| 摘要 |
PURPOSE: To satisfactorily detect a feedback beam from an information recording medium by integrally forming 1st and 2nd diffraction grating surfaces and a light take-out surface. CONSTITUTION: An optical element 3 provided with integrally the 1st diffraction grating surface 3a, the 2nd diffraction grating surface 3b and the light take-out surface 3c is arranged between a light source 2 and the information recording medium 1, and a photodetector 5 is arranged opposite to the light take-out surface 3c. A beam emitted from the light source 2 is splitted into plural beams and transmitted by the 1st diffraction grating surface 3a, and a beam from the 1st diffraction grating surface 3a is guided to the side of the information recording medium 1, while the feedback beam from the information recording medium 1 is guided to the light take-out surface 3c by the 2nd diffraction grating surface 3b. By this method, a wave surface of the feedback beam emitted from the light take-out surface 3c is made to approach parallel with the light take-out surface 3c to reduce the impartment of undesired aberration to the feedback beam to be detected by the photodetector 5 and the occurrence of reflected light by the light take-out surface 3c, so that the feedback beam from the information recording medium 1 can satisfactorily be detected out. |
