Patent ID: 6781945
Filing Date: 2004-08-24
Classification: G11B

Abstract:
An optical head comprising:a laser source for irradiating a laser beam having a wavelength not longer than 500 nm; a collimator lens for collimating the laser beam to the parallel rays; an optical beam shaping system for adjusting a cross sectional shape of the laser beam from the collimator lens; and an objective lens for converging the laser beam on an optical information medium. wherein a relationship between a focal length fCL of the collimator lens and a magnification M of beam shaping satisfies the following equation: ASO&GreaterEqual;(CfCL)2&it;arcsin&af;[(M-1)(n2&it;M-1)]wherein C is a constant not smaller than 29 and no greater tan 33 in (&lgr;Â·mm)1/2, ASO is a maximum astigmatism per displacement of the collimator lens from the focal position, and n is a refractive index of a member of the optical beam shaping system.