| 摘要 |
PURPOSE:To conduct focusing with high accuracy and to obtain a tracking error signal and an RF signal by providing a quadripartite detector so that a reflected beam from a medium passing through a lambda/2 wavelength plate, a detective lens is converged on the back and forth of a focus by a PBS. CONSTITUTION:The reflected beam passing through the lambda/2 wavelength plate 6, the PBS 3 is incident on the quadripartite detectors 1, 2 provided on the back and forth of the focus of the detective lens 4 respectively. In the detector 1, the center of the reflected beam is placed on light receiving parts B, D side and the +1st order beam of the reflected beam is placed on the light receiving parts C, D side and the -1st order beam is placed on the light receiving parts A, B side and further, in the detector 2, the center of the reflected beam is placed on the light receiving parts a, c side and the +1st order beam of the reflected beam is placed on the light receiving parts a, c side and the -1st order is placed on the light receiving parts c, d side. Thus. a focusing error signal is obtained as (A+C+a+c)-(B+D+b+D), the track error signal is obtained as (C+D+a+b)-(A+B+c+d) and the RF signal is obtained as (A+B +C+D)-(a+b+c+d). |
