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Abstract

An optical device for detecting focus error, tracking error and recorded data in an optical head system has a grating plate having a plurality of gratings and waveguides. The gratings are fabricated by holographic exposure of a resist layer spin-coated onto a glass substrate. The gratings include a processing grating to efficiently input couple light into the waveguide and to effect a desired change in the input coupling efficiency with defocus of a beam of light at an optical disk. The optimum pattern of the processing grating is based on the location and intensity variation of diffraction orders in the beam returning from the optical disk and appodization of the beam. Unfocused beams and large active areas of the detectors relax the tolerance for detector placement so that placement is not critical. The four focus and tracking detectors and data detector needed for complete signal processing are compactly formed on single chip.

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First Claim