JPH04113382A - Hologram exposing method - Google Patents

Abstract

PURPOSE:To improve the quality of an image by arranging a fiber array plate in the optical path of at least one laser light beam as a light emission source which has finite area. CONSTITUTION:Laser light 2 from a laser device 1 is made incident on objective lenses 5 and 5' through mirrors 3 and 3' and a beam splitter 4 to become diverged light beams 6 and 6'. The light 6' irradiates a hologram photosensitive material 8 as it is, but the fiber array plate 7 is arranged in the optical path of the light 6 and the laser light passes through the plate 7 to emit laser light 7' from all points on the plate surface, thereby irradiating a photosensitive material 8. The plate 7 is placed at the position of a reference light source at the time of reproduction and the light source which has finite area is used at this position to reproduce an image of good quality. In this case, the numerical aperture of a fiber is preferably increased with the distance from the center of the fiber array plate. This value varies depending upon the magnification of the objective lens 5 and the numerical aperture of the periphery of the plate 7 is made larger proportionate to the magnification.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for exposing a hologram used as a combiner in a head-up display of an automobile or the like.

[Prior Art] Head-up displays have recently come into use as a method of displaying information to drivers and the like in automobiles. This system projects optical information projected from an information projection means such as a liquid crystal display onto a half mirror, which is a combiner built into a car's windshield, etc., so that the driver can hardly change his or her viewpoint from the driving position. This makes it possible to read information without having to worry about it.

Recently, holograms have been attracting attention as the above-mentioned combiner due to their simplicity as optical elements and the richness of added functions. The holographic combiner has not only a reflection function but also a diffraction function, a lens function, etc., so it can diffract optical information in the direction of the driver's field of vision or form an image at any position. becomes possible.

[Problems to be Solved by the Invention] Since such a combiner for a head-up display is a bolographic diffraction grating having a certain area, coherent light with a certain degree of spread is emitted during exposure to produce a hologram. It becomes necessary.

Therefore, when creating a hologram for such a purpose, a diffuser plate is placed a predetermined distance away from the hologram during exposure, and a laser beam is applied from the front or back side of the diffuser plate to detect the transmitted or reflected light. A method has been adopted in which the light beam is used as an object beam and a reference beam.

However, normally when reproducing a hologram, a point light source is placed at the same position as the reference point light source at the time of creation, but when the reproduction light source has a finite size, such as a head-up display for a car , a reduction in the quality of the reconstructed image occurs. This is considered to be because the reproduction irradiation light from a finite area does not satisfy the black condition satisfied by the laser light emitted from a point light source during production. Further, when a diffuser plate is used, there is a problem in that the laser light is randomly polarized by the diffuser plate, and the brightness distribution becomes uneven, resulting in poor quality of the finished hologram.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and in an exposure method when creating a hologram, a laser beam in the optical path of at least one of the two laser beams used for exposure is The present invention provides a hologram exposure method characterized by arranging a fiber array plate.

[Function] The fiber array plate introduced in the present invention has a structure in which a large number of fibers are arranged perpendicularly to the plate as shown in FIG. 2, and the laser beam 6 incident on the plate end 7a of each fiber is Since the light is emitted from the plate end 7b while being repeatedly reflected within, this end face has almost the same function as the light emitting light. In other words, each fiber end of the fiber array plate 7 acts as if it were emitting light. Therefore, it is possible to manufacture a diffraction grating that has the same diffraction conditions as the spread reproduction light, so that the quality of the image during reproduction can be improved.

In this case, it is desirable to increase the numerical aperture of the fiber as it moves away from the center of the fiber array plate in order to make the exposure intensity uniform. The value varies depending on the magnification of the objective lens 5 used, and the higher the magnification, the larger the numerical aperture around the plate 7.

[Example 1] FIG. 1 is a schematic diagram of a new exposure method according to the present invention. Laser light 2 from laser device 1 passes through mirrors 3, 3
° and objective lens 5,5° via beam splitter 4
When the beam enters the beam, it becomes 6.6゛ of light with a spread. The 6° beam is directly irradiated onto the hologram photosensitive material 8, but a fiber array plate 7 is placed in the optical path of the 6° beam so that the laser beam that has passed through the plate is emitted from every point on the plate surface. A laser beam of 7゛ is emitted to
The photosensitive material 8 is irradiated. The plate 7 is placed at the position of the reference light source during reproduction, and if a light source with a finite area is used at this position, a high quality image can be reproduced.

In this case, it is preferable that the numerical aperture of the fiber increases as it moves away from the center of the fiber array plate. Its value varies depending on the magnification of the objective lens 5 used; the higher the magnification, the larger the numerical aperture around the plate 7 (
do.

In this embodiment, the fiber array plate is placed in the optical path of only one of the laser beams used for exposure, but it may be placed in the optical path of both the object beam and the reference beam.

FIG. 3 shows another embodiment. As the object light, a laser device is used as the light source, and the spread light 6 that has passed through the objective lens 5 is reflected from the object 9, and the light 9 is used, and as the reference light, the laser light that has passed through the objective lens 5 is used. Light 7' transmitted through the fiber array plate 7 is used.

During reproduction, a light source having a light emitting surface with a finite area is placed at position 7. This light may be of red color, fringe color, or white light depending on the reproduction wavelength of the hologram.

Further, as in the previous embodiment, it is also possible to arrange a fiber array plate in the optical path of both the object beam and the reference beam.

[Effects of the Invention] In the present invention, when holography is used in a head-up display for an automobile, taking into consideration that the light source during reproduction has a spread, the hologram is manufactured as a light emitting source with a finite area. By arranging a fiber array plate in the optical path of at least one of the laser beams, it is possible to satisfy the same Bragg condition during reproduction and during exposure, thereby improving image quality.

Furthermore, if a fiber that preserves the polarization plane is used as a fiber array plate, it becomes possible to align the polarization directions of two diffused lights, which is impossible with a normal diffuser plate, and improves diffraction efficiency (i.e., reproduced image This is preferable because it can increase the brightness.

[Brief explanation of the drawing]

1 and 3 are conceptual diagrams showing the concept of the exposure method of the present invention, and FIG. 2 is a sectional view showing the concept of a fiber array plate. 1... Laser device 2... Laser light 3.3°... ζ2 4... Beam splitter 5,5°... Objective lens 6.6°... Spreading light 7 ...Fiber array plate 8...Photosensitive material 9...Object

Claims (1)

[Claims] 1) A hologram exposure method when creating a hologram, which comprises arranging a fiber array plate in the optical path of at least one of two laser beams used for exposure.