Gas sensor

Abstract

The invention provides a gas sensor capable of reducing the size of a filter and easily designing an optical path. This gas sensor is provided with: a light source (20) having an active layer; a first sensor unit (32) that is disposed so that the light emitted from the light source enters, and that detects the state of the space; a second sensor unit (31) that is disposed so that light emitted from the light source is incident thereon, and that compensates for a temperature change or an aging change of the first sensor unit; a first wavelength limiting body that limits the wavelength of light that comes out of the active layer and reaches the first sensor unit and the second sensor unit, and that is connected to the light source without a space therebetween; and a second wavelength limiting body that limits the wavelength of light that comes out of the active layer and reaches the second sensor unit, and that is connected to the second sensor unit without a space therebetween.

Description

Technical Field

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

[0002] Light sources are used in many applications, such as indoor or indoor lighting applications, optical devices, etc. Optical devices use light sources that emit light of a specific wavelength, such as sterilization devices that use ultraviolet light, distance measuring devices that use reflected light, etc. In addition, there are known light-receiving and light-emitting devices that combine a light source and a light-receiving part (sensor) to detect the spatial state between the light source and the light-receiving part. The light-receiving and light-emitting device is, for example, a gas sensor that uses infrared light, and detects the concentration of the detected gas in the gas introduced into the space as a spatial state detection. In gas sensors, further accuracy improvements are sought. For example, Patent Document 1 discloses a gas concentration detection device of the NDIR (Non-Dispersive Infrared) method that is configured to be corrected in consideration of changes in output characteristics.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2016 / 021495 Summary of the invention

[0006] Problems to be solved by the invention

[0007] 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 in calibration. In recent years, further miniaturization of gas sensors has been pursued. In the technology of Patent Document 1, if only the filter is miniaturized, the optical distance will change, so the optical path design may become difficult. In addition, there will be problems of filter interference and light loss.

[0008] The present disclosure has been made in view of the above circumstances and aims to provide a gas sensor in which the size of a filter can be reduced and an optical path design can be easily performed.

[0009] Means for solving problems

[0010] (1) A gas sensor according to one embodiment of the present disclosure includes:

[0011] a light source having an active layer;

[0012] A first sensor unit is arranged in a manner for receiving light emitted from the light source, and detects a state of a space;

[0013] a second sensor portion, arranged in a manner for receiving light emitted from the light source, for compensating for temperature change or time-dependent change of the first sensor portion;

[0014] a first wavelength limiter that limits the wavelength of light that exits the active layer and reaches the first sensor unit and the second sensor unit, and is connected to the light source without interposing the space; and

[0015] The second wavelength limiter limits the wavelength of light that exits the active layer and reaches the second sensor unit, and is connected to the second sensor unit without interposing the space therebetween.

[0016] (2) As one embodiment of the present disclosure, in (1),

[0017] The gas sensor includes a third wavelength limiter that limits the wavelength of light that exits the active layer and reaches the first sensor unit, and is connected to the first sensor unit without interposing the space.

[0018] (3) As one embodiment of the present disclosure, in (1),

[0019] The first wavelength limiter is formed by stacking materials having different refractive indices, and is a part of the light source or a substrate on which the light source is provided.

[0020] (4) As one embodiment of the present disclosure, in (1),

[0021] The second wavelength limiter is formed by stacking 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.

[0022] (5) As one embodiment of the present disclosure, in (2),

[0023] The third wavelength limiter is formed by stacking 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.

[0024] (6) As one embodiment of the present disclosure, in (2), (4) or (5),

[0025] The light source has a peak wavelength λp at which the intensity of light becomes maximum.

[0026] The maximum transmittance of the first wavelength limiter in the wavelength range of (λp×0.6) nm to (λp×0.8) nm is 5% or less.

[0027] (7) As one embodiment of the present disclosure, in (1),

[0028] The first wavelength limiter does not transmit light of a certain wavelength and is a part of the light source or a substrate on which the light source is provided.

[0029] (8) As one embodiment of the present disclosure, in (1),

[0030] The second wavelength limiter does not transmit light of a certain wavelength and is a part of the second sensor unit or a substrate on which the second sensor unit is provided.

[0031] (9) As one embodiment of the present disclosure, in (2),

[0032] The third wavelength limiter does not transmit light of a certain wavelength and is a part of the first sensor unit or a part of a substrate on which the first sensor unit is provided.

[0033] (10) As one embodiment of the present disclosure, in any one of (1) to (5),

[0034] The first wavelength limiter is provided on an optical path from when the light exits the active layer and reaches the second sensor unit to when the light reaches the substrate on which the light source is provided.

[0035] (11) As one embodiment of the present disclosure, in any one of (1) to (5),

[0036] The second wavelength limiter is provided on an optical path from when the light exits the active layer and reaches the second sensor unit to when the light reaches a substrate on which the second sensor unit is provided and enters the second sensor unit.

[0037] (12) As one embodiment of the present disclosure, in (10),

[0038] The wavelength limiter has a reflective structure that reflects light of a specific wavelength.

[0039] (13) As one embodiment of the present disclosure, in (1),

[0040] The gas sensor includes a fourth wavelength limiter that limits the wavelength of light that exits the active layer and reaches the first sensor unit, and is connected to the front surface of the substrate on which the light source is provided without interposing the space.

[0041] (14) As one embodiment of the present disclosure, in (13),

[0042] The light source has a peak wavelength λp at which the intensity of light becomes maximum.

[0043] The fourth wavelength limiter has a maximum transmittance of 5% or less in a wavelength range of (λp×0.6) nm to (λp×0.8) nm.

[0044] (15) As one embodiment of the present disclosure, in (1),

[0045] The gas sensor includes an optical filter provided on an optical path of light that exits the active layer and reaches the first sensor unit.

[0046] (16) As one embodiment of the present disclosure, in any one of (1) to (5),

[0047] The first sensor unit has the same structure as the light source.

[0048] (17) As one embodiment of the present disclosure, in any one of (1) to (5),

[0049] 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.

[0050] Effects of the Invention

[0051] According to the present disclosure, it is possible to provide a gas sensor in which the size of a filter can be reduced and an optical path design can be easily performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a diagram showing a configuration example of a gas sensor according to an embodiment of the present disclosure.

[0053] Figure 2 It is a diagram showing a structural example of a wavelength limiter.

[0054] Figure 3A It is a diagram showing a structural example of a wavelength limiter.

[0055] Figure 3B It is a diagram showing a structural example of a wavelength limiter.

[0056] Figure 3C It is a diagram showing a structural example of a wavelength limiter.

[0057] Figure 4A It is a diagram showing a structural example of a wavelength limiter.

[0058] Figure 4B It is a diagram showing a structural example of a wavelength limiter.

[0059] Description of Reference Numerals

[0060] 16 optical filters

[0061] 20 Light Sources

[0062] 31 Second sensor unit

[0063] 32 first sensor unit

[0064] 41 first substrate

[0065] 42 second substrate

[0066] 51 First Floor

[0067] 52 Second Floor

[0068] 53Active layer

[0069] 54Specific wavelength reflection layer

[0070] 55 Open

[0071] 56 filters

[0072] 57 Half Mirror

[0073] 58 absorption layer

[0074] 104 Operation Unit DETAILED DESCRIPTION

[0075] Hereinafter, a gas sensor according to an embodiment of the present disclosure will be described with reference to the accompanying drawings. In each figure, the same or corresponding parts are marked with the same reference numerals. In the description of this embodiment, the description of the same or corresponding parts will be appropriately omitted or simplified.

[0076] (Gas Sensor)

[0077] Figure 1 is a diagram showing the structure of a gas sensor according to the present embodiment. The gas sensor measures the presence or concentration of a detection gas in a gas. Figure 1 In the example of FIG. 1 , the gas sensor has a gas chamber depicted in a semicircular shape. Here, the gas sensor is not limited to Figure 1 For example, the air chamber may have a shape other than a semicircular shape. Figure 1 In the example, the inner surface of the gas chamber is a reflective surface, but a gas chamber with a non-reflective inner surface can be used. The gas sensor introduces gas into the internal space of the gas chamber and measures the presence or concentration of the detected gas in the introduced gas. The gas sensor involved in this embodiment is an NDIR gas sensor. The gas sensor involved in this embodiment can be applied to various devices. For example, it can be used for environmental measurement in buildings, as a small and movable measurement device installed in portable communication devices such as smartphones, detection of gas concentration indoors in mobile mechanisms such as cars, trains or airplanes, etc.

[0078] Moreover, according to the structure of the gas sensor involved in the present embodiment, it can be applied as a light-receiving and light-emitting device for purposes other than gas sensors. That is, the disclosure content derived by changing the "gas sensor" described above to "light-receiving and light-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 is possible to detect the state of the optical path space outside the substrate (as an example other than gas, the presence or concentration of a specific component of the fluid, etc.). For example, it can be used as a component detection device or a component concentration measuring device for a substance (such as water or body fluid) present in the optical path space between the light source 20 and the first sensor unit 32. For example, when the substance present in the optical path space is blood, the component detection device or the component concentration measuring device can be used for measuring the glucose concentration in the blood, etc.

[0079] The component detection device or the component concentration measuring device can measure the glucose concentration in blood sugar by measuring the absorption of light with a wavelength of 1 to 10 μm. In the measurement of the glucose concentration in blood sugar, it is preferred to measure the absorption of light at 1.6 μm, 2.0 to 2.3 μm, and 9.6 μm. A small, high-precision, and highly reliable non-invasive glucose concentration meter can be realized. With such a glucose concentration meter, for example, a diabetic patient can check the blood sugar level by himself with high precision without causing damage to the skin that would be caused by an invasive method. In addition, more accurate management of medication (such as insulin) can be achieved based on the blood sugar level that is checked.

[0080] The gas sensor includes a light source 20, a second sensor unit 31, and a wavelength limiter. In addition, the gas sensor may include a first substrate 41, a second substrate 42, and a first sensor unit 32. The wavelength limiter is a functional unit that limits the wavelength of light reaching the second sensor unit 31, and as described later, it 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. Figure 1 2 is a cross-sectional view showing a cross section of a gas sensor including these components. Details of the components of the gas sensor will be described later.

[0081] Here, if Figure 1 In this way, the gas sensor may further include an optical filter 16. In addition, the gas sensor may further include a computing unit 104. The optical filter 16 is provided on the optical path of the light coming out of the light source 20 and reaching the first sensor unit 32, and limits the transmission band of the light. The optical filter 16 may be, for example, a bandpass filter of a known structure. The computing unit 104 may be, for example, composed of a processor, and calculates the concentration of the detected gas using the output signals from the second sensor unit 31 and the first sensor unit 32. The concentration of the detected gas may be calculated using a known method.

[0082] The structure of the gas sensor according to the present embodiment is summarized as follows. In the gas sensor, the second sensor unit 31 and the first sensor unit 32 are respectively arranged so that light emitted from the light source 20 is incident. The inner surface of the gas chamber (the surface on the inner space side) reflects the light. Figure 1 In FIG. 1 , the optical path of the light emitted from the light source 20, reflected on the inner surface of the gas chamber, and incident on the first sensor unit 32 is indicated by an arrow. In addition, the optical path of the light that is a part of the light emitted from the light source 20, reflected on one surface of the first substrate 41 (the inner side of the second main surface described later), and incident on the second sensor unit 31 is indicated by an arrow. The gas sensor includes a first substrate 41, the first substrate 41 has a first main surface and a second main surface opposite to the first main surface, and the light source 20 and the second sensor unit 31 are arranged on the first main surface. Here, the light source 20 and the second sensor unit 31 may not be arranged in the same substrate. In addition, the gas sensor includes a second substrate 42, the second substrate 42 has a first main surface and a second main surface opposite to the first main surface, and the first sensor unit 32 is arranged 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 changes in the use environment or aging, the detection signal of the second sensor unit 31 can be used to accurately detect the spatial state of the first sensor unit 32. 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 for detecting the spatial state. Figure 1 In the example, light is emitted from the back side of the first substrate 41 (the side where the light source 20 etc. is not arranged) and light is incident from the back side of the second substrate 42, but light may be emitted from the front side and incident from the front side.

[0083] Here, in the gas sensor, according to the relationship between the emission efficiency of the light source and the amount of reflection, the first substrate 41 can be designed so that the angle of light incident on the second sensor portion 31 is 20° to 70°. More preferably, the first substrate 41 can be designed so that the angle of light incident on the second sensor portion 31 is 30° to 60°. In other words, when the distance between the second sensor portion 31 and the light source 20 is set to d and the thickness of the substrate (first substrate 41) on which the light source 20 is provided is set to T, d / T is, for example, in the range of 0.70 to 6.00. Here, d / T can be in the range of 0.72 to 5.50 corresponding to the above-mentioned angle of light. More preferably, d / T can be in the range of 1.15 to 3.50.

[0084] In addition, in the gas sensor, the second sensor unit 31 and the first sensor unit 32 preferably have the same temperature characteristics. The same temperature characteristics do not need to be strictly identical, and the temperature characteristics may be roughly the same. In addition, in order to achieve a high S / N ratio of the gas sensor as a whole, the area of ​​the second sensor unit 31 and the first sensor unit 32 may be different. In addition, the second sensor unit 31 and the first sensor unit 32 may be formed by a plurality of light receiving elements.

[0085] Here, as described above, the detection signal of the second sensor unit 31 can be used to compensate for the temperature change or time-dependent change of the first sensor unit 32. However, in particular, when the gas sensor is configured to include the optical filter 16, compensation with higher accuracy is sometimes required for the change in the light emission characteristics of the light source 20. For example, if the second sensor unit 31 receives substantially all wavelengths of light from the light source 20, the change in the amount of light received (integrated intensity) of the second sensor unit 31 is small before and after the wavelength shift (change in wavelength distribution) occurs in the light source 20. In contrast, in the first sensor unit 32 that receives only light of a specific wavelength through the optical filter 16, the change in the amount of light received (integrated intensity) becomes large before and after the 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 deviates from the true value, and the compensation becomes insufficient, and sometimes a high-accuracy gas sensor cannot be provided. There is the following solution to such a problem: a filter component similar to the optical filter 16 is also provided in the second sensor unit 31, so that both the second sensor unit 31 and the first sensor unit 32 only receive light of a specific wavelength. However, further miniaturization is pursued for gas sensors. Therefore, if a filter similar to the optical filter 16 is arranged on the optical path of the light incident on the second sensor unit 31, the size of the gas sensor becomes larger. In addition, if the filter is miniaturized, problems of filter interference and light loss will arise, and the optical path design becomes difficult. The gas sensor involved in this embodiment can reduce the size of the filter and can also easily perform optical path design by having a wavelength limiter described later.

[0086] (light source)

[0087] The following describes the details of the components of the gas sensor. The light source 20 emits light having a wavelength absorbed by the gas to be detected. As the light source 20, for example, a lamp, an LED (Light Emitting Diode), a MEMS (Micro Electro Mechanical Systems) emitter, a laser (Light Amplification by Stimulated Emission of Radiation), etc. can be used. In the present embodiment, the light source 20 is an LED having an active layer 53 (see Figure 2 ). Here, the active layer 53 is a layer that performs photoelectric conversion, and is a light-emitting layer in an LED and a light-receiving layer in a sensor.

[0088] The light source 20 preferably has a stacked structure of a PN junction or a PIN junction formed by a film forming method such as MBE (Molecular Beam Epitaxy) or CVD (Chemical Vapor Deposition). By supplying power to the stacked structure, it can operate as an LED and emit light of a wavelength corresponding to the band gap of the material of the stacked structure. By including In or Sb in the active layer 53, infrared rays can be emitted. Specifically, by using InSb, InAlSb or InAsSb for the active layer 53, light with a wavelength of 1 to 12 μm can be output.

[0089] (Second sensor unit)

[0090] The second sensor unit 31 receives light (infrared rays) and outputs a signal corresponding to the amount of light received. As the second sensor unit 31, for example, a photodiode, a photoconductor, a thermopile, a pyroelectric sensor, etc. can be used. From the perspective of the response speed of signal processing, the second sensor unit 31 can be a diode structure of a PN junction or a PIN junction, containing indium or antimony as a material. The second sensor unit 31 may also include a mixed crystal material, and the mixed crystal material includes at least one material selected from the group consisting of Ga, Al, and As. In addition, from the perspective of making the temperature characteristics or wavelength characteristics consistent, the material and stacking structure of the second sensor unit 31 are preferably the same as the material and stacking structure of the light source 20. In the present embodiment, the second sensor unit 31 is a photodiode having the same structure as the light source 20 and having an active layer 53.

[0091] (First Substrate)

[0092] 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 used. From the viewpoint of being able to easily electrically insulate the second sensor unit 31 and the light source 20, the material of the first substrate 41 is preferably a semi-insulating substrate. From the viewpoint of being able to increase the aperture, the material of the first substrate 41 is particularly preferably a GaAs substrate. From the viewpoint of improving the measurement sensitivity, the material of the first substrate 41 is preferably a material with high transmittance of the light emitted from the light source 20. In addition, from the viewpoint of compensating the output variation of the light source 20 with high accuracy, the material of the first substrate 41 is preferably a material that efficiently reflects the light emitted from the light source 20 at the second main surface. The first substrate 41 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 becomes the maximum. It is possible to measure efficiently while maintaining a small size.

[0093] (First sensor unit)

[0094] The first sensor unit 32 receives light (infrared rays) and outputs a signal corresponding to the amount of light received. As the first sensor unit 32, for example, a photodiode, a photoconductor, a thermopile, a pyroelectric sensor, etc. can be used. From the perspective of the response speed of signal processing, the first sensor unit 32 can be a diode structure of a PN junction or a PIN junction, containing indium or antimony as a material. The first sensor unit 32 may also include a mixed crystal system material, and the mixed crystal system material includes at least one material selected from the group consisting of Ga, Al, and As. The material and stacked structure of the first sensor unit 32 are preferably the same as the material and stacked structure of the light source 20.

[0095] In this embodiment, from the viewpoint of improving measurement sensitivity, the optical filter 16 that transmits only a specific wavelength band is provided on the optical path until the light radiated from the second main surface of the first substrate 41 enters the first sensor unit 32. However, the provision of the optical filter 16 is not essential and is optional.

[0096] (Second Substrate)

[0097] The second substrate 42 has the first sensor unit 32 on the first main surface. Light incident from the second main surface side passes through the inside of the second substrate 42 and enters the first sensor unit 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 used. From the viewpoint of improving the measurement sensitivity, the material of the second substrate 42 is preferably a material with high transmittance to the light incident from the second main surface side.

[0098] (Wavelength Limiter)

[0099] The wavelength limiter limits the wavelength of light that comes out of the active layer 53 of the light source 20 and reaches the second sensor unit 31, and is provided in a manner connected to the light source 20 without a space therebetween. The connection between the wavelength limiter and the light source 20 is sufficient as long as there is no space therebetween, including both direct and indirect connections, and also including the wavelength limiter being in the light source 20. Here, not being separated by a space may mean not being separated by a space where a measurement object exists (for example, a gas space), and there may be a space without a measurement object between the wavelength limiter and the light source 20. The wavelength limiter has the same filter function as the optical filter 16, so that both the second sensor unit 31 and the first sensor unit 32 receive only light of a specific wavelength. The wavelength limiter is not limited to a specific structure, and may be implemented by any of the structures described below, for example.

[0100] like Figure 2 As shown in FIG. 1 , the wavelength limiter can be formed by stacking materials with different refractive indices and is a part of the light source 20. The light source 20 is a structure including a first layer 51, a second layer 52 and an active layer 53, and at least the first layer 51 corresponds to the wavelength limiter. Figure 2In the example of , the wavelength limiter is provided in the optical path until the light coming out of the active layer 53 and reaching the second sensor unit 31 reaches the first substrate 41. The first layer 51 is a layer on the first main surface side of the first substrate 41, and only transmits light of a specific wavelength in the same way as the optical filter 16, for example, through a resonant structure (DBR: Distributed Bragg Reflector). Therefore, the second sensor unit 31 can only receive light of a specific wavelength. Here, the second layer 52 can be, for example, a resonant structure (DBR) formed by stacking layers with different refractive indices. In addition, the second layer 52 can be a layer of a metal that reflects light. In this case, the wavelength limiter becomes a structure having 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 as a metal layer. In the case where the wavelength limiter is a part of the light source 20, the second sensor unit 31 can also be similarly configured to include the wavelength limiter. In addition, with respect to the first layer 51 and the active layer 53, since the same wavelength of light can be used, it is preferable to include the same wavelength limiter. In addition, the wavelength band limited by the optical filter 16 is not particularly limited, but since the influence can be reduced even when the deviation of the wavelength distribution of light is large, it is preferable that the wavelength distribution of light passing through the optical filter 16 is narrower than the wavelength distribution of light passing through the wavelength limiter. The gas sensor can have a plurality of wavelength limiters. Multiple wavelength limiters with different structures are sometimes referred to as, for example, a first wavelength limiter, a second wavelength limiter, a third wavelength limiter, or a fourth wavelength limiter for the purpose of distinction. For example, the first wavelength limiter can be provided between the light source 20 and the first substrate 41. For example, the second wavelength limiter can be provided between the second sensor unit 31 and the first substrate 41. For example, the third wavelength limiter can be provided between the first sensor unit 32 and the second substrate 42. For example, the fourth wavelength limiter can be provided between the space and the first substrate 41 (or the second substrate 42). That is, the fourth wavelength limiter can be a structure connected to the front surface of the substrate. In addition, for example, the maximum transmittance of the first wavelength limiter and the fourth wavelength limiter in the wavelength range of (λp×0.6)nm to (λp×0.8)nm can be 5% or less. The light source 20 has a peak wavelength at which the intensity of light reaches a maximum, and this peak wavelength is λp.

[0101] like Figure 3A to Figure 3C As shown, the wavelength limiting body may be a part of the substrate, which reflects only light of a specific wavelength toward the second sensor unit 31. Figure 3A and Figure 3B In the example of FIG. 5 , the specific wavelength reflection layer 54 corresponds to the wavelength limiter. Figure 2The specific wavelength reflection 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 becomes the maximum. Here, Figure 3A The specific wavelength reflection layer 54 in the example has a property similar to that of the half mirror 57 , transmits a part of the light toward the first sensor unit 32 , and reflects a part of the light toward the second sensor unit 31 . Figure 3B In the example of FIG. 5 , the specific wavelength reflection layer 54 is provided with an opening 55, and the light passing through the opening 55 goes to the first sensor unit 32. The light reflected by the specific wavelength reflection layer 54 goes to the second sensor unit 31. Figure 3C In the example of FIG. 5 , the wavelength limiter is composed of a layer of a half mirror 57 and a filter 56. Only light of a specific wavelength is transmitted through the filter 56, and the half mirror 57 transmits a part of the light toward the first sensor unit 32 and reflects a part of the light toward the second sensor unit 31. In addition, the wavelength limiter may be configured to include a dichroic mirror.

[0102] like Figure 4A and Figure 4B As shown, the wavelength limiter can be composed of an absorption layer 58. The absorption layer 58 absorbs light of a part of the wavelength (light of a wavelength other than the above-mentioned "specific wavelength") in a manner that does not allow it to pass through. 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 with a wavelength of less than 1 μm or less than 2 μm, Si, GaAs, GaInAsP, etc. can be used as the material of the absorption layer 58. From the viewpoint of ease of film formation, GaAs is preferably used. In addition, from the viewpoint of insulation, the absorption layer 58 can be a structure including an oxide layer. For example, when it is desired to absorb light with a wavelength of more than 6 μm, AlInAsSb can be used as the material of the absorption layer 58, and InSb is more preferably used. From the viewpoint of increasing the amount of absorption, the absorption layer 58 preferably contains a dopant such as Si or Sn. From the viewpoint of increasing the light intensity, a part of the absorption layer 58 can be a void. The void can be used to change the direction of travel of light, and after reflecting several times in the direction parallel to the surface of the substrate inside the absorption layer, the light is released into the space. In addition, the materials listed as the materials of the absorption layer 58 can be used in combination as appropriate. The absorption layer 58 can be a part of the light source 20 or the first substrate 41. As a specific example, Figure 4A In this way, the absorption layer 58 can be disposed close to the active layer 53 inside the light source 20. Figure 4B Thus, the absorption layer 58 can be provided inside the light source 20 at a position in contact with the first substrate 41. Preferably, the light intensity of the wavelength not absorbed by the wavelength limiter in the light emitted from the light source 20 is greater than the light intensity of the wavelength absorbed by the wavelength limiter.

[0103] As described above, the gas sensor involved in this embodiment can realize the filter for light incident to the second sensor part 31 by using the wavelength limiter through the above-mentioned structure, thereby reducing its size. In addition, in the gas sensor involved in this embodiment, the filter for light incident to the second sensor part 31 can be configured as a part of the light source 20 or the substrate (first substrate 41), so the optical path design can also be easily performed.

[0104] (Method for measuring refractive index)

[0105] The refractive indexes of the first layer and the second layer can be measured using an ellipsometer in accordance with "JIS K7142".

[0106] (Method for measuring transmittance of optical filter)

[0107] The transmittance of the optical filter can be measured using a microscopic FT-IR device (manufactured by Bruker Corporation, Hyperion 3000+TENSOR 27).

[0108] The embodiments of the present disclosure are described based on the drawings and embodiments, but it should be noted that a person skilled in the art can easily make various modifications or corrections based on the present disclosure. Therefore, please note that these modifications or corrections are included in the scope of the present disclosure.

[0109] In addition, the above-mentioned wavelength limiting body structures can be combined as long as they are not exclusive combinations. For example, the gas sensor may be configured to include Figure 2 The first layer 51 of the light source 20 and Figure 3A Such a specific wavelength reflection layer 54 , the first layer 51 and the specific wavelength reflection layer 54 function as a wavelength limiter.

Claims

1. A gas sensor comprising: a light source having an active layer; A first sensor unit is arranged in a manner for receiving light emitted from the light source, and detects a state of a space; a second sensor portion, arranged in a manner for receiving light emitted from the light source, for compensating for temperature change or time-dependent change of the first sensor portion; a first wavelength limiter that limits the wavelength of light that exits the active layer and reaches the first sensor unit and the second sensor unit, and is connected to the light source without interposing the space; and The second wavelength limiter limits the wavelength of light that exits the active layer and reaches the second sensor unit, and is connected to the second sensor unit without interposing the space therebetween.

2. The gas sensor according to claim 1, wherein: The gas sensor includes a third wavelength limiter that limits the wavelength of light that exits the active layer and reaches the first sensor unit, and is connected to the first sensor unit without interposing the space.

3. The gas sensor according to claim 1, wherein: The first wavelength limiter is formed by stacking materials having different refractive indices, and is a part of the light source or a substrate on which the light source is provided.

4. The gas sensor according to claim 1, wherein: The second wavelength limiter is formed by stacking 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.

5. The gas sensor according to claim 2, wherein: The third wavelength limiter is formed by stacking 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.

6. The gas sensor according to claim 2, 4 or 5, wherein: The light source has a peak wavelength λp at which the intensity of light becomes maximum. The maximum transmittance of the first wavelength limiter in the wavelength range of (λp×0.6) nm to (λp×0.8) nm is 5% or less.

7. The gas sensor according to claim 1, wherein: The first wavelength limiter does not transmit light of a certain wavelength and is a part of the light source or a substrate on which the light source is provided.

8. The gas sensor according to claim 1, wherein: The second wavelength limiter does not transmit light of a certain wavelength and is a part of the second sensor unit or a substrate on which the second sensor unit is provided.

9. The gas sensor according to claim 2, wherein: The third wavelength limiter does not transmit light of a certain wavelength and is a part of the first sensor unit or a part of a substrate on which the first sensor unit is provided.

10. The gas sensor according to any one of claims 1 to 5, wherein: The first wavelength limiter is provided on an optical path from when the light exits the active layer and reaches the second sensor unit to when the light reaches the substrate on which the light source is provided.

11. The gas sensor according to any one of claims 1 to 5, wherein: The second wavelength limiter is provided on an optical path from when the light exits the active layer and reaches the second sensor unit to when the light reaches a substrate on which the second sensor unit is provided and enters the second sensor unit.

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

13. The gas sensor according to claim 1, wherein: The gas sensor includes a fourth wavelength limiter that limits the wavelength of light that exits the active layer and reaches the first sensor unit, and is connected to the front surface of the substrate on which the light source is provided without interposing the space.

14. The gas sensor according to claim 13, wherein: The light source has a peak wavelength λp at which the intensity of light becomes maximum. The fourth wavelength limiter has a maximum transmittance of 5% or less in a wavelength range of (λp×0.6) nm to (λp×0.8) nm.

15. The gas sensor according to claim 1, wherein: The gas sensor includes an optical filter provided on an optical path of light that exits the active layer and reaches the first sensor unit.

16. The gas sensor according to any one of claims 1 to 5, wherein: The first sensor unit has the same structure as the light source.

17. The gas sensor according to any one of claims 1 to 5, wherein: 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.

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