Focusing error detecting device in head assembly for optical dis

Details Focusing error detecting device in head assembly for optical dis Focusing error detecting device in head assembly for optical dis

1985-10-15

1987-06-09

LaRoche, Eugene R.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

250237G, 369 45, G01J 120, G01J 130, H01J 314

Patent

active

046721878

ABSTRACT:
A focusing error detecting device used in a head assembly for recording information to a recording surface of an optical disc or reading out information already recorded, the focusing error detecting device including a diffraction grating for focusing light which has been introduced from a light source into a thin-film waveguide layer, onto the recording surface, and two light receiving diffraction gratings for conducting the light reflected by the recording surface again into the waveguide layer. The two light receiving diffraction gratings have optical characteristics which differ from each other, depending the position of a focused spot of the light focused on the recording surface by the focusing diffraction grating. Therefore, by comparing the intensity of light from one light receiving diffraction grating with that from the other light receiving diffraction grating, there can be seen a positional relationship between the focused spot and the recording surface.

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