Elasto-optic device for spot wobble in a video disc player

Claim 1

A radial tracking servo system for an optical-pickup video disc player of the type comprising means for producing a light beam and means for causing said beam to read a record track on a rotating record disc, which servo system comprises: an elasto-optic light beam deflector including a transparent prism interposed in the path of said beam and an electromechanical transducer mechanically coupled to said prism and adapted to establish vibration therein in a mechanically resonant vibration mode; a reference signal oscillator including said elasto-optic light beam deflector as its frequency-determining element, for causing periodic lateral deflection of said light beam relative to said record track; means including a photoreceptor responsive to said light beam for developing an output signal including an amplitude modulation component representative of deviations of said periodically laterally deflected light beam from a centered relationship to said record track; a quadrature phase corrector coupled to said reference signal oscillator for developing a phase-shifted reference signal; means coupled to said photoreceptor for deriving said amplitude modulation component; and a synchronous detector coupled to said phase corrector and to said last-mentioned means and responsive to said phase-shifted reference signal and to said amplitude modulation component for developing a radial tracking error correction signal.