| 摘要 |
PURPOSE:To prevent a trouble due to a leaked laser beam caused by a broken transmission line by applying interruption control of the laser beam depending on the result of deciding the optical level of a received modulated laser beam and the result of deciding the presence of an extraction clock. CONSTITUTION:An optical level deciding device 25 applies the mean value detection of an output signal of an automatic gain control (AGC) amplifier 23, compares an obtained mean voltage with a 1st prescribed reference voltage to decide a laser beam level and to generate an optical level deciding signal, it is fed to an AND circuit 26. A clock level deciding device 30 detects the peak of and extracted clock, compares the obtained peak voltage with a 2nd prescribed reference voltage to decide the clock level, thereby generating a clock leave deciding signal, and it is fed to the AND circuit 26. Upon the receipt of an L level deciding signal from either the optical level deciding device 20 or the clock level deciding device 30, the AND circuit 26 generates an L level interruption control signal, it is fed optical transmitters 14, 15 from a terminal 31 to interrupt a laser beam output. Thus, the trouble due to leaked laser beam is prevented. |
