JP2010277016A - Optical filter and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact optical filter which attains a large detected light quantity, a wide spectrum band and small number of optical elements and to provide an imaging apparatus using the optical filter. <P>SOLUTION: The optical filter 202 has a function of controlling the phase difference between two orthogonal polarized light components and includes: a liquid crystal layer 1024 which gives the phase difference to the two orthogonal polarized light components; and a dielectric substrate 1021 which supports the liquid crystal layer 1024, wherein a polarized light selection structure 1025 composed of a metallic fine pattern having a size not larger than the wavelength of incident light is provided on the boundary face or on the inner face of the dielectric substrate 1021, thus the detected light quantity is increased, the spectrum band is broadened and the number of the optical components is reduced. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical filter having a function of controlling the phase difference between two orthogonal polarization components, and an image photographing apparatus that dynamically modulates light transmission characteristics and acquires image data using the optical filter. It is.

  Spectroscopes are widely used as devices for acquiring spectral information. A general spectroscope cannot obtain spatial information because the light incident on the light receiving element is decomposed into a plurality of wavelength components using a prism or a diffraction grating. On the other hand, in recent years, a technique using a two-dimensional distribution of spectrum information has attracted attention, and an image capturing apparatus capable of acquiring spectrum information has been provided.

There are roughly three methods for acquiring spectrum information in a conventional image capturing apparatus.
The first is a method using a wavelength selection filter (bandpass filter, low-pass / high-pass filter), which switches the wavelength selection filter, arranges the wavelength selection filter in a minute region, and uses a liquid crystal wavelength tunable filter as the wavelength selection filter. Then, the light intensity of a desired wavelength is acquired by dynamically switching the transmission wavelength.
The second method uses a dispersion element such as a prism or a diffraction grating. By spatially separating the spectrum of incident light, one-dimensional spatial information and spectral information are acquired by a two-dimensional image sensor. Two-dimensional (image) spectrum information is acquired by scanning the spatial information in the orthogonal direction.
The third method is called Fourier spectroscopy, which divides an incident light beam into two optical paths (or polarization components) and applies a phase difference to one of them to cause interference to perform Fourier transform on a computer. The method of obtaining spectral information is used. When using this Fourier spectroscopy, it is necessary to scan the detection position two-dimensionally (or one-dimensionally), or to dynamically give different phase differences to two orthogonal polarization components to acquire image data in time series. There is.

In the above image capturing apparatus, a method using a wavelength selective filter requires a narrow band filter to obtain a high spectral resolution, resulting in a strong incident angle characteristic that lowers the detection intensity or requires a long exposure time. Therefore, there is a problem that parallel light must be incident.
In addition, in the method using a dispersive element, in order to obtain a high spectral resolution, it is necessary to transmit an extremely narrow slit, which reduces the amount of light, requires a scanning mechanism, requires measurement time, and reduces the size of the apparatus. There is a problem that it is difficult to do.
In the method using Fourier spectroscopy, in order to divide into two optical paths and give a phase difference, it is necessary to create parallel light rays as much as possible, and as in the case of using a dispersive element, a narrow slit and a small opening are required, and the amount of light is small. There are problems such as being unable to be large and having a large angle dependency.
On the other hand, in the Fourier spectroscopic method using polarized light, an interference signal of two polarization components can be obtained in the same optical path, so that a larger amount of light is obtained and incident angle dependency is weaker than the others. That is, it is superior to image acquisition. In addition, since a dynamic phase control element such as a liquid crystal phase shifter is used, there is no scanning portion, which is advantageous in terms of miniaturization and portability.
In the above three methods, it is also known that the Fourier spectroscopy method is the largest and can acquire the light amount.

In view of the above, a plurality of image capturing apparatuses capable of acquiring spectral information using a liquid crystal phase shifter have been proposed.
For example, the following technologies are disclosed as image capturing apparatuses that can acquire spectral images while being small.

The conventional technique described in Patent Document 1 (Japanese Patent Laid-Open No. 2009-033222) relates to an imaging apparatus, an imaging apparatus control program, and an imaging apparatus control method, and obtains a spectral image for each spectral band while being small. It is an object of the present invention to provide an imaging device capable of performing the above. And as the solution means, like the flowchart of patent document 1 shown in FIG. 14, a spectral image is acquired with the following procedures.
The wavelength band λ1 is set in the electronic control filter (spectral filter) (S14). The image data from the image sensor unit is stored in the buffer memory (A) (S15). If each exposure time (t / n) has elapsed, the spectral image data photographed in S15 and stored in the buffer memory (A) is read and converted to R, G, B data (S19). The R, G, B data of each pixel of the captured spectral image of each wavelength band is combined and synthesized by multiplane and stored in the buffer memory (B) (S20). The processing from S14 is repeated until n spectral images with n bands are captured (S21). When the processing of S14 to S21 is repeated n times, a single composite image in which R, G, B data of each pixel of n spectral images in each wavelength band is subjected to multiplane addition synthesis is stored.

  The prior art described in Patent Document 2 (Japanese Patent Application Laid-Open No. 2005-057541) relates to a spectroscopic camera head, can shoot a subject with a spectral band set, and is used in a virtual studio. An object of the present invention is to provide a spectroscopic camera device that can capture an image that can be handled even when the illumination condition changes as a composite image. As a means for solving this problem, the spectroscopic camera head 10 shoots a subject by remote control from the controller 13 as in the configuration example of the spectroscopic camera head described in Patent Document 2 shown in FIG. Objective lens (lens system) 1, a liquid crystal tunable filter (set wavelength band transmitting means) 3 that is disposed in the optical path of light passing through the lens system and transmits an arbitrarily set wavelength band, and An image pickup device (high-sensitivity image pickup device) 4 that receives a wavelength band that has passed through a set wavelength band transmission unit, and an image output unit 8 that outputs an image of the subject received by the image pickup device as image data. Yes.

  The prior art described in Patent Document 3 (Japanese Patent Application Laid-Open No. 2006-067183) relates to an image sensor unit and an image capturing device, and is easy to control to switch the wavelength range of transmitted light and has a fast response. It is an object of the present invention to provide an image pickup device unit and an image photographing device including a color filter. Then, as a solution, the color filter changes the alignment state of the liquid crystal molecules according to the state of the electric field, as in the configuration example of the imaging element unit described in Patent Document 3 shown in FIG. Off-state that transmits light in a predetermined visible light region, and absorbs or reflects only light in a predetermined wavelength region of the visible light region, and the rest of the visible light region excluding the predetermined wavelength region A liquid crystal layer that switches to an on state that transmits light in a wavelength band, and each liquid crystal layer that receives a voltage independently for each of the plurality of liquid crystal layers, the liquid crystal layers having different predetermined wavelength ranges from each other And an electrode for forming an electric field independently.

  The prior art described in Patent Document 4 (Japanese Patent Application Laid-Open No. 2001-074555) relates to an acousto-optic filter type spectroscopic camera using non-spectral light in a finder system, and is spectrally separated by a spectroscopic camera using an acousto-optic filter function. In response to the desire to specify the position of the observation target when comparing images and to compare spectral images with real images, that is, non-spectral images, there is little disparity in real time and without any disparity, as the captured images An object of the present invention is to provide a finder optical system that can obtain an observation image and that is bright and does not affect the observation light. As a means for solving the problem, in the configuration example of the acousto-optic filter type spectroscopic camera described in Patent Document 4 shown in FIG. 17, the light from the subject is converted into light having a uniform polarization plane through a polarizer, and the acoustooptic device A monochromatic light of a specific wavelength range whose polarization plane is changed by the ultrasonic wave propagating inside and a mixed light of other wavelengths whose polarization plane is not changed by the ultrasonic wave are made, and the mixed light is converted into a polarization prism. To separate the monochromatic light as transmitted light and the other wavelength light as reflected light, and take a spectral image using one monochromatic light, and use the other wavelength light for the finder system. Is reflected again to invert the image and obtain a real-time monitor image corresponding to the photographed image.

Further, the following technologies are disclosed as technologies related to an apparatus that acquires spectral information.
The prior art described in Patent Document 5 (Japanese Patent Application Laid-Open No. 2005-31007) relates to a spectroscopic device, and uses a liquid crystal that is light in weight, bright in transmitted light, high in spectral accuracy, and easy to manufacture. It is an object to provide a spectroscopic device. As a means for solving the problem, in the configuration example of the spectroscopic device described in Patent Document 5 shown in FIG. 18, a pair of one or a plurality of liquid crystal cells 12 is used as the interferometer 10 of the device that performs spectroscopy by Fourier transform spectroscopy. The light 1 incident on the liquid crystal panel is divided into two components of ordinary light 1A and extraordinary light 1B, and the cell voltage of the liquid crystal cell is changed by changing the cell voltage of the liquid crystal cell. A component configured to emit interference light 2 obtained by adding an optical path difference δ to component light and combining them is used.

Furthermore, the following techniques are disclosed as techniques for using a polarization selective structure with a metal microstructure as an electrode.
The prior art described in Patent Document 6 (Japanese Patent Application Laid-Open No. 2007-17762) relates to a method for manufacturing a wire grid polarizer and a liquid crystal device, and wire grid polarization having excellent optical characteristics easily and efficiently. It is an object to provide a child manufacturing method and the like. And as the solution, in the manufacturing method of the wire grid polarizer 60 of patent document 6 shown in FIG. 19, many substantially parallel linear metal protrusions 9a and metal protrusions 9a are provided on the substrate. In the method of manufacturing the wire grid polarizer 60 having the covering protective layer 29a, the cavity 9b is formed between the metal protrusions 9a while forming the protective layer 29a obliquely on the metal protrusions 9a. Yes.

Further, as an optical element having a function similar to that of the optical filter used in the image photographing apparatus of the present invention, there is a prior application technique previously filed by the present applicant.
The prior application technique described in Patent Document 7 (Japanese Patent Application Laid-Open No. 2007-226047) relates to an optical element and an image projection apparatus, and the first polarization component of light and the first over a wider wavelength range of light. It is an object of the present invention to provide an optical element or the like that can provide a predetermined range of phase difference between the second polarization component of the light orthogonal to the polarization component of the first polarization component. And as the solution means, like the example of a structure of the optical element of patent document 7 shown in FIG. 20, an optical element is the 1st thickness and 1st arrange | positioned periodically with a 1st fine period. A plurality of first fine periodic structures including a plurality of first dielectric plates having a refractive index and a plurality of second thicknesses and second refractive indices periodically arranged in a second fine period The second fine periodic structure including the second dielectric plate, and the refractive index of the medium between the plurality of first dielectric plates and the refractive index of the medium between the plurality of second dielectric plates are Unlike the first refractive index and the second refractive index, the first fine period and the second fine period, the ratio of the first thickness to the first fine period and the second to the second fine period The thickness ratio and at least one of the first refractive index and the second refractive index are different from each other. That.

  The image capturing device, the image capturing device, the image sensor, and the spectroscopic camera head according to the conventional techniques described in Patent Documents 1 to 3 described above are small in size and can acquire invisible information such as spectrum information. In order to obtain, an active color (wavelength) filter using a dye material or a liquid crystal is used. In such a wavelength filter, light in a desired spectral band is cut out, and light of other wavelengths is removed by absorption or reflection. Therefore, there is a problem that it is difficult to obtain instantaneous spectral information, and furthermore, the amount of light that can be detected is remarkably small.

  In order to use a large amount of light, it is known that Fourier spectroscopy that acquires intensity information in the time domain and converts it into spectral information by Fourier transform is an effective method. Realizes spectral image acquisition based on this Fourier spectroscopy. However, unlike the image capturing device, the spectroscopic device described in Patent Document 4 only acquires spectroscopic information at one point. Therefore, a configuration for increasing the detected light amount is not used, and is insufficient for use as an image capturing device.

  The optical element described in Patent Document 7 by the present applicant has wavelength selectivity due to a dielectric fine structure, but this is a solid-state element and only takes an image in a specific spectral region (in the visible light region). I can't. The present invention is also intended for an image projection apparatus such as a projector.

  The prior art described in Patent Document 5 relates to a method for manufacturing a metal microstructure, and describes that the metal microstructure is used as an electrode. However, with an image projection apparatus such as a projector in mind. Therefore, there is no description about a specific configuration or electrode pattern related to the image capturing apparatus.

  The image capturing apparatus using the liquid crystal phase shifter according to the present invention has a large number of stacked optical elements, and cannot detect a large amount of detected light. Further, an ITO film is generally provided as an electrode for driving the liquid crystal material, but the ITO film has a low transmittance and reduces the amount of light detected. In addition, an image capturing apparatus using a liquid crystal phase shifter is suitable for acquiring an image of a static object, but is limited in dynamic characteristics of a liquid crystal material and is difficult to operate at high speed. In addition, when the subject is to be photographed from the visible light to the near infrared light region, the characteristics of the commercially available polarizing film are poor in the near infrared light region, and there is a problem that an expensive polarizing element needs to be used.

In order to solve the above problems, the present invention has the following objects.
A first object is to provide an optical filter and an image photographing apparatus that can realize a large amount of detected light, a wide spectral band, a reduction in the number of optical elements, and downsizing.
A second object is to provide an optical filter and an image photographing apparatus that can realize a large detection light amount, a wide spectral band, a reduction in the number of optical elements, a reduction in size, and a high-speed time response.
A third object is to provide an optical filter and an image photographing apparatus that can realize a large amount of detected light, a wide spectral band, a reduction in the number of optical elements, a reduction in size, and a larger amount of phase modulation.
A fourth object is to provide an optical filter and an image photographing apparatus that can realize a large detection light amount, a wide spectral band, a reduction in the number of optical elements, a reduction in size, and a high-speed time response.
A fifth object is to provide a specific metal arrangement pattern of a polarization selection structure that constitutes an optical filter used in the image photographing apparatus of the present invention.

In order to solve the above-described problems and achieve the above object, the present invention employs the following solutions.
The first solution of the present invention is an optical filter having a function of controlling the phase difference between two orthogonal polarization components, a liquid crystal layer that gives different phase differences to the two orthogonal polarization components, and the liquid crystal layer And a polarization selection structure constituted by a metal fine pattern having a size equal to or smaller than the wavelength of incident light on a boundary surface or an inner surface of the dielectric substrate. Item 1).
According to a second solving means of the present invention, in the optical filter of the first solving means, the polarization selection structure is used as an electrode for driving the liquid crystal layer.

According to a third aspect of the present invention, there is provided an optical filter having a function of controlling a phase difference between two orthogonal polarization components, a liquid crystal layer that gives different phase differences to the two orthogonal polarization components, and the liquid crystal layer And a reflection structure that folds incident light in the regular reflection direction, and is formed by a metal fine pattern having a size equal to or smaller than the wavelength of the incident light on the boundary surface or the inner surface of the dielectric substrate. A polarization selection structure is provided.
According to a fourth solution means of the present invention, in the optical filter of the third solution means, the polarization selection structure and the reflection structure are used as electrodes for driving the liquid crystal layer. .

According to a fifth solving means of the present invention, in the optical filter according to any one of the first to fourth solving means, the polarization selection structure has a width and a period less than or equal to a wavelength of incident light in a light transmitting region. It is a metal fine wire (wire grid) structure (Claim 5).
According to a sixth solving means of the present invention, in the optical filter of any one of the first to fourth solving means, the polarization selection structure has two comb teeth made of a metal material in a region where light is transmitted. It has the structure which has arrange | positioned the structure facing (Claim 6).

  A seventh solving means of the present invention is an image photographing device, an optical system for forming an image of a subject on an imaging surface, an optical filter having a function of controlling a phase difference between two orthogonal polarization components, and the optical A drive control unit that electrically controls the filter; an imaging unit that converts an object image into an electrical signal; and a signal processing device that processes image information. The optical filter includes any one of first to sixth optical filters. The optical filter of the solving means is used (claim 7).

The optical filter of the first solving means includes a liquid crystal layer that gives different phase differences to two orthogonal polarization components, and a dielectric substrate that supports the liquid crystal layer, and a boundary surface or an inner surface of the dielectric substrate. By providing a polarization selection structure composed of a metal fine pattern having a size equal to or smaller than the wavelength of incident light, it is possible to increase the amount of detected light, broaden the spectrum band, and reduce the number of optical elements. it can.
Further, in the optical filter of the second solving means, in addition to the configuration of the first solving means, the polarization selection structure is used as an electrode for driving the liquid crystal layer, thereby increasing the detected light amount, widening the spectral band, optical There is an effect that the number of elements can be reduced.

The optical filter of the third solving means includes a liquid crystal layer that gives different phase differences to two orthogonal polarization components, a dielectric substrate that supports the liquid crystal layer, and a reflection structure that folds incident light in the regular reflection direction. By providing a polarization selection structure composed of a fine metal pattern having a size equal to or smaller than the wavelength of incident light on the boundary surface or the inner surface of the dielectric substrate, the amount of detected light is increased, the spectral bandwidth is increased, and the number of optical elements It is possible to achieve an effect that the reduction of the phase modulation amount and the increase of the phase modulation amount are possible.
Further, in the optical filter of the fourth solution means, in addition to the structure of the third solution means, the polarization selection structure and the reflection structure are used as electrodes for driving the liquid crystal layer, thereby increasing the detected light amount and wide spectrum band. It is possible to achieve an effect that it is possible to reduce the number of optical elements and increase the amount of phase modulation.

In the optical filter of the fifth solving means, in addition to the configuration of any one of the first to fourth solving means, the polarization selection structure has a width and a period less than or equal to the wavelength of the incident light in the light transmitting region. By being a metal fine wire (wire grid) structure, the effect that the concrete metal arrangement pattern which implement | achieves the optical filter of any 1st-4th solution means can be provided can be show | played.
Further, in the optical filter of the sixth solving means, in addition to the configuration of any one of the first to fourth solving means, the polarization selection structure has two comb teeth made of a metal material in a region where light is transmitted. By having the configuration in which the structures are arranged to face each other, it is possible to provide an effect that a specific metal arrangement pattern that realizes the optical filter of any one of the first to fourth solving means can be provided. .

  In an image photographing device of a seventh solving means, an optical system for forming an image of a subject on an imaging surface, an optical filter having a function of controlling a phase difference between two orthogonal polarization components, and electrically controlling the optical filter A drive control unit, an imaging unit that converts an object image into an electrical signal, and a signal processing device that processes image information, and the optical filter of any one of the first to sixth solving means is used as the optical filter. By using it, the effect of any one of the first to sixth solving means can be obtained, and the effect that the image capturing apparatus can be reduced in size and operated at high speed can be achieved.

It is a schematic block diagram explaining the image imaging device of the 1st-3rd Example of this invention. It is sectional drawing and a top view of an optical filter used for the image pick-up device of the 1st example of the present invention. It is a figure explaining arrangement | positioning of a polarization | polarized-light selection structure. It is a figure explaining the measurement result of the transmission spectrum of a polarizing filter. It is a figure explaining the model of numerical simulation. It is a figure explaining the result of numerical simulation. It is sectional drawing and the top view of an optical filter used for the imaging device of the 2nd Example of this invention. It is sectional drawing explaining the example of a different structure of the optical filter used for the image imaging device of the 2nd Example of this invention. It is a top view explaining the polarization | polarized-light selection structure pattern of the optical filter used for the image imaging device of the 3rd Example of this invention. It is a figure explaining the gradient force which acts on a liquid-crystal layer. It is a schematic block diagram explaining the image imaging device of the 4th, 5th Example of this invention. It is sectional drawing and a top view of an optical filter used for the image pick-up device of the 4th example of the present invention. It is sectional drawing and the top view of an optical filter used for the image pick-up apparatus of the 5th Example of this invention. It is a figure which shows the flowchart as described in patent document 1. FIG. It is a figure which shows the structural example of the spectroscopic camera head described in patent document 2. FIG. FIG. 10 is a diagram illustrating a configuration example of an image sensor unit described in Patent Document 3. It is a figure which shows the structural example of the acousto-optic filter type | mold spectral camera of patent document 4. FIG. It is a figure which shows the structural example of the spectrometer described in patent document 5. FIG. It is a figure which shows the manufacturing method of the wire grid polarizer of patent document 6. It is a figure which shows the structural example of the optical element of patent document 7.

  Exemplary embodiments of an optical filter and an image capturing device according to the present invention will be described below in detail with reference to the accompanying drawings.

[First Embodiment] (Embodiments of the first, fifth and seventh solving means)
An optical filter and an image photographing apparatus according to a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a schematic configuration diagram illustrating a configuration example of an image capturing device according to a first embodiment of the present invention. The image capturing apparatus 100 according to the present embodiment includes a lens 1011 and a lens barrel (not shown), an optical system 101 that forms an image of a subject on an imaging surface, a dielectric substrate, and a liquid crystal layer, and is electrically modulated. An optical filter 102, a drive control unit 104 that controls the optical filter 102, an imaging unit 103 that has an imaging element and converts an object image into an electrical signal, and a signal processing device 105 that processes image information. Yes. The optical filter 102 is an element that dynamically obtains a phase-modulated image with respect to two orthogonally polarized components utilizing the birefringence of the liquid crystal layer, and the dielectric substrate disposed with the liquid crystal layer sandwiched between the liquid crystal layer Supports and has a polarization selection function. FIG. 1A shows a configuration in which the optical filter 102 is arranged on the back surface of the optical system 101. However, the optical filter 102 may be arranged on the front surface of the optical system as shown in FIG. 1B. . Moreover, the structure arrange | positioned on the sensor surface in the imaging unit 103 may be sufficient.

  Next, a specific configuration of the optical filter 102 in the image capturing apparatus 100 of the present embodiment will be described. FIG. 2A is a cross-sectional view for explaining the arrangement of the polarization selection structure provided on or in the dielectric substrate, and FIG. 2B is a dotted line AA ′ in FIG. It is sectional drawing cut | disconnected by the surface shown. In order to align the liquid crystal material, the dielectric substrate 1021, the transparent electrode film 1022, the alignment film 1023, the liquid crystal material (liquid crystal layer) 1024, the alignment film 1023, the transparent electrode 1022, and the dielectric substrate 1021 are stacked in this order. ing. Further, as shown in a plan view (cross section A-A ′) shown in FIG. 2B, a metal fine wire structure (wire grid) can be used as the polarization selection structure 1025.

FIG. 3A is a cross section in the vicinity of the boundary surface between the dielectric substrate 1021 and the liquid crystal layer 1024, and the metal wire grid structure as the polarization selection structure 1025 is changed to the boundary surface between the dielectric substrate 1021 and the air (or vacuum) region. The structure formed on (upper surface) is shown. At the interface between the dielectric substrate 1021 and the liquid crystal layer 1024, the transparent electrode film 1022 is used as an electrode for modulating the liquid crystal material in the liquid crystal layer, and the movement of the dielectric material is fixed in a certain direction and the electrode and the liquid crystal material are insulated. In order to achieve this, an alignment film 1023 is stacked.
On the other hand, FIG. 3B shows a configuration in which a metal wire grid structure is embedded in a dielectric substrate, and the dielectric substrate 1021 has a polarization selection function and also plays a role of protecting damage and deterioration of the metal wire grid. I'm in charge. Further, although the manufacturing process is complicated in FIG. 3B, a smooth boundary surface can be formed between air (or vacuum) and the dielectric substrate 1021, and a structure such as a total reflection coating is added. There is an advantage that can be.

  Next, the material and manufacturing method of the optical filter 102 in the image capturing apparatus 100 of the present embodiment will be described. As the dielectric substrate 1021, a glass substrate with high transmittance is used. In the configuration shown in FIG. 3A, a metal wire grid that is a polarization selection structure 1025 is provided on the upper surface of the glass substrate 1021. The metal wire grid needs to have a width and a period equal to or less than the wavelength in order to avoid disturbance of the spatial distribution of light intensity due to diffraction. Such a structure can be produced by a method using electron beam lithography, DUV / EUV lithography, nanoimprinting, etching utilizing alteration of material properties, and the like. A manufacturing method by electron beam lithography will be described below, but the manufacturing method is not necessarily limited.

As a manufacturing method by electron beam lithography, first, a metal film is deposited on a glass substrate by a sputtering method or a vacuum evaporation method.
Subsequently, a photoresist material is applied and the metal fine line pattern is exposed by an electron beam. The resist material may be either negative or positive, and the exposure pattern is a negative pattern or a positive pattern depending on the photoresist material.
Thereafter, unnecessary metal portions are etched by RIE or the like, and then the remaining photoresist pattern is removed, whereby a metal wire grid having a width and a period equal to or less than the wavelength can be formed on the dielectric substrate.

  When a metal microstructure is formed inside a dielectric substrate as shown in FIG. 3B, a spin-on-glass film is applied on the metal wire grid produced by the above electron beam lithography, and chemical mechanical polishing is performed. The surface is planarized by (CMP) method. As the metal material, Al is known to exhibit good polarization selectivity, but any metal material may be used as long as it is a metal material exhibiting broadband polarization selectivity.

  In order to provide an electrode structure for controlling the liquid crystal layer 1024 on the dielectric substrate 1021 having the metal microstructure (polarization selection structure) 1025 manufactured as described above, a transparent electrode film 1022 such as ITO is provided on a smooth dielectric interface. Is deposited by a sputtering method, etc., an alignment film 1023 is applied by spin coating, and a rubbing process is performed to align the alignment of liquid crystal molecules. A body substrate 1021 is disposed (FIG. 2A). As the spacer, a sealing material containing spherical fine particles of polystyrene or silica having a uniform size is used. The rubbing direction of the liquid crystal layer 1024 needs to have an angle of 45 ° with the direction of the polarization selection structure 1025. Thereby, two orthogonal polarization components of the light transmitted through the polarization selection structure 1025 on the incident side are equally distributed to the ordinary ray and extraordinary ray components of the liquid crystal layer 1024. Further, the pair of the polarization selection structures 1025 on the incident side and the emission side may be parallel or orthogonal. Light that passes through the optical filter 102 of this embodiment undergoes different phase differences between the ordinary ray and extraordinary ray components in the liquid crystal layer 1024, and is polarized light that vibrates in the same plane when passing through the polarization selection structure 1025 on the output side. Only the component is cut out and detected as an interference signal within the image pickup element plane of the image pickup unit 103 shown in FIG.

Next, an image acquisition method using the image capturing apparatus 100 of the present embodiment will be described.
One application of the image capturing apparatus 100 of the present embodiment is acquisition of a spectral image. The principle of obtaining spectral information is based on Fourier spectroscopy. This separates the incident light into two different optical paths, gives a phase difference to one, or gives a different phase difference to both, and obtains an interference signal corresponding to the phase difference. Spectral information is obtained using the Fourier transform relationship between the two.
Here, in the image capturing apparatus 100 shown in FIG. 1A or 2B, two orthogonal polarization components become two different optical paths, and the optical filter 102 including the liquid crystal layer is dynamically modulated by the drive control unit 104. By doing so, the phase difference is arbitrarily set, and an interference image is acquired in the imaging element plane of the imaging unit 103.
Fourier spectroscopy is characterized in that a large amount of light can be obtained compared to a spectroscope using a diffraction element and spectral information extraction using a color filter. In addition, since it has a configuration of a polarization interferometer using liquid crystal, it has high resistance to vibration and noise.

The interference image formed on the imaging element is converted into an electrical signal by the imaging unit 103 and transferred to the signal processing device 105 via a USB interface or the like. The signal processing device 105 may be an ordinary personal computer, and displays spectral intensity information estimated by a Fourier transform method or the like on a monitor. The spectrum estimation method does not necessarily use the Fourier transform or the fast Fourier transform. For example, a method such as a maximum entropy method can be used.
Further, the use of the optical filter 102 of the present embodiment is not limited to acquisition of a spectrum image by Fourier spectroscopy. For example, it is also possible to function as a variable wavelength filter by taking a plurality of images having a desired phase difference and multiplying all pixels.

Next, the effect of the optical filter 102 used in the image capturing apparatus 100 of the present embodiment will be described based on the measurement result and the numerical simulation result.
In a phase shift device or a spatial modulation element using liquid crystal, a film-like polarizing filter (polarizing film) is attached to the front and back of a liquid crystal cell having a configuration in which a liquid crystal layer is sandwiched between glass substrates. FIG. 4 shows the measurement results of the transmittance of a commercially available polarizing filter (polarizing film) with a spectroscope.
As shown in FIG. 4, a polarizing filter (polarizing film) produced by stretching an organic material generally has reduced polarization selectivity in the near-infrared region from the wavelength of about 750 nm to the long wavelength side. Further, the transmittance is about 70 to 90% in the polarization selective component and is not necessarily high.

On the other hand, in order to investigate the characteristics of the metal wire grid structure, a numerical simulation based on a finite difference time domain (FDTD) method was performed. The FDTD method is a method for obtaining a numerical solution by approximating the Maxwell equation to a difference relating to space and time. A light pulse is incident at a certain time, and a transmission spectrum is calculated by Fourier transforming the time evolution of the electric field. FIG. 5A is a model of the metal wire grid structure used in the numerical simulation, and FIG. 5B is a cross-sectional view taken along the plane indicated by the dotted line BB ′ in FIG. FIG. In this numerical simulation, the metal wire grid is made of Al having a width of 72 nm, a height of 152 nm, and a horizontal pitch of 164 nm, and periodic boundary conditions are applied to the horizontal and vertical calculation region boundaries of the cross section BB ′ in FIG. Thus, a metal wire grid was modeled. The dielectric substrate supporting the Al wire grid was assumed to be SiO ₂ having a refractive index of 1.508. The physical property values of Al were expressed by giving a dielectric function based on the Drude model describing free electrons. A plane wave pulse having a polarization plane inclined by 45 ° with respect to the direction of the metal wire and having a wavelength of 600 nm as a central wavelength was used as an incident light source.

  FIG. 6 shows calculation results obtained by numerical simulation. Here, the polarization component orthogonal to the direction of the metal wire is P-polarized light, and the polarization component in the periodic direction of the metal wire is S-polarized light. As a result of this numerical simulation, in the polarization selective structure in which the metal wire grid is arranged on the dielectric substrate, it was possible to obtain a stable characteristic in a wide band with a transmittance of 80% or more from the short wavelength side to the near infrared region. In addition, since the polarization selective structure is provided directly at the dielectric substrate interface, the influence of the interface due to the polarizing film attached to the front and back surfaces of the conventional liquid crystal cell can be eliminated, and the transmittance of the entire optical filter can be reduced. Reduction could be suppressed.

  As described above, the optical filter 102 used in the image capturing apparatus 100 of the present embodiment is provided with the metal wire grid as the polarization selection structure 1025 on the dielectric substrate 1021 that supports the liquid crystal layer 1024 or inside the dielectric substrate 1021. Thus, the transmittance is improved, and the amount of light incident on the image sensor in the image capturing apparatus 100 of the present embodiment can be increased. In addition, a wide spectral band from visible light to near infrared light can be realized by using a metal wire grid. Furthermore, the number of optical elements such as a polarizing film can be reduced, and the image capturing apparatus can be reduced in size and space.

[Second Embodiment] (Embodiments of the first, second, fifth and seventh solving means)
An optical filter and an image capturing device according to a second embodiment of the present invention will be described with reference to FIGS. 1 and 6 to 8.
FIG. 7A is a cross-sectional view for explaining the arrangement of the polarization selection structure 1025 provided on or inside the dielectric substrate in the optical filter 102 according to the second embodiment of the present invention, and FIG. It is the top view cut | disconnected by the surface shown by dotted line CC 'in the figure of the figure (a).
A difference from the first embodiment is that a transparent electrode is not used as an electrode for applying an electric field to the liquid crystal layer 1025, and the polarization selective structure (metal microstructure) 1025 also serves as an electrode. In order to generate a uniform electric field in the metal microstructure, the metal pattern has a region uniformly filled with a metal material at one end or a plurality of ends, as shown in FIG. Yes.

  The configuration of the image capturing apparatus 100 of the present embodiment is the same as that of the first embodiment, and as shown in FIGS. 1A and 1B, the image capturing apparatus 100 includes a lens 1011 and a lens barrel (not shown). An optical system 101 for forming an image of a subject, an optical filter 102 composed of a dielectric substrate and a liquid crystal layer and electrically modulated, a drive control unit 104 for controlling the optical filter 102, and an image sensor. The imaging unit 103 that converts to an electrical signal and a signal processing device 105 that processes image information are configured.

As shown in FIG. 7A, the optical filter 102 in the image capturing apparatus 100 of this embodiment includes a dielectric substrate 1021, an alignment film 1023, a liquid crystal material (liquid crystal layer) 1024, an alignment film 1023, and a dielectric substrate 1021. A thin metal wire structure (wire grid) is arranged as the polarization selection structure 1025 inside the dielectric substrate.
Here, the metal wire grid is not necessarily arranged inside the dielectric substrate, and may be configured to be disposed at the interface of the dielectric substrate 1021 and coated with the alignment film 1023 as shown in FIG. . In both cases of FIGS. 7A and 8, the alignment film 1023 also serves as an insulating film that insulates the metal wire grid electrode and the liquid crystal layer.

  The material and the manufacturing method of the optical filter 102 in the image capturing apparatus 100 of the present embodiment are the same as those described in the first embodiment. A method using electron beam lithography, DUV / EUV lithography on a glass substrate with high transmittance. Then, a metal wire grid is produced by nanoimprinting, etching utilizing alteration of material properties, etc., and a glass substrate is opposed so that the surface on which the metal wire grid is formed faces the liquid crystal layer, and a liquid crystal material is injected. As the metal material, Al showing good polarization selectivity is used. Further, in order to obtain an interference signal, the alignment film 1023 is subjected to a rubbing process in a direction inclined by 45 ° from the direction of the metal wire grid.

  As described in the first embodiment, the image capturing apparatus 100 according to the present embodiment can be used as an apparatus for capturing a spectrum image based on the principle of Fourier spectroscopy. It can also function as a variable wavelength filter.

Next, the effect of the optical filter 102 used in the image capturing apparatus 100 of the present embodiment will be described.
By using a metal wire grid as the polarization selection structure 1025 and as an electrode, it becomes unnecessary to dispose a transparent electrode that has been conventionally formed of an ITO film or the like. Since the transparent electrode has conductivity, it has absorption associated with charge transfer and reduces the transmittance somewhat. Therefore, it is possible to improve the transmittance of the optical filter of this embodiment by eliminating the transparent electrode structure. In addition, the number of optical elements and the number of films can be reduced. In addition, a metal material such as Al has higher conductivity than the transparent electrode, and a stronger electric field can be applied to the liquid crystal layer using the same power consumption. Therefore, it is suitable for driving an element having a large liquid crystal cell thickness, and is an advantageous characteristic in a spectral image capturing apparatus that can improve spectral resolution by obtaining a large phase difference. For the same reason, the liquid crystal layer can be driven at a higher speed. Moreover, since a metal wire grid is used, as shown in FIG. 6, it is possible to acquire an image in the optical spectrum band from visible light to near infrared.

  As described above, the optical filter 102 used in the image capturing apparatus 100 of the present embodiment is provided with the metal wire grid as the polarization selection structure 1025 on the dielectric substrate 1021 that supports the liquid crystal layer 1024 or inside the dielectric substrate 1021. By using the metal wire grid as an electrode for driving the liquid crystal layer, it is possible to improve the transmittance and increase the amount of light incident on the image sensor in the image capturing apparatus of the present embodiment. In addition, the operation speed of the liquid crystal can be improved. Furthermore, it is possible to obtain an image in a wide spectral band from visible light to near-infrared light, reduce the number of optical elements, reduce the size of the image capturing apparatus, and save space.

[Third Embodiment] (First, Second, Sixth and Seventh Embodiments of Solution)
An optical filter and an image capturing device according to a third embodiment of the present invention will be described with reference to FIGS. 1 and 7 to 10.
In the present embodiment, as in the second embodiment, the metal fine structure that is the polarization selection structure 1025 is used as an electrode for applying an electric field to the liquid crystal layer 1024, but this metal pattern is different from that in the second embodiment. It has a structure.
FIG. 9 is a plan view illustrating a two-dimensional array pattern of the polarization selection structure 1025 provided on or in the dielectric substrate in the optical filter 102 according to the third embodiment. The polarization selection structure 1025 of this embodiment forms an electrode pattern made of a metal material divided into two regions. The region corresponding to the metal wire grid (light transmission region) has a structure in which the upper and lower comb-tooth structures in FIG. 9 are engaged with each other, and the electric wiring 1026 is connected to the electrodes 1 and 2 of each comb-tooth structure. Has been.

  The configuration of the image capturing apparatus 100 of the present embodiment is the same as that of the first embodiment, and as shown in FIGS. 1A and 1B, the image capturing apparatus 100 includes a lens 1011 and a lens barrel (not shown). An optical system 101 for forming an image of a subject, an optical filter 102 composed of a dielectric substrate and a liquid crystal layer and electrically modulated, a drive control unit 104 for controlling the optical filter 102, and an image sensor. The imaging unit 103 that converts to an electrical signal and a signal processing device 105 that processes image information are configured.

  The configuration of the optical filter 102 in the image capturing apparatus 100 of the present embodiment is as described with reference to FIG. 7A in the second embodiment. The dielectric substrate 1021, the alignment film 1023, the liquid crystal material (liquid crystal layer) 1024, an alignment film 1023, and a dielectric substrate 1021 are stacked in this order, and a thin metal wire structure (wire grid) is disposed as the polarization selection structure 1025 inside the dielectric substrate 1021. The metal wire grid is not necessarily disposed inside the dielectric substrate, and may be configured to be disposed at the interface of the dielectric substrate 1021 and coated with the alignment film 1023 as shown in FIG. In both cases of FIGS. 7A and 8, the alignment film 1023 also serves as an insulating film that insulates the metal wire grid electrode and the liquid crystal layer.

  The material and the manufacturing method of the optical filter 102 in the image capturing apparatus 100 of the present embodiment are the same as those described in the first embodiment. A method using electron beam lithography, DUV / EUV lithography on a glass substrate with high transmittance. Then, a metal wire grid is produced by nanoimprinting, etching utilizing alteration of material properties, etc., and a glass substrate is opposed so that the surface on which the metal wire grid is formed faces the liquid crystal layer, and a liquid crystal material is injected. As the metal material, Al showing good polarization selectivity is used. Further, in order to obtain an interference signal, the alignment film is rubbed in a direction inclined by 45 ° from the direction of the metal wire grid.

  As described in the first embodiment, the image capturing apparatus 100 according to the present embodiment can be used as an apparatus for capturing a spectrum image based on the principle of Fourier spectroscopy. It can also function as a variable wavelength filter.

Next, the effect of the optical filter 102 used in the image capturing apparatus 100 of the present embodiment will be described.
As described in the second embodiment, since the polarization selection structure 1025 also serves as an electrode, it is not necessary to dispose a transparent electrode, and the transmittance of the optical filter of this embodiment can be improved. And the number of films can be reduced. In addition, a strong electric field can be applied, which can be used for an element having a thick liquid crystal cell thickness, and is advantageous for high-speed driving of the liquid crystal layer. Moreover, since a metal wire grid is used, it is possible to acquire an image in the optical spectrum band from visible light to near infrared.

In the present embodiment, as shown in FIG. 9, since the two electrodes 1 and 2 having a comb-tooth structure are provided in the same plane, the polarity of the applied voltage can be controlled. . That is, by applying voltages having different polarities in the plane, as shown in FIG. 10, it is possible to generate a gradient force due to electric lines of force on a plane parallel to the alignment film 1023.
In the liquid crystal layer 1024 driven by applying a voltage of the same polarity in the same plane, the gradient force acts in the propagation direction of incident light to align the orientation of the liquid crystal molecules, but until the voltage returns to its initial state when the voltage is released. Takes several seconds. Therefore, by applying a voltage having a different polarity, a time for returning to the initial state can be shortened by generating a gradient force in a direction orthogonal to the alignment of the liquid crystal.

  As described above, the optical filter 102 used in the image capturing apparatus 100 of the present embodiment is provided with the metal wire grid as the polarization selection structure 1025 on the dielectric substrate 1021 that supports the liquid crystal layer 1024 or inside the dielectric substrate 1021. By using the metal wire grid as an electrode for driving the liquid crystal layer 1024, it is possible to improve the transmittance and increase the amount of incident light on the image sensor in the image capturing apparatus 100 of the present embodiment. Further, by configuring the comb-like electrode, the quasi / reverse operation of the liquid crystal layer can be accelerated, and the operation speed of the image photographing apparatus of the present embodiment can be improved. Furthermore, it is possible to obtain an image in a wide spectral band from visible light to near-infrared light, reduce the number of optical elements, reduce the size of the image capturing apparatus, and save space.

[Fourth Embodiment] (Third, Fifth and Seventh Embodiments)
An optical filter and an image capturing device according to a fourth embodiment of the present invention will be described with reference to FIGS.
In this embodiment, the same image photographing apparatus as in the first to third embodiments is realized in a reflective type. By adopting the reflection type structure, the light incident on the optical filter having the liquid crystal layer is reciprocated. As a result, the phase difference between the ordinary ray and the extraordinary ray in the liquid crystal layer can be obtained twice, and the spectral image can be obtained. In the case of acquisition, the resolution can be improved.

  FIG. 11 is a schematic configuration diagram illustrating a configuration example of the image capturing device 200 according to the present embodiment, in which a lens 2011 that forms an image of a subject on the imaging surface, a lens barrel (not shown), and reflected light is captured. An optical system 201 composed of a beam splitter 2012 to be introduced into the element, an optical filter 202 composed of a dielectric substrate, a liquid crystal layer, and a reflective structure, electrically modulated, a drive control unit 204 for controlling the optical filter 202, and an image sensor And an image pickup unit 203 that converts an image of a subject into an electrical signal, and a signal processing device 205 that processes image information.

  The configuration of the optical filter 202 in the image capturing apparatus 200 of the present embodiment will be described with reference to FIG. FIG. 12A is a cross-sectional view illustrating the configuration of the optical filter 202. The optical filter 202 of this example includes a reflective structure 2022, an alignment film 2023, a liquid crystal material (liquid crystal layer) 2024 on a support substrate 2021, and FIG. An alignment film 2025, a transparent electrode 2026, and a dielectric substrate 2027 are stacked in this order. FIG. 12B is a cross-sectional view (cross-section DD ′) taken along the line DD ′ of the optical filter 202 of the present embodiment. The polarization selection structure 2028 is formed on the upper boundary surface of the dielectric substrate 2027. It has a fine metal wire structure (wire grid). Note that the metal wire grid may be disposed inside the dielectric substrate in the same manner as that shown in FIG. The reflection structure 2022 may be a structure having high reflectivity, and a metal film formed on the support substrate 2021, a multilayer film structure having a transparent electrode film as a surface layer, or the like can be used. Here, since the reflective structure 2022 also serves as an electrode for driving the liquid crystal layer 2024, it is necessary to dispose a conductive material on the liquid crystal layer side. FIG. 12 shows an example in which a transparent electrode film is arranged.

  The material and the manufacturing method of the optical filter 202 in the image capturing apparatus 200 of the present embodiment are the same as those described in the first embodiment, and the electron substrate lithography is performed on a glass substrate having a high transmittance, which is the dielectric substrate 2027. A metal wire grid produced by a method, DUV / EUV lithography, nanoimprinting, etching utilizing alteration of material properties, etc., and a metal film or dielectric multilayer film and a transparent electrode film such as ITO on a smooth support substrate 2021 A liquid crystal material is injected with the laminated reflective structure 2022 opposed so that the surface on which the metal wire grid is formed faces the liquid crystal layer. As a material constituting the metal wire grid, Al showing good polarization selectivity can be used. Further, in order to obtain an interference signal, the alignment films 2023 and 2025 are subjected to a rubbing process in a direction inclined by 45 ° from the direction of the metal wire grid.

  As described in the first embodiment, the image capturing apparatus 200 according to the present embodiment can be used as an apparatus for capturing a spectrum image based on the principle of Fourier spectroscopy. It can also function as a variable wavelength filter.

Next, the effect of the optical filter 202 used in the image capturing apparatus 200 of the present embodiment will be described.
The optical filter 202 of the present embodiment is realized by a single-layer metal wire grid in which the polarization selection structure 2028 on the incident side and the emission side is arranged on the boundary surface or inside of the dielectric substrate 2027 by adopting a reflection type configuration. be able to. Thereby, a manufacturing process can be reduced. Further, by adopting a reflective configuration, the optical path length of the light passing through the liquid crystal layer 2024 can be acquired twice, and the spectral resolution can be improved in the spectral image acquisition and the variable wavelength filter function.

  As described above, the optical filter 202 used in the image capturing apparatus 200 of this embodiment is provided with the metal wire grid as the polarization selection structure 2028 on the dielectric substrate 2027 that supports the liquid crystal layer 2024 or inside the dielectric substrate 2027. This eliminates the need for a polarization selection element such as a polarizing film, thereby improving the transmittance and increasing the amount of light incident on the imaging element in the image capturing apparatus 200 of the present embodiment. In addition, it is possible to obtain an image in a wide spectral band from visible light to near-infrared light, reduce the number of optical elements, downsize the image capturing device, and save space. Further, a large phase difference can be obtained by the reflection type configuration, and the spectral resolution and wavelength selectivity can be improved.

[Fifth Embodiment] (Third, Fourth, Fifth, Sixth and Seventh Embodiments)
An optical filter and an image capturing device according to a fifth embodiment of the present invention will be described with reference to FIGS.
In the present embodiment, as in the fourth embodiment, an image photographing apparatus is realized with a reflective configuration. The difference from the fourth embodiment is that the metal microstructure which is the polarization selection structure 2028 also serves as an electrode for driving the liquid crystal layer 2024. Thereby, the fall of the emitted light amount of the optical filter 202 of a present Example can be suppressed. Similarly to the fourth embodiment, incident light travels back and forth through the optical filter 202 having the liquid crystal layer 2024, so that the phase difference between the ordinary ray and the extraordinary ray in the liquid crystal layer 2024 can be doubled. In the case of spectrum image acquisition, the resolution can be improved.

  The configuration of the image capturing apparatus 200 of the present embodiment is as shown in the schematic configuration diagram of FIG. 11, and a lens 2011 that forms an image of a subject on the imaging surface, a lens barrel (not shown), and reflected light is folded back. An optical system 201 including a beam splitter 2012 to be introduced into the imaging device, an optical filter 202 including a dielectric substrate, a liquid crystal layer, and a reflective structure, an electrically modulated optical unit 202, a drive control unit 204 for controlling the optical filter 202, and an imaging The imaging unit 203 includes an element and converts an image of a subject into an electrical signal, and a signal processing device 205 that processes image information.

  The configuration of the optical filter 202 in the image capturing apparatus 200 of the present embodiment will be described with reference to FIG. FIG. 13A is a cross-sectional view illustrating the configuration of the optical filter 202. The optical filter 202 of this embodiment includes a reflective structure 2022, an alignment film 2023, a liquid crystal material (liquid crystal layer) 2024 on a support substrate 2021, An alignment film 2025 and a dielectric substrate 2027 are sequentially stacked, and a metal thin wire structure (wire grid) is provided as a polarization selection structure 2028 on the boundary surface between the dielectric substrate 2027 and the alignment film 2025. FIG. 13B is a cross-sectional view (cross-section EE ′) of the EE ′ line portion of the optical filter 202 of the present embodiment, in order to use the metal wire grid as an electrode for driving the liquid crystal layer 2024. Moreover, it has the area | region filled with the metal material in the edge part. In FIG. 13B, a single electrode is formed by a two-dimensional pattern of a metal wire grid. However, similarly to the case shown in FIG. 9, an electrode pattern having a two-tooth structure can be used. good. In that case, an electric field can be generated in the electrode surface, and a gradient force in two directions, horizontal and vertical, can be applied to the liquid crystal layer.

  The material and the manufacturing method of the optical filter 202 in the image capturing apparatus 200 of the present embodiment are the same as those described in the first embodiment, and the electron substrate lithography is performed on a glass substrate having a high transmittance, which is the dielectric substrate 2027. A metal wire grid produced by a method, DUV / EUV lithography, nanoimprint, etching using alteration of material properties, etc., and a metal film or dielectric multilayer film and a transparent electrode film such as ITO on a smooth support substrate 2021 A liquid crystal material is injected with the laminated reflective structure 2022 opposed so that the surface on which the metal wire grid is formed faces the liquid crystal layer. As a material constituting the metal wire grid, Al showing good polarization selectivity can be used. Further, in order to obtain an interference signal, the alignment films 2023 and 2025 are rubbed in a direction inclined by 45 ° from the direction of the metal wire grid.

  As described in the first embodiment, the image capturing apparatus according to the present embodiment can be used as an apparatus for capturing a spectrum image based on the principle of Fourier spectroscopy. It can also function as a variable wavelength filter.

Next, the effect of the optical filter 202 used in the image capturing apparatus 200 of the present embodiment will be described.
The optical filter 202 of the present embodiment is realized by a single-layer metal wire grid in which the polarization selection structure 2028 on the incident side and the emission side is arranged on the boundary surface or inside of the dielectric substrate 2027 by adopting a reflection type configuration. be able to. Thereby, a manufacturing process can be reduced. Further, by adopting a reflective configuration, the optical path length of the light passing through the liquid crystal layer 2024 can be acquired twice, and the spectral resolution can be improved in the spectral image acquisition and the variable wavelength filter function. Further, since the metal wire grid also serves as an electrode, a transparent electrode film is not necessary, and a decrease in the amount of emitted light can be suppressed, and the direction of the gradient force of the electric lines of force acting on the liquid crystal layer 2024 can be controlled. The high-speed operation of the image photographing apparatus according to the embodiment is possible.

  As described above, the optical filter 202 used in the image capturing apparatus 200 of this embodiment is provided with the metal wire grid as the polarization selection structure 2028 on the dielectric substrate 2027 that supports the liquid crystal layer 2024 or inside the dielectric substrate 2027. Thus, it is possible to improve the transmittance and increase the amount of light incident on the image sensor in the image capturing apparatus 200 of the present embodiment. In addition, the operation speed of the liquid crystal can be improved. In addition, it is possible to obtain an image in a wide spectral band from visible light to near-infrared light, reduce the number of optical elements, downsize the image capturing device, and save space. Further, a large phase difference can be obtained by the reflection type configuration, and the spectral resolution and wavelength selectivity can be improved.

  The optical filter and the image capturing apparatus according to the present invention described above can be used in a spectral imaging system, a multi-hyperspectral imaging system, or the like that acquires spectrum information continuously or selectively. Further, it can be used for a spectrum measuring apparatus or the like.

100, 200: Image capturing apparatus 101, 201: Optical system 102, 202: Optical filter 103, 203: Imaging unit 104, 204: Drive control unit 105, 205: Signal processing apparatus 1021, 2027: Dielectric substrate 1022, 2026: Transparent electrode film 1023, 2023, 2025: orientation 1024, 2024: liquid crystal layer (liquid crystal material)
1025, 2028: Polarization selective structure (metal thin wire structure)
1026, 2029: Electrical wiring

JP 2009-033222 A JP 2005-057541 A JP 2006-067183 A JP 2001-074555 A Japanese Patent Laid-Open No. 2005-31007 JP 2007-17762 A JP 2007-226047 A

Claims (7)

An optical filter having a function of controlling a phase difference between two orthogonal polarization components,
It has a liquid crystal layer that gives different phase differences to two orthogonal polarization components, and a dielectric substrate that supports the liquid crystal layer, and has a size equal to or smaller than the wavelength of incident light on the boundary surface or the inner surface of the dielectric substrate. An optical filter comprising a polarization selection structure composed of a metal fine pattern. The optical filter according to claim 1.
An optical filter using the polarization selection structure as an electrode for driving the liquid crystal layer. An optical filter having a function of controlling a phase difference between two orthogonal polarization components,
A liquid crystal layer that gives different phase differences to two orthogonal polarization components; a dielectric substrate that supports the liquid crystal layer; and a reflection structure that folds incident light in a regular reflection direction; An optical filter comprising a polarization selection structure constituted by a fine metal pattern having a size equal to or smaller than the wavelength of incident light on the surface. The optical filter according to claim 3.
An optical filter using the polarization selection structure and the reflection structure as an electrode for driving the liquid crystal layer. In the optical filter as described in any one of Claims 1-4,
The optical filter, wherein the polarization selection structure is a thin metal wire structure having a width and a period equal to or less than a wavelength of incident light in a light transmitting region. In the optical filter as described in any one of Claims 1-4,
The optical filter, wherein the polarization selection structure has a configuration in which two comb-tooth structures made of a metal material are arranged to face each other in a region where light is transmitted. An optical system for imaging a subject on an imaging surface, an optical filter having a function of controlling the phase difference between two orthogonal polarization components, a drive control unit for electrically controlling the optical filter, and an electrical signal for the subject image An image pickup unit for converting into a signal processing device and a signal processing device for processing image information,
An image photographing apparatus using the optical filter according to claim 1 as the optical filter.

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