Patent ID: 7027377

Claim:
An optical head device that converges first and second laser beams having different wavelengths through a single light converging optical system, the optical head device comprising: an objective lens composing a part of the light converging optical system, the objective lens including a refracting surface divided into a central refracting surface region with an optical axis thereof being as a center and an outer circumferential refracting surface region that surrounds an outer circumference of the central refracting surface region, and a diffraction grating formed generally entirely over the central refracting surface region, and a second diffraction grating formed over an entire area of the outer circumferential refracting surface region to diffract the first laser beam so as not to converge on a beam spot forming position of the beam spot, wherein the objective lens forms a beam spot of the second laser beam with the 1 st order diffracted beam obtained by the central refracting surface region and a 0 th order diffracted beam obtained by the outer circumferential refracting surface region, wherein the objective lens forms a beam spot of the first laser beam at the first focal distance with a 0 th order diffracted beam or a 1 st order diffracted beam obtained by the diffraction grating of the central refracting surface region, and the objective lens forms a beam spot of the second laser beam at the second is focal distance with a beam portion that passes the outer circumferential refracting surface region and a 1 st order diffracted beam obtained by the diffraction grating in the central refracting surface region, and wherein the beam spot of the first laser beam is formed at the first focal distance with the 0 th order diffracted beam obtained by the diffraction grating of the central refracting surface region.