Patent ID: 7746736
Filing Date: 2010-06-29
Classification: G11B

Abstract:
1. An optical head, comprising: a light source for radiating laser light an objective lens for focusing the laser light that is radiated from the light source onto an information recording medium; light splitting device for spatially dividing the laser light that is reflected by the information recording medium and that passes through the objective lens into a plurality of light fluxes; a light receiving element for receiving the plurality of light fluxes divided by the light splitting device; tracking error signal detection part for detecting a tracking error signal based on the plurality of light fluxes received by the light receiving element; and spherical aberration detection part for detecting spherical aberration that occurs between the radiation of the laser light from the light source and the focusing of the laser light onto the information recording medium, based on the plurality of light fluxes received by the light receiving element; wherein the light splitting device has seven regions that are divided by first and second splitting lines arranged in parallel that are substantially perpendicular to the longitudinal direction of the information track formed on the information recording medium and are substantially symmetrical about the optical axis of the objective lens, a third splitting line that is circular, positioned between the first and second splitting lines and centered on the optical axis of the objective lens, a fourth splitting line that is substantially perpendicular to the first splitting line, the fourth splitting line taking a first point on the third splitting line as a starting point, and a fifth splitting line that is substantially perpendicular to the second splitting line, the fifth splitting line taking a second point on the third splitting line as a starting point; wherein the tracking error signal detection part generates a first push pull signal by calculating signals detected by receiving light fluxes created by laser light passing through those two of the seven regions that are disposed on the outer side of the third splitting line and between the first and second splitting lines, and generates a signal for correcting the offset of the first push pull signal caused by movement of the objective lens, by calculating signals detected by receiving light fluxes created by laser light passing through four regions, of the seven regions, that are disposed on the outer side of the first and second splitting lines; and wherein the spherical aberration detection part compares a first focal point shift amount obtained by detecting changes in the shape of a light spot that is focused on the light receiving element by applying an astigmatism to light fluxes created by laser light passing through a region on the inner side of the third splitting line, and a second focal point shift amount obtained by detecting changes in the shape of a light spot that is focused on the light receiving element by applying an astigmatism to light fluxes created by laser light passing through the entire region of the light splitting device, to generate a spherical aberration error signal for detecting the spherical aberration generated between the radiation of the laser light from the light source and the focusing of the laser light onto the information recording medium.