 81 connected to unit circuits 301 and 304 located at both ends of the array direction Y may be positioned facing the side surface of the optical integrated circuit element 20 and edge-coupled. On the other hand, the wavelength monitor 71 and power monitor 81 connected to unit circuits 302 and 303 located on the inside of the array direction Y may be flip-chip mounted and grating-coupled. In addition, by guiding a portion of the output light Lo1 from unit circuits 302 and 303 to the side surface of the optical integrated circuit element 20 using a cross waveguide or the like, the wavelength monitor 71 and power monitor 81 connected to unit circuits 302 and 303 may also be positioned facing the side surface of the optical integrated circuit element 20 and edge-coupled.

[0075] Furthermore, the light incident on the wavelength monitor 71 and the power monitor 81 does not necessarily have to be light branched from the output waveguide 60. For example, the power monitor 81 may be optically connected to the portion of waveguide 42 that corresponds to the passport in a ring resonator composed of waveguide 42, ring waveguide 43, and waveguide 44.

[0076] Furthermore, as shown in Figure 6, the power monitor 81 may be positioned opposite the second end face 10b of each laser element 10. For example, the power monitor 81 may be fixed to a submount 84 or the like, which is placed on the carrier substrate 4. In this case, the power monitor 81 can measure the output of the light amplified in the unit circuit 30 based on the light emitted from the second end face 10b.

[0077] The light source unit 1 is equipped with a wavelength monitor 71 and a power monitor 81, which allows monitoring of the wavelength and output power of the light amplified in the unit circuit 30. Based on the monitoring results of the wavelength monitor 71 and the power monitor 81, the power supplied to the phase shifter 49 and the laser element 10 can be adjusted to the desired wavelength and output power of the output light Lo1. The wavelength monitor 71 and the power monitor 81 may be placed in locations other than on the cooling element 3.

[0078] In this embodiment, as shown in Figure 2, the output waveguides 60 of each unit circuit 30 are integrated into a single output waveguide 63 via a multiplexer 62. The multiplexer 62 may be configured, for example, by an AWG (Arrayed Waveguide Grating) or by a combination of multiple Y-shaped branches. The multiplexer 62 and the output waveguide 63 are provided, for example, on a substrate 22 (Ge layer 25). As a result, the light Lo1 from each unit circuit 30 that is not branched to the wavelength monitor 71 and power monitor 81 but is instead guided to the multiplexer 62 is integrated by the multiplexer 62. As an example, the light integrated by the multiplexer 62 is output to the outside of the optical integrated circuit element 20 as output light Lo2 from the side of the optical integrated circuit element 20 (the end of the output waveguide 63). In this disclosure, "side of the optical integrated circuit element 20" means the end face of the optical integrated circuit element 20 along the thickness direction Z. As shown in Figure 2, in this embodiment, the output light Lo2 is emitted along the resonance direction X, but the emission direction of the output light Lo2 can be arbitrarily determined according to the configuration of the output waveguide 63 (such as the position of the end of the output waveguide 63). Furthermore, the lens section 5 and the output window 6 should be provided at positions corresponding to the emission direction of the output light Lo2.

[0079] The output light Lo2 is output to the outside of the optical integrated circuit element 20, then passes through the lens 5b, the output window 6, and the aperture 2b1 in that order, and is output to the outside of the package 2. The output light Lo2 is collimated by passing through the lens 5b and is output to the outside of the package 2 as output light Lo.

[0080] Referring to Figure 7, an example of the control configuration of the light source unit 1 will be described. The light source unit 1 is electrically connected to the control device 200 via, for example, a cable (not shown). The control device 200 may be configured by, for example, a computer device. As an example, the control device 200 has, as elements for controlling the light source unit 1, a laser drive unit 201, a unit circuit drive unit 202, a monitor information acquisition unit 203, and a cooling element control unit 204, and a control unit 210 that comprehensively controls the operation of each of the above elements. The control unit 210 may be configured by an arithmetic circuit including, for example, a processor such as a CPU or FPGA, and a storage device (memory, auxiliary storage device, etc.) configured with ROM and RAM.

[0081] The laser drive unit 201 is electrically connected to each laser element 10 and supplies a drive current to each laser element 10 based on a signal from the control unit 210. The unit circuit drive unit 202 is electrically connected to each phase shifter 49 (heater) provided near the waveguide constituting each unit circuit 30 and supplies a current to each phase shifter 49 based on a signal from the control unit 210. This adjusts the amount of heat generated in each phase shifter 49. but Yes, it is possible. As a result, the wavelength of the output light Lo1 in each unit circuit 30 can be adjusted. The control unit 210 may control each laser element 10 so that each laser element 10 is pulsed at a desired timing.

[0082] The monitor information acquisition unit 203 is electrically connected to each wavelength monitor 71 and each power monitor 81, and transmits information on the wavelength and output power of each unit circuit 30 to the control unit 210. Based on the signals received from the monitor information acquisition unit 203, the control unit 210 adjusts the amount of current supplied from the laser drive unit 201 and the unit circuit drive unit 202 to each laser element 10 and each phase shifter 49.

[0083] The cooling element control unit 204 controls the cooling element 3 based on temperature information obtained from the temperature sensor 7 so that the temperature of each laser element 10 and optical integrated circuit element 20, etc., reaches a desired temperature.

[0084] As described above, in the light source unit 1, each of the multiple unit circuits 30 has an input / output waveguide 31 into which light emitted from the laser element 10 is incident, and an optical feedback unit 40. The optical feedback unit 40 returns light of a predetermined wavelength from the light emitted by the laser element 10 back to the laser element 10. As a result, light of a predetermined wavelength is amplified in the laser element 10. Here, a space S is provided between the first end face 10a of the laser element 10 on the unit circuit 30 side and the optical input / output end face 31a of the unit circuit 30. With the above configuration, the first end face 10a of the laser element 10 and the optical input / output end face 31a of the unit circuit 30 can be optically connected without contact between them. As a result, variations in product quality and a decrease in yield caused by burrs etc. that may occur on the first end face 10a or the optical input / output end face 31a can be avoided. Furthermore, the size of the space S is configured to be one-quarter or less of the shortest wavelength λ1 in the wavelength range of the output light Lo adjusted by the optical feedback unit 40. Generally, the divergence angle of light in quantum cascade laser elements and interband cascade laser elements is larger than that of other laser elements. However, by making the distance between the first end face 10a and the optical input / output end face 31a sufficiently small relative to the shortest wavelength λ1 in the wavelength tuning range, as in the above configuration, the loss of light in space S can be suppressed.

[0085] It is also conceivable that the light source unit 1 could be configured to bring the first end face 10a or the optical input / output end face 31a into contact with each other by removing the burrs formed on the latter. However, in this case, an additional step for removing the burrs would be required during the manufacturing process of the light source unit 1. In contrast, according to this embodiment, there is no need to perform a step for removing the burrs, thus avoiding the increase in manufacturing costs associated with adding such a step.

[0086] Furthermore, in this embodiment, the light source unit 1 is equipped with multiple laser elements 10. For example, if the wavelength range of the light emitted from the multiple laser elements 10 is the same, the output of the output light Lo can be increased compared to a light source unit composed of a single laser element. Also, by staggering the timing of light output in the multiple laser elements 10, a high duty cycle can be achieved for the multiple laser elements 10 as a whole while keeping the duty cycle of each laser element 10 at a low value (e.g., 50% or less). An example of drive control for each laser element 10 will be described in more detail with reference to Figures 8 and 9.

[0087] In Figures 8 and 9, the horizontal axis represents time, and the vertical axis represents applied voltage. When the applied voltage is high, each laser element 10 is in the "ON" state and emits laser light. When the applied voltage is low, each laser element 10 is in the "OFF" state and does not emit laser light. Figure 8 shows an example of pulse timing to achieve a high duty cycle using three laser elements 10 (laser elements 101, 102, and 103). In the example shown in Figure 8, the multiple laser elements 10 are controlled so that two or more laser elements 10 are not in the ON state at the same time.

[0088] In the example shown in Figure 8, the pulse period of each laser element 10 is the same, and the duty cycle of each is 33%. Furthermore, when laser element 101 switches from ON to OFF, laser element 102 switches from OFF to ON at the same time. Similarly, the timing of switching OFF and ON between laser elements 102 and 103, and between laser elements 103 and 101, are controlled to be simultaneous. With this control, it is possible to achieve a high overall duty cycle (almost 100%) while keeping the duty cycle of each laser element 10 at a relatively low value (33%). Note that, as shown in Figure 9, the pulse timing may be set so that there is a time when all of the multiple laser elements 10 are OFF. That is, the next laser element 10 may switch from OFF to ON after a predetermined period has elapsed after a laser element 10 has switched from ON to OFF.

[0089] Furthermore, by making the wavelength ranges of the light emitted from multiple laser elements 10 different from each other, the wavelength tuning range of the output light Lo can be widened compared to a light source unit composed of a single laser element. For example, consider the case where laser element 101 is configured to emit light in the range of 6 μm to 6.8 μm, laser element 102 is configured to emit light in the range of 6.7 μm to 7.7 μm, laser element 103 is configured to emit light in the range of 7.6 μm to 8.9 μm, and laser element 104 is configured to emit light in the range of 8.8 μm to 10.6 μm. In this case, the wavelength tuning range of the light source unit 1 can be made wider (6 μm to 10.6 μm in the above example) than when there is a single laser element, by using multiple laser elements 10 (laser elements 101 to 104). Furthermore, as in the example above, if the wavelength ranges of the emitted light from each laser element 10 are different from each other, and accordingly the variable wavelength ranges in each optical feedback unit 40 corresponding to each laser element 10 are different from each other, then the shortest wavelength λ1 in the above embodiment may differ from each other among the multiple unit circuits 30.

[0090] In this embodiment, the size of the space S in the resonance direction X was configured to be one-quarter or less of the shortest wavelength λ1 in the wavelength range of the output light Lo1 adjusted by the optical feedback unit 40, but the size of the space S is not limited to the above configuration. For example, the size of the space S in the resonance direction X may be configured to be 2 μm or less. The laser element 10 may be composed of a quantum cascade laser element or an interband cascade laser element, and in these laser elements, if the size of the space S is 2 μm or less, it is possible to sufficiently suppress the reduction in the amount of light incident from the laser element 10 to the optical input / output end face 31a due to light divergence. Therefore, the same effect as in the above embodiment can be obtained by configuring the size of the space S to be 2 μm or less. Furthermore, from the viewpoint of enhancing the above effect, the size of the space S may be set to be less than or equal to the smaller of one-quarter of the shortest wavelength λ1 and 2 μm.

[0091] Each of the multiple laser elements 10 has an active layer 122, and the size of the space S in the resonance direction X may be configured to be smaller than the thickness tW in the thickness direction Z of the input / output waveguide 31 at the optical input / output end face 31a (see Figure 4) and the thickness tL in the thickness direction Z of the active layer 122 (see Figure 5). In this case, the distance between the first end face 10a of the laser element 10 and the optical input / output end face 31a can be reduced with respect to the thickness tL of the active layer 122 and the thickness tW of the input / output waveguide 31. As a result, the distance between the first end face 10a of the laser element 10 and the optical input / output end face 31a becomes a suitable size (i.e., a size that can suitably suppress the reduction in the amount of light incident from the laser element 10 to the optical input / output end face 31a, so as to be suitable), thus suitably suppressing the loss of light in space S.

[0092] The size of the space S in the resonance direction X may be configured to be 1 μm or less. In this case, by bringing the first end face 10a of each laser element 10 and the corresponding optical input / output end face 31a of the unit circuit 30 into sufficient proximity, the loss of light in space S can be suppressed more effectively.

[0093] In the light source unit 1, the output light Lo2 is configured to be output to the outside of the optical integrated circuit element 20 from the side of the optical integrated circuit element 20 along the thickness direction Z. In the light source unit 1, the output light Lo1 passing through the output waveguide 60 of each unit circuit 30 is integrated into the output light Lo2 passing through a single output waveguide 63 via a multiplexer 62. Then, the output light Lo2 is configured to be output to the outside of the optical integrated circuit element 20 from the end of the output waveguide 63 that extends to the side of the optical integrated circuit element 20 by so-called edge coupler emission. When a grating coupler is used to output the output light to the outside of the optical integrated circuit element 20, the angle at which the output light is output changes depending on the wavelength of the output light. Therefore, it is difficult to output the output light in a desired direction (a predetermined specific direction) regardless of its wavelength. In contrast, the configuration in which the output light Lo2 is output from the side of the optical integrated circuit element 20 avoids the problems that occur when using the grating coupler described above. In other words, with the above configuration, compared to a configuration in which a grating coupler is used to output light to the outside of the optical integrated circuit element 20, the output light Lo2 can be easily emitted in a desired direction (a direction perpendicular to the output end face of the optical integrated circuit element 20).

[0094] In this embodiment, a configuration is shown in which multiple output waveguides 60 are integrated into a single output waveguide 63 by a multiplexer 62, but the configuration of the output waveguides 60 is not limited to the above configuration. For example, as shown in Figure 10, each output waveguide 60 may extend to different positions on the side surface of the optical integrated circuit element 20. In this case, the output light Lo1 from each unit circuit 30 will be output from different side surface positions of the optical integrated circuit element 20. Note that when some of the light is branched from each output waveguide 60 to the wavelength monitor 71 and the power monitor 81, as in Figure 2 of the above embodiment, the light that does not branch to the wavelength monitor 71 and the power monitor 81 from the output light Lo1 passing through each output waveguide 60 will be output from the side surface position of the optical integrated circuit element 20. In such a configuration, the output sections 61, which are the ends of each output waveguide 60, may be aggregated so that they are closer to each other than a certain distance at the ends of the optical integrated circuit element 20. For example, the distance d between two adjacent output units 61 may be configured to be smaller than the width BL1 in the arrangement direction Y of each laser element 10. As an example, the distance d between two adjacent output units 61 may be configured to be between 1 μm and 50 μm. In this case, the output units 61 of each output waveguide 60 of the multiple unit circuits 30 can be concentrated in a relatively narrow range. This makes it possible to suppress large shifts in the position where the output light Lo1 is emitted for each laser element 10. In addition, by omitting the multiplexer 62, the manufacturing cost of the light source unit 1 can be reduced and the light source unit 1 can be miniaturized.

[0095] In the light source unit 1, at least one of the multiple laser elements 10 is composed of a quantum cascade laser element. In this embodiment, as an example, all of the multiple laser elements 10 are composed of quantum cascade laser elements. In this case, by utilizing the output light Lo1 generated by at least one quantum cascade laser element (laser element 10) and the unit circuit 30 corresponding to the laser element 10, spectroscopic analysis in the fingerprint region (i.e., the mid-infrared region, which is suitable for identifying molecular structures and materials) can be performed.

[0096] The light source unit 1 has a cooling element 3 on which multiple laser elements 10 and optical integrated circuit elements 20 are mounted. With the above configuration, the temperature of the laser elements 10 and optical integrated circuit elements 20 can be kept uniform. As a result, variations in the performance of the light source unit 1 caused by temperature changes can be suppressed. In this embodiment, as an example, the multiple laser elements 10 and optical integrated circuit elements 20 are arranged on the cooling element 3 via a carrier substrate 4, but the multiple laser elements 10 and optical integrated circuit elements 20 may be arranged directly on the cooling element 3.

[0097] The light source unit 1 includes a lens section 5 that transmits output light Lo2, and a package 2 that houses multiple laser elements 10 and optical integrated circuit elements 20, as well as the lens section 5. As an example, in the light source unit 1, the lens section 5 is housed in the package 2 and placed on the carrier substrate 4. In this case, each component constituting the light source unit 1 (lens section 5, multiple laser elements 10, and optical integrated circuit elements 20) can be appropriately protected by the package 2, and external influences on each component can be suppressed. In addition, the output light Lo2 can be appropriately extracted to the outside through the lens section 5 housed in the package 2. In a configuration without a multiplexer 62 (for example, the configuration shown in Figure 10), the output light transmitted through the lens section 5 is multiple output light Lo1. Furthermore, as described above, the lens 5b (lens section 5) may be provided in the opening 2b1 of the package 2. In this case, the lens section 5 is held in the package 2, and the components other than the lens section 5 are housed in the package 2.

[0098] In the light source unit 1, the width BP (see Figure 2) of package 2 in the array direction Y may be configured to be greater than the height HP (see Figure 1) of package 2 in the thickness direction Z. In this case, the height HP of package 2 can be suppressed. As a result, the light source unit 1 can be miniaturized.

[0099] In the light source unit 1, the substrate 22 has an extended portion 22a that extends in the resonance direction X from the optical input / output end face 31a toward the side where the laser element 10 is provided, and the laser element 10 is mounted on the extended portion 22a. As shown in Figure 5, as an example, in the light source unit 1, the laser element 10 is mounted on a support portion 22b provided on the extended portion 22a. In this case, the laser element 10 is mounted on the same substrate (i.e., substrate 22) as the substrate on which the multiple unit circuits 30 are provided. By arranging the laser element 10 in this way, the height in the thickness direction Z of the active layer 122 of the laser element 10 and the optical input / output end face 31a can be easily and accurately matched. For example, the thickness of the extended portion 22a may be adjusted so that when the laser element 10 is mounted on the extended portion 22a, the positions of the active layer 122 and the optical input / output end face 31a in the thickness direction Z are aligned. With the above configuration, compared to a configuration in which the laser element 10 is mounted on a substrate different from the substrate 22 that constitutes the optical integrated circuit element 20, the alignment of the active layer 122 and the optical input / output end face 31a in the thickness direction Z can be performed easily and with high precision.

[0100] As shown in Figure 5, in the light source unit 1, the optical integrated circuit element 20 has a third end face 20a that faces the first end face 10a and includes the optical input / output end face 31a, and when viewed from the arrangement direction Y, the third end face 20a has a first portion 20a1 on which the optical input / output end face 31a is provided, and in the resonance direction X from the first end face 10a to the first portion 20a1The third end face 20a is configured to have a second portion 20a2 that is further away from the first portion 20a1. According to the above configuration, each laser element 10 and the corresponding optical input / output end face 31a are separated by a space S of a suitable size. Furthermore, the second portion 20a2 of the third end face 20a, which does not have an optical input / output end face 31a, is configured to be at a greater distance from the laser element 10 than the first portion 20a1, which has an optical input / output end face 31a. That is, when viewed from the array direction Y, the distance between the first portion 20a1, which affects the coupling of light between each laser element 10 and the corresponding input / output waveguide 31, is set to a size that minimizes light loss, while the distance between each laser element 10 and the optical integrated circuit element 20 (third end face 20a) is set to be large for the second portion 20a2. This makes it possible to suppress the interference of burrs or the like from hindering the close arrangement of each laser element 10 with the corresponding optical input / output end face 31a (first part 20a1) even if burrs or the like occur in the second part 20a2.

[0101] Furthermore, by providing a second portion 20a2 that is spaced further away from the laser element 10 than the first portion 20a1 on which the optical input / output end face 31a is provided, heat from the laser element 10 is less likely to be transferred to the optical integrated circuit element 20. In addition, the existence of a space larger than space S between the laser element 10 and the second portion 20a2 improves the heat dissipation of the laser element 10.

[0102] Figure 11 shows the configuration of the first modified example of the third end face 20a. The first modified example differs from the first embodiment mainly in that a second portion 20a2 is provided on the substrate 22. In the first modified example, the SiO2 layer 23, the Si layer 24, and the Ge layer 25 are configured to be flush with the third end face 20a. On the other hand, the third end face 20a of the substrate 22 is tapered such that, when viewed from the arrangement direction Y, the distance between the third end face 20a and the first end face 10a in the resonance direction X increases as it moves away from the Ge layer 25 in the thickness direction Z. In other words, in the first modified example, the portions of the Ge layer 25, Si layer 24, and SiO2 layer 23 on the third end face 20a correspond to the first portion 20a1, and the portion of the substrate 22 corresponds to the second portion 20a2. The same effects as described above can be obtained with the third end face 20a configured in this way.

[0103] Furthermore, in the first modified example, in order to easily match the height of the optical input / output end face 31a and the active layer 122 in the thickness direction Z, the laser element 10 is arranged on the extended portion 22a in an inverted configuration compared to the first embodiment. As a result, the surface of the laser element 10 opposite to the extended portion 22a is exposed to space. Also, in the first modified example, the support portion 22b is not formed on the extended portion 22a. In the above configuration, for example, the second portion 20a2 (i.e., the portion that is recessed in the direction away from the laser element 10 in the resonance direction X compared to the first portion 20a1) may be provided across the Si layer 24, the SiO2 layer 23, and the substrate 22, or it may be provided across the SiO2 layer 23 and the substrate 22. Furthermore, in the example shown in Figure 11, the second portion 20a2 is formed in a tapered shape such that the distance between the first end face 10a and the second portion 20a2 changes when viewed from the arrangement direction Y. However, the second portion 20a2 may be configured such that the distance between the first end face 10a and the second portion 20a2 remains constant when viewed from the arrangement direction Y, similar to the first embodiment (see Figure 5).

[0104] Figure 12 shows the configuration of a second modified example of the third end face 20a. In the second modified example, the third end face 20a has a third portion 20a3 and a fourth portion 20a4. The third portion 20a3 is the portion on which the optical input / output end face 31a is provided. The fourth portion 20a4 is the portion that, when viewed from the thickness direction Z, is further away from the first end face 10a of the laser element 10 than the third portion 20a3. In the second modified example, when viewed from the thickness direction Z, the third end face 20a is configured such that the input / output waveguide 31 and the area near where the input / output waveguide 31 is provided become the third portion 20a3, and the remaining portion (i.e., the portions on both sides of the third portion 20a3 in the array direction Y) becomes the fourth portion 20a4. Furthermore, the width of the third portion 20a3 in the array direction Y is configured to be smaller than the width BL1 of each laser element 10 in the array direction Y. Furthermore, the fourth portion 20a4 extends in the thickness direction Z to the height where the lower end of each laser element 10 is located.

[0105] In the second modified example described above, each laser element 10 and the corresponding optical input / output end face 31a are separated by a space S of a suitable size. Furthermore, the fourth portion 20a4 of the third end face 20a, which does not have an optical input / output end face 31a, is configured to be at a greater distance from the laser element 10 than the third portion 20a3, which has an optical input / output end face 31a. That is, when viewed from the thickness direction Z, the distance between the laser element 10 and the optical input / output end face 31a in the third portion 20a3, which affects the coupling of light between each laser element 10 and the corresponding input / output waveguide 31, is set to a size that minimizes light loss, while the distance between each laser element 10 and the optical integrated circuit element 20 (third end face 20a) in the fourth portion 20a4 is set to be larger. As a result, even if burrs or the like occur in the fourth portion 20a4, it is possible to suppress the interference of such burrs or the like from hindering the close arrangement of each laser element 10 and the corresponding optical input / output end face 31a (third portion 20a3).

[0106] Furthermore, by providing a fourth portion 20a4 that is positioned further away from the laser element 10 than the third portion 20a3 on which the optical input / output end face 31a is provided, heat from the laser element 10 is less likely to be transferred to the optical integrated circuit element 20. In addition, the existence of a space larger than the space S between the laser element 10 and the fourth portion 20a4 improves the heat dissipation of the laser element 10.

[0107] Furthermore, the configuration of the third end face 20a described in the above embodiment (Figure 5) or the first modified example (Figure 11) can be combined with the configuration of the third end face 20a described in the second modified example (Figure 12). That is, the third end face 20a may be configured to have a first portion 20a1 and a second portion 20a2 when viewed from the arrangement direction Y, and a third portion 20a3 and a fourth portion 20a4 when viewed from the thickness direction Z. [Second Embodiment]

[0108] Next, with reference to Figures 13 to 15, the light source unit 1A of the second embodiment will be described. The light source unit 1A mainly differs from the light source unit 1 of the first embodiment in that it outputs light (output light Lo3) output from the second end face 10b side of each laser element 10 to the outside of the package 2. In relation to the above difference, the light source unit 1A differs from the light source unit 1 in that it has multiple unit circuits 30A instead of multiple unit circuits 30.

[0109] As shown in Figures 13 and 14, in the light source unit 1A, the light amplified by each laser element 10 and the corresponding unit circuit 30 is configured to be output from the second end face 10b of each laser element 10. The output light Lo3 output from the second end face 10b passes through the lens 5b, the output window 6, and the aperture 2b1 in that order and is output to the outside of the package 2. The output light Lo3 is collimated by passing through the lens 5b and is output to the outside of the package 2 as output light Lo.

[0110] In this embodiment, for example, multiple lens portions 5 corresponding to each of the multiple laser elements 10 may be provided on the carrier substrate 4. Furthermore, the output window 6 and aperture 2b1 may be configured to output multiple output beams Lo3, emitted from the second end face 10b of each laser element 10 at different positions in the array direction Y, to the outside of the package 2. For example, the output window 6 and aperture 2b1 may be configured to have an elongated outer shape, where the length in the array direction Y is greater than the length in the thickness direction Z. In this embodiment, the distance dL in the array direction Y between two adjacent laser elements 10 is, for example, about 10 μm to 100 μm.

[0111] Referring to Figures 14 and 15, an example of the configuration of multiple unit circuits 30A included in the light source unit 1A will be described. Here, we will focus on one of the multiple unit circuits 30A (301A to 304A). Unit circuit 30A mainly differs from unit circuit 30 in that it has a monitor waveguide 85 connected to a wavelength monitor 71 and a power monitor 81 instead of an output waveguide 60.

[0112] In the light source unit 1A, the output light Lo3 is output from the second end face 10b of the laser element 10, so there is no need to provide an output waveguide 60 for outputting the light amplified by the laser element 10 and the unit circuit 30A to the outside of the package 2. Therefore, in the light source unit 1A, in the 2x2 coupler that constitutes the mirror section 50, the port on the side to which the waveguide 48 is connected is optically connected to the monitor waveguide 85. The mirror section 50 is configured to branch a portion of the light incident from the wavelength adjustment section 41 to the monitor waveguide 85, and return the remaining light to the input / output waveguide 31.

[0113] In the light source unit 1A, the same mechanism as in the light source unit 1 amplifies the light at the resonant peak wavelength inside the laser element 10. That is, when the reflected light Lr is incident on the laser element 10, the light at the resonant peak wavelength is amplified inside the laser element 10. A portion of the light amplified inside the laser element 10 is emitted again from the first end face 10a to the input / output waveguide 31, and similarly, the reflected light Lr is returned to the laser element 10, further amplifying the light at the resonant peak wavelength inside the laser element 10. In other words, the laser element 10, the input / output waveguide 31, and the optical feedback unit 40 form an external resonator. A portion of the light amplified in this way is output as output light Lo3 from the second end face 10b of the laser element 10.

[0114] A portion of the intermediate light Lmid that has passed through the mirror section 50 is output to the monitor waveguide 85 as output light Lo1. In this embodiment, the output light Lo1 passing through the monitor waveguide 85 is branched by the coupler 74 and guided to the wavelength monitor 71 and the power monitor 81. The wavelength monitor 71 is configured to measure the wavelength of the light amplified in the unit circuit 30A. The power monitor 81 is configured to measure the output of the light amplified in the unit circuit 30A by detecting a portion of the output light Lo1 that has passed through the coupler 74.

[0115] In the light source unit 1A, at least one of the plurality of laser elements 10 is configured to output output light Lo3 from a second end face 10b opposite to the first end face 10a in the resonance direction X. As an example, in the light source unit 1A, all of the plurality of laser elements 10 are configured to output output light Lo3 from a second end face 10b opposite to the first end face 10a. According to the above configuration, in the unit circuit 30A corresponding to the laser element 10 configured to output output light Lo3 from the second end face 10b, it is not necessary to provide some optical circuits (such as the output waveguide 60, etc.) required when outputting light from the optical integrated circuit element 20. Thereby, the circuit on the substrate 22 (Ge layer 25) can be simplified, and the optical integrated circuit element 20 can be miniaturized. Further, according to the above configuration, the output light Lo3 from the laser element 10 is directly output to the outside from the second end face 10b of the laser element 10 without passing through an optical circuit such as the output waveguide 60. Thereby, it is possible to suppress the optical loss caused by the output light Lo3 passing through the above optical circuit.

[0116] As shown in FIG. 14, in the light source unit 1A, the distance dL in the arrangement direction Y between two adjacent laser elements 10 among the plurality of laser elements 10 may be configured to be smaller than the length LL in the resonance direction X of each of the plurality of laser elements 10. In this case, the plurality of laser elements 10 can be arranged in a state of being close to each other. As a result, the positions where the output light Lo3 is output from each of the plurality of laser elements 10 can be made closer to each other.

[0117] Also, the distance dL in the arrangement direction Y between two adjacent laser elements 10 among the plurality of laser elements 10 may be configured to be smaller than twice the width BL1 in the arrangement direction Y of each of the plurality of laser elements 10. In this case, similar to the configuration in which the relationship of "dL < LL" described above holds, the plurality of laser elements 10 can be arranged in a state of being close to each other. As a result, the positions where the output light Lo3 is output from each of the plurality of laser elements 10 can be made closer to each other.

[0118] In this embodiment (Figure 15), the unit circuit 30A has a wavelength adjustment section 41 composed of three ring resonators, but the configuration of the wavelength adjustment section included in the unit circuit 30A is not limited to the above configuration. For example, as shown in Figure 16, the unit circuit 30A may have a wavelength adjustment section 41A instead of the wavelength adjustment section 41. The wavelength adjustment section 41A is composed of a plurality (four as an example) of Mach-Zehnder interferometers 91 to 94. As an example, a Mach-Zehnder interferometer has a configuration in which two directional couplers are arranged in series, and a thermal phase shifter is arranged along one of the two waveguides connecting the two directional couplers. In this configuration, the refractive index of a part of the waveguide constituting the Mach-Zehnder interferometer can be changed by adjusting the power supplied to each thermal phase shifter. By changing the refractive index of a part of the waveguide as described above, the phase adjustment amount (phase shift amount) of the wavelength adjustment section 41A can be controlled.

[0119] Furthermore, as shown in Figure 17, the unit circuit 30A may have a wavelength adjustment unit 41B instead of a wavelength adjustment unit 41. The wavelength adjustment unit 41B is composed of a combination of a ring resonator and a Mach-Zehnder interferometer. For example, the wavelength adjustment unit 41B is composed of three ring resonators (waveguides 42, 44, 46, 48 and ring waveguides 43, 45, 47) and one Mach-Zehnder interferometer 91. Note that in the unit circuit 30 of the first embodiment, wavelength adjustment units 41A and 41B can also be used instead of the wavelength adjustment unit 41.

[0120] Thus, the filter elements constituting the wavelength adjustment section included in the optical feedback section 40 can be arbitrarily selected. Furthermore, the types of filter elements constituting the wavelength adjustment section are not limited to the ring resonator and Mach-Zehnder interferometer described above. For example, the wavelength adjustment section may include a distributed Bragg reflector (DBR) or other configuration different from that of the ring resonator and Mach-Zehnder interferometer as filter elements. Also, the number of filter elements (stages) constituting the wavelength adjustment section may be increased or decreased depending on the required Q value. For example, by setting the number of stages of filter elements to five, a wavelength adjustment section with higher wavelength selectivity can be constructed.

[0121] Furthermore, in the light source unit 1A, the optical feedback section 40 included in the unit circuit 30A had a configuration consisting of a wavelength adjustment section (for example, wavelength adjustment section 41A or 41B) and a mirror section 50 connected in series independently of each other (a so-called series filter). However, the optical feedback section 40 is not limited to the above configuration. For example, the unit circuit 30A may have a configuration in which the wavelength adjustment section and the mirror section are integrally coupled (a so-called loop filter). Hereinafter, with reference to Figures 18 and 19, modified examples of the optical feedback section configured as a loop filter (optical feedback sections 40A, 40B) will be described.

[0122] The optical feedback section 40A shown in Figure 18 consists of a coupler 32, which is a 1x2 coupler, and a plurality of waveguides (waveguides 42a, 44a, 46a, 48a and ring waveguides 43a, 45a, 47a). The coupler 32 is optically connected to the input / output waveguide 31. Waveguide 42a is optically connected to one of the ports of the coupler 32 (the upper port in Figure 18).

[0123] Waveguide 44a is optically connected to waveguide 42a via ring waveguide 43a. Specifically, when an integer multiple of the wavelength of light passing through waveguide 42a in the direction of arrow A1 in Figure 18 is equal to the circumference of ring waveguide 43a, light passing through waveguide 44a in the direction of arrow A2 in Figure 18 is generated.

[0124] Waveguide 46a is optically connected to waveguide 44a via ring waveguide 45a. Specifically, when an integer multiple of the wavelength of light passing through waveguide 44a in the direction of arrow A2 in Figure 18 is equal to the circumference of ring waveguide 45a, light passing through waveguide 46a in the direction of arrow A3 in Figure 18 is generated.

[0125] Waveguide 48a is optically connected to waveguide 46a via ring waveguide 47a. Specifically, when an integer multiple of the wavelength of light passing through waveguide 46a in the direction of arrow A3 in Figure 18 is equal to the circumference of ring waveguide 47a, light passing through waveguide 48a in the direction of arrow A4 in Figure 18 is generated.

[0126] The end of waveguide 48a in the direction of arrow A4 is optically connected to the port of coupler 32 on the opposite side from the side to which waveguide 42a is connected. In other words, the optical feedback section 40A has a loop configuration such as "coupler 32 → waveguide 42a → ring waveguide 43a → waveguide 44a → ring waveguide 45a → waveguide 46a → ring waveguide 47a → waveguide 48a → coupler 32".

[0127] The coupler 32 is configured to split the input light Lin incident from the laser element 10 into waveguides 42a and 48a at a predetermined splitting ratio (for example, 1:1). The light split from the coupler 32 to waveguide 42a passes through the optical feedback section 40A along the directions of arrows A1 to A4 as described above, and is incident on the first end face 10a of the laser element 10 via the coupler 32. On the other hand, the light split from the coupler 32 to waveguide 48a passes through the optical feedback section 40A in the opposite direction to the light described above (i.e., "coupler 32 → waveguide 48a → ring waveguide 47a → waveguide 46a → ring waveguide 45a → waveguide 44a → ring waveguide 43a → waveguide 42a → coupler 32"), and is incident on the first end face 10a of the laser element 10 via the coupler 32. In Figure 18, the direction of light transmission is indicated by arrows B1 to B4. As an example, the coupling coefficients between each waveguide 42a, 44a, 46a, 48a and the ring waveguides 43a, 45a, 47a are approximately 0.1 to 0.2.

[0128] The optical feedback section 40A configured as described above is configured to return light of a predetermined wavelength from the input light Lin incident from the laser element 10 back to the laser element 10. In other words, the optical feedback section 40A has a configuration that combines the roles of both the wavelength adjustment section 41 and the mirror section 50 of the optical feedback section 40. A phase shifter (not shown) may be arranged along each waveguide constituting the optical feedback section 40A. In this case, the phase adjustment amount (phase shift amount) of the optical feedback section 40A can be controlled by adjusting the power supplied to the phase shifter. In this loop-type optical feedback section 40A, the light emitted from the laser element 10 passes through the wavelength adjustment section 41 only once before being returned to the laser element 10, resulting in smaller waveguide losses compared to the series-type optical feedback section 40 described above.

[0129] Alternatively, the wavelength monitor 71 and power monitor 81 may be connected to the passports of each waveguide 42a, 44a, 46a, and 48a, or each waveguide 42a, 44a, 46a, and 48a may be branched and connected to the wavelength monitor 71 and power monitor 81.

[0130] The optical feedback section 40B shown in Figure 19 has a configuration in which the ring resonator consisting of a ring waveguide 45a in the optical feedback section 40A is replaced with a Mach-Zehnder interferometer 91a. Similar to the optical feedback section 40A described above, this optical feedback section 40B also has a configuration that serves both the roles of the wavelength adjustment section 41 and the mirror section 50. In addition, in the optical feedback sections 40A and 40B, the waveguides 42a, 44a, 46a, and 48a may be partially branched to output light from the side of the optical integrated circuit element 20, similar to the first embodiment.

[0131] Furthermore, as shown in Figure 20, the output light Lo3 emitted from the second end faces 10b of the multiple laser elements 10 may be configured to be integrated by a multiplexer 62A. In the example of Figure 20, the substrate 22 further has an extended portion 22c that extends from the end opposite to the side of the extended portion 22a where each unit circuit 30 is provided. The extended portion 22c has the same configuration as the portion of the substrate 22 where each unit circuit 30A is provided. That is, in the extended portion 22c, an SiO2 layer 23, a Si layer 24, and a Ge layer 25 are stacked on the substrate 22 in this order. The optical integrated circuit element 20 has a fourth end face 20b that faces the second end face 10b of each laser element 10. The fourth end face 20b is a flat surface perpendicular to the resonance direction X. In this configuration, the second end face 10b and the fourth end face 20b face each other in the resonance direction X with the multiple laser elements 10 in between.

[0132] The optical integrated circuit element 20 includes, on the extended portion 22c described above, a plurality of output waveguides 60A corresponding to each laser element 10, a multiplexer 62A, and an output waveguide 63A. The output waveguides 60A extend from the optical input end face 60Aa at the fourth end face 20b of the optical integrated circuit element 20. The optical input end face 60Aa faces the second end face 10b of the corresponding laser element 10 in the resonance direction X. As a result, the output waveguides 60A (each optical input end face 60Aa) are optically connected to the corresponding laser element 10.

[0133] Here, as shown in Figure 20, the optical input end face 60Aa and the second end face 10b of the laser element 10 are separated by a space S1. That is, the second end face 10b and the optical input end face 60Aa are optically connected via space S1. The size of space S1 in the resonance direction X may be configured to be less than or equal to one-quarter of the shortest wavelength λ1 in a predetermined wavelength range (e.g., the range of λ1 to λ2) that can be adjusted by the optical feedback units 40, 40A, and 40B, similar to space S. This makes it possible to obtain the same effect in space S1 as in space S described above. Note that the size of space S1 in the resonance direction X is not limited to the above configuration. That is, various configurations of space S described above may be applied to space S1. Also, space S1 may not be provided. That is, the second end face 10b and the optical input end face 60Aa may be arranged to be in contact with each other.

[0134] Each output waveguide 60A is integrated into a single output waveguide 63A via a multiplexer 62A. The multiplexer 62A has a configuration similar to, for example, the multiplexer 62. As a result, the output light Lo3 emitted from each laser element 10 is integrated by the multiplexer 62A. For example, the output light Lo3 integrated by the multiplexer 62A is output as output light Lo4 to the outside of the optical integrated circuit element 20 from the fifth end face 20c (the end of the output waveguide 63A), which is the end face of the optical integrated circuit element 20 opposite to the fourth end face 20b with the multiplexer 62A in between. For example, the output light Lo4 is emitted along the resonance direction X. The direction of emission of the output light Lo4 can be arbitrarily determined according to the configuration of the output waveguide 63A (such as the position of the end of the output waveguide 63A). The lens section 5 and the output window 6 should be provided at positions corresponding to the emission direction of the output light Lo4.

[0135] The output light Lo4 is output to the outside of the optical integrated circuit element 20, then passes through the lens 5b, the output window 6, and the aperture 2b1 in that order, and is output to the outside of the package 2. In other words, the output light Lo4 is collimated by passing through the lens 5b and is output to the outside of the package 2 as output light Lo.

[0136] Furthermore, similar to the configuration shown in Figure 10, each output waveguide 60A may extend to different positions on the fifth end face 20c of the extension portion 22c without using a multiplexer 62A. In this case, the output light Lo3 from each laser element 10 will be output from different side positions of the optical integrated circuit elements 20. In such a configuration, the output portion, which is the end of each output waveguide 60A, is shown in Figure 10 Similar to the configuration shown, the optical integrated circuit elements 20 may be aggregated so that they are closer to each other than a certain distance at the fifth end face 20c.

[0137] Although several embodiments of this disclosure have been described above, this disclosure is not limited to the configurations shown in each of the embodiments described above. The materials and shapes of each configuration are not limited to the specific materials and shapes described above, but a variety of other materials and shapes can be used. Furthermore, some of the configurations included in each of the embodiments and their variations may be omitted or modified as appropriate, or can be combined in any way.

[0138] For example, in the configuration of the optical feedback unit 40A shown in Figure 18, a waveguide may be connected to the passport of waveguide 44a or 46a, and the output light may be output to the outside of the optical integrated circuit element 20 via the waveguide. Alternatively, for example, in the optical feedback unit 40 shown in Figures 15 to 17, a mirror unit 50 composed of a 1x2 coupler may be configured to reflect the intermediate light Lmid to the input / output waveguide 31. In this case, the wavelength monitor 71 and power monitor 81 can be configured to monitor the wavelength and output power of the light amplified in the unit circuit 30A, for example, via the passports of the wavelength adjustment units 41, 41A, and 41B, or via waveguides that branch the light from the various waveguides constituting the wavelength adjustment units 41, 41A, and 41B.

[0139] Furthermore, a coupler is not required in the output waveguide 60 to branch off a portion of the output light Lo1 to each monitor. In this case, for example, in the configuration shown in Figure 2, the multiple output light Lo1s are integrated by the multiplexer 62 without being branched and output as output light Lo2 to the outside of the optical integrated circuit element 20.

[0140] Furthermore, for example, in the optical integrated circuit element 20 shown in Figures 10 and 14, in multiple pairs of laser elements 10 and corresponding unit circuits 30, 30A, some pairs may be configured to output output light Lo1 from the output waveguide 60, and other pairs may be configured to output output light Lo3 from the second end face 10b of the laser element 10. In the above configuration, the output light Lo1 and Lo3 may be integrated via multiplexers 62, 62A.

[0141] Furthermore, within package 2, there may be laser elements and unit circuits with configurations different from those shown in this disclosure. For example, there may be additional laser elements on the substrate 22 that are composed of laser elements other than quantum cascade laser elements or interband cascade laser elements, or there may be laser elements whose resonance direction does not coincide with that of the multiple laser elements 10 (i.e., laser elements whose resonance direction does not coincide with the resonance direction X and which are not arranged along the array direction Y together with the multiple laser elements 10). In addition, there may be pairs of laser elements and unit circuits configured such that the size of the space S in the resonance direction X is larger than that of the configuration shown in this disclosure, or there may be pairs of laser elements and unit circuits arranged so that the first end face 10a and the optical input / output end face 31a are in contact with each other.

[0142] Furthermore, in Figure 3, the width BL2 of the active layer 122 of the laser element 10 in the array direction Y coincides with the width BW of the optical input / output end face 31a corresponding to the laser element 10 in the array direction Y, but the light source units 1,1A are not limited to such a configuration. As an example, Figure 12 As shown in Figure 31a, the width BL2 of the active layer 122 in the alignment direction Y may be configured to be smaller than the width BW of the input / output waveguide 31 in the alignment direction Y at the optical input / output end face 31a. 12In the configuration shown, the width of the input / output waveguide 31 in the alignment direction Y is the same as the width BW in the alignment direction Y at the optical input / output end face 31a throughout the entire input / output waveguide 31. In this case, since the width BW of the input / output waveguide 31 is larger than the width BL2 of the active layer 122, light can be sufficiently propagated from the laser element 10 to the input / output waveguide 31. As a result, compared to a configuration in which the width BL2 of the active layer 122 in the alignment direction Y is larger than the width BW of the input / output waveguide 31 in the alignment direction Y at the optical input / output end face 31a, the mode matching efficiency between the laser element 10 and the input / output waveguide 31 can be improved and coupling loss can be reduced.

[0143] Conversely, the width BL2 of the active layer 122 in the alignment direction Y may be configured to be larger than the width BW of the input / output waveguide 31 in the alignment direction Y at the optical input / output end face 31a. In this case, the output of the laser element 10 can be increased compared to the above configuration. As a result, the output of the output optical fiber Lo can be increased. As an example, the width BL2 of the active layer 122 in the alignment direction Y is about 1 μm to 20 μm. Also, the width BW of the input / output waveguide 31 in the alignment direction Y at the optical input / output end face 31a may be about 1 μm to 20 μm.

[0144] Furthermore, the relationship between distance dL and length LL or width BL1 described in the second embodiment can also be applied to other embodiments and modifications. For example, in the configurations shown in Figures 2, 10, and 20, the distance dL in the alignment direction Y between two adjacent laser elements 10 may be configured to be smaller than the length LL in the resonance direction X of each of the laser elements 10. Similarly, in the configurations shown in Figures 2, 10, and 20, the distance dL in the alignment direction Y between two adjacent laser elements 10 may be configured to be smaller than twice the width BL1 in the alignment direction Y of each of the laser elements 10. This allows the multiple laser elements 10 to be arranged close to each other. As a result, the light source units 1 and 1A can be miniaturized. Also, according to the above configuration, the input and output waveguides 31 corresponding to each of the multiple laser elements 10 are close to each other. Therefore, a configuration in which multiple unit circuits 30 are arranged within a relatively uniform temperature region in the optical integrated circuit element 20 (i.e., a configuration in which multiple unit circuits 30 are concentrated in a relatively narrow area) can be easily realized, and the control of the multiple unit circuits 30 becomes easier.

[0145] Furthermore, the configuration of the optical integrated circuit element 20 is not limited to the configuration described above. For example, as shown in Figure 21(a), the Ge layer 25 may be provided in a flat shape, and only the portion corresponding to the waveguide 25a may be formed in a rib shape. In this case, as an example, the thickness of the Ge layer 25 in the rib-shaped portion is about 3.0 μm, and the thickness of the Ge layer 25 other than the rib-shaped portion is about 1.0 to 1.5 μm. Also, as shown in Figure 21(b), the pair of trenches T may be formed to extend from the surface of the Ge layer 25 to the surface of the substrate 22 on the Ge layer 25 side. Also, as shown in Figure 21(c), the Ge layer 25 may be composed only of waveguides 25a. That is, the waveguide 25a may be a so-called strip-type waveguide. In this case, the thickness tW of the waveguide 25a is, for example, about 3.0 μm. Furthermore, each layer constituting the optical integrated circuit element 20 (substrate 22, SiO2 layer 23, Si layer 24, and Ge layer 25) may be made of other materials.

[0146] Furthermore, although this disclosure shows a configuration comprising multiple pairs of laser elements 10 and corresponding unit circuits 30, the light source units 1,1A are not limited to such a configuration. For example, a light source unit 1,1A may be composed of a pair of laser elements 10 and unit circuits 30. In a light source unit 1,1A configured in this way, the same effects as those obtained by the configuration can be obtained by having the pair of laser elements 10 and unit circuits 30 have configurations similar to those of each of the multiple pairs of laser elements 10 and unit circuits 30 shown in this disclosure.

[0147] As an example relating to the above, a single laser element 10 may have an active layer 122, and the size of the space S in the resonance direction X may be configured to be smaller than the thickness tW in the thickness direction Z of the input / output waveguide 31 at the optical input / output end face 31a and the thickness tL in the thickness direction Z of the active layer 122. In this case, the distance between the first end face 10a of the laser element 10 and the optical input / output end face 31a can be reduced with respect to the thickness tL of the active layer 122 and the thickness tW of the input / output waveguide 31. As a result, the distance between the first end face 10a of the laser element 10 and the optical input / output end face 31a becomes a suitable size (i.e., a size that can suitably suppress the reduction in the amount of light incident from the laser element 10 to the optical input / output end face 31a, so as to be suitable), thus suitably suppressing the loss of light in space S.

[0148] Furthermore, when performing spectroscopic analysis using the light source units 1,1A of this disclosure, if there is only one type of object to be analyzed, the wavelength of the output light emitted from the light source units 1,1A (i.e., the wavelengths emitted by the multiple laser elements 10 included in the light source units 1,1A) may be fixed to a specific wavelength.

[0149] Furthermore, in this disclosure, the laser element 10 is composed of a quantum cascade laser element or an interband cascade laser element (a laser element that outputs light in the mid-infrared region), but the type of laser element 10 is not limited to the above. For example, the laser element 10 may be a laser element that outputs light in the near-infrared region. Even when a laser element that outputs light in the near-infrared region is used as the laser element 10, the same effects as the light source units 1 and 1A described above can be obtained. In addition, when outputting light in the near-infrared region, it is possible to adopt a waveguide structure other than the waveguide structure described above (Figures 4 and 21, etc.), thereby improving the design freedom of the optical integrated circuit element 20. [Explanation of symbols]

[0150] 1,1A...light source unit, 2...package, 3...cooling element, 5...lens section, 10...laser element, 10a...first end face, 10b...second end face, 11...substrate (first substrate), 12...semiconductor laminate, 20...optical integrated circuit element, 22...substrate (second substrate), 22a...extension section, 20a...third end face, 20a1...first section, 20a2...second section, 20a3...third section, 20a4...fourth section, 30,30A...unit circuit, 31...input / output waveguide, 31a...optical input / output end face, 40,40A,40B...optical feedback section, 122...active layer, BL2,BP,BW...width, HP...height, Lo,Lo1,Lo2,Lo3,Lo4...output light, S...space, tL,tW...thickness, λ1...shortest wavelength.

Claims

1. A laser element comprising a first substrate and a quantum cascade laser element or interband cascade laser element having a semiconductor laminate formed on the first substrate and including at least an active layer, The system comprises a second substrate and an optical integrated circuit element having a unit circuit provided on the second substrate, The laser element has a first end face and a second end face that face each other in the resonance direction of the laser element. The aforementioned unit circuit is The first end face of the laser element and the optical input / output end face facing each other across space, An input / output waveguide extending from the aforementioned optical input / output end face, The system includes an optical feedback unit that is optically connected to the input / output waveguide and configured to guide light of a predetermined wavelength incident from the first end face of the laser element and return the light of the predetermined wavelength to the laser element, thereby changing the wavelength of the output light within a predetermined wavelength range. A light source unit in which the size of the space in the resonance direction is smaller than the thickness of the active layer in the stacking direction of the semiconductor laminate and the thickness of the input / output waveguide at the optical input / output end face in the thickness direction of the second substrate.

2. The light source unit according to claim 1, wherein the size of the space in the resonance direction is 1 μm or less.

3. The light source unit according to claim 1, wherein the size of the space in the resonance direction is one-quarter or less of the shortest wavelength in the predetermined wavelength range.

4. Having a plurality of the aforementioned laser elements, Each of the plurality of laser elements has a plurality of unit circuits provided in correspondence with each of the plurality of laser elements, The light source unit according to claim 1, wherein the plurality of unit circuits are arranged along an array direction perpendicular to the resonance direction and the thickness direction.

5. The light source unit according to claim 4, wherein at least one of the plurality of laser elements outputs the output light from the second end face.

6. The second substrate has an extended portion that extends in the resonance direction toward the side where the laser element is provided, rather than toward the optical input / output end face. The light source unit according to claim 1, wherein the laser element is mounted on the extended portion.

7. The optical integrated circuit element has a third end face that faces the first end face and includes the optical input / output end face, The light source unit according to claim 1, wherein, when viewed from an array direction perpendicular to the resonance direction and the thickness direction, the third end face has a first portion on which the optical input / output end face is provided, and a second portion that is further away from the first end face than the first portion in the resonance direction.

8. The optical integrated circuit element has a third end face that faces the first end face and includes the optical input / output end face. The light source unit according to claim 1, wherein, when viewed from the thickness direction, the third end face has a third portion on which the optical input / output end face is provided, and a fourth portion that is further from the first end face than the third portion in the resonance direction.

9. The light source unit according to claim 1, wherein the width of the active layer in the alignment direction perpendicular to the resonance direction and the thickness direction is greater than the width of the input / output waveguide in the alignment direction at the optical input / output end face.

10. The light source unit according to claim 1, wherein the width of the active layer in the arrangement direction perpendicular to the resonance direction and the thickness direction is smaller than the width of the input / output waveguide in the arrangement direction at the optical input / output end face.

11. The light source unit according to claim 1, further comprising a cooling element on which the laser element and the optical integrated circuit element are mounted.

12. The lens portion that transmits the output light, The light source unit according to claim 1, further comprising a package that houses the laser element and the optical integrated circuit element and also houses or holds the lens portion.

13. The light source unit according to claim 12, wherein the width of the package in the arrangement direction perpendicular to the resonance direction and the thickness direction is greater than the height of the package in the thickness direction.

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