Optical joint structure and gas detection device

Abstract

To provide an optical bonding structure capable of optically bonding optical members used for mid-infrared light, and a gas detector.SOLUTION: An optical bonding structure (10) includes: a first optical member (11) through which mid-infrared light having a wavelength λ transmits; a second optical member (12) through which the mid-infrared light having a wavelength λ transmits; and a bonding layer (13) capable of bonding the first optical member (11) to the second optical member (12) and through which the mid-infrared light having a wavelength λ transmits. The bonding layer (13) is formed of the mixture of a resin (14) and high refraction particles (15) having a refractive index np, and the size of the high refraction particle (15) is λ / (2np) or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an optical joining structure and a gas detection device. [Background technology]

[0002] Optical bonding structures are used in fields such as optical communications. For example, Patent Document 1 discloses an optical bonding structure that optically bonds an optical element and an optical fiber without the use of air. In recent years, with the development of semiconductor devices in the mid-infrared region, optical bonding technology using mid-infrared light is required to expand optical functions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-48628 Summary of the Invention [Problem to be solved by the invention]

[0004] Compared to visible light semiconductor devices, mid-infrared semiconductor devices have the characteristic that it is difficult to radiate light into space due to the large difference in refractive index between the materials used in the devices and air. Because of this characteristic, when optical components that expand optical functions, such as lenses, optical filters, and optical fibers, are incorporated into an optical system, if they are optically coupled to a mid-infrared semiconductor device via air, there is a problem that large reflection losses occur between the air and the mid-infrared semiconductor device.

[0005] In view of the above circumstances, an object of the present disclosure is to provide an optically joined structure and a gas detection device that can optically join optical members used for mid-infrared light. [Means for solving the problem]

[0006] An optical bonding structure according to an embodiment of the present disclosure includes: a first optical member through which mid-infrared light of wavelength λ passes; a second optical member through which mid-infrared light having the wavelength λ passes; a bonding layer that bonds the first optical member and the second optical member and transmits mid-infrared light of the wavelength λ, The bonding layer is made of a resin and a material having a refractive index n p and a mixture of highly refractive particles of The size of the highly refractive particles is λ / (2n p ) is as follows.

[0007] A gas detection device according to an embodiment of the present disclosure includes: a light emitting unit that emits mid-infrared light of the wavelength λ; a light receiving unit having sensitivity to mid-infrared light of wavelength λ; a light guide section that guides the mid-infrared light of the wavelength λ from the light emitting section to the light receiving section; The optical bonding structure described above, The optical connection structure is included in at least one of the light emitting section, the light receiving section, and the light guiding section. [Effects of the Invention]

[0008] According to the embodiments of the present disclosure, it is possible to provide an optically joined structure and a gas detection device that can optically join optical members used for mid-infrared light. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of an optical connection structure according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a perspective view of a gas detection device according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a diagram illustrating the transmittance of a highly refractive particle that is Si. [Figure 4] FIG. 4 is a diagram illustrating the relationship between the volume fraction and transmittance of highly refractive particles made of Si. [Figure 5] FIG. 5 is a diagram illustrating the relationship between the thickness and transmittance of the bonding layer. [Figure 6] FIG. 6 is a diagram illustrating the relationship between the thickness and transmittance of the bonding layer. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following description of the drawings, identical or similar parts are designated by identical or similar reference numerals. However, the drawings are schematic. For example, the relationship between thickness and width may differ from the actual relationship. Furthermore, the embodiments shown below are intended to exemplify devices embodying the technical ideas of the present disclosure, and the materials, shapes, structures, arrangements, etc. of the components are not limited to those described below, and various modifications may be made within the technical scope defined by the claims.

[0011] <Optical bonded structure> Fig. 1 is a schematic diagram of an optical bonded structure 10 according to this embodiment. The optical bonded structure 10 includes a first optical member 11, a second optical member 12, and a bonding layer 13. The detailed principle will be described later, but with the configuration shown in Fig. 1, the optical bonded structure 10 makes it possible to optically bond optical members used for mid-infrared light. The optical bonded structure 10 is incorporated into an optical system for use.

[0012] Here, infrared light in the short wavelength to medium and long wavelength infrared region (referred to as the mid-infrared region) with wavelengths of about 2 to 15 μm in particular exhibits a specific absorption band for gas molecules, and is therefore used, for example, in non-dispersive infrared absorption gas concentration measuring devices. Mid-infrared light refers to infrared light in the mid-infrared region, i.e., infrared light with a wavelength of 2 to 15 μm.

[0013] <Optical components> The first optical member 11 and the second optical member 12 are optical components that transmit mid-infrared light, and are composed of optical members that transmit mid-infrared light. Here, transmission means that 50% or more of the light energy passes through to the back of the object when light is perpendicularly incident on the object.

[0014] In this embodiment, the first optical member 11 is a part of a mid-infrared light emitting diode (LED). As another example, the first optical member 11 may be a light receiving element, a laser diode, an optical fiber, an optical filter, or a diffraction grating.

[0015] In this embodiment, the second optical member 12 is a lens. As another example, the second optical member 12 may be a light emitting / receiving element, a laser diode, an optical fiber, an optical filter, or a diffraction grating.

[0016] The first optical member 11 and the second optical member 12 are composed of a material that transmits mid-infrared light. In this embodiment, the first optical member 11 is an LED and is composed of GaAs. In this embodiment, the second optical member 12 is a lens and is composed of Si. As another example, the material of the first optical member 11 and the second optical member 12 may be Ge, InP, InAs, ZnSe, or the like that transmits mid-infrared light. Furthermore, the material of the first optical member 11 and the second optical member 12 may be fluorite, a dielectric, or the like. It is desirable that the material of the first optical member 11 and the second optical member 12 has a high refractive index in the mid-infrared range to prevent mid-infrared light from leaking out and causing loss. As an example, the refractive index of the first optical member 11 and the second optical member 12 is 2.5 or more.

[0017] The first optical member 11 and the second optical member 12 may have uneven surfaces. The surfaces of the first optical member 11 and the second optical member 12 that come into contact with the bonding layer 13 are most preferably flat from the viewpoint of preventing a decrease in the amount of transmitted light due to diffuse reflection, but may have unevenness that is half or less the thickness of the bonding layer 13. The unevenness of the surfaces of the first optical member 11 and the second optical member 12 that come into contact with the bonding layer 13 is preferably, for example, 1 / 10 or less the thickness of the bonding layer 13.

[0018] <Joining layer> The bonding layer 13 is present between the first optical member 11 and the second optical member 12, and physically bonds the first optical member 11 and the second optical member 12, while also transmitting mid-infrared light to achieve optical bonding. The thickness of the bonding layer 13 is, for example, 2 μm. The bonding layer 13 is made of a mixture of a resin 14 and high-refractive-index particles 15 for improving the refractive index. The high-refractive-index particles 15 are fine particles with a higher refractive index than the resin 14.

[0019] In this embodiment, the resin 14 of the bonding layer 13 is an acrylic resin. However, the material of the resin 14 of the bonding layer 13 is not limited to an acrylic resin as long as it can bond the first optical member 11 and the second optical member 12. The material of the resin 14 of the bonding layer 13 can be, for example, an epoxy resin, a silicone resin, a urethane resin, or the like that is commonly used as an adhesive.

[0020] In this embodiment, the high refractive index particles 15 contained in the bonding layer 13 are Si. FIG. 3 is a diagram illustrating the transmittance of the high refractive index particles 15 made of Si. As shown in FIG. 3, the high refractive index particles 15 made of Si are opaque to visible light (having a wavelength of approximately 380 nm to 780 nm), but are transparent in the infrared region. As another example, the material of the high refractive index particles 15 may be Ge, GaAs, InP, InAs, ZnSe, etc. Furthermore, the material of the high refractive index particles 15 may be fluorite, a dielectric, etc. Here, from the viewpoint of preventing light from being lost due to surface reflection on large particles, the size of the high refractive index particles 15 is determined so that the high refractive index particles 15 have a refractive index n p When the wavelength of the transmitted mid-infrared light is 1 / (2n p ) is set to be:

[0021] Here, the size of the highly refractive particles 15 may be determined using a statistical method. For example, the median value in the distribution of the equivalent circle diameters of the highly refractive particles 15 may be the size of the highly refractive particles 15. Furthermore, since the presence of large particles causes loss due to reflection, it is preferable that the bottom 90% of the cumulative frequency distribution in the distribution of the equivalent circle diameters of the highly refractive particles 15 be equal to or less than the wavelength λ of light. The size of the highly refractive particles 15 can be obtained by cross-sectional image analysis of the bonding layer 13. For example, the boundary between the highly refractive particles 15 and the resin 14 can be identified by brightness analysis of a cross-sectional SEM image or a cross-sectional TEM image, and the equivalent circle diameter (1.128 times the square root of the area) of each individual region surrounded by the boundary can be determined as the size of each highly refractive particle 15. Furthermore, the refractive index of the highly refractive particles 15 and the resin 14 can be determined by, for example, estimating the components through component analysis and using literature values ​​for the corresponding components.

[0022] It is desirable to surface-modify the highly refractive particles 15 in order to improve the mixing property between the resin material and the highly refractive particles 15. There are no limitations on the modifier and method used for the surface modification.

[0023] The bonding layer 13 may be formed by applying a mixture of resin 14 and highly refractive particles 15 to the first optical member 11 and pressing the applied surface against the second optical member 12. From the viewpoint of mass productivity, a mounting device used in semiconductor manufacturing may be used.

[0024] <Gas detection device> 2 is a perspective view of gas detection device 1 according to an embodiment of the present disclosure. Gas detection device 1 is a small device measuring, for example, 30 mm × 20 mm × 10 mm, and is sometimes referred to as a gas sensor. In this embodiment, gas detection device 1 is an NDIR (Non Dispersive Infrared) type device that measures the concentration of a gas to be detected based on infrared light that passes through an introduced gas.

[0025] Gas detection device 1 includes a substrate 2, a light-emitting unit 3, a light-receiving unit 4, and a light-guiding member 5. In FIG. 2, a configuration example of gas detection device 1 is shown with part of light-guiding member 5 made transparent, so that light-emitting unit 3 and light-receiving unit 4 provided on main surface 20 of substrate 2 are visible. In FIG. 2, an orthogonal coordinate system is set so that the xy plane is parallel to main surface 20 of substrate 2. The z-axis direction is perpendicular to main surface 20 of substrate 2.

[0026] Substrate 2 is a plate-like member on which components of gas detection device 1 are mounted and which electrically connects the mounted electronic components. Substrate 2 has light-emitting section 3 and light-receiving section 4 provided on main surface 20. Substrate 2 may also have other electronic components mounted thereon. For example, substrate 2 may have a controller for controlling at least one of light-emitting section 3 and light-receiving section 4 provided on main surface 20 or on the bottom surface, which is the surface opposite to main surface 20.

[0027] The light-emitting unit 3 is a component that emits light used to detect the gas to be detected. There are no particular limitations on the light-emitting unit 3 as long as it outputs light that includes wavelengths that are absorbed by the gas to be detected. In this embodiment, the light emitted by the light-emitting unit 3 is mid-infrared light. In this embodiment, the light-emitting unit 3 is an LED, but as another example, it may be an incoherent light source such as an organic light-emitting unit or a MEMS (Micro Electro Mechanical Systems) heater.

[0028] The light-emitting unit 3 has a rectangular light-emitting surface 31. The light-emitting unit 3 is a surface light source that emits light from the entire light-emitting surface 31. As shown in FIG. 2 , the light-emitting unit 3 emits light from the light-emitting surface 31 in the z-axis direction, i.e., in the thickness direction of the substrate 2.

[0029] The light receiving unit 4 is a component that receives light that has passed through the introduced gas. There are no particular limitations on the light receiving unit 4 as long as it is sensitive to a band of light that includes wavelengths absorbed by the gas to be detected. In this embodiment, the light receiving unit 4 is sensitive to mid-infrared light and receives light that includes mid-infrared light. In this embodiment, the light receiving unit 4 is a photodiode, but other examples include a phototransistor, a thermopile, a pyroelectric sensor, and a bolometer. The light receiving unit 4 converts the received light into an electrical signal and outputs the converted electrical signal. The concentration of the gas to be detected is calculated based on the electrical signal. The light receiving unit 4 is located opposite a fifth mirror 513 (described later) in the z-axis direction.

[0030] The light receiving section 4 has a rectangular light receiving surface 41. As shown in Fig. 2, the light receiving section 4 receives light in the z-axis direction, that is, the thickness direction of the substrate 2, at the light receiving surface 41.

[0031] The light-guiding member 5 is a member that guides the light emitted by the light-emitting unit 3 to the light-receiving unit 4. The light-guiding member 5 includes optical members and forms an optical path from the light-emitting unit 3 to the light-receiving unit 4. Here, the optical members are, for example, mirrors and lenses.

[0032] In this embodiment, the light-guiding member 5 includes a first reflecting portion 51 and a second reflecting portion 52. The first reflecting portion 51 includes, as optical members, a first mirror 511, a third mirror 512, and a fifth mirror 513. The first reflecting portion 51 directly reflects light emitted from the light-emitting portion 3 and light received by the light-receiving portion 4. The second reflecting portion 52 includes, as optical members, a second mirror 521 and a fourth mirror 522. The second reflecting portion 52 reflects light between itself and the first reflecting portion 51. The light-guiding member 5 reflects the light emitted by the light-emitting portion 3 off the first mirror 511, the second mirror 521, the third mirror 512, the fourth mirror 522, and the fifth mirror 513 in this order, and guides the light to the light-receiving portion 4. The optical path is configured to pass through a cell 54 into which a gas is introduced, which is provided between the light-guiding member 5 and the substrate 2. The number of mirrors provided in the light-guiding member 5 is not limited to five, and may be one or more. The light-guiding member 5 may also be configured to include a lens in part of the optical path.

[0033] The materials constituting the first mirror 511, the second mirror 521, the third mirror 512, the fourth mirror 522, and the fifth mirror 513 may be, but are not limited to, metal, glass, ceramics, stainless steel, etc. From the viewpoint of improving detection sensitivity, it is preferable that the materials constituting these mirrors be made of a material with a small light absorption coefficient and high reflectance.

[0034] Here, the light-emitting unit 3 may further include a lens. In this case, the gas detector 1 is configured to include an optically bonded structure 10 in which the first optical member 11 is an LED and the second optical member 12 is a lens. Furthermore, the light-receiving unit 4 may further include an optical filter having a wavelength selection function. In this case, the gas detector 1 is configured to include an optically bonded structure 10 in which the first optical member 11 is an optical filter and the second optical member 12 is a photodiode. As another example, when a light-guiding unit that guides mid-infrared light from the light-emitting unit 3 to the light-receiving unit 4 is configured to include an optical fiber or the like, the optically bonded structure 10 may be included in the light-guiding unit. Furthermore, the optically bonded structure 10 may be provided between the light-guiding unit and the light-emitting unit 3 or the light-receiving unit 4. In other words, the gas detector 1 may be configured to include the optically bonded structure 10 in at least one of the light-emitting unit 3, the light-receiving unit 4, and the light-guiding unit. Furthermore, the number of optically bonded structures 10 included in the gas detector 1 is not limited and may be one or more.

[0035] <Principle> The principle by which the optical bonded structure 10 according to this embodiment transmits mid-infrared light will be described below. Conventional bonding, such as that shown in Patent Document 1, is intended for visible light and near-infrared light (for example, wavelengths of 0.85 μm or 1.3 μm), and optical bonding for mid-infrared light is difficult.

[0036] In the optical bonding structure of this embodiment, the bonding layer 13 contains fine particles such as Si, which has a high refractive index even in the mid-infrared range, and therefore has a high refractive index. The difference in refractive index between the first optical member 11 and the bonding layer 13 and the difference in refractive index between the second optical member 12 and the bonding layer 13 are small, and reflection of mid-infrared light is reduced, resulting in good optical bonding.

[0037] The higher the refractive index of the high-refractive-index particles 15, the more the overall refractive index of the bonding layer 13 can be sufficiently increased even when the concentration (ratio) of the particles mixed with the resin 14 is low, and the presence of a large amount of resin 14 can increase the adhesive strength. The high-refractive-index particles 15 preferably have a refractive index of 2.5 or higher. For example, Si, GaAs, Ge, InP, InAs, and ZnSe have high refractive indices and are relatively easily available, making them preferable materials for the high-refractive-index particles 15. Si is particularly preferable because it is less susceptible to denaturation due to humidity and is inexpensive. When the refractive index of the bonding layer 13 is the same as that of the first optical member 11 or the second optical member 12, mid-infrared light can be transmitted without reflection, so it is more preferable that the bonding layer 13 contain the same material as the first optical member 11 or the second optical member 12.

[0038] As described above, from the viewpoint of increasing adhesive strength, the higher the refractive index of the high refractive index particles 15, the more preferable. However, since mid-infrared light penetrates the high refractive index particles 15 as evanescent light, the higher the refractive index, the more difficult it becomes for mid-infrared light to penetrate the high refractive index particles 15. Therefore, it is necessary to make the size of the high refractive index particles 15 sufficiently small. Quantitatively speaking, the refractive index of the resin 14 of the bonding layer 13 is set to n r , the refractive index of the high refractive index particles 15 is n p , where λ is the wavelength of mid-infrared light, the penetration characteristic length of mid-infrared light into a material (L p ) is given by the following equation (1): where the penetration characteristic length (L p ) is three times the evanescent length, which is the length at which the penetration attenuation is approximately 5%. p ) can be a threshold value indicating whether light penetrates inside. However, the refractive index n r is the refractive index n of the highly refractive particles 15 p is assumed to be sufficiently low.

[0039]

number

[0040] The size of the highly refractive particles 15 is λ / (2n p ) or less, the mid-infrared light that has entered the high refractive index particles 15 also exits the high refractive index particles 15, and the mid-infrared light propagates through the high refractive index particles 15 while passing through the bonding layer 13. The bonding layer 13 can behave as if it has a higher overall refractive index than the case of only the resin 14, without the mid-infrared light being randomly scattered by the high refractive index particles 15.

[0041] Here, the size is the above L p When the following high refractive index particles 15 are dispersed in the bonding layer 13, if the volume ratio of the high refractive index particles 15 in the bonding layer 13 is c (that is, if the volume ratio of the resin 14 is 1-c), the refractive index n of the bonding layer 13 is A is given by the following equation (2):

[0042]

number

[0043] The higher the volume fraction (c) of the high refractive index particles 15, the higher the refractive index n A This increases the transmittance from the first optical member 11 to the second optical member 12, thereby improving the transmittance from the first optical member 11 to the second optical member 12. FIG. 4 is a diagram illustrating the relationship between the volume fraction of the high refractive index particles 15 made of Si and the transmittance. The volume fraction on the horizontal axis of FIG. 4 corresponds to the volume ratio (c). From the results of FIG. 4, it is preferable that the volume of the high refractive index particles 15 contained in the bonding layer 13 is 10% or more of the volume of the bonding layer 13. Here, the simulation of FIG. 4 was performed assuming that the thickness of the bonding layer 13 is 2 μm, the wavelength of the mid-infrared light is 4.26 μm, the refractive index of the resin 14 is 1.4, and the refractive index of the high refractive index particles 15 is 3.3.

[0044] Furthermore, the thickness of the bonding layer 13 is related to the transmittance from the first optical member 11 to the second optical member 12. When the thickness of the bonding layer 13 is d, the transmittance T from the first optical member 11 to the second optical member 12 can be expressed by the following formula (3):

[0045]

number

[0046] Here, if the thickness d of the bonding layer 13 is sufficiently thin, the transmittance T is approximated by the following equation (4).

[0047]

number

[0048] From the formula (4), the thickness d of the bonding layer 13 is calculated as the film thickness characteristic length L A The transmittance T is high when:

[0049]

number

[0050] Here, the transmittance T reaches its maximum value when n2 = n1. In other words, the transmittance T reaches its maximum value when the first optical member 11 and the second optical member 12 have the same refractive index. The first optical member 11 and the second optical member 12 have the same refractive index when, for example, they are made of the same material.

[0051] However, even if they are not made of the same material, the refractive indices of the first optical member 11 and the second optical member 12 may be sufficiently close that they can be treated as the same. For example, the refractive indices of Si, GaAs, Ge, InP, InAs, and ZnSe are similar to each other, and when the materials of the first optical member 11 and the second optical member 12 are selected from these, they can be treated as having the same refractive index. Transforming equation (5) with n1 = n2 = n yields the following equation (6). Here, the approximation equation of equation (7) is used in the transformation.

[0052]

number

[0053] From the second term of equation (6), by setting the thickness d of the bonding layer 13 to one-tenth of the wavelength λ / n in the material, that is, λ / (10n) or less, the mid-infrared light tunnels through the bonding layer 13 like evanescent light and propagates from the first optical member 11 to the second optical member 12, and therefore the transmittance T can be increased. Also, from at least the first term of equation (6), by setting the thickness d of the bonding layer 13 to λ / (π(nn A )) or less, the transmittance T can be increased for the same reason. Here, if n1 and n2 are different, the average refractive index of them is set to n, and L can be calculated using equation (6). A can be evaluated.

[0054] FIG. 5 is a diagram illustrating the relationship between the thickness d of the bonding layer and the transmittance. The horizontal axis of FIG. 5 is the normalized thickness, d / (λ / (π(nn A ))) is used. In other words, the part of the horizontal axis of FIG. 5 that is less than 1 indicates that the thickness d of the bonding layer 13 is λ / (π(nn A As shown in FIG. 5, the thickness d of the bonding layer 13 is set to λ / (π(nn A )) or less, the transmittance T can be increased. FIG. 6 is a diagram showing another example of the relationship between the thickness d of the bonding layer and transmittance. The horizontal axis of FIG. 6 uses d / (λ / (10n)) as the normalized thickness. In other words, the portion of the horizontal axis of FIG. 6 that is 1 or less corresponds to the thickness d of the bonding layer 13 being λ / (10n) or less. As shown in FIG. 6, by setting the thickness d of the bonding layer 13 to λ / (10n) or less, the transmittance T can be increased and most of the mid-infrared light can be transmitted. Here, the simulations of FIGS. 5 and 6 were performed assuming that the wavelength of the mid-infrared light is 4.26 μm, the refractive index of the resin 14 is 1.4, and the refractive index of the high refractive index particles 15 is 3.3.

[0055] Here, since the optical coupling effect is most pronounced at the thinnest portion, the thickness d may be defined as the shortest portion of the distance between the first optical member 11 and the second optical member 12.

[0056] The optically bonded structure and gas detector according to this embodiment, configured as described above, can optically bond optical components used for mid-infrared light. Here, as described with reference to FIG. 3, the high refractive index particles 15 are opaque to visible light, so the bonding layer 13 has a filter function that transmits mid-infrared light but not visible light, without requiring any additional components. Therefore, the optically bonded structure and gas detector according to this embodiment are particularly suitable for optical systems that handle mid-infrared light.

[0057] Although the embodiments have been described above based on the drawings and examples, it should be noted that those skilled in the art would easily be able to make various modifications and alterations based on the present disclosure. Therefore, it should be noted that these modifications and alterations are included within the scope of the present disclosure. For example, the functions included in each component, each means, etc. can be rearranged so as not to be logically inconsistent, and multiple means, etc. can be combined or divided into one.

[0058] <Other embodiments> In the above embodiment, the first optical member 11 and the second optical member 12 are mechanically bonded by a single bonding layer 13. However, the present embodiment achieves the same effect even if the location where the first optical member 11 and the second optical member 12 are mechanically bonded and the location where they are optically bonded are separated. That is, the bonding layer 13 may include a region that does not contain high refractive index particles 15, a region that contains a small amount of high refractive index particles 15, or a region that uses a different resin 14 to form the bonding layer 13. In this way, the decrease in adhesive strength that occurs when a large amount of high refractive index particles 15 is contained can be compensated for by the adhesive strength of the region that contains a different amount of high refractive index particles 15, and optical connection can be ensured in the region that contains a large amount of high refractive index particles 15. [Explanation of symbols]

[0059] 1 Gas detection device 2 boards 3 Light-emitting element 4 Photodetector 5 Light guide member 10 optical junction structure, 11 First optical member 12 Second optical member 13 Bonding layer 14 Resin 15 High refractive index particles 20 Main Surface 31 Light-emitting surface 41 Photosensitive surface 51 First reflector 52 Second reflector 511 First Mirror 512 Third Mirror 513 Fifth Mirror 521 Second Mirror 522 Fourth Mirror

Claims

1. a first optical member through which mid-infrared light of wavelength λ passes; a second optical member through which mid-infrared light having the wavelength λ passes; a bonding layer that bonds the first optical member and the second optical member and transmits mid-infrared light of the wavelength λ, The bonding layer is made of a resin and a refractive index n ｐ and a mixture of highly refractive particles of The size of the highly refractive particles is λ / (2n ｐ ) or less, When the average refractive index of the first optical member and the second optical member is n and the refractive index of the bonding layer is n A , the thickness of the bonding layer is λ / (π(nn A )) or less.

2. The optical bonded structure according to claim 1 , wherein the first optical member and the second optical member have a refractive index of 2.5 or more.

3. 2. The optical bonded structure according to claim 1, wherein the first optical member and the second optical member contain at least one of GaAs, Si, Ge, InP, InAs, and ZnSe.

4. The optical bonded structure according to claim 1 , wherein the highly refractive particles have a refractive index of 2.5 or more.

5. The optical bonded structure according to claim 1 , wherein the highly refractive particles include at least one of GaAs, Si, Ge, InP, InAs, and ZnSe.

6. The optical bonded structure according to claim 1 , wherein the high refractive index particles contained in the bonding layer occupy 10% or more of a volume of the bonding layer.

7. An optical bonding structure described in any one of claims 1 to 6, wherein the surfaces of the first optical element and the second optical element that contact the bonding layer have unevenness that is 1 / 10 or less of the thickness of the bonding layer.

8. The optical bonded structure according to claim 1 , wherein the thickness of the bonding layer is λ / (10n) or less.

9. The optical bonding structure according to claim 1 , wherein the bonding layer includes at least one of regions having different contents of the high refractive index particles and regions having different resins.

10. a light emitting unit that emits mid-infrared light of the wavelength λ; a light receiving unit having sensitivity to mid-infrared light of wavelength λ; a light guide section that guides the mid-infrared light of the wavelength λ from the light emitting section to the light receiving section; The optical bonded structure according to any one of claims 1 to 9, The gas detection device, wherein the optical connection structure is included in at least one of the light emitting section, the light receiving section, and the light guiding section.

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