Patent ID: 6151288
Filing Date: 2000-11-21
Classification: G11B

Abstract:
An optical head assembly comprising:a laser light source;an objective lens for converging a laser light emitted from said laser light source on an optical recording medium;an optical detector for detecting a returning light from said optical recording medium;a diffraction grating unit mounted in an optical path between said laser light source and said objective lens for positioning multiple diffraction grating means;a base of the optical head assembly for supporting said objective lens, said laser light source, and said optical detector; anda diffraction grating unit retaining portion formed on said base for holding said diffraction grating unit, said diffraction grating unit having a holder for positioning and holding each of said diffraction grating means, said holder having a circumferential surface which extends along an optical axis of said optical head assembly, and said diffraction grating unit retaining portion having a positioning portion for determining a mounting position of said diffraction grating unit in said optical axis direction of said optical head assembly and a guiding plane with which said circumferential surface fittingly contacts when said diffraction grating unit is turned around an axial line thereof;said multiple diffraction grating means including separate diffraction-grating optical elements;said diffraction grating unit having a common holder for positioning and holding each of said diffraction-grating optical elements, said common holder having separate positioning portions for positioning each of said diffraction-grating optical elements so that a distance between one and the other of said diffraction-grating optical elements is substantially identical and a relationship of diffraction patterns of one and the other of said diffraction-grating optical elements is also identical when said diffraction grating unit is turned around the axial line thereof.