| 摘要 |
PURPOSE:To suppress the generation of crosstalk by using a modified phase type diffraction grating with a phase type diffraction grating only to a part where the surrounding of a light beam is made incident. CONSTITUTION:The modified phase type diffraction grating 2b is used as an optical split means 2 of an optical system, a main beam 21a has a stepwise intensity distribution and the intensity distribution of a reproduction light spot 22a formed by converging the main beam onto an optical disc 10 through an objective lens 5 is that the intensity of a light ring 23 is reduced remarably. With respect to the luminous flux cross section of the main beam 21a converged by an objective lens 5, for example, the modified phase type diffraction grating 2b provided with a grating 40 with 1.5 of refractive index and lambda/2 of geometrical slot depth is used as a light split means 2, then the intensity of the light ring of the reproducing light spot 22a is reduced nearly a half or below. Thus, the crosstalk is suppressed. |
