Patent ID: 7724617
Filing Date: 2010-05-25
Classification: G11B

Abstract:
1. An optical head device comprising: a twin laser light source which is integrally provided with a first laser beam emitting element for emitting a first laser beam and a second laser beam emitting element for emitting a second laser beam whose wavelength is different from a wavelength of the first laser beam; a light receiving element; and an optical system including an objective lens; wherein the optical system converges a laser beam which is emitted from the twin laser light source on an optical recording medium through the objective lens and guides return light beams of the first laser beam and the second laser beam reflected by the optical recording medium to the light receiving element; wherein the optical system is provided with a detection lens which is disposed before the light receiving element to apply astigmatic difference to the return light beams for detecting focusing error signals by an astigmatism method; wherein an optical axis of one of the return light beams of the first laser beam and the second laser beam is located on an axis of the detection lens, and an optical axis of the other of the return light beams is located off-axis of the detection lens; wherein the detection lens is a toric lens, and the toric lens applies an astigmatic difference caused by a toric face to the one of the return light beams, and the toric lens applies the other of the return light beams an astigmatic difference caused by a toric face and astigmatism composed of astigmatism and curvature of image field caused by passing off-axis position to coincide a focusing position of the return light beam of the first laser beam with a focusing position of the return light beam of the second laser beam.