Optical scanning apparatus which detects scanning spot focus err

Details Optical scanning apparatus which detects scanning spot focus err Optical scanning apparatus which detects scanning spot focus err

1988-02-01

1989-07-25

Bovernick, Rodney B.

Radiant energy

Ionic separation or analysis

Static field-type ion path-bending selecting means

250237G, 369 45, 369109, 369112, 369122, G02B 2744, G11B 2110

Patent

active

048506737

ABSTRACT:
An apparatus for optically scanning a surface, such as the information surface of an optical record carrier. An error in focus of the scanning spot on the surface is detected by providing two gratings in succession in the path of the beam reflected from the surface. The grating periods of the two gratings are related in accordance with the nominal beam divergence at zero focus error, and the grating strips thereof are parallel but offset with respect to each other. A bounding line between detectors in a composite radiation-sensitive detection system extends parallel to the grating strips. An interference pattern of light and dark bands is projected by the second grating on the detection system, such pattern having an intensity distribution which varies with variations in focus error and can be enhanced by an appropriate value of the offset between the two gratings.

REFERENCES:
patent: 3108383 (1963-10-01), Gabor
patent: 3482107 (1969-12-01), Hock
patent: 3822930 (1974-07-01), Douklias
patent: 3938894 (1976-02-01), Nanba
patent: 4091281 (1978-05-01), Willhelm et al.
patent: 4293188 (1981-10-01), McMahon
patent: 4465540 (1984-08-01), Albert
patent: 4771411 (1988-09-01), Greve

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