| 摘要 |
PROBLEM TO BE SOLVED: To easily adjust a position between optical elements by dividing an emission laser beam to three beams containing a 0-order beam and ± 1st-order beams, generating astigmatism, light receiving return three beams reflected by a recording surface and detecting a focusing error signal, based on the astigmatism incorporated in the ± 1st-order beams. SOLUTION: The three beams are converged on a recording track 4b formed on the recording surface 4a of an optical recording medium 4 through an objective lens 3 as light spots a, b, c. The return three beams Lr (0), Lr (+4), Lr (-1) are returned to a 1/4 wavelength plate 8 through the objective lens 3, and pass through it to be converted again to linear polarization. The return three beams are diffracted respectively to three beams when they pass through a diffraction grating 6, and the -1st-order beam Lr (-1)-1 is converged on a light receiving surface of a focusing error and tracking error signals detecting photodetector as a light spot c1. |
