JP2007286499A - Diffraction optics and authentication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an authentication apparatus to which a diffractive optical element is applied. <P>SOLUTION: The authentication apparatus 100 is constituted to have an authentication means 20 provided with the diffractive optical element 1, and a diffracted light beam detector 80. An object 30 to be authenticated provided with a diffractive optical element 50 is positioned with respect to the authentication means 20, and the diffracted light from the diffractive optical element 1 by the incident light made incident on the diffraction face of the diffractive optical element 1 is made incident on the diffraction face of the diffractive optical element 50 and is detected by the diffracted light beam detector 80, thereby making possible the collation of the object 30 and the authentication means 20. The authentication means 20 has alignment marks 21, 22 at which the authentication means 20 performs positioning with respect to the authentication means 20 of the object 30, and the object 30 has alignment marks 31, 32 at which the object 30 performs positioning with respect to the authentication means 20 of the object 30. The object 30 is thus optically positioned with respect to the authentication means 20. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a diffractive optical system having a diffractive optical element and an authentication apparatus.

  Conventionally, there is provided a hologram transfer sheet having an optical element that is provided on a whole surface or a part of a transfer object such as a card, a certificate, a bill, or the like and used to display various patterns, marks, and designs by a hologram. Are known. The hologram transfer sheet is useful for preventing counterfeiting of the card and the like by irradiating light onto the hologram transfer sheet and reading it with a visual or reading machine.

  There are various types of optical elements, and those having a diffractive optical element (Diffractive Optical Element, DOE) having a diffractive action of light on a lens surface are well known. A diffractive optical element is an optical element having a slit-like or groove-like lattice structure with a few hundreds per minute gap (about 1 mm), and when light enters, the pitch of slits or grooves ( The diffraction pattern (diffracted image) is formed by generating a diffracted light beam in a direction determined by the distance) and the wavelength of light. Such a diffractive optical element is used in various diffractive optical systems. For example, in order to reduce chromatic aberration, one that collects diffracted light of a specific order at one point and uses it as a lens is known.

Some of the diffractive optical elements used in the diffractive optical system have a structure in which a lens having a sawtooth cross section is approximated in phase to a staircase shape. Such a diffractive optical element is similar to an electronic integrated circuit. By repeating the process of forming the staircase on the surface of the substrate N times by etching the substrate or sputtering the substrate, a step of 2 N level is formed. For example, by repeating lithography and etching four times, a diffractive optical element having 16 steps can be manufactured. Such a diffractive optical element has a structure in which the number of steps is increased by a factor of 2 by repeating a process such as etching, and therefore is called a binary optical element (BOE) (for example, non-optical element). (See Patent Document 1).
"Introduction to diffractive optical elements" Optonics Corporation 2002

  By the way, the binary optical element as described above has a property that a diffracted light beam is generated in a direction determined by the shape of the stepped diffraction surface (phase pattern) and the wavelength of light, thereby forming a diffraction image. Therefore, when light of a certain wavelength is incident, the diffracted light can be condensed in a specific direction to form a diffraction image, but when light of a different wavelength is incident, the light is condensed. The wavelength used as incident light of a diffractive optical element that can be condensed (condensation efficiency is higher than a predetermined value) is limited such that the diffraction pattern cannot be formed (condensation efficiency is reduced). It had been. For this reason, if the diffractive optical element can form a diffracted image regardless of the wavelength of incident light, it is considered that the diffractive optical element can be used for various applications.

  In addition, the binary optical element as described above is generally used without changing the incident angle of incident light incident on the diffraction surface, but the incident angle of incident light is not determined. Even when the incident light is incident on the diffractive surface in various ways, the diffracted light is condensed in a predetermined direction and the incident light is incident on the predetermined projection surface in the same way as when the incident light incident angle is not changed. If it is possible to project different diffracted images for each angle, there is a high possibility that the use of the diffractive optical element will be expanded particularly in the field of security such as forgery prevention of the card as described above.

  In view of the above problems, in the present invention, a different diffraction image is formed for each wavelength with respect to incident light incident on the diffractive surface, and for incident light incident on the diffractive surface at different incident angles. It is an object of the present invention to provide a diffractive optical system and an authentication device having a diffractive optical element that forms a different diffraction image for each incident angle.

  In order to solve the above-mentioned problem, a diffractive optical system according to claim 1 of the present invention is configured to form a diffractive image different in each wavelength with respect to incident light of a plurality of specific wavelengths incident on the diffractive surface. Are arranged so that the diffracted light diffracted by the diffractive surface is incident on the diffractive surface, and incident light of at least two types of wavelengths incident on the diffractive surface at the same incident angle for each incident light. And diffracted light detecting means (for example, transmitted light detector 280 in the embodiment) capable of detecting diffracted light that forms different diffraction images.

  In order to solve the above problem, the diffractive optical system according to claim 2 of the present invention forms a diffraction image different for each wavelength with respect to incident light of a plurality of specific wavelengths incident on the diffractive surface. A diffractive optical element whose diffractive surface is configured to form different diffracted images for each incident angle with respect to incident light incident on the surface at different incident angles, and arranged so that diffracted light diffracted by the diffractive surface is incident Diffracted light detecting means capable of detecting diffracted light that forms different diffracted images for each incident light with respect to at least two types of incident light incident on the diffraction surface at different incident angles for each wavelength (for example, implementation) And a transmitted light detector 380) in the form.

  In the diffractive optical system configured as described above, it is preferable that the wavelength width of incident light incident on the diffractive surface of the diffractive optical element is 30 nm or more.

  In the diffractive optical system configured as described above, it is preferable that the diffractive optical element is formed of a binary optical element having a diffractive surface having a step having at least two steps and having a stepped cross section.

  Furthermore, in the diffractive optical system configured as described above, it is preferable that the height of at least one step of the diffractive optical element is λ or less, where λ is the wavelength of incident light.

  In the diffractive optical system configured as described above, it is preferable that a diffracted image is formed by transmitted light transmitted through the diffractive surface of the diffractive optical element or reflected light reflected by the diffractive surface.

  On the other hand, in the diffractive optical system configured as described above, a diffracted image may be formed by transmitted light transmitted through the diffractive surface of the diffractive optical element and reflected light reflected by the diffractive surface.

  In the diffractive optical system configured as described above, the diffractive surface of the diffractive optical element is preferably formed by a printing method, a photolithography method, a nanoprint method, an injection molding method, or a glass mold method.

  On the other hand, an authentication apparatus according to the present invention for solving the above-described problems includes an authentication unit in which the diffractive optical element according to any one of claims 1 to 9 is provided as a first diffractive optical element, and claim 1 or And a diffractive optical element according to any one of claims 1 to 9, wherein the diffractive optical element according to any one of claims 1 to 9 is used as the second diffractive optical element. The position of the provided object to be authenticated is adjusted to be close to the authentication means, and the diffracted light from the first diffractive optical element by the incident light incident on the diffractive surface of the first diffractive optical element is The object to be authenticated and the authentication means can be verified by making the light incident on the diffraction surface of the diffractive optical element and detecting the diffracted light from the second diffractive optical element by the diffracted light detecting means.

  Further, in the authentication apparatus having the above-described configuration, the authentication unit includes a first positioning unit that positions the authentication target authentication unit, and the authentication target includes a second positioning unit that positions the authentication target authentication unit. It is preferable to have.

  In the authentication apparatus having the above-described configuration, it is preferable that the authentication target is optically positioned with respect to the authentication unit by irradiating the first positioning unit and the second positioning unit with the positioning light beam.

  Furthermore, in the authentication apparatus having the above configuration, it is preferable that at least two or more first positioning means are provided in the authentication means, and at least two or more second positioning means are provided in the authentication target.

  Further, in the authentication apparatus having the above configuration, when the positioning error from the ideal positioning position with respect to the authentication means to be authenticated is 5 μm or less or 2 μm or less, it is possible to collate the authentication target with the authentication means. preferable.

  In the authentication device having the above-described configuration, it is preferable that the wavelength of the verification light beam incident on the diffraction surface of the first diffractive optical element is the same as the wavelength of the positioning light beam.

  On the other hand, in the authentication device having the above-described configuration, the wavelength of the verification light beam incident on the diffraction surface of the first diffractive optical element may be different from the wavelength of the positioning light beam.

  According to the diffractive optical system and the authentication apparatus according to the present invention, the diffracted light from the authentication unit incident on the diffractive surface of the diffractive optical element provided on the authentication unit is incident on the diffractive surface of the diffractive optical element provided on the authentication target. Then, by detecting the diffracted light from the object to be authenticated by the diffracted light detection means, it is possible to collate the object to be authenticated and the authentication means. Such an authentication device can be used mainly for security purposes such as discovery of counterfeit bills and counterfeit cards.

  Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS. First, a method for designing a phase pattern (diffractive surface shape) representing a phase distribution within one pitch of the diffractive surface of the diffractive optical element constituting the diffractive optical system according to the present invention will be described. In this embodiment, a computer-generated hologram (CGH (Computer Generated Hologram)) based on the phase recovery method is used for calculating the shape of the diffractive surface of the diffractive optical element. You may design using CGH by a method.

  Conventionally, the shape of the diffractive surface of a diffractive optical element when monochromatic light is perpendicularly incident on the diffractive optical element is designed by the phase recovery method, and the following phase recovery algorithm is used ( FIG. 1 (a)). First, an initial phase pattern (initial diffractive surface shape of the diffractive optical element) is determined (S11), and Fourier transform is performed to obtain a diffraction pattern (pattern projected as a diffraction image) (S13). At this time, a random pattern is preferable as the initial phase pattern. Then, the phase of the obtained diffraction pattern is maintained as it is, and only the intensity is replaced with a desired pattern (S14). The phase pattern (diffractive surface shape) of the diffractive optical element can be obtained by performing inverse Fourier transform on the replaced diffraction pattern (S15), and this is forcibly matched with the discretized phase pattern (S12). This is one loop. Then, by repeating such a loop, that is, by repeating the acquisition of the diffraction pattern by the Fourier transform of the phase pattern and the acquisition of the phase pattern by the inverse Fourier transform of the diffraction pattern, the shape of the diffraction surface of the diffractive optical element Converge to a certain shape.

The above is a phase recovery algorithm in the case where monochromatic light is perpendicularly incident on the diffractive optical element. In this embodiment, the phase recovery algorithm is applied to change the diffraction pattern depending on the incident wavelength. A diffractive optical element whose diffraction pattern changes depending on the incident angle of light is designed (see FIG. 1B). In this embodiment, the initial surface shape of the diffractive element is first given in the same manner as in the conventional case. The phase recovery algorithm is executed for one loop for each wavelength of incident light and each incident angle (λ _{1 to} λ _N , θ _{1 to} θ _N ) (S21, S23, S25). A phase pattern (the shape of the diffraction surface) of the diffraction grating is acquired for each wavelength and incident angle of incident light (S22, S24, S26). However, since the phase pattern obtained by the above algorithm is different for each wavelength and incident angle of the incident light, in this embodiment, the difference in the phase pattern depending on the wavelength and the incident angle of the incident light is considered by the least square method. One optimum phase pattern is obtained (S27). Then, the phase pattern based on the least square method is used as the initial phase pattern of the next loop, and after obtaining the phase pattern for each wavelength, the optimum phase pattern is obtained by the least square method. By repeating this, the surface shape of the diffraction element converges to a certain predetermined state. Here, the calculation of the shape of the diffractive surface is stopped when the predicted light collection efficiency of the diffractive optical element (the ratio of the diffracted light collected in a specific range out of all diffracted light) reaches about 80% That is, the phase recovery algorithm is stopped, and the phase pattern acquired at that time is determined as the shape of the diffraction surface of the diffractive element in consideration of the difference in wavelength.

  Next, an actual manufacturing method of the multi-stage diffractive optical element in which the shape of the diffractive surface is obtained as described above will be described with reference to FIG. A multi-stage diffractive optical element is manufactured by repeating the processes of photolithography and etching as follows. First, a resist film 3 is applied on a silicon substrate 2 (which is not limited to silicon but may be a substrate made of a semiconductor material such as GaAs) and exposed through a reticle mask corresponding to the shape of the diffraction surface determined by the above calculation. (See FIG. 2A). The light beam used for the exposure may be g-ray (436 nm), i-ray (365 nm), electron beam, or X-ray radiation. Moreover, the exposure method by direct drawing using a laser beam may be used. Further, the exposure may be performed with two light beam interference. Development is performed following the exposure, and a subsequent etching process is performed.

  Etching is performed by dry etching using an etching apparatus. At this time, the etching gas is arbitrarily selected according to the type of the substrate (silicon, GaAs, etc.) 2. As an example, a carbon tetrafluoride gas is used. In this way, when one photolithography and etching process is completed, as shown in FIG. 2B, a two-stage lens (2BOE element) having a diffraction groove of a desired depth and corresponding to a desired pattern is obtained. ) Is produced.

  Further, a photolithography and etching process is repeated on the two-stage lens to produce a four-stage lens (see FIGS. 2C and 2D). The photolithography and etching process is further performed on the four-stage lens. Is repeated to produce an eight-stage lens (see FIGS. 2E and 2F). From this 8-stage lens, a diffractive optical element having a multi-stage binary shape can be obtained by repeating a plurality of photolithography and etching processes such as a 16-stage lens, a 32-stage lens, and so on. is there.

  It is also possible to transfer the shape of the diffractive surface of the multi-stage diffractive optical element manufactured as described above to a mold by electrodeposition by electroforming. Then, an ultraviolet curable resin that is sufficiently heated and has plasticity is dropped onto the substrate glass. Thereafter, the above-mentioned mold in which a desired surface reversal shape is formed is pressed against the dropped ultraviolet curable resin. Further, the ultraviolet curable resin is cured by irradiating ultraviolet rays from the substrate glass side, and the cured ultraviolet curable resin is removed from the mold and the substrate glass. Thereby, the shape of the surface formed in the mold is transferred to the ultraviolet curable resin, and this ultraviolet curable resin can be used as a replica of the diffractive optical element. Such a method of forming a diffractive surface of a diffractive optical element is called a glass mold method, but is not limited thereto, and the diffractive surface may be formed by a printing method, a nanoprint method, or an injection molding method.

  Next, an example of the shape of the diffractive surface of the diffractive optical element designed by the above phase recovery method is shown. The diffractive optical element 1 shown as an example in FIG. 3 is a so-called binary optical element in which a plurality of diffraction grooves 5 having a predetermined depth are formed at a predetermined pitch, and its incident surface has a predetermined number of steps and is stepped. (So-called binary shape). As shown in FIG. 3, the diffractive optical element 1 is composed of an eight-stage lens having eight steps. However, the diffractive optical element 1 is not necessarily an eight-stage lens, and may be a four-stage lens or a two-stage lens. Alternatively, a 16-stage lens, a 32-stage lens, or the like having more stages than 8 stages may be used. The height H of one step of the diffractive optical element 1 is designed to be equal to or less than the wavelength λ nm of incident light, for example. The depth D of the diffraction groove 5 of the diffractive optical element 1 is preferably 2 μm or more or 4 μm or more. Further, the pitch width P of the diffraction grooves 5 is preferably 4 μm or less, but may be 2 μm or less. Further, the pitch width P may be equal to or less than the wavelength λ nm of the incident light, or may be equal to or less than 2/3 of the wavelength λ nm of the incident light.

  Next, a diffractive optical system having a diffractive optical element designed as described above will be described with reference to FIGS. The diffractive optical system 200 shown in FIG. 4A includes a diffractive optical element 250, a mirror 210, a transmitted light detector 280, and a reflected light detector 285. The mirror 210 can reflect light from a light source (not shown) and enter the diffraction surface of the diffractive optical element 250. The transmitted light detector 280 and the reflected light detector 285 are arranged so that the diffracted light diffracted by the diffraction surface of the diffractive optical element 250 is incident thereon, and can detect the diffracted light that forms a diffraction image. The transmitted light detector 280 and the reflected light detector 285 are equipped with a light receiving element that receives diffracted light, and an image of a personal computer or the like connected to the transmitted light detector 280 and the reflected light detector 285. A diffraction image can be displayed on the display screen.

  The diffractive optical element 250 is formed by transferring to a subject to be authenticated, which will be described later, such as a banknote, a card 220, or the like, using a nanoprint method or a printing method. The surface of the transferred diffractive optical element 250 is coated with a protective film. The protective film may be a thin film produced by sputtering or vapor deposition, or may be a film with a protective film attached, or a so-called hard coat coated with a super-hard ceramic film.

  The mirror 210 is provided with a piezoelectric drive type MEMS (Micro-electro-mechanical System) element, and the incident light to the mirror 210 becomes a predetermined incident angle by controlling the magnitude of the voltage applied to the element. Thus, the mirror 210 can be rotated. Then, the mirror 210 is rotated by the MEMS element to change the incident angle of the incident light from the light source, and the incident angle of the reflected light reflected by the mirror 210 with respect to the diffraction surface of the diffractive optical element 250 can be changed. Similarly, a piezoelectric drive type MEMS is provided on a table (not shown) on which the card 220 is placed, and the card 220 is rotated by rotating the table (not shown) by the MEMS element. It is also possible to change the incident angle of the incident light on the diffractive surface of the diffractive optical element 250 so as to become a predetermined incident angle.

  As shown in FIG. 4A, when blue light, red light, and green light emitted from a light source (not shown) are reflected by the mirror 210, and this reflected light is incident on the diffraction surface of the diffractive optical element 250 in a substantially vertical direction. The blue light, the red light, and the green light are diffracted in different directions for each wavelength on the diffraction surface of the diffractive optical element 250, pass through the diffractive optical element 250, and enter the transmitted light detector 280 as diffracted light. The transmitted light detector 280 can detect diffracted light that forms a different diffraction image for each wavelength.

  4A, any one of blue light, red light, and green light is selected and monochromatic light is incident on the mirror 210, and the mirror 210 is rotated, so that the diffraction surface of the diffractive optical element 250 is rotated. When the incident angle of incident light is changed by a predetermined angle, incident light incident on the diffraction surface of the diffractive optical element 250 at different incident angles is diffracted in different directions for each incident angle, and the diffracted light is detected for transmitted light. 280 is detected. Note that the incident light incident on the diffractive surface of the diffractive optical element 250 is not changed by rotating the mirror 210, but the incident light incident on the diffractive surface of the diffractive optical element 250 is rotated by rotating the card 220. In this case, the incident light is diffracted by the diffractive optical element 250 in different directions for each incident angle, and the diffracted light is detected by the transmitted light detector 280.

  Further, in FIG. 4A, for example, blue light, red light, and green light is selected from the blue light, and diffracted light that is diffracted in different directions for each incident angle on the diffraction surface of the diffractive optical element 250 is transmitted light. After detection by the detector 280, for example, when red light is selected as incident light and the incident angle on the diffraction surface of the diffractive optical element 250 is changed as in the case of incident blue light, the incident of blue light is changed. Diffracted light that is diffracted for each incident angle in a direction different from the case is detected by the transmitted light detector 280. That is, the diffracted light diffracted in different directions for each wavelength and for each incident angle is detected by the transmitted light detector 280.

  The diffractive optical system 200 is not limited to the configuration that detects the diffracted light by the transmitted light that has passed through the diffractive optical element 250 as described above, and a diffracted image that is different for each wavelength by the reflected light that is reflected by the diffractive optical element 250. The diffracted light to be formed may be detected by the reflected light detector 285, or the diffracted light is detected using the transmitted light detector 280 by the transmitted light that has passed through a part of the diffractive surface of the diffractive optical element 250. The detection of the diffracted light using the reflected light detector 285 by the reflected light reflected by the remaining part of the diffractive surface of the diffractive optical element 250 may be combined.

  Further, the incident light incident on the diffractive surface of the diffractive optical element 250 is not limited to a combination of monochromatic light composed of blue light, red light, and green light, and white light having a wavelength width of 30 nm or more may be incident. When white light is incident on the diffractive surface of the diffractive optical element 250, the incident light of each wavelength is diffracted by the diffractive optical element 250 in a direction determined by the wavelength, and a full color image is formed by superimposing the diffraction images for each wavelength. The diffracted light to be detected can be detected.

  A diffractive optical system 300 shown in FIG. 4B includes a diffractive optical element 350 and a transmitted light detector 380. Similarly to the transmitted light detector 280, the transmitted light detector 380 is connected to a personal computer or the like and can display a diffraction image on the image display screen. The diffractive optical element 350 is formed by transferring onto a banknote, a card 320, or the like by a nanoprint method or the like, similar to the diffractive optical element 250 described above. In the diffractive optical system 300, light from a light source (not shown) is incident on the diffractive surface of the diffractive optical element 350, and the transmitted light detector 380 is disposed so that diffracted light diffracted by the diffractive surface of the diffractive optical element 350 is incident. The diffracted light that forms the diffraction image can be detected.

As shown in FIG. 4B, in the diffractive optical system 300, blue light is incident on the diffractive surface of the diffractive optical element 350 at an incident angle θ ₁ with respect to the normal direction of the diffractive surface of the diffractive optical element 350, The green light enters the diffractive surface of the diffractive optical element 350 at the same incident angle as the normal direction of the diffractive surface of the diffractive optical element 350, and the red light further enters the normal direction of the diffractive surface of the diffractive optical element 350. On the other hand, it enters the diffractive surface of the diffractive optical element 350 at an incident angle θ ₂ .

When blue light enters the diffractive surface of the diffractive optical element 350 at the above incident angle, the diffractive surface of the diffractive optical element 350 diffracts in a direction that forms an angle θ ₃ with respect to the normal direction of the diffractive optical element 350. The light passes through the diffractive optical element 350 and enters the transmitted light detector 380 as diffracted light. When green light is incident on the diffractive surface of the diffractive optical element 350 at the above incident angle, the diffractive surface of the diffractive optical element 350 diffracts in the incident direction of green light, that is, in the normal direction of the diffractive surface of the diffractive optical element 350. Then, the light passes through the diffractive optical element 350 and enters the transmitted light detector 380 as diffracted light. Further, when the red light is incident on the diffractive surface of the diffractive optical element 350 at the above incident angle, the diffractive surface of the diffractive optical element 350 forms an angle θ ₄ with respect to the normal direction of the diffractive surface of the diffractive optical element 350. The light is diffracted and transmitted through the diffractive optical element 350 to enter the transmitted light detector 380 as diffracted light.

  As described above, the transmitted light detector 380 has two or more types of incident light incident on the diffractive surface of the diffractive optical element 350 at different incident angles for each wavelength (in FIG. 4B, blue light, It is possible to detect diffracted light that forms a different diffraction image for each incident light.

  Although the diffractive optical system according to the present invention has been described above, the authentication apparatus 100 using the diffractive optical element constituting the diffractive optical system will be described below. FIG. 5 shows a schematic configuration of the authentication device 100. This authentication device 100 determines authenticity of an object 30 to be authenticated, such as a card or banknote, by using the authentication means 20. The authentication means 20 and the object 30 to be authenticated are substantially flat. In addition to the drive system 60 for driving the light source, the alignment detectors 70 and 75, and the diffracted light detector 80, the beam splitters 13 and 14 and the mirror 15 are included. The authentication means 20 is provided with the diffractive optical element 1 (the first diffractive optical element described in claim 10) configured as described above. On the other hand, the object 30 to be authenticated is also provided with the diffractive optical element 50 (second diffractive optical element described in claim 10) configured as described above.

  The authentication target 30 is placed on an XY stage (not shown), and slit-shaped alignment marks 31 and 32 are formed at two locations in a substantially cross shape. The authentication target 30 is fixed and held on the XY stage by a vacuum chuck (not shown). The object 30 to be authenticated can be fixed to the XY stage by operating and stopping the vacuum chuck, or can be exchanged after being removed from the XY stage. The XY stage on which the authentication target 30 is placed can be moved in the X-axis direction, the Y-axis direction, and the Z-axis direction by a drive system 60 composed of a motor or the like. On the other hand, the authentication means 20 is provided below the authentication target 30 and is fixed on a stage (not shown). The authentication means 20 is also formed with two slit-shaped alignment marks 21 and 22 in a substantially cross shape. Note that the alignment marks 21 and 22 formed on the authentication means 20 and the alignment marks 31 and 32 formed on the authentication target 30 do not necessarily have to be formed in a substantially cross shape. Any shape may be used as long as the detectors 70 and 75 can detect light.

  The polychromatic light composed of blue light, red light and green light emitted from a light source (not shown) is reflected by the beam splitter 13 and travels upward, that is, toward the lower surface side of the substantially flat authentication means 20. The authentication means 20 is fixed on the stage at a position where the light from the light source reflected by the beam splitter 13 passes through the alignment mark 21, and the authentication means 20 reaches the lower surface side of the authentication means 20 from the beam splitter 13. The reflected light passes through the alignment mark 21 and travels toward the lower surface side of the authentication target 30. In addition to being reflected by the beam splitter 13 as described above, the light emitted from the light source passes through the beam splitter 13 and the beam splitter 14 and reaches the mirror 15, and is reflected by the mirror 15 and travels upward. It reaches the lower surface side of the authentication means 20. The authentication means 20 is fixed on the stage at a position where the light from the light source 10 reflected by the mirror 15 passes through the alignment mark 22, and from the mirror 15 reaching the lower surface side of the authentication means 20. The reflected light passes through the alignment mark 22 and travels toward the lower surface side of the authentication target 30.

  As described above, the XY stage on which the authentication target 30 is placed is movable in the X-axis direction and the Y-axis direction by the drive system 60, and the XY stage is moved in the X-axis and Y-axis directions. The object 30 to be authenticated is moved to a position where the light transmitted through the alignment mark 21 passes through the alignment mark 31 and the position where the light transmitted through the alignment mark 22 passes through the alignment mark 32. The authentication object 30 is optically positioned with respect to the authentication means 20.

  An alignment detector 70 is provided above the authentication target 30. When the light from the light source is blocked by the authentication target 30 and does not pass through the alignment mark 31 or the alignment mark 32, the alignment detector 70. , 75, no light is detected. However, when the light passes through the alignment mark 31 of the authentication target 30, the light is detected by the alignment detector 70. On the other hand, when the light passes through the alignment mark 32 of the authentication target 30, Light is detected by the alignment detector 75. Examples of such an alignment detector 75 include those equipped with a light receiving element such as an optical power meter. The alignment marks 21, 31, 22 and 32 displayed on the image display screen connected to the optical power meter. It is possible to perform positioning while viewing.

  When the light from the light source is detected by the alignment detectors 70 and 75, the movement control of the authentication target 30 in the X-axis direction and the Y-axis direction by the drive system 60 is stopped, and the X of the authentication target 20 with respect to the authentication means 20 of the authentication target 30 is stopped. The alignment in the axial direction and the Y-axis direction is completed. When the subject 30 is aligned, the subject 30 is separated from the authenticator 20 above the authenticator 20, and the alignment mark 31 and the alignment mark 21 coincide with the Z-axis direction. The alignment mark 32 and the alignment mark 22 are in a state matching the Z-axis direction, and the authentication target 30 can be authenticated. In addition, it is preferable that the positioning error with respect to the ideal positioning position where the authentication target 30 can be authenticated is 5 μm or less or 2 μm or less.

  Authentication of the authentication target 30 is performed as follows. The polychromatic light composed of blue light, red light and green light emitted from a light source (not shown) and transmitted through the beam splitter 13 passes through the beam splitter 14 and enters the mirror 15, and is reflected by the beam splitter 14 and travels upward. It reaches the lower surface side of the authentication means 20. The light reaching the authentication means 20 enters the diffractive surface of the diffractive optical element 1 as incident light and is diffracted in a predetermined direction. The diffracted light from the diffractive optical element 1 that has passed through the diffractive optical element 1 enters the diffractive optical element 50 from the lower surface side of the authentication target 30, and is diffracted in a predetermined direction on the diffractive surface of the diffractive optical element 50.

  A diffracted light detector 80 is arranged above the authentication target 30 so that the diffracted light diffracted by the diffractive surface of the diffractive optical element 50 is incident, and the diffracted light that forms the diffraction image can be detected. The diffracted light detector 80 includes a light receiving element that receives the diffracted light, and can display a diffracted image on an image display screen of a personal computer or the like connected to the diffracted light detector 80. When the authentication target 30 is not a counterfeit bill or counterfeit card, the diffracted light from the diffractive optical element 1 of the authentication means 20 is diffracted in a predetermined direction on the diffractive surface of the diffractive optical element 50, and the diffracted light detector 80 Thus, diffracted light is detected. When the diffracted light is detected by the diffracted light detector 80, the authentication target 30 is authenticated.

  As described above, the XY stage on which the authentication target 30 is placed is movable in the Z-axis direction in addition to the X-axis direction and the Y-axis direction, and the drive system 60 is operated to move the XY stage to the Z-axis direction. By moving in the direction (up and down), the diffracted light from the authentication means 20 is diffracted in a predetermined direction by the diffractive optical element 50 of the authentication target 30, and the diffracted light detector 80 detects the diffracted light. That is, when the vertical separation distance of the authentication target 20 with respect to the authentication unit 20 reaches a predetermined length, the diffracted light detector 80 detects the diffracted light, and the authentication target 30 is authenticated.

  The above is a case where the authentication target 30 is authenticated. However, when the authentication target 30 is a counterfeit bill or a counterfeit card, even if the authentication target 30 is moved in the Z-axis direction (up and down), Since the diffracted light from the diffractive optical element 1 of the authentication means 20 does not diffract in a predetermined direction on the diffractive surface of the diffractive optical element 50, the alignment marks 31 and 21 are aligned with the Z-axis direction, and the alignment marks 32 and 22 are Z Even if the authentication target 30 is positioned with respect to the authentication means 20 in a state where the authentication target 30 can be authenticated in conformity with the axial direction, the diffracted light detector 80 detects from the diffractive optical element 50. The diffracted light is not detected, and the authentication target 30 is not authenticated.

  As described above, if the authentication apparatus according to the present invention is used, a bill or a card is to be authenticated by using diffraction of incident light on the diffraction surfaces of the diffractive optical element 1 and the diffractive optical element 50. It is possible to perform authentication.

  In this embodiment, as shown in FIG. 5, the diffracted light is detected by being diffracted by the positioning light rays to be detected by the alignment detectors 70 and 75 and the diffraction surfaces of the diffractive optical element 1 and the diffractive optical element 50. The collation light beams to be detected by the detector 80 are all multicolor light composed of blue light, red light, and green light. For example, the positioning light beam is converted into blue light, and the collation light beam is converted into red light. Thus, the wavelengths of the positioning light beam and the verification light beam may be made different. Further, the positioning light source and the collation light source may be provided separately. Further, the positioning light beam and the collating light beam are not limited to visible light, but may be infrared light or laser light in a wavelength band of 1.5 μm.

  In the above embodiment, blue light, red light, and green light are all incident on the diffractive surface of the diffractive optical element 1 at the same incident angle, but blue light, red light, and green light are Each diffracted light is incident on the diffractive surface of the diffractive optical element 1 at a different incident angle (corresponding to the content described in claim 2 of the claims), and each diffracted light is detected by the diffracted light detecting means installed for each incident. You may comprise so that it may detect.

  Although the preferred embodiments of the present invention have been described so far, the scope of the present invention is not limited to the above-described embodiments. For example, in the above embodiment, the diffractive optical element 1 and the diffractive optical element 50 designed as described above are used as the incident light incident surface, and the diffracted diffracted light is detected. However, the diffractive surfaces of the diffractive optical element 1 and the diffractive optical element 50 may be configured to detect the diffracted light from the exit surface by using the exit surface of the incident light.

  In the above description based on FIG. 5, the diffracted light detector 80 detects the transmitted light transmitted through the diffractive optical element 1 and the diffractive optical element 50 as diffracted light. Is not limited to transmitted light, but is diffracted light reflected by diffractive optical element 1 and transmitted through diffractive optical element 50, diffracted light transmitted through diffractive optical element 1 and reflected by diffractive optical element 50, or diffractive optical element 1 and The diffracted light reflected by the diffractive optical element 50 may be detected by the diffracted light detector 80.

It is a block diagram which shows the algorithm for acquiring the diffraction pattern of the diffractive optical element which comprises the diffractive optical system which concerns on this invention with a computer-synthesis hologram, (a) is the phase recovery algorithm for monochromatic light used conventionally. (B) is an algorithm for applying a phase recovery algorithm for monochromatic light and obtaining a diffraction pattern when white light is used as incident light and the incident angle of the incident light with respect to the diffraction surface of the diffractive optical element is changed. . It is a figure which shows the manufacturing process of the diffractive optical element which comprises the diffractive optical system which concerns on this invention in order of (a) to (f). It is a schematic cross section which shows the shape of the diffraction surface of the said diffractive optical element. (A) is a schematic diagram of a diffractive optical system that detects diffracted light by incident light of two or more wavelengths incident on the diffraction surface of the diffractive optical element at the same incident angle, and (b) is for each wavelength. It is a schematic diagram of a diffractive optical system that detects diffracted light for each incident light with respect to two or more types of incident light incident on the diffraction surface of the diffractive optical element at different incident angles. It is a schematic diagram which shows the authentication apparatus comprised by having an authentication means provided with the said diffractive optical element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diffractive optical element (1st diffractive optical element) 2 Substrate 3 Resist film 5 Diffraction groove 13, 14 Beam splitter 15 Mirror 20 Authentication means 21, 22, 31, 32 Alignment mark 50 Diffractive optical element (2nd diffractive optical element) ) 60 Drive system 70, 75 Alignment detector 80 Diffracted light detector (diffracted light detecting means) 100 Authentication device 200 Diffraction optical system 210 Mirror 220 Card 250 Diffraction optical element 280 Transmitted light detector (diffracted light detecting means) 285 Reflected light detector (diffracted light detecting means) 300 Diffraction optical system 320 Card 350 Diffraction optical element 380 Transmitted light detector (diffracted light detecting means)

Claims (17)

A diffractive optical element in which the diffractive surface is configured to form different diffracted images for each wavelength with respect to incident light of a plurality of wavelengths incident on the diffractive surface;
Diffraction that is arranged so that the diffracted light diffracted by the diffractive surface is incident, and that forms different diffracted images for each incident light with respect to incident light having at least two types of wavelengths incident on the diffractive surface at the same incident angle. A diffractive optical system comprising: diffracted light detecting means capable of detecting light. Different diffraction images are formed for each wavelength with respect to incident light of a plurality of specific wavelengths incident on the diffractive surface, and different diffracted images for each incident angle with respect to incident light incident on the diffractive surface at different incident angles. A diffractive optical element in which the diffractive surface is configured to form:
It is arranged so that the diffracted light diffracted by the diffractive surface is incident, and different diffracted images are formed for each incident light with respect to at least two types of incident light incident on the diffractive surface at different incident angles for each wavelength. And a diffracted light detecting means capable of detecting the diffracted light to be diffracted.   The diffractive optical system according to claim 1 or 2, wherein a wavelength width of incident light incident on the diffractive surface of the diffractive optical element is 30 nm or more.   Any of 1 to 3, wherein the diffractive optical element is composed of a binary optical element having a diffractive surface having a step having at least two steps and having a stepped cross section. The diffractive optical system described.   5. The diffractive optical system according to claim 4, wherein when the wavelength of incident light is λ, the height of at least one step of the diffractive optical element is λ or less.   The diffractive optical system according to claim 1, wherein the diffracted image is formed by transmitted light transmitted through the diffractive surface of the diffractive optical element.   6. The diffractive optical system according to claim 1, wherein the diffracted image is formed by reflected light reflected by the diffractive surface of the diffractive optical element.   6. The diffractive optical system according to claim 1, wherein the diffracted image is formed by transmitted light transmitted through the diffractive surface of the diffractive optical element and reflected light reflected by the diffractive surface.   The diffractive optical element according to claim 1, wherein the diffractive surface of the diffractive optical element is formed by a printing method, a photolithography method, a nanoprint method, an injection molding method, or a glass mold method. system. Authentication means provided with the diffractive optical element according to any one of claims 1 to 9 as a first diffractive optical element;
The diffracted light detecting means according to claim 1 or 2,
The diffractive optical element according to any one of claims 1 to 9 is aligned with a state in which an authentication target provided as a second diffractive optical element is brought close to the authentication unit, Diffracted light from the first diffractive optical element is incident on the diffractive surface of the second diffractive optical element by incident light incident on the diffractive surface of the diffractive optical element, and is diffracted from the second diffractive optical element. By detecting the diffracted light by the diffracted light detecting means, it is possible to collate the authentication target with the authentication means. The authentication means includes first positioning means for positioning the authentication target with respect to the authentication means,
The authentication apparatus according to claim 10, wherein the authentication target includes second positioning means for positioning the authentication target with respect to the authentication means.   The authentication apparatus according to claim 11, wherein the authentication target is optically positioned with respect to the authentication unit by irradiating the first positioning unit and the second positioning unit with a positioning beam. .   The authentication according to claim 12, wherein at least two or more of the first positioning means are provided in the authentication means, and at least two or more of the second positioning means are provided in the authentication target. apparatus.   14. The verification object and the authentication unit can be collated when a positioning error between the authentication target and the ideal positioning position of the authentication target with respect to the authentication unit is 5 μm or less. Authentication device.   The verification target and the authentication unit can be collated when a positioning error between the authentication target and the ideal positioning position of the authentication target with respect to the authentication unit is 2 μm or less. Authentication device.   The authentication apparatus according to claim 12, wherein the wavelength of the collimating light beam incident on the diffractive surface of the first diffractive optical element is the same as the wavelength of the positioning light beam. .   The authentication apparatus according to any one of claims 12 to 15, wherein a wavelength of the verification light beam incident on the diffraction surface of the first diffractive optical element is different from a wavelength of the positioning light beam.

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