Patent ID: 7272083
Filing Date: 2007-09-18
Classification: G11B

Abstract:
1. An optical head device comprising: a light source; a collimator lens for converting light emitted from the light source into parallel rays; a first objective lens which condenses the parallel rays on a medium surface of an information recording medium and which puts together a first reflection light obtained by reflecting the condensed light at the medium surface and a second reflection light obtained by reflecting the condensed light at the surface of a light transmission layer formed on the medium surface; a converging lens for converging the first reflection light and the second reflection light; a first detector receiving the first reflection light converged to detect a first focal error with respect to the medium surface; a second detector receiving the second reflection light converged to detect a second focal error with respect to the surface of the light transmission layer; and a moving unit moving the collimator lens in correspondence with the detection by the second detector.