Optical reproducing apparatus ultilizing a polarization beam splitter

Claim 1

Apparatus for reading a return light beam reflected from an optical recording medium comprising: a dual diffraction grating aligned with the return light beam having first and second, oppositely facing diffraction gratings of the same selected pitch and depth, the diffraction gratings being rotated at a selected angle with respect to one another, the pitch and depth being selected to transmit a first component of the return light beam and to diffract a second component of the return light beam, the components emerging from the dual diffraction grating at a small angle with respect to one another; a lens for focusing the first and second components of the light beam emerging from the dual diffraction grating; a photodetector array upon which the first and second components are focused by the lens, the photodetector array including a first detector means upon which one of the components is focused to generate a tracking error signal and a second detector means upon which the other of the components is focused for generating a focus error signal wherein the first detector means comprises first and second photodetector elements with an interface therebetween oriented in a selected direction and wherein second detector means comprises third, fourth, and fifth photodetector elements, with the fourth photodetector element being juxtaposed with the third and fifth photodetector elements along parallel interfaces oriented in a second direction, the parallel interfaces being oriented with respect to the second component so that variations in the second component move parallel to the interface, providing wavelength-insensitive focus detection and the focus error signal; means for summing and differencing the output of the first and second detector means to generate a density RF signal and a M-O (magneto-optical) differential RF signal; and a quad prism disposed between the lens and the detector array, the quad prism having facets tipped about the track direction, with first and second oppositely positioned facets tipped at an equal but opposite angle to one another, a third facet tipped in the same angular direction as the first facet but at about twice the angle of the first facet, and a fourth facet tipped in the same angular direction as the second facet but at about twice the angle of the second facet, the facets dividing the first and second components into four sub-beams each, the detector array including a first array of four photodetectors for detecting the four sub-beams of the first component and a second array of four photodetectors for detecting the four sub-beams of the second component.