Patent ID: 7876659
Filing Date: 2011-01-25
Classification: G11B

Abstract:
1. An optical pickup comprising: a first laser light source for emitting an optical beam of a first wavelength; a second laser light source for emitting an optical beam of a second wavelength longer than the first wavelength; an objective lens for focusing the optical beams of the first and second wavelength on the information-recorded surface of an optical disc; a detector for receiving the optical beams of the first and second wavelength reflected on the information-recorded surface of the optical disc; and a grating interposed between the objective lens and the first and second laser light sources for emitting the optical beams of the first and second wavelength to split each of the optical beams of the first and second wavelength into at least one main optical beam and two sub-optical beams; wherein the grating is so configured that a first grating pattern area for splitting the optical beam of the first wavelength and a second grating pattern area for splitting the optical beam of the second wavelength are arranged in a single plane; wherein the first and second grating pattern areas have a predetermined grating groove depth and a predetermined duty factor; wherein the first grating pattern area of the grating is larger than the second grating pattern area of the grating; and wherein the relation η≦0.83 holds, where η is the ratio between the light quantity of the optical beam of the first wavelength incident to the grating and the light quantity of the main optical beam of the first wavelength obtained from the incident optical beam split by the grating.