Photoelectric information and focus detector

Claim 1

Apparatus for reading information stored in a track pattern on a radiation reflecting record comprising: a source of radiation for supplying at least a reading beam; a diffraction grating disposed in the optical path of said reading beam for providing at least at zero order beam component and a pair of first order bean components; an objective lens means for passing said reading beam components to said record and for controllably focusing said reading beam components at a plane of focus; a photodetector array disposed in an optical path which includes said objective lens means, said photodetector array comprising a unitary data photodetector disposed for impingement thereon of said zero order reading beam component for sensing said stored information and at least first and second paired photodetector arrays adjacent to said data photodetector, said paired photodetector arrays including separated sectors disposed along an axis including said data photodetector for sensing relative differences of said first order beams impinging on said sectors of each pair to provide at least focus error correction signals to said objective lens means; and means provided in the optical path between the focal plane of said objective lens means and said photodetector array for providing a first portion of said reading beam components which has a minimum size greater than the separation between the ones of said pairs of photodetectors and a second portion of said reading beam components which varies substantially linearly in size as said record deivates from said plane of focus.