| 摘要 |
<P>PROBLEM TO BE SOLVED: To correct a spherical aberration caused by the thickness error of a light-transmissive protection film formed between the laser beam incident surface of an optical disk to a signal recording surface when irradiating the signal recording surface of the optical disk with 3 beams. <P>SOLUTION: After carrying out photoelectric conversion of light quantity of returned light of a main beam reflected by the signal recording surface 11b of the optical disk 11 by a four-block type photo detector 33M and carrying out photoelectric conversion of the light quantity of each returned light of a pair of sub beams reflected by the signal recording surface 11b by a pair of two-block type optical detectors 33S1 and 33S2, a main beam offset voltage value and a sub beam offset voltage value are obtained by calculation, and liquid crystal element driving voltage corresponding to a coincident voltage value where the main beam offset voltage value and the sub beam offset voltage value are coincident with each other is applied to a liquid crystal element 25. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
