Method and apparatus for detecting focussing error signal of obj

Details Method and apparatus for detecting focussing error signal of obj Method and apparatus for detecting focussing error signal of obj

1982-01-15

1985-03-19

Rosenberger, R. A.

Optics: measuring and testing

Focal position of light source

250201, 369 45, G01J 136

Patent

active

045055840

ABSTRACT:
In order to derive a focussing error signal of an objective lens with respect to a video disc on which a light beam is focussed by the objective lens, the P-polarized light beam is made incident upon a prism and then upon a thin film which is applied to the prism and has a refractive index higher than that of the prism, and the light beam reflected by a boundary surface between the thin film and the air is detected by a photo-detector having two light receiving regions. The thin film is made of material having a higher refractive index than that of the prism. Between the prism and the thin film there may be interposed at least one additional thin film in such a manner that the lower and higher refractive index thin films are alternately arranged.

REFERENCES:
patent: 3043976 (1962-07-01), Kossel
patent: 4390781 (1983-06-01), Musha

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