| 摘要 |
PURPOSE:To reduce end point position fluctuation of guided optical wave caused by the fluctuation of the light source wave length, prevent the reduction in detection efficiency of Fo signals and to improve an S/N by using a guided wave path mirror in a guided wave path conversion element. CONSTITUTION:Light beams reflected by guided wave mirrors 7a and 7b are detected by photodetectors 8a and 8b. When a magneto-optical information recording medium 5 is located at a focus position against an objective lens 4, each element is placed so that the reflected beams from the mirrors 7a and 7b are converged at the center of the detectors 8a and 8b. Outputs Pa and Pb of the detectors 8a and 8b are adjusted to be made equal and Fo signals are obtained as the difference of these outputs. The signals become smaller than zero if the medium 5 moves away from the focus of the lens 4 and have a tendency to converge compared with a focused condition, and if the medium moves toward the focus, the signals become larger than zero and have a tendency to diverge. As can be seen above, a focus signal detection section is configured by the combination of waveguides and detectors, thus, no focus position fluctuation occurs due to the wave length fluctuation of the light source and the detection sensitivity is not degraded. |
