| 摘要 |
PURPOSE:To monitor projection-side luminous flux securely by detecting laser diodes put in multiple constitution by a photodetectors composed of plural photodetecting elements through a lens. CONSTITUTION:The quantities of pieces LMA and LMB of monitor-side luminous flux of two laser diodes 2A and 2B which are photodetected by photodetecting elements 4A and 4B are converted photoelectrically into electric signals having levels corresponding to their quantities of photodetection, and they are inputted to and amplified by amplifiers 5A and 5B. Those signals amplified by the amplifiers 5A and 5B are applied to one-terminal sides of comparators 7A and 7B through LPFs 6A and 6B respectively. A reference voltage VR for reading and a reference voltage VW for writing are applied to the other-terminal sides of the comparators 7A and 7B and the amplified signals are compared with the reference voltages VR and VW and their variation components are applied to, for example, control terminals of LD driving circuits 8A and 8B. Thus, currents supplied to the laser diodes 2A and 2B are controlled with the voltages applied to the control terminals. |
