| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical detector of the optical scanning device which is hardly affected by w foreign matter present at the photodetection part of the optical detector by providing the photodetection part off the focus of laser light. SOLUTION: Scanning laser light from a polygon mirror after having its beam diameter widened by an Fθlens is converged again and sent out and the laser light L1 which is sent to a mirror is reflected by the mirror and sent to an optical detector (BD sensor) 8. Here, the BD sensor 8 detects it and generates a write-out signal for the laser light to a nonscanning surface. Here, the photodetection surface 81a of the SD sensor 8 is provided off the focus P of the laser light L1 and the longitudinal diameter of the laser light L1 on the photodetection surface 81a is made large. In this constitution, the majority of the laser light L1 is sent in the DB sensor 8 even of part of the laser light L1 is disturbed accidentally by a foreign matter such as dust sticking on the photodetection surface 81a of the DB sensor 8, so that the laser light L1 is detected.
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