| 摘要 |
PROBLEM TO BE SOLVED: To use a 1/4 wavelength plate and a diffraction grating with low surface precision and to realize a device with large torelance for wave front aberration of other optical elements by tilting a 1/4 wavelength plate by a prescribed angle for an incident luminous flux and arranging it. SOLUTION: Reflection light by a recording surface 21 becomes return light, and transmits again through an objective lens 18 and the 1/4 wavelength plate 16 to be made incident on a polarizing beam splitter 14. At this time, the return light is separated from an optical path facing to the surface 21 from a light source LD 10. The separated return light is converged by a condenser lens 22, and is bisected by a knife edge prism 24 on the way of convergence to be made incident on tracking controlling and focusing controlling photodetectors 28, 26. At this time, the wavelength plate 16 is formed by the material quality having a refractive index n, and is arranged tilting for the incident luminous flux so that the incident angle θ of the luminous flux from the LD 10 is satisfied with |(η/cosθ)-n.η/√ 1-(sinθ/n<2> }|<λ/45 according to a wavelength λ of laser light and the surface precision η. |
