Method and apparatus for detecting focusing errors utilizing chr

Details Method and apparatus for detecting focusing errors utilizing chr Method and apparatus for detecting focusing errors utilizing chr

1990-08-08

1992-04-14

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

369 4437, G01J 120

Patent

active

051050765

ABSTRACT:
An objective lens having chromatic aberration is disposed in an optical system for focusing recording and/or reproducing light beams upon a surface of an optical disc, and two detecting light beams having different wavelengths are passed through the lens. When the surface of the optical disc is positioned at a focal point of one of the beams, the other beam is not focused on the optical disc. When the surface of the disc is positioned midway between the focal points of the two beams, two light spots formed on the optical disc by the two beams have equal intensity. The light intensity of the two spots is detected, so that focusing errors can be determined based on the difference between the detected intensities.

REFERENCES:
patent: 4450547 (1984-05-01), Nakamura et al.
patent: 4600831 (1986-07-01), Hutley
patent: 4725721 (1988-02-01), Nakamura et al.
patent: 4815058 (1989-03-01), Nakamura et al.
patent: 4970707 (1990-11-01), Hara et al.

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