Gas sensor

Abstract

To provide a gas sensor capable of reducing the size of a filter and facilitating an optical path design.SOLUTION: The gas sensor includes a light source (20) which has an active layer, a first sensor part (32) which is arranged so that light emitted from the light source is made incident and detects the state of a space, a second sensor part (31) which is arranged so that the light emitted from the light source is made incident and used for the compensation of the temperature change or secular change of the first sensor part, a first wavelength restriction body which restricts the wavelength of the light emitted from the active layer and reaching the first sensor part and the second sensor part and is connected to the light source not through the space, and a second wavelength restriction body which restricts the wavelength of the light emitted from the active layer and reaching the second sensor part and is connected to the second sensor part not through the space.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to gas sensors. [Background technology]

[0002] Light sources are used in many applications, such as indoor or indoor lighting applications and optical devices. Optical devices use light sources that emit light of a specific wavelength, and include, for example, sterilization devices that use ultraviolet light and distance measuring devices that use reflected light. Also, light receiving and emitting devices that combine a light source with a light receiving unit (sensor) to detect the spatial state between the light source and the light receiving unit are known. The light receiving and emitting device is, for example, a gas sensor that uses infrared light, and detects the concentration of a gas to be detected in a gas introduced into a space as the detection of the spatial state. Further improvement in the accuracy of gas sensors is required. For example, Patent Document 1 discloses a gas concentration detection device of the NDIR (Non-Dispersive Infrared) type that is configured to be calibrated taking into account fluctuations in output characteristics. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 021495 Summary of the Invention [Problem to be solved by the invention]

[0004] Here, the gas concentration detection device (gas sensor) of Patent Document 1 is provided with a first bandpass filter and a second bandpass filter used for calibration. In recent years, there has been a demand for further miniaturization of gas sensors. With the technology of Patent Document 1, simply miniaturizing the filters would change the optical path design, which could make it difficult. In addition, problems of filter interference and light loss would arise.

[0005] In view of the above circumstances, an object of the present disclosure is to provide a gas sensor that allows the filter size to be reduced and the optical path to be easily designed. [Means for solving the problem]

[0006] (1) A gas sensor according to an embodiment of the present disclosure includes: a light source having an active layer; A first sensor unit that is disposed so that light emitted from the light source is incident thereon and detects a state of a space; a second sensor unit disposed so that light emitted from the light source is incident thereon and used to compensate for temperature changes or changes over time of the first sensor unit; a first wavelength limiting body that limits a wavelength of light emitted from the active layer and reaching the first sensor unit and the second sensor unit and is connected to the light source without passing through the space; a second wavelength limiting body that limits the wavelength of light that leaves the active layer and reaches the second sensor unit and is connected to the second sensor unit without passing through the space.

[0007] (2) As an embodiment of the present disclosure, in (1), The optical fiber further includes a third wavelength limiting body that limits the wavelength of light emitted from the active layer and reaches the first sensor unit and is connected to the first sensor unit without the space therebetween.

[0008] (3) As an embodiment of the present disclosure, in (1), The first wavelength limiting body is configured by laminating materials having different refractive indices, and is a part of the light source or a substrate on which the light source is provided.

[0009] (4) As an embodiment of the present disclosure, in (1), The second wavelength limiting body is configured by laminating materials having different refractive indices, and is a part of the second sensor unit or a substrate on which the second sensor unit is provided.

[0010] (5) As an embodiment of the present disclosure, in (2), The third wavelength limiting body is configured by laminating materials having different refractive indices, and is a part of the first sensor unit or a substrate on which the first sensor unit is provided.

[0011] (6) As an embodiment of the present disclosure, in (2), (4), or (5), the light source has a peak wavelength λp at which the light intensity is maximized; The first wavelength limiting body has a maximum transmittance of 5% or less in a wavelength range from (λp×0.6) nm to (λp×0.8) nm.

[0012] (7) As an embodiment of the present disclosure, in (1), The first wavelength limiting body does not transmit light of some wavelengths, and is a part of the light source or a substrate on which the light source is provided.

[0013] (8) As an embodiment of the present disclosure, in (1), The second wavelength limiting body does not transmit light of some wavelengths, and is a part of the second sensor unit or a substrate on which the second sensor unit is provided.

[0014] (9) As an embodiment of the present disclosure, in (2), The third wavelength limiting body does not transmit light of some wavelengths, and is a part of the first sensor unit or a substrate on which the first sensor unit is provided.

[0015] (10) As an embodiment of the present disclosure, in any one of (1) to (5), The first wavelength limiting body is provided on an optical path of light that leaves the active layer and reaches the second sensor unit until the light reaches a substrate on which the light source is provided.

[0016] (11) As an embodiment of the present disclosure, in any one of (1) to (5), The second wavelength limiting body is provided on an optical path of light emitted from the active layer and reaching the second sensor unit, reaching a substrate on which the second sensor unit is provided, and being incident on the second sensor unit.

[0017] (12) As an embodiment of the present disclosure, in (10), The wavelength limiting body has a reflective structure that reflects light of a specific wavelength.

[0018] (13) As an embodiment of the present disclosure, in (1), A fourth wavelength limiting body is provided which limits the wavelength of light emitted from the active layer and reaching the first sensor portion, and which is connected to the surface of the substrate on which the light source is provided without the space therebetween.

[0019] (14) As an embodiment of the present disclosure, in (13), the light source has a peak wavelength λp at which the light intensity is maximized; The fourth wavelength limiting body has a maximum transmittance of 5% or less in a wavelength range from (λp×0.6) nm to (λp×0.8) nm.

[0020] (15) As an embodiment of the present disclosure, in (1), The optical filter is provided on an optical path of light that leaves the active layer and reaches the first sensor unit.

[0021] (16) As an embodiment of the present disclosure, in any one of (1) to (5), The first sensor portion has the same configuration as the light source.

[0022] (17) As an embodiment of the present disclosure, in any one of (1) to (5), When the distance between the first sensor unit and the light source is d and the thickness of the substrate on which the light source is provided is T, (d / T) is within the range of 0.70 to 6.00. Effect of the Invention

[0023] According to the present disclosure, it is possible to provide a gas sensor in which the filter size can be reduced and the optical path can be easily designed. [Brief description of the drawings]

[0024] [Figure 1]FIG. 1 is a diagram illustrating an example of the configuration of a gas sensor according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a diagram showing a configuration example of the wavelength limiting body. [Figure 3A] FIG. 3A is a diagram showing a configuration example of a wavelength limiting body. [Figure 3B] FIG. 3B is a diagram showing a configuration example of a wavelength limiting body. [Figure 3C] FIG. 3C is a diagram showing a configuration example of a wavelength limiting body. [Figure 4A] FIG. 4A is a diagram showing a configuration example of a wavelength limiting body. [Figure 4B] FIG. 4B is a diagram showing a configuration example of a wavelength limiting body. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, a gas sensor according to an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals. In the description of this embodiment, the description of the same or corresponding parts will be omitted or simplified as appropriate.

[0026] (Gas sensor) FIG. 1 is a diagram showing the configuration of a gas sensor according to the present embodiment. The gas sensor measures the presence or concentration of a gas to be detected in a gas. In the example of FIG. 1, the gas sensor has a gas cell drawn in a semicircular shape. Here, the gas sensor is not limited to the configuration of FIG. 1, and for example, a gas cell of a shape other than a semicircular shape may be adopted. In addition, although the inner surface of the gas cell in the example of FIG. 1 is a reflective surface, it is possible to adopt a gas cell whose inner surface is not reflective. The gas sensor introduces a gas into the internal space of the gas cell and measures the presence or concentration of a gas to be detected in the introduced gas. The gas sensor according to the present embodiment is an NDIR type gas sensor. The gas sensor according to the present embodiment can be applied to various devices. For example, it can be used for environmental measurement in a building, for installation in a mobile communication device such as a smartphone as a portable small measuring device, and for detecting the gas concentration in a room of a means of transportation such as a car, a train, or an airplane.

[0027] Furthermore, according to the configuration of the gas sensor according to the present embodiment, it can be applied as a light receiving / emitting device for purposes other than a gas sensor. That is, the disclosure derived by replacing the above-described "gas sensor" with "light receiving / emitting device", "optical device", "optical concentration measuring device", "optical physical quantity measuring device", etc., is included in the scope of the present disclosure. For example, it becomes possible to detect the state of the optical path space outside the substrate (existence or concentration of a specific component of a fluid, as an example other than gas). For example, it can be used as a component detection device or component concentration measurement device for a substance (e.g., water or body fluid) present in the optical path space between the light source 20 and the first sensor unit 32. For example, the component detection device or component concentration measurement device can be used to measure the glucose concentration in blood when the substance present in the optical path space is blood.

[0028] The component detection device or component concentration measurement device can measure the glucose concentration in blood glucose by measuring the absorption of light with a wavelength of 1 to 10 μm. In measuring the glucose concentration in blood glucose, it is preferable to measure the absorption of light with wavelengths of 1.6 μm, 2.0 to 2.3 μm, and 9.6 μm. A small, highly accurate, and highly reliable non-invasive glucose concentration measurement device can be realized. With such a glucose concentration measurement device, for example, a diabetic patient can accurately check his or her own blood glucose level without causing damage to the skin that occurs with invasive methods. Furthermore, more accurate management of medication (e.g., insulin) can be realized based on the blood glucose level thus measured.

[0029] The gas sensor includes a light source 20, a second sensor unit 31, and a wavelength limiting body. The gas sensor may also include a first substrate 41, a second substrate 42, and a first sensor unit 32. The long limiting body is a functional part that limits the wavelength of light that reaches the second sensor part 31, and may be, for example, a part of the light source 20 or a substrate (first substrate 41) on which the light source 20 is provided, as described later. Fig. 1 is a cross-sectional view showing a cross section of a gas sensor including these components. The components of the gas sensor will be described in detail later.

[0030] Here, as shown in FIG. 1, the gas sensor may further include an optical filter 16. The gas sensor may further include a calculation unit 104. The optical filter 16 is provided on the optical path of light emitted from the light source 20 and reaching the first sensor unit 32, and limits the transmission wavelength band of the light. The optical filter 16 may be, for example, a bandpass filter of a known configuration. The calculation unit 104 is composed of, for example, a processor, and may calculate the concentration of the detected gas using output signals from the second sensor unit 31 and the first sensor unit 32. A known method may be used to calculate the concentration of the detected gas.

[0031] The configuration of the gas sensor according to this embodiment is as follows. In the gas sensor, the second sensor unit 31 and the first sensor unit 32 are arranged so that the light emitted from the light source 20 is incident thereon. The inner surface (the surface on the inner space side) of the gas cell reflects light. In FIG. 1, the optical path of the light emitted from the light source 20, reflected by the inner surface of the gas cell, and incident on the first sensor unit 32 is indicated by an arrow. Also, the optical path of the light that is part of the light emitted from the light source 20, reflected by one surface (the inner side of the second main surface described later) of the first substrate 41, and incident on the second sensor unit 31 is indicated by an arrow. The gas sensor includes a first substrate 41 having a first main surface and a second main surface opposite to the first main surface, and having the light source 20 and the second sensor unit 31 provided on the first main surface. Here, the light source 20 and the second sensor unit 31 do not have to be arranged on the same substrate. The gas sensor also includes a second substrate 42 having a first main surface and a second main surface opposite to the first main surface, and a first sensor unit 32 provided on the first main surface. A part of the light emitted from the light source 20 and incident on the first sensor unit 32 is incident on the second sensor unit 31. Therefore, even if the light emission characteristics of the light source 20 change due to a change in the usage environment or deterioration over time, the first sensor unit 32 can accurately detect the spatial state using the detection signal of the second sensor unit 31. In other words, the second sensor unit 31 is used to compensate for the temperature change or aging change of the first sensor unit 32 that detects the spatial state. In addition, in the example of FIG. 1, light is emitted from the back surface of the first substrate 41 (the surface on which the light source 20 and the like are not arranged) and light is incident on the back surface of the second substrate 42, but the light may be emitted from and incident on the front surface.

[0032] Here, the gas sensor may be designed such that the angle of light incident on the second sensor unit 31 is 20° to 70° based on the relationship between the emission efficiency of the light source and the amount of reflection. More preferably, the first substrate 41 may be designed such that the angle of light incident on the second sensor unit 31 is 30° to 60°. In other words, when the distance between the second sensor unit 31 and the light source 20 is d and the thickness of the substrate (first substrate 41) on which the light source 20 is provided is T, (d / T) is set within a range of, for example, 0.70 to 6.00. Here, (d / T) may be set within a range of 0.72 to 5.50 in correspondence with the above-mentioned angle of light. More preferably, (d / T) may be set within a range of 1.15 to 3.50.

[0033] In the gas sensor, the second sensor portion 31 and the first sensor portion 32 preferably have the same temperature characteristics. The same temperature characteristics do not necessarily have to be strictly the same, but may be generally the same temperature characteristics. In order to achieve a high S / N ratio in the entire gas sensor, the second sensor portion 31 and the first sensor portion 32 may have different areas. The second sensor portion 31 and the first sensor portion 32 may be formed of a large number of light receiving elements.

[0034] Here, the detection signal of the second sensor unit 31 can be used to compensate for temperature changes or changes over time in the first sensor unit 32 as described above. However, particularly when the gas sensor is configured to include the optical filter 16, more accurate compensation may be required for changes in the light emission characteristics of the light source 20. For example, if the second sensor unit 31 receives almost all wavelengths of light from the light source 20, the change in the amount of light received (integral intensity) of the second sensor unit 31 is small before and after a wavelength shift (change in wavelength distribution) occurs in the light source 20. In contrast, in the first sensor unit 32, which receives only light of a specific wavelength by the optical filter 16, the change in the amount of light received (integral intensity) is large before and after a wavelength shift (change in wavelength distribution) occurs in the light source 20. In such a case, the relationship between the amount of light received by the second sensor unit 31 and the amount of light received by the first sensor unit 32 may deviate from the true value, resulting in insufficient compensation and making it impossible to provide a highly accurate gas sensor. To solve this problem, there is a solution in which the second sensor unit 31 is provided with a filter member similar to the optical filter 16, and both the second sensor unit 31 and the first sensor unit 32 receive only light of a specific wavelength. However, further miniaturization is required for gas sensors. Therefore, if a filter similar to the optical filter 16 is placed on the optical path of the light incident on the second sensor unit 31, the size of the gas sensor increases. Furthermore, miniaturizing the filter causes problems of filter interference and light loss, making the optical path design difficult. The gas sensor according to this embodiment is provided with a wavelength limiter, which will be described later, so that the size of the filter can be reduced and the optical path design can be made easier.

[0035] (light source) The components of the gas sensor will be described in detail below. The light source 20 emits light having a wavelength that is absorbed by the gas to be detected. For example, a lamp, an LED (Light Emitting Diode), a MEMS (Micro Electro Mechanical Systems) emitter, or a laser (Light Amplification by Stimulated Emission of Radiation) is used as the light source 20. In this embodiment, the light source 20 is an LED and has an active layer 53 (see FIG. 2). Here, the active layer 53 is a layer where photoelectric conversion is performed, and is a light-emitting layer in an LED and a light-receiving layer in a sensor.

[0036] The light source 20 preferably has a laminated structure of a PN junction or a PIN junction formed by a film formation method such as MBE (Molecular Beam Epitaxy) or CVD (Chemical Vapor Deposition). By supplying power to this laminated structure, it operates as an LED and can emit light with a wavelength according to the band gap of the material of the laminated structure. The active layer 53 contains In or Sb, which makes it possible to emit infrared rays. Specifically, by using InSb, InAlSb or InAsSb for the active layer 53, it is possible to output light with a wavelength of 1 to 12 μm.

[0037] (Second sensor part) The second sensor unit 31 receives light (infrared rays) and outputs a signal according to the amount of received light. For example, a photodiode, a photoconductor, a thermopile, a pyroelectric sensor, or the like can be used as the second sensor unit 31. From the viewpoint of the response speed of the signal processing, the second sensor unit 31 has a PN junction or PIN junction diode structure and may contain indium or antimony as a material. The second sensor unit 31 may further contain a mixed crystal material containing at least one material selected from the group consisting of Ga, Al, and As. In addition, from the viewpoint of aligning the temperature characteristic or wavelength characteristic, it is preferable that the material and the laminated structure of the second sensor unit 31 are similar to the material and the laminated structure of the light source 20. In this embodiment, the second sensor unit 31 is a photodiode having the same configuration as the light source 20 and including an active layer 53.

[0038] (First board) The first substrate 41 has the light source 20 and the second sensor unit 31 on the first main surface. The material of the first substrate 41 is not particularly limited. The material of the first substrate 41 may be, for example, Si, GaAs, sapphire, InP, InAs, Ge, etc., but is not limited thereto, and may be selected according to the wavelength band to be used. It is preferable to use a semi-insulating substrate as the material of the first substrate 41 from the viewpoint of easily electrically insulating the second sensor unit 31 and the light source 20. It is particularly preferable to use a GaAs substrate as the material of the first substrate 41 from the viewpoint of enabling a large diameter. It is preferable that the material of the first substrate 41 is one that has high transmittance of light emitted from the light source 20 from the viewpoint of improving measurement sensitivity. In addition, it is preferable that the material of the first substrate 41 is a material that efficiently reflects the light emitted from the light source 20 on the second main surface from the viewpoint of highly accurately compensating for output fluctuations of the light source 20. The first substrate 41 may be one that suppresses the transmission of light on the shorter wavelength side than the peak wavelength at which the intensity of the light emitted from the light source 20 is maximum. It is possible to perform efficient measurements while keeping the size small.

[0039] (First sensor section) The first sensor unit 32 receives light (infrared rays) and outputs a signal according to the amount of received light. For example, a photodiode, a photoconductor, a thermopile, a pyroelectric sensor, or the like can be used as the first sensor unit 32. From the viewpoint of the response speed of signal processing, the first sensor unit 32 has a PN junction or PIN junction diode structure and may contain indium or antimony as a material. The first sensor unit 32 may further contain a mixed crystal material containing at least one material selected from the group consisting of Ga, Al, and As. The material and layered structure of the first sensor unit 32 are preferably similar to the material and layered structure of the light source 20.

[0040] In this embodiment, from the viewpoint of improving measurement sensitivity, an optical filter 16 that transmits only a specific wavelength band is provided in the optical path from the light emitted from the second main surface of the first substrate 41 to the light incident on the first sensor unit 32. However, the installation of the optical filter 16 is not essential and is optional.

[0041] (Second board) The second substrate 42 has the first sensor portion 32 on the first main surface. Light incident from the second main surface side passes through the second substrate 42 and enters the first sensor portion 32. The material of the second substrate 42 is not particularly limited. The material of the second substrate 42 may be, for example, Si, GaAs, sapphire, InP, InAs, Ge, etc., but is not limited thereto, and may be selected according to the wavelength band to be used. From the viewpoint of improving the measurement sensitivity, it is preferable that the material of the second substrate 42 is highly transparent to the light incident from the second main surface side.

[0042] (wavelength limiter) The wavelength limiting body is provided so as to limit the wavelength of light that leaves the active layer 53 of the light source 20 and reaches the second sensor unit 31, and to be connected to the light source 20 without passing through a space. The connection between the wavelength limiting body and the light source 20 includes direct connection and indirect connection as long as there is no space, and further includes the wavelength limiting body being inside the light source 20. Here, "without passing through a space" may mean not passing through a space (e.g., a gas space) in which a measurement object exists. For example, the existence of a space in which no measurement object exists between the wavelength limiting body and the light source 20 may be included in "without passing through a space". The wavelength limiting body has a filter function similar to that of the optical filter 16, and both the second sensor unit 31 and the first sensor unit 32 receive only light of a specific wavelength. The wavelength limiting body is not limited to a specific configuration, and may be realized by, for example, any of the configurations described below.

[0043] As shown in FIG. 2, the wavelength limiting body is configured by laminating materials having different refractive indices, and may be a part of the light source 20. The light source 20 is configured to include a first layer 51, a second layer 52, and an active layer 53, and at least the first layer 51 corresponds to the wavelength limiting body. That is, in the example of FIG. 2, the wavelength limiting body is provided on the optical path of the light that leaves the active layer 53 and reaches the second sensor unit 31 until it reaches the first substrate 41. The first layer 51 is a layer on the first main surface side of the first substrate 41, and transmits only light of a specific wavelength, similar to the optical filter 16, by using a resonant structure (DBR: Distributed Bragg Reflector). Therefore, the second sensor unit 31 can receive only light of a specific wavelength. Here, the second layer 52 may be, for example, a resonant structure (DBR) in which layers having different refractive indices are laminated. Also, the second layer 52 may be a metal layer that reflects light. In this case, the wavelength limiting body is configured to have a reflective structure that reflects light of a specific wavelength by combining the first layer 51 of the resonant structure and the second layer 52, which is a metal layer. When the wavelength limiting body is a part of the light source 20, the second sensor unit 31 may also be configured to include a wavelength limiting body. In addition, since the first layer 51 and the active layer 53 can use light of the same wavelength, it is desirable that they include similar wavelength limiting bodies. In addition, the wavelength band limited by the optical filter 16 is not particularly limited, but it is desirable that the wavelength distribution of light passing through the optical filter 16 is narrower than the wavelength distribution of light passing through the wavelength limiting body, since the influence can be reduced even when the variation in the wavelength distribution of light is large. The gas sensor may include multiple wavelength limiting bodies. Each of the multiple wavelength limiting bodies having different configurations may be referred to as, for example, a first wavelength limiting body, a second wavelength limiting body, a third wavelength limiting body, or a fourth wavelength limiting body for distinction. For example, the first wavelength limiting body may be provided between the light source 20 and the first substrate 41. For example, the second wavelength limiting body may be provided between the second sensor unit 31 and the first substrate 41. For example, the third wavelength limiting body may be provided between the first sensor unit 32 and the second substrate 42. For example, the fourth wavelength limiting body may be provided between the space and the first substrate 41 (or the second substrate 42). In other words, the fourth wavelength limiting body may be configured to be connected to the surface of the substrate.Also, for example, the first wavelength limiting body and the fourth wavelength limiting body may have a maximum transmittance of 5% or less in the wavelength range from (λp×0.6) nm to (λp×0.8) nm. The light source 20 has a peak wavelength at which the light intensity is maximum, and the peak wavelength is λp.

[0044] As shown in FIG. 3A to FIG. 3C, the wavelength limiting body may be a part of the substrate and may reflect only light of a specific wavelength to the second sensor unit 31. In the examples of FIG. 3A and FIG. 3B, the specific wavelength reflecting layer 54 corresponds to the wavelength limiting body. The specific wavelength reflecting layer 54 has a resonant structure similar to that of the example of FIG. 2. The specific wavelength reflecting layer 54 can suppress the transmission of light on the shorter wavelength side than the peak wavelength at which the intensity of the light emitted from the light source 20 is maximum. Here, the specific wavelength reflecting layer 54 in the example of FIG. 3A has a property similar to that of a half mirror 57, and transmits a part of the light to the first sensor unit 32 and reflects a part of the light to the second sensor unit 31. The specific wavelength reflecting layer 54 in the example of FIG. 3B has an opening 55, and the light that passes through the opening 55 heads toward the first sensor unit 32. The light reflected by the specific wavelength reflecting layer 54 heads toward the second sensor unit 31. In the example of FIG. 3C, the wavelength limiting body is composed of a layer of the half mirror 57 and the filter 56. Only light of a specific wavelength is transmitted by the filter 56, and the half mirror 57 transmits a portion of the light to the first sensor unit 32 and reflects a portion of the light to the second sensor unit 31. The wavelength limiting body may be configured to include a dichroic mirror.

[0045] As shown in FIG. 4A and FIG. 4B, the wavelength limiting body may be composed of an absorption layer 58. The absorption layer 58 absorbs light of some wavelengths (light of wavelengths other than the above-mentioned "specific wavelengths") so as not to transmit them. The material of the absorption layer 58 is selected according to the wavelength to be absorbed. For example, when it is desired to absorb light having a wavelength of 1 μm or less or 2 μm or less, Si, GaAs, GaInAsP, or the like can be used as the material of the absorption layer 58. From the viewpoint of ease of film formation, it is preferable to use GaAs. Also, from the viewpoint of insulation, the absorption layer 58 may have a structure including an oxide layer. For example, when it is desired to absorb light having a wavelength of 6 μm or more, it is preferable to use InSb as the material of the absorption layer 58. From the viewpoint of increasing the amount of absorption, it is preferable that the absorption layer 58 contains a dopant such as Si or Sn. From the viewpoint of improving the light intensity, a part of the absorption layer 58 may be a void. The void changes the traveling direction of the light, and the light may be emitted into the space after being reflected several times inside the absorption layer in a direction parallel to the surface of the substrate. Moreover, the materials listed as the materials of the absorption layer 58 may be used in appropriate combination. The absorption layer 58 may be a part of the light source 20 or the first substrate 41. As a specific example, as shown in FIG. 4A, the absorption layer 58 may be provided in the light source 20 adjacent to the active layer 53. As shown in FIG. 4B, the absorption layer 58 may be provided in the light source 20 at a position in contact with the first substrate 41. It is preferable that the light intensity of the wavelength of the light emitted from the light source 20 that is not absorbed by the wavelength limiter is greater than the light intensity of the wavelength of the light absorbed by the wavelength limiter.

[0046] As described above, the gas sensor according to this embodiment has the above-mentioned configuration, and the filter for the light incident on the second sensor portion 31 is realized by the wavelength limiting body, thereby making it possible to reduce the size of the gas sensor. Furthermore, in the gas sensor according to this embodiment, the filter for the light incident on the second sensor portion 31 can be configured as a part of the light source 20 or the substrate (first substrate 41), and therefore the optical path can be easily designed.

[0047] (Method of measuring refractive index) The refractive indexes of the first layer and the second layer can be measured by an ellipsometer in accordance with "JIS K7142."

[0048] (Method for measuring transmittance of optical filters) The transmittance of the optical filter can be measured by a microscopic FT-IR device (Hyperion3000+TENSOR27, manufactured by Bruker).

[0049] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications or corrections based on the present disclosure. Therefore, it should be noted that these modifications and corrections are included in the scope of the present disclosure.

[0050] In addition, the above-mentioned configurations of the wavelength limiting body can be combined as long as they are not exclusive combinations. For example, the gas sensor may be configured to include the first layer 51 of the light source 20 as shown in Fig. 2 and the specific wavelength reflecting layer 54 as shown in Fig. 3A, and the first layer 51 and the specific wavelength reflecting layer 54 may function as the wavelength limiting body. [Explanation of symbols]

[0051] 16 Optical Filters 20 light source 31 Second sensor section 32 First sensor section 41 First board 42 Second board 51 1st layer 52 2nd layer 53 Active layer 54 Specific wavelength reflective layer 55 Aperture 56 Filters 57 Half Mirror 58 Absorbing Layer 104 Arithmetic section

Claims

1. a light source having an active layer; a first sensor unit that is disposed so that light emitted from the light source is incident thereon and detects a state of a space; a second sensor unit disposed so that light emitted from the light source is incident thereon and used for compensating for temperature changes or changes over time of the first sensor unit; a first wavelength limiting body that limits a wavelength of light emitted from the active layer and reaching the first sensor unit and the second sensor unit and is connected to the light source without passing through the space; a second wavelength limiting body that limits the wavelength of light that leaves the active layer and reaches the second sensor unit, and is connected to the second sensor unit without passing through the space.

2. 2. The gas sensor according to claim 1, further comprising a third wavelength limiting body that limits a wavelength of light that leaves the active layer and reaches the first sensor portion and is connected to the first sensor portion without passing through the space.

3. 2. The gas sensor according to claim 1, wherein the first wavelength limiting body is configured by laminating materials having different refractive indices, and is a part of the light source or a substrate on which the light source is provided.

4. 2. The gas sensor according to claim 1, wherein the second wavelength limiting body is configured by laminating materials having different refractive indices, and is a part of the second sensor portion or a substrate on which the second sensor portion is provided.

5. 3. The gas sensor according to claim 2, wherein the third wavelength limiting body is configured by laminating materials having different refractive indices, and is a part of the first sensor portion or a substrate on which the first sensor portion is provided.

6. the light source has a peak wavelength λp at which the light intensity is maximized; 6. The gas sensor according to claim 2, wherein the first wavelength limiting body has a maximum transmittance of 5% or less in a wavelength range from ([lambda]p x 0.6) nm to ([lambda]p x 0.8) nm.

7. 2. The gas sensor according to claim 1, wherein the first wavelength limiting body does not transmit light of some wavelengths and is a part of the light source or a substrate on which the light source is provided.

8. 2. The gas sensor according to claim 1, wherein the second wavelength limiting body does not transmit light of some wavelengths and is a part of the second sensor portion or a substrate on which the second sensor portion is provided.

9. 3. The gas sensor according to claim 2, wherein the third wavelength limiting body does not transmit light of some wavelengths and is a part of the first sensor portion or a substrate on which the first sensor portion is provided.

10. 6. The gas sensor according to claim 1, wherein the first wavelength limiting body is provided on an optical path of light that leaves the active layer and reaches the second sensor portion until the light reaches a substrate on which the light source is provided.

11. 6. The gas sensor according to claim 1, wherein the second wavelength limiting body is provided on an optical path of light that leaves the active layer and reaches the second sensor unit, reaches a substrate on which the second sensor unit is provided, and is incident on the second sensor unit.

12. The gas sensor according to claim 10 , wherein the wavelength limiting body has a reflective structure that reflects light of a specific wavelength.

13. 2. The gas sensor according to claim 1, further comprising a fourth wavelength limiting body that limits the wavelength of light that leaves the active layer and reaches the first sensor portion and is connected to a surface of a substrate on which the light source is provided without passing through the space.

14. the light source has a peak wavelength λp at which the light intensity is maximized; 14. The gas sensor according to claim 13, wherein the fourth wavelength limiting body has a maximum transmittance of 5% or less in a wavelength range from ([lambda]p x 0.6) nm to ([lambda]p x 0.8) nm.

15. 2. The gas sensor according to claim 1, further comprising an optical filter provided on an optical path of light that leaves the active layer and reaches the first sensor portion.

16. The gas sensor according to claim 1 , wherein the first sensor portion has the same configuration as the light source.

17. 6. The gas sensor according to claim 1, wherein (d / T) is within a range of 0.70 to 6.00, where d is a distance between the first sensor portion and the light source, and T is a thickness of a substrate on which the light source is provided.

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