PURPOSE: To attain light weight and ease of positioning by forming a face where a crystal having double refraction is stuck to a polarized optical beam splitter as a polarized light separating face and setting the polarized light separating face to a critical angle to a reflected parallel light.
CONSTITUTION: The polarized optical beam splitter consists of a triangular prism part 4a and a quadrangular prism part 4b, and they are tiled respectively with the polarized light separating face 13. A vertex angle θ of the triangular part 4a is in parallel with an optical axis 16 and set to an angle so that a light being the S polarized light in the direction of polarization is reflected totally at the critical angle. The parallel light transmitted through a collimator lens 3 is transmitted through the polarized light separating face 13 of the polarized beam splitter 4 without being reflected thereupon, made incident to a 1/4-wavelenght plate 5, becomes a circularly polarized light and is collected on the face of a disc 7 by means of an objective lens 6. A focusing error signal is obtained through the change in the reflectance in the vicinity of the critical angle by using a Foster prism in this way.
SAEKI RIICHI
TAKEI TOSHIO
