Method for producing a display with a diffraction grating pattern and a display produced by the method

Abstract: A method for producing a display with a diffraction grating pattern comprising the steps of reading image data, assigning color for light exposure and moving a slit of an optical system to a position corresponding to the assigned color, moving an origin of an X-Y stage and setting a head of data of the assigned color, reading data of an assigned address of the image data and opening a shutter of the optical system for light exposure when data of the assigned color exists, moving the X-Y stage to increase the address by one and repeating the data-reading and shutter-opening step until no further data exists, and changing the assigned color and repeating the above sequence of steps until no further color exists.

Description: The present invention relates to a method for producing a display composed of a plurality of minute diffractive dots. JP-A-60-156004 discloses a method for producing a display with a diffraction grating pattern formed by two-luminous flux interference. According to this method, a minute interference fringe is sequentially light-exposed on a photosensitive film while changing its pitch, direction and light intensity. According to this conventional method, varying the pitch, direction and light intensity of an interference fringe requires that an optical system for an exposing head be moved for each event. Since the conventional method cannot have the optical system fixed, it is susceptible to an external vibration and cannot therefore form a highly-accurate diffraction grating. Further, the conventional method cannot change the direction of the diffraction grating, formed in dots, for each dot. Furthermore, even if the conventional method can linearly form a diffraction grating, it cannot curvedly form a diffraction grating, so that the field of view of a display cannot be widened. In addition, since this method cannot form a diffraction grating that has a plurality of spatial frequencies for a single dot, the produced display cannot express an intermediate colour. US-A-3 917 378 shows a method for producing a display having a plurality of minute diffractive dots which makes use of a colour separation positive element. From an image to be reproduced colour separated positives are formed so that each positive corresponds to a predetermined process colour. From each of the colour separated positives a frequency encoded diffraction grating is holographically recorded in a photosensitive medium. Additionally, EP-A-0 105 099 shows a method for producing a display with a diffraction grating pattern by interfering two laser beams. The grating parameters of the elements vary from element to element so that the visual colour patterns produced by the device of this reference move along trajectories with a predetermined velocity when rotated with respect to an illumination source. A gradual variation of the grating orientation results in a quasicontinuous movement of the colour pattern during rotation with respect to the illumination source. According to this reference, the display produced comprises a diffraction grating pattern in which the grating parameters of neighbouring diffractive elements are correlated in accordance with a desired movement of the visual pattern. It is an object of the present invention to provide a method for producing a display composed of a plurality of diffractive dots which has a widened field of view. This object is achieved by the features of claim 1. Advantageous further developments are set out in the dependent claims. According to the invention, the method is not susceptible to an external vibration and can therefore form a highly-accurate diffraction grating pattern. The direction of a diffraction grating is varied for each dot. The field of view is widened by forming a dot-formed diffraction grating with curved lines. An intermediate color can be shown by giving a dot-formed diffraction grating a plurality of spatial frequencies. According to the method, first, color is assigned and a diffraction grating corresponding to this colour is formed for each dot by moving the X-Y stage. When forming this diffraction grating is completed, the colour is changed and a diffraction grating corresponding to the new colour is similarly formed for each dot. According to the invention, the direction of the diffraction grating formed in dots varies dot by dot, so that the display can be observed or viewed at various angles. Since the diffraction grating is formed with curved lines, its visual field can be increased. If the diffraction grating is formed with closed curved lines, the visual field is 360 degree. In addition, since the diffraction grating has a plurality of spatial frequencies, an intermediate color can be expressed. An electron beam exposing device is used so that various shapes of diffraction gratings can be delineated on an EB resist. Further, with the use of such an electron beam exposing device, the direction of the diffraction grating can be changed for each dot and the diffraction grating can be formed with curved lines. Furthermore, it is possible to form a diffraction grating with a plurality of spatial frequencies. Other advantages will be apparent from the following description taken in conjunction with the accompanying drawings in which: Fig. 1 is a schematic diagram of an apparatus for producing a display with a diffraction grating according to this invention; Fig. 2 is a diagram illustrating an EB resist placed on an X-Y stage; Fig. 3 is a diagram schematically illustrating the method of the embodiment of this invention; Fig. 4 is a flowchart for a method for producing a display with a diffraction grating according to the second embodiment of this invention; Fig. 5 is a diagram for explaining how to observe the display of this invention; Fig. 6 is a diagram illustrating a dot having a diffraction grating with a plurality of spatial frequencies; Fig. 7 is a diagram illustrating a pattern having the direction of a diffraction grating varying dot by dot; Fig. 8 is a diagram illustrating a pattern with a diffraction grating having a plurality of directions; Fig. 9 is a diagram illustrating a dot having a diffraction grating formed with curved lines; and Fig. 10 is a diagram illustrating a dot having a concentric diffraction grating. With reference to the accompanying drawings, a description will be given below of a method for producing a dot with a diffraction grating. According to this embodiment, a dot having a diffraction grating is formed for each colour using an X-Y stage, so that it is unnecessary to move the optical system, thus ensuring the formation of a highly-accurate diffraction grating pattern. Providing a highly-accurate diffraction grating pattern means that a clear display can be produced. Since a diffraction grating pattern is formed using an X-Y stage and a computer, it is possible to provide a finer pattern with a fine hue, which is constituted by fine dots. Such a display can be used for security checking. Further, since image data in a computer can be reproduced as it is using the computer, the overall production process can be simplified. Referring now to Figs. 1 to 4, a description will be given of the method for producing a display with a diffraction grating pattern according to this invention, by using an electron beam exposing device. As shown in Fig. 1, the electron beam exposing apparatus comprises an electron gun 50, an alignment 52, a blanker 54, a condenser lens 56, a stigmator 58, a deflector 60, an objective lens 62 and an X-Y stage 20. On the X-Y stage 20 is placed EB resist (dry plate) 14. Blanker 54, deflector 60 and X-Y stage 20 are coupled through a control interface 64 to a computer 66. An electron beam emitted from electron gun 50 scans on dry plate 14 under the control of computer 66. Fig. 2 illustrates dry plate 14 disposed on X-Y stage 20. An electron beam 70 emitted from electron gun 50 delineates diffraction grating pattern 18 with dots 16 as units. Diffraction grating patterns 18 are sequentially delineated dot by dot, by moving X-Y stage 20. Referring to Figs. 3 and 4 the operation sequence will be described below. First, in step a, image data is scanned using an image scanner and is entered in the computer. Alternately, image data prepared by computer graphics may be entered in the computer. Then, the image data is corrected for better appearance in step b; this image correction is done because the scanned image data has rugged edge portions. Visual field data is entered in the computer in step c. This visual field data is used to determine, for each dot, the visible direction and visual field of a display attained by reproducing the input image data. The origin of the X-Y stage is then moved in step d and dot data is input to the computer in step e. This dot data is associated with the location, color (spatial frequency), visible direction and visible range of one dot of the corrected image data. In step f, the pitch of a diffraction grating is determined so that the colour of the dot input to the computer in step e can be reproduced. In the next step g, the direction of the diffraction grating is determined so that the visible direction of the dot input in step e can be reproduced. In the subsequent step h, the curvature of the diffraction grating is determined so that the visible range of the dot input in step e can be reproduced. The sequence of these steps f, g and h is not limited to the above particular one, but may be changed in any sequence. Then, in step i the X-Y stage is moved to the position of the dot input in step e, and in step j the diffraction grating for that dot is delineated. The delineation of the diffraction grating corresponding to one dot is completed through the above sequence of steps. In the next step k, the address for referring to data is incremented by one in order to input data of the next dot. If image data at this address is found to exist in step ℓ, the flow returns to step e where the next dot data is input to the computer, and the sequence of steps f to k is repeated. The overall sequence of steps is repeated until there exists no further image data corresponding to the dots. With the use of such an electron beam exposing device, it is possible to scan a target with an electron beam in various directions, thus ensuring the delineation of a desired diffraction grating pattern. As shown in Fig. 6, by overlapping patterns respectively having spatial frequencies f1 and f2, a diffraction grating pattern with a mixture of spatial frequencies f1 and f2 can be formed. Such a diffraction grating pattern having a plurality of frequencies can express an intermediate colour. Further, the direction of the diffraction grating can be changed dot by dot as shown in Fig. 7. In addition, diffraction gratings having different directions may be mixed in a single dot, as shown in Fig. 8. With the use of the patterns as shown in Figs. 7 and 8, a display imaged can be changed depending on the viewing direction of a viewer. Furthermore, as shown in Fig. 9, it is possible to form a dot having a curved diffraction grating, which can widen the visual field. It is also possible to form a dot with a concentric diffraction grating, which provides a 360-degree visual field and can eliminate the restriction on the visual field that is inherent to the prior art hologram. Accordingly, a viewer can view the display at any position or from any direction. The use of the electron beam exposing device can provide a display with a greater number of expressions as compared with the case where two laser beams are used. The dry plate having thus formed diffraction gratings can be used as a master plate for a copying occasion. The copying is executed using the well-known embossing method. As described above, this embodiment can form dots with various diffraction gratings on the surface of a target plate, so that a display with the following various expressions can be provided. (a) Since an image is constructed by the collection of dots having fine diffraction gratings with different spatial frequencies, illumination light reaches the eyes of a viewer without being diffused. Accordingly, a bright display can be provided. (b) Since a pattern is formed by the combination of fine dots, colour matching with an accuracy of less than 0.1 mm is possible. Accordingly, it is possible to prepare a fine pattern. (c) It is possible to provide a diffraction grating pattern whose diffraction gratings have different directions. Accordingly, it is possible to provide a display whose pattern varies depending on the direction from which a viewer is viewing the display. Such a display can be provided more easily by using an electron beam exposing device. (d) Since a dot is constructed by a curved diffraction grating pattern, it is possible to provide a display having a significantly wide visual field as compared with a conventional display. Such a display can be provided more easily by using the above-mentioned electron beam exposing device. (e) Since a diffraction grating having a plurality of spatial frequencies is formed dot by dot, it is possible to provide a display showing an intermediate colour. Such a display can also be provided more easily by using the electron beam exposing device.

Claims: A method for producing a display composed of a plurality of minute diffractive dots (16), the grating (18) of each dot (16) representing a predetermined colour and being designed such that, when properly illuminated, an incident beam of light is diffracted, with a predetermined angular range, into a predetermined direction, the method comprising: a) reading image data into a computer (66); b) inputting visual field data to said computer (66), the data comprising the direction and the angular range into which the incident light beam is to be diffracted; c) adjusting an origin of an X-Y-stage (20) on which an electron beam sensitive medium (14) is disposed; d) generating on the basis of the data input specified in steps a) and b) an initial dot data set, the dot data set representing the location of a dot (16), the colour to be displayed by said dot (16) and the direction and the angular range into which the light incident on the dot is to be diffracted; e) determining on the basis of said initial dot data set a grating data set including the pitch, the orientation and the curvature of the grating forming the dot; the pitch, the orientation and the curvature being determined so that the previously defined colour, direction and angular range are obtained; f) moving said X-Y-stage (20) to a position corresponding to the location of the diffractive dot (16), and when image data for this dot exists, delineating, in accordance with the grating data set, a diffraction grating (18) using an electron beam exposing device (50), and h) repeating steps d) to f) until all of the dots (16) constituting the display are processed. A method according to claim 1, characterized in that said plurality of minute diffractive dots (16) are formed by delineating said diffraction grating (18) by using said electron beam exposing device (50) to form a diffraction grating array. A method according to claim 1 or 2, characterized in that said electron beam sensitive medium is prepared as a plane substrate (14) on a surface of which a diffraction grating pattern divided into a plurality of minute diffractive dots (16) is formed and each of said diffraction gratings (18) is formed with curved lines. A method according to claim 1 or 2 characterized in that said electron beam sensitive medium is prepared as a plane substrate (14) on a surface of which a diffraction grating pattern divided into a plurality of minute diffractive dots (16) is formed, wherein in one minute dot (16) diffraction gratings (18) with a plurality of spatial frequency components are included. A method according to claim 3 or 4, characterized in that directions of said diffraction gratings (18) are varied dot by dot. A display comprising a substrate (14) having a diffraction grating pattern directly obtained by any of the preceding method claims.

Inventors: TAKAHASHI SUSUMU, TAKAHASHI, SUSUMU
Applicants: TOPPAN PRINTING CO LTD, TOPPAN PRINTING CO., LTD.
Application year: 1988
Main classification: G03H1
IPC codes: G03H1, H04N1, G02B5