Optical device and optical filter

Abstract

To provide an optical device and an optical filter which are small and allow high-accuracy density measurement.SOLUTION: The optical device comprises an optical filter and an infrared optical element. The center wavelength of transmission band is denoted by λp. In a wavelength region from (λp×0.6) nm to (λp×0.8) nm when an incident angle at which infrared emitted from or incident to the infrared optical element enters the optical filter is 0°, maximum transmittance of the optical filter is denoted by T1 and average sensitivity of the infrared optical element is denoted by S1; and in a wavelength region from (λp×0.6) nm to (λp×0.8) nm when an incident angle at which infrared emitted from or incident to the infrared optical element enters the optical filter is 45°, the maximum transmittance of the optical filter is denoted by T2 and the average sensitivity of the infrared optical element is denoted by S2. In this case, T2 is greater than T1 and S2 is smaller than S1.SELECTED DRAWING: Figure 8

Description

[Technical Field]

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

[0002] Conventionally, non-dispersive infrared absorption (NDIR) gas concentration measurement devices have been known as gas concentration measurement devices for measuring the concentration of a target gas in the atmosphere. Non-dispersive infrared absorption gas concentration measurement devices utilize the fact that different types of gas absorb different wavelengths of infrared light, and measure the gas concentration by detecting the amount of absorption. Non-dispersive infrared absorption gas concentration measurement devices are configured with an infrared optical element and a filter (transmitting member) that transmits infrared light limited to wavelengths that the target gas has absorption characteristics. For example, Patent Document 1 discloses a measurement device in which carbon dioxide gas is used as the target gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-33431 Summary of the Invention [Problem to be solved by the invention]

[0004] The gas to be measured is not limited to carbon dioxide, but can be varied. The optimal combination of infrared optical element and optical filter for each target gas has not yet been explored. In particular, the optical filter specifications have not been optimized, taking into account the effect of the angle of incidence.

[0005] In view of the above circumstances, an object of the present disclosure is to provide an optical device and an optical filter that are small and enable high-precision concentration measurement. Here, the optical device is a device that includes an infrared optical element and an optical filter and is used in gas concentration measurement devices and the like. [Means for solving the problem]

[0006] (1) An optical device according to an embodiment of the present disclosure includes: an optical filter including a substrate and a multilayer film having a plurality of layers with different refractive indices formed on at least one surface of the substrate; an infrared optical element that emits or receives infrared light, the optical filter includes a transmission band of 50 nm or more in a wavelength range of 2500 nm to 10000 nm, the transmission band having a transmittance of more than 70%, and the maximum transmittance in a wavelength range of (λp×0.6) nm to (λp×0.8) nm is 2% or more, where λp is the center wavelength of the transmission band, and the maximum transmittance is at least twice as large as the minimum transmittance in a wavelength range of (λp×0.8) nm to (λp×0.9) nm, the infrared optical element has a peak sensitivity at which sensitivity is maximum, and an average sensitivity in a wavelength range from (λp×0.6) nm to (λp×0.8) nm is 70% or less of the peak sensitivity; When the incident angle of the infrared ray emitted from or incident on the infrared optical element to the optical filter is 0°, the maximum transmittance of the optical filter is T1 and the average sensitivity of the infrared optical element is S1 in the wavelength range of (λp×0.6) nm to (λp×0.8) nm; when the incident angle of the infrared ray emitted from or incident on the infrared optical element to the optical filter is 45°, the maximum transmittance of the optical filter is T2 and the average sensitivity of the infrared optical element is S2; T2 is greater than T1 and S2 is smaller than S1.

[0007] (2) An optical device according to an embodiment of the present disclosure includes: an optical filter including a substrate and a multilayer film having a plurality of layers with different refractive indices formed on at least one surface of the substrate; an infrared optical element that emits or receives infrared light, the optical filter includes a transmission band of 50 nm or more with a transmittance of more than 70% in a wavelength range of 2500 nm to 10000 nm, and, where λp is the center wavelength of the transmission band, the maximum transmittance in the wavelength range of (λp×0.6) nm to (λp×0.8) nm is at least two times greater than the minimum transmittance in the wavelength range of (λp×0.8) nm to (λp×0.9) nm, and further the maximum transmittance in the wavelength range of (λp×0.4) nm to (λp×0.6) nm is 2% or more; the infrared optical element has a peak sensitivity at which sensitivity is maximum, and an average sensitivity in a wavelength range from (λp×0.6) nm to (λp×0.8) nm is 70% or less of the peak sensitivity; When the incident angle of the infrared ray emitted from or incident on the infrared optical element to the optical filter is 0°, the maximum transmittance of the optical filter is T1 and the average sensitivity of the infrared optical element is S1 in the wavelength range of (λp×0.6) nm to (λp×0.8) nm; when the incident angle of the infrared ray emitted from or incident on the infrared optical element to the optical filter is 45°, the maximum transmittance of the optical filter is T2 and the average sensitivity of the infrared optical element is S2; T2 is greater than T1 and S2 is smaller than S1.

[0008] (3) As an embodiment of the present disclosure, in (1) or (2), The optical filter has a transmittance at λp, which is the center wavelength of the transmission band, that is 1.1 times or more the maximum transmittance in the wavelength range from (λp×0.6) nm to (λp×0.8) nm.

[0009] (4) As an embodiment of the present disclosure, in any one of (1) to (3), The optical filter has a maximum transmittance of 2% or more in the wavelength range from (λp×0.4) nm to (λp×0.6) nm.

[0010] (5) As an embodiment of the present disclosure, in any one of (1) to (4), The optical filter has a maximum transmittance of 60% or less and an average transmittance of 40% or less in the wavelength range from (λp×0.6) nm to (λp×0.8) nm.

[0011] (6) As an embodiment of the present disclosure, in any one of (1) to (5), The optical filter is a bandpass filter with a half-width of 1000 nm or less.

[0012] (7) As an embodiment of the present disclosure, in any one of (1) to (6), The infrared optical element is an infrared light emitting element that emits infrared light, and has an average sensitivity in the wavelength range of (λp×0.6) nm to (λp×0.8) nm that is 30% or less of the peak sensitivity.

[0013] (8) As an embodiment of the present disclosure, in any one of (1) to (7), The total thickness of the multilayer film is 30 μm or less.

[0014] (9) As an embodiment of the present disclosure, in (1) or (2), The infrared optical element includes a first conductive type semiconductor layer, an active layer, and a second conductive type semiconductor layer.

[0015] (10) As an embodiment of the present disclosure, in (1) or (2), The infrared optical element is an infrared light emitting element.

[0016] (11) As an embodiment of the present disclosure, in (1) or (2), The T2 is greater than the T1 by 1% or more.

[0017] (12) As an embodiment of the present disclosure, in (8), The maximum transmittance in the wavelength range from (λp×0.4) nm to (λp×0.6) nm is 25% or more.

[0018] (13) An optical filter according to an embodiment of the present disclosure includes: Used in optical devices (1) or (2). [Effects of the Invention]

[0019] According to the present disclosure, it is possible to provide a small-sized optical device and an optical filter that enable highly accurate concentration measurement even in the case of oblique incidence, which is highly affected by leaked light. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram showing an example of a cross section of an optical filter. [Figure 2] FIG. 2 is a diagram illustrating an example of a concentration measurement apparatus including an optical device according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a diagram 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. [Figure 4] FIG. 4 is a diagram showing the difference between an optical filter according to a comparative example and the optical filter of the present disclosure. [Figure 5] FIG. 5 is a diagram showing the laminate structure of each layer of the infrared optical elements according to Examples 1 to 6. As shown in FIG. [Figure 6A] FIG. 6A is a diagram for comparing the transmittance of the example and the comparative example. [Figure 6B] FIG. 6B is a diagram for comparing the transmittance of the example and the comparative example. [Figure 7] FIG. 7 is a diagram comparing the sensitivity of the example and the comparative example. [Figure 8] FIG. 8 is a diagram comparing the characteristics at normal incidence (incident angle of 0°) and at 45 degrees incidence (incident angle of 45°). DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an optical device and an optical filter according to an embodiment of the present disclosure will be described with reference to the drawings.

[0022] (Optical Devices) The optical device according to this embodiment includes an optical filter and an infrared optical element. The optical filter includes a substrate and a multilayer film having multiple layers with different refractive indices formed on at least one surface of the substrate. The infrared optical element is a collective term for an infrared light receiving element or an infrared light emitting element. Hereinafter, "light receiving and emitting" refers to having at least one of the functions of receiving and emitting light. The infrared optical element includes a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer, and receives and emits infrared light. That is, the optical device according to this embodiment is an infrared device. An infrared light emitting element can be realized with the structure described below (see FIG. 5), and an infrared light receiving element can be realized with the same structure. The infrared light emitting element may be, for example, a light emitting diode (LED), an incandescent lamp, a laser, an organic light emitting element, a VCSEL, a PCSEL, or a MEMS heater. The infrared light emitting element is preferably a light emitting diode (LED) from the viewpoint of wavelength selectivity. The infrared light receiving element may be, for example, a photodiode (PD), a phototransistor, a thermopile, a current collecting sensor, or a bolometer. The infrared receiving element is preferably a photodiode (PD) from the viewpoint of wavelength selectivity.

[0023] Hereinafter, the optical device according to this embodiment will be described as being used in a concentration measurement device. In this embodiment, the concentration measurement device is a gas sensor that measures the concentration of a gas to be measured. The concentration measurement device may be, for example, a non-dispersive infrared (NDIR) gas sensor equipped with a light receiving unit that receives infrared light transmitted through the gas. Alternatively, the concentration measurement device may be, for example, a photoacoustic gas sensor that measures gas concentration by picking up the vibrations of gas molecules that absorb light as sound using a high-performance microphone. Here, the optical device according to this embodiment is not limited to a concentration measurement device, and may also be used in an infrared radiation thermometer, infrared spectroscopic imaging, or a human body detection sensor.

[0024] As will be described in detail later, the optical filter includes a transmission band of 50 nm or more with a transmittance of over 70% in the wavelength range of 2500 nm to 10000 nm. Furthermore, the optical filter has a maximum transmittance of 2% or more in the wavelength range of (λp × 0.6) nm to (λp × 0.8) nm, where λp is the center wavelength of the transmission band. Furthermore, the optical filter has a maximum transmittance that is at least twice as large as the minimum transmittance in the wavelength range of (λp × 0.8) nm to (λp × 0.9) nm. Here, the center wavelength is the wavelength in the wavelength range of 2500 nm to 10000 nm that is the center of the half-width of the transmission band having the maximum transmittance. Furthermore, the half-width is the wavelength range where the transmittance is half of the maximum transmittance (i.e., the difference between the maximum wavelength and the minimum wavelength).

[0025] As will be described in detail later, the infrared optical element has a peak sensitivity where sensitivity is at its maximum, and its average sensitivity in the wavelength range from (λp × 0.6) nm to (λp × 0.8) nm is 70% or less of the peak sensitivity. Here, when the incident angle of infrared light emitted from or incident on the infrared optical element to the optical filter is 0°, the maximum transmittance of the optical filter in the wavelength range from (λp × 0.6) nm to (λp × 0.8) nm is defined as T1, and the average sensitivity of the infrared optical element is defined as S1. Furthermore, when the incident angle of infrared light emitted from or incident on the infrared optical element to the optical filter is 45°, the maximum transmittance of the optical filter in the wavelength range from (λp × 0.6) nm to (λp × 0.8) nm is defined as T2, and the average sensitivity of the infrared optical element is defined as S2. Here, T2 is greater than T1, and S2 is less than S1.

[0026] According to the optical device of this embodiment, even when a simplified optical filter is used, it is possible to selectively receive or emit only infrared light in a desired wavelength band. By using a simplified optical filter, the optical device of this embodiment can be made smaller. Furthermore, because it is possible to receive and emit infrared light in a desired wavelength band, the optical device of this embodiment enables highly accurate concentration measurement.

[0027] FIG. 1 shows an example of a cross section of an optical filter. In this embodiment, the optical filter is formed by alternately laminating layers of low-refractive-index materials (L) made of SiO, SiO2, TiO2, ZnS, Al2O3, or the like and layers of high-refractive-index materials (H) made of Si, Ge, or the like on both sides of a Si substrate. A material having a refractive index of 1.2 to 2.5 is preferably selected as the low-refractive-index material (L). Furthermore, a material having a refractive index 0.5 or more higher than that of the low-refractive-index material (L) is preferably selected as the high-refractive-index material (H). The alternately laminated multilayer film is formed such that the layer directly disposed on the Si substrate is the high-refractive-index material (H). However, the optical filter is not limited to the configuration shown in FIG. 1. For example, the high-refractive-index material (H) does not have to be disposed directly on the substrate.

[0028] In this embodiment, the optical filter is a mid-infrared interference bandpass filter. In general, mid-infrared interference bandpass filters have a large number of layers, which makes it easy for defects to increase during film formation. Furthermore, if the optical filter has a large number of layers, it becomes difficult to miniaturize the concentration measuring device. Therefore, it is preferable to have a small number of layers in the optical filter. However, simply reducing the number of layers in the optical filter to simplify the device may result in a deterioration in the accuracy of the gas sensor.

[0029] Furthermore, in order to realize a highly accurate concentration measurement device, it is necessary to reduce the influence of infrared absorption by gases other than the gas to be detected.

[0030] Furthermore, in order to realize a highly accurate concentration measuring device, it is necessary to reduce the influence of leakage light when infrared light is incident on the optical filter at an angle.

[0031] The inventors have studied the optimum combination of infrared optical elements and optical filters, and as a result have realized an optical device in which accuracy does not deteriorate even when a simplified optical filter is used, as will be described below.

[0032] Here, a simplified optical filter is an optical filter that does not block areas where the sensor is not sensitive, thereby reducing the number of optical thin film layers required to block those areas. Using a simplified optical filter with fewer layers can be expected to improve mass productivity. Furthermore, reducing the number of layers can reduce defects during film formation, which can result in improved yield. Furthermore, reducing warpage caused by multiple layers suppresses chipping during dicing, thereby improving mass production stability.

[0033] Fig. 2 is a diagram showing an example of a concentration measurement apparatus using the optical device according to this embodiment. In the optical device according to this embodiment, as shown in Fig. 2, an infrared receiving element (IR) is installed in the optical path of infrared light output from an infrared light emitting element (light source), and an optical filter that selectively transmits the absorption wavelength of the gas to be detected is installed in front of the infrared receiving element. The optical device corresponds to, for example, the optical filter and the infrared receiving element.

[0034] Here, the measurement target gas of the concentration measuring device is, for example, carbon dioxide, but is not limited to this. For example, the measurement target gas may be a combustible gas such as breath alcohol (ethanol, etc.), methane, propane, hydrogen, ethylene, or MCH (methylcyclohexane). The measurement target gas may also be a toxic gas such as carbon monoxide, hydrogen sulfide, formaldehyde, or ammonia. Furthermore, the measurement target gas may be a greenhouse gas such as nitrous oxide or a refrigerant gas used in air conditioners or refrigerators. In addition, the measurement target gas may be a mixed gas in which the above-mentioned measurement target gases are mixed.

[0035] FIG. 3 is a diagram illustrating a comparison between the optical filter of the optical device according to this embodiment and an optical filter according to a comparative example. The sensor (infrared receiving element) in the comparative example does not have wavelength selectivity (sensitivity change due to wavelength) in its spectral sensitivity. On the other hand, the sensor included in the optical device according to this embodiment (or included in a concentration measuring device using the optical device according to this embodiment) has wavelength selectivity. Therefore, in this embodiment, the optical filter does not need to cut wavelengths for which the optical filter is insensitive, and the optical filter can be simplified. Similarly, in the case of an infrared light-emitting element having wavelength selectivity in its emission intensity, the optical filter does not need to cut wavelengths for which no light is emitted, and the optical filter can be simplified. Here, FIG. 3 shows the above-mentioned wavelengths for which no sensitivity and no light are emitted both on the longer wavelength side (high wavelength side) and the shorter wavelength side (short wavelength side) of the peak wavelength, but this is a conceptual example. In this embodiment, the cut specification of the optical filter is relaxed on the shorter wavelength side.

[0036] 4 is a diagram showing the difference between an optical filter according to a comparative example and the optical filter of the present disclosure. In the optical filter of the optical device according to this embodiment, the film thickness of the multilayer film called the cut surface, which determines the cut characteristics, can be significantly reduced. For example, when the multilayer film is formed on both sides of the substrate, the ratio of the total film thickness on each surface can be set to a range of 0.5 to 2.0.

[0037] The components of the optical device according to this embodiment will be 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 emission intensity of the infrared light emitting element will be described as "sensitivity." That is, if the optical device includes an infrared light receiving element, sensitivity can be interpreted as light receiving sensitivity, and if the optical device includes an infrared light emitting element, sensitivity can be interpreted as light emission intensity.

[0038] (optical filter) As described above, the optical filter includes a substrate and a multilayer film formed on the substrate and having multiple layers with different refractive indices. The multilayer film may be formed on only one surface of the substrate, or may be formed on both surfaces. In a concentration measuring device, the optical filter is installed in an optical path through which infrared rays emitted from an infrared light emitting element reach an 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. The optical filter may also be installed at a predetermined location in the optical path. In a concentration measuring device, multiple optical filters may be installed. The optical filter can be produced by depositing a first layer and a second layer on a substrate by vapor deposition.

[0039] The optical filter of this embodiment includes a 50 nm or more transmission band with a transmittance exceeding 70% in the wavelength range of 2500 nm to 10000 nm. Furthermore, the optical filter has a maximum transmittance of 2% or more in the wavelength range of (λp × 0.6) nm to (λp × 0.8) nm, where λp is the center wavelength of the transmission band. Furthermore, the maximum transmittance of the optical filter is at least twice as large as the minimum transmittance in the wavelength range of (λp × 0.8) nm to (λp × 0.9) nm. Here, T1 denotes the maximum transmittance of the optical filter in the wavelength range 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 to the optical filter is 0°. Furthermore, T2 denotes the maximum transmittance of the optical filter in the wavelength range 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 to the optical filter is 45°. In this case, T2 is greater than T1 (see Figure 8). In Figure 8, the wavelength range (target range) from (λp × 0.6) nm to (λp × 0.8) nm is expressed as λp * (0.6-0.8). It is generally known that the transmission spectrum of optical filters using multilayer films changes depending on the angle of incidence. Therefore, the value of λp can be different when the angle of incidence is 0° and when it is 45°.

[0040] Here, transmittance varies depending on the measurement conditions. Specifically, it varies depending on the temperature and the angle of incidence of light. Unless otherwise specified, the temperature in the transmittance measurements is 25°C. The angle of incidence of light can be, for example, 0°, 10°, 20°, 30°, 40°, or 45° depending on the design of the concentration measurement device. Unless otherwise specified, it is sufficient that the above characteristics are satisfied at any angle of incidence. For example, an optical filter is sufficient to satisfy the above characteristics at at least one of the angles of incidence that can be set in the design (e.g., 30°). Here, it is more preferable that the optical filter satisfy the above characteristics at all angles of incidence that can be set in the design.

[0041] The optical filter preferably has a transmittance at λp, the center wavelength of the transmission band, that is 1.1 times or more the maximum transmittance in the wavelength range from (λp×0.6) nm to (λp×0.8) nm. Increasing the transmittance in the transmission band can improve the performance of optical devices.

[0042] The optical filter has a maximum transmittance of 2% or more, preferably 25% or more, in the wavelength range of (λp×0.4) nm to (λp×0.6) nm. By satisfying this requirement, the film thickness of the optical filter can be further reduced. In addition, the number of times the first layer and the second layer are laminated can be reduced.

[0043] 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 requirements, the film thickness of the optical filter can be reduced while maintaining the performance of the optical device.

[0044] The optical filter is preferably a bandpass filter with a half-width of 1000 nm or less.

[0045] (substrate) The substrate may be any suitable substrate as long as it is 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.

[0046] (Multilayer film) The multilayer film is a film having multiple layers with different refractive indices. In this embodiment, the multilayer film has a structure in which first layers having a refractive index of 1.2 or more and 2.5 or less in the wavelength range of 6 μm to 10 μm and second layers having a refractive index of 3.2 or more and 4.3 or less in the wavelength range of 6 μm to 10 μm are alternately stacked. The first layers are made of the low refractive index material (L) described above. The second layers are made of the high refractive index material (H) described above.

[0047] (1st layer) Specific materials for the first layer include TiO2, ZnS, SiO, and SiO2.

[0048] (2nd layer) Specific examples of the material for the second layer include Si and Ge.

[0049] (Method for measuring refractive index) The refractive index of the first layer and the second layer can be measured by an ellipsometer in accordance with "JIS K7142".

[0050] Here, the sensitivity range of an infrared optical element affects the density of states and the Boltzmann distribution. As explained with reference to Figure 3, for example, by optimally designing the band gap energy, it is possible to realize an infrared optical element that has high sensitivity in a specific absorption wavelength range corresponding to the gas to be detected and low sensitivity in other wavelength ranges. As a result, for example, cutting off the wavelength range of 2500 nm to 3500 nm (corresponding to λp × 0.6 to 0.8 when λp is 4280 nm) becomes less important, simplifying the design of the optical filter, thereby achieving cost reduction and improving mass productivity.

[0051] (Method for measuring the average transmittance of optical filters) The average transmittance of an 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 calculated using a micro FT-IR instrument (Hyperion 3000 + TENSOR 27 manufactured by Bruker) for a wavenumber range of, for example, 500 cm-1 From 4200cm -1 , wave number resolution 8cm -1 The number of measurement points is 200 per 1000 nm (= 1 per 5 nm).

[0052] Here, the materials and thicknesses of the first layers may be the same or different, and the materials and thicknesses of the second layers may be the same or different. The multilayer film may further include a layer different from the first and second layers.

[0053] The total thickness of the multilayer film is the sum of the thicknesses of the cut surface and the bandpass surface. By reducing the total thickness, the manufacturing time is shortened and the yield is improved in the manufacture of optical filters. 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. Furthermore, to ensure the filter performance of the optical filter, the total film thickness is preferably 3 μm or more, and more preferably 8 μm or more.

[0054] (infrared optical element) The infrared optical element emits or receives infrared light and may have a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer as described above. Specifically, the infrared optical element may be an infrared light emitting diode (LED) or an infrared photodiode (PD). However, without being limited thereto, the infrared optical element may be an incandescent lamp, a laser, an organic light emitting unit, a PCSEL, a MEMS heater, a VCSEL (Vertical Cavity Surface Emitting Laser), or the like. The infrared optical element may be a phototransistor, a thermopile, a pyroelectric sensor, a bolometer, or the like.

[0055] The active layer is a light absorbing layer or a light emitting layer (see FIG. 5). In this embodiment, the active layer is Al y In 1-y Sb(0.04≦y≦0.14) or InAs y Sb1-y (0.1≦y≦0.2) y In 1-y "Sb (0.04≦y≦0.14)" means that the layer contains Al, In, and Sb, but this expression also includes cases where other elements are contained. Specifically, this expression also includes cases where the composition of this layer is slightly changed by adding small amounts of other elements (for example, elements such as As, P, Ga, N, etc., in amounts of a few percent or less). This also applies to expressions of other compositions.

[0056] The Al composition or As composition can be determined by, for example, secondary ion mass spectrometry (SIMS), using, for example, a magnetic field type SIMS device IMS 7f manufactured by CAMECA Corporation.

[0057] The second conductivity type is a conductivity type different from the first conductivity type. The first conductivity type and the second conductivity type may be n-type (containing n-type impurities), i-type (containing no impurities), or p-type (containing p-type impurities), respectively. The first conductivity type semiconductor layer is made of, for example, n-type InSb (see FIG. 5). The second conductivity type semiconductor layer is made of, for example, p-type InSb (see FIG. 5). In this embodiment, the first conductivity type is n-type, and the second conductivity type is p-type.

[0058] The first conductivity type semiconductor layer, the active layer, and the second conductivity type semiconductor layer may be formed on a semiconductor substrate such as a GaAs substrate or a Si substrate. In this embodiment, the infrared optical element is provided with the first conductivity type semiconductor layer, the active layer, and the second conductivity type semiconductor layer in this order from the substrate. As another example, the infrared optical element is provided with the second conductivity type semiconductor layer, the active layer, and the first conductivity type semiconductor layer in this order from the substrate.

[0059] One or more barrier layers may be provided between the first conductivity type semiconductor layer and the active layer. Also, one or more barrier layers may be provided between the active layer and the second conductivity type semiconductor layer. In this embodiment, an n-type barrier layer is provided between the first conductivity type semiconductor layer and the active layer, and a p-type barrier layer is provided between the active layer and the second conductivity type semiconductor layer. The n-type barrier layer is, for example, n-type Al x In 1-x The p-type barrier layer is made of Sb (0.15≦x≦0.35) (see Figure 5). z In 1-z It is composed of Sb (0.15≦z≦0.35) (see Figure 5).

[0060] In this embodiment, the infrared optical element has a peak sensitivity where sensitivity is at its maximum, and its average sensitivity in the wavelength range from (λp × 0.6) nm to (λp × 0.8) nm is 70% or less of the peak sensitivity. An optical device including such an infrared optical element and the simplified optical filter described above can selectively receive or emit only infrared light in a desired wavelength band, enabling compact, high-precision concentration measurement. Here, it is preferable that the average sensitivity of the infrared optical element in the wavelength range from (λp × 0.6) nm to (λp × 0.8) nm is 30% or less of the peak sensitivity. Here, the average sensitivity of the infrared optical element in the wavelength range from (λp × 0.6) nm to (λp × 0.8) nm when the incident angle of infrared light emitted from or incident on the infrared optical element to the optical filter is 0° is defined as S1. Furthermore, let S2 be the average sensitivity of the infrared optical element in the wavelength range from (λp×0.6) nm to (λp×0.8) nm when the incident angle of infrared light emitted from or incident on the infrared optical element to the optical filter is 45°. In this case, S2 is preferably smaller than S1 (see FIG. 8).

[0061] (Example) The effects of the present disclosure will be specifically described below based on examples, but the present disclosure is not limited to these examples.

[0062] Evaluations were carried out for Examples 1 to 6 and Comparative Examples 1 to 3 shown in Table 1. Examples 1 to 6 are optical devices of this embodiment, and the characteristics are defined as shown in Table 1. Comparative Examples 1 to 3 are unsimplified filters. The active layer of the optical devices of Examples 1 to 4 and 6 is Al. y In 1-y The active layer of the optical device of Example 5 is made of InAs, and y is 0.048 in Example 1, 0.057 in Example 2, 0.089 in Example 3, 0.089 in Example 4, and 0.057 in Example 6. y Sb 1-y and y is 0.13.

[0063] [Table 1]

[0064] The PIN diode structures of the infrared optical elements of Examples 1 to 6 were fabricated by the MBE method. Figure 5 shows the stacked structure of each layer of the infrared optical elements of Examples 1 to 6. N-type and p-type barrier layers were provided to sandwich the active layer. A positive i-line photoresist was applied to the surface of the semiconductor wafer, and exposure was performed using i-line light using a reduced projection exposure machine. Development was then performed, and multiple regular resist patterns were formed on the surface of the semiconductor stack. Next, multiple mesas were formed by dry etching. A SiO2 film was formed as a hard mask on the mesa-shaped element, followed by element isolation using dry etching. A SiN film was formed as a protective film, and contact holes were formed by photolithography and dry etching. Subsequently, multiple mesas were connected in series using photolithography and sputtering, and the element surface was covered with a polyimide resin protective film. The wafer fabricated in this way was diced into individual pieces, and Au wires were bonded to lead frames and connected, and the light-receiving surface was sealed with an epoxy-based molding resin so that it was exposed. The infrared light receiving element fabricated in this way has sensitivity to infrared rays in the vicinity of λp, but the sensitivity is 70% or less of the peak sensitivity in the wavelength band from (λp×0.6) nm to (λp×0.8) nm.

[0065] The optical filters were designed using simulations. The optical filters of Examples 1 to 6 are simplified optical filters, and all include a transmission band of 50 nm or more with a transmittance of over 70% in the wavelength range of 2500 nm to 10000 nm. As shown in Table 1, the optical filters of Examples 1 to 6 have a ratio of (a) / (b) of 2 or more. Here, (a) is the maximum transmittance in the wavelength range of (λp×0.6) nm to (λp×0.8) nm. Of the values ​​shown as (a), T1 is for 0° and T2 is for 45°. For the optical filters of Examples 1 to 6, (a) is 2% or more, and T2 is greater than T1. Furthermore, (b) is the minimum transmittance in the wavelength range of (λp×0.8) nm to (λp×0.9) nm. Furthermore, the infrared optical elements of Examples 1 to 6 have an average sensitivity in the wavelength range of (λp×0.6) nm to (λp×0.8) nm that is 70% or less of the peak sensitivity. Furthermore, in the infrared optical elements of Examples 1 to 6, in the average sensitivity in the wavelength range of (λp×0.6) nm to (λp×0.8) nm, the average sensitivity S2 at 45° incidence is smaller than the average sensitivity S1 at 0° incidence.

[0066] As shown in Table 1, the optical filters of Examples 1 to 6 have a ratio of (c) / (a) of 1.1 or more. Here, (c) is the transmittance at λp. Furthermore, the optical filters of Examples 1, 5, and 6 have a maximum transmittance of 2% or more in the wavelength range from (λp×0.4) nm to (λp×0.6) nm. As mentioned above, the incident angle of light may vary depending on the design of the concentration measurement device, but it is sufficient that the characteristics are satisfied at at least one incident angle. In Example 1, the maximum transmittance is 2% or more in the wavelength range from (λp×0.4) nm to (λp×0.6) nm at an incident angle of at least 0°. Whether the above (a) satisfies 2% or more is also determined in a similar manner. Furthermore, the optical filters of Examples 1 to 6 have a maximum transmittance of 60% or less and an average transmittance of 40% or less in the wavelength range from (λp×0.6) nm to (λp×0.8) nm. The optical filters of Examples 1 to 6 are bandpass filters with a half-width of 1000 nm or less.

[0067] In contrast, in Comparative Examples 1 to 3, (a) is less than 2%.

[0068] 6A and 6B are graphs comparing the transmittance of the Example (FIG. 6B) and the Comparative Example (FIG. 6A). The vertical axis represents transmittance, and the horizontal axis represents infrared wavelength. The graph of the Example shows the graph of Example 1 as a representative, but similar trends were observed in Examples 1 to 6. The graph of the Comparative Example shows the graph of Comparative Example 1 as a representative, but similar trends were observed in Comparative Examples 1 to 3. The graph also shows transmittance at multiple incident angles (0°, 10°, 20°, 30°, 40°, and 45°) superimposed. As shown in FIG. 6B, in the graph of the Example, the maximum transmittance in the wavelength range from (λp×0.6) nm to (λp×0.8) nm sometimes exceeds 2%, indicating that the blocking characteristics in this wavelength range are relaxed.

[0069] FIG. 7 is a graph comparing the sensitivity of Examples and Comparative Examples. The vertical axis represents sensitivity, and the horizontal axis represents infrared wavelength. The graph of Examples shows Example 1 as a representative example, but similar trends were observed in Examples 1 to 6. The graph of Comparative Examples shows Comparative Example 1 (used in combination with an infrared optical element) as a representative example, but similar trends were observed in Comparative Examples 1 to 3. When a concentration measuring device (see FIG. 2) is configured using the optical device, the optical device according to this embodiment achieves performance equivalent to that of the Comparative Example using a non-simplified optical filter, as shown in FIG. 7. In other words, it was confirmed that the accuracy of the optical device according to this embodiment does not deteriorate even when a simplified optical filter is used. Here, for the Comparative Example, an optical device was configured by combining the optical filter of the Comparative Example with an infrared optical element, and then a concentration measuring device was configured using this optical device.

[0070] As described above, the optical device according to this embodiment is small due to the simplification of the optical filter, yet is capable of receiving and emitting light of a desired wavelength, and is used in gas concentration measurement devices, etc., to enable highly accurate concentration measurement. The optical filter according to this embodiment is used in an optical device that enables highly accurate concentration measurement.

[0071] 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 alterations based on the present disclosure, and therefore, it should be noted that these modifications and alterations are included within the scope of the present disclosure.

Claims

1. an optical filter including a substrate and a multilayer film having a plurality of layers with different refractive indices formed on at least one surface of the substrate; an infrared optical element that emits or receives infrared light, the optical filter includes a transmission band of 50 nm or more in a wavelength range of 2500 nm to 10000 nm, the transmission band having a transmittance of more than 70%, and, where λp is the center wavelength of the transmission band, the maximum transmittance in a wavelength range of (λp×0.6) nm to (λp×0.8) nm is 2% or more, and the maximum transmittance is at least twice as large as the minimum transmittance in a wavelength range of (λp×0.8) nm to (λp×0.9) nm; the infrared optical element has a peak sensitivity at which sensitivity is maximum, and an average sensitivity in a wavelength range from (λp×0.6) nm to (λp×0.8) nm is 70% or less of the peak sensitivity; an optical device in which, when an incident angle at which infrared light emitted from or incident on the infrared optical element is incident on the optical filter is 0°, the maximum transmittance of the optical filter is T1 and the average sensitivity of the infrared optical element is S1 in the wavelength range of (λp×0.6) nm to (λp×0.8) nm; when an incident angle at which infrared light emitted from or incident on the infrared optical element is incident on the optical filter is 45°, the maximum transmittance of the optical filter is T2 and the average sensitivity of the infrared optical element is S2, T2 is greater than T1 and S2 is smaller than S1.

2. an optical filter including a substrate and a multilayer film having a plurality of layers with different refractive indices formed on at least one surface of the substrate; an infrared optical element that emits or receives infrared light, the optical filter includes a transmission band of 50 nm or more having a transmittance of more than 70% in a wavelength range of 2500 nm to 10000 nm, and, where λp is the center wavelength of the transmission band, the maximum transmittance in the wavelength range of (λp×0.6) nm to (λp×0.8) nm is at least two times greater than the minimum transmittance in the wavelength range of (λp×0.8) nm to (λp×0.9) nm, and further the maximum transmittance in the wavelength range of (λp×0.4) nm to (λp×0.6) nm is 2% or more; the infrared optical element has a peak sensitivity at which sensitivity is maximum, and an average sensitivity in a wavelength range from (λp×0.6) nm to (λp×0.8) nm is 70% or less of the peak sensitivity; an optical device in which, when an incident angle at which infrared light emitted from or incident on the infrared optical element is incident on the optical filter is 0°, the maximum transmittance of the optical filter is T1 and the average sensitivity of the infrared optical element is S1 in the wavelength range of (λp×0.6) nm to (λp×0.8) nm; when an incident angle at which infrared light emitted from or incident on the infrared optical element is incident on the optical filter is 45°, the maximum transmittance of the optical filter is T2 and the average sensitivity of the infrared optical element is S2, T2 is greater than T1 and S2 is smaller than S1.

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

4. 3. The optical device according to claim 1, wherein the optical filter has a maximum transmittance of 2% or more in a wavelength range from ([lambda]p*0.4) nm to ([lambda]p*0.6) nm.

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

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

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

8. 3. The optical device according to claim 1, wherein the total thickness of the multilayer film is 30 [mu]m or less.

9. 3. The optical device according to claim 1, wherein the infrared optical element comprises a first conductivity type semiconductor layer, an active layer, and a second conductivity 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 , wherein T2 is greater than T1 by 1% or more.

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

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

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