Optical device and optical filter

Abstract

The invention provides an optical device and an optical filter which are small and can perform high-precision concentration measurement. The optical device is provided with an optical filter and an infrared optical element, and when [lambda] p is the center wavelength of the transmission wavelength band, T1 is the maximum transmittance of the optical filter in a wavelength region from ([lambda] p * 0.6) nm to ([lambda] p * 0.8) nm when the incidence angle at which infrared light emitted or incident on the infrared optical element enters the optical filter is 0 DEG, T1 is the maximum transmittance of the optical filter, and T1 is the maximum transmittance of the infrared optical element in the wavelength region from ([lambda] p * 0.6) nm to ([lambda] p * 0.8) nm to ([lambda] p * 0.8) nm to ([lambda] p * 0.8) nm. The maximum transmittance of the optical filter is set to be T2 and the average sensitivity of the infrared optical element is set to be S2 in a wavelength region of ([lambda] p * 0.6) nm to ([lambda] p * 0.8) nm when the average sensitivity of the infrared optical element is set to be S1, and the incident angle of infrared rays emitted or incident to the infrared optical element is 45 degrees, the maximum transmittance of the optical filter is set to be T2 and the average sensitivity of the infrared optical element is set to be S2, so that T2 is greater than T1. S2 is smaller than S1.

Description

Technical Field

[0001] The present disclosure relates to optical devices and optical filters. Background Art

[0002] Conventionally, non-dispersive infrared absorption (NDIR) gas concentration measuring devices are known as gas concentration measuring devices for measuring the concentration of target gases in the atmosphere. NDIR gas concentration measuring devices utilize the fact that the wavelengths of infrared light absorbed by different gases differ, and measure the gas concentration by detecting the amount absorbed. NDIR gas concentration measuring devices are configured to include an infrared optical element and a filter (transmitting member) that transmits infrared light of wavelengths limited to those at which the target gas has absorption characteristics. For example, Patent Document 1 discloses a measuring device that uses carbon dioxide as the target gas.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 9-33431 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] The target gas to be measured is not limited to carbon dioxide but can be a variety of gases. Currently, the optimal combination of infrared optical elements and optical filters for each target gas has not been studied. In particular, optimization of optical filter specifications, including the influence of incident angle, has not been conducted.

[0008] The present disclosure, which was made in view of the above circumstances, aims to provide a compact optical device and an optical filter capable of performing high-precision concentration measurement. The optical device includes an infrared optical element and an optical filter, and is used in gas concentration measuring devices and the like.

[0009] Technical solutions to problems

[0010] (1) An optical device according to one embodiment of the present disclosure includes:

[0011] An optical filter comprising a substrate and a multilayer film, wherein the multilayer film is formed on at least one surface of the substrate and comprises a plurality of layers having different refractive indices; and

[0012] Infrared optical elements, emitting or receiving infrared rays,

[0013] The optical filter includes a transmission band of 50 nm or more in a wavelength range of 2500 nm to 10000 nm, the transmittance of the transmission band exceeds 70%, the center wavelength of the transmission band is λp, the maximum transmittance in the wavelength range of (λp×0.6) nm to (λp×0.8) nm is 2% or more, and the maximum transmittance is more than twice the minimum transmittance in the wavelength range of (λp×0.8) nm to (λp×0.9) nm.

[0014] The infrared optical element has a peak sensitivity at which sensitivity is the highest, and an average sensitivity in a wavelength range of (λp×0.6) nm to (λp×0.8) nm is 70% or less of the peak sensitivity.

[0015] If the maximum transmittance of the optical filter is set to T1 and the average sensitivity of the infrared optical element is set to S1 in the wavelength region of (λp×0.6)nm to (λp×0.8)nm when the incident angle of the infrared ray emitted or incident on the optical filter is 0° relative to the infrared optical element, and the maximum transmittance of the optical filter is set to T2 and the average sensitivity of the infrared optical element is set to S2 in the wavelength region of (λp×0.6)nm to (λp×0.8)nm when the incident angle of the infrared ray emitted or incident on the optical filter is 45° relative to the infrared optical element, then T2 is greater than T1 and S2 is smaller than S1.

[0016] (2) An optical device according to one embodiment of the present disclosure includes:

[0017] An optical filter comprising a substrate and a multilayer film, wherein the multilayer film is formed on at least one surface of the substrate and comprises a plurality of layers having different refractive indices; and

[0018] Infrared optical elements, emitting or receiving infrared rays,

[0019] The optical filter includes a transmission band of 50 nm or more in a wavelength range of 2500 nm to 10000 nm, the transmittance of the transmission band exceeds 70%, the center wavelength of the transmission band is λp, the maximum transmittance in the wavelength range of (λp×0.6) nm to (λp×0.8) nm is more than twice the minimum transmittance in the wavelength range of (λp×0.8) nm to (λp×0.9) nm, and the maximum transmittance in the wavelength range of (λp×0.4) nm to (λp×0.6) nm is more than 2%.

[0020] The infrared optical element has a peak sensitivity at which sensitivity is the highest, and an average sensitivity in a wavelength range of (λp×0.6) nm to (λp×0.8) nm is 70% or less of the peak sensitivity.

[0021] If the maximum transmittance of the optical filter is set to T1 and the average sensitivity of the infrared optical element is set to S1 in the wavelength region of (λp×0.6)nm to (λp×0.8)nm when the incident angle of the infrared ray emitted or incident on the optical filter is 0° relative to the infrared optical element, and the maximum transmittance of the optical filter is set to T2 and the average sensitivity of the infrared optical element is set to S2 in the wavelength region of (λp×0.6)nm to (λp×0.8)nm when the incident angle of the infrared ray emitted or incident on the optical filter is 45° relative to the infrared optical element, then T2 is greater than T1 and S2 is smaller than S1.

[0022] (3) As one embodiment of the present disclosure, in (1) or (2),

[0023] The transmittance of the optical filter at λp, which is the center wavelength of the transmission wavelength band, is 1.1 times or more the maximum transmittance in a wavelength region of (λp×0.6) nm to (λp×0.8) nm.

[0024] (4) As one embodiment of the present disclosure, in any one of (1) to (3),

[0025] The optical filter has a maximum transmittance of 2% or more in a wavelength region of (λp×0.4) nm to (λp×0.6) nm.

[0026] (5) As one embodiment of the present disclosure, in any one of (1) to (4),

[0027] The optical filter has a maximum transmittance of 60% or less and an average transmittance of 40% or less in a wavelength range of (λp×0.6) nm to (λp×0.8) nm.

[0028] (6) As one embodiment of the present disclosure, in any one of (1) to (5),

[0029] The optical filter is a bandpass filter having a half-value width of 1000 nm or less.

[0030] (7) As one embodiment of the present disclosure, in any one of (1) to (6),

[0031] The infrared optical element is an infrared light emitting element that emits infrared light, and an average sensitivity in a wavelength range of (λp×0.6) nm to (λp×0.8) nm is 30% or less of the peak sensitivity.

[0032] (8) As one embodiment of the present disclosure, in any one of (1) to (7),

[0033] The total film thickness of the multilayer film is 30 μm or less.

[0034] (9) As one embodiment of the present disclosure, in (1) or (2),

[0035] The infrared optical element includes a first conductive type semiconductor layer, an active layer, and a second conductive type semiconductor layer.

[0036] (10) As one embodiment of the present disclosure, in (1) or (2),

[0037] The infrared optical element is an infrared light emitting element.

[0038] (11) As one embodiment of the present disclosure, in (1) or (2),

[0039] The T2 is greater than the T1 by more than 1%.

[0040] (12) As one embodiment of the present disclosure, in (8),

[0041] The maximum transmittance in the wavelength region of (λp×0.4) nm to (λp×0.6) nm is 25% or more.

[0042] (13) An optical filter according to one embodiment of the present disclosure is used in the optical device of (1) or (2).

[0043] Effects of the Invention

[0044] According to the present disclosure, it is possible to provide an optical device and an optical filter that are compact and capable of performing high-precision concentration measurement even in the case of oblique incidence where the influence of light leakage is significant. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 1 is a diagram showing an example of a cross section of an optical filter.

[0046] Figure 2 This is a diagram showing an example of a concentration measurement apparatus including an optical device according to an embodiment of the present disclosure.

[0047] Figure 3These are diagrams illustrating a comparison between an optical filter of an optical device according to an embodiment of the present disclosure and an optical filter according to a comparative example.

[0048] Figure 4 It is a diagram showing the difference between the optical filter according to the comparative example and the optical filter according to the present disclosure.

[0049] Figure 5 It is a diagram showing the stacked structure of each layer of the infrared optical element according to Examples 1 to 6.

[0050] Figure 6A This is a graph for comparing transmittances of Examples and Comparative Examples.

[0051] Figure 6B This is a graph for comparing transmittances of Examples and Comparative Examples.

[0052] Figure 7 This is a graph comparing the sensitivity of Examples and Comparative Examples.

[0053] Figure 8 This graph compares the characteristics at vertical incidence (incident angle of 0°) and at 45-degree incidence (incident angle of 45°). DETAILED DESCRIPTION

[0054] Hereinafter, an optical device and an optical filter according to an embodiment of the present disclosure will be described with reference to the drawings.

[0055] (Optical Devices)

[0056] The optical device involved in this embodiment includes an optical filter and an infrared optical element. The optical filter has a substrate and a multilayer film, and the multilayer film is formed on at least one side of the substrate and has multiple layers with different refractive indices. The infrared optical element is an infrared light-receiving element or an infrared light-emitting element, which is a name that collectively refers to them. In addition, hereinafter, light-receiving and light-emitting refer to having at least one function of receiving and emitting light. The infrared optical element is constructed to include a first conductive semiconductor layer, an active layer and a second conductive semiconductor layer, and performs infrared light-receiving and light-emitting. That is, the optical device involved in this embodiment is an infrared device. By the structure described below (refer to Figure 5) to realize the infrared light emitting element, and in addition, the infrared light receiving element is realized by the same structure. Specifically, the infrared light emitting element can be a light emitting diode (LED), an incandescent bulb, a laser, an organic light emitting part, a VCSEL (vertical cavity surface emitting laser), a PCSEL (photonic crystal surface emitting laser) or a MEMS (micro electro mechanical system) heater, etc. From the viewpoint of wavelength selectivity, the infrared light emitting element is preferably a light emitting diode (LED). In addition, specifically, the infrared light receiving element can be a photodiode (PD), a phototransistor, a thermopile, a collector sensor or a bolometer, etc. From the viewpoint of wavelength selectivity, the infrared light receiving element is preferably a photodiode (PD).

[0057] The following description assumes that the optical device involved in this embodiment is used for a concentration measuring device. In this embodiment, the concentration measuring device is a gas sensor that measures the concentration of the gas to be measured. The concentration measuring device can be, for example, a non-dispersive infrared absorption (NDIR) type gas sensor having a light receiving portion that receives infrared light transmitted through the gas. In addition, the concentration measuring device can be, for example, a photoacoustic type gas sensor that measures the gas concentration by picking up the vibration of gas molecules that have absorbed light as sound using a high-performance microphone. Here, the optical device involved in this embodiment is not limited to a concentration measuring device, and can also be used in an infrared radiation thermometer, infrared spectroscopy imaging, and a human body detection sensor.

[0058] As will be described in detail later, the optical filter includes a transmission band of 50 nm or more in the wavelength range of 2500 nm to 10000 nm, and the transmittance of this transmission band exceeds 70%. In addition, in the optical filter, the center wavelength of the transmission band is set to λp, and the maximum transmittance in the wavelength range of (λp×0.6) nm to (λp×0.8) nm is 2% or more. In addition, in the optical filter, the maximum transmittance is more than twice the minimum transmittance in the wavelength range of (λp×0.8) nm to (λp×0.9) nm. Here, the center wavelength is the wavelength that is the center of the half-value width of the transmission band with maximum transmittance in the wavelength range of 2500 nm to 10000 nm. In addition, the half-value width is the width of the wavelength that becomes half the transmittance of the maximum transmittance (i.e., the difference between the maximum wavelength and the minimum wavelength).

[0059] As will be described in detail later, the infrared optical element has a peak sensitivity with the highest sensitivity, and the average sensitivity in the wavelength range of (λp×0.6)nm to (λp×0.8)nm is less than 70% of the peak sensitivity. Here, in the wavelength range of (λp×0.6)nm to (λp×0.8)nm when the angle of incidence of infrared light emitted from or incident on the optical filter is 0° with respect to the infrared optical element, the maximum transmittance of the optical filter is T1, and the average sensitivity of the infrared optical element is S1. Furthermore, in the wavelength range of (λp×0.6)nm to (λp×0.8)nm when the angle of incidence of infrared light emitted from or incident on the optical filter is 45° with respect to the infrared optical element, the maximum transmittance of the optical filter is T2, and the average sensitivity of the infrared optical element is S2. In this case, T2 is greater than T1, and S2 is less than S1.

[0060] The optical device of this embodiment can selectively receive or emit only infrared light within a desired wavelength range even when using a simplified optical filter. By using a simplified optical filter, the optical device of this embodiment can be miniaturized. Furthermore, since it can receive and emit infrared light within a desired wavelength range, the optical device of this embodiment can perform highly accurate concentration measurements.

[0061] Figure 1 An example of a cross section of an optical filter is shown. In this embodiment, the optical filter alternately stacks layers composed of a low refractive index material (L) such as SiO, SiO2, TiO2, ZnS or Al2O3 and layers composed of a high refractive index material (H) such as Si or Ge on both sides of a Si substrate. As the low refractive index material (L), it is preferred to select a material with a refractive index of 1.2 to 2.5. In addition, as the high refractive index material (H), it is preferred to select a material with a refractive index greater than or equal to 0.5 of the low refractive index material (L). The alternately stacked multilayer film is formed in such a way that the layer directly provided on the Si substrate is the high refractive index material (H). However, the optical filter is not limited to Figure 1 The structure, such as the high refractive index material (H), may not be directly disposed on the substrate.

[0062] In this embodiment, the optical filter is an interferometric bandpass filter in the mid-infrared region. Typically, an interferometric bandpass filter in the mid-infrared region has many layers, which can easily increase defects during film formation. Furthermore, if the optical filter has many layers, miniaturization of the concentration measuring device becomes difficult. Therefore, it is preferred that the optical filter have fewer layers. However, if the optical filter is simplified by simply reducing the number of layers, the accuracy of the gas sensor may deteriorate.

[0063] Furthermore, in order to realize a high-precision concentration measuring device, it is necessary to reduce the influence of the absorption of infrared rays by gases other than the detection target gas.

[0064] Furthermore, in order to realize a high-precision concentration measuring device, it is necessary to reduce the influence of light leakage when infrared light is incident on the optical filter from an oblique direction.

[0065] The inventors have studied the optimal combination of an infrared optical element and an optical filter, and as a result, have realized an optical device that does not deteriorate in accuracy even when a simplified optical filter is used, as described below.

[0066] Here, a simplified optical filter refers to one that eliminates cutoff in areas without sensor sensitivity, thereby reducing the number of optical thin film layers required for cutoff in those areas. Using simplified optical filters with fewer layers can improve mass production. Furthermore, reducing the number of layers can reduce defects during film formation, resulting in improved yield. Furthermore, reducing warping caused by multiple layers suppresses chipping during cutting, which can improve mass production stability.

[0067] Figure 2 FIG. 1 is a diagram showing an example of a concentration measuring device using the optical device according to the present embodiment. Figure 2 As shown, an infrared receiving element (IR) is placed in the optical path of infrared light output from an infrared emitting element (light source), and an optical filter that selectively transmits wavelengths absorbed by the gas being detected is placed before the IR receiving element. The optical device corresponds, for example, to the optical filter and the IR receiving element.

[0068] Here, the target gas for measurement by the concentration measuring device is, for example, carbon dioxide, but is not limited thereto. For example, the target gas for measurement may be a combustible gas such as breath alcohol (ethanol, etc.), methane, propane, hydrogen, ethylene, MCH (methylcyclohexane), etc. In addition, the target gas for measurement may also be a toxic gas such as carbon monoxide, hydrogen sulfide, formaldehyde, ammonia, etc. Furthermore, the target gas for measurement may also be a greenhouse gas such as nitrous oxide, refrigerant gas used in air conditioners or refrigerators, etc. Furthermore, the target gas for measurement may also be a mixed gas formed by mixing the aforementioned target gases.

[0069] Figure 3This is a diagram comparing and explaining the optical filter of the optical device involved in the present embodiment and the optical filter based on the comparative example. In the sensor (infrared light receiving element) in the comparative example, the spectral sensitivity does not have wavelength selectivity (sensitivity changes due to wavelength). On the other hand, the sensor possessed by the optical device involved in the present embodiment (or possessed by the concentration measuring device using the optical device involved in the present embodiment) has wavelength selectivity. Therefore, in the present embodiment, there is no need for the optical filter to cut off the wavelengths to which there is no sensitivity, and the optical filter can be simplified. In addition, in the case of an infrared light emitting element whose luminous intensity has wavelength selectivity, there is also no need for the optical filter to cut off the wavelengths that do not emit light, and the optical filter can be simplified. Here, in Figure 3 In the figure, the wavelengths with no sensitivity and no luminescence are shown on both the wavelength side longer than the peak wavelength (long wavelength side) and the wavelength side shorter than the peak wavelength (short wavelength side), but this is just an example of a concept. In this embodiment, the cutoff specification of the optical filter is relaxed on the short wavelength side.

[0070] Figure 4 This figure shows the difference between an optical filter based on a comparative example and the optical filter of the present disclosure. In the optical filter of the optical device according to this embodiment, the thickness of the multilayer film, known as the cutoff surface, which determines the cutoff characteristics, can be significantly reduced. For example, when the multilayer film is formed on both surfaces of a substrate, the ratio of the total film thickness on each surface can be set within a range of 0.5 to 2.0.

[0071] The components of the optical device involved in this embodiment are described in detail. Here, the optical device includes an infrared light-receiving element or an infrared light-emitting element, and the light-receiving sensitivity of the infrared light-receiving element and the light-emitting intensity of the infrared light-emitting element are described as "sensitivity." That is, if the optical device includes an infrared light-receiving element, sensitivity can be replaced by light-receiving sensitivity, and if the optical device includes an infrared light-emitting element, sensitivity can be replaced by light-emitting intensity.

[0072] (Optical Filter)

[0073] As described above, the optical filter includes a substrate and a multilayer film, which is formed on the substrate and has a plurality of layers with different refractive indices. The multilayer film may be formed on only one side of the substrate or on both sides. In the concentration measuring device, the optical filter is arranged between the light path from the infrared light radiated from the infrared light emitting element to the infrared light receiving element. The optical filter may be formed integrally with the infrared light emitting element, or may be formed integrally with the infrared light receiving element. In addition, the optical filter may be arranged at a predetermined location within the light path. In the concentration measuring device, a plurality of optical filters may be provided. The optical filter may be produced by forming a first layer and a second layer on the substrate using a vapor deposition method.

[0074] The optical filter in this embodiment includes a transmission band of more than 50 nm in the wavelength range of 2500 nm to 10000 nm, and the transmittance of this transmission band exceeds 70%. In addition, in the optical filter, the center wavelength of the transmission band is set to λp, and the maximum transmittance in the wavelength range of (λp×0.6) nm to (λp×0.8) nm is greater than 2%. In addition, in the optical filter, the maximum transmittance is more than twice the minimum transmittance in the wavelength range of (λp×0.8) nm to (λp×0.9) nm. Here, in the wavelength range of (λp×0.6) nm to (λp×0.8) nm when the incident angle of infrared light emitted or incident on the optical filter is 0° relative to the infrared optical element, the maximum transmittance of the optical filter is set to T1. In addition, in the wavelength region of (λp×0.6)nm to (λp×0.8)nm when the incident angle of the infrared light emitted from or incident on the infrared optical element is 45°, the maximum transmittance of the optical filter is set to T2. In this case, T2 is greater than T1 (refer to Figure 8 ). Here, in Figure 8 In the λp*(0.6-0.8) nm wavelength range (target range), the wavelength range from (λp×0.6) nm to (λp×0.8) nm is indicated as λp*(0.6-0.8). It is generally known that in optical filters using multilayer films, the transmission spectrum changes depending on the angle of incidence. Therefore, different λp values can be achieved for angles of incidence of 0° and 45°.

[0075] Here, the transmittance varies according to the measurement conditions. Specifically, it varies according to the temperature and the incident angle of light. Unless otherwise specified, the temperature is assumed to be 25°C in the measurement of the transmittance. In addition, the incident angle of light can be, for example, 0°, 10°, 20°, 30°, 40°, 45°, etc., depending on the design of the concentration measuring device. Unless otherwise specified, the above-mentioned characteristics can be satisfied at any incident angle. For example, the optical filter satisfies the above-mentioned characteristics at at least one of the incident angles that can be set in the design (30° as an example). Here, the optical filter further preferably satisfies the above-mentioned characteristics at all incident angles that can be set in the design.

[0076] The optical filter preferably has a transmittance at λp, the center wavelength of the transmission band, of at least 1.1 times the maximum transmittance in the wavelength range of (λp × 0.6) nm to (λp × 0.8) nm. Improving the transmittance in the transmission band can improve the performance of the optical device.

[0077] The maximum transmittance of the optical filter in the wavelength range of (λp×0.4)nm to (λp×0.6)nm is 2% or more, more preferably 25% or more. By satisfying this condition, the film thickness of the optical filter can be further reduced. In addition, the number of times the first and second layers are stacked can be reduced.

[0078] The optical filter preferably has a maximum transmittance of 60% or less and an average transmittance of 40% or less in the wavelength range of (λp×0.6)nm to (λp×0.8)nm. By satisfying these conditions, the thickness of the optical filter can be reduced while maintaining the performance of the optical device.

[0079] The optical filter is preferably a bandpass filter having a half-value width of 1000 nm or less.

[0080] (Substrate)

[0081] The substrate may be any substrate suitable for forming each layer constituting the multilayer film, and examples thereof include, but are not limited to, GaAs substrates, Si substrates, Ge substrates, ZnS substrates, and sapphire substrates.

[0082] (Multilayer Film)

[0083] A multilayer film is a film having multiple layers with different refractive indices. In this embodiment, the multilayer film comprises a structure in which a first layer having a refractive index of 1.2 to 2.5 in the wavelength range of 6 μm to 10 μm and a second layer having a refractive index of 3.2 to 4.3 in the wavelength range of 6 μm to 10 μm are alternately stacked. The first layer is composed of the low refractive index material (L) described above. In addition, the second layer is composed of the high refractive index material (H) described above.

[0084] (First floor)

[0085] Specific materials for the first layer include TiO 2 , ZnS, SiO, and SiO 2 .

[0086] (Second floor)

[0087] Specific materials for the second layer include Si, Ge, and the like.

[0088] (Method for measuring refractive index)

[0089] The refractive index of the first layer and the second layer can be measured using an ellipsometer in accordance with "JIS K7142".

[0090] Here, the sensitivity region of the infrared optical element affects the density of states and the Boltzmann distribution. Figure 3 As described above, by optimizing the bandgap energy, for example, it is possible to realize an infrared optical element that has high sensitivity in the absorption wavelength region unique to the target gas, while having low sensitivity in other wavelength regions. As a result, for example, the cutoff range of 2500 nm to 3500 nm (corresponding to λp × 0.6 to 0.8 for a λp of 4280 nm) becomes less critical, simplifying the design of the optical filter and enabling cost reduction and improved mass production.

[0091] (Method for measuring average transmittance of optical filter)

[0092] The average transmittance of the optical filter is calculated by dividing the numerical integral value of the transmittance in the target wavelength range by the wavelength range (range). The numerical integral value of the transmittance is obtained by using a microscopic FT-IR device (Bruker, Hyperion 3000 + TENSOR 27) in a wave number range of, for example, 500 cm -1 to 4200cm -1 , wave number resolution 8cm -1 The transmission spectrum was obtained under the following conditions: The number of measurement points was 200 points per 1000 nm (= 1 point per 5 nm).

[0093] Here, the material and film thickness of each of the plurality of stacked first layers may be the same or different. In addition, the material and film thickness of each of the plurality of stacked second layers may be the same or different. The multilayer film may further include a layer different from the first layer and the second layer.

[0094] The total film thickness of a multilayer film is the combined thickness of the cutoff surface and the bandpass surface. By reducing the total film thickness, manufacturing time is shortened and the yield rate is improved in optical filter manufacturing. The film thickness can be measured by cross-sectional SEM observation. The total film thickness is preferably 30 μm or less, more preferably 14 μm or less, and even more preferably 10 μm or less. In addition, to ensure the filtering performance of the optical filter, the total film thickness is preferably 3 μm or more, and more preferably 8 μm or more.

[0095] (Infrared optical elements)

[0096] The infrared optical element emits or receives infrared rays, and as described above, may have a first conductive type semiconductor layer, an active layer, and a second conductive type semiconductor layer. Specifically, the infrared optical element may be an infrared light emitting diode (LED) or an infrared photodiode (PD). However, this is not limiting, and the infrared optical element may be an incandescent bulb, a laser, an organic light emitting portion, a PCSEL (photonic crystal surface emitting laser), a MEMS (microelectromechanical system) heater, or a VCSEL (Vertical Cavity Surface Emitting Laser). The infrared optical element may also be a phototransistor, a thermopile, a pyroelectric sensor, or a bolometer.

[0097] The active layer is a light absorbing layer or a light emitting layer (see Figure 5 In this embodiment, the active layer is made of Al y In 1-y Sb (0.04≤y≤0.14) or InAs y Sb 1-y (0.1≤y≤0.2). y In 1-y "Sb (0.04 ≤ y ≤ 0.14)" means that Al, In, and Sb are contained in the layer, but the inclusion of other elements is also included in this expression. Specifically, the addition of other elements in small amounts (for example, elements such as As, P, Ga, and N are reduced to a few percent or less) to slightly change the composition of the layer is also included in this expression. The same applies to the expression of other components.

[0098] Here, the Al composition or the As composition can be determined, for example, by secondary ion mass spectrometry (SIMS). For the measurement, for example, a magnetic field type SIMS apparatus IMS 7f manufactured by CAMECA can be used.

[0099] The second conductivity type is a conductivity type different from the first conductivity type. The first conductivity type and the second conductivity type can be any one of n-type (containing n-type impurities), i-type (containing no impurities) and p-type (containing p-type impurities). The first conductivity type semiconductor layer is, for example, made of n-type InSb (see Figure 5 ) is formed. In addition, the second conductive semiconductor layer is composed of, for example, p-type InSb (refer to Figure 5 In this embodiment, the first conductivity type is n-type and the second conductivity type is p-type.

[0100] The first conductivity-type semiconductor layer, active layer, and second conductivity-type semiconductor layer can be formed on a semiconductor substrate such as a GaAs substrate or a Si substrate. In this embodiment, the infrared optical element is configured such that the layers are arranged in the order from the substrate: the first conductivity-type semiconductor layer, the active layer, and the second conductivity-type semiconductor layer. As another example, the infrared optical element can be configured such that the layers are arranged in the order from the substrate: the second conductivity-type semiconductor layer, the active layer, and the first conductivity-type semiconductor layer.

[0101] One or more barrier layers may be provided between the first conductive semiconductor layer and the active layer. In addition, one or more barrier layers may be provided between the active layer and the second conductive semiconductor layer. In this embodiment, an n-type barrier layer is provided between the first conductive semiconductor layer and the active layer, and a p-type barrier layer is provided between the active layer and the second conductive semiconductor layer. The n-type barrier layer is, for example, made of n-type Al x In 1-x Sb (0.15≤x≤0.35) composition (refer to Figure 5 ). The p-type barrier layer is made of p-type Al z In 1-z Sb (0.15≤z≤0.35) composition (refer to Figure 5 ).

[0102] In this embodiment, the infrared optical element has a peak sensitivity with the highest sensitivity, and the average sensitivity in the wavelength region of (λp×0.6)nm to (λp×0.8)nm is less than 70% of the peak sensitivity. An optical device having such an infrared optical element and the simplified optical filter described above can selectively receive or emit only infrared rays of a desired wavelength band, is compact, and can perform high-precision concentration measurement. Here, it is preferred that the average sensitivity of the infrared optical element in the wavelength region of (λp×0.6)nm to (λp×0.8)nm is less than 30% of the peak sensitivity. Here, in the wavelength region of (λp×0.6)nm to (λp×0.8)nm when the incident angle of the infrared ray emitted or incident relative to the infrared optical element to the optical filter is 0°, the average sensitivity of the infrared optical element is set to S1. In addition, in the wavelength region of (λp×0.6)nm to (λp×0.8)nm when the incident angle of the infrared light emitted from or incident on the optical filter is 45° relative to the infrared optical element, the average sensitivity of the infrared optical element is set to S2. In this case, it is preferable that S2 is smaller than S1 (refer to Figure 8 ).

[0103] (Example)

[0104] Hereinafter, the effects of the present disclosure will be described in detail based on examples, but the present disclosure is not limited to these examples.

[0105] Examples 1 to 6 and Comparative Examples 1 to 3 shown in Table 1 were evaluated. Examples 1 to 6 are optical devices of this embodiment, and their characteristics were determined as shown in Table 1. Comparative Examples 1 to 3 are single filters without simplification. The active layers of the optical devices of Examples 1 to 4 and 6 are made of Al y In 1-y In Example 1, y is 0.048, in Example 2, y is 0.057, in Example 3, y is 0.089, in Example 4, y is 0.089, and in Example 6, y is 0.057. The active layer of the optical device of Example 5 is composed of InAs. y Sb 1-y Composition, y is 0.13.

[0106]

Table 1

[0107]

[0108] The PIN diode structures of the infrared optical elements of Examples 1 to 6 were produced by the MBE method. Figure 5This is a diagram showing the stacked structure of each layer of the infrared optical element of Examples 1 to 6. N-type and p-type barrier layers are provided in a manner that sandwiches the active layer. A positive photoresist for i-line is applied to the surface of the semiconductor wafer, and exposure is performed using i-line using a reduced projection exposure machine. Next, development is performed to regularly form a plurality of resist patterns on the surface of the semiconductor stack. Next, a plurality of mesas are formed by dry etching. After SiO2 is formed as a hard mask on the element having the mesa shape, the element is separated by dry etching, SiN is formed as a protective film, and contact holes are formed by photolithography and dry etching. Thereafter, the plurality of mesas are connected in series by photolithography and sputtering, and the surface of the element is covered with polyimide resin as a protective film. The wafer thus produced is cut into pieces, Au wires are bonded and connected to the lead frame, and then sealed with an epoxy molding resin in such a way that the light-receiving surface is exposed. The infrared light receiving element manufactured in this manner has sensitivity to infrared rays near λp, but the sensitivity is 70% or less of the peak sensitivity in the wavelength band of (λp×0.6) nm to (λp×0.8) nm.

[0109] The design of the optical filter is implemented using simulation. The optical filters of Examples 1 to 6 are simplified optical filters, all of which contain a transmission band of more than 50 nm in the wavelength range of 2500 nm to 10000 nm, and the transmittance of this transmission band exceeds 70%. As shown in Table 1, the ratio of (a) / (b) of the optical filters of Examples 1 to 6 is more than 2 times. Here, (a) is the maximum transmittance in the wavelength range of (λp×0.6) nm to (λp×0.8) nm. In the numerical value shown as (a), the case of 0° is T1, and the case of 45° is T2. In the optical filters of Examples 1 to 6, (a) is more than 2%, and T2 is greater than T1. In addition, (b) is the minimum transmittance in the wavelength range of (λp×0.8) nm to (λp×0.9) nm. Furthermore, in the infrared optical elements of Examples 1 to 6, the average sensitivity in the wavelength range of (λp × 0.6) nm to (λp × 0.8) nm was 70% or less of the peak sensitivity. Furthermore, in the infrared optical elements of Examples 1 to 6, the average sensitivity S2 at 45° incidence was less than the average sensitivity S1 at 0° incidence, among the average sensitivities in the wavelength range of (λp × 0.6) nm to (λp × 0.8) nm.

[0110] As shown in Table 1, the ratio of (c) / (a) of the optical filters of Examples 1 to 6 is 1.1 times or more. Here, (c) is the transmittance at λp. In addition, in the optical filters of Examples 1, 5, and 6, the maximum transmittance in the wavelength region of (λp×0.4)nm to (λp×0.6)nm is 2% or more. Here, as mentioned above, the incident angle of light can vary depending on the design of the concentration measuring device, etc., but it is sufficient as long as the characteristics are satisfied at at least one incident angle. In Example 1, the maximum transmittance in the wavelength region of (λp×0.4)nm to (λp×0.6)nm is 2% or more at least at an incident angle of 0°. The same judgment was made as to whether the above-mentioned (a) satisfies 2% or more. In addition, in the optical filters of Examples 1 to 6, the maximum transmittance in the wavelength region of (λp×0.6)nm to (λp×0.8)nm is 60% or less, and the average transmittance is 40% or less. Furthermore, the optical filters of Examples 1 to 6 are bandpass filters having a half-value width of 1000 nm or less.

[0111] On the other hand, in Comparative Examples 1 to 3, (a) was less than 2%.

[0112] Figure 6A and Figure 6B This is an example ( Figure 6B ) and the comparative example ( Figure 6A ) are compared. The vertical axis is the transmittance, and the horizontal axis is the wavelength of infrared light. The graph of the embodiment shows the graph of Example 1 as a representative, but the same tendency was obtained in Examples 1 to 6. In addition, the graph of the comparative example shows the graph of Comparative Example 1 as a representative, but the same tendency was obtained in Comparative Examples 1 to 3. In addition, the graphs show the transmittance at multiple incident angles (0°, 10°, 20°, 30°, 40°, 45°) in an overlapping manner. As Figure 6B As shown in the graph of the examples, the maximum transmittance in the wavelength range of (λp×0.6) nm to (λp×0.8) nm may exceed 2%, and the cutoff characteristics in this wavelength range may be relaxed.

[0113] Figure 7 This is a graph comparing the sensitivity of the embodiment and the comparative example. The vertical axis is the sensitivity, and the horizontal axis is the wavelength of infrared light. The graph of the embodiment shows the graph of embodiment 1 as a representative, but the same tendency was obtained in embodiments 1 to 6. In addition, the graph of the comparative example shows the graph of comparative example 1 (used in combination with an infrared optical element) as a representative, but the same tendency was obtained in comparative examples 1 to 3. Figure 2 ), if Figure 7As shown, the optical device according to this embodiment achieves performance equivalent to that of the comparative example using an unsimplified optical filter. In other words, it was confirmed that even with the simplified optical filter, the optical device according to this embodiment does not degrade in accuracy. Regarding the comparative example, an optical device was constructed by combining the optical filter of the comparative example with an infrared optical element, and this optical device was used to construct a concentration measurement device.

[0114] As described above, the optical device according to this embodiment is compact due to the simplification of the optical filter, and can achieve light emission and reception of light of a desired wavelength, and can be used in gas concentration measurement devices and the like to perform high-precision concentration measurement. The optical filter according to this embodiment is used in an optical device capable of high-precision concentration measurement.

[0115] Although the embodiments of the present disclosure have been described based on the drawings and embodiments, it should be noted that those skilled in the art can easily make various variations or modifications based on the present disclosure. Therefore, it should be noted that these variations or modifications are included within the scope of the present disclosure.

Claims

1. An optical device, wherein: The optical device comprises: An optical filter comprising a substrate and a multilayer film, wherein the multilayer film is formed on at least one surface of the substrate and comprises a plurality of layers having different refractive indices; and Infrared optical elements, emitting or receiving infrared rays, The optical filter includes a transmission band of 50 nm or more in a wavelength range of 2500 nm to 10000 nm, the transmittance of the transmission band exceeds 70%, the center wavelength of the transmission band is λp, the maximum transmittance in the wavelength range of (λp×0.6) nm to (λp×0.8) nm is 2% or more, and the maximum transmittance is more than twice the minimum transmittance in the wavelength range of (λp×0.8) nm to (λp×0.9) nm. The infrared optical element has a peak sensitivity at which sensitivity is the highest, and an average sensitivity in a wavelength range of (λp×0.6) nm to (λp×0.8) nm is 70% or less of the peak sensitivity. If the maximum transmittance of the optical filter is set to T1 and the average sensitivity of the infrared optical element is set to S1 in the wavelength region of (λp×0.6)nm to (λp×0.8)nm when the incident angle of the infrared ray emitted or incident on the optical filter is 0° relative to the infrared optical element, and the maximum transmittance of the optical filter is set to T2 and the average sensitivity of the infrared optical element is set to S2 in the wavelength region of (λp×0.6)nm to (λp×0.8)nm when the incident angle of the infrared ray emitted or incident on the optical filter is 45° relative to the infrared optical element, then T2 is greater than T1 and S2 is smaller than S1.

2. An optical device, wherein: The optical device comprises: An optical filter comprising a substrate and a multilayer film, wherein the multilayer film is formed on at least one surface of the substrate and comprises a plurality of layers having different refractive indices; and Infrared optical elements, emitting or receiving infrared rays, The optical filter includes a transmission band of 50 nm or more in a wavelength range of 2500 nm to 10000 nm, the transmittance of the transmission band exceeds 70%, the center wavelength of the transmission band is λp, the maximum transmittance in the wavelength range of (λp×0.6) nm to (λp×0.8) nm is more than twice the minimum transmittance in the wavelength range of (λp×0.8) nm to (λp×0.9) nm, and the maximum transmittance in the wavelength range of (λp×0.4) nm to (λp×0.6) nm is more than 2%. The infrared optical element has a peak sensitivity at which sensitivity is the highest, and an average sensitivity in a wavelength range of (λp×0.6) nm to (λp×0.8) nm is 70% or less of the peak sensitivity. If the maximum transmittance of the optical filter is set to T1 and the average sensitivity of the infrared optical element is set to S1 in the wavelength region of (λp×0.6)nm to (λp×0.8)nm when the incident angle of the infrared ray emitted or incident on the optical filter is 0° relative to the infrared optical element, and the maximum transmittance of the optical filter is set to T2 and the average sensitivity of the infrared optical element is set to S2 in the wavelength region of (λp×0.6)nm to (λp×0.8)nm when the incident angle of the infrared ray emitted or incident on the optical filter is 45° relative to the infrared optical element, then T2 is greater than T1 and S2 is smaller than S1.

3. The optical device according to claim 1, wherein The transmittance of the optical filter at λp, which is the center wavelength of the transmission wavelength band, is 1.1 times or more the maximum transmittance in a wavelength region of (λp×0.6) nm to (λp×0.8) nm.

4. The optical device according to claim 1 or 2, wherein: The optical filter has a maximum transmittance of 2% or more in a wavelength region of (λp×0.4) nm to (λp×0.6) nm.

5. The optical device according to claim 1 or 2, wherein: The optical filter has a maximum transmittance of 60% or less and an average transmittance of 40% or less in a wavelength range of (λp×0.6) nm to (λp×0.8) nm.

6. The optical device according to claim 1 or 2, wherein: The optical filter is a bandpass filter having a half-value width of 1000 nm or less.

7. The optical device according to claim 1 or 2, wherein: The infrared optical element is an infrared light emitting element that emits infrared light, and an average sensitivity in a wavelength range of (λp×0.6) nm to (λp×0.8) nm is 30% or less of the peak sensitivity.

8. The optical device according to claim 1 or 2, wherein: The total film thickness of the multilayer film is 30 μm or less.

9. The optical device according to claim 1 or 2, wherein: The infrared optical element includes a first conductive type semiconductor layer, an active layer, and a second conductive type semiconductor layer.

10. The optical device according to claim 1 or 2, wherein: The infrared optical element is an infrared light emitting element.

11. The optical device according to claim 1 or 2, wherein: The T2 is greater than the T1 by more than 1%.

12. The optical device according to claim 8, wherein The maximum transmittance in the wavelength region of (λp×0.4) nm to (λp×0.6) nm is 25% or more.

13. An optical filter used in the optical device according to claim 1 or 2.

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