| 摘要 |
PURPOSE:To extend the optical path length between a condenser lens and an optical sensor and to easily adjust the position of the optical sensor by fully reflecting a light beam focused through the condenser lens by a trapezoidal prism twice until the beam led into the focusing optical sensor. CONSTITUTION:Laser beams radiated from a light source 10 are made parallel beams by a coupling lens 12, transmitted through a polarized beam splitter 14, a 1/4 wavelength plate 16 and an objective lens 20 and converged into the recording surface of a disk 30. The reflected light reflected by the optical disk 30 is reflected to the right direction by the beam splitter 14 through the objective lens 20 and the 1/4 wavelength plate 16, converged by a condenser lens 22 and made incident upon the trapezoidal prism, a part of the output of the prism 24 is transmitted and made incident upon an optical sensor 26 and the other is reflected and guided into an optical sensor 28 to constitute a photodetecting system. The photodetecting surface part of the optical sensor 26 is divided into two parts 26A, 26B so that the sectional shape LT of the incident light beams is symmetrized about a photodetecting surface dividing lie 26C, the photodetecting surface of the optical sensor 28 is also divided into two parts 28A, 28B and their arranging positions are fixed so that the incident light beams are converged on the border part as a spot LF. |
