Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Patent
1991-04-04
1993-04-06
Psitos, Aristotelis
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
369112, 2502015, 359569, 385 14, 385 37, G11B 700, G02B 634, G02B 2742
Patent
active
052009394
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an optical head apparatus capable of recording/reproducing information from an optical disc.
Hitherto, a technology for forming an optical head apparatus by a thin layer has been proposed, the optical head being capable of recording/reproducing information from an optical disc. For example, there has been a technology disclosed in PCT/JP 88/01344. FIG. 1 is a view which illustrates the structure of the conventional thin-film optical head apparatus. Referring to FIG. 1, a transparent substrate 2S holds a hollow Si-substrate 1 therebetween, the transparent substrate 2S having the surface on which gratings 4B and 4C are formed. The transparent substrate 2S is made of, for example, thermosetting resin. The concavities and convexities formed on the surface of the gratings 4B and 4C are formed by transferring the grating of a stamper. The grating 4C is formed in a circular region whose central axis is arranged to be an axis L passing through a point O, the grating 4C being in the form of a concentric or spiral cyclic concave and convex structure formed around the central axis L. The gratings 4B and 4C do not overlap each other and annular gaps are present therebetween. Waveguide layers 3B and 3C are formed on the transparent substrate 2S with a transparent layer 5 having a low refractive index formed therebetween, the waveguide layers 3B and 3C respectively having a higher refractive index than that of the transparent layer 5. Since the thickness of the transparent layer 5 is thin, the concavities and convexities of the gratings on the transparent substrate 2S remain on the transparent layer 5. The waveguide layers 3B and 3C formed thereon with concavities and convexities serve as grating couplers. The refractive index of the waveguide layer 3B is larger than that of the waveguide layer 3C, but the film thickness of the waveguide layer 3B is smaller than that of the waveguide layer 3C. The waveguide layer 3B is formed in an annular region relative to the central axis L, while the waveguide layer 3C is formed in a circular region relative to the central axis L. The inner peripheral portion of the waveguide layer 3B and the outer peripheral portion of the waveguide layer 3C overlap each other in such a manner that the waveguide layer 3C covers the waveguide layer 3B, the overlapped portion being positioned in an annular region positioned between the grating coupler 4C and the grating coupler 4B. A ring-like photo detector 6 is formed on the substrate 1 at the innermost portion of the waveguide layer 3B.
Laser beams emitted from the semiconductor laser 8 are turned into parallel ray light by a converging lens 9. The laser beam 11 converted into concentric polarization (a state of polarization in which a plane of vibration is tangent to a circle) or radial polarization (a state of polarization in which a plane of polarization is tangent to a circle) by a quarter wavelength plate 10C and a polarizing element 10, is made incident upon and coupled by the grating coupler 4C so as to be waveguide light 12C in a TE mode or a TM mode, the waveguide light 12C being propagated radially in the waveguide layer 3C. The waveguide light 12C is converted into waveguide light 12B after it has been shifted from the waveguide layers 3C and 3B, the waveguide light 12B being then converted into radiation mode light 13 which is converged at a point F on the central axis after being radiated from the grating coupler 4B. A reflection surface 16 of the optical disc is orthogonal to the axis L, the reflection surface 16 being positioned at substantially the same position as the focal point F. Therefore, the light is reflected by the reflection surface 16 so as to become reflected light 17B, the reflected light 17B being then made incident upon and coupled by the grating coupler 4B. As a result, the light is converted into waveguide light 18B which moves toward the center of the waveguide layer 3B. The thus formed waveguide light 18B is radiated at the in
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Asada Jun-ichi
Nishiwaki Seiji
Taketomi Yoshinao
Tomita Takaaki
Uchida Shinji
Matsushita Electric - Industrial Co., Ltd.
Psitos Aristotelis
Tran Thang V.
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