Optical: systems and elements – Diffraction – From grating
Patent
1998-03-31
2000-09-12
Henry, Jon
Optical: systems and elements
Diffraction
From grating
359576, 359494, 359569, 349201, 369112, 369110, G02B 518, G11B 1100
Patent
active
061185868
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an optical head device for writing optical information on or reading out optical information from optical discs and magneto-optical discs such as CD (compact disks), CD-ROM and video discs, and a process for its production.
BACKGROUND ART
Heretofore, as an optical head device for writing optical information on or reading out optical information from optical discs and optical magnetic discs, one using a prism type beam splitter, and one using a diffraction grating or hologram element, as an optical part for introducing (beam splitting) a signal light reflected from the recording surface of a disc to a detecting section, have been known.
Heretofore, the diffraction grating or the hologram element for an optical head device has been prepared by forming a rectangular grating (relief) having a rectangular cross-section on a glass or plastic substrate by a dry etching method or an injection molding method, thereby to diffract light and provide a beam splitting function.
Further, in a case where it is attempted to improve the light utilization efficiency over an isotropic diffraction grating whereby the light utilization efficiency is about 10%, it is conceivable to utilize polarization. For utilizing polarization, there has been a method of increasing the go and return efficiency by increasing the efficiency of both going (in the direction from the light source to the recording surface) and returning (in the direction from the recording surface to the detecting section) by combining a quarter-wave sheet to a prism type beam splitter.
However, the prism type polarized beam splitter is expensive, and other systems have been sought. As one system, a method has been known in which a flat plate of berefringence crystal such as LiNbO.sub.3 is used, and an anisotropic diffraction grating is formed on its surface to provide deflection selectivity. However, the berefringence crystal itself is expensive, and it is difficult to apply such a method to the consumer product field.
With the isotropic diffraction grating, the utilization efficiency in going (in the direction from the light source to the recording surface) is about 50%, and the utilization efficiency in returning (in the direction from the recording surface to the detecting section) is 20%, as mentioned above, whereby the go and return utilization is at a level of 10% at best.
It is an object of the present invention to solve the above-described problems and to provide an optical head device which improves the light utilization efficiency and which can be prepared at a low cost with high productivity, and a process for its production.
DISCLOSURE OF THE INVENTION
The present invention provides an optical head device whereby writing of information and/or reading out of information is carried out by irradiating light from a light source on an optical recording medium through a diffracting element, wherein the diffracting element is provided with an optically anisotropic diffraction grating having lattice-like projections and recesses formed on the surface of a transparent substrate, and liquid crystal having an optical anisotropy filled in said projections and recesses.
Further, the present invention provides a process for producing an optical head device whereby writing of information and/or reading out of information is carried out by irradiating light from a light source on an optical recording medium through a diffracting element, which comprises coating a transparent thin film on the surface of a transparent substrate for the diffracting element, then forming lattice-like projections and recesses on the transparent thin film by a photolithographic method, and filling liquid crystal having an optical anisotropy in said projections and recesses to form an optically anisotropic diffraction grating.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a transverse cross-sectional view of a basic structure of a diffracting element employing an optically anisotropic diffraction grating by means of liquid crystal, rep
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Gunjima Tomoki
Hotaka Hiroki
Sato Hiromasa
Tanabe Yuzuru
Asahi Glass Company Ltd.
Henry Jon
LandOfFree
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