JP6185245B2 - Optical system - Google Patents

Description

  The present invention relates to an optical system.

  Conventionally, an optical system that simultaneously obtains a plurality of images using a plurality of optical systems is known. For example, an image in the visible light region and an image in the near-infrared light region are photographed by different optical systems, and this visible There is a video display device that displays a video by superimposing two images of an optical region image and a near-infrared light region image. When taking an image in the visible light region and an image in the near-infrared light region as described above with different optical systems, this optical system determines the angle of view of each optical system according to the distance to the subject. It was necessary to design an optical system according to the distance to the subject. Further, since a plurality of optical systems are provided, there is a problem that the cost increases and the size increases.

  As a technique for solving this problem, for example, in Patent Document 1, an imaging element having a first imaging area and a second imaging area different from the first imaging area is arranged in the first imaging area. An imaging device that captures a subject image across the first imaging region and the second imaging region, the image capturing filter including the color image capturing filter and the invisible light image capturing filter disposed in the second imaging region. Have been described.

  On the other hand, Patent Document 2 discloses a polarization beam splitter in which the polarization conversion device itself has a function of removing light in the infrared wavelength band, thereby realizing simplification and miniaturization of an optical system such as a liquid crystal image display device. . The polarization beam splitter is a dielectric laminated polarization beam splitter in which a polarization separation film in which a plurality of dielectric films having different refractive indexes are alternately laminated is sandwiched between transparent media having a high refractive index. The polarization separation film is laminated in multiple layers with a constant optical film thickness nd (n: refractive index of dielectric film, d: physical film thickness of dielectric film) of two types of dielectric films having different refractive indexes. In the stacked group, first, second and third stacked groups having different optical film thicknesses nd are stacked for each group, and the optical film thickness nd of the first stacked group is 219 nm ≦ nd ≦ It is characterized by being set to 235 nm.

JP 2011-82855 A JP-A-11-167026

  In the biometric authentication field, by superimposing an image in the visible light region and an image in the near-infrared light region separated by polarization, for example, information on the surface of the human body such as a fingerprint that is a subject and information in the human body such as a vein Can be authenticated at the same time, so improvement in authentication accuracy can be expected. Further, in the security field, it is possible to expect an effect such as image degradation reduction related to a subject that occurs when a camera photographing environment such as a surveillance camera changes in brightness. When considering the use of the optical system disclosed in Patent Document 1 in the biometric authentication field and the security field, since light having image information is in the same optical path, a predetermined analysis for highly analyzing the image information is performed. A polarization separation element (a so-called analysis filter) capable of polarization separation of only light having a wavelength is required. The polarization conversion device described in Patent Document 2 is a device that gives polarized illumination light to a liquid crystal image display device or the like (so-called polarization filter), and improves the authentication accuracy of the authentication device and reduces image deterioration of a monitoring camera or the like. Therefore, it is not used for polarization separation of light incident on a light receiver such as an image sensor (a so-called light detection filter).

  The present invention has been made in view of the above points, and can be used in the biometric authentication field and the security field, and provides an optical system capable of imaging information of light of different wavelengths with high accuracy with a simple configuration. Objective.

The optical system of the present invention reflects a first specific wavelength light from a subject and transmits a second specific wavelength light having a wavelength region different from that of the first specific wavelength light, and the second mirror. A reflective polarizing mirror that reflects and reflects the specific wavelength light, and a light receiver that receives the first specific wavelength light reflected by the dielectric mirror and the polarized and reflected light by the reflective polarizing mirror, and A dielectric mirror and the reflective polarizing mirror are provided on an optical path between the subject and the light receiver, the reflective polarizing mirror is attached to the dielectric mirror, and the reflective polarizing mirror is A polarizing plate having a specific polarization axis that does not depend on a polarization axis direction of the light that has been polarized and separated, depending on an incident direction and an incident angle of incident light, and the reflective polarizing mirror is closer to the subject than the dielectric mirror. It is characterized by being arranged in .

  In the optical system of the present invention, the reflective polarizing mirror is preferably a wire grid polarizing plate.

  According to the present invention, a dielectric mirror that can act as an analysis filter and can reflect light of a specific wavelength (first specific wavelength light), and light of a desired wavelength other than the specific wavelength (second specific wavelength) Therefore, an optical system capable of imaging information of light of each wavelength with high accuracy can be obtained with a simple configuration.

It is a schematic diagram which shows schematic structure of the optical system which concerns on the 1st Embodiment of this invention. It is a cross-sectional schematic diagram of a wire grid polarizing plate. It is a schematic diagram which shows schematic structure of the optical system which concerns on the 2nd Embodiment of this invention.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited to the following embodiment, In the range with the effect of this invention, it can change suitably and can implement.

(First embodiment)
FIG. 1 is a schematic diagram showing a schematic configuration of an optical system according to the first embodiment of the present invention. The optical system shown in FIG. 1 reflects the first specific wavelength light (solid arrow in FIG. 1) from the subject, and the second specific wavelength light (FIG. 1) having a wavelength region different from that of the first specific wavelength light. A dielectric mirror 11 that transmits the second specific wavelength light, a reflective polarizing mirror 12 that polarizes and reflects the second specific wavelength light, and the first specific wavelength light that is reflected by the dielectric mirror 11, and the reflective polarizing mirror 12 And the light receiver 13 that receives the light reflected and reflected by the light.

  In the optical system, the dielectric mirror 11 and the reflective polarizing mirror 12 are provided on the optical path between the subject and the light receiver 13, and the dielectric mirror 11 is on the subject side and the light receiver 13 side of the reflective polarizing mirror 12. Is arranged. For this reason, light from the subject passes through the dielectric mirror 11 and the reflective polarizing mirror 12 in this order.

  The subject is not particularly limited as long as it is a subject from which different images are acquired by reflected light when two types of wavelength light having different wavelength bands are irradiated. For example, in the case of acquiring a human body image such as a fingerprint and a human body image such as a vein in biometric authentication at the same time, or in a case where a monitoring camera acquires a visible light image and an infrared light image simultaneously. The target is the subject.

  The light reflected by the subject is a reflection of the light applied to the subject, and may be any light in the wavelength band such as ultraviolet light, visible light, and infrared light, and the polarization state of these lights is not limited. . In addition, there is no limitation on the light applied to the subject. When the optical system of the present invention is used for a sensor or the like, LED light, laser light, or the like is used. .

  The specific wavelength light means a desired wavelength or wavelength band (wavelength range) in the ultraviolet light, visible light, infrared light region, etc., and the light of the first specific wavelength and the light of the second specific wavelength. The wavelength or wavelength band is different. Here, the fact that the wavelength or wavelength band of the light having the first specific wavelength and the light having the second specific wavelength is different means that the light does not completely match, and even if there are overlapping wavelengths or wavelength bands. I do not care. The first and second specific wavelengths may be composed of a single wavelength band or a plurality of wavelength bands, and the wavelength bands may be continuous or discontinuous.

  The dielectric mirror 11 is not particularly limited as long as it has a characteristic of reflecting at least the first specific wavelength light and transmitting the second specific wavelength light. A configuration having a dielectric layer on the surface of the optical substrate is preferable. Examples of such a dielectric mirror include a cold mirror that transmits infrared light and reflects visible light, and a hot mirror that transmits visible light and reflects infrared light.

If the said translucent board | substrate transmits the light of a specific wavelength, there will be no problem in particular. Examples of the material constituting the dielectric include TiO ₂ , CeO ₂ , ZrO ₂ , ZnS, CaF ₂ , MgF ₂ , SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , In ₂ O ₃ , WO ₃ and mixtures thereof. Depending on the desired characteristics, layers made of dielectrics having different refractive indexes may be stacked.

  Here, the reflection means that the light traveling in the medium such as air changes its direction upon hitting the boundary surface of the medium such as the dielectric mirror 11 and travels back to the original medium. The state is unquestioned. Of the incident light, light having a desired wavelength is preferably reflected to such an extent that an image is formed in the light receiver 13, and more preferably 50% or more of light is reflected. In addition, when there is a wavelength that is superimposed on the first specific wavelength and the second specific wavelength (hereinafter referred to as a superimposed wavelength), the light of the superimposed wavelength is reflected.

  The reflective polarizing mirror 12 is not particularly limited as long as it has a characteristic capable of polarizing and reflecting and transmitting polarized light of a specific wavelength. For example, a polarizing plate made of a birefringent resin laminate, a wire grid type polarizing plate, or the like. Further, it is possible to use a reflective polarizing plate such as a polarizing plate made of cholesteric phase liquid crystal or a polarizing plate in which a dielectric is laminated. Of the light polarized and separated by the reflective polarizing mirror, transmission of polarized light is referred to as polarized light transmission, and reflected light is referred to as polarized light reflection.

  The reflective polarizing mirror 12 preferably includes a polarizing plate having a specific polarization axis. A polarizing plate having a specific polarization axis (reflective polarizing plate) is a polarizing separation layer (polarization separation layer) having a specific axial direction and parallel or orthogonal to the specific axial direction. It means the one that transmits or reflects the light component. Accordingly, since the polarization axis direction of the polarized light does not depend on the light incident direction and light incident angle of the light incident on the polarizing plate, the reflective polarizing mirror 12 is provided on the surface side where the light source light enters. Thus, the polarized light can be transmitted and reflected without changing the polarization state of the light from the subject entering the wide angle, and the light reflected by the reflective mirror 12 and the light reflected by the dielectric mirror 11 are received by the light receiver 13. Can be incident. Examples of the reflective polarizing plate having a specific polarization axis include a wire grid polarizing plate, a laminate film in which birefringent films having different birefringence are laminated, and the like. In particular, since the polarization separation layer is a single layer, a wire grid polarizing plate that is capable of polarizing and separating broadband light with a small change in transmission or reflection intensity accompanying a change in incident light angle is preferable.

  Here, the wire grid polarizer will be described. FIG. 2 is a schematic cross-sectional view of a wire grid polarizer. As shown in FIG. 2, the wire grid polarizer includes a base material 20, a fine concavo-convex structure 20 a provided on the surface of the base material 20, a metal wire 21 formed on at least a convex portion of the fine concavo-convex structure, Have The fine concavo-convex structure 20a has a plurality of convex portions A and a plurality of concave portions B provided so as to continuously extend in the in-plane direction (left-right direction and depth direction in FIG. 4) of the reference surface of the optical element.

  The base material 20 should just be substantially transparent in the target wavelength range, and it is preferable to use a resin material. By using a resin base material as the base material, there are merits such that a roll process is possible and the wire grid polarizing plate can have flexibility. Examples of the resin that can be used for the substrate include polymethyl methacrylate resin, polycarbonate resin, polystyrene resin, cycloolefin resin (COP), cross-linked polyethylene resin, polyvinyl chloride resin, polyarylate resin, polyphenylene ether resin, modified Amorphous thermoplastic resins such as polyphenylene ether resin, polyetherimide resin, polyether sulfone resin, polysulfone resin, polyether ketone resin, polyethylene terephthalate (PET) resin, polyethylene naphthalate resin, polyethylene resin, polypropylene resin, Crystalline thermoplastic resins such as polybutylene terephthalate resin, aromatic polyester resin, polyacetal resin, and polyamide resin, and ultraviolet rays such as acrylic, epoxy, and urethane ( Etc. V) curable resin or thermosetting resin. In addition, UV curable resins and thermosetting resins can be combined with the above thermoplastic resins and triacetate resins, or can be used alone to form a base material, and inorganic materials such as glass (for example, glass It is also possible to combine fillers). In order to cure the UV curable resin, it is possible to use a light source that emits UV light or a light source that emits an electron beam.

  A metal wire can be formed by selectively providing a metal film on the convex portion A of the fine concavo-convex structure 20 a provided on the base material 20. Although the period (pitch P between convex parts) of the fine concavo-convex structure 20a is not particularly limited, it is desirable to set the period to exhibit polarization characteristics. Generally, a wire grid polarizing plate exhibits better polarization characteristics in a wider wavelength band as the interval (period) of metal wires becomes smaller. When the metal wire is in contact with air (refractive index 1.0) and is not covered with an adhesive substance, the interval between the metal wires is set to ¼ to ３ of the wavelength of the target light. However, when the metal wire is coated with an adhesive material, the distance between the metal wires is set to the wavelength of the target light in consideration of the influence of the refractive index of the adhesive material. More preferably, the period is 1/5 to 1/4. For this reason, when considering the use of light in the visible light region, the interval between the metal wires is preferably 150 nm or less, more preferably the interval between the metal wires is 130 nm or less, and most preferably, the interval between the metal wires. The interval is set to 100 nm or less. In addition, the minimum of the space | interval of a metal wire is 50 nm on a manufacturing process.

  Examples of the shape of the fine concavo-convex structure formed on the substrate surface include a trapezoidal shape, a rectangular shape, a rectangular shape, a prism shape, and a sine wave shape such as a semicircular shape. Here, the sinusoidal shape means having a curved portion formed by repetition of a concave portion and a convex portion. In addition, the curved part should just be a curved curve, for example, the shape which has a constriction in a convex part is also included in a sine wave form. From the viewpoint of transmittance, the cross-sectional shape of the substrate is preferably rectangular or sinusoidal.

  In addition, a base material is formed by combining a resin film such as an ultraviolet curable resin or a thermosetting resin and an inorganic base material such as glass (for example, a glass filler) or a resin base material such as a thermoplastic resin or a triacetate resin. May be. In this case, a fine concavo-convex structure having a predetermined cycle can be formed on the surface of the resin coating formed on the inorganic substrate or the resin substrate. From the viewpoint of obtaining a highly smooth surface with excellent specularity, the film thickness of the resin film is preferably 0.005 μm or more and 3 μm or less.

  The metal wire is formed on at least the convex portion of the fine concavo-convex structure. In this case, a metal wire extending continuously in a predetermined direction can be provided by depositing a metal partially on at least the side surface of the convex portion.

  The metal wire can be formed using a conductive material such as aluminum, silver, copper, platinum, gold, or an alloy containing each of these metals as a main component. In particular, the absorption loss in the visible region can be reduced by forming a metal wire using aluminum or silver.

  The period (pitch P) of the metal wire is as described above, but the duty ratio of the metal wire is 0.2 or more and 0.8 in a cross-sectional view perpendicular to the direction in which the metal wire continuously extends. The following is preferable. The aspect ratio of the metal wire is preferably 0.5 or more and 2.0 or less. Thereby, the total light transmittance can be improved.

  There is no restriction | limiting in particular in the formation method of a metal wire. For example, a method of forming using mask patterning and dry etching by an electron beam lithography method or an interference exposure method, a method of forming by an oblique deposition method, and the like can be given. Since it is necessary to form the metal wire very thinly, it is preferable to use an oblique deposition method from the viewpoint of productivity and optical symmetry.

  Further, from the viewpoint of optical characteristics, unnecessary metal may be removed by etching. The etching method is not particularly limited as long as the metal part can be selectively removed without adversely affecting the substrate and the dielectric layer described later, but a method of immersing in an alkaline aqueous solution is preferable from the viewpoint of productivity. . However, since the metal wire is formed very thin, the above etching removal is not essential.

  In order to improve the adhesion between the material constituting the substrate and the metal wire, a dielectric material having a high adhesion between them may be interposed therebetween. When the adhesion between the base material and the metal wire is high, peeling of the metal wire from the base material can be prevented, and a decrease in the degree of polarization can be suppressed. Examples of dielectrics that can be suitably used include silicon (Si) oxides, nitrides, halides, carbides, or composites thereof (dielectrics in which other elements, simple substances, or compounds are mixed in the dielectric alone). Body), aluminum (Al), chromium (Cr), yttrium (Y), zirconia (Zr), tantalum (Ta), titanium (Ti), barium (Ba), indium (In), tin (Sn), zinc (Zn), magnesium (Mg), calcium (Ca), cerium (Ce), copper (Cu) and other metal oxides, nitrides, halides, carbides alone or a composite thereof can be used. The dielectric material is preferably substantially transparent in a wavelength region where transmission polarization performance is to be obtained. There are no particular limitations on the method of laminating the dielectric material, and physical vapor deposition methods such as vacuum vapor deposition, sputtering, and ion plating can be suitably used.

  The reflective polarizing mirror 12 is preferably attached to the dielectric mirror 11. This is because if there is a space between the reflective polarizing mirror 12 and the dielectric mirror 11, the polarization state changes due to interface reflection. For example, when the image information is polarized and separated for image analysis, the space between the reflective polarizing mirror 12 and the dielectric mirror 11 may cause image duplication (ghost). In order to prevent ghosting, it is effective to attach the reflective polarizing mirror 12 to the dielectric mirror 11. In order to prevent ghosts, for example, it is effective to shorten the distance between the polarization separation layer constituting the reflective polarizing mirror and the dielectric layer of the dielectric mirror, and the base material is a resin wire. Since the grid polarizing plate can be made thin, it is preferably used.

  The light receiver 13 can be an image sensor, a photoresistor, or the like, but is not particularly limited as long as it can convert incident light into an image.

  The dielectric mirror 11 and the reflective polarizing mirror 12 in the optical system having the above-described configuration are not subjected to polarization separation of the first specific wavelength light for highly analyzing light from a subject having information such as an image. Acts as an analysis filter capable of polarization-separating only the specific wavelength light. For example, in order to authenticate with high accuracy using information on the surface of a human body such as a fingerprint as a subject and information on the human body such as a vein, the information on the surface of the human body is received as a bright image in the visible light range, This information can be achieved by receiving light of a specific polarization state in the near-infrared light region from the subject. For example, the dielectric mirror 11 and the reflective polarizing mirror 12 can reflect the light in the visible light region without polarization separation by using the dielectric mirror 11 as a cold mirror and the reflective polarizing mirror 12 as a wire grid polarizing plate. Therefore, light in the near-infrared light region can be polarized and separated, so that it is optimal as an analysis filter for the authentication. Therefore, by using this configuration together with the light receiver, an optical system capable of imaging with high accuracy with a simple configuration can be obtained.

  In the optical system having the above configuration, the first specific wavelength light (solid arrow) is reflected and the second specific wavelength light (broken arrow) is transmitted by the dielectric mirror 11 among the light reflected from the subject. To do. The reflected first specific wavelength light is incident on the light receiver 13 with its optical path changed. On the other hand, the second specific wavelength light transmitted through the dielectric mirror 11 is polarized and separated by the reflective polarizing mirror 12, and the light of a predetermined polarization component (polarized reflected light) is reflected to change the optical path, so that the predetermined polarized light is reflected. Light having a polarization component orthogonal to the component (polarized transmitted light) is transmitted. The reflected S-polarized component in the infrared region enters the light receiver 13.

  Thereby, from the light reflected from the subject, the first specific wavelength light is incident on the light receiver 13 and imaged, and the S-polarized component of the second specific wavelength light is incident on the light receiver 13 and imaged. can do. As described above, the optical system of the present embodiment can image information of light having different wavelengths with high accuracy with a simple configuration. This optical system can be used in the biometric authentication field and the security field.

(Second Embodiment)
FIG. 3 is a schematic diagram showing a schematic configuration of an optical system according to the second embodiment of the present invention. The optical system shown in FIG. 3 has a configuration in which the positions of the dielectric mirror 11 and the reflective polarizing mirror 12 of the optical system shown in FIG. 1 are changed. In FIG. 3, the same members as those in FIG. 1 are denoted by the same reference numerals as those in FIG.

  The optical system shown in FIG. 3 reflects the first specific wavelength light (solid arrow in FIG. 3) from the subject, and the second specific wavelength light (FIG. 3) having a wavelength region different from that of the first specific wavelength light. A dielectric mirror 11 that transmits the second specific wavelength light, a reflective polarizing mirror 12 that polarizes and reflects the second specific wavelength light, and the first specific wavelength light that is reflected by the dielectric mirror 11, and the reflective polarizing mirror 12 And the light receiver 13 that receives the light reflected and reflected by the light.

  In the optical system, the dielectric mirror 11 and the reflective polarizing mirror 12 are provided on the optical path between the subject and the light receiver 13, and the reflective polarizing mirror 12 is on the subject side and the light receiver 13 side of the dielectric mirror 11. Is arranged. For this reason, light from the subject passes through the reflective polarizing mirror 12 and the dielectric mirror 11 in this order.

  In the optical system having the above configuration, the light having the predetermined polarization component (polarized reflected light) of the second specific wavelength light (broken arrow) is reflected by the reflective polarizing mirror 12 among the light reflected from the subject, Light having a polarization component orthogonal to the predetermined polarization component of the second specific wavelength light (polarized transmitted light) and the first specific wavelength light (solid arrow) are transmitted. The reflected polarization component of the second specific wavelength light is incident on the light receiver 13 with the optical path changed. On the other hand, the first specific wavelength light transmitted through the reflective polarizing mirror 12 is reflected by the dielectric mirror 11, the optical path is changed, and enters the light receiver 13, and the polarized transmitted light of the second specific wavelength light is the dielectric mirror. 11 is transmitted. Since the reflective polarizing mirror 12 is disposed on the subject side and the light receiver 13 side of the dielectric mirror 11, the second specific wavelength light enters the polarizing reflective mirror 12 before entering the dielectric mirror 11. That is, since the polarization separation can be performed without changing the polarization state of the second specific wavelength light from the subject, image analysis can be performed with high accuracy. Furthermore, when a reflective polarizing plate having a specific polarization axis is used as the polarizing reflector 12, the polarization separation layer has a specific axis direction, so that it does not depend on the light incident direction and light incident angle of incident light. Since polarization separation can be performed, image analysis can be performed with higher accuracy, which is preferable.

  As a result, from the light reflected from the subject, the predetermined polarization component of the second specific wavelength light is incident on the light receiver 13 to form an image, and the first specific wavelength light is incident on the light receiver 13 to form an image. Can be As described above, the optical system of the present embodiment can image information of light having different wavelengths with high accuracy with a simple configuration. This optical system can be used in the biometric authentication field and the security field.

  In particular, when the polarized light applied to the subject is reflected by the subject and enters the present optical system, the dielectric mirror 11 made of a dielectric enters the incident light depending on the incident direction of the incident light source light and the polarization axis direction. May change the polarization state. Therefore, as in the present embodiment, the polarization state of the incident light is changed by arranging the reflective polarizing mirror 12 on the subject side with respect to the dielectric mirror 11 on the optical path between the subject and the light receiver 13. Can be prevented.

  The present invention is not limited to the embodiment described above, and can be implemented with various modifications. Further, in the above-described embodiment, the size, shape, material, quantity, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effect of the present invention is exhibited. is there. In addition, the present invention can be appropriately modified and implemented without departing from the scope of the object of the present invention.

  The optical system of the present invention is suitably used in an image inspection apparatus, an imaging apparatus, and the like in the biometric authentication field and the security field.

DESCRIPTION OF SYMBOLS 11 Dielectric mirror 12 Reflective polarizing mirror 13 Light receiver 20 Base material 20a Fine uneven structure 21 Metal wire A Convex part B Concave part

Claims (2)

A dielectric mirror that reflects the first specific wavelength light from the subject and transmits the second specific wavelength light having a wavelength region different from that of the first specific wavelength light;
A reflective polarizing mirror that polarizes and reflects the second specific wavelength light;
Receiving a first specific wavelength light reflected by the dielectric mirror, and receiving light polarized and reflected by the reflective polarizing mirror,
The dielectric mirror and the reflective polarizing mirror are provided on an optical path between the subject and the light receiver;
The reflection polarizing mirror is attached to the dielectric mirror, and the polarization axis direction of the polarized light does not depend on the incident direction and the incident angle of the light incident on the reflective polarizing mirror. A polarizing plate having a polarization axis of
An optical system, wherein the reflective polarizing mirror is disposed closer to the subject than the dielectric mirror. The optical system according to claim 1 , wherein the reflective polarizing mirror is a wire grid polarizer.

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