| 摘要 |
PURPOSE:To obtain a device which has symmetry property, is small-sized, lightweight and high in the performance by providing the diffraction grating having the brazing characteristic between a light source and a convergent lens, dividing the return light from the recording support with the diffraction grating, guiding it to a photodetector and obtaining a photodetecting signal. CONSTITUTION:A diffraction grating 3' is constituted to have a brazing characteristic, the light generated from the arranging point D of a semiconductor laser 7 is diffracted by the diffraction grating 3', and the optical spot is formed only at two points A and B on a recording support 1. Out of these, the reproducing signal by the light modulated in the point A of the recording support 1 is a correct signal, and the reflecting light is diffracted by the diffraction grating 3', and arrives at the position F of a detector 6 and the arranging point D of the semiconductor laser 7. On the other hand, the light, which is not diffracted by a diffracted grating 3 due to the return light modulated in the point B (on the other track) of the position a little separated from a correct spot position A, arrives at a position E not provided with the detector 6 and the arranging point D of the semiconductor laser 7. Consequently, only the return light from a correct spot position A arrives at the detector 6. |
