Patent ID: 7339876
Filing Date: 2008-03-04
Classification: G11B

Abstract:
1. An optical system of an optical pick-up for recording data to and/or reproducing data from at least two types of optical discs including a first optical disc and a second optical disc whose recording density is higher than that of the first optical disc, comprising: a light source unit that is capable of emitting at least two light beams having different wavelengths respectively corresponding to the first and second optical discs; an objective lens that is used for respectively converging the at least two light beams on data recording surfaces of the at least two types of optical discs; and a photo detector that has a main sensor for receiving a main beam of returning light from a disc side, and sub-sensors for receiving sub-beams of the returning light from the disc side, wherein said optical system further comprises an optical surface to satisfy compatibility between the at least two types of optical discs, said optical surface being located between said light source unit and one of the at least two type of optical discs; wherein said optical surface comprises: an inner region including an optical axis of said objective lens and satisfying a numerical aperture for the first optical disc; an outer region located outside said inner region for satisfying a numerical aperture for the second optical disc; and an intermediate region that is located within said outer region at a periphery of the inner region, wherein transmissivity for a light beam having a wavelength suitable for the first optical disc in said intermediate region is lower than that in said inner region, wherein when the first optical disc is tilted by a certain minute angle with respect to a plane perpendicular to the optical axis of said objective lens during reproducing operation of the first optical disc, intensity of a portion of the returning light passed through said intermediate region is reduced on the sub-sensors of said photo detector so that the portion of the returning light does not interfere with photo detection operation of the sub-sensors.