| 摘要 |
PURPOSE:To discriminate accurately a photo signal level when arrival of a reference signal stops due to the break, etc., of a reference-signal optical fiber, by storing a memory with the level of the reference signal to be transmitted together with a photo signal. CONSTITUTION:A reference signal of a constant level is sent out from transmitter 1 through optical fiber F1 while photo signals are also sent out from transmitters 2- n through optical fibers F2-Fn, and the reference signal is converted into a constant-level electric signal by reception part 1'. Through LPF, this electric signal is applied to A/D converter AD, whose output is stored in memory M and also applied to D/A converter DA through switch SW, and an output converted into an analog signal is applied to comparators CON2-CONn. Further, photo signals are converted by receivers 2'-n' into electric signals, which are compared by comparators CON2-n with the reference signal. When no reference signal arrives from optical fiber F1, switch SW is put into operation by the output of comparator CON1 to discriminate the photo signal levels by the output of memory M. |
