JP2020053910A - Optical device and imaging device - Google Patents

Abstract

To provide an optical device which enables the suppression of the worsening of wavelength resolution of an encoding element.SOLUTION: An optical device comprises: a filter array having a plurality of light transmissive filters arrayed in two dimensions, provided that the plurality of filters include two or more filters different from each other in the wavelength dependence of an optical transmittance, and the wavelength dependence of each optical transmittance of the plurality of filters varies according to an incident angle of light; an optical system disposed between a target object and the filter array and serving to focus light coming from the target object on a face of the filter array; and a light-shielding element located between the target object and the optical system or between the optical system and the filter array, and having one or more light transmissive regions and one or more light-shielding regions, provided that the one or more light-shielding regions serve to reduce the intensity of light incident at one or more particular incident angles, which is a part of light travelling from the optical system toward the filter array.SELECTED DRAWING: Figure 9

Description

  The present disclosure relates to an optical device and an imaging device.

  By utilizing the spectral information of a large number of bands each having a narrow band, it is possible to grasp the detailed physical properties of the observed object that were impossible with the conventional RGB image. The number of bands is, for example, several tens or more. A camera that acquires this multi-wavelength information is called a “hyperspectral camera”. Hyperspectral cameras are used in all fields, including food testing, biopsy, drug development, and mineral component analysis. Patent Documents 1 to 4 disclose examples of such a hyperspectral camera.

International Publication No. 13/002350 JP 2007-108124 A JP 2011-89895 A U.S. Pat. No. 7,283,231

  The image of light from the object can be encoded and captured by the coding element.

  The present disclosure provides a novel optical device that can suppress a decrease in the wavelength resolution of an encoding element.

  An optical device according to an aspect of the present disclosure is a filter array arranged in an optical path of light incident from an object, and a plurality of translucent pluralities arranged two-dimensionally along a plane intersecting the optical path. A filter, wherein the plurality of filters include two or more filters having different wavelength dependences of light transmittance, and the wavelength dependence of light transmittance of the plurality of filters changes according to an incident angle of light. A filter array, an optical system disposed between the object and the filter array, and configured to focus the light incident from the object on the surface of the filter array, and the object and the optical system. Or a light-blocking element located between the optical system and the filter array, comprising one or more light-transmitting regions and one or more light-blocking regions, wherein the one or more light-blocking regions are , The optical system Of the light toward the filter array, to reduce the intensity of light incident on a particular one or more incident angles, comprising a shielding element.

  The general or specific aspects of the present disclosure may be implemented by a device, a system, a method, or any combination thereof.

  According to the present disclosure, it is possible to suppress a decrease in the wavelength resolution of the encoding element. Further, the spectral transmittance of each region can be changed according to the structure of each region of the encoding element.

FIG. 1A is a diagram schematically illustrating an example of an encoding element. FIG. 1B is a diagram illustrating an example of a spatial distribution of transmittance of light in each of a plurality of wavelength ranges included in the target wavelength range. FIG. 1C is a diagram illustrating an example of the spectral transmittance of one of two regions included in the plurality of regions of the encoding element illustrated in FIG. 1A. FIG. 1D is a diagram illustrating an example of the spectral transmittance of the other of the two regions included in the plurality of regions of the encoding element illustrated in FIG. 1A. FIG. 2A is a diagram for explaining a relationship between a target wavelength band and a plurality of wavelength bands included therein. FIG. 2B is a diagram for explaining a relationship between a target wavelength band and a plurality of wavelength bands included therein. FIG. 3A is a diagram for explaining the characteristic of the spectral transmittance in a certain region of the coding element. FIG. 3B is a diagram illustrating a result of averaging the spectral transmittance illustrated in FIG. 3A for each wavelength region. FIG. 4A is a diagram schematically illustrating an example of a filter. FIG. 4B is a diagram illustrating a calculation result of a relationship between the thickness of the optical waveguide layer illustrated in FIG. 4A and an effective refractive index. FIG. 4C is a diagram illustrating a calculation result of a spectral transmittance when light is vertically incident on the filter illustrated in FIG. 4A. FIG. 4D is a diagram illustrating a calculation result of a relationship between an incident angle and a spectral transmittance of the filter illustrated in FIG. 4A. FIG. 5A is a diagram schematically illustrating an example in which an optical system is arranged above the filter illustrated in FIG. 4A. FIG. 5B is a diagram illustrating a calculation result of a spectral transmittance when vertically incident light is focused by the optical system and enters the filter. FIG. 6A is a diagram schematically illustrating an example in which a light shielding element is disposed above the optical system illustrated in FIG. 5A. FIG. 6B is a diagram illustrating a calculation result of a spectral transmittance when vertically incident light passes through the light blocking element, is focused by the optical system, and enters the filter. FIG. 6C is a diagram schematically showing the shape of the light shielding element in the XZ plane and the XY plane in the upper and lower figures, respectively. FIG. 7A is a diagram illustrating a calculation result of a spectral transmittance when vertically incident light passes through a light blocking element, is focused by an optical system, and enters a filter. FIG. 7B is a diagram illustrating a calculation result of the spectral transmittance when the vertically incident light passes through the light blocking element, is focused by the optical system, and enters the filter. FIG. 8 is a diagram illustrating a calculation result of the spectral transmittance of the filter in three regions of the encoding elements arranged immediately above the imaging element. FIG. 9 is a diagram schematically illustrating an example of an imaging device according to the present embodiment. FIG. 10A is a diagram schematically illustrating a modified example of the filter. FIG. 10B is a diagram illustrating a calculation result of a spectral transmittance when light is vertically incident on the filter illustrated in FIG. 10A. FIG. 10C is a diagram illustrating a calculation result of a relationship between an incident angle and a spectral transmittance of the filter illustrated in FIG. 10A. FIG. 11A is a diagram schematically illustrating a modified example of the filter. FIG. 11B is a diagram illustrating a calculation result of a spectral transmittance when light is vertically incident on the filter illustrated in FIG. 11A. FIG. 11C is a diagram illustrating a calculation result of a relationship between an incident angle and a spectral transmittance of the filter illustrated in FIG. 11A. FIG. 12A is a diagram schematically illustrating a modified example of the filter. FIG. 12B is a diagram illustrating a calculation result of a spectral transmittance when light is vertically incident on the filter illustrated in FIG. 12A. FIG. 12C is a diagram illustrating a calculation result of a relationship between an incident angle and a spectral transmittance of the filter illustrated in FIG. 12A. FIG. 13A is a diagram schematically illustrating a modified example of the filter. FIG. 13B is a diagram illustrating a calculation result of a spectral transmittance when light is vertically incident on the filter illustrated in FIG. 13A. FIG. 13C is a diagram illustrating a calculation result of a relationship between an incident angle and a spectral transmittance of the filter illustrated in FIG. 13A.

  Before describing the embodiments of the present disclosure, the knowledge that became the basis of the present disclosure will be described.

  As an example of using an image obtained by restricting the wavelength of an observation target to a narrow band, Patent Document 1 discloses an apparatus for discriminating between a tumor site and a non-tumor site of a subject. This apparatus detects that protoporphyrin IX accumulated in cancer cells emits 635 nm fluorescence and photo-protoporphyrin emits 675 nm fluorescence by irradiation with excitation light. Thus, a tumor site and a non-tumor site are identified.

  Patent Literature 2 discloses a method of determining the freshness of fresh food that decreases with time by acquiring information on the reflectance characteristics of continuous multi-wavelength light.

Hyperspectral cameras that can measure multi-wavelength images or reflectivity can be broadly classified into the following four methods.
(A) Line sensor method (b) Electronic filter method (c) Fourier transform method (d) Interference filter method

  (A) In the line sensor method, one-dimensional information of an object is acquired using a member having a linear slit. The light that has passed through the slit is separated according to the wavelength by a spectral element such as a diffraction grating or a prism. The separated light for each wavelength is detected by an image sensor having a plurality of pixels arranged two-dimensionally. The image sensor is, for example, an image sensor. In this method, only one-dimensional information of an object can be obtained at a time. Therefore, two-dimensional spectrum information is obtained by scanning the entire camera or the object perpendicular to the slit direction. The line sensor method has an advantage that a high-resolution multi-wavelength image can be obtained. Patent Document 3 discloses an example of a line sensor type hyperspectral camera.

  (B) The electronic filter method includes a method using a liquid crystal tunable filter (Liquid Crystal Tunable Filter: LCTF) and a method using an acousto-optic element (Acousto-Optical Tunable Filter: AOTF). The liquid crystal tunable filter is an element in which a linear polarizer, a birefringent filter, and a liquid crystal cell are arranged in multiple stages. Light of an unnecessary wavelength can be eliminated by only voltage control, and only light of an arbitrary specific wavelength can be extracted. The acousto-optic element is made of an acousto-optic crystal to which a piezoelectric element is bonded. When an electric signal is applied to the acousto-optic crystal, an ultrasonic wave is generated, and a dense standing wave is formed in the crystal. Due to the diffraction effect, only light of an arbitrary specific wavelength can be extracted. This method has an advantage that the wavelength is limited, but high-resolution moving image data can be acquired.

  (C) The Fourier transform method uses the principle of a two-beam interferometer. The light beam from the object to be measured is split by the beam splitter, and each light beam is reflected by the fixed mirror and the moving mirror, recombined, and observed by the detector. By varying the position of the moving mirror over time, data indicating a change in the intensity of interference depending on the wavelength of light can be obtained. By performing Fourier transform on the obtained data, spectrum information can be obtained. An advantage of the Fourier transform method is that information of multiple wavelengths can be obtained simultaneously.

  (D) The interference filter method is a method using the principle of the Fabry-Perot interferometer. A configuration is used in which an optical element having two surfaces with high reflectance separated by a predetermined distance is arranged on the sensor. The distance between the two surfaces of the optical element differs for each region and is determined so as to match the interference condition of light having a desired wavelength. The interference filter method has an advantage that information of multiple wavelengths can be acquired simultaneously and as a moving image.

  In addition to these methods, there is a method using compressed sensing as disclosed in Patent Document 4, for example. The device disclosed in Patent Literature 4 disperses light from a measurement target using a first spectral element such as a prism, marks the image using an encoding mask, and returns the path of the light beam using a second spectral element. Thereby, an image that is coded and multiplexed with respect to the wavelength axis is acquired by the sensor. By applying compressed sensing from a multiplexed image, a plurality of images of multiple wavelengths can be reconstructed.

  Compressed sensing is a technique for restoring more data from acquired data with a small number of samples. Assuming that the two-dimensional coordinates of the measurement target are (X, Y) and the wavelength is λ, the data to be obtained is three-dimensional data of X, Y, λ. On the other hand, image data obtained by the sensor is two-dimensional data compressed and multiplexed in the λ-axis direction. The problem of obtaining data having a relatively large data amount from an acquired image having a relatively small data amount is a so-called defect setting problem, and cannot be solved as it is. However, in general, the data of a natural image has redundancy, and by utilizing this data skillfully, this defective setting problem can be converted into a good setting problem. An example of a technique for reducing the amount of data by utilizing image redundancy is jpeg compression. The jpeg compression uses a method of converting image information into frequency components and removing non-essential parts of the data, for example, components with low visual recognition. In the compressed sensing, such a technique is incorporated into arithmetic processing, and a data space to be obtained is converted into a space represented by redundancy to reduce unknowns and obtain a solution. For this conversion, for example, a discrete cosine transform (DCT), a wavelet transform, a Fourier transform, a total variation (TV), or the like is used.

  The present inventors have studied the above-described conventional hyperspectral camera. (A) The line sensor method requires scanning a camera to obtain a two-dimensional image, and is not suitable for capturing a moving image of a measurement target. (C) The Fourier transform method is also unsuitable for moving image capturing because the reflecting mirror needs to be moved. (B) The electronic filter method acquires images one wavelength at a time, and therefore cannot acquire images of multiple wavelengths at the same time. (D) In the interference filter method, the number of wavelength bands at which an image can be acquired is traded off with the spatial resolution, so that when acquiring a multi-wavelength image, the spatial resolution is sacrificed. As described above, there is no existing hyperspectral camera that simultaneously satisfies three of high resolution, multiple wavelengths, and one-shot moving image shooting.

  At first glance, it seems that the configuration using the compressed sensing can simultaneously satisfy high resolution, multiple wavelengths, and moving image shooting. However, since the image is reconstructed based on the guess from the originally small amount of data, the spatial resolution of the obtained image tends to be lower than that of the original image. In particular, the higher the compression ratio of the acquired data is, the more the effect appears. Further, since a spectral element such as a prism is inserted on the optical path, coma occurs and the resolution is reduced.

  On the other hand, the image of the light from the object can be encoded by the encoding element and captured. By appropriately designing the spectral transmittance of each region of the encoding element, the occurrence of coma can be suppressed and the resolution can be improved. Further, the three requirements of high-resolution, multi-wavelength, and one-shot moving image shooting can be simultaneously satisfied. Further, in imaging using an encoding element, information in the wavelength direction among the three-dimensional information in the X direction, the Y direction, and the wavelength direction is compressed. Therefore, it is only necessary to hold two-dimensional data, and the amount of data can be reduced. For this reason, data acquisition for a long time becomes possible.

  An encoding element may be configured using various methods.

  For example, in a configuration using an organic material, a different light absorbing material such as a pigment or a dye is arranged in each region. In such a configuration, the number of manufacturing steps increases by the number of light absorbing materials to be arranged. For this reason, it is not easy to manufacture the encoding element and the cost is high.

  On the other hand, for example, in a configuration using a multilayer structure, a diffraction grating, or a fine structure including a metal, the spectral transmittance of each region can be changed by changing the structure of each region. Therefore, the production is easier as compared with the configuration using the above organic material.

However, in the configuration using the above fine structure, in principle, the spectral transmittance depends on the incident angle of the incident light. If such a configuration is applied to the coding element as it is, the wavelength resolution of the coding element may be reduced. An image of light from the object is formed through an optical system on an image sensor on which an encoding element is disposed immediately above. At this time, the numerical aperture (Numerical Aperture) of the optical system 40 is expressed as NA, and when the incident angle of vertical incidence is 0 °, the encoding element 100C provides the encoding element 100C with the minimum angle 0 ° to the maximum angle sin ⁻¹ (NA ) Light having a continuous incident angle of up to ° is incident. Therefore, the spectral transmittance of the light that has passed through the encoding element is a superposition of the spectral transmittance according to each incident angle. As a result, the wavelength resolution of the encoding element may decrease. Thus, there is room for improvement in the configuration of the coding element.

  The present inventor has arrived at a spectroscopic system described in the following items based on the above study.

  The optical device according to the first item is a filter array arranged in an optical path of light incident from an object, and a plurality of translucent filters arranged two-dimensionally along a plane intersecting the optical path. Wherein the plurality of filters include two or more filters having different wavelength dependences of light transmittance, and the wavelength dependence of light transmittance of the plurality of filters changes according to an incident angle of light. A filter array, disposed between the object and the filter array, an optical system for focusing the light incident from the object on the surface of the filter array, and the object and the optical system Or a light-blocking element located between the optical system and the filter array, comprising one or more light-transmitting regions and one or more light-blocking regions, wherein the one or more light-blocking regions are Front from the optical system Of the light towards the filter array, to reduce the intensity of light incident on a particular one or more incident angles, comprising a shielding element.

  In this optical device, light having a specific incident angle can be selectively transmitted toward the filter by the light shielding element. As a result, it is possible to suppress a decrease in the wavelength resolution due to the dependency of the incident angle.

  An optical device according to a second item is the optical device according to the first item, wherein the optical system includes a convex lens. The one or more light-transmitting regions have a concentric structure centered on the optical axis of the convex lens. The one or more light-shielding regions have a concentric structure centered on the optical axis of the convex lens, and reflect or absorb incident light.

  With this optical device, the same effects as those of the optical device according to the first item can be obtained.

The optical device according to the third item is the optical device according to the first or second item, wherein NA is the numerical aperture of the optical system, and the minimum incident angle of light incident on the filter array from the optical system. The value is 0 degree, and the maximum value of the incident angle is sin ^-1 (NA) degree.

In this optical device, the specific incident angle of the light passing through the light blocking element when entering the filter array is between 0 degrees and sin ^-1 (NA) degrees.

  The optical device according to the fourth item is the optical device according to any one of the first to third items, wherein each of the plurality of filters is a waveguide resonance grating filter, a waveguide plasmon filter, a Fabry-Perot filter, This is one filter selected from the group consisting of a multilayer filter and a filter having a laminated structure of metal-insulator-metal.

  With this optical device, the same effects as those of the optical device according to any of the first to third items can be obtained.

  An optical device according to a fifth item is the optical device according to any one of the first to fourth items, wherein each of the plurality of filters includes a substrate, an optical waveguide layer on the substrate, and the optical waveguide layer. A waveguide resonant grating filter including the above grating.

  With this optical device, the same effects as those of the optical device according to any of the first to fourth items can be obtained. Further, by changing the period of the grating, it is possible to realize a filter array having a uniform thickness and a different spectral transmittance for each filter.

を満たし、かつ、

または、

を満たす。 The optical device according to the sixth item is the optical device according to the fifth item, wherein the wavelength of light incident on the filter array is λ, the incident angle of the light incident on the filter array is θ, and the grating is The number of modes of light diffracted by the optical waveguide layer is m ₁ , the thickness of the optical waveguide layer is T, the effective refractive index of the waveguide mode of light propagating in the optical waveguide layer is n _eff, and the refractive index of the substrate is rates and n _s, a refractive index of the optical waveguide layer and n _f, the refractive index of the medium is on the grating and n _c, the number of modes of the guided mode of light propagating through the optical waveguide layer m _{Assuming 2} ,

Satisfy and

Or

Meet.

  With this optical device, the same effects as those of the optical device according to the fifth item can be obtained.

  An optical device according to a seventh item is the optical device according to the first to fourth items, wherein each of the plurality of filters includes a substrate, an optical waveguide layer on the substrate, and a metal on the optical waveguide layer. And a grating formed from the above.

  With this optical device, the same effects as those of the optical devices according to the first to fourth items can be obtained. Further, by changing the period of the grating, it is possible to realize a filter array having a uniform thickness and a different spectral transmittance for each filter.

  An optical device according to an eighth item is the optical device according to any one of the first to fourth items, wherein each of the plurality of filters includes a substrate, an optical waveguide layer on the substrate, and the optical waveguide layer. A waveguide plasmon filter including an upper buffer layer and a grating formed of a metal on the buffer layer.

  With this optical device, the same effects as those of the optical device according to any of the first to fourth items can be obtained. Further, by changing the period of the grating, it is possible to realize a filter array having a uniform thickness and a different spectral transmittance for each filter.

  An optical device according to a ninth item is the optical device according to any one of the first to fourth items, wherein each of the plurality of filters includes a substrate, a first mirror on the substrate, and the first mirror. A Fabry-Perot filter comprising an upper intermediate layer and a second mirror on the intermediate layer.

  With this optical device, the same effects as those of the optical device according to any of the first to fourth items can be obtained.

  An optical device according to a tenth item is the optical device according to any of the first to fourth items, wherein each of the plurality of filters includes a substrate and a dielectric multilayer film on the substrate Filter. The dielectric multilayer film has a structure in which first dielectric layers and second dielectric layers are alternately stacked in a direction perpendicular to the substrate. The refractive index of the first dielectric layer is different from the refractive index of the second dielectric layer.

  With this optical device, the same effects as those of the optical device according to any of the first to fourth items can be obtained.

  An optical device according to an eleventh item is the optical device according to any one of the first to fourth items, wherein each of the plurality of filters includes a substrate and a grating on the substrate. The grating includes a plurality of stacked structures arranged at equal intervals along the surface of the substrate. Each of the plurality of stacked structures includes a first metal layer on the substrate, an insulator layer on the first metal layer, and a second metal layer on the insulator layer.

  With this optical device, the same effects as those of the optical device according to any of the first to fourth items can be obtained. Further, by changing the period of the grating, it is possible to realize a filter array having a uniform thickness and a different spectral transmittance for each filter.

  An imaging device according to a twelfth item, the optical device according to any one of the first to eleventh items, disposed in an optical path of light that has passed through the optical device, and has a plurality of wavelength ranges that have passed through the optical device An imaging element for acquiring an image on which components are superimposed.

  With this imaging device, it is possible to suppress a decrease in wavelength resolution due to the dependence of the incident angle on an image in which an image of light incident from a target is encoded.

  Hereinafter, more specific embodiments of the present disclosure will be described with reference to the drawings. However, an unnecessary detailed description may be omitted. For example, detailed descriptions of well-known matters and redundant description of substantially the same configuration may be omitted. This is to prevent the following description from being unnecessarily redundant and to facilitate understanding of those skilled in the art. The inventors provide the accompanying drawings and the following description so that those skilled in the art can fully understand the present disclosure, and they are intended to limit the subject matter described in the claims. is not. In the following description, the same or similar components are denoted by the same reference numerals.

(Embodiment)
<Coding element>
Hereinafter, the coding element according to the present embodiment will be described. The coding element is used in a spectral system that generates an image for each of a plurality of wavelength ranges included in the wavelength range to be imaged. In this specification, it may be referred to as “target wavelength range”. The encoding element is arranged in an optical path of light incident from an object, and modulates the intensity of the incident light for each wavelength and outputs the modulated light. This process by the coding element is referred to herein as "coding".

  FIG. 1A is a diagram schematically illustrating an example of the coding element 100C. The coding element C has a plurality of regions arranged two-dimensionally. In this specification, the region may be referred to as a “cell”. In each region, a filter having an individually set spectral transmittance is arranged. Here, “spectral transmittance” means a wavelength-dependent light transmittance. The spectral transmittance is represented by a function T (λ), where λ is the wavelength of the incident light. The spectral transmittance T (λ) can take a value of 0 or more and 1 or less. The coding element 100C may be said to be a filter array including a plurality of filters arranged two-dimensionally along a plane intersecting the optical path. Details of the configuration of the filter will be described later.

  In the example shown in FIG. 1A, the encoding element 100C has 48 rectangular regions arranged in 6 rows and 8 columns, but in an actual application, more regions may be provided. The number can be, for example, about the same as the number of pixels of a general image sensor such as an image sensor. The number of pixels is, for example, hundreds of thousands to tens of millions. In one example, the encoding element 100C is disposed immediately above the image sensor, and may be disposed such that each region corresponds to one pixel of the image sensor. Each region faces, for example, one pixel of the image sensor.

  FIG. 1B is a diagram illustrating an example of a spatial distribution of light transmittance of each of a plurality of wavelength ranges W1, W2,..., Wi included in the target wavelength range. In the example shown in FIG. 1B, the difference in shading of each region indicates the difference in transmittance. The lighter the region, the higher the transmittance, and the darker the region, the lower the transmittance. As shown in FIG. 1B, the spatial distribution of the light transmittance differs depending on the wavelength region.

  1C and 1D are diagrams illustrating examples of the spectral transmittances of the regions A1 and A2 included in the plurality of regions of the encoding element 100C illustrated in FIG. 1A, respectively. The spectral transmittance of the area A1 and the spectral transmittance of the area A2 are different from each other. As described above, the spectral transmittance of the encoding element 100C differs depending on the region. However, it is not necessary that the spectral transmittances of all the regions be different. In the encoding element 100C, at least some of the plurality of regions have different spectral transmittances from each other. The at least part of the region is two or more regions. That is, the encoding element 100C includes two or more filters having different spectral transmittances from each other. In one example, the number of patterns of the spectral transmittance of the plurality of regions included in the encoding element 100C may be equal to or greater than the number i of the wavelength ranges included in the target wavelength range. Typically, encoding element 100C is designed so that more than half of the regions have different spectral transmittances.

  2A and 2B are diagrams for explaining the relationship between the target wavelength range W and a plurality of wavelength ranges W1, W2,..., Wi included therein. The target wavelength range W can be set in various ranges depending on the application. The target wavelength range W is, for example, a visible light wavelength range of about 400 nm to about 700 nm, a near infrared wavelength range of about 700 nm to about 2500 nm, a near ultraviolet wavelength range of about 10 nm to about 400 nm, other mid-infrared rays, It may be a radio wave region such as far infrared, terahertz wave, or millimeter wave. Thus, the wavelength range used is not limited to the visible light range. In the present specification, not only visible light but also invisible light such as near-ultraviolet light, near-infrared light, and radio waves are referred to as “light” for convenience.

  In the example shown in FIG. 2A, i is an arbitrary integer equal to or greater than 4, and the target wavelength band W is equally divided into i, and the wavelength bands are W1, W2,..., Wi. However, it is not limited to such an example. A plurality of wavelength ranges included in the target wavelength range W may be set arbitrarily. For example, the bandwidth may be non-uniform depending on the wavelength range. There may be gaps between adjacent wavelength ranges. In the example shown in FIG. 2B, the bandwidth differs depending on the wavelength range, and there is a gap between two adjacent wavelength ranges. As described above, the plurality of wavelength ranges only need to be different from each other, and how to determine them is arbitrary. The number of wavelength divisions i may be 3 or less.

  FIG. 3A is a diagram for explaining the characteristic of the spectral transmittance in a certain region of the encoding element 100C. In the example illustrated in FIG. 3A, the spectral transmittance has a plurality of maximum values P1 to P5 and a plurality of minimum values for the wavelength within the target wavelength range W. In the example shown in FIG. 3A, the light transmittance in the target wavelength region W is normalized such that the maximum value is 1 and the minimum value is 0. In the example shown in FIG. 3A, the spectral transmittance has a maximum value in a wavelength range such as the wavelength range W2 and the wavelength range Wi-1. As described above, in the present embodiment, the spectral transmittance of each region has a local maximum value in at least two of the plurality of wavelength ranges W1 to Wi. As can be seen from FIG. 3A, the maximum values P1, P3, P4, and P5 are 0.5 or more.

  As described above, the light transmittance of each region differs depending on the wavelength. Therefore, the encoding element 100C transmits a large amount of components in a certain wavelength range and does not transmit much components in other wavelength ranges in the incident light. For example, the transmittance of light of k wavelength ranges of the i wavelength ranges is greater than 0.5, and the transmittance of light of the remaining ik wavelength ranges is 0.5. May be less than. k is an integer satisfying 2 ≦ k <i. If the incident light is white light including all the wavelength components of visible light equally, the encoding element 100C has a plurality of intensity peaks that are discrete with respect to wavelength for each region of the incident light. The light is modulated into light, and these multi-wavelength lights are superimposed and output.

  FIG. 3B is a diagram illustrating, as an example, a result of averaging the spectral transmittance illustrated in FIG. 3A for each of the wavelength ranges W1, W2,. The averaged transmittance is obtained by integrating the spectral transmittance T (λ) for each wavelength region and dividing by the bandwidth of the wavelength region. In this specification, the value of the transmittance averaged for each wavelength region in this manner is referred to as the transmittance in that wavelength region. In this example, the transmittance is prominently high in three wavelength ranges having the maximum value P1, the maximum value P3, and the maximum value P5. In particular, the transmittance exceeds 0.8 in two wavelength ranges having the maximum value P3 and the maximum value P5.

  The resolution in the wavelength direction of the spectral transmittance of each region can be set to about the bandwidth of a desired wavelength region. In other words, in the wavelength range including one local maximum value in the spectral transmittance curve, the width of the range that takes a value equal to or more than the average value of the local minimum value closest to the local maximum value and the local maximum value is the desired wavelength range. Of bandwidth. In this case, if the spectral transmittance is decomposed into frequency components by, for example, Fourier transform, the value of the frequency component corresponding to the wavelength range becomes relatively large.

  The encoding element 100C is typically divided into a plurality of cells divided in a grid, as shown in FIG. 1A. These cells have different spectral transmittances. The wavelength distribution and the spatial distribution of the light transmittance of each region in the encoding element 100C may be, for example, a random distribution or a quasi-random distribution.

  The concept of random distribution and quasi-random distribution is as follows. First, each region in the encoding element 100C can be considered as a vector element having a value of, for example, 0 to 1 according to the light transmittance. Here, when the transmittance is 0, the value of the vector element is 0, and when the transmittance is 1, the value of the vector element is 1. In other words, a set of regions arranged in a line in the row or column direction can be considered as a multidimensional vector having a value from 0 to 1. Therefore, it can be said that the coding element 100C includes a plurality of multidimensional vectors in the column direction or the row direction. At this time, the random distribution means that any two multidimensional vectors are independent, that is, not parallel. The quasi-random distribution means that some multidimensional vectors include configurations that are not independent. Therefore, in the random distribution and the quasi-random distribution, the value of the light transmittance of the first wavelength band in each region belonging to a set of regions arranged in one row or column included in a plurality of regions is used as an element. The vector and the vector having the value of the transmittance of light in the first wavelength band in each region belonging to the set of regions arranged in another row or column are independent of each other. Similarly, for a second wavelength region different from the first wavelength region, the transmittance of light in the second wavelength region in each region belonging to a set of regions arranged in one row or column included in the plurality of regions. And the vector having the element of the value of the light transmittance of the second wavelength band in each region belonging to the set of regions arranged in another row or column are independent of each other.

  When the encoding element 100C is arranged near or directly above the imaging element, the cell pitch, which is the interval between a plurality of regions in the encoding element 100C, may be substantially equal to the pixel pitch of the imaging element. In this case, the resolution of the image of the encoded light emitted from the encoding element 100C substantially matches the resolution of the pixel. By making the light transmitted through each cell incident on only one corresponding pixel, it is possible to facilitate the later-described calculation. When the encoding element 100C is arranged apart from the imaging element, the cell pitch may be reduced according to the distance.

  In the example shown in FIG. 1, a gray scale transmittance distribution in which the transmittance of each region can take any value of 0 or more and 1 or less is assumed. However, it is not always necessary to provide a gray scale transmittance distribution. For example, a binary-scale transmittance distribution in which the transmittance of each region can take a value of approximately 0 or approximately 1 may be adopted. In the binary-scale transmittance distribution, each region transmits most of the light in at least two wavelength ranges of the plurality of wavelength ranges included in the target wavelength range, and transmits most of the light in the remaining wavelength ranges. Do not transmit. Here, “most” indicates approximately 80% or more.

  A part of all the cells, for example, half of the cells may be replaced with a transparent area. Such a transparent region transmits the light in the wavelength range Wi from all the wavelength ranges W1 included in the target wavelength range at the same high transmittance. The high transmittance is, for example, 0.8 or more. In such a configuration, the plurality of transparent regions may be arranged, for example, in a checkered pattern. That is, in the two arrangement directions of the plurality of regions in the encoding element 100C, regions in which the light transmittance differs depending on the wavelength and transparent regions can be alternately arranged. In the example shown in FIG. 1A, the two arrangement directions are a horizontal direction and a vertical direction.

<Filter in the region of the coding element>
Hereinafter, an example of a filter that can be arranged in at least one region of the encoding element 100C to realize encoding will be described.

  FIG. 4A is a diagram schematically illustrating an example of the filter 100. In the example shown in FIG. 4A, the filter 100 includes a substrate 10, an optical waveguide layer 20 on the substrate 10, and a grating 30 on the optical waveguide layer 20. In this specification, the filter 100 shown in FIG. 4A may be referred to as a “waveguide resonance grating filter”. The downward arrow at the top represents light vertically incident on the filter 100, and the downward arrow at the bottom represents light vertically transmitting through the substrate 10. The same applies to the following figures.

The substrate 10, the optical waveguide layer 20, and the grating 30 are transparent in a target wavelength range. Transparent means that the absorption loss is very small. For example, in the visible light region, the substrate 10, at least one of the optical waveguide layer 20, and the grating 30 may be formed from a dielectric material such as SiO ₂ or _Si 3 _{N 4.} Further, the optical waveguide layer 20 and the grating 30 may be formed from the same material or may be integrated. Each of the substrate 10, the optical waveguide layer 20, and the grating 30 may have a multilayer structure including two or more types of dielectric layers. In the example shown in FIG. 4A, the grating 30 is periodic in the X direction, but may be periodic in another direction in the XY plane.

  Next, the basic principle of the filter 100 shown in FIG. 4A will be described.

Light incident from above is diffracted by the grating 30. Thereby, the guided light propagating in the optical waveguide layer 20 is excited. The guided light is diffracted again by the grating 30 and re-emitted to the upper part. As a result, the filter 100 shown in FIG. 4A has a spectral characteristic in which light of a specific wavelength is reflected and light of other wavelengths is transmitted. The wavelength of the light that is diffracted and reflected by the grating 30 satisfies the following equation (1).

Here, λ is the wavelength of incident light in air. θ is an incident angle of light incident on the encoding element 100C. The incident angle is an angle between a line perpendicular to the encoding element 100C and light incident on the encoding element 100C. Λ is the period of the grating 30. m is an order and is an integer of 1 or more. n _eff is the effective refractive index of the guided mode. Equation (1) shows that the wavelength λ of light diffracted and reflected by the grating 30 depends on the incident angle θ. That is, the spectral transmittance of the filter 100 shown in FIG. 4A indicates the dependency of the incident angle.

  Next, conditions and design of the optical waveguide layer 20 will be described. From the above-mentioned principle, the guided light excited by the grating 30 is confined in the optical waveguide layer 20. In the optical waveguide layer 20 shown in FIG. 4A, there are a TM waveguide mode and a TE waveguide mode. In the TM guided mode, the electric field has components in the X and Z directions, and the magnetic field has components in the Y direction. In the TE guided mode, the electric field has a component in the Y direction and the magnetic field has components in the X and Z directions.

The eigenvalue equation in the TM guided mode is represented by the following equation (2).

Here, T is the thickness of the optical waveguide layer 20. n _{s, n f,} and _{n c} are each substrate 10, the optical waveguide layer 20, and the refractive index of the cladding. In the example shown in FIG. 4A, the cladding is a medium on the grating 30. The medium is, for example, air. The refractive index of the optical waveguide layer 20 is higher than the refractive index of the substrate 10 and the refractive index of the clad. At this time, the optical waveguide layer 20 confines the guided light.

The eigenvalue equation in the TE guided mode is represented by the following equation (3).

  Hereinafter, the TM waveguide mode will be described as an example, but the present invention is not limited to this. The following discussion can also be applied to the TE guided mode.

FIG. 4B is a diagram illustrating a calculation result of a relationship between the thickness T of the optical waveguide layer 20 illustrated in FIG. 4A and an effective refractive index n _eff . For the calculation, MathWorks' MATLAB was used. The substrate 10 was formed from SiO ₂ having a refractive index of n _s = 1.46. The optical waveguide layer 20 was formed from Si ₃ N ₄ having a refractive index of n _s = 2.05. The cladding is air with a refractive index n _c = 1.0. The wavelength is λ = 541.6 nm. When the thickness T of the optical waveguide layer 20 is reduced, the effective refractive index of the waveguide mode of each order decreases. The thickness T of the optical waveguide layer 20 when the effective refractive index n _eff matches the refractive index n _{s of the} substrate corresponds to a cutoff. In the example shown in FIG. 4B, when the thickness T of the optical waveguide layer 20 is 100 nm or more, at least one waveguide mode exists. Strictly speaking, there is a grating 30 on the optical waveguide layer 20. However, ignoring the grating 30, the general conditions and design can be determined.

FIG. 4C is a diagram illustrating a calculation result of a spectral transmittance when light is vertically incident on the filter 100 illustrated in FIG. 4A. The substrate 10 was formed from SiO ₂ having a refractive index of n _s = 1.46. The optical waveguide layer 20 and the grating 30 were formed from Si ₃ N ₄ having a refractive index of n _s = 2.05. The thickness of the optical waveguide layer 20 is T = 100 nm. The height of the grating 30 is 50 nm, the width of the projection is 175 nm, and the period is 350 nm. The concave portion of the grating 30 penetrates. The incident light is TM mode normal incident light. For the calculation, DiffractMOD based on Rigorous Coupled-Wave Analysis (RCWA) of RSSoft was used. 4C shows that the filter 100 shown in FIG. 4A has a function of reflecting light having a wavelength of 540 nm. The reflection is due to the incident light being re-emitted to the top after coupling into the TM guided mode.

  On the other hand, the filter 100 shown in FIG. 4A shows the dependency of the incident angle as shown in Expression (1).

  FIG. 4D is a diagram illustrating a calculation result of a relationship between an incident angle and a spectral transmittance of the filter 100 illustrated in FIG. 4A. As shown in FIG. 4D, as the angle of incidence increases, one dip in transmittance at an angle of incidence of 0 ° splits into two dips. As the angle of incidence increases, one split dip shifts to shorter wavelengths and the other dip shifts to longer wavelengths. Thus, it can be seen that the spectral transmittance of the filter 100 shown in FIG. 4A shows the dependence on the incident angle. It can be said that the spectral transmittance of the filter 100 shown in FIG. 4 changes according to the incident angle of light.

  In the example described above, the light from the target is vertically incident on each region of the encoding element 100C. In practice, in imaging using the coding element 100C, light incident from the object is focused on the surface of the coding element 100C by an optical system disposed between the object and the coding element 100C. You.

  FIG. 5A is a diagram schematically illustrating an example in which the optical system 40 is disposed above the filter 100 illustrated in FIG. 4A. In the example illustrated in FIG. 5A, when the image of the light from the object passes through the center of the lens configuring the optical system 40, the image of the light is perpendicularly incident on the filter 100. On the other hand, when an image of light from the object passes through a part other than the center of the lens constituting the optical system 40, the image of the light obliquely enters the filter 100 at a finite incident angle. The finite incident angle is determined by the numerical aperture NA of the optical system 40. That is, the minimum value of the incident angle of light incident on the encoding element 100C from the optical system 40 is 0 °, and the maximum value of the incident angle is sin−1 (NA) °.

FIG. 5B is a diagram illustrating a calculation result of the spectral transmittance when vertically incident light is focused by the optical system 40 and enters the filter 100. In the example shown in FIG. 5B, the maximum incident angle is 10 °. The maximum angle corresponds to a numerical aperture NA of the optical system 40 = sin10 ° = 0.1736. The spectral transmittance shown in FIG. 5B is broader than the spectral transmittance shown in FIG. 4C. This is because the spectral transmittance shown in FIG. 5B is a superposition of the spectral transmittance from the minimum angle θ _min = 0 ° to the maximum angle θ _max = 10 °. Therefore, as it is, the filter 100 cannot sufficiently encode the light from the object.

  Therefore, in the present embodiment, the light shielding element 50 is used in order to encode the light from the object by the filter 100.

  FIG. 6A is a diagram schematically illustrating an example in which the light shielding element 50 is disposed above the optical system 40 illustrated in FIG. 5A. The light shielding element 50 includes one or more light shielding regions 50a and one or more light transmitting regions 50b. The light blocking element 50 may be disposed below the optical system 40 shown in FIG. Details of the shape of the light shielding element 50 will be described later. The light shielding element 50 allows light having a specific incident angle to be selectively transmitted toward the filter 100. The light is light incident from a plurality of discrete directions. The one or more light-shielding regions of the light-shielding element 50 reduce the intensity of light incident at one or more specific incident angles among the light traveling from the optical system 40 to the encoding element 100C. As a result, it is possible to suppress a decrease in the wavelength resolution due to the dependency of the incident angle.

  FIG. 6B is a diagram illustrating a calculation result of the spectral transmittance when vertically incident light passes through the light blocking element 50, is focused by the optical system 40, and enters the filter 100. In the example shown in FIG. 6B, the light passing through the light blocking element 50 and being focused by the optical system 40 is applied to the filter 100 at an incident angle of 0 ° to 1 °, 2 ° to 4 °, 5 ° to 7 °, and It is incident at 8 ° to 10 °. This makes it possible to suppress a decrease in the spectral resolution of the spectral transmittance by overlapping the spectral transmittances in the range of the selected incident angle. The spectral transmittance in the range of the selected incident angle can be known from the example shown in FIG. 4D.

  Next, the shape of the light shielding element 50 will be described.

  FIG. 6C is a diagram schematically showing the shape of the light blocking element 50 in the XZ plane and the XY plane in the upper and lower figures, respectively. In the example shown in FIG. 6C, the light blocking element 50 is arranged at the pupil position of the optical system 40 including the convex lens. One or more light-shielding regions 50a and one or more light-transmitting regions 50b have a concentric structure centered on the optical axis of the convex lens. One or more light-shielding regions 50a reflect or absorb incident light. A part of two adjacent light-shielding regions 50a may be connected. One light shielding area 50a may have a spiral structure. The light shielding element 50 shown in FIG. 6C can be manufactured, for example, by depositing a chromium thin film on a glass substrate and patterning the chromium thin film. The shape of the light shielding element 50 depends on the shape of the optical system 40. When the optical system 40 includes a cylindrical lens that is uniform along the Y direction, the light shielding element 50 has a cross section shown in the upper diagram of FIG. 6C in the XZ plane, and has a uniform cross section along the Y direction in the XY plane. It has a stripe shape.

  Even without changing the spectral transmittance of the filter 100 itself, the spectral transmittance can be changed by changing the shape of the light transmitting region 50b of the light shielding element 50.

  FIGS. 7A and 7B show calculation results of the spectral transmittance when vertically incident light passes through the light-blocking element 50 having a different shape of the light-transmitting region 50b, is focused by the optical system 40, and enters the filter 100. FIG. In the example shown in FIG. 7A, the light passing through the light blocking element 50 and being focused by the optical system 40 is applied to the filter 100 at an incident angle of 0 ° to 2 °, 3 ° to 5 °, 6 ° to 8 °, and It is incident at 9 ° to 10 °. In the example shown in FIG. 7B, the light passing through the light shielding element 50 and focused by the optical system 40 is applied to the filter 100 at incident angles of 1 ° to 3 °, 4 ° to 6 °, and 7 ° to 9 °. Incident.

  As shown in FIGS. 7A and 7B, the dip or peak of the spectral transmittance can be adjusted according to the design of the width and the number of the light-transmitting regions 50b of the light-blocking element 50. The line width of the dip or peak is determined by the width of the light transmitting region 50b of the light shielding element 50. The number of dips or peaks is determined by the number of light transmitting regions 50b of the light shielding element 50. The wavelength of the dip or peak is the operating wavelength of the filter 100. That is, in the present embodiment, the coding element 100C that operates at an arbitrary number of wavelengths can be configured by designing the width and the number of the light transmitting regions 50b of the light shielding element 50.

As described above, by arranging the grating 30 satisfying the expression (1) on the optical waveguide layer 20, it is possible to design the encoding element 100C that operates at an arbitrary wavelength. For example, under the analysis conditions shown in FIG. 4B, the effective refractive index n _eff of the optical waveguide layer 20 is 1.46 <n _eff <2.05. The lower limit 1.46 is the refractive index n _s of the substrate 10, and the upper limit 2.05 is the refractive index n _f of the optical waveguide layer 20. At normal incidence at θ = 0 °, Λ = λ / n _eff is obtained from equation (1). Therefore, in order to operate in the visible light range of wavelengths from 400 nm to 700 nm, the period の of the grating 30 is 195 nm <Λ <480 nm. The lower limit 195 nm was calculated from 400 nm / 2.05, and the upper limit 480 nm was calculated from 700 nm / 1.46.

  In the present embodiment, by changing the period of the grating 30 of the filter 100 in each region, it is possible to manufacture the encoding element 100C having a different spectral transmittance for each region. Therefore, there is an advantage that it can be easily manufactured as compared with a configuration in which different light absorbing materials are arranged in each region.

  FIG. 8 is a diagram illustrating a calculation result of the spectral transmittance of the filter 100 in three regions of the encoding device 100 </ b> C disposed immediately above the imaging device 60. In the example illustrated in the left diagram of FIG. 8, the filter 100 in the three regions surrounded by the thick lines has the periods of the grating 30 of Λ = 350 nm, 400 nm, and 300 nm in a counterclockwise direction from above. The right side of FIG. 8 shows the spectral transmittance of the filter 100 in these three regions. As shown in the right diagram of FIG. 8, even if the design of the width and the number of the light-transmitting regions 50 b of the light-blocking element 50 is the same, by changing the period of the grating 30 of the filter 100 in each region, the visible wavelength of 400 nm to 700 nm is changed. An encoding device 100C that covers the entire optical region can be manufactured.

<Imaging device>
Next, the imaging device 300 according to the present embodiment will be described.

  FIG. 9 is a diagram schematically illustrating an example of the imaging device 300 according to the present embodiment. The imaging device 300 includes an imaging device 60 and an optical device 150 that focuses light on the imaging device 60. The optical device 150 is arranged in an optical path of light incident from the object 70. The optical device 150 includes an encoding element 100C, a light shielding element 50, and the optical system 40.

  The light blocking element 50 can be arranged between the object 70 and the optical system 40 or between the optical system 40 and the coding element 100C. In the example shown in FIG. 9, the light blocking element 50 is arranged at a pupil position of the optical system 40 between the object 70 and the optical system 40.

  The optical system 40 includes at least one imaging lens. Although FIG. 9 shows one lens, the optical system 40 may be configured by a combination of a plurality of lenses. The optical system 40 forms an image on the imaging surface of the imaging device 60 via the encoding device 100C.

  The encoding device 100C is arranged near or directly above the imaging device 60. Here, “near” means that the image of the light from the optical system 40 is close enough to be formed on the surface of the encoding element 100C in a somewhat clear state. “Directly above” means that the two are close to each other so that a gap hardly occurs. The encoding device 100C and the imaging device 60 may be integrated. The coding element 100C is a mask having a spatial distribution of light transmittance. The encoding element 100C modulates the intensity of the incident light and passes the modulated light.

  Due to the light shielding element 50, light enters the encoding element 100C from a plurality of discrete directions. In this case, the plurality of discrete directions of light incident on each region of the encoding element 100C are strictly different. For example, it is considered that the difference between a plurality of discrete directions in which light enters near the center and near the end of the coding element 100C is not small. However, in practice, the light image from the object 70 is focused by the optical system 40 near the center of the coding element 100C. In each region near the center, it is considered that the plurality of discrete directions in which light is incident are almost the same. Therefore, the above discussion of the encoding is also valid for the imaging device 300 shown in FIG.

  The imaging element 60 is arranged on the optical path of the light that has passed through the optical device 150, and acquires an image in which components in a plurality of wavelength ranges that have passed through the optical device 150 are superimposed.

  FIG. 9 also shows a signal processing circuit 200 that processes an image signal output from the image sensor 60. The signal processing circuit 200 may be incorporated in the imaging device 300, or may be a component of the signal processing device electrically connected to the imaging device 300 by wire or wirelessly. The signal processing circuit 200 estimates a plurality of images 220 separated for each wavelength band of light from the object 70 based on the image 120 acquired by the image sensor 60. Details of the estimation method are disclosed in US Patent Application Publication No. 2016/138975. The entire disclosure of this document is incorporated herein by reference.

<Modified example of filter>
Hereinafter, a modified example of the filter 100 in the present embodiment will be described. For the following calculations, DiffMOD based on RSSoft's RCWA was used.

  FIG. 10A is a diagram schematically illustrating a modified example of the filter 100. In the example shown in FIG. 10A, the filter 100 includes the substrate 10, the optical waveguide layer 20 on the substrate 10, the buffer layer 22 on the optical waveguide layer 20, and the metal grating 32 on the buffer layer 22. The refractive index of the optical waveguide layer 20 is higher than the refractive index of the substrate 10, the refractive index of the buffer layer 22, and the refractive index of the medium on the metal grating 32. In this specification, the filter 100 shown in FIG. 10A may be referred to as a “waveguide plasmon filter”.

  The buffer layer 22 may not be provided. In that case, the filter 100 includes the substrate 10, the optical waveguide layer 20 on the substrate 10, and the metal grating 32 on the optical waveguide layer 20. The refractive index of the optical waveguide layer 20 is higher than the refractive index of the substrate 10 and the refractive index of the medium on the metal grating 32.

The substrate 10, the optical waveguide layer 20, and the buffer layer 22 are transparent in a target wavelength range. For example, in the visible light region, the substrate 10, the optical waveguide layer 20, and at least one of the buffer layer _22, a dielectric material such as _{SiO 2, TiO 2, Nb 2} O 5, Ta 2 O 5 or _Si 3 _{N 4} Can be formed from Each of the substrate 10, the optical waveguide layer 20, and the buffer layer 22 may have a multilayer structure including two or more types of dielectric layers.

  The metal grating 32 can be formed from a metal having a high reflectance and a small absorption loss in the target wavelength range. For example, in the visible light range, the metal can be formed from gold, silver, or aluminum. In the example shown in FIG. 10A, the metal grating 32 is periodic in the X direction, but may be periodic in another direction in the XY plane.

FIG. 10B is a diagram illustrating a calculation result of the spectral transmittance when light is vertically incident on the filter 100 illustrated in FIG. 10A. Each of the substrate 10 and the buffer layer 22 was formed from SiO ₂ . The optical waveguide layer 20 was formed from Si ₃ N ₄ . The metal grating 32 was formed from silver. The thickness of the optical waveguide layer 20 is 100 nm. The thickness of the buffer layer 22 is 50 nm. The height of the metal grating 32 is 40 nm, the width of the projection is 260 nm, and the period is 350 nm. The concave portion of the metal grating 32 penetrates. The incident light is TM mode normal incident light.

  FIG. 10C is a diagram illustrating a calculation result of the relationship between the incident angle and the spectral transmittance of the filter 100 illustrated in FIG. 10A. It can be seen that the spectral transmittance shown in FIG. 10C shows the dependence of the incident angle based on equation (1). Therefore, the effect of the present disclosure described above can be obtained by arranging the filter 100 shown in FIG. 10A in at least a part of the region of the encoding element 100C.

  FIG. 11A is a diagram schematically illustrating a modified example of the filter 100. In the example illustrated in FIG. 11A, the filter 100 includes the substrate 10, a first mirror 24a on the substrate 10, an intermediate layer 26 on the first mirror 24a, and a second mirror 24b on the intermediate layer 26. In this specification, the filter 100 shown in FIG. 11A may be referred to as a “Fabry-Perot filter”.

The intermediate layer 26 is transparent in the target wavelength range. For example, in the visible light region, the intermediate layer _{26 may} be formed from a dielectric material such as _{SiO 2, TiO 2, Nb 2} O 5, Ta 2 O 5 or _Si 3 _{N 4.} The intermediate layer 26 may have a multilayer structure including two or more dielectric layers.

  At least one of the first mirror 24a and the second mirror 24b may be formed from, for example, a dielectric multilayer film or a metal thin film.

FIG. 11B is a diagram illustrating a calculation result of a spectral transmittance when light is vertically incident on the filter 100 illustrated in FIG. 11A. Each of the substrate 10 and the intermediate layer 26 was formed from SiO ₂ . Each of the first mirror 24a and the second mirror 24b was formed from silver. The thickness of the intermediate layer 26 is 150 nm. The thickness of each of the first mirror 24a and the second mirror 24b is 15 nm. The incident light is TM mode normal incident light.

FIG. 11C is a diagram illustrating a calculation result of a relationship between the incident angle and the spectral transmittance of the filter 100 illustrated in FIG. 11A. In the filter 100 shown in FIG. 11A, multiple reflection occurs in the intermediate layer 26 due to light incident from the outside. Therefore, the following equation (4) is obtained.

  Here, λ is the wavelength of the incident light. θ is the incident angle of the incident light. L is the thickness of the intermediate layer 26. m is an integer of 1 or more. n is the refractive index of the intermediate layer. It can be seen that the spectral transmittance shown in FIG. 11C shows the dependence of the incident angle based on equation (4). Therefore, the effect of the present disclosure described above can be obtained by disposing the filter 100 illustrated in FIG. 11A in at least a part of the region of the encoding element 100C.

  FIG. 12A is a diagram schematically illustrating a modified example of the filter 100. In the example illustrated in FIG. 12A, the filter 100 includes the substrate 10 and the dielectric multilayer film 28 on the substrate 10. In this specification, the filter 100 illustrated in FIG. 12A may be referred to as a “multilayer filter”.

The dielectric multilayer film 28 has a structure in which first dielectric layers 28a and second dielectric layers 28b are alternately stacked in a direction perpendicular to the substrate 10. The refractive index of the first dielectric layer 28a is different from the refractive index of the second dielectric layer 28b. In the example shown in FIG. 12A, the refractive index of the first dielectric layer 28a is higher than the refractive index of the second dielectric layer 28b. The substrate 10 and the first and second dielectric layers 28a and 28b are transparent in the target wavelength range. For example, in the visible light range, the substrate 10 and at least one of the first dielectric layer 28a and the second dielectric layer 28b are made of SiO ₂ , TiO ₂ , Nb ₂ O ₅ , Ta ₂ O _5, or Si ₃ N _4. And the like.

FIG. 12B is a diagram illustrating a calculation result of a spectral transmittance when light is vertically incident on the filter 100 illustrated in FIG. 12A. Substrate 10 was formed of SiO _2. The first dielectric layer 28a was formed from Si ₃ N ₄ and the second dielectric layer 28b was formed from SiO ₂ . The thickness of the first dielectric layer 28a is 70 nm, and the thickness of the second dielectric layer 28b is 90 nm. Nine first dielectric layers 28a and eight second dielectric layers 28b were alternately stacked. The incident light is TM mode normal incident light. In the filter 100 illustrated in FIG. 12A, light in a specific wavelength range that is incident from the outside is strongly reflected by Bragg reflection caused by the periodic structure.

  FIG. 12C is a diagram illustrating a calculation result of the relationship between the incident angle and the spectral transmittance of the filter 100 illustrated in FIG. 12A. It can be seen that the spectral transmittance shown in FIG. 12C shows the dependency of the incident angle. Therefore, the effect of the present disclosure described above can be obtained by arranging the filter 100 shown in FIG. 12A in at least a part of the region of the encoding element 100C.

  FIG. 13A is a diagram schematically illustrating a modified example of the filter 100. In the example illustrated in FIG. 13A, the filter 100 includes the substrate 10 and the grating 34 on the substrate 10. The grating 34 includes a plurality of stacked structures arranged at equal intervals along the surface of the substrate 10. Each of the plurality of stacked structures includes a first metal layer 29a on the substrate 10, an insulator layer 27 on the first metal layer 29a, and a second metal layer 29b on the insulator layer 27. In this specification, the filter 100 illustrated in FIG. 13A may be referred to as a “filter including a metal-insulator-metal stacked structure”.

The substrate 10 and the insulator layer 27 are transparent in a target wavelength range. For example, in the visible light region, at least one of the substrate 10 and insulator layer 27 _may be formed from a dielectric material such as _{SiO 2, TiO 2, Nb 2} O 5, Ta 2 O 5 or _Si 3 _{N 4.}

  At least one of the first metal layer 29a and the second metal layer 29b can be formed from, for example, gold, silver, or aluminum.

FIG. 13B is a diagram illustrating a calculation result of a spectral transmittance when light is vertically incident on the filter 100 illustrated in FIG. 13A. Each of the substrate 10 and the insulator layer 27 was formed from SiO ₂ . Each of the first metal layer 29a and the second metal layer 29b was formed from silver. The thickness of the insulator layer 27 is 75 nm. Each thickness of the first metal layer 29a and the second metal layer 29b is 75 nm. The width of the convex portion of the grating 34 is 300 nm, and the period is 350 nm. The concave portion of the grating 34 penetrates. The incident light is TM mode normal incident light.

  FIG. 13C is a diagram illustrating a calculation result of the relationship between the incident angle and the spectral transmittance of the filter 100 illustrated in FIG. 13A. It can be seen that the spectral transmittance shown in FIG. 13C shows the dependency of the incident angle. Therefore, the effect of the present disclosure described above can be obtained by arranging the filter 100 illustrated in FIG. 13A in at least a part of the region of the encoding element 100C.

  Each of the plurality of filters of the encoding element 100C is selected from the group consisting of a waveguide resonance grating filter, a waveguide plasmon filter, a Fabry-Perot filter, a multilayer filter, and a filter having a metal-insulator-metal stacked structure. Filter.

  Of the above-described filters 100, the filters 100 shown in FIGS. 4A, 10A, and 13A include a grating 30, a metal grating 32, and a grating 34, respectively. In the filter 100 shown in FIGS. 4A, 10A, and 13A, different spectral transmittances can be obtained by changing the periods of the grating 30, the metal grating 32, and the grating 34 without changing the thickness of the filter 100. be able to. Therefore, by arranging the filter 100 shown in FIG. 4A, FIG. 10A, or FIG. 13A in each region of the coding element 100C, the coding is uniform in thickness and the spectral transmittance differs in each region. The element 100C can be realized.

  The optical device and the imaging device according to the present disclosure are useful for, for example, a camera and a measurement device that acquire a two-dimensional image of multiple wavelengths. The optical device and the imaging device according to the present disclosure can also be applied to sensing for living organisms, medical care, and beauty, a foreign matter / pesticide residue inspection system for food, a remote sensing system, a vehicle-mounted sensing system, and the like.

Reference Signs List 10: substrate 20: optical waveguide layer 22: buffer layer 24 a: first mirror 24 b: second mirror 26: intermediate layer 27: insulator layer 28: dielectric multilayer film 28 a: first dielectric layer 28 b: second dielectric Layer 29a: First metal layer 29b: Second metal layer 30: Grating 32: Metal grating 34: Grating 40: Optical system 50: Light-shielding element 50a: Light-shielding area 50b: Light-transmitting area 60: Imaging element 70: Object 100: Filter 100C: Coding element 120: Image 150: Optical device 200: Signal processing circuit 220: Image 300: Imaging device

Claims (12)

A filter array arranged in an optical path of light incident from an object, comprising a plurality of translucent filters two-dimensionally arranged along a plane intersecting the optical path, wherein the plurality of filters include A filter array including two or more filters having different wavelength dependencies of transmittance, wherein the wavelength dependency of light transmittance of the plurality of filters changes according to an incident angle of light;
An optical system disposed between the object and the filter array, for focusing the light incident from the object on the surface of the filter array;
A light-blocking element located between the object and the optical system, or between the optical system and the filter array, comprising one or more light-transmitting regions and one or more light-blocking regions, One or more light-shielding regions, among light traveling from the optical system toward the filter array, a light-shielding element that reduces the intensity of light incident at one or more specific incident angles;
Comprising,
Optical device. The optical system includes a convex lens,
The one or more light-transmitting regions have a concentric structure centered on the optical axis of the convex lens,
The one or more light-shielding regions have a concentric structure centered on the optical axis of the convex lens, and reflect or absorb incident light,
The optical device according to claim 1. When the numerical aperture of the optical system is NA,
The minimum value of the incident angle of light incident on the filter array from the optical system is 0 degrees,
The maximum value of the incident angle is sin ⁻¹ (NA) degrees.
The optical device according to claim 1. Each of the plurality of filters is one selected from the group consisting of a waveguide resonance grating filter, a waveguide plasmon filter, a Fabry-Perot filter, a multilayer filter, and a filter having a metal-insulator-metal stacked structure. Filter
The optical device according to claim 1. Each of the plurality of filters is a waveguide resonance grating filter comprising a substrate, an optical waveguide layer on the substrate, and a grating on the optical waveguide layer,
The optical device according to claim 1. The wavelength of light incident on the filter array is λ,
The incident angle of the light incident on the filter array is θ,
The number of modes of light diffracted by the grating and m _1,
T is the thickness of the optical waveguide layer,
An effective refractive index of a guided mode of light propagating in the optical waveguide layer is n _eff ,
The refractive index of the substrate as n _s,
The refractive index of the optical waveguide layer and n _f,
The refractive index of the medium is on the grating and n _c,
Assuming that the number of guided modes of light propagating in the optical waveguide layer is m ₂ ,

Satisfy and

Or

Meet,
The optical device according to claim 5. Each of the plurality of filters is a waveguide plasmon filter comprising a substrate, an optical waveguide layer on the substrate, and a grating formed of metal on the optical waveguide layer,
The optical device according to claim 1. Each of the plurality of filters is a waveguide plasmon filter including a substrate, an optical waveguide layer on the substrate, a buffer layer on the optical waveguide layer, and a grating formed of metal on the buffer layer. is there,
The optical device according to claim 1. Each of the plurality of filters is a Fabry-Perot filter including a substrate, a first mirror on the substrate, an intermediate layer on the first mirror, and a second mirror on the intermediate layer.
The optical device according to claim 1. Each of the plurality of filters is a multilayer filter including a substrate and a dielectric multilayer film on the substrate,
The dielectric multilayer film has a structure in which first dielectric layers and second dielectric layers are alternately stacked in a direction perpendicular to the substrate,
A refractive index of the first dielectric layer is different from a refractive index of the second dielectric layer;
The optical device according to claim 1. Each of the plurality of filters includes a substrate, and a grating on the substrate,
The grating includes a plurality of laminated structures arranged at equal intervals along the surface of the substrate,
Each of the plurality of stacked structures includes a first metal layer on the substrate, an insulator layer on the first metal layer, and a second metal layer on the insulator layer.
The optical device according to claim 1. An optical device according to any one of claims 1 to 11,
An image sensor that is arranged in an optical path of light that has passed through the optical device and acquires an image in which components in a plurality of wavelength ranges that have passed through the optical device are superimposed,
Comprising,
Imaging device.

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