| 摘要 |
PURPOSE:To make the titled pickup thin with simple constitution which has decreased the number of parts, by providing a 4-split photodetector for detecting reflected light which has been separated by a reflection type diffraction grating lens. CONSTITUTION:When light is made incident on the reflection type diffraction grating lens 16, converging light 19 can be converted to an astigmatic bundle having the first focal line 20, the second focal line 22 and a circle of least confusion 21, and when a 4-quadrant photodetector 14 is installed to the position of the circle of least confusion 21 of the converging light 19, an autofocus error signal is obtained. The variation of a pattern can be obtained as an output of a differential amplifier 24 which has been connected to the 4-quadrant photodetector 14, and an information signal is obtained by adding the respective outputs of the 4-quadrant photodetector 14. Accordingly, the reflection type diffraction grating lens 16 used for light pickup can be formed by drawing directly a grating pattern by an electron beam to a glass plate to which an electron beam resist has been applied, performing the post-treatment, and plating or vapor-depositing a metal such as Al, etc. on its surface. |
