| 摘要 |
PURPOSE:To secure the monitor for the transmission quality by measuring the extinction ratio of the optical output signal in the optical digital transmission system based on the mean value rectifying output of the input pulse and that of the modulated optical output. CONSTITUTION:Semiconductor laser 2A is driven by digital pulse input given from driving circuit 1 and then generates the optical output according to the input. Part of the optical output is received at photo diode PD4, and this output is rectified through mean value rectifier circuit 5 to obtain mean value signal (a) corresponding to the optical output. Then part of the driving signals of circuit 1 is rectified through mean value rectifier circuit 6 to obtain mean value signal (b). Signals (a) and (b) are then compared with signal (c) voltage-divided by resistances R1 and R2 via operational amplifier 8 in amplifier circuit 7, and R2 is controlled so that output V of amplifier 8 may be zero. After this, the mark factor of the input pulse of circuit 1 is varied to prevent variation of output V into 0. At the same time, resistance R4 is controlled so that voltage V may have no change although the mark factor may be changed. In that case, output voltage VO is proportional to the extinction ratio of the laser, and thus the extinction ratio can be monitored under the operation state. |
