Synchronous photodetector

Abstract

Abstract PURPOSE:To prevent the occurrence of jitters as well as to reduce an effect of dust on a photodetecting window, by providing a cylindrical lens before a photodetecting element. CONSTITUTION:A cylindrical lens Lc having a bus in the scanning direction is provided to obtain a conjugate relation between a deflecting point and a photodetecting element. At the same time, the scanning line which scans on the photodetecting surface of the photodetecting element is made to scan the same area on the photodetecting surface regardless of the fall, etc. of the reflecting surface of a rotary polyhedral mirror. As a result, the jitters due to a shift of the scanning position can be eliminated. It is allowed for a photodetecting element PD to receive the scanning light via an ftheta lens. In this case, the subject point of the lens Lc coincides with the output pupil of the ftheta lens. The beam diameter increases only in the direction vertical to the deflecting surface owing to the function of the lens Lc, and therefore, the effect due to dust, flaws, etc. can be reduced on a photodetecting window. The beam diameter can be properly set by selecting the focal distance of the lens Lc.

Inventors

• 👤 Yutaka Kaneko
• 👤 豊 金子

Bibliographic Details