| 摘要 |
PURPOSE:To detect a focus position by detecting the focus position by utilizing the fact that the difference signal output of a split photodetector is inverted in phase at a focusing point where a reflector is positioned. CONSTITUTION:Divergent light from a laser 1 is converged on the reflecting surface 4 of an optical disk, etc., through a lens 3 and reflected light from the reflecting surface 4 is passed through the lens 3 again and returned to a BDLD 1 which operates as the split detector. The direction of the peak intensity of divergent light from the BDLD 1 is deflected periodically by flowing a high frequency current to divided electrodes. Divergent light 2' whose direction of the peak internsity is deflected periodically is converged on the reflecting surface 4 through the lens 3. In this case, the converged spot 2'' on the reflecting surface 4 is fixed regardless of the deflection when the reflecting surface 4 is positioned at the focusing position (b), but in phase and opposite in phase on the basis of the deflection direction when the reflecting surface 4 is at positions (a) and (c) before and behind the focusing point. Consequently, which side of the focusing point the spot is defocused to is detected from the phase of the difference signal. |
