| 摘要 |
PROBLEM TO BE SOLVED: To perform synchronous detection even if a light amount for obtaining a threshold of a laser light-emitting element is low, and determine the threshold and a bias current of the laser light-emitting element with high accuracy.SOLUTION: First and second light amount detection elements 206, 214 are arranged on a scanning line of a laser beam. The first light amount detection element 206 receives a laser beam having a first light amount Pa, and the second light amount detection element 214 receives a laser beam having a second light amount Pb that is lower than the first light amount Pa. The detection signal that is output by the second light amount detection element 214 is amplified by an amplifier 403 and used as a synchronization signal BD2. Here, an amplification factor G2 of this amplifier 403 is greater than an amplification factor GI of another amplifier 402 for amplifying the detection signal that is output by the first light amount detection element 206. The detection signals amplified by the amplifiers 403 are modified by a modification coefficient that correspond to the amplification factors G1, G2, and used as signals that indicate the light amounts. |
