Sensor system and method of detecting target object

Abstract

To detect a target object substance stably with high sensitivity and high resolution.SOLUTION: A sensor system includes a detector element, an incident optical system including a light source and configured to obliquely illuminate the detector element, and a detector device configured to detect light reflected off the detector element. The detector element includes a chemical detection layer configured to change in an optical characteristic in response to contact with a target object substance, a reflection layer configured to reflect at least part of incident light, and an intermediate layer located between the reflection layer and the chemical detection layer. The detector device is configured to separately detect p-polarized light and s-polarized light reflected off the detector element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a sensor system and a method for detecting an object using a sensing element. [Background technology]

[0002] Chemical sensors have been developed to detect the type and concentration of chemical substances, such as hydrogen gas leak detection sensors. While several hydrogen gas sensors with different detection methods are known, most require high-temperature operation to improve response speed and provide cleaning effects. Hydrogen gas sensors that require high-temperature operation must be designed to prevent the risk of explosion caused by overcurrent or sparks in electrical circuits coming into contact with hydrogen.

[0003] Another example of a chemical sensor is one that uses optical techniques to detect hydrogen gas. For example, the hydrogen gas sensor disclosed in Japanese Patent Application Laid-Open No. 2017-172993 has a sensing element with a laminated structure including a magnetic layer and a hydrogen gas sensing layer. When measurement light is incident on the film surface of the sensing element, the polarization angle of the measurement light rotates due to the magneto-optical effect generated in the magnetic layer. When the hydrogen gas sensing film comes into contact with hydrogen, the optical properties of the sensing film change, changing the amount of rotation of the polarization angle. Hydrogen is detected by measuring this change. The main components of this hydrogen gas sensor—the light source, photodetector, sensing element, and magnetic field application device—are arranged on either side of the atmosphere to be measured. Optical hydrogen gas sensors do not require high temperature heating or the placement of conductive parts in the measurement atmosphere, thereby avoiding the above-mentioned problems and enabling safer hydrogen gas leak detection.

[0004] This hydrogen gas sensor requires a magnetic material in its construction to perform measurements using the magneto-optical effect, but also requires a magnetic field application mechanism to control the magnetization of the magnetic material. According to the disclosed film configuration, the laminated film uses a metal magnetic film in addition to a hydrogen gas sensing layer and a metal reflective layer, and configurations with an increased number of layers are also disclosed. The need for a magnetic field application mechanism and the complexity of the laminated film configuration increase costs. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-172993 [Patent Document 2] U.S. Patent Application Publication No. 2020 / 0309679 Summary of the Invention [Problem to be solved by the invention]

[0006] Chemical substance sensors that use sensing elements are required to have high detection accuracy and a high degree of freedom in the sensing element structure so that it can be selected according to the purpose. [Means for solving the problem]

[0007] A sensor system according to one embodiment of the present disclosure includes a sensing element, an incident optical system including a light source that directs light obliquely toward the sensing element, and a detection device that detects light reflected by the sensing element. The sensing element includes a chemical sensing layer whose optical properties change upon contact with a substance to be sensed, a reflective layer that reflects at least a portion of the incident light, and an intermediate layer between the reflective layer and the chemical sensing layer. The detection device detects both p-polarized light and s-polarized light reflected by the sensing element.

[0008] One aspect of the present disclosure is a method for detecting a target substance using a detection element. The detection element includes a chemical detection layer whose optical properties change upon contact with a target substance, a reflective layer that reflects at least a portion of incident light, and an intermediate layer between the reflective layer and the chemical detection layer. The detection method includes irradiating light obliquely onto the detection element, detecting p-polarized light and s-polarized light reflected by the detection element, and generating a detection result for the target substance based on a comparison of the intensities of the p-polarized light and the s-polarized light. [Effects of the Invention]

[0009] According to one aspect of the present disclosure, a detection target substance can be detected with high sensitivity, high resolution, and stability. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram illustrating a configuration example of a hydrogen gas sensor system according to an embodiment of the present specification. [Figure 2A] 1 shows an example of the configuration of a detector element. [Figure 2B] 1 shows an example of the configuration of a detector element. [Figure 3] 1 is a cross-sectional view schematically illustrating an example of the configuration of a laminated film of a sensing element according to an embodiment of the present specification. [Figure 4] The results of a simulation illustrating the principle of hydrogen gas detection using the sensing element shown in FIG. 3 are shown below. [Figure 5A] The graph shows the results of a simulation of the change in reflectance of p-polarized light and s-polarized light due to the reaction between the detection stacked film and hydrogen gas in the detection element shown in FIG. [Figure 5B] The graph shows the results of a simulation of the change in reflectance of p-polarized light and s-polarized light due to the reaction between the detection stacked film and hydrogen gas in the detection element shown in FIG. [Figure 6] The ratio (Ip / Is) of the intensity of reflected p-polarized light Ip to the intensity of reflected s-polarized light Is calculated from the simulation results of p-polarized light and s-polarized light shown in FIG. 5 is shown. [Figure 7] 1 is a schematic diagram illustrating a configuration example of a hydrogen gas sensor system according to an embodiment of the present specification. [Figure 8] 1 is a cross-sectional view schematically illustrating a configuration example of a sensing element according to an embodiment of the present specification. [Figure 9] 9 shows graphs of measurement results in the configuration examples shown in FIGS. 7 and 8. [Figure 10] 1 is a cross-sectional view schematically illustrating a configuration example of a sensing element according to an embodiment of the present specification. [Figure 11] 11 shows graphs of measurement results in the configuration examples shown in FIGS. [Figure 12A] 1 is a schematic diagram illustrating a configuration example of a hydrogen gas sensor system according to an embodiment of the present specification. [Figure 12B] 1 is a schematic diagram illustrating a configuration example of a hydrogen gas sensor system according to an embodiment of the present specification. [Figure 13] 1 is a cross-sectional view schematically illustrating a configuration example of a sensing element according to an embodiment of the present specification. [Figure 14] 14 shows graphs of measurement results in the configuration examples shown in FIGS. 12A and 13. [Figure 15] 1 is a schematic diagram illustrating a configuration example of a hydrogen gas sensor system according to an embodiment of the present specification. [Figure 16] 1 is a cross-sectional view schematically illustrating a configuration example of a sensing element according to an embodiment of the present specification. [Figure 17] The simulation results for the laminated film shown in FIG. 16 are shown. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. The size and scale of each component in each drawing have been appropriately changed to ensure visibility of the drawings. Furthermore, hatching in each drawing is used to distinguish each component and does not necessarily represent a cross section. It should be noted that this embodiment is merely an example for realizing the present disclosure and does not limit the technical scope of the present disclosure.

[0012] The following describes embodiments of a sensor system. The sensor system in some embodiments herein is an optical chemical sensor system. The optical chemical sensor system detects an object to be detected by measuring changes in the optical properties of a sensing element that comes into contact with the object to be detected. The optical chemical sensor system in the embodiments herein irradiates light obliquely onto the sensing element and measures the reflected p-polarized and s-polarized light.

[0013] The sensing element includes a thin film stack, which includes, for example, a chemical sensing layer, an optical interference layer, and a reflective layer. The optical interference layer is an intermediate layer sandwiched between the chemical sensing layer and the reflective layer. The chemical sensing layer and the reflective layer each totally or partially reflect light of a predetermined wavelength. The constituent materials of the stack are selected and the film thickness is set so that the reflected light from the reflective layer and the chemical sensing layer interfere with each other for the wavelength of light used for detection, and the conditions for resonance of p-polarized light or s-polarized light are close to each other. Light incident on the sensing element is incident on the stack, and the reflected light reflecting the results of the above interference is detected by the detection device.

[0014] In an embodiment of the present disclosure, an oblique incidence optical system is configured in which light for detection is incident obliquely on the thin film stack of the detection element. A portion of the light that is obliquely incident on the detection element is reflected at the incident-side interface of the reflective film. A portion of the light that passes through the reflective film passes through the intermediate layer, is reflected by the chemical detection layer, passes through the intermediate layer again, and then passes through the reflective film to interfere with the light reflected at the incident surface and is detected by the detection device.

[0015] In an oblique incidence optical system, the polarization components can be defined as p-polarized light and s-polarized light. Because the interference effect that occurs in the stack differs between p-polarized light and s-polarized light, the ratio of the incident light and the reflected light detected by the detection device, i.e., the reflectance, is observed to be different.

[0016] When the chemical sensing layer comes into contact with a substance to be detected, the optical properties of the chemical sensing layer change depending on the concentration of the substance, changing the interference conditions that occur in the laminate. As mentioned above, the laminate is set close to the resonance conditions for p-polarized or s-polarized light. Therefore, even a slight change in the optical properties of the chemical sensing layer causes it to move away from the resonance conditions, resulting in an extremely large change in reflectance. This change in reflectance results in a large change in the detected light intensity in the detection device, allowing for high-sensitivity and high-resolution detection of the substance to be detected.

[0017] Changes in the chemical sensing layer are reflected in the reflectance of both p-polarized and s-polarized light, but if there is a fluctuation in the light intensity of the light source, the effect of this fluctuation is reflected in both p-polarized and s-polarized light at the same rate, so by comparing the detected light intensities of p-polarized and s-polarized light, the effect of fluctuations in the light source's light intensity can be eliminated. In this way, target substances can be detected stably with high sensitivity and high resolution.

[0018] The detection target of an optical chemical sensor system is the concentration of a substance, such as pH, hydrogen, oxygen, carbon dioxide, chlorine, nitrogen oxides, or other gases, DNA, or enzymes. The optical chemical sensor system may be, for example, an optical ion sensor system that detects pH, an optical gas sensor system that detects gases, or an optical biosensor system that detects DNA or enzymes. In the following embodiment, an optical hydrogen gas sensor system that detects hydrogen gas will be described in detail as an example. Note that an optical sensor system may also be simply referred to as a sensor system.

[0019] [Embodiment 1] FIG. 1 shows a schematic diagram of a hydrogen gas sensor system according to an embodiment of the present specification. The hydrogen gas sensor system is an example of an optical chemical sensor system, and the object to be detected is hydrogen gas. The hydrogen gas sensor system can detect the concentration of hydrogen gas. The single arrow in the figure indicates the optical path, and the hydrogen gas sensor is based on an oblique incidence optical system.

[0020] The hydrogen gas sensor system includes a light source 11, a polarization separation element (polarization separator) 13, a sensing element 14, a light detection device 17, and a detection control device 40. The incident optical system includes the light source 11 and the polarization separation element 13. The detection control device 40 controls the other components of the hydrogen gas sensor system, measures the intensity of light reflected by the sensing element 14, and calculates a measurement value based on the intensity of the reflected light.

[0021] The detection element 14 includes a transparent substrate 141 and a laminated film 140 formed on the transparent substrate 141. The laminated film 140 includes a half mirror layer 142, an optical interference layer 143, and a hydrogen gas detection layer 144, which are laminated from the transparent substrate 141 side. A prism 146 is provided on the opposite side of the transparent substrate 141 from the laminated film 140, and is optically coupled to the transparent substrate 141 by immersion oil or the like (not shown). The prism 146 reduces reflection of incident light on the back surface of the transparent substrate 141, where the laminated film 140 is not formed.

[0022] FIG. 2A shows another example configuration of the sensing element 14. In the example configuration shown in FIG. 2A, instead of the prism 146, an antireflection film 147 is formed on the transparent substrate 141 opposite the laminated film 140. The antireflection film 147 may be, for example, a dielectric multilayer film, and may have a structure in which a ZnO thin film as a high-refractive index layer and a SiO thin film as a low-refractive index layer are laminated in this order on the transparent substrate 141. The transparent substrate 141 is sandwiched between the antireflection film 147 and the laminated film 140. Similar to the prism 146, the antireflection film 147 can reduce reflection of incident light on the back surface of the transparent substrate 141 where the laminated film 140 is not formed.

[0023] 2B shows another example configuration of the sensing element 14. The sensing element 14 shown in FIG. 2B has a configuration in which the transparent substrate 141 is omitted from the example configuration of the sensing element 14 shown in FIG. The laminated film 140 is formed directly on the surface of the prism 146. Since immersion oil for optically coupling the transparent substrate 141 and the prism 146 is not required, contamination of the area around the element by oil can be avoided.

[0024] Returning to FIG. 1 , the surface of the hydrogen gas sensing layer 144 is in contact with the hydrogen gas 30, which is the object to be sensed. The hydrogen gas sensor system detects hydrogen gas by measuring changes in the optical properties of the sensing element 14 caused by the hydrogen gas 30. More specifically, the hydrogen gas concentration is detected by measuring the difference in reflectance between p-polarized light and s-polarized light by the laminated film 140 depending on the hydrogen gas concentration.

[0025] 1, the hydrogen gas sensor system irradiates light obliquely onto the stacked film 140, via a prism 146, from the rear surface side of the transparent substrate 141, on which the stacked film 140 for detecting hydrogen gas 30 is not formed. The photodetector 17 detects the reflected p-polarized light 32p and the reflected s-polarized light 32s, and the detection control device 40 determines the hydrogen concentration based on the difference in intensity between them. As will be described later, the difference in intensity can be expressed by a function using, for example, a difference or a ratio.

[0026] The laminated film 140 has a structure in which light reflected at the interface between the half mirror layer 142 and the transparent substrate 141 interferes with light that penetrates the interior and is reflected by the hydrogen gas sensing layer 144. For ease of illustration, the light reflected at the interface between the half mirror layer 142 and the transparent substrate 141 is not shown in FIG. 1 . This is also true for other figures. In the hydrogen gas sensor system, light emitted from the light source 11 is incident on the sensing element 14 from an oblique direction. In an oblique incidence optical system, the reflectance of p-polarized light and s-polarized light generally differs. Furthermore, in a laminated film such as that of the embodiment of the present disclosure, different interference conditions are superimposed for p-polarized light and s-polarized light.

[0027] The behavior of the reflection of p-polarized light and s-polarized light in the combined stacked film 140 is reflected in the reflectance of p-polarized light and s-polarized light. If the ratio between the intensities of incident p-polarized light 31p and incident s-polarized light 31s is kept constant, the intensity ratio can be calculated by detecting the intensities of reflected p-polarized light 32p and reflected s-polarized light 32s with photodetectors 171 and 172, respectively. By taking the intensity ratio between reflected p-polarized light 32p and reflected s-polarized light 32s, the influence of fluctuations in the intensity of light emitted from the light source can be eliminated.

[0028] The light source 11 emits light that is incident on the laminated film 140 formed on the transparent substrate 141 via the prism 146. As the light source 11, a monochromatic light source that emits light of a single wavelength, such as a semiconductor laser, an LED, or a gas laser, can be used.

[0029] The polarization separation element 13 is disposed on the optical path between the light source 11 and the detection element 14. The polarization separation element 13 separates the light from the light source 11 into p-polarized light 31p and s-polarized light 31s. The p-polarized light 31p and s-polarized light 31s are incident on the detection element 14. The p-polarized light 31p and s-polarized light 31s enter the detection element 14 at different positions along different optical paths.

[0030] The p-polarized light 31p and the s-polarized light 31s separated by the polarization separation element 13 travel along different optical paths through the prism 146 and are incident on the back surface of the transparent substrate 141 on which the laminated film 140 is not formed. The incident direction is oblique to the lamination direction of the laminated film 140 (the normal direction of the transparent substrate 141). The angle is, for example, 45°.

[0031] A portion of the p-polarized light 31p and s-polarized light 31s incident on the laminated film 140 is reflected at the interface between the half mirror layer 142 and the transparent substrate 141. The remaining portion is transmitted through the half mirror layer 142, passes through the optical interference layer 143, is reflected by the chemical detection layer 144, passes through the optical interference layer 143 again in the opposite direction, and then transmits through the half mirror layer 142 to interfere with the light reflected at the interface between the half mirror layer 142 and the transparent substrate 141 described above.

[0032] At this time, p-polarized light and s-polarized light have different interference conditions. The laminated film 140 is set so that the interference of p-polarized light or s-polarized light approaches the resonance condition for the wavelength of the light emitted from the light source 11 used for detection. The reflected light intensity of the polarization component that approaches the resonance condition is extremely small due to interference. On the other hand, the reflected light intensity of the polarization component that deviates from the resonance condition is relatively large.

[0033] The p-polarized light 32p and the s-polarized light 32s reflected by the sensing element 14 travel along different optical paths. The reflected p-polarized light 32p and the reflected s-polarized light 32s are detected by a first photodetector 171 and a second photodetector 172, respectively. The first photodetector 171 and the second photodetector 172 are components of the detection device 17 and are installed at different positions. The first photodetector 171 and the second photodetector 172 are located on the optical paths of the reflected p-polarized light 32p and the reflected s-polarized light 32s, respectively, and detect the intensities of the reflected p-polarized light 32p and the reflected s-polarized light 32s, respectively.

[0034] The detection control device 40 controls the light emission of the light source 11 and receives detection signals from the first photodetector 171 and the second photodetector 172. The detection control device 40 receives signals indicating the intensities of the reflected p-polarized light 32p and the reflected s-polarized light 32s from the first photodetector 171 and the second photodetector 172. The detection control device 40 calculates the hydrogen gas concentration based on the comparison results.

[0035] For example, the detection control device 40 uses a preset function (including a lookup table) to determine the hydrogen concentration from the intensities of the reflected p-polarized light 32p and the reflected s-polarized light 32s. The function can include, for example, the ratio of the p-polarized light intensity to the s-polarized light intensity as a variable. When the ratio of the p-polarized light component to the s-polarized light component on the incident side is kept constant, fluctuations in the intensity of the light emitted from the light source 11 can be eliminated by calculating the ratio of the reflected light intensities of the p-polarized light and the s-polarized light.

[0036] 1, the sensing element 14 includes a laminated film 140 in which a half mirror layer 142, an optical interference layer 143, and a hydrogen gas sensing layer 144 are laminated in this order on a transparent substrate 141. Each of these layers may be composed of a single layer or multiple layers. The hydrogen gas sensing layer 144 is a chemical sensing layer and is made of an appropriate material depending on the substance to be sensed.

[0037] The hydrogen gas sensing layer 144 changes its optical properties, such as refractive index and absorption coefficient, upon contact with hydrogen gas. The hydrogen gas sensor system detects hydrogen gas by measuring the change in intensity of the p-polarized and s-polarized reflected light that occurs due to the change in the optical properties of the hydrogen gas sensing layer 144.

[0038] The optical interference layer 143 is an intermediate layer, and has a structure in which, of the light irradiated onto the laminated film 140, the light reflected at the interface between the half mirror layer 142 and the transparent substrate 141 interferes with the light that penetrates the interior and is reflected by the hydrogen gas detection layer 144. For example, the value obtained by multiplying and adding the thicknesses and refractive indices of the half mirror layer 142 and the optical interference layer 143 is thicker than about ¼ of the wavelength of the irradiated light.

[0039] The half mirror layer 142 reflects a portion of the incident light and transmits a portion of it. The half mirror layer 142 has a thickness that allows light irradiated onto the laminated film 140 to penetrate into the laminated film 140. For example, the half mirror layer 142 can have a thickness greater than 0 nm and not greater than 30 nm. The hydrogen gas sensing layer 144 has a thickness sufficient to reflect light that has penetrated into the laminated film 140, and can have a thickness of, for example, 20 nm or more. Increasing the thickness of the hydrogen gas sensing layer 144 can reduce the influence of fluctuations in the surface condition of the sensing layer, enabling more stable detection of the sensing target.

[0040] The hydrogen gas sensing layer 144 can be made of any material whose optical properties, such as refractive index or absorption coefficient, change upon reaction with hydrogen gas. One example is a thin film containing Pd (palladium), whose optical properties change significantly upon contact with hydrogen gas. Since Pd has the ability to absorb and release hydrogen gas at room temperature, a hydrogen gas sensor can be provided that can operate at room temperature and has high detection sensitivity.

[0041] Examples of materials used for the light interference layer 143 include common transparent oxides, transparent nitrides, and transparent fluorides such as SiO2 (silicon dioxide), ZnO (zinc oxide), MgO (magnesium oxide), TiO2 (titanium oxide), AlN (aluminum nitride), Si3N4 (silicon nitride), and MgF2 (magnesium fluoride). The light interference layer 143 may be a dielectric material having high transmittance for the wavelength of light emitted from the light source 11.

[0042] Examples of materials used for the half mirror layer 142 include general metal materials such as Ag (silver), Al (aluminum), Au (gold), Cu (copper), and Ta (tantalum), and alloys containing these metals. The material of the half mirror layer 142 may have high reflectivity at the wavelength of light emitted from the light source 11. The transparent substrate 141 is, for example, a glass substrate with a thickness of about 0.5 mm (500 μm).

[0043] In one embodiment of this specification, the stacked film 140 of the sensing element 14 is made of a non-magnetic material. In Patent Document 1, the operating principle was detection by rotation of the polarization plane due to the magneto-optical effect, so it was necessary to include a magnetic material. However, in the embodiment of this specification, it is not necessary to have a configuration that includes a magnetic material. However, it is not necessary to have a configuration that is made of only non-magnetic materials. It is sufficient to select an appropriate material by focusing only on the requirements necessary to achieve the characteristics required in the embodiment, and it is not necessary to be particular about whether the material is magnetic or not.

[0044] However, if you choose to include a magnetic material in the configuration, you can suppress the effects of external magnetic fields and improve the stability of the characteristics by selecting a material with a large coercive force that prevents magnetization reversal even in the maximum magnetic field expected in the usage environment and a material with a highly rectangular hysteresis loop.

[0045] As described above, the hydrogen gas sensor system irradiates the film stack 140 with light from a direction oblique to the normal direction, and detects p-polarized light and s-polarized light reflected by the film stack 140. The hydrogen gas sensor system detects changes in the optical properties of the hydrogen gas sensing layer 144 due to contact with hydrogen gas 30 as optical signals indicating changes in the intensity of the p-polarized light and s-polarized light reflected by the film stack 140, thereby detecting hydrogen gas.

[0046] When hydrogen gas comes into contact with the hydrogen gas sensing layer 144, the optical properties of the hydrogen gas sensing layer 144 change, thereby changing the interference conditions of the laminated film 140. The interference conditions change differently for p-polarized light and s-polarized light, and the reflectance of the polarization component near the resonance condition in particular changes significantly due to the change in the optical properties of the hydrogen gas sensing layer 144 caused by contact with hydrogen. As a result, the ratio of the reflected light intensities of p-polarized light and s-polarized light changes significantly. In this way, the optical signal can be greatly enhanced by the interference of light generated in the laminated film 140, allowing hydrogen gas to be detected with high sensitivity. This is also true for laminated films of other sensing objects and chemical sensing layers.

[0047] 3 is a cross-sectional view schematically illustrating an example of the structure of a laminated film (detection laminated film) of a detection element according to one embodiment of the present specification. A laminated film 200 for detecting hydrogen gas is formed on a transparent substrate 201 made of glass. The laminated film 200 is composed of a half mirror layer 202, an optical interference layer 203, and a hydrogen gas detection layer 204.

[0048] The half mirror layer 202 is composed of a 3 nm thick Cr thin film and an 11 nm thick Au thin film. The optical interference layer 203 is composed of a 114 nm thick Si3N4 (silicon nitride) thin film. The hydrogen gas detection layer 204 is composed of a 100 nm thick Pd thin film. The half mirror layer 202, optical interference layer 203, and hydrogen gas detection layer 204 are laminated in this order on the transparent substrate 201.

[0049] An anti-reflection film or a prism may be disposed on the back surface of the transparent substrate 201 on which the laminated film 200 is not formed, in order to reduce the amount of light reflected from the transparent substrate 201 .

[0050] Figure 4 shows the simulation results for the reflectance characteristics of the sensing stack 200 shown in Figure 3. The horizontal axis of Figure 4 represents the wavelength of the light source, and the vertical axis represents the reflectance of p-polarized light and s-polarized light. Figure 3 shows an example of the thickness conditions for the sensing stack 200, where the p-polarized light is in resonance when the wavelength is 670 nm. The vertical axis is a logarithmic scale, and significant changes in reflectance are observed near the resonance condition, which, in principle, is zero at the resonance condition. Under the same conditions, the reflectance of s-polarized light is several orders of magnitude higher than that of p-polarized light, and the change is slight. Specifically, in Figure 4, the reflectance of s-polarized light at a wavelength of 670 nm is approximately 14%, while the reflectance of p-polarized light is approximately 0.0008%. Therefore, the reflectance ratio for s-polarized light is four orders of magnitude higher (approximately 17,500 times) than that of p-polarized light.

[0051] There is also a resonance condition for s-polarized light, but it is at a different wavelength than p-polarized light, and the change in reflectance near the resonance condition is more gradual than for p-polarized light. Here, we have used an example design in which a steep resonance condition appears for p-polarized light, but depending on the design of the laminated film, it is also possible to create a laminated film in which a steep resonance condition appears for s-polarized light. Here, we have shown an example calculation with wavelength on the horizontal axis, but a similar response can be obtained near the resonance condition even if another parameter that affects the interference condition (for example, the angle of incidence, the optical properties of the laminated film, etc.) is used on the horizontal axis.

[0052] FIG. 5 shows the results of a simulation of the reflectance characteristics of the sensing stack 200 shown in FIG. 3, illustrating the change in characteristics depending on the hydrogen concentration when the hydrogen gas sensing layer comes into contact with hydrogen. FIG. 5A shows the results of a simulation of the wavelength dependence of reflectance shown in FIG. 4, illustrating the change in characteristics when the concentration of hydrogen in contact with the hydrogen gas sensing layer is changed. The horizontal axis of FIG. 5A represents the wavelength of the light source, and the vertical axis represents the reflectance of p-polarized light and s-polarized light. As explained in FIG. 4, when the hydrogen concentration is 0%, the resonance condition is reached at a wavelength of 670 nm for p-polarized light. As the hydrogen concentration increases, the resonance condition shifts toward longer wavelengths, and the change in reflectance near the resonance condition becomes more gradual.

[0053] On the other hand, the reflectance of s-polarized light decreases slightly overall as the hydrogen concentration increases within the range of this graph. When the wavelength is fixed at 670 nm, where p-polarized light is at the resonance condition, the reflectance of p-polarized light increases as the hydrogen concentration increases. On the other hand, the reflectance of s-polarized light is originally high, and although there is a change with hydrogen concentration, there is almost no change on this graph, which has a logarithmic vertical axis. Although the vertical axis of Figure 5A is reflectance, what can actually be detected is the reflected light intensity.

[0054] By designing the element as shown in Figure 5A, the hydrogen concentration of the atmosphere to which the hydrogen detection film is exposed can be determined by combining the reflectance of s-polarized light and the reflectance of p-polarized light. Figure 5B shows data extracted from Figure 5A at a wavelength of 670 nm. The horizontal axis represents the hydrogen concentration, and the vertical axis is a logarithmic axis showing the reflectance of p-polarized light and s-polarized light by the detection film stack 200. The solid line shows the change in reflectance of p-polarized light versus hydrogen concentration, and the dashed line shows the change in reflectance of s-polarized light versus hydrogen concentration.

[0055] In the simulation results shown in Figure 5B, the reflectance of p-polarized light changed by approximately three orders of magnitude when the hydrogen concentration was changed from 0 to 100%. On the other hand, the reflectance of s-polarized light barely changed when the hydrogen concentration was changed from 0 to 100%, showing little change with changes in p-polarized light. Therefore, in this configuration example, if the reflected light intensity of s-polarized light is considered constant, the hydrogen concentration can be detected using only the reflected light intensity of p-polarized light. However, even in this example, by measuring the reflected light intensity of both p-polarized and s-polarized light and calculating their ratio, the effects of fluctuations in the light intensity of the light source and subtle changes in s-polarized light can be eliminated, allowing for highly accurate detection of hydrogen gas. Furthermore, the reflectance of each of p-polarized and s-polarized light can be adjusted by adjusting the material and thickness of each layer in the stacked film.

[0056] Figure 6 shows the ratio (Ip / Is) of the reflected p-polarized light intensity Ip to the reflected s-polarized light intensity Is, calculated from the simulation results of p-polarized light and s-polarized light shown in Figure 5B, comparing a single-layer film with a stacked film. The horizontal axis represents hydrogen concentration, and the vertical axis is a logarithmic axis representing the ratio (Ip / Is) of the reflected p-polarized light intensity Ip to the reflected s-polarized light intensity Is. The vertical axis is normalized so that the intensity ratio (Ip / Is) is 1 when the hydrogen concentration is 0%. The dashed line represents the change in the intensity ratio (Ip / Is) versus hydrogen concentration for a Pd single-layer film (100 nm) that does not have a half mirror layer or optical interference layer. The solid line represents the change in the intensity ratio (Ip / Is) versus hydrogen concentration for the stacked film 200 shown in Figure 3.

[0057] The calculation results in Figure 6 show that the laminated film 200, which has an optical interference effect, responds sensitively to changes in hydrogen concentration. Although the Pd single layer film (100 nm) also changes in its reflectivity when it comes into contact with hydrogen, the change is very small compared to the laminated film 200, which has an optical interference effect.

[0058] [Embodiment 2] FIG. 7 is a schematic diagram illustrating a configuration example of a hydrogen gas sensor system according to an embodiment of the present specification. Differences from the configuration example shown in FIG. 1 will be mainly described below. Similar to the configuration example shown in FIG. 1, the hydrogen gas sensor system is based on an oblique incidence optical system, and detects hydrogen gas by irradiating light obliquely through a prism 146 onto the back surface of a transparent substrate 141 on which a laminated film 140 for detecting hydrogen gas is not formed. The sensing element 14 has a structure similar to that of the configuration example shown in FIG. 1.

[0059] The incident optical system includes a light source 11 and a polarizer 12. The polarizer 12 is disposed on the optical path of the incident light 31 between the light source 11 and the detection element 14. The polarizer 12 passes linearly polarized light in a specific direction and attenuates polarized light in other directions. The polarizer 12 may be adjusted in advance so that the difference in intensity between the reflected p-polarized light and the reflected s-polarized light in the hydrogen concentration measurement range is within a predetermined range. For example, the rotation angle of the polarizer 12 may be adjusted so that the intensities of the reflected p-polarized light and the reflected s-polarized light are approximately the same when no hydrogen gas is present. In this way, by appropriately adjusting the rotation angle of the polarizer 12, accuracy can be improved. The polarizer 12 may be omitted.

[0060] Furthermore, a polarization separator 15 is disposed on the optical path between the sensing element 14 and the photodetector. In Fig. 7, for ease of illustration, the frame illustrating the photodetector 17 shown in Fig. 1 has been omitted, but similar to the configuration example of Fig. 1, the photodetector 17 includes a first photodetector 171 and a second photodetector 172. The polarization separator 15 separates the p-polarized light 32p and the s-polarized light 32s from the light reflected by the sensing element 14. The p-polarized light 32p and the s-polarized light 32s from the polarization separator 15 travel along different optical paths.

[0061] Linearly polarized light 31 emitted from light source 11 and passing through polarizer 12 is incident on stacked film 140 of sensing element 14 via prism 146, with the intensity ratio of the p-polarized light component and the s-polarized light component corresponding to the polarization angle. As described above, linearly polarized light 31 is incident on stacked film 140 at an angle inclined with respect to the normal direction of stacked film 140. Unlike embodiment 1, the incident light is not separated into p-polarized light and s-polarized light, and linearly polarized light 31 is incident at a single point. This makes it possible to avoid the influence of differences in characteristics within the plane of stacked film 140.

[0062] As explained in the first embodiment, the p-polarized light (component) and s-polarized light (component) of the incident light interfere under different interference conditions in the laminated film 140. Furthermore, the optical properties of the hydrogen gas sensing layer 144 change depending on the hydrogen gas 30, which changes the reflectance of the p-polarized light and s-polarized light in the hydrogen gas sensing layer 144 and the interference conditions of the laminated film 140. As a result, the ratio of the reflected light intensities of the p-polarized light and the s-polarized light reflected by the laminated film 140 changes significantly.

[0063] The light reflected by the stacked film 140 enters the polarization separator 15 and is split into p-polarized light 32p and s-polarized light 32s, which travel along different optical paths. The first photodetector 171 receives the p-polarized light 32p and outputs its intensity to the detection control device 40. The second photodetector 172 receives the s-polarized light 32s and outputs its intensity to the detection control device 40. In this way, by splitting the light reflected by the sensing element 14 into p-polarized light and s-polarized light, detecting the light intensities of each, and calculating the ratio, it is possible to eliminate fluctuations in the light intensity of the light source.

[0064] 8 is a cross-sectional view schematically illustrating an example of the configuration of a sensing element 250 according to one embodiment of the present specification. The sensing element 250 includes a laminated film 260 for detecting hydrogen gas on a transparent substrate 251 made of glass. The laminated film 260 is composed of a half mirror layer 253, an optical interference layer 254, and a hydrogen gas sensing layer 255. The half mirror layer 253, the optical interference layer 254, and the hydrogen gas sensing layer 255 are laminated in this order on the transparent substrate 251.

[0065] The half mirror layer 253 is composed of a 14 nm thick Ag thin film. The optical interference layer 254 is composed of a laminated film consisting of a 30 nm thick ZnO thin film and a 143 nm thick Al2O3 thin film. The hydrogen gas detection layer 255 is composed of a 100 nm thick PdCuSi alloy thin film.

[0066] A seed layer 252 is present between the laminated film 260 and the transparent substrate 251. The seed layer 252 is made of a ZnO thin film with a thickness of 30 nm. The seed layer 252 maintains the adhesive force between the laminated film 260 and the transparent substrate 251.

[0067] On the back surface of the transparent substrate 251, on which the laminated film 260 is not formed, a prism 256 is optically coupled to the transparent substrate 251 by optical coupling oil 257. The prism 256 can suppress reflection of light on the back surface of the transparent substrate 251. The optical coupling oil 257 reduces reflection of light at the interface between the transparent substrate 251 and the prism 256.

[0068] 7 and 8. The horizontal axis represents time, and the vertical axis represents the ratio (Ip / Is) of the intensity of reflected p-polarized light Ip to the intensity of reflected s-polarized light Is. In the measurements, the polarization angle of the incident light (the rotation angle of polarizer 12) was set so that the light intensities of the reflected p-polarized light and the reflected s-polarized light were equal when the hydrogen concentration was 0%.

[0069] The solid line shows the change in the intensity ratio (Ip / Is) of p-polarized light to s-polarized light in response to the introduction and shutoff of hydrogen gas. Measurements were performed by introducing hydrogen at a concentration of 100%, and then shutting off the hydrogen. In response to the introduction of hydrogen, the reflected light intensity ratio (Ip / Is) increased significantly. When the hydrogen was shut off, the reflected light intensity ratio (Ip / Is) gradually decreased. Thus, the configuration of this embodiment also enabled highly sensitive detection of hydrogen concentration.

[0070] 10 is a cross-sectional view schematically illustrating an example of the configuration of a sensing element 270 according to one embodiment of the present specification. The sensing element 270 includes a laminated film 280 for detecting hydrogen gas on a prism 276 made of glass. The laminated film 280 is composed of a half mirror layer 273, an optical interference layer 274, and a hydrogen gas sensing layer 275. The half mirror layer 273, the optical interference layer 274, and the hydrogen gas sensing layer 275 are laminated in this order on the prism 276.

[0071] The half mirror layer 273 is made of a 6.4 nm thick Ta thin film, the optical interference layer 274 is made of a 68 nm thick Si3N4 thin film, and the hydrogen gas sensing layer 275 is made of a 100 nm thick PdCuSi alloy thin film.

[0072] The seed layer 272 is located between the film stack 280 and the prism 276. The seed layer 272 is made of a 5 nm thick Si3N4 thin film. The seed layer 272 maintains the adhesive force between the film stack 280 and the prism 276.

[0073] A catalyst layer 278 is present so as to cover the hydrogen gas sensing layer 275. The catalyst layer 278 is made of a 5 nm thick Pt (platinum) thin film and is formed on the laminated film 280 on the side opposite the prism 276. The catalyst layer 278 is in contact with the hydrogen gas sensing layer 275. The catalyst layer 278 comes into contact with hydrogen gas and decomposes hydrogen molecules into hydrogen atoms. The hydrogen gas sensing layer 275 changes its optical properties depending on the concentration of hydrogen atoms generated by the catalyst layer 278.

[0074] Considering applications where the device is constantly exposed to high concentrations of hydrogen, the long-term stability of the sensing element can be improved by suppressing unwanted reactions between hydrogen and layers other than the hydrogen gas sensing layer. Among the transparent oxides that are candidates for the light interference layer, there are some materials in which the hydrogen compounds (hydroxides) produced by reaction with hydrogen are more stable. When selecting a material for the light interference layer, if the light interference layer material is considered to be more stable than the hydrogen compounds of the elements that make up the light interference layer, the reaction between the light interference layer and hydrogen can be suppressed, thereby improving the long-term stability of the sensing element. One example is silicon nitride. In this embodiment, silicon nitride is used as the light interference layer, as described with reference to FIG. 10 .

[0075] When the optical interference layer is made of silicon nitride, several metal materials were tried as the half mirror material, but the adhesion at the interface between the optical interference layer and the half mirror layer was sometimes weak. If the adhesion at the interface is weak, the interface will not be maintained stably over long-term use, reducing the reproducibility and reliability of the measurement results. While investigating combinations with silicon nitride, it was found that the adhesion at the interface is sufficiently high when tantalum (Ta) is used for the half mirror. In this embodiment, a Ta thin film is used as the half mirror material in combination with silicon nitride to stabilize the detection element.

[0076] 7 and 10. The horizontal axis represents time, and the vertical axis represents the ratio (Ip / Is) of the intensity of reflected p-polarized light Ip to the intensity of reflected s-polarized light Is. In the measurements, the polarization angle of the incident light (the rotation angle of polarizer 12) was set so that the light intensities of the reflected p-polarized light and the reflected s-polarized light were equal when the hydrogen concentration was 0%.

[0077] The solid line shows the change in the intensity ratio (Ip / Is) of p-polarized light to s-polarized light in response to the introduction and shutoff of hydrogen gas. Measurements were performed by introducing hydrogen at a concentration of 100%, and then shutting off the hydrogen. In response to the introduction of hydrogen, the reflected light intensity ratio (Ip / Is) increased significantly. When the hydrogen was shut off, the reflected light intensity ratio (Ip / Is) gradually decreased. Thus, the configuration of this embodiment also enabled highly sensitive detection of hydrogen concentration.

[0078] [Embodiment 3] FIG. 12A is a schematic diagram illustrating a configuration example of a hydrogen gas sensor system according to an embodiment of the present specification. Differences from the configuration example shown in FIG. 1 will be mainly described below. Similar to the configuration example shown in FIG. 1, the hydrogen gas sensor system is based on an oblique incidence optical system, and detects hydrogen gas by irradiating light obliquely through a prism 146 onto the back surface of a transparent substrate 141 on which a laminated film 140 for detecting hydrogen gas is not formed. The sensing element 14 has a structure similar to that of the configuration example shown in FIG. 1.

[0079] 12A includes a polarization modulator 122 on the incident side. The polarization state of the incident light is switched by time-division controlling the polarization modulator 122. This allows a single photodetector to detect reflected p-polarized light and reflected s-polarized light.

[0080] 12A, the incident optical system includes a light source 11, a polarizer 121, and a polarization modulator 122. The polarizer 121 is disposed on the optical path of the incident light between the light source 11 and the sensing element 14. The polarizer 121 passes light linearly polarized in a specific direction and attenuates light polarized in other directions.

[0081] Furthermore, a polarization modulator 122 is disposed on the optical path of the incident light between the polarizer 121 and the sensing element 14. The polarization modulator 122 switches the polarization direction of the linearly polarized light from the polarizer 121. For example, a liquid crystal can be used for the polarization modulator 122. By controlling the polarization modulator 122, the linearly polarized light from the polarizer 121 can be modulated into two orthogonal linearly polarized lights corresponding to p-polarized light or s-polarized light.

[0082] A polarizer 123 is disposed on the optical path between the sensing element 14 and the photodetector. The polarizer 123 may be adjusted in advance so that the difference in intensity between the reflected p-polarized light and the reflected s-polarized light in the hydrogen concentration measurement range falls within a predetermined range. For example, the rotation angle of the polarizer 123 may be adjusted so that the intensities of the reflected p-polarized light and the reflected s-polarized light are approximately the same when no hydrogen gas is present. In this way, by appropriately adjusting the rotation angle of the polarizer 123, accuracy can be improved. Note that the polarizer 123 may be omitted.

[0083] The photodetector is composed of one photodetector 173. That is, the one photodetector 173 receives reflected p-polarized light and reflected s-polarized light in a time-division manner and transmits their intensities to the detection control device 40.

[0084] The linearly polarized light that has passed through the polarizer 121 from the light source 11 is incident on the polarization modulator 122. The detection control device 40 controls the polarization modulator 122 to modulate the linearly polarized light from the polarizer 121 into s-polarized light 31s or p-polarized light 31p. For example, p-polarized light 31p is output during a first period, and s-polarized light 31s is output during the subsequent second period.

[0085] The p-polarized light 31p and the s-polarized light 31s are incident on the laminated film 140 of the sensing element 14 via the prism 146. The p-polarized light 31p and the s-polarized light 31s are incident on the laminated film 140 at an angle inclined with respect to the normal direction of the laminated film 140. The p-polarized light 31p or the s-polarized light 31s is incident on the laminated film 140 at a single point. This makes it possible to avoid the influence of differences in characteristics within the plane of the laminated film 140.

[0086] As described in the first embodiment, the p-polarized light 31p and the s-polarized light 31s interfere with each other in the laminated film 140. Furthermore, the optical properties of the hydrogen gas sensing layer 144 change due to the hydrogen gas 30, which changes the reflectance of the p-polarized light 31p and the s-polarized light 31s at the hydrogen gas sensing layer 144 and the interference conditions of the laminated film 140. As a result, the ratio of the reflected light intensities of the p-polarized light 31p and the s-polarized light 31s by the laminated film 140 changes significantly.

[0087] The reflected p-polarized light and the reflected s-polarized light by the laminated film 140 are incident on the polarizer 123 at different periods. Linearly polarized light at a predetermined angle that passes through the polarizer 123 is incident on the photodetector 173. The photodetector 173 receives the reflected p-polarized light and the reflected s-polarized light at different periods and outputs their intensities to the detection control device 40. By detecting the p-polarized light and the s-polarized light at different periods in this way, the reflected light intensities of the reflected p-polarized light and the reflected s-polarized light can be detected by a single photodetector, making it possible to detect the hydrogen concentration.

[0088] 12A has been described as a configuration in which the polarization modulator 122 is arranged on the incident side, but as shown in Fig. 12B, the polarization modulator 122 may also be arranged on the detection side. That is, it may be arranged on the optical path of the reflected light between the sensing element 14 and the polarizer 123. In this case, the rotation angle of the polarizer 121 is set so that the ratio between the intensities of p-polarized light and s-polarized light is constant, and light containing both p-polarized and s-polarized light components is reflected from the sensing element 14.

[0089] The polarization modulator 122 rotates the polarization axis of the reflected light by 90 degrees using time-division control. At this time, by setting the polarizer 123 to be able to pass either p-polarized light or s-polarized light, one polarization component passes during a first period, and the other polarization component rotated by 90 degrees passes during the subsequent second period. This allows the polarization modulator 122 to have the same function as when it is placed on the incident side.

[0090] 13 is a cross-sectional view schematically illustrating an example of the configuration of a sensing element 300 according to one embodiment of the present specification. The sensing element 300 includes a laminated film 310 for detecting hydrogen gas on a transparent substrate 301 made of glass. The laminated film 310 is composed of a half mirror layer 303, an optical interference layer 304, and a hydrogen gas sensing layer 305. The half mirror layer 303, the optical interference layer 304, and the hydrogen gas sensing layer 305 are laminated in this order on the transparent substrate 301.

[0091] The half mirror layer 303 is made of a 14 nm thick Ag thin film, the optical interference layer 304 is made of a 120 nm thick AZO (aluminum doped zinc oxide) thin film, and the hydrogen gas sensing layer 305 is made of a 100 nm thick PdAg alloy thin film.

[0092] A seed layer 302 is present between the laminated film 310 and the transparent substrate 301. The seed layer 302 is made of an Al2O3 thin film with a thickness of 5 nm. The seed layer 302 maintains the adhesive force between the laminated film 310 and the transparent substrate 301.

[0093] A catalyst layer 308 is present so as to cover the hydrogen gas sensing layer 305. The catalyst layer 308 is made of a 5 nm thick Pt (platinum) thin film, and is formed on the laminated film 310 on the side opposite to the transparent substrate 301. The catalyst layer 308 is in contact with the hydrogen gas sensing layer 305. The catalyst layer 308 comes into contact with hydrogen gas and decomposes hydrogen molecules into hydrogen atoms. The hydrogen gas sensing layer 305 changes its optical properties depending on the concentration of hydrogen atoms generated by the catalyst layer 308.

[0094] On the back surface of the transparent substrate 301, on which the laminated film 310 is not formed, a prism 306 is optically coupled to the transparent substrate 301 by optical coupling oil 307. The prism 306 can suppress light reflection on the back surface of the transparent substrate 301. The optical coupling oil 307 reduces light reflection at the interface between the transparent substrate 301 and the prism 306.

[0095] The polarization modulator 122 has a structure in which liquid crystal is sandwiched between two glass plates. The surfaces of both glass plates facing the liquid crystal are covered with transparent electrodes made of ITO (indium tin oxide). In the polarization modulation element according to this embodiment, the liquid crystal is approximately 3.5 μm thick, but the optimum liquid crystal thickness can be selected in relation to the optical anisotropy of the liquid crystal, which will be described later.

[0096] The polarization modulation element used in this example uses liquid crystal with an optical anisotropy of approximately 0.2 and a liquid crystal thickness of 3.5 μm. This allows for a maximum phase change of 0.7 μm, so with a light source wavelength of 0.63 μm, an applied voltage of 10 V or less can achieve a phase difference of half the wavelength of 0.315 μm. The surfaces of these glass substrates facing the liquid crystal are each coated with a polyimide film, and the surface is rubbed in one direction to align the liquid crystal molecules uniformly in one direction.

[0097] A polarization modulator using liquid crystal configured as described above imparts a phase difference between two polarized lights when passing orthogonal polarized lights, and can control this phase difference with an applied voltage. In other words, it functions as an optical phase plate whose phase change amount changes with an externally applied voltage, and can convert linearly polarized light incident from the polarizer 121 into elliptically polarized light, circularly polarized light, linearly polarized light, or the like. In this embodiment, it is used to switch the polarization axis of linearly polarized light.

[0098] For example, when the polarization axis of the incident linearly polarized light is π / 4 relative to the axis of the polarization modulator, applying a voltage that results in a phase difference of an integer multiple of the wavelength of the light source during the first period results in a phase difference of zero, and the output light is linearly polarized light with the same polarization axis as the incident light. Furthermore, applying a voltage that results in a phase difference of half the wavelength in addition to an integer multiple of the wavelength during the second period exerts an effect similar to that of a half-wave plate, resulting in the output light being linearly polarized light whose polarization axis is rotated by π / 2 relative to the incident linearly polarized light. In this example, a polarization modulation element is used to switch the polarization direction, but a similar effect can also be achieved using a 90-degree twisted nematic element.

[0099] 12A and 13. The horizontal axis represents time, and the vertical axis represents the ratio (Ip / Is) of the intensity of reflected p-polarized light Ip to the intensity of reflected s-polarized light Is. In the measurements, the rotation angle of polarizer 123 was set so that the light intensities of reflected p-polarized light and reflected s-polarized light were equal when the hydrogen concentration was 0%.

[0100] The solid line shows the change in the intensity ratio (Ip / Is) of p-polarized light to s-polarized light in response to the introduction and shutoff of hydrogen gas. For the measurement, a hydrogen-nitrogen mixed gas with a hydrogen concentration of 4% was introduced, and then the mixed gas was shut off. In response to the introduction of hydrogen, the reflected light intensity ratio (Ip / Is) increased significantly. When hydrogen was shut off, the reflected light intensity ratio (Ip / Is) gradually decreased. Thus, the configuration of this embodiment also enabled highly sensitive detection of hydrogen concentration.

[0101] [Embodiment 4] FIG. 15 is a schematic diagram showing an example of the configuration of a hydrogen gas sensor system according to an embodiment of the present specification. The following mainly describes the differences from the configuration shown in FIG. 1. Like the configuration shown in FIG. 1, the hydrogen gas sensor system is based on an oblique incidence optical system. Unlike the configuration shown in FIG. 1, the configuration shown in FIG. 15 detects hydrogen gas 30 by irradiating light from an oblique direction onto the stacked film side that detects hydrogen gas 30. The incident optical system includes a light source 11.

[0102] The sensing element 54 includes a laminated film 540 on a substrate 541. The laminated film 540 includes a metal reflective layer 542, an optical interference layer 543, and a hydrogen gas sensing layer 544, which are laminated in this order on the substrate 541. The metal reflective layer 542 totally reflects the light for hydrogen gas detection. The hydrogen gas sensing layer 544 is a half mirror that transmits part of the light for hydrogen gas detection and reflects part of it.

[0103] Light from the light source 11 is incident on the laminated film 540 of the detection element 54 from the hydrogen gas detection layer 544 side. As described above, the light is incident on the laminated film 540 at an angle inclined with respect to the normal direction of the laminated film 540. The incident light is not separated into p-polarized light and s-polarized light, and the light is incident at a single point. This makes it possible to avoid the influence of differences in characteristics within the plane of the laminated film 540.

[0104] As described in the first embodiment, the p-polarized light (component) and s-polarized light (component) of the incident light interfere with each other in the laminated film 540. Furthermore, hydrogen gas changes the optical properties of the hydrogen gas sensing layer 544, which changes the reflectance of the p-polarized light and s-polarized light in the hydrogen gas sensing layer 544 and the interference conditions of the laminated film 540. As a result, the ratio of the reflected light intensities of the p-polarized light and the s-polarized light reflected by the laminated film 540 changes significantly.

[0105] A polarization separator 55 is disposed on the optical path between the sensing element 54 and the photodetector 17. The photodetector 17 includes a first photodetector 171 and a second photodetector 172. The polarization separator 55 separates the light reflected by the sensing element 54 into p-polarized light 32p and s-polarized light 32s. The p-polarized light 32p and s-polarized light 32s from the polarization separator 55 travel along different optical paths.

[0106] The first photodetector 171 receives the p-polarized light 32p and outputs its intensity to the detection control device 40. The second photodetector 172 receives the s-polarized light 32s and outputs its intensity to the detection control device 40. In this way, by splitting the light reflected by the sensing element 54 into p-polarized light and s-polarized light, detecting the intensity of each reflected light, and calculating the ratio, it is possible to detect the hydrogen concentration while eliminating fluctuations in the intensity of the light emitted from the light source.

[0107] FIG. 16 is a cross-sectional view schematically illustrating an example of the configuration of a sensing element 54 according to one embodiment of the present specification. The sensing element 54 includes a laminated film 540 for detecting hydrogen gas on a transparent substrate 541 made of glass. An opaque substrate may be used instead of the transparent substrate 541. The laminated film 540 is composed of a metal reflective layer 542, an optical interference layer 543, and a hydrogen gas sensing layer 544. The metal reflective layer 542, the optical interference layer 543, and the hydrogen gas sensing layer 544 are laminated in this order on the transparent substrate 541. Note that in this embodiment, a prism and an anti-reflection film are not required on the back surface of the transparent substrate 541 on which the laminated film 540 is not formed.

[0108] The metal reflective layer 542 is composed of a 100 nm thick Au thin film. The optical interference layer 543 is composed of a 140 nm thick SiO2 thin film. The hydrogen gas sensing layer 544 is composed of an 8.1 nm thick Pd thin film. The hydrogen gas sensing layer 544 also functions as a half mirror layer.

[0109] FIG. 17 shows simulation results for the optical characteristics of the laminated film 540 shown in FIG. 16. The horizontal axis represents hydrogen concentration, and the vertical axis is a logarithmic axis representing the ratio (Ip / Is) of the intensity Ip of reflected p-polarized light to the intensity Is of reflected s-polarized light by the laminated film 540. The vertical axis is normalized so that the intensity ratio (Ip / Is) is 1 when the hydrogen concentration is 0%. The dashed line represents the change in the intensity ratio (Ip / Is) versus hydrogen concentration for a Pd single-layer film (100 nm) without a laminated structure. The solid line represents the change in the intensity ratio (Ip / Is) versus hydrogen concentration for the laminated film 540 shown in FIG. 16. The wavelength λ of the incident light was 661 nm. The calculation results in FIG. 17 indicate that the laminated film 540, which has an optical interference effect, responds sensitively to changes in hydrogen concentration.

[0110] In the above embodiments, a glass substrate is used as the transparent substrate, but the present invention is not limited to this. In the first, second, and third embodiments, a substrate made of another material can be used as long as it is transparent to the light used for measurement. For example, when a light source in the infrared region is used, a semiconductor substrate such as Si or GaAs can be used.

[0111] An optical fiber can also be used as a method for irradiating light from a light source onto the sensing element and guiding the reflected light from the sensing element to a photodetector. In this case, the sensing element can be integrated into the tip of the optical fiber.

[0112] The intensity of light irradiated from the light source to the detector element may be periodically changed to modulate the optical signal detected by the photodetector, and synchronous detection or Fourier analysis may be performed, thereby further improving detection sensitivity by reducing noise in the optical signal.

[0113] In the above embodiment, an optical hydrogen gas sensor was described as an example of an optical chemical sensor, but the optical chemical sensor of the present invention is not limited to an optical hydrogen gas sensor and can also be applied to, for example, an optical ion sensor that detects pH, an optical gas sensor that detects gas, or an optical biosensor that detects DNA or enzymes. In this way, even when applied to an optical ion sensor that detects pH, an optical gas sensor that detects gas, or an optical biosensor that detects DNA or enzymes, the same effects as those of the above embodiment can be achieved.

[0114] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments. Those skilled in the art can easily modify, add, or convert each element of the above embodiments within the scope of the present disclosure. It is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. [Explanation of symbols]

[0115] 11 Light source 13 Polarization separation element 14, 54, 250, 270, 300 sensing element 15, 55 polarization separator 17 Photodetector 146, 256, 276, 306 Prism 30 Hydrogen gas 31p, 32p p polarization 31s, 32s s polarization 40 Detection control device 122 Polarization Modulator 140, 200, 260, 280, 310, 540 laminated film 142, 202, 253, 273, 303 Half mirror layer 143, 203, 254, 274, 304, 543 Optical interference layer 144, 204, 255, 275, 305, 544 Hydrogen gas sensing layer 147 Anti-reflection coating 171, 172, 173 Photodetectors 542 Metal reflective layer

Claims

1. 1. A sensor system comprising: A sensing element; an incident optical system including a light source and directing light obliquely onto the detector element; a detection device that detects light reflected by the sensing element; Including, The sensing element is a chemical sensing layer whose optical properties change upon contact with a substance to be sensed; a reflective layer that reflects at least a portion of incident light; an intermediate layer between the reflective layer and the chemical sensing layer; Including, the detection device detects p-polarized light and s-polarized light reflected by the sensing element, respectively; Sensor system.

2. 2. The sensor system of claim 1, the p-polarized light and the s-polarized light reflected by the reflective layer and the chemical sensing layer interfere with each other, increasing the difference in reflectance of the p-polarized light and the s-polarized light by the sensing element; Sensor system.

3. 2. The sensor system of claim 1, The sensing element is made of a non-magnetic material. Sensor system.

4. 2. The sensor system of claim 1, The chemical sensing layer is made of a material containing palladium. Sensor system.

5. 2. The sensor system of claim 1, Light is incident on the detection element from the reflective layer side, the reflective layer is a half mirror layer, the chemical sensing layer is a totally reflective layer; Sensor system.

6. 2. The sensor system of claim 1, Light is incident on the sensing element from the chemical sensing layer side, the chemical sensing layer is a half mirror layer, The reflective layer is a totally reflective layer. Sensor system.

7. 2. The sensor system of claim 1, a polarization separator between the light source and the sensing element or between the sensing element and the detection device, which separates p-polarized light and s-polarized light from the incident light; The detection device includes: a first detector that detects p-polarized light reflected by the sensing element; a second detector different from the first detector that detects s-polarized light reflected by the sensing element; Including, Sensor system.

8. 2. The sensor system of claim 1, a polarization modulator between the light source and the sensing element or between the sensing element and the detection device; The polarization modulator comprises: outputting one of p-polarized light and s-polarized light from the incident light during a first period, and outputting the other of the p-polarized light and the s-polarized light from the incident light during a second period after the first period; The detection device includes: detecting the one of the p-polarized light and the s-polarized light reflected by the sensing element during the first period; detecting the other of the p-polarized light and the s-polarized light reflected by the detector element during the second period; Sensor system.

9. 2. The sensor system of claim 1, one of an anti-reflection film and a prism is formed on a side of the detection element on which light from the light source is incident, light from the light source is incident on the reflective layer via one of the anti-reflection film and the prism; Sensor system.

10. 2. The sensor system of claim 1, the reflective layer is a tantalum layer; The intermediate layer is a nitride layer. Sensor system.

11. The sensor system of claim 1, The chemical detection layer is composed of multiple layers. Sensor system.

12. The sensor system according to claim 1 or 11, the sensing element further comprises a catalyst layer covering the chemical sensing layer; Sensor system.

13. A method for detecting an object using a detection element, comprising: The sensing element is a chemical detection layer whose optical properties change upon contact with a predetermined detection target substance; a reflective layer that reflects at least a portion of incident light; an intermediate layer between the reflective layer and the chemical sensing layer; Including, The detection method includes: Light is incident on the detector element at an angle; Detecting p-polarized light and s-polarized light reflected by the sensing element, generating a detection result of the detection object based on a comparison result of the intensities of the p-polarized light and the s-polarized light; Detection method.

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