| 摘要 |
PURPOSE: To detect a signal with high sensitivity by eliminating the effect of a dead band of a split photo detector and to prevent malfunction due to movement of a lens. CONSTITUTION: A tracking deviation signal and an out-of-focus signal are obtained from a luminous flux component (±1st-order light) diffracted by a hologram element 2. An RF signal is detected by utilizing a 0-order light component not subject to diffraction to only obtain the RF signal without the use of a split beam detector and magnitude of output signal is made constant even when diameter of spot is increased/decreased and position of the spot is moved. An optical system 7 correcting aberration by a half mirror 3 is arranged between the half mirror 3 and a light receiving element being a component of a photodetector 6. Even when an objective lens 4 moves, the spot moves on the light receiving element so that the detected spot on the light receiving element is not offset. |
