| 摘要 |
PURPOSE:To attain transmission with high quality by controlling a pulse width of a digital main signal to any of T,T-DELTA1 and DELTA2 for digital supervisory signal transmis sion. CONSTITUTION:A digital main signal (a) is inputted from a terminal 15 and a digital supervisory signal (b) is inputted from a terminal 17 and a clock signal is inputted from a terminal 17 to a pulse width selection circuit 18 selectively. The circuit 18 transmits each pulse of a pulse width T when the signal (a) is logical 1 and the signal (b) is logical 0, of a pulse width T-DELTA1(DELTA1<T/2) when the signals (a), (b) are logical 1, of pulse width DELTA2/T/2 when the signal (a) is logical 0 and the signal (b) is logical 1 and 0 when both signals (a), (b) are logical 0. An output of the circuit 18 drivers a light source 21 via a light source driving circuit 19 and the light output is transmitted to a photodetector 28 via an optical fiber. A part of output light of the light source 21 controls the circuit 19 via an automatic output control circuit 24 to make the output pulse constant. The element 28 converts a light signal into an electric signal and outputs a main signal to a terminal 33 via an equalizing amplifier 29 and an identification device 31. A supervisory signal is detected from the output of the identifi cation device 31 and the amplifier 29 via a subtractor, a rectifier and an LPF. |
