| 摘要 |
PROBLEM TO BE SOLVED: To improve the reliability of tracking control by providing two light sources and diffraction gratings corresponding to them and driving the light sources independently of each other, and then making two light beams, which are different in wavelength from each other, nearly equal in three-spot interval and different in gradient. SOLUTION: A 1st light source 11 emits a TM-mode light beam of 635nm and a 2nd light source 12 emits a TE-mode light beam of 780nm. A 1st polarization-dependent three-beam diffraction grating 171 provides a 3-beam diffracting function only for the TM-mode light beam and the 2nd polarization- dependent 3-beam diffraction grating 172 provides a 3-beam diffracting function only for the TE-mode light beam. And, the 1st light source 11 or 2nd light source 12 is driven selectively by unillustrated driving selecting means. |
