JP2009264888A - Optical system and infrared imaging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical system comprising a simple structure and an infrared imaging system using the same. <P>SOLUTION: The optical system includes a filter element including a resonance mode grating reflecting light of a specific wavelength region resonating with a periodic structure by minute irregularities; a first optical system guiding light of the first wavelength region radiated from an object to the resonance mode grating; a light source emitting light of a second wavelength region; a second optical system guiding the light of the second wavelength region emitted by the light source to the resonance mode grating; a photodetector detecting the intensity of the light; and a third optical system guiding the light of the specific wavelength region reflected by the resonance mode grating from among the light of the second wavelength region emitted by the light source to the photodetector. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical system using a resonant mode grating and an infrared imaging system using the optical system.

  In recent years, there has been an increasing demand for infrared cameras capable of recognizing living bodies and object images as images even in the dark, such as small security cameras for crime prevention and night vision cameras mounted on automobiles. Along with this, development of an infrared detector or an infrared imaging element, which is a main part of an infrared camera, has been rapidly advanced. In particular, far-infrared rays in the wavelength region of 7 μm to 15 μm are well transmitted through the atmosphere and are in a wavelength region that is often contained in blackbody radiation from objects with human body temperature and general outside temperature. An infrared imaging device capable of imaging is important.

  There are many infrared detection methods, and a representative one is a bolometer that utilizes the property that the resistance value of the thermal resistor changes according to the temperature. This is to detect the amount of received infrared light by measuring the amount of change in the resistance value of the thermal resistor according to the temperature change caused by the infrared light reception. Many techniques have been proposed for infrared imaging devices using bolometers (see, for example, Patent Document 1).

  However, since bolometers are very expensive, they are not very popular for general applications such as in-vehicle cameras and night vision cameras. In order to solve this problem, a technique using an element having a thermo-optic function in which the light transmittance or reflectance in a specific wavelength region is changed by a temperature change due to infrared light reception has been proposed.

  According to this technology, an element having a thermo-optical function is irradiated with light having a wavelength region different from that of the infrared ray to be detected, and the reflected light or transmitted light is received by a light-receiving element such as inexpensive silicon. Detects the amount of light received. Therefore, unlike a technique using a conventional bolometer, a silicon light receiving element can be used as the light receiving element, so that the price of the infrared detection device can be reduced (see, for example, Patent Documents 2 and 3).

  More specifically, in Patent Document 2, as a device having a thermo-optic function, a device in which a metal film and a thin film having a thermo-optic effect are formed on a dielectric block, and the plasmon resonance wavelength region is shifted by a thermal change. A radiation temperature measuring device utilizing this is shown. Patent Document 3 discloses an infrared camera using an optical multilayer filter containing a thermo-optic material as an element having a thermo-optic function, and utilizing the fact that the transmission wavelength region of the multilayer filter changes due to a thermal change. Yes.

  The configuration shown in Patent Document 3 will be described with reference to FIGS. 25 and 26. FIG. FIG. 25 is a diagram illustrating an example of a schematic configuration of a conventional infrared camera. Referring to FIG. 25, the infrared camera 10 includes a near-infrared light source 11, a collimator lens 12, a dichroic mirror 13, a thermo-optic element 14 (Focal Plane Array, hereinafter referred to as FPA 14), a condenser lens 15, A near-infrared light detector 16 and an infrared lens 17 are included.

  The FPA 14 includes an infrared transmission window 14a, a pixel element array 14b, a substrate 14c, a reference filter 14d, and an electronic cooling element 14e. The infrared transmission window 14a, the pixel element array 14b, the substrate 14c, and the reference filter 14d are packaged under reduced pressure, and the temperature is adjusted by the electronic cooling element 14e. 20 indicates near infrared light, 21 indicates an image, and 22 indicates infrared light.

  In the infrared camera 10 shown in FIG. 25, near infrared light 20 emitted from the near infrared light source 11 is converted into parallel light by the collimator lens 12, and has the property of reflecting near infrared light and transmitting infrared light. The light is reflected by the dichroic mirror 13 and enters the FPA 14 that is an element having a thermo-optic function. The near-infrared light 20 that has passed through the FPA 14 is collected by the condenser lens 15 onto the near-infrared light detector 16.

  On the other hand, the infrared light 22 emitted from the image 21 is condensed on the FPA 14 by the infrared lens 17. Each of the pixel element arrays 14b constituting the FPA 14 has a multilayer film structure, and the transmission wavelength region is shifted by a change in refractive index due to temperature. The infrared light 22 condensed on the pixel element array 14b corresponds to the intensity distribution from the image 21, and a temperature change occurs according to the intensity of the incident infrared light 22, and the transmission wavelength is shifted.

  FIG. 26 is a diagram illustrating an example of filter characteristics of the pixel element array. FIG. 26A shows the spectral distribution of light that passes through the pixel element array 14b at the temperature T1. FIG. 26B shows a spectral distribution of light that passes through the pixel element array 14b at the temperature T2. In FIGS. 26A and 26B, the horizontal axis represents the wavelength of light incident on the pixel element array 14b, and the vertical axis represents the intensity of light transmitted through the pixel element array 14b.

As shown in FIGS. 26 (a) and 26 (b), there is a peak of transmitted light intensity at wavelength λ2 at temperature T1, and a peak of transmitted light intensity at wavelength λ3 at temperature T2. Therefore, when the temperature changes from T1 to T2 corresponding to the intensity of infrared light, the transmission spectrum changes as shown in FIG. 26 (a) to FIG. 26 (b). For example, when a narrow-band laser that oscillates near-infrared light having a wavelength λ1 is used as the near-infrared light source 11, the shaded portion shown in FIGS. 26A and 26B is the transmitted light intensity. By capturing a two-dimensional image of transmitted light intensity with the near-infrared detector 16, an image 21 that emits infrared light 22 can be captured.
JP 2002-214035 A Japanese Patent Laid-Open No. 2004-245684 US Patent Application Publication No. 2007/0023661

  However, for example, with the technique disclosed in Patent Document 2, it is not easy to control the peak position and wavelength region of the resonance wavelength. Further, since attenuation of total reflected light is used, in order to generate total reflection, it is necessary that the substrate has a prismatic or diffractive structure, and there is a problem that the structure becomes complicated.

  Further, for example, in the technique disclosed in Patent Document 3, in the case where the infrared detection device is a device that obtains a two-dimensional image, an element (FPA) having a thermo-optic function is formed from a plurality of matrix pixels. Need to be. In order to form a matrix-like pixel, a multilayer film having a complicated structure has to be divided into a large number of fine pixels, which causes a problem that processing is difficult.

  The present invention has been made in view of the above, and an object thereof is to provide an optical system having a simple structure and an infrared imaging system using the optical system.

  In order to achieve the above object, according to a first aspect of the present invention, a filter element having a resonance mode grating that reflects light in a specific wavelength region that resonates with the periodic structure by a periodic structure with fine irregularities, and radiation from an object. A first optical system that guides light in a first wavelength region to the resonance mode grating; a light source that emits light in a second wavelength region; and light in the second wavelength region emitted by the light source. A second optical system that guides the light, a light receiving element that detects light intensity, and light in the specific wavelength region that is reflected by the resonance mode grating among light in the second wavelength region that is emitted from the light source. And a third optical system leading to the optical system.

  According to a second aspect of the present invention, there is provided a filter element having a resonance mode grating that transmits light in a specific wavelength region resonating with the periodic structure by a periodic structure having fine irregularities, and light in the first wavelength region radiated from the object. A first optical system that guides light to the resonance mode grating, a light source that emits light in the second wavelength region, and a second optical system that guides light in the second wavelength region emitted from the light source to the resonance mode grating A light receiving element for detecting the intensity of the light, and a third optical system for guiding the light in the specific wavelength region transmitted through the resonance mode grating among the light in the second wavelength region emitted from the light source to the light receiving device And an optical system.

A third invention is the optical system according to any one of claims 1 to 20, a control unit that controls the optical system, a signal processing unit that processes an output signal from the optical system, and an external signal. An infrared imaging system having an external interface unit for exchanging
The first wavelength region in the optical system is included in an infrared region.

  According to the present invention, an optical system having a simple structure and an infrared imaging system using the optical system can be provided.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

<First Embodiment>
An optical system according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing an example of a schematic configuration of an optical system according to the first embodiment of the present invention. Referring to FIG. 1, an optical system 100 includes a light source 110, a second optical system 120, a half mirror 130, a filter element 140, a third optical system 150, a light receiving element 160, a first optical system And an optical system 170. Reference numeral 200 denotes light having a second wavelength region emitted from the light source 110 (hereinafter referred to as probe light 200), 210 denotes a target object, and 220 denotes radiation light from the target object 210.

  The light source 110 has a function of emitting light having a predetermined wavelength. As the light source 110, for example, a semiconductor laser or the like can be used. The second optical system 120 has a function of making incident light parallel light. As the second optical system 120, for example, a collimator lens formed of optical glass, optical plastic, or the like can be used. The half mirror 130 has a function of reflecting a part of incident light and transmitting a part thereof. The filter element 140 is an element having a thermo-optic effect. The thermo-optic effect is a phenomenon in which the refractive index changes with temperature. The first optical system 170 has a function of collecting incident light. The third optical system 150 has a function of collecting incident light.

  The probe light 200 emitted from the light source 110 is collimated by the second optical system 120 and then guided to the filter element 140 having a thermo-optic effect by the half mirror 130. Further, the radiation light 220 from the target object 210 is taken into the filter element 140 by the first optical system 170. The filter element 140 absorbs light in the first wavelength region (hereinafter referred to as signal light 220a) out of the captured radiation light 220 and converts it into heat. The converted heat corresponds to the intensity of the signal light 220a.

  The filter element 140 reflects the probe light 200. The probe light 200 reflected by the filter element 140 is guided to the light receiving element 160 by the third optical system 150. As will be described later, the reflectance of the filter element 140 with respect to the probe light 200 changes due to heat generated by absorbing the signal light 220a. That is, the intensity of the signal light 220a from the target object 210 can be known from the intensity of the probe light 200 incident on the light receiving element 160.

  In the optical system 100, particularly, the first wavelength region corresponds to far infrared rays in the wavelength region of 7 μm to 15 μm, and the filter element 140 absorbs light in this wavelength region and has sensitivity to far infrared rays. It is preferable. Since light in this wavelength region is well transmitted through the atmosphere and is contained in a large amount of black body radiation from an object having a human body temperature or a general outside air temperature, the optical system 100 has a sensitivity of 7 μm to 15 μm. It can be used as a night vision camera in the dark.

  The first wavelength region may be a wavelength region called a terahertz band (wavelength of about 100 μm to 1000 μm), for example. In the terahertz band, research has recently progressed for reasons such as high permeability to living bodies and the existence of a large number of vibration levels of molecules, and an image sensor for receiving the terahertz band is desired.

  In order to increase the sensitivity to a specific wavelength, a wavelength filter that attenuates light outside the desired first wavelength region out of the wavelength of light incident on the filter element 140 may be provided. In the following description, the first wavelength region is described as the far infrared region, but the present invention is not limited to this.

  The second wavelength region is preferably a wavelength between 0.4 μm and 1.1 μm. When the wavelength region included in this wavelength range is the second wavelength region, it is possible to use a CCD, CMOS, or the like using silicon as the light receiving unit as the light receiving element 160. Such an element is widespread and available at a very low price, so that the optical system 100 can be configured at low cost. In the following description, the second wavelength region is described as the near infrared region, but the present invention is not limited to this.

  Here, a specific configuration of the filter element 140 will be described. FIG. 2 is a diagram illustrating an example of a schematic configuration of the filter element. Referring to FIG. 2, the filter element 140 includes a window 141, a resonance mode grating 142, a substrate 143, a column 144, and a support material 145.

  In the filter element 140 shown in FIG. 2, a plurality of resonance mode gratings 142 are formed on a substrate 143 in a two-dimensional array, and are supported by columns 144. The resonance mode grating 142 absorbs light in the first wavelength region, and changes the reflectance of light from the light source 110 by absorbing the signal light 220a and converting it into heat.

  In FIG. 2A, the first optical system 170 (not shown) is disposed on the window 141 side, and the signal light 220a is incident on the resonance mode grating 142 from the window 141. The optical path is schematically illustrated. This is indicated by a dotted line in the figure. The signal light 220 a passes through the window 141 and is absorbed by the resonance mode grating 142. In addition, the signal light 220 a that could not be absorbed by the resonance mode grating 142 is incident on the substrate 143.

  In order to increase the signal light 220a absorbed by the resonance mode grating 142 and increase the sensitivity, the substrate 143 has a high reflectance with respect to the wavelength region of the signal light 220a, and the signal light 220a incident on the substrate 143 is reflected. More preferably, the light enters the resonance mode grating 142 again.

  In FIG. 2A, the second optical system 120 (not shown) and the third optical system 150 (not shown) are arranged on the substrate 143 side, and the substrate 143 to the resonance mode grating 142. The probe light 200 is configured to be incident, and the optical path is schematically shown in practice in the figure. The probe light 200 passes through the substrate 143 and is reflected by the resonance mode grating 142. Here, the non-reflected probe light 200 enters the window 141, and if reflected by the window 141, it becomes noise light and leads to a decrease in sensitivity of the optical system 100. It is preferable that the reflectance is low.

  The filter element 140 and the light receiving element 160 may not have a pixel structure, but a two-dimensional image of an object can be obtained by having a two-dimensional array pixel structure. In particular, a sharp two-dimensional image can be obtained because the pixel is in contact with the column 144 with a small area and each pixel is thermally isolated.

  FIG. 3 is a diagram illustrating an example of a schematic configuration of a two-dimensional array pixel structure in the filter element. FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along the line AA in FIG. Referring to FIG. 3, a column 144 is formed on a substrate 143, and a membrane-like resonance mode grating 142 is fixed from the outside by the column 144. Since the resonance mode grating 142 has a membrane shape, the heat capacity of the resonance mode grating 142 can be reduced, and the reaction rate to heat can be increased.

  Further, by forming the resonance mode grating 142 into a membrane shape, the resonance mode grating 142 is thermally isolated from the substrate 143 constituting the filter element 140. Thus, the resonance mode grating 142 can avoid the influence of heat propagation from the substrate 143, and an optical system with less thermal noise can be realized. As the thickness of the membrane, the thinner the membrane, the smaller the heat capacity, which is preferable. However, if it is too thin, processing becomes difficult, and problems such as weak mechanical strength occur, and therefore, about 1 μm to 10 μm is preferable.

  Furthermore, in order to reduce the influence of heat due to convection or the like, the resonance mode grating 142 is preferably sealed in a reduced pressure atmosphere or an inert gas atmosphere sealed by a micro vacuum package or the like. In FIG. 2, the filter element 140 is decompressed and packaged by a window 141, a substrate 143, and a support material 145. Since the resonant mode grating 142 is packaged in a reduced pressure state or filled with an inert gas, the influence of heat from the outside due to convection or the like is reduced, and the optical system 100 with less thermal noise is realized. Can do.

  As described above, the material constituting the window 141 has a high transmittance with respect to the signal light 220a and a low reflectance with respect to the probe light 200, and the material that constitutes the substrate 143 with respect to the signal light 220a. Therefore, it is preferable to use a probe having a high reflectance with respect to the probe light 200. For example, when the signal light 220a is far-infrared and the probe light 200 is near-infrared, the material constituting the window 141 is a material having a high transmittance with respect to both far-infrared and near-infrared, such as ZnS and ZnSe. Alternatively, a material having high absorption with respect to near infrared rays such as Ge can be used.

In order to further reduce the reflectance of the probe light 200, the window 141 is more preferably provided with an antireflection film or an antireflection structure. FIG. 4 is a diagram illustrating an example of a window antireflection structure. For example, as shown in FIG. 4, the window 141 may have a structure having a triangular shape 141 a smaller than the wavelength of the probe light 200 as an antireflection structure. As the material constituting the substrate 143, or the like can be used SiO ₂ and Si. In order to further increase the reflectance of the signal light 220a, it is more preferable that a reflective film is formed on the substrate 143.

  As described above, a material having a high transmittance with respect to the signal light 220 a and a low reflectance with respect to the probe light 200 is used as a material constituting the window 141 of the filter element 140, and a signal light is used as a material constituting the substrate 143. By using a material having a high reflectance with respect to 220a and a high transmittance with respect to the probe light 200, the signal light 220a is well absorbed by the filter element 140, and the probe light is noise due to reflection from the material constituting the window 141. Therefore, the optical system 100 can be realized with less noise and high sensitivity.

  As shown in FIG. 2B, contrary to FIG. 2A, the signal light 220a may be incident from the substrate 143 side and the probe light 200 may be incident from the window 141 side. At this time, as described above, in order to better absorb the signal light 220a by the resonance mode grating 142, the window 141 preferably has a higher reflectance than the signal light 220a. Further, the window 141 should have a high transmittance with respect to the probe light 200, and it is desirable that the probe light 200 transmitted through the resonance mode grating 142 is not reflected by the substrate 143 in order to reduce noise of the probe light 200.

  Therefore, the material constituting the window 141 has a high reflectance with respect to the signal light 220a and the transmittance with respect to the probe light 200, and the material constituting the substrate 143 has a transmittance with respect to the signal light 220a. It is preferable to use one having a high reflectance and a low reflectance with respect to the probe light 200. As for the material and structure, an antireflection film, an antireflection structure, or a reflection film can be used as described above.

  As described above, a material having a high transmittance with respect to the signal light 220 a and a low reflectance with respect to the probe light 200 is used as a material constituting the substrate 143 of the filter element 140, and a signal light is used as a material constituting the window 141. By using a material having a high reflectance with respect to 220a and a high transmittance with respect to the probe light 200, the signal light 220a is well absorbed by the filter element 140, and the probe light 200 is reflected by reflection from the material constituting the substrate 143. A configuration with less noise can be achieved, and the optical system 100 with less noise and high sensitivity can be realized.

  Here, the resonance mode grating will be described in detail. A resonant mode grating is one of the anomalous phenomena in a diffraction grating. A resonance phenomenon occurs when the grating pitch and the wavelength of the incident light satisfy certain resonance conditions. A filter can be produced. The reflectivity at the resonant wavelength theoretically reaches 100%. Much research has been conducted on resonant mode gratings, for example, as described in Optics Letters Vol.19 919-921 (1994), Applied Optics Vol.34 8106-81109 (1995) and the like.

  FIG. 5 is a diagram illustrating an example of a schematic configuration of a resonance mode grating. The resonant mode grating 300 shown in FIG. 5 is composed of two kinds of materials having different refractive indexes, and has a higher refractive index nH on a substrate layer 301 made of a low refractive index material having a lower refractive index nL. A waveguide layer 302 made of a high refractive index material is formed with a thickness h1, and a lattice layer 303 made of a low refractive index material is formed with a thickness h2. Here, refractive index nH> refractive index nL, and when two types of materials are used thereafter, a material with a higher refractive index is a high refractive index material, and a material with a lower refractive index is a low refractive index. Called material.

  In the resonant mode grating 300, only the wavelength of the incident light that resonates with the grating layer 303 is coupled to the waveguide mode of the waveguide layer 302 and is resonantly reflected. The lattice layer 303 has a periodic structure in which uneven structures are arranged in one direction with a period p. In such a unidirectional periodic structure, dependence on the polarization direction occurs, and therefore, as shown in FIG. 5, the component having electric field vibration parallel to the groove has TE polarization and the electric field vibration perpendicular to the groove direction. The component will be called TM polarized light.

In FIG. 5, the waveguiding layer 302 is formed of a thermo-optic material. A thermo-optic material is a material having a large amount of change in refractive index with respect to a thermal change, and there is no clear definition, but in this specification, the temperature change of the refractive index with respect to a specific wavelength at room temperature. A material satisfying that Δn / ΔT (hereinafter referred to as a thermo-optic coefficient) is 5 × 10 ⁻⁵ or more will be referred to. The thermo-optic coefficient for various materials is described in, for example, Handbook of Thermo-Optic Coefficients of Optical Materials with Applications.

  As the thermo-optic material, it is preferable that the thermo-optic coefficient is large because the characteristic change with respect to the thermal change of the resonant mode grating becomes large. As the material having a relatively high refractive index, a semiconductor material such as Si, GaP, or GaN is preferred. A polymer material such as PMMA is preferable as a material having a relatively low value.

  By using a semiconductor material that is a high refractive index material having a high thermooptic effect, a more sensitive optical system can be realized. In particular, a semiconductor material is more suitable because it has a small coefficient of thermal expansion, and changes in structure due to heat are small. Further, by using a polymer material which is a low refractive index material having a high thermo-optic effect, a more sensitive optical system can be realized.

For example, the approximate thermo-optic coefficients (units are all K ⁻¹ ) of Si, GaP, and GaN semiconductor materials are 3 × 10 ⁻⁴ , 2 × 10 ⁻⁴ , and 0.6 × 10 ⁻⁴ , respectively. The thermo-optic coefficient of the polymer material PMMA is approximately −1 × 10 ⁻⁴ . On the other hand, thermo-optic coefficients of general optical materials such as SiO ₂ , Al ₂ O ₃ , and CaF ₂ are approximately −0.6 × 10 ⁻⁵ , 1.26 × 10 ⁻⁵ , and −1.18 ×. It is about 10 ^−5, which is one digit or more smaller than the above thermo-optic material.

  In particular, a semiconductor material has a large thermo-optic coefficient, but has a small coefficient of thermal expansion, so that a change in shape due to heat is small and more suitable. The resonance mode grating needs to have absorption with respect to signal light. Therefore, the thermo-optic material is more preferably a material that absorbs light in the first wavelength region and transmits light in the second wavelength region.

In the resonant mode grating 300 shown in FIG. 5, as an example, the waveguide layer 302 is made of GaP, which is a material having a high refractive index and a large thermooptic coefficient, and the substrate layer 301 and the grating layer 303 are made of a low refractive index and a small thermooptic coefficient. The reflection characteristics in the case of using the material SiO ₂ were calculated by rigorous coupled wave analysis (RCWA). Here, the refractive index nH of GaP is 3.3122 at 20 ° C., the thermooptic coefficient is 1.6 × 10 ⁻⁴ , the refractive index nL of SiO ₂ is 1.46, and the thermooptic coefficient is considered to be negligibly small. Zero. The thickness h1 of the waveguide layer 302 was 24.5 nm, the thickness h2 of the grating layer 303 was 200 nm, and the period p of the grating layer 303 was 500 nm.

  6 to 8 are diagrams showing examples of calculation results of reflection characteristics by strict coupling wave analysis (RCWA) in the resonant mode grating 300. FIG. FIG. 6 shows the reflection spectral characteristics with respect to the TE polarized light incident at a temperature of 20 ° C. In FIG. 6, the horizontal axis represents the wavelength of light incident on the resonance mode grating 300, and the vertical axis represents the reflected light intensity of light reflected by the resonance mode grating 300. As shown in FIG. 6, it can be seen that resonance reflected light having a peak near the wavelength of 0.8 μm appears.

  FIG. 7 shows the change in reflection characteristics when the refractive index of GaP changes with temperature. In FIG. 7, the horizontal axis represents the wavelength of light incident on the resonance mode grating 300, and the vertical axis represents the reflectance of the resonance mode grating 300. n is the value of the refractive index at the temperature in (). Since the thermo-optic coefficient changes with temperature, the refractive index value n at the temperature displayed here is strictly different from the actual one, but as shown in FIG. 7, the peak position of the resonant reflected light depends on the temperature. You can see that it shifts.

  In FIG. 8, changes in reflected light intensity at a wavelength of 0.8 μm are plotted with temperature as a variable. In FIG. 8, the horizontal axis represents the temperature of the resonance mode grating 300, and the vertical axis represents the reflected light intensity of the light reflected by the resonance mode grating 300. As shown in FIG. 8, it can be seen that the reflected light intensity is modulated by the temperature change of the resonant mode grating 300. Therefore, for example, in a configuration such as the optical system 100 shown in FIG. 1, the resonance mode grating 300 absorbs the signal light 220a and changes in temperature, so the probe light 200 (here, the intensity of the signal light 220a changes). The reflectance of light having a wavelength of 0.8 μm will change.

  Thus, unlike the complex multilayer film structure as shown in Patent Document 3 (USP 2007-0023661), the resonance mode grating 300 has the necessary functions with a small number of films and a simple configuration as shown in FIG. Obtainable. Therefore, when an array structure as shown in FIG. 3 is produced, it can be easily processed as compared with a complicated multilayer film structure as shown in Patent Document 3 (USP 2007-0023661).

  Another merit of the multilayer film structure is that the sharpness of the reflection spectrum (that is, the sharpness of the reflected light change due to the temperature change) can be easily adjusted. This will be described with reference to FIGS. FIG. 9 is a diagram (part 1) illustrating another example of a schematic configuration of a resonance mode grating. The resonance mode grating 310 shown in FIG. 9 has a structure different from that of the resonance mode grating 300 shown in FIG. 5, and the waveguide layer 311 and the grating layer 312 have a single thermo-optic with thicknesses h1 and h2, respectively. It is made of material.

In the resonant mode grating 310 shown in FIG. 9, as an example, the reflection characteristics when PMMA is used as the thermo-optic material constituting the waveguide layer 311 and the grating layer 312 were calculated by rigorous coupled wave analysis (RCWA). Here, the refractive index n = 1.49 of the PMMA at a temperature of 20 ° C. and the thermo-optic coefficient were set to −1.1 × 10 ⁻⁴ . The thickness h1 of the waveguide layer 311 was changed to 314 nm, the thickness h2 of the grating layer 312 was changed from 35 nm to 100 nm, and the period p of the grating layer 312 was 500 nm.

  FIG. 10 is a diagram showing an example of the reflection spectral characteristic of the resonant mode grating 310, and shows the reflection spectral characteristic with respect to the vertically incident TE polarized light at a temperature of 20 ° C. FIG. In FIG. 10, the horizontal axis represents the wavelength of light incident on the resonance mode grating 310, and the vertical axis represents the reflected light intensity of light reflected by the resonance mode grating 310. As shown in FIG. 10, the peak wavelength of the resonance reflected light changes as the thickness h2 of the grating layer 312 changes, and the steepness of the reflection spectrum also changes. As described above, since the reflection spectrum width and the steepness can be easily changed only by changing the structure, it is possible to easily adjust the optical characteristics according to the specifications of the optical system.

  The resonance mode grating can take various configurations in addition to the configurations shown in FIGS. 5 and 9. Another example of the configuration of the resonant mode grating will be described with reference to FIGS. 11 and 12. FIG. 11 is a diagram (part 2) illustrating another example of a schematic configuration of a resonance mode grating. FIG. 12 is a third diagram illustrating another example of the schematic configuration of the resonance mode grating.

  A resonance mode grating 320 shown in FIG. 11 has a configuration in which a low refractive index layer 323 made of a low refractive index material is formed so as to fill the grating layer 322 on the substrate layer 321 made of a high refractive index material and the grating layer 322. It is. Here, the high refractive index material constituting the substrate layer 321 may be a thermo-optic material, the low refractive index material constituting the low refractive index material 323 may be a thermo-optic material, or both are thermo-optic materials. Also good. The resonance mode grating 330 shown in FIG. 12 has a configuration in which a grating layer 333 made of a high refractive index material is formed on a substrate layer 331 made of a low refractive index material and a grating layer 332.

  In the case where the resonance mode grating is made of a single material like the resonance mode grating 310 shown in FIG. 9, it is not necessary to stack different materials with few components, so that an optical system can be manufactured with fewer steps. it can. However, when the resonance mode grating is formed of a single material, a material that is a thermo-optic material and has absorption in the first wavelength region must be used as the material constituting the resonance mode grating. Don't be.

  In contrast, the resonance mode grating 320 shown in FIG. 11 uses two types of materials. As a merit of using two or more kinds of materials, even if the thermo-optic material does not absorb the signal light, if the different materials constituting the resonance mode grating can absorb the signal light and change it into heat, it can be used as a filter element. It functions, and the shape of the reflection spectrum can be adjusted by a combination of a plurality of materials.

For example, ZnS is a thermo-optic material, but cannot absorb signal light because of its high transmittance with respect to far infrared rays, but ZnS is used as the high refractive index material and SiO ₂ is used as the low refractive index material shown in FIG. In combination with other materials, SiO ₂ can absorb far-infrared rays and convert it into heat, so that it can be used as a material for forming the resonant mode grating according to the present invention.

  Thus, by configuring the resonant mode grating from a plurality of materials, the thermo-optic material may not necessarily have absorption in the first wavelength region, and another different material may be in the first wavelength region. As long as the absorption rate is high. Thereby, the selection range of the material constituting the optical system according to the present invention is widened, and the production becomes easier.

  FIG. 13 is a diagram (part 4) illustrating another example of a schematic configuration of a resonance mode grating. A resonance mode grating 340 shown in FIG. 13 has a waveguide layer 342 made of a high refractive index material on a substrate layer 341 made of a low refractive index material as in the resonance mode grating 300 shown in FIG. A grating layer 343 made of a refractive index material is formed with a thickness h2. As shown in FIG. 13, the lattice layer 343 may have a two-dimensional period as a periodic structure.

  The lattice layer 343 has a two-dimensional periodic structure composed of a concavo-convex structure having periods of px and py in the x and y directions shown in FIG. When px and py are equal to each other, the reflection spectral characteristics are the same for both x-polarized light (light having electric field vibration in the x direction) and y-polarized light (light having electric field vibration in the y direction). There is a merit that a mode grating can be used, and any polarized light can be used as the probe light.

  FIG. 14 is a diagram illustrating an example of the relationship between the wavelength of the resonant mode grating 340 and the reflected light intensity. In FIG. 14, the horizontal axis represents the wavelength of light incident on the resonance mode grating 340, and the vertical axis represents the reflected light intensity of the light reflected by the resonance mode grating 340. FIG. 15 is a diagram illustrating an example of the relationship between the temperature of the resonance mode grating 340 and the reflected light intensity. In FIG. 15, the horizontal axis represents the temperature of the resonance mode grating 340, and the vertical axis represents the reflected light intensity of the light reflected by the resonance mode grating 340.

  When the values of px and py are different, that is, in a periodic structure having in-plane anisotropy, as shown in FIG. 14, the relationship between the wavelength and reflected light intensity (reflection spectral characteristics) is x-polarized light and y-polarized light. The peak position is shifted. At this time, the reflected light intensity with respect to the temperature change at the wavelength λ1 is as shown in FIG.

  Uses light with both x-polarized light and y-polarized light as probe light, and a light receiving element that can detect the light intensity of polarized light components in both x- and y-directions to detect a wider temperature range It becomes possible to do. This can be achieved, for example, by providing two light receiving elements after the optical path is divided by the polarization component by the polarization beam splitter. In this way, an optical system with a wide dynamic range can be realized.

  As the light source, it is preferable to use a light source having a narrow wavelength band in order to increase the sensitivity of the reflected light intensity change with respect to the temperature change. In order to control the wavelength of the probe light to a narrow band, it is more preferable that the light source includes a narrow band wavelength filter. By providing the light source with a narrow-band wavelength filter, a more sensitive optical system can be realized. Further, by providing the light source with a narrow band wavelength filter, even if there is a slight fluctuation in the wavelength of the light source, it is less affected and a more stable optical system can be realized.

  Furthermore, by using a variable filter in which the wavelength region transmitted by the filter is variable, the wavelength can be controlled in accordance with the temperature of the resonance mode grating and the intensity of the signal light. Therefore, it is possible to cope with problems such as a change in temperature of the resonant mode grating due to a change in environmental temperature and saturation of the light receiving element. For example, when the light receiving element is saturated because the intensity of the far-infrared ray that is the signal light is too strong, the reflected light of the probe light is shifted so that the wavelength of the light source is shifted by the temperature control mechanism and the light receiving element is not saturated. It is conceivable to control the strength.

  FIG. 16 is a diagram illustrating an example of a schematic structure of a variable filter. As the variable filter, an etalon filter in which a liquid crystal material 403 is sandwiched between transparent electrode substrates 401 and 402 as in the variable filter 400 shown in FIG. 16, and the transmission wavelength is changed by controlling the voltage V applied to the liquid crystal. A liquid crystal type wavelength tunable filter that can be used can be used.

  As the light source, it is particularly preferable to use a semiconductor laser that is inexpensive in a narrow wavelength band. However, wavelength fluctuations due to mode hops exist in ordinary semiconductor lasers. As shown in FIG. 6, the resonant mode grating changes the reflected light intensity not only due to temperature change but also due to wavelength fluctuation. Therefore, when the mode hop exists in the light source, the received light intensity may fluctuate.

  On the other hand, among semiconductor lasers, it is more preferable to use a distributed feedback laser (DFB laser), a distributed Bragg reflection laser (DBR laser), or a vertical cavity surface emitting laser (VCSEL) having a small wavelength variation as a light source. In these lasers, a distributed feedback type structure or a distributed reflection type structure is formed in the resonator of the semiconductor laser, so that the resonating wavelength band is very narrow and light in a very narrow band can be obtained. Therefore, by using these lasers as the light source of the optical system according to the present invention, a more sensitive and stable optical system can be obtained.

  Furthermore, the light source as described above preferably includes a temperature control mechanism. The semiconductor laser light source has a wavelength variation depending on the temperature, and the oscillation wavelength can be controlled by precisely controlling the temperature. In particular, a DFB laser or VCSEL is more preferable because the oscillation wavelength can be precisely controlled by temperature control. As the temperature adjustment mechanism, for example, a mechanism that is electrically controlled using a Peltier element is conceivable.

  Further, as described in the explanation of the variable filter, the provision of the temperature adjusting mechanism makes it possible to control the wavelength in accordance with the temperature of the resonance mode grating and the intensity of the signal light. Therefore, it is possible to cope with problems such as a change in temperature of the resonant mode grating due to a change in environmental temperature and saturation of the light receiving element. As another example, the incident angle of the probe light incident on the resonance mode grating may be adjusted.

  This can be achieved because the second optical system that guides the light from the light source to the filter element includes an incident angle adjustment mechanism. Specifically, for example, the angle adjustment mechanism is attached to the half mirror 130 in the optical system 100 shown in FIG. 1, or the drive mechanism that can move in the direction perpendicular to the optical axis is provided in the collimator lens 102. realizable.

  FIG. 17 is a diagram showing the reflection spectral characteristics when light is incident on the resonance mode grating 310 shown in FIG. 9 while changing the incident angle. In FIG. 17, the horizontal axis represents the wavelength of light incident on the resonance mode grating 310, and the vertical axis represents the reflected light intensity of light reflected by the resonance mode grating 310. When the thickness h1 of the waveguide layer 311 is 314 nm, the thickness h2 of the grating layer 312 is 100 nm, and the period p of the grating layer 312 is 500 nm, the incident angle is changed from 0 degree to 3 degrees, and the reflectance is calculated by RCWA. Went. As is clear from FIG. 17, in the resonant mode grating 310 shown in FIG. 9, the reflection wavelength region greatly changes depending on the incident angle.

  As described above, by providing the probe light incident angle adjustment mechanism, the probe light reflected by the resonance mode grating is adjusted in accordance with the temperature of the resonance mode grating and the intensity of the signal light in the same manner as the variable filter described above. The strength can be adjusted. Therefore, it is possible to cope with problems such as a change in temperature of the resonant mode grating due to a change in environmental temperature and saturation of the light receiving element.

  According to the optical system of the first embodiment of the present invention, the intensity of the temperature dependence of the reflected light intensity or transmitted light intensity is controlled by controlling the shape of the resonant mode grating constituting the optical system. Therefore, a more sensitive optical system can be realized. Further, since a complicated configuration such as a multilayer film is not used, the pixel structure can be made easier, and an optical system having a simple configuration can be realized.

<Second Embodiment>
An optical system according to a second embodiment of the present invention will be described with reference to FIG. FIG. 18 is a diagram illustrating an example of a schematic configuration of an optical system 500 according to the second embodiment of the present invention. 18, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof may be omitted.

  Referring to FIG. 18, the optical system 500 includes a light source 110, a second optical system 120, a third optical system 150, a light receiving element 160, and a filter element 510. The filter element 510 is integrated with the first optical system 520. Reference numeral 200 denotes light having a second wavelength region emitted from the light source 110 (hereinafter referred to as probe light 200), 210 denotes a target object, and 220 denotes radiation light from the target object 210.

  The probe light 200 emitted from the light source 110 is collimated by the second optical system 120 and then enters a filter element 510 having a resonance mode grating made of a plurality of materials having different thermal expansion coefficients at a predetermined incident angle. . As described above, the light incident on the filter element 510 is not perpendicularly incident but may have a predetermined incident angle, and thus the half mirror 130 used in the optical system 100 shown in FIG. 1 can be omitted.

  Further, the radiation light 220 from the target object 210 is taken into the filter element 510 by the first optical system 520 composed of a microlens array formed integrally with the filter element 510. As described above, the first optical system 520 may be formed integrally with the material constituting the window of the filter element 510.

  The filter element 510 absorbs light in the first wavelength region (hereinafter referred to as signal light 220a) out of the captured radiation light and converts it into heat. As will be described later, a part of the filter element 510 changes due to a heat change, and the reflectance with respect to the probe light 200 changes. The reflected probe light 200 is guided to the light receiving element 160 by the third optical system 150.

  As the filter element 510, a filter element 140 made of a resonance mode grating including the thermo-optic material used in the optical system 100 shown in FIG. 1 may be used, but here, as another example, a plurality of filter elements having different coefficients of thermal expansion are used. A filter element having a resonance mode grating formed of a material was used. Details regarding this will be described with reference to FIG.

  FIG. 19 is a diagram illustrating an example of a schematic configuration of a filter element. A filter element 510 shown in FIG. 19 has a plurality of resonance mode gratings 512 having a two-dimensional array pixel structure formed on a substrate 511 and supported by support columns 513. The resonant mode grating 512 has absorption with respect to light in the first wavelength region, and its shape is changed by absorbing the signal light 220a and changing it to heat, thereby changing the reflectance of light from the light source 110. .

  Details of the resonant mode grating 512 will be described with reference to FIG. FIG. 20 is a diagram illustrating an example of a schematic configuration of the resonance mode grating 512. 20, the same components as those in FIG. 19 are denoted by the same reference numerals, and the description thereof may be omitted. As shown in FIG. 20 (a), the resonant mode grating 512 has a high refractive index material portion 512b with a high thermal expansion coefficient formed on a low refractive index material portion 512a with a low thermal expansion coefficient. The upper surface of the material part 512b has a periodic uneven structure.

Further, only one side surface of the resonance mode grating 512 is supported by the support column 513. The low-refractive index material part 512a or the high-refractive index material part 512b or both absorb the signal light and convert it into heat. As specific materials, for example, it is conceivable to use SiO ₂ as a low refractive index material and TiO ₂ as a high refractive material. The thermal expansion coefficients (linear expansion coefficient, all units are K ⁻¹ ) of SiO ₂ and TiO ₂ are approximately 0.5 × 10 ⁻⁶ and 9 × 10 ⁻⁶ , respectively.

  When the temperature of the resonance mode lattice 512 changes, the difference between the thermal expansion coefficients of the two types of materials causes a deflection as shown in the drawing with reference to the column 513 as shown in FIG. 20B. become. As a result, the incident angle at which the probe light 200 enters the resonance mode grating 512 is increased.

FIG. 21 is a diagram illustrating an example of an incident angle change of the reflection spectral characteristic related to the TE polarized light of the resonance mode grating 512. In FIG. 21, the horizontal axis represents the wavelength of light incident on the resonance mode grating 512, and the vertical axis represents the reflected light intensity of light reflected by the resonance mode grating 512. The characteristics shown in FIG. 21 use SiO ₂ having a thickness of 1 μm as the low refractive index material portion 512a, and TiO ₂ having a thickness of 0.25 μm (thickness of the concavo-convex structure portion) as the high refractive index material portion 512b. It is the one when it was. As is clear from FIG. 21, the reflection characteristics are greatly changed by the change in the incident angle due to the minute deformation.

  FIG. 22 is a diagram illustrating an example of a change in reflected light intensity with respect to the incident angle of the resonance mode grating 512. In FIG. 22, the horizontal axis represents the incident angle of light incident on the resonance mode grating 512, and the vertical axis represents the reflected light intensity of light reflected by the resonance mode grating 512. The characteristics shown in FIG. 22 are obtained when the wavelength of the probe light (second wavelength region) is 0.8 μm. As shown in FIG. 22, when the wavelength of the probe light (second wavelength region) is 0.8 μm, the reflected light intensity greatly changes when the incident angle changes due to the deflection of the resonance mode grating 512.

  FIG. 21 and FIG. 22 simulate only the change in the incident angle, and it is assumed that the deformation is linear. However, since the reflected light intensity changes even in such a state, even a resonance mode grating that warps due to thermal deformation can be used as the configuration of the filter element according to the present invention. .

  As described above, since the reflection characteristic is very sensitive to the change in the incident angle, it is possible to configure an optical system with very high sensitivity. Further, the resonant mode grating using the thermo-optic material shown in FIG. 5 and the like can be formed by a general optical material without using a special material having a large thermo-optic coefficient. Easy.

  Further, as shown in FIG. 19, the filter element 510 is decompressed and packaged by a substrate 511, a support member 514, and a window 515 in order to avoid the influence of thermal diffusion. The window 515 is formed integrally with the first optical system 520 composed of a microlens array. Therefore, as described above, the first optical system 520 and the window 515 can be integrated, and the number of parts can be reduced. The first optical system 520 formed of a microlens array corresponds to a plurality of pixels, and is a compound eye imaging system that forms an image of an object in a pixel portion.

  According to the optical system according to the second embodiment of the present invention, it is possible to use a more general optical material without using a thermo-optic material as a material constituting the optical system, Since the reflected or transmitted light intensity change of the filter constituting the resonance mode grating is very sensitive to the angle change, a highly sensitive optical system can be realized. In addition, since a complicated structure such as a multilayer film is not used, the pixel structure can be made easier, so that an optical system having a simple structure can be realized.

<Third Embodiment>
An optical system according to a third embodiment of the present invention will be described with reference to FIG. FIG. 23 is a diagram illustrating an example of a schematic configuration of an optical system 600 according to the third embodiment of the present invention. 23, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof may be omitted.

  Referring to FIG. 23, the optical system 600 uses a dichroic mirror 610 instead of the half mirror 130, except that the dichroic mirror 610 is disposed between the filter element 140 and the first optical system 170. 1 is configured similarly to the optical system 100 shown in FIG.

  In the optical system 600, the probe light 200 is guided to the filter element 140 by the dichroic mirror 610, and the intensity of the light transmitted through the filter element 140 is detected by the light receiving element 160. Further, the signal light 220 passes through the dichroic mirror 610 and is guided to the filter element 140. Here, a dichroic mirror 610 that transmits the signal light 220 and reflects the probe light 200 is used. However, a dichroic mirror 610 that reflects the signal light 220 and transmits the probe light 200 may be used.

  The optical systems 100 and 500 shown in FIGS. 1 and 18 are not configured to detect the intensity of the probe light 200 reflected by the filter element 140 or 510, and like the optical system 600 shown in FIG. A configuration may be adopted in which the intensity of the probe light 200 that passes through is detected.

  The optical system according to the third embodiment of the present invention has the same effects as those of the first and second embodiments of the present invention.

<Fourth embodiment>
An infrared imaging system according to the fourth embodiment of the present invention will be described with reference to FIG. FIG. 24 is a diagram illustrating an example of a schematic configuration of an infrared imaging system 700 according to the fourth embodiment of the present invention. Referring to FIG. 24, the infrared imaging system 700 includes an optical system 100, an optical system control unit 710, a signal processing unit 720, a processor 730, and an external interface 740. An infrared imaging system 700 shown in FIG. 24 is an infrared imaging system using the optical system 100 shown in FIG.

  In the infrared imaging system 700, the optical system control unit 710 has a function of controlling the optical system 100. The signal processing unit 720 has a function of processing an output signal from the optical system 100. The processor 730 has a function of driving the optical system control unit 710 and the signal processing unit 720. The external interface 740 has a function of exchanging signals with the outside of the infrared imaging system 700.

  The infrared imaging system 700 is particularly preferably used as an imaging system for imaging far-infrared wavelengths. Since such an imaging system can obtain an image of a person or animal even in the dark, a surveillance camera, an automobile, etc. It can also be used as an in-vehicle camera mounted on a moving body. Needless to say, instead of the optical system 100, the optical system 500, the optical system 600, or an optical system obtained by adding various modifications and substitutions thereto can be used.

  According to the infrared imaging system of the fourth embodiment of the present invention, it is possible to realize an infrared imaging system capable of imaging with high sensitivity with a simple configuration using the optical system according to the present invention.

  The preferred embodiment of the present invention has been described in detail above. However, the present invention is not limited to the above-described embodiment, and various modifications can be made to the above-described embodiment without departing from the scope of the present invention. And substitutions can be added.

It is a figure which shows the example of a schematic structure of the optical system which concerns on the 1st Embodiment of this invention. It is a figure which shows the example of a rough structure of a filter element. It is a figure which shows the example of a rough structure of the two-dimensional array pixel structure in a filter element. It is a figure which shows the example of the reflection preventing structure of a window. It is a figure which shows the example of a rough structure of a resonance mode grating | lattice. FIG. 6 is a diagram (part 1) illustrating an example of a calculation result of reflection characteristics by a strict coupled wave analysis (RCWA) in a resonance mode grating 300; FIG. 6 is a diagram (part 2) illustrating an example of a calculation result of reflection characteristics by a strict coupling wave analysis (RCWA) in the resonance mode grating 300; FIG. 11 is a diagram (part 3) illustrating an example of a calculation result of reflection characteristics by a strict coupling wave analysis (RCWA) in the resonance mode grating 300; FIG. 10 is a diagram (part 1) illustrating another example of a schematic configuration of a resonance mode grating; 6 is a diagram illustrating an example of reflection spectral characteristics of a resonance mode grating 310. FIG. FIG. 10 is a second diagram illustrating another example of a schematic configuration of a resonance mode grating. FIG. 10 is a third diagram illustrating another example of a schematic configuration of a resonance mode grating. FIG. 14 is a diagram (part 4) illustrating another example of a schematic configuration of a resonance mode grating; It is a figure which shows the example of the relationship between the wavelength of the resonance mode grating | lattice 340, and reflected light intensity. It is a figure which shows the example of the relationship between the temperature of the resonance mode grating | lattice 340, and reflected light intensity. It is a figure which shows the example of the schematic structure of a variable filter. FIG. 10 is a diagram illustrating reflection spectral characteristics when light is incident on the resonance mode grating 310 illustrated in FIG. 9 while changing an incident angle. It is a figure which shows the example of a schematic structure of the optical system 500 which concerns on the 2nd Embodiment of this invention. It is a figure which shows the example of a rough structure of a filter element. 5 is a diagram illustrating an example of a schematic configuration of a resonance mode grating 512. FIG. It is a figure which shows the example of the incident angle change of the reflective spectral characteristic regarding the TE polarized light of the resonance mode grating | lattice 512. FIG. It is a figure which shows the example of the change of the reflected light intensity with respect to the incident angle of the resonance mode grating | lattice 512. FIG. It is a figure which shows the example of a schematic structure of the optical system 600 which concerns on the 3rd Embodiment of this invention. It is a figure which shows the example of a schematic structure of the infrared imaging system 700 which concerns on the 4th Embodiment of this invention. It is a figure which shows the example of a schematic structure of the conventional infrared camera. It is a figure which shows the example of the filter characteristic of a pixel element array.

Explanation of symbols

100, 500, 600 Optical system 110 Light source 120 Second optical system 130 Half mirror 140, 510 Filter element 141, 515 Window 141a Triangular shape 142, 300, 310, 320, 330, 340, 512 Resonant mode grating 143, 511 Substrate 144, 513 Posts 145, 514 Support 150 Third optical system 160 Light receiving element 170, 520 First optical system 200 Probe light 210 Target object 220 Radiation light 301, 321, 331, 341 Substrate layer 302, 311, 342 Wave layer 303, 312, 343 Lattice layer 322, 332, 333 Grating layer 323 Low refractive index layer 400 Variable filter 401, 402 Transparent electrode substrate 512a Low refractive index material part 512b High refractive index material part 610 Dichroic mirror 70 IR imaging system 710 optical system control unit 720 signal processing unit 730 the processor 740 external interface h1, h2 thickness p Pitch

Claims (21)

A filter element having a resonance mode grating that reflects light in a specific wavelength region resonating with the periodic structure by a periodic structure with fine irregularities;
A first optical system for guiding light in a first wavelength region radiated from the object to the resonance mode grating;
A light source that emits light in the second wavelength region;
A second optical system for guiding the light in the second wavelength region emitted from the light source to the resonance mode grating;
A light receiving element for detecting the intensity of light;
And a third optical system for guiding the light in the specific wavelength region reflected by the resonance mode grating out of the light in the second wavelength region emitted from the light source to the light receiving element. A filter element having a resonance mode grating that transmits light in a specific wavelength region resonating with the periodic structure by a periodic structure with fine irregularities;
A first optical system for guiding light in a first wavelength region radiated from the object to the resonance mode grating;
A light source that emits light in the second wavelength region;
A second optical system for guiding the light in the second wavelength region emitted from the light source to the resonance mode grating;
A light receiving element for detecting the intensity of light;
An optical system comprising: a third optical system that guides the light in the specific wavelength region that has passed through the resonance mode grating out of the light in the second wavelength region emitted from the light source to the light receiving element.   3. The optical system according to claim 1, wherein the resonance mode grating absorbs light in the first wavelength region and has a thermooptic effect.   The resonance mode grating is composed of a plurality of materials having different coefficients of thermal expansion, and the plurality of materials include a material that absorbs light in the first wavelength region. The optical system described.   The resonance mode grating is made of a single material, and the single material is a material that absorbs light in the first wavelength region and has a thermo-optic effect. Item 4. The optical system according to Item 3.   The resonance mode grating is composed of a plurality of materials, and the plurality of materials include a material that absorbs light in the first wavelength region and a material having a thermo-optic effect. Item 4. The optical system according to Item 3.   The optical system according to claim 5, wherein the single material or the plurality of materials is a material transparent to light in the second wavelength region.   The optical system according to claim 5, wherein the material having the thermo-optic effect is made of a semiconductor material.   The optical system according to any one of claims 5 to 7, wherein the material having the thermo-optic effect is composed of a polymer material.   The filter element has a pixel structure in which a plurality of the resonance mode gratings are formed in a two-dimensional array, and the light receiving element has a pixel structure in a two-dimensional array. Item 10. The optical system according to any one of Items 1 to 9.   The optical system according to claim 1, wherein the resonance mode grating has a membrane shape.   12. The optical system according to claim 1, wherein the resonance mode grating has anisotropy in two directions in which the periodic structure is orthogonal in a plane.   The filter element has a cavity, the resonance mode grating is sealed in the cavity, and the cavity is in a reduced pressure state or filled with an inert gas. The optical system as described in any one of thru | or 12.   The cavity is formed by a member including a substrate and a window, and the window has a high transmittance with respect to the light in the first wavelength region and a reflectance with respect to the light in the second wavelength region. The substrate is made of a material having a high reflectance with respect to the light in the first wavelength region and a high transmittance with respect to the light in the second wavelength region. The optical system according to claim 13.   The cavity is formed by a member including a substrate and a window, and the window has a high reflectance with respect to the light in the first wavelength region and a transmittance with respect to the light in the second wavelength region. The substrate is made of a material having a high transmittance with respect to the light in the first wavelength region and a low reflectance with respect to the light in the second wavelength region. The optical system according to claim 13.   16. The optical system according to claim 1, wherein the light source includes a wavelength selection filter that transmits only light having a narrow band wavelength.   The optical system according to claim 16, wherein the wavelength selection filter is a variable wavelength selection filter, and is configured to be able to change a wavelength of transmitted light by an external signal.   The optical system according to any one of claims 1 to 17, wherein the light source is one of a distributed feedback laser, a distributed Bragg reflection laser, or a vertical cavity surface emitting laser.   The optical system according to claim 18, wherein the light source includes a temperature control mechanism.   The optical system according to claim 1, wherein the second optical system includes an incident angle adjustment mechanism that adjusts an incident angle of light incident on the filter element. 21. The optical system according to claim 1, a control unit that controls the optical system, a signal processing unit that processes an output signal from the optical system, and an external interface unit that exchanges signals with the outside. An infrared imaging system comprising:
The infrared imaging system, wherein the first wavelength region in the optical system is included in an infrared region.

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