Patent ID: 7414951
Filing Date: 2008-08-19
Classification: G11B

Abstract:
1. An optical head device, comprising: a first light source for emitting a light having a first wavelength; a second light source for emitting a light having a second wavelength; a photo detector; a wavelength selective filter; and an objective lens, wherein: an optical system is formed by, a light emitted from said first light source is transmitted to a first optical recording medium containing a first substrate having a first thickness through said wavelength selective filter and said objective lens, a light emitted from said second light source is transmitted to a second optical recording medium containing a second substrate having a second thickness through said wavelength selective filter and said objective lens, a light reflected from said first optical recording medium is transmitted to said photo detector through said objective lens and said wavelength selective filter, and a light reflected from said second optical recording medium is transmitted to said photo detector through said objective lens and said wavelength selective filter, wherein: recording and reproducing information is executed for said first optical recording medium by using said light having said first wavelength, and recording and reproducing information is executed for said second optical recording medium by using said light having said second wavelength, wherein: the magnification of said objective lens for said light having said first wavelength is different from the magnification of said objective lens for said light having said second wavelength, and said wavelength selective filter changes a phase distribution for said light so that a spherical aberration remaining for said light having said first wavelength or said light having said second wavelength at corresponding said magnification of said objective lens is deceased.