| 摘要 |
PURPOSE:To reduce the loss of signal received light quantity to the stagnation of a dust and a stain, etc., and to stably detect a signal by deviating and arranging a photodetector from a lens focusing position and defocusing a converged beam on the surface of the photodetector. CONSTITUTION:After a laser beam 4 reflected from a disk transmits through the optical element 1 of a beam splutter, etc., and a lens 2, converges to the photodetector 3. In such a case, the photodetector 3 is arranged a little to the lens from the focusing position 2a of the lens 2. In such a state, since the diameter of the laser beam on the cover glass 3a of the photodetector 3 is larger than the same by conventional technique, the loss of the receiving light quantity to the stagnation of a dust and a stain, etc., is reduced and the signal is detected stably. |
