Patent ID: 6181491
Filing Date: 2001-01-30
Classification: G11B

Abstract:
An optical head device comprising:a light source emitting a light beam;a converging optical system converging said light beam emitted from said light source to an information recording medium on which information is recorded; anda holding means maintaining a constant distance between said information recording medium and said converging optical system, and satisfying the following equations 1, 2, 3, and 4:L2=f.times.L1/(L1-f) (equation 1)h<L2 (equation 2).DELTA.z=.lambda./(2.pi..times.NA.times.NA) (equation 3)h<L2-.DELTA.z (equation 4)wherein f denotes a focal length of said converging optical system;L1 denotes a distance between said light source and a first principal point located on a light source side of said converging optical system;h denotes a distance between a second principal point located on an information recording medium side of said converging optical system and said information recording medium held by said holding means;.lambda. denotes a wavelength of said light beam emitted from said light source; andNA denotes a numerical aperture on the information recording medium side of said converging optical system.