| 摘要 |
PROBLEM TO BE SOLVED: To make a luminous flux of symmetric intensity distribution incident on a diffraction grating in the optical system of an optical head even when eccentricity is generated in a member constituting the optical system of the optical head and to obtain a prescribed diffraction state. SOLUTION: An optical system of optical head is provided with a reflection block 331 of a right-angled triangular prism having a light transmissive surface 331x, a half mirror surface 331y and a set of reflection surfaces 331a, 331b being orthogonal to each other. Even when intensity distribution of polarized luminous fluxes P1 , P'1 transmitted through a polarizing beam splitter 31 and made incident on the reflection block 331 has the eccentricity of δto the optical axis 0, the intensity distribution of the reflected luminous flux from the reflection block 331 is composed of PR reflected by the half mirror 331y and PT transmitted through it with respect to the intensity distribution of reflected luminous flux P1 and of P'R reflected by the half mirror 331y and P'T transmitted through it with respect to the luminous flux P'1 . They are made to have symmetry with respect to the optical axis 0, reflected by the polarizing beam splitter 31 through a quarter wavelength plate 32 and reach a diffraction grating 351 through a quarter wavelength plate 34. |
