| 摘要 |
PURPOSE:To detect the focus error on a basis of the output signal from a photodetector by giving the change of phase accompanied with the change of the angle of incidence of light to a reflecting face, which is caused by the focus error of a condenser lens, to the two-divided photodetector as the change of the intensity of light by a polarizing element. CONSTITUTION:An all reflecting prism APR is a rhombic prism 5. A linearly polarized light made incident on the prism 5 has a phase difference between an Ep component and an Es component by a prescribed number of total reflec tion is the rhombic prism 5 and is made incident on a polarizing plate (polariz ing element) PLP in this state. The light emitted from the polarizing plate PLP is made incident on a photodetector BD divided into two by the optical axis, and two signals outputted from two parts 6 and 7 of this photodetector PD are given to a differential amplifier SUB, and a differential signal between two signals is outputted from the differential amplifier SUB to an output termi nal 8 as a focus error signal. Thus, the change of the angle of incidence of the light incident on the all reflecting prism is detected to detect the focus error. |
