Patent ID: 7986595
Filing Date: 2011-07-26
Classification: G11B

Abstract:
1. An optical pickup configured to perform recording and/or playback of information by selectively irradiating a corresponding wavelength optical beam as to a first optical disc having a protection layer formed with first thickness, a second optical disc having a protection layer formed with second thickness which is thicker than said first thickness, and a third optical disc having a protection layer formed with third thickness which is thicker than said second thickness, said optical pickup comprising: a first emission unit configured to emit a first-wavelength optical beam corresponding to said first optical disc; a second emission unit configured to emit a second-wavelength optical beam which corresponds to said second optical disc, the second wavelength being longer than said first wavelength; a third emission unit configured to emit a third-wavelength optical beam which corresponds to said third optical disc, the third wavelength being longer than said second wavelength; a condensing optical device configured to condense each of said first-wavelength through third-wavelength optical beams on a corresponding optical disc signal recording face; a divergence angle transformation device disposed in an optical path between said first through third emission units and said condensing optical device, configured to move in an optical axis direction, and configured to transform divergence angles of said first-wavelength through third-wavelength optical beams according to a moved position of the divergence angle transformation device in the optical axis direction so as to obtain a corresponding predetermined divergence angle; a detector having a common light receiving unit configured to receive return optical beams of said first-wavelength through third-wavelength optical beams reflected from corresponding optical discs, the detector having a light receiving point positioned in an axis which extends through a center of the divergence angle transformation device, and the detector being positioned at a different position than positions of the first, second, and third emission units; and a multi lens configured to transform the divergence angles of said first-wavelength through third-wavelength optical beams of said return optical beams to condense the return optical beams on said light receiving unit, the multi lens being provided between said divergence angle transformation device and said light receiving unit, wherein said condensing optical device is configured to condense said first-wavelength optical beam of which the divergence angle has been transformed into approximate parallel light by said divergence angle transformation device on a signal recording face of said first optical disc, condense said second-wavelength optical beam of which the divergence angle has been transformed into diffusion light with a corresponding predetermined divergence angle by said divergence angle transformation device on a signal recording face of said second optical disc, and condense said third-wavelength optical beam of which the divergence angle has been transformed into diffusion light with a corresponding predetermined divergence angle by said divergence angle transformation device on a signal recording face of said third optical disc, and said divergence angle transformation device and said multi lens are configured such that a material dispersion 1/νcl of a material making up said divergence angle transformation device, and a material dispersion 1/νml of a material making up said multi lens satisfy a relational expression of (νml/νcl)≦1.