Focus servo loop off-set compensation
Focus servo system having object lens protection circuit for an
Focus-servo correction utilizing storage of detected focus error
Focused-spot-position detection device for optical information r
Focusing control circuitry for an optical memory system
Focusing detection apparatus
Focusing error detection apparatus
Focusing optical head movable radially by a carriage
Focusing system for video disc player
Focussing error detection device for use in optical disk type re
Focussing lens servo driving device for optical information read
Frequency modulation to biphase data conversion for writable CD