| 摘要 |
PROBLEM TO BE SOLVED: To set a light spot at an optimum focal position by providing an astigmatism generating means in the light converging optical system of an optical head and changing the position of the least circle of confusion of a spot to be converged on an optical disk in an optical axis. SOLUTION: The direction of an astigmatism to be generated in a semiconductor laser 3 or the astigmatism generating means is set in the direction of 45 degrees to the radial direction of an optical disk 9 in order to correct an astigmatism. In this state, an astigmatism quantity to be generated in the semiconductor laser 3 or the astigmatism generating means is controlled so that the amplitude of a reproduced signal becomes maximum and an offset is not generated in a focus error signal. Moreover, at the initial adjustment time of an optical disk device, when the wave front aberration of a light beam from the objective lens of the optical head is measured with a wave front measuring device and it has the astigmatism of the direction of 45 degrees, the astigmatism aberration quantity to be generated in the laser 3 or the astigmatism generating means is controlled so as to correct this astigmatism. |
