JP7263702B2 - Optical modulator and information recording medium - Google Patents

Description

The present invention relates to an optical modulation element that reproduces an image by diffracting light, and an information recording medium having such an optical modulation element.

Various types of light modulation elements have been proposed as light modulation elements such as holograms capable of reproducing an original image. For example, Patent Literatures 1 to 3 disclose a phase modulation type light modulation element having an uneven pattern, which diffracts light to reproduce an optical image.

JP-A-10-153943 JP-A-2004-126535 Japanese Patent No. 4730527

By the way, in order to improve the design of the light modulation element, to make the counterfeiting of the light modulation element difficult, or to facilitate the authenticity determination, it is desired to realize the light modulation element having the following characteristics. That is, the intended optical image is not observed when the light modulation element is observed from the normal observation position, but the intended optical image is observed when the optical modulation element is observed from an observation position different from the normal observation position. It is a characteristic.

The present invention has been made in view of the above-mentioned circumstances, and when observed from a normal observation position, the intended optical image is not observed, and when observed from an observation position different from the normal observation position, the intended optical image is not observed. An object of the present invention is to provide an optical modulation element with which an optical image can be observed.

The optical modulation element according to this embodiment is
Equipped with an element element that reproduces an image by diffracting light from a point light source,
The element element reproduces a first image observed within the angle range of viewing the reproduction area from a position other than the position where the point light source is observed within the angle range of viewing the reproduction area provided with the element element. do.

The above-described light modulation element further reproduces a second image observed together with the point light source within the angular range of viewing the reproduction area from a position where the point light source is observed within the angle range of viewing the reproduction area. good too.

In this case, the light modulation element described above may further include viewing direction display means for displaying the viewing direction of the light modulation element. In this case, the observation direction display means may display the observation direction in which the first image can be observed.

Further, the element element includes a computer-generated hologram,
The original image of the first image at the time of producing the computer-generated hologram is the first image observed when the reproduction area is observed from a position other than the position where the point light source is observed. The image may be reduced in a direction along the direction of observing the reproduction area from a position other than the observed position.

Further, the above light modulation element is provided with a light shielding layer having an opening on one side of the element element,
When viewed from the light shielding layer toward the element element, the reproduction region may be partitioned by the opening.

Alternatively, the information display medium according to the present embodiment includes the light modulation element described above. In this case, the information recording medium may be an ID card, a passport (passport), a credit card, or the like on which personal information is recorded. The ID card may be, for example, a national ID card, a driver's license, a membership card, an employee card, a student card, or the like. Further, the information recording medium according to the present embodiment may record information other than personal information. For example, banknotes, cash vouchers, gift certificates, other tickets, other media recording various types of information such as official documents and confidential information, and other media with monetary value may be used.

According to the present invention, the intended optical image is not observed when observed from a normal observation position, and the intended optical image is observed when observed from an observation position different from the normal observation position. element can be provided. Also, an information recording medium having such an optical modulation element can be provided.

FIG. 1 is a diagram for explaining an embodiment according to the present invention, and is a cross-sectional view showing an example of an optical modulation element. FIG. 2 is a front view for explaining a case where light is made incident on the light modulation element shown in FIG. 1 and observed from a normal observation position. FIG. 3 is a perspective view for explaining a case where light is made incident on the light modulation element shown in FIG. 1 and observed from an observation position different from the normal observation position. FIG. 4 is a conceptual diagram of a reflective hologram structure. FIG. 5 is a conceptual diagram of a transmissive hologram structure. FIG. 6 is a conceptual diagram showing the planar structure of the hologram structure. FIG. 7 is a cross-sectional view of an element element showing an outline of an example of a stepped structure of an uneven surface. FIG. 8 is a cross-sectional view of an element element schematically showing another example of the stepped structure of the uneven surface. FIG. 9 is a graph showing an example of the relationship between the wavelength distribution of first-order diffracted light and the diffraction efficiency of each element element. FIG. 10 is a schematic diagram for explaining a light image reproduced by a general hologram structure. FIG. 11 is a schematic diagram for explaining a light image reproduced by the hologram structure of this embodiment. FIG. 12 is a graph showing an example of diffraction characteristics of each element element. FIG. 13 is a diagram showing an example of a light image reproduced by a hologram structure provided with element elements having diffraction characteristics shown in FIG. FIG. 14 is a graph showing another example of diffraction characteristics of each element. FIG. 15 is a diagram for explaining the relationship between the observation position and the observed image in the light modulation element according to this embodiment. FIG. 16 is a diagram showing original images of the first image and the second image. FIG. 17 is a cross-sectional view corresponding to FIG. 1 and showing a modification of the light modulation element. FIG. 18 is a front view for explaining a case where light is made incident on the light modulation element shown in FIG. 17 and observed from a normal observation position. FIG. 19 is a perspective view for explaining a case where light is made incident on the light modulation element shown in FIG. 17 and observed from an observation position different from the normal observation position.

An optical modulation element according to an embodiment of the present invention will be described below. In the drawings attached to this specification, for the convenience of illustration and ease of understanding, the scale and the ratio of vertical and horizontal dimensions are changed and exaggerated from those of the real thing.

In addition, terms such as "parallel", "perpendicular", "identical", length and angle values, etc. that specify shapes and geometric conditions and their degrees used in this specification are strictly It is interpreted to include the extent to which similar functions can be expected without being bound by any particular meaning.

FIG. 1 shows a cross section of the optical modulation element of this embodiment. 2 and 3 respectively show a plan view and a perspective view of the light modulation element shown in FIG. FIG. 1 shows a cross section of the light modulation element shown in FIG. 2 along line II. 2 and 3 show, respectively, the light modulation element to which the light from the point light source is incident, the light modulation element viewed from a normal observation position, and the light modulation element viewed from an observation position different from the normal observation position. and a light modulation element.

As shown in FIG. 1, the light modulation element in this embodiment reproduces an image by diffracting light from a point light source. As can be understood from FIGS. 2 and 3, when the light modulation element is observed from the normal observation position, the intended optical image is not observed, and when it is observed from the observation position different from the normal observation position. It is devised so that the intended optical image can be observed. Such a light modulating element can change the appearance of the light modulating element depending on the observation position of the observer, and can improve the design of the light modulating element. In addition, it is difficult to forge an optical modulation element that does not provide an intended image when viewed from a normal viewing position. Also, in the first place, an image that cannot be observed from a normal viewing position is difficult to notice. Therefore, if the information display medium is provided with such a light modulation element, the intended image can be used for authentication of the information display medium.

The light modulation element of the following embodiments is configured as a hologram holder having a phase modulation type hologram structure that modulates the phase of incident light (incident light) to reproduce an optical image. The hologram structure includes elementary elements which are constituted in particular by Fourier transform holograms. A Fourier transform hologram is a hologram produced by recording wavefront information of a Fourier transform image of an original image, and functions as a so-called Fourier transform lens. In particular, the phase modulation type Fourier transform hologram is a hologram with an uneven surface that is produced by recording the phase information of the Fourier transform image into multiple values and recording it as depth on the medium. is used to reproduce a light image of the original image from the incident light. This Fourier transform hologram, for example, is advantageous in that it can reproduce a desired optical image (that is, the original image) with high precision and that it can be produced relatively easily. Such a phase modulation type optical modulation element is also called a kinoform. It should be noted that such a hologram can be designed using a computer based on the wavelength and direction of incidence of incident light and the shape and position of an image to be reproduced. A hologram obtained in this way is also called a computer generated hologram (CGH). However, the element elements of the light modulation element to which the present invention can be applied are not limited to Fourier transform holograms, and the present invention can be applied to light modulation elements having other structures such as holograms that reproduce optical images by other methods. can be applied.

In the following description, white light containing various wavelengths is taken as an example of light (incident light) to be incident on the hologram structure, but the incident light does not necessarily have to be white light. That is, the wavelength included in the reconstructed light is not particularly limited as long as the reconstructed light contains light of a wavelength corresponding to the color of the optical image reconstructed by the hologram structure. Further, in the following description, unless otherwise specified, it is assumed that the incident angle of the incident light with respect to the hologram structure is 0° (that is, the angle along the normal direction of the incident surface of the hologram structure). Further, the specific values of the refractive index shown in this specification are based on light with a wavelength of 589.3 nm unless otherwise specified. In the following description, unless otherwise specified, the refractive index and the characteristic values of the uneven surface shown for the hologram structure 11 are based on the case where the hologram structure 11 is used in an air environment with a refractive index of 1.0. It is a value derived on assumption. It is also assumed that the light modulation element is observed from a position about 20 cm away from the light modulation element.

Hereinafter, the light modulation element of this embodiment will be described in more detail with reference to FIGS. 1 to 16. FIG.

A hologram holder 10 shown in FIG. Prepare. A reflective hologram structure 11 is provided on a part of the hologram holder 10 . In this hologram structure 11, the other surface of the hologram layer 1 forms an uneven surface 1a, and the reflective layer 2 covering this uneven surface 1a also has an uneven shape. The uneven surface 1a of the hologram structure 11 has an uneven pattern corresponding to the Fourier transform image of the original image, and has an uneven depth corresponding to each pixel of the Fourier transform image. For example, a resin (e.g., UV curable resin or thermoplastic resin) that forms the hologram layer 1 is formed on a substrate 4 (e.g., PET: polyethylene terephthalate) by coating, and the hologram layer 1 is subjected to UV curing treatment. and heat-pressing treatment, and a concavo-convex forming process in which the concavo-convex surface of the original plate is pressed, and then the reflective layer 2 (for example, Al, ZnS, or TiO ₂ ) is formed on the concavo-convex surface 1a of the hologram layer 1. Thus, the hologram holder 10 shown in FIG. 1 can be manufactured. Although illustration is omitted, other members such as an adhesive material, an adhesive, and/or a heat seal layer may be further formed on the reflective layer 2 .

When light is incident on the hologram structure 11 from a point light source or a parallel light source, a light image (that is, an original image) corresponding to the uneven pattern of the uneven surface 1a is reproduced. A light modulation element having this kind of hologram structure 11 does not require a screen or the like for projecting an optical image, and is particularly good when light from a specific light source such as a point light source or a parallel light source is incident. Since it reproduces an optical image, it can be widely used with good convenience for design applications, security applications, and other applications. The optical image that can be reproduced by such an optical modulation element is not particularly limited, and for example, characters, symbols, line drawings, pictures, patterns, combinations thereof, etc. can be used as the original image and the optical image that can be reproduced.

As described above, the hologram holder (optical modulation element) 10 shown in the figure including the hologram structure 11 and the base material 4 that supports the hologram structure 11 can be suitably applied to an information recording medium such as a passport as an example. is. For example, by designing the hologram structure 11 so that the optical image reproduced by the hologram structure 11 represents information based on at least one of characters, symbols, and patterns, the hologram structure 11 can be used as the above information. It can be suitably used for security applications such as authenticity determination of recording media.

In addition, in FIG. 1 and other figures, the area occupied by the hologram structure 11 when the hologram holder 10 is viewed from the substrate 4 side is indicated by reference numeral "20". Hereinafter, this area 20 will be referred to as a "reproduction area" in the sense of an area that contributes to the reproduction of the optical image.

The hologram structure 11 includes a reflection hologram structure in which the observer 50 and the light source 51a are arranged on the same side with respect to the hologram structure 11 as shown in FIG. 51b are arranged on different sides of the hologram structure 11, and can be classified into transmission type hologram structures. As the reflective hologram structure, for example, in addition to a structure provided with an additional layer for reflecting incident light, such as the reflective layer 2 shown in FIG. There is a structure in which the uneven surface 1a is exposed to the air and incident light is reflected using the difference in refractive index between the hologram layer 1 made of UV curable resin or the like and the air. On the other hand, a transmission hologram structure is not provided with such a reflective layer. However, the reflection hologram structure and the transmission hologram structure are common in that an uneven surface 1a is formed on the hologram layer 1 and a desired optical image is reproduced by the diffraction phenomenon caused by the optical path length difference of the uneven surface 1a. do. As for the specific unevenness depth of the uneven surface 1a, there is an optimum value for each of the transmission hologram structure and the reflection hologram structure. In the following, unless otherwise specified, the description of only one of the reflection hologram structure and the transmission hologram structure basically applies to both the reflection hologram structure and the transmission hologram structure. It can be applied to

FIG. 6 is a conceptual diagram showing the planar structure of the hologram structure 11. As shown in FIG. The hologram structure 11 of this embodiment includes a plurality of element elements (also called “hologram cells”) 21 that are regularly arranged two-dimensionally. Each element element 21 has the uneven surface 1a described above, and has a planar size of several nanometers to several millimeters square (for example, 2 millimeters square), and modulates the phase of reproduction light to reproduce an optical image.

The uneven surface 1a has a multi-stage shape (that is, two or more steps), and the number of steps of the uneven surface 1a is not particularly limited. When an optical image is reproduced with a plurality of colors, the uneven surface 1a preferably has three or more steps, and in particular, the uneven surface 1a having four or more steps can reproduce an original image having a complicated composition with high definition. It is possible to play. 7 and 8 are cross-sectional views of an element element 21 showing an outline of the stepped structure of the uneven surface 1a. FIG. 7 shows an 8-step type uneven surface 1a, and FIG. 8 shows a 4-step type uneven surface 1a. show. 7 and 8 show an element element 21 having an uneven surface 1a in which the same stepped shape is periodically repeated at intervals corresponding to the number of steps, but the actual uneven surface 1a is reproduced. It has a stepped shape corresponding to the optical image (that is, the original image). In addition, below, the space|interval (refer code|symbol "S" shown in FIG. 7 and FIG. 8) of the top part which the uneven|corrugated surface 1a adjoins is called a pitch. The pitch S may not be constant within the uneven surface 1a of each element element 21, and may take various values.

The pixel size of the uneven surface 1a (the dimension of each surface corresponding to each pixel of the Fourier transform image (see the symbol "T" shown in FIGS. 7 and 8)) is 0.1 μm from the viewpoint of accurately reproducing the optical image. It is preferably in the range of up to 80.0 μm, and usually preferably 1 μm or more.

FIG. 9 is a graph showing an example of the relationship between the wavelength distribution of first-order diffracted light and the diffraction efficiency of each element element 21. In FIG. In FIG. 9, the horizontal axis indicates wavelength, and the vertical axis indicates diffraction efficiency. The diffraction efficiency is expressed by the amount obtained by dividing the radiant flux of light diffracted in a certain direction by the radiant flux of light incident on each element element 21. The diffracted radiant flux in a certain direction is denoted by P, and the incident radiant flux is denoted by P0. , the diffraction efficiency η is a dimensionless number expressed by "η=P/P0". Each element element 21 exhibits a unique diffraction efficiency depending on the wavelength, and in the example shown in FIG. 9, light having a wavelength near 580 nm (see symbol "H1" in FIG. 9) has the maximum diffraction efficiency Dmax with respect to first-order diffracted light. indicates FIG. 9 shows an example of the wavelength distribution of 1st-order diffracted light, and the wavelength distribution of -1st-order diffracted light also exhibits a unique diffraction efficiency depending on the wavelength and a maximum diffraction efficiency at a specific wavelength.

FIG. 10 is a schematic diagram for explaining an optical image 100 reproduced by a general hologram structure 11. As shown in FIG. FIG. 11 is a schematic diagram for explaining the optical image 100 reproduced by the hologram structure 11 of this embodiment. 10 and 11, the light source used in the reflective hologram structure 11 is indicated by reference numeral 51a, and the light source used in the transmission hologram structure 11 is indicated by reference numeral 51b. . Also, in the following description, these light sources 51a and 51b are collectively represented using the symbol "51".

Generally, in the diffraction phenomenon, the larger the wavelength of incident light, the larger the diffraction angles of diffracted lights other than the 0th order diffracted light. Therefore, when white light from the light source 51 is incident on a general hologram structure 11 having the same degree of diffraction efficiency over the entire visible light wavelength band, the hologram structure 11 has rainbow colors as shown in FIG. Reproduce the optical image 100 . On the other hand, when white light from the light source 51 is incident on the hologram structure 11 of the present embodiment, which has the maximum diffraction efficiency in the wavelength band of 380 nm or more and 780 nm or less, the hologram structure 11 becomes as shown in FIG. A monochromatic light image 100 is reproduced. That is, the hologram structure 11 (especially the concave-convex surface 1a) of the present embodiment has a diffraction structure optimized for light of a specific wavelength and a wavelength band in the vicinity thereof. and the light of the wavelength band in the vicinity thereof are selectively used to reproduce a light image 100 of a specific color. For example, the hologram structure 11 in FIG. 11 exhibits the maximum diffraction efficiency in the blue wavelength band and reproduces the blue optical image 100 .

Thus, the hologram structure 11 exhibiting a maximum value (especially a single maximum value) in diffraction efficiency in a wavelength band of 380 nm or more and less than 780 nm reproduces a monochromatic optical image 100 even when white light is incident. be able to. The optical image 100 reproduced in this way is a clear image with little blur due to chromatic dispersion. In addition, since the optical image 100 can be reproduced in a specific color, it is possible to give the observer 50 a specific impression based on the color. It is also possible to reproduce the light image 100 in color to clearly convey to the observer 50 the concept that the light image 100 represents. Furthermore, since the hologram structure 11 is configured to reproduce a specific monochromatic optical image 100, for example, in authenticity determination, not only the "pattern" of the reproduced optical image 100 but also the light The "color" of the image 100 can be used, allowing reliable authentication. In addition, since the hologram structure 11 of the present embodiment does not require an additional layer that selectively transmits or reflects light in a specific wavelength band, the manufacturing cost can be reduced, and the observer 50 can see the surroundings through the hologram structure 11. There is no sense of incongruity in the observed image.

As an example, in FIG. 12, the refractive index of the hologram layer 1 is 1.5, the number of steps on the uneven surface 1a is set to 8, and the depth of each step (see symbol “d” in FIG. 7) is 200 nm. and the diffraction characteristics of the reflective hologram structure 11 (that is, the reflective element element 21) with a maximum depth (see symbol "D" in FIG. 7) of 1400 nm. In FIG. 12, the horizontal axis indicates the wavelength (nm), the vertical axis indicates the diffraction efficiency, the wavelength distribution of the 0th order diffracted light is indicated by "W0", and the wavelength distribution of the 1st order diffracted light is indicated by "W1". The wavelength distribution of the -1st order diffracted light is indicated by "W-1".

In the example shown in FIG. 12, in each element element 21, the wavelength indicating the maximum value of the 0th-order diffracted light is set to 600 nm, and the wavelength indicating the maximum value of the 1st-order diffracted light is set to 533 nm in the wavelength band of 380 nm or more and less than 780 nm. The wavelength indicating the maximum value of the -1st order diffracted light is set to 685 nm.

As shown in FIG. 13, each element element 21 having such a diffraction characteristic has a light image 100a corresponding to the point light source 51 (hereinafter also simply referred to as "point light source") and a light image 100b by first-order diffracted light. , and an optical image 100c by the -1st order diffracted light. The optical image 100b by the 1st-order diffracted light is reproduced as a green image. Also, the optical image 100c by the -1st order diffracted light is reproduced as a red image.

As another example, in FIG. 14, the refractive index of the hologram layer 1 is 1.5, the number of steps in the uneven surface 1a is set to 8, and the depth per step (see symbol "d" in FIG. 7) ) is 234 nm, and the maximum depth (see symbol “D” in FIG. 7) is 1638 nm. In FIG. 14, the horizontal axis indicates the wavelength (nm), the vertical axis indicates the diffraction efficiency, the wavelength distribution of the 0th order diffracted light is indicated by "W0", and the wavelength distribution of the 1st order diffracted light is indicated by "W1". The wavelength distribution of the -1st order diffracted light is indicated by "W-1".

In the example shown in FIG. 14, in each element element 21, the wavelength indicating the maximum value of the 0th-order diffracted light is set to 702 nm, and the wavelength indicating the maximum value of the 1st-order diffracted light is set to 642 nm. The wavelength showing the maximum value is set to a wavelength greater than 780 nm (specifically, 802 nm).

Each of the element elements 21 having such diffraction characteristics also has a point light source 100a, a light image 100b due to first-order diffracted light, and a light image 100c due to −1st-order diffracted light, similarly to the element element 21 having diffraction characteristics shown in FIG. and reproduce the optical image 100 including . However, while the optical image 100b by the 1st-order diffracted light is reproduced as a visible red optical image, the optical image 100c by the −1st-order diffracted light is not reproduced as a visible optical image. In reality, the optical image 100c mainly composed of light outside the visible light wavelength band includes some light inside the visible light wavelength band, and thus may be visible depending on the observer 50. Even in such a case, it is recognized as a very unclear light image.

In order to reproduce a light image in a specific color even when white light is incident on each element element 21, each element element 21 is preferably formed as follows. That is, the maximum diffraction efficiency Dmax in the wavelength band of 380 nm or more and 780 nm or less in the wavelength distribution of the diffraction efficiency of the 1st-order diffracted light and the wavelength distribution of the -1st-order diffracted light for each element element 21 is the maximum diffraction efficiency Dmax. is formed so as to form a maximum value having a full width at half maximum FWHM of 200 nm or less in the wavelength distribution of the diffraction efficiency including . The full width at half maximum FWHM referred to here indicates a wavelength band (wavelength width) at a position having a value (Dmax/2) half the maximum diffraction efficiency Dmax in the diffraction efficiency wavelength distribution (see FIG. 9).

Since each element element 21 has such a diffraction characteristic, the light of the wavelength corresponding to the maximum diffraction efficiency Dmax and the wavelengths in the vicinity thereof are diffracted more efficiently than the light of other wavelength bands, contributing to the reconstruction of the image. . Therefore, even when white light including light of various wavelengths is incident on each element element 21, each element element 21 is exposed to light having a wavelength corresponding to the maximum diffraction efficiency Dmax and wavelengths in the vicinity thereof. reproduces the light image in the colors of Therefore, by adjusting the diffraction characteristics of each element element 21 (especially the wavelength distribution of the 1st-order diffracted light and the wavelength distribution of the −1st-order diffracted light) and making the wavelength corresponding to the maximum diffraction efficiency Dmax correspond to the color of the reproduced image, white Even if light is incident on each element element 21, it is possible to reproduce a light image in a specific color.

The uneven surface 1a of each element element 21 includes three or more different heights, and the wavelength band of 380 nm or more and 780 nm or less in the wavelength distribution of the diffraction efficiency of the 1st-order diffracted light and the wavelength distribution of the diffraction efficiency of the −1st-order diffracted light. It is preferred that there be no other maxima at which the diffraction efficiency is more than half the maximum diffraction efficiency. That is, the second largest diffraction efficiency in the wavelength band of 380 nm or more and 780 nm or less in the wavelength distribution of the diffraction efficiency of the 1st-order diffracted light and the -1st-order diffracted light of each element element 21 (marked " in FIG. 9) H2”) is preferably less than half the maximum diffraction efficiency Dmax. In this case, it is possible to effectively prevent color blurring and thickening of lines in the reproduced image, and to reproduce the optical image with high definition.

By the way, when light is incident on the hologram structure 11 as described above, an optical image 100 is reproduced centering on the point light source 100a. Also, the point light source 100a is bright and conspicuous. Therefore, the observer 50 normally observes the reproduced optical image 100 together with the point light source 100a. That is, normally, when observer 50 observes hologram structure 11, observer 50 not only observes hologram structure 11 from a position where hologram structure 11 (and therefore reproduction region 20) can be seen, but also observes hologram structure 11. 11 (reproduction area 20) from a position where the point light source 100a is observed (for example, the position X0 shown in FIG. 2). Such an observation position is hereinafter also referred to as a "normal observation position".

Here, the incident angle of incident light with respect to the hologram structure 11 is usually assumed to be 0° or an angle near 0° in many cases. Correspondingly, the observation angle (ordinary observation angle) of the observer 50 who observes the light image together with the point light source 100a with respect to the hologram structure 11 is usually 0° (that is, the normal direction of the incident surface of the hologram structure 11). ) or an angle relatively close to 0°. On the other hand, when the observer 50 observes the hologram structure 11 at a position other than the normal observation position (that is, a position other than the position where the point light source 100a is observed within the angle range R looking into the hologram structure 11 (reproduction area 20) ( For example, when viewed from the position X1)) shown in FIG. 3, the viewing angle with respect to the hologram structure 11 is larger than the normal viewing angle.

In consideration of the above, as shown in FIG. 15, in the illustrated hologram holder 10, the hologram structure 11 (reconstruction region 20) is not intended when the hologram holder 10 is observed from the normal observation position X0. Although the first image 101, which is an optical image, is not observed, the first image 101 is observed when observed from an observation position X1 other than the normal observation position X0. Furthermore, in the illustrated example, when the hologram holder 10 is observed from the normal observation position X0, the second image 102 is observed together with the light source 100a, and when it is observed from the observation position X1 other than the normal observation position X0, The second image 102 is not observed.

Specifically, first, as shown in FIG. 16, an original image 200 including a first original image 201 that is the original image of the first image 101 and a second original image 202 that is the original image of the second image 102 is created. . At this time, when the second original image 202, which is the original image of the second image 102 observed when observed from the normal observation position X0, is arranged in the center of this original image 200, and when observed from the normal observation position X0 A first original image 201 that is an original image of the first image 101 that is not observed in the original image 200 is arranged at a position away from the center of the original image 200 . The position of the first original image 201 with respect to the center of the original image 200 is the observation angle when the hologram structure 11 is observed from the observation position intended as the position for observing the first image 101 (for example, the observation position X1 shown in FIG. 3). determined based on Then, based on the produced original image 200, each element element 21 constituting the hologram structure 11 is produced by computer synthesis. The hologram structure 11 thus obtained is located at a position farther from the center of the original image 200 than the light L2 that reproduces the second original image 202 placed in the center of the original image 200, as shown in FIG. The light L1 that reproduces the arranged first original image 201 is diffracted at a large angle. Therefore, when light is incident on the hologram structure 11 from a point light source or the like, the light L2 for reproducing the second image 102 is directed toward the eyes of the observer 50 who observes the hologram structure 11 from the normal observation position X0. . On the other hand, the light L1 that reproduces the first image 101 is not directed to the eyes of the observer 50 observing from the normal observation position X0, and is located at a position outside the normal observation position X0 (in the illustrated example, the observation position X1). head to

If there is an image to be reproduced in an area distant from the center of the original image 200, the pitch S of the uneven surfaces 1a of the element elements 21 produced based on this original image 200 becomes smaller as a whole. More specifically, the average number of pixels per pitch is reduced. As a result, the light for reproducing the first original image 201 is diffracted at a larger angle than the light for reproducing the second original image 202 in the hologram structure 11 .

By reducing the pixel size T, the pitch S of the uneven surface 1a can also be reduced. Therefore, even if the first original image 201 is arranged near the center of the original image 200, if the pixel size T of the uneven surface 1a produced based on this original image 200 is reduced to reduce the pitch S, the first original image The light reproducing 201 can be directed away from the normal viewing position X0.

By designing each element element 21 as described above, when observed from the normal observation position X0, the first image 101 is not observed and only the second image 102 is observed, which is different from the normal observation position X0. It is possible to realize the hologram structure 11 in which the first image 101 can be observed when observed from the observation position X1.

Note that, as described above, the first image 101 is intended to be viewed from an observation position X1 different from the normal observation position X0. In this case, as can be understood from FIGS. 3 and 16, the first image 101 is projected in the direction DL along the direction in which the first original image 201 observes the hologram structure 11 (reconstruction region 20) from the observation position X1. It is observed as a stretched image. Therefore, as shown in FIG. 16, the first original image 201 is an image intended as the first image 101 observed when the hologram structure 11 (reproduction area 20) is observed from the observation position X1 (see ) is reduced in the direction DL.

Furthermore, in the illustrated example, the hologram holder 10 is provided with observation direction display means 15 for displaying the observation direction of the reproduction area 20 . In the example shown in FIG. 1, the viewing direction display means 15 is an arrow mark provided by printing on the light shielding layer 30, but is not limited to this. For example, a lenticular lens or the like may be used to display the observation direction. For example, the viewing direction display means 15 can be produced by providing a printed layer on the hologram holder 10 and further disposing a lenticular lens on the printed layer. In this case, an image designed to give different impressions (color, pattern, sharpness, etc.) depending on the viewing angle when viewed through a lenticular lens is printed on the printed layer. According to such observation direction display means 15, a specific observation direction (observation position) can be indicated by a change in the impression obtained when the image is observed through the lenticular lens, depending on the observation angle. That is, for example, when the observation direction display means 15 is observed from the observation position X1 where the first image 101 can be observed, a specific impression can be grasped from the image through the lenticular lens. A viewing position X1 can be indicated. The observation direction display means 15 can also be produced by the following method. That is, a laser coloring layer is provided on the hologram holder 10, and a lenticular lens is arranged on the laser coloring layer. Then, a laser beam is incident on the laser coloring layer from a specific direction through a lenticular lens to mark the laser coloring layer by laser marking. The observation direction display means 15 manufactured in this way allows the marking provided on the laser coloring layer to be clearly observed when observed from the direction coinciding with the incident direction of the laser light. Therefore, for example, by matching the incident direction of the laser beam with the direction of observing the reproduction area 20 from the observation position X1 where the first image 101 can be observed, the observation direction display means 15 can be observed from the observation position X1. , the mark applied to the laser coloring layer is most clearly observed. That is, the observation direction display means 15 can indicate the observation position X1 by a change in the sharpness of the mark on the laser coloring layer due to a change in the observation direction.

In addition, in the example shown in FIG. 1, the observation direction display means 15 displays the observation direction in which the first image 101 can be observed. Such an observation direction display means 15 can guide the observer 50 so that the observation position is the observation position X1 different from the normal observation position X0. As a result, it becomes easier for the observer 50 to find the first image 101 . If it is desired to prevent the observer 50 from easily finding the first image 101, the observation direction display means 15 may display the observation direction in which the second image 102 can be observed. In this case, the observation direction display means 15 guides the observer 50 so that the observation position becomes the normal observation position X0 (thus, the observation position does not become the observation position X1 different from the normal observation position X0). can do.

As described above, when the light from the point light source 51 is incident on the hologram structure 11 (reproduction region 20), the first image 101 is reproduced in addition to the point light source 100a and the second image 102. , the light amount of the light from the point light source 100a and the light L2 for reproducing the second image 102 can be reduced. Further, by increasing the diffraction angle of the light L1 that reproduces the first image 101, the light L1 that reproduces the first image 101 is prevented from reaching the eyes of the observer 50 observing from the normal observation position X0. ing. This reduces the glare felt by the observer 50 observing the hologram structure 11 (reproduction area 20) from the normal observation position X0 when receiving the light from the point light source 100a and the light L2 for reproducing the second image 102. be able to.

[Method for producing hologram structure 11]
Next, an example of a method for manufacturing the hologram structure 11 (in particular, the uneven surface 1a) will be described. The method described below is merely an example, and other methods capable of appropriately manufacturing the hologram structure 11 including the desired uneven surface 1a can be adopted. The manufacturing method described below can be applied to both the reflection type hologram structure 11 (see FIG. 4) and the transmission type hologram structure 11 (see FIG. 5).

First, a two-dimensional image of an original image is read by a computer (Step 1). Then, the computer obtains a two-dimensional complex amplitude image by setting each pixel value of the read two-dimensional image as an amplitude value and assigning a random value between 0 and 2π to each pixel as a phase value ( Step 2). The computer then obtains a two-dimensional Fourier transform image by performing a two-dimensional Fourier transform on this two-dimensional complex amplitude image (Step 3). Note that the computer may perform arbitrary optimization processing, such as an iterative Fourier transform method or a genetic algorithm, if necessary (Step 4). Then, the computer converts the phase value of each pixel of the two-dimensional Fourier transform image into multiple stages (for example, four stages of "0", "π/2", "π" and "3π/2", or "0", " π/4”, “π/2”, “3π/4”, “π”, “5π/4”, “3π/2” and “7π/4”) (Step 5).

Then, a hologram structure 11 (in particular, the concave-convex surface 1a) corresponding to the two-dimensional Fourier transform image is produced so that each pixel has a depth corresponding to the corresponding discretized phase value (Step 6). For example, when the pixel values of the two-dimensional Fourier transform image are discretized into four stages in Step 5 described above, an uneven surface 1a (see FIG. 8) having four stages of depth is formed on the hologram layer 1 in Step 6. be. The depth of the concave-convex surface 1a is determined by taking into consideration not only the diffraction efficiency characteristics to be achieved, but also various other related parameters (for example, the refractive index of the material that constitutes the hologram structure 11 (especially the hologram layer 1)). determined by For example, as a reflection type hologram structure 11 for reproducing a blue light image, the hologram structure 11 having four steps of the uneven surface 1a and an optical path length of 330 nm per step of the uneven surface 1a is manufactured. be able to. Note that the reflection type hologram structure 11 and the transmission type hologram structure 11 each have a unique depth structure of the uneven surface 1a. A specific value of the depth of the uneven surface 1a of the body 11 differs between the reflective type and the transmissive type.

The apparatus for manufacturing the hologram structure 11 is not particularly limited, and may be, for example, an apparatus controlled by a computer that executes Steps 1 to 5 described above, or may be an apparatus provided separately from the computer. . If necessary, a matrix (that is, a master original) corresponding to the structure of the hologram structure 11 (especially the concave-convex surface 1a) may be made using an exposure device, an electron beam lithography device, or the like based on photolithography technology. (Step 7). For example, a liquid ultraviolet curable resin is dropped onto the matrix, and the ultraviolet curable resin sandwiched between the substrate film (for example, PET film (polyethylene terephthalate film)) and the matrix is irradiated with ultraviolet rays. The hologram structure 11 having the desired uneven surface 1a can be produced by curing the UV-curable resin together with the base film from the mold. As other methods, for example, a method using a thermoplastic ultraviolet curable resin, a method using a thermoplastic resin, a method using a thermosetting resin, and a method using an ionizing radiation curable resin may be employed. By using the matrix in this way, it is possible to easily and mass-produce the hologram structure 11 having the desired concave-convex surface 1a.

In the case of the reflective hologram structure 11, a reflective layer 2 (for example, a reflective layer made of Al or a reflective layer (high refractive index layer) made of ZnS or TiO ₂ ) is further formed on the uneven surface 1a by a manufacturing apparatus. may be formed. However, in the case of the hologram structure 11 that reflects the reproduction light by utilizing the difference in refractive index between the hologram layer 1 and the air, the hologram layer 1 does not need to be additionally provided with the reflective layer 2 . 1a may remain exposed to the air. Furthermore, other functional layers such as an adhesive layer (for example, a heat seal layer, a primer layer for enhancing adhesion between adjacent layers, etc.) may be formed on the hologram layer 1 as necessary. Further, for example, when the reflective layer 2 is formed on the uneven surface 1a of the hologram layer 1, an adhesive layer is formed on the uneven surface of the reflective layer 2 (the surface opposite to the hologram layer 1), The recesses on the surface of the reflective layer 2 may be filled with the layer.

[Depth of uneven surface]
As an example, in the reflection hologram structure 11, the refractive index of the hologram layer 1 is 1.5, and the depth per step of the concave-convex surface 1a (see symbol "d" in FIGS. 7 and 8) is 110 nm. In this case, the optical path length per step of the uneven surface 1a is 330 nm. In this case, the hologram structure 11 exhibits the above-mentioned maximum diffraction efficiency in the blue wavelength band and reproduces a blue optical image because the concave-convex surface 1a has a four-step depth structure.

As another example, in the reflective hologram structure 11, the hologram layer 1 has a refractive index of 1.5, the uneven surface 1a has a depth structure of 8 steps, and the depth of each step is 130 nm. In this case, the hologram structure 11 reproduces a blue light image. In the transmissive hologram structure 11, when the hologram layer 1 has a refractive index of 1.5, the uneven surface 1a has a four-step depth structure, and the depth of each step is 660 nm, the hologram structure Body 11 reproduces a blue light image. Further, in the reflective hologram structure 11, when the hologram layer 1 has a refractive index of 1.5, the uneven surface 1a has a depth structure of 8 steps, and the depth of each step is 230 nm, the hologram structure Body 11 reproduces a red light image. Further, in the reflective hologram structure 11, when the hologram layer 1 has a refractive index of 1.5, the uneven surface 1a has a structure with a depth of 6 steps, and the depth of each step is 220 nm, the hologram structure Body 11 reproduces a green light image.

The color (wavelength band) of the light image reproduced by the transmission type hologram structure 11 described above assumes that it is used in an air environment with a refractive index of 1.0. When an observer observes the optical image 100 reproduced by the reflection-type hologram structure 11, the uneven surface 1a of the hologram layer 1 is arranged on the opposite side of the observer, and the observer can see the uneven surface through the hologram layer 1. The structure (that is, the uneven surface 1a) is to be observed. When the uneven surface 1a of the hologram layer 1 is arranged on the same side as the observer, the reflected image from the hologram structure 11 observed by the observer is formed by the light reflected on the surface without passing through the hologram layer 1. Configured. For example, when an uneven surface 1 a is formed on the surface of a card-shaped hologram holder 10 , an observer observes light reflected by the uneven surface 1 a without passing through the hologram layer 1 . In such a case, the optical path length is based not on the refractive index of the hologram layer 1, but on the refractive index of the medium closer to the viewer than the hologram layer 1, such as the refractive index of air, which is 1.0. You need to set the depth of hit. Therefore, an observer can observe a desired image by designing the structure of the uneven surface 1a while assuming that the refractive index of the hologram layer 1 (hologram structure 11) is 1.0, which is the refractive index of air. be. Specifically, when the refractive index of air is 1.0 and the depth of one step of the uneven surface 1a is 165 nm, the optical path length of one step of the uneven surface 1a is 330 nm. In this case, since the uneven surface 1a has a four-step depth structure, the hologram structure 11 exhibits the maximum diffraction efficiency in the blue wavelength band and reproduces a blue optical image.

[Relationship between depth of uneven surface and peak wavelength of diffracted light]
When the number of steps of the uneven surface 1a of the hologram structure 11 is represented by N, the optical path length modulated per step of the uneven surface 1a is represented by l, and the natural number is represented by m, the peak wavelength λ of the diffracted light is given below. is represented by the formula

λ=N·l/(mN±1)

As described above, the hologram structure 11 of the present embodiment can reproduce a monochromatic optical image even when white light is incident. This is realized, for example, when one of the 1st-order diffracted light and the −1st-order diffracted light of the hologram structure 11 has only one peak wavelength λ in the range of the visible light wavelength band for an arbitrary natural number m. It is possible. For example, when the optical path length l is 330 nm and the step number N of the uneven surface 1a is 4, λ=1320/(4m±1). Thus, λ=440 nm and 264 nm for m=1, λ=188 nm and 146 nm for m=2, and λ=120 nm and 101 nm for m=3. When m is 4 or more, the peak wavelength λ becomes even smaller. Of these, the peak wavelength λ included in the visible light wavelength band is only λ=440 nm when m=1. Therefore, in the case of using the hologram structure 11 in which the number of steps of the uneven surface 1a is N=4 and the optical path length per step is l=330 nm, the observer 50 can visually recognize light having a wavelength of 440 nm and wavelengths in the vicinity thereof. Possible monochromatic light images can be reproduced.

According to the embodiment as described above, the light modulation element 10 includes the element element 21 that reproduces an image by diffracting the light from the point light source 51 . The element element 21 is observed within the angular range R viewing the reproduction region 20 from the position X1 other than the position X0 where the point light source 100a is observed within the angle range R viewing the reproduction region 20 provided with the element element 21. Reproduce the first image 101 . With such an optical modulation element 10, the first image 101, which is the intended optical image, is observed when observed from the observation position X1 different from the normal observation position X0, so that the design of the optical modulation element 10 is improved. can be made Also, such an optical modulation element 10 is difficult to forge. Moreover, since the first image 101 that is not observed from the normal observation position X0 is difficult to notice, the first image 101 can be used for authenticity determination of the light modulation element 10 .

Further, the light modulation element 10 according to the above-described embodiment is observed together with the point light source 100a within the angular range R over which the reproduction region 20 is viewed from the position X0 where the point light source 100a is observed within the angle range R over which the reproduction region 20 is viewed. The second image 102 is also reproduced. With such a light modulation element 10, the second image 102 is observed when the reproduction region 20 is observed from the normal observation position X0, and the second image 102 is observed when the reproduction region 20 is observed from the observation position X1 different from the normal observation position X0. A first image 101 is observed at . Therefore, by changing the observation position, the optical image observed in the light modulation element 10 can be changed. Therefore, the designability of the optical modulation element 10 can be improved. Alternatively, since the optical image (second image 102) is observed when the reproduction area 20 is observed from the normal observation position X0, the first image 101 becomes even less noticeable. Furthermore, by reproducing the first image 101 in addition to the point light source 100a and the second image 102, the light amount of the light from the point light source 100a and the light L2 for reproducing the second image 102 can be reduced. As a result, when viewing the reproduction area 20 from the normal viewing position X0, the glare felt by the viewer 50 upon receiving the point light source 100a and the light L2 of the second image 102 can be reduced.

Further, the light modulation element 10 according to the above embodiment further includes observation direction display means 15 for displaying the observation direction of the reproduction area 20 . Specifically, the observation direction display means 15 displays the observation direction in which the first image 101 can be observed. In this case, the observer 50 can be guided so that the observation position is the observation position X1 where the first image 101 can be observed. As a result, the observer 50 can easily find the first image 101 . Note that the observation direction display means 15 may display the observation direction in which the second image 102 can be observed. In this case, the observer 50 can be guided so that the observation position becomes the normal observation position X0 (thus, the observation position does not become the observation position X1 other than the normal observation position X0). As a result, it is possible to prevent the observer 50 from easily finding the first image 101 .

Further, in the light modulation element 10 according to the above embodiment, the element element 21 includes a computer-generated hologram, and the original image 201 of the first image 101 at the time of producing the computer-generated hologram is located at a position other than the position X0 where the point light source 100a is observed. The first image 101 observed when the reproduction region 20 is observed from the position X1 of is reduced in the direction DL along the direction of observing the reproduction region 20 from the position X1 other than the position X0 where the point light source 100a is observed. It is a statue. In this case, the first image 101 observed when the reproduction area 20 is observed from an observation position X1 other than the normal observation position X0 can be made into an image having an intended shape.

[Modification]
Various modifications can be made to the embodiment described above. Modifications of the above-described embodiment will be described below with reference to the drawings. In the following description and the drawings used in the following description, the same reference numerals as those used for the corresponding portions in the above-described embodiment are used for the portions that can be configured in the same manner as in the above-described embodiment. Description is omitted.

FIG. 17 shows a cross section of a hologram holder 10a in a modified example. 18 and 19 respectively show a front view and a perspective view of the hologram holder 10a shown in FIG. FIG. 17 shows a cross section of the hologram holder 10a shown in FIG. 18 along line II-II. 18 and 19 respectively show the hologram holder 10a on which the light from the point light source is incident, the hologram holder 10a viewed from the normal observation position, and the observation position different from the normal observation position. The hologram holder 10a viewed from the bottom is shown.

A hologram holder 10a shown in FIG. It is different in that only the That is, the difference is that the reproduction area 20 occupies only a partial area of the hologram holder 10a. Another difference is that a light shielding layer 30 is provided on one side of the hologram holder 10a (thus, on one side of the hologram structure 11). In addition, the reproduction area 20 is different in that a pattern 25 is provided by printing or the like. Other configurations are substantially the same as those of the hologram holder 10 shown in FIG.

First, since the pattern 25 is provided in the reproduction area 20 by printing or the like, the observer 50 can observe the light images 101 and 102 reproduced by the hologram structure 11 together with the pattern 25 . This improves the design of the hologram holder 10a. Note that such a pattern 25 may be provided in a region around the reproduction region 20 (for example, on a light shielding layer 30 which will be described later).

Next, the light shielding layer 30 will be described. The light shielding layer 30 regulates transmission of light, and is provided on one surface of the substrate 4 in the hologram holder 10a shown in FIG. 17a. The light shielding layer 30 may be formed on the base material 4 by printing. Alternatively, as the light shielding layer 30 , a sheet-like member made of paper, resin, metal, synthetic fiber, or the like may be arranged adjacent to the base material 4 . The light shielding layer 30 has an opening 30a. When the hologram holder 10a is viewed from the light shielding layer 30 toward the hologram structure 11, the reproduction area 20 is defined by the opening 30a. That is, the light shielding layer 30 covers the area of the substrate 4 other than the reproduction area 20 (area other than the area overlapping the hologram structure 11). As shown in FIG. 17, a hole (space) may be provided in the opening 30a, and only the opening 30a may be transparent (i.e. transparent substrate).

In addition, in the case where the hologram holder 10a shown in FIG. 17 is not provided with the light shielding layer 30, even if the hologram holder 10a is observed from the observation position X1 other than the normal observation position X0, the hologram holder 10a will not be visible through the hologram holder 10a. A point light source 100a is observed. Taking this into consideration, in the hologram holder 10a shown in FIG. 17, the light shielding layer 30 and the opening 30a thereof provide an observation position range in which the observer 50 can observe the point light source 100a through the hologram holder 10a. is restricted.

A light-shielding base material may be used as the base material 4 instead of further laminating the light-shielding layer 30 on one side of the transparent base material 4 . In that case, for example, an opening 4a may be formed in a region overlapping the hologram structure 11 of the substrate 4, and the reproduction region 20 may be partitioned by the opening 4a. The opening 4a may be provided with a hole (space) in the same manner as the opening 30a of the light shielding layer 30, or only the opening may be provided together with the hole (space) or instead of providing the hole (space). It may be composed of a transparent body (that is, a transparent substrate).

[Use]
The hologram structure 11 and the hologram holders (light modulation elements) 10 and 10a described above are not particularly limited in usage or application, and can be used, for example, for entertainment purposes such as reproducing character images, and for design purposes. . For security purposes, the hologram structure 11 can be applied to, for example, the following objects. When applying the hologram holders 10 and 10a to information recording media and other media, for example, passports, ID cards, banknotes, credit cards, cash vouchers, gift certificates, other tickets, official documents, personal information, confidential information, etc. The optical modulation element according to the present invention can be applied to other media that record various types of information and other media that have monetary value, and counterfeiting of these media can be prevented. The ID card referred to here includes, for example, a national ID card, a driver's license, a membership card, an employee card, and a student card. In the hologram holders 10 and 10a, the base material for holding the hologram structure 11 (see reference numeral "4" in FIG. 1) can be made of paper, resin, metal, synthetic fiber, or a combination thereof, for example.

Further, it is possible to apply the hologram structure 11 according to the present invention to the hologram holders 10 and 10a described above by any method. The hologram structure 11 according to the present invention can be held by any object (that is, the hologram holders 10 and 10a) using techniques such as sticking, sandwiching, or embedding. Therefore, the hologram structure 11 may be formed using part of the members constituting the hologram holders 10 and 10a, or the hologram structure 11 may be additionally provided for the hologram holders 10 and 10a. good too.

The hologram structure 11 described above may be used alone for various purposes, or may be used together with other functional layers such as a printed layer for various purposes.

[Constituent material of hologram layer]
The material forming the hologram layer 1 is not particularly limited, but the hologram layer 1 can be formed from various resins as described above. Specific examples of various resins are listed below.

Examples of thermosetting resins forming the hologram layer 1 include unsaturated polyester resins, acrylic-modified urethane resins, epoxy-modified acrylic resins, epoxy-modified unsaturated polyester resins, alkyd resins, and phenol resins. Examples of thermoplastic resins constituting the hologram layer 1 include polycarbonate (PC), polyethylene terephthalate (PET), glycol-modified polyethylene terephthalate (PET-G), polyvinyl chloride (PVC), acrylic acid ester resin, and acrylamide. resins, nitrocellulose resins, polystyrene resins, and the like. These resins may be homopolymers or copolymers composed of two or more constituents. Moreover, these resins may be used alone, or two or more of them may be used in combination.

The above-mentioned thermosetting resins or thermoplastic resins include various isocyanate compounds, metallic soaps such as cobalt naphthenate and zinc naphthenate, organic peroxides such as benzoyl peroxide and methyl ethyl ketone peroxide, benzophenone, acetophenone, anthraquinone, naphthoquinone, A thermal or ultraviolet curing agent such as azobisisobutyronitrile, diphenyl sulfide, etc. may be included.

Examples of the ionizing radiation-curable resin constituting the hologram layer 1 include epoxy-modified acrylate resins, urethane-modified acrylate resins, acrylic-modified polyester resins, and the like. A urethane-modified acrylic resin represented by a chemical formula shown in a publication is preferred.

When curing the ionizing radiation-curable resin, a monofunctional or polyfunctional monomer, oligomer, or the like can be used in combination for the purpose of adjusting the crosslinked structure and viscosity. Examples of the monofunctional monomer include mono(meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, hydroxyethyl (meth)acrylate, vinylpyrrolidone, (meth)acryloyloxyethyl succinate, and (meth)acryloyloxyethyl phthalate. etc. In addition, as the bifunctional or higher monomers, when classified by the skeleton structure, polyol (meth)acrylate (e.g., epoxy-modified polyol (meth)acrylate, lactone-modified polyol (meth)acrylate, etc.), polyester (meth)acrylate, epoxy (meth)acrylate, ) acrylates, urethane (meth)acrylates, polybutadiene-based, isocyanuric acid-based, hydantoin-based, melamine-based, phosphoric acid-based, imide-based, and phosphazene-based poly(meth)acrylates having a skeleton. In addition, various monomers, oligomers and polymers that are UV and electron beam curable are available.

More specifically, examples of bifunctional monomers and oligomers include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth) acrylates and the like. Examples of trifunctional monomers, oligomers, and polymers include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and aliphatic tri(meth)acrylate. Examples of tetrafunctional monomers and oligomers include pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and aliphatic tetra(meth)acrylate. Penta- or higher-functional monomers and oligomers include, for example, dipentaerythritol penta(meth)acrylate and dipentaerythritol hexa(meth)acrylate. Also included are (meth)acrylates having a polyester skeleton, a urethane skeleton, and a phosphazene skeleton. The number of functional groups is not particularly limited, but when the number of functional groups is less than 3, the heat resistance tends to decrease, and when the number of functional groups exceeds 20, the flexibility tends to decrease. Those within the range of 3 to 20 are preferred.

Although the content of the monofunctional or polyfunctional monomers and oligomers as described above can be adjusted as appropriate, it is usually preferably 50 parts by weight or less with respect to 100 parts by weight of the ionizing radiation curable resin, especially 0.5 parts by weight. parts to 20 parts by weight is preferred.

Further, the hologram layer 1 may optionally contain a photopolymerization initiator, a polymerization inhibitor, a deterioration inhibitor, a plasticizer, a lubricant, a coloring agent such as a dye or a pigment, a surfactant, an antifoaming agent, a leveling agent, and Additives such as thixotropic agents may be added as appropriate.

When the hologram layer 1 has self-supporting properties, the film thickness of the hologram layer 1 is preferably in the range of 0.05 mm to 5 mm, more preferably in the range of 0.1 mm to 3 mm. On the other hand, when the hologram layer 1 is formed on a transparent substrate without self-supporting properties, the film thickness of the hologram layer 1 is preferably in the range of 0.1 μm to 50 μm, more preferably in the range of 2 μm to 20 μm. It is preferable to Also, the size of the hologram layer 1 (for example, the size in plan view) can be appropriately set according to the application of the hologram structure 11 .

[Other Modifications]
The hologram structure 11 used in each of the above-described embodiments and modifications is composed of a plurality of element elements 21 as shown in FIG. may be

Also, the planar view size and planar view shape of each element element 21 are not particularly limited, and each element element 21 can have any size and shape. For example, the planar shape of each element element 21 may be a quadrangle such as a square, rectangle, or trapezoid, another polygonal shape (for example, a triangle, a pentagon, a hexagon, etc.), a perfect circle, an ellipse, another circle, a star shape, or the like. It may be heart-shaped or the like, and the hologram structure 11 may have two or more types of element elements 21 having a plan view shape.

Any functional layer may be added to the hologram structure 11, for example, the hologram structure 11 may be covered with a transparent deposition layer. The hologram structure 11 can also be concealed by preventing the hologram structure 11 from being glossy by providing a transparent deposition layer that does not have gloss. From the viewpoint of hiding the hologram structure 11, the total light transmittance of such a transparent deposition layer is preferably 80% or more, and more preferably 90% or more. Also, in the reflective hologram structure 11, the hologram structure 11 can be covered with a reflective deposited layer (see the reflective layer 2 in FIG. 1). Examples of constituent materials of the reflective deposition layer include Mg, Al, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Se, Rb, Pd, Ag, Cd, In, Sn, Sb, Te, Metals such as Au, Pb, or Bi can be used. Further, examples of the constituent material of the transparent deposition layer include oxides and sulfides of the above metals such as ZnS and TiO ₂ . These materials may be used alone to form the vapor deposition layer, or two or more materials may be combined to form the vapor deposition layer.

The thickness of the deposited layer provided on the hologram layer 1 (especially on the uneven surface 1a) can be set as appropriate from the viewpoint of desired reflectivity, color tone, design and application, and is, for example, within the range of 50 Å to 1 μm. It is preferably within the range of 100 Å to 1000 Å. In particular, when the transparency of the deposited layer is given priority, the thickness of the deposited layer is preferably 200 Å or less, while when the concealability of the deposited layer is given priority, the thickness of the deposited layer is more than 200 Å. is preferred. As a method for forming the vapor deposition layer, a general method for forming a vapor deposition layer can be employed, and examples thereof include a vacuum vapor deposition method, a sputtering method and an ion plating method.

The invention is not limited to the embodiments and variants described above. For example, various modifications may be made to each element of the embodiments and modifications described above. Forms including components and/or methods other than the components and/or methods described above may also be included in embodiments of the present invention. Forms that do not include some of the components and/or methods described above may also be included in embodiments of the present invention. In addition, a form including some components and/or methods included in one embodiment of the present invention and some components and/or methods included in other embodiments of the present invention may also be included in the present invention. can be included in an embodiment. Therefore, the components and/or methods included in each of the above-described embodiments and modifications, and other embodiments of the present invention may be combined with each other, and the forms according to such combinations may also be implemented in the present invention. can be included in the form. Further, the effects achieved by the present invention are not limited to those described above, and specific effects according to the specific configurations of the respective embodiments can also be exhibited. Thus, various additions, changes, and partial deletions can be made to each element described in the claims, specification, abstract, and drawings without departing from the technical idea and gist of the present invention. is.

1 hologram layer 1a uneven surface 2 reflective layer 4 substrate 10, 10a hologram holder 11 hologram structure 15 viewing direction display means 21 element element 50 observer 51, 51a, 51b point light source 100 light image 100a point light source 100b 1st order diffracted light Image 100c −1st order diffracted light image 101 First image 102 Second image 201 First original image 202 Second original image

Claims (6)

Equipped with an element element that reproduces an image by diffracting light from a point light source,
In the wavelength band of 380 nm or more and 780 nm or less, the element element exhibits a diffraction efficiency corresponding to the wavelength of the first-order diffracted light and the −1st-order diffracted light, exhibits a maximum diffraction efficiency at a specific wavelength, and The diffraction efficiency is formed so as to form a maximum value with a full width at half maximum of 200 nm or less in the wavelength distribution of the diffraction efficiency including the maximum diffraction efficiency,
The element element is observed within the angle range over which the reproduction area is viewed from a position other than the position at which the optical image corresponding to the point light source is observed within the angle range over which the reproduction area in which the element element is provided is viewed. A first image is reproduced , and observed together with a light image corresponding to the point light source within the angular range of viewing the reproducing region from a position where the optical image corresponding to the point light source is observed within the angular range of viewing the reproducing region. a light modulating element that further reproduces the second image obtained . 2. The light modulation element according to claim 1 , further comprising observation direction display means for displaying the observation direction of said reproduction area. 3. The light modulation element according to claim 2 , wherein said viewing direction display means displays a viewing direction in which said first image can be viewed. The element element includes a computer-generated hologram,
The original image of the first image at the time of producing the computer-generated hologram is the first image observed when the reproduction area is observed from a position other than the position where the light image corresponding to the point light source is observed. 4. The image according to any one of claims 1 to 3 , wherein the light image corresponding to the point light source is a reduced image in a direction along the direction in which the reproduction area is observed from a position other than the position where the light image corresponding to the point light source is observed. light modulation element. A light shielding layer having an opening is provided on one side of the element element,
5. The light modulation element according to claim 1 , wherein said reproduction region is partitioned by said opening when viewed from said light shielding layer toward said element element. An information recording medium comprising the light modulation element according to any one of claims 1 to 5 .

Images