Patent ID: 6181668
Filing Date: 2001-01-30
Classification: G02B,G11B

Abstract:
An optical pickup device for recording and/or reproducing a first optical disc having a transparent substrate (31) of a first thickness and a second optical disc having a transparent substrate (32) of a second thickness different from said first thickness, comprisingan objective lens (21) provided opposing to said first or second optical disc,a numerical aperature changing element (22, 100, 120, 130, 180, 186, 210, 215, 683, 762, 811) for changing numerical aperature of said objective lens (21) in accordance with the thickness of the transparent substrate (31, 32) of said first or second optical disc,a laser beam generator (23, 410) for selectively generating a first laser beam having a first wavelength and a second laser beam having a second wavelength different from said first wavelength,an optical system (25,263,271,300,340,350,682) for guiding said first laserbeam to a first direction, said second laser beam to a second direction different from said first direction, and guiding said first or second laser beam to said objective lens, andwherein said optical system includes a bifocal collimator lens (271, 300, 340, 350) having two focal points.