Optical reproducer

Abstract

Abstract PURPOSE:To obtain a correct tracking error signal as well as a focus error signal from a photodetector, by constituting a transparent parallel flat plate with the 1st and the 2nd areas split with a plane including an optical axis in symmetry with the optical axis into plural areas and having different optical thickness so as to make the positioning of an optical element to the photodetector easy. CONSTITUTION:Notches 7'a, 7'c having a 1/4 of 90 deg. of center angle are formed in point symmetry to a transparent parallel flat plate 7, the air layer at the inside is taken as regions 7a, 7c of the 1st and the 3rd quadrant, and the other part is taken as the regions 7b, 7d of the 2nd and the 4th quadrant. The optical thickness of a light transmitting medium is a physical thickness multiplied with the refractive index of the medium. Thus, the 1st and the 3rd regions 7a, 7c of the transparent parallel flat plate 7 and the 2nd and the 4th regions 7b, 7d are made different from the physical thickness or the refractive index of the medium. A beam 5 incident to the region 7a of the 1st quadrant of the transparent parallel flat plate 7 goes straight and passes through the image forming point M1 on the Z axis. A beam 6 incident to the region 7d of the 4th quadrant is refracted in the region 7d as shown in Figure and passes through an image forming point M2 at the other side of the image forming point M1 on the Z axis.

Inventors

• 👤 Shigeo Kubota
• 👤 重夫 久保田

Bibliographic Details