Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Patent
1997-03-06
1999-05-18
Young, W. R.
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
369116, 369121, G11B7/095
Patent
active
059056991
ABSTRACT:
An optical disc apparatus is provided by putting together two substrates with a combined thickness "h", as a recording medium. The two substrates each have a signal mark or a reflective layer which is capable of being the signal mark at least on the backside of the substrates. A laser beam is radiated onto the optical disc through an objective lens, and a reflected light from the reflective layer is detected by means of an optical detection device. One output of the optical detection device is supplied to a signal reader; the other of output thereof is supplied to a focusing apparatus for detecting a focus error of the objective lens and for controlling the positions of the objective lens with respect to the optical disc. Further, in the optical disc apparatus, if a principal wavelength of laser beam source is set as .lambda..sub.0 ; a half-width of laser beam source is set as .DELTA..lambda.; a numerical aperture of the objective lens is set as NA; and a refractive index of substrate material is set as n.sub.2, the half-width .DELTA..lambda. of the laser beam source satisfies the following equation:
REFERENCES:
patent: 4744073 (1988-05-01), Sugiki
patent: 5614708 (1997-03-01), Koishi et al.
patent: 5659534 (1997-08-01), Terasaki et al.
patent: 5703856 (1997-12-01), Hayashi et al.
Kabushiki Kaisha Toshiba
Young W. R.
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