| 摘要 |
PURPOSE:To avoid the generation of a transient DC bias on the reception signal output and to improve the transmission efficiency by transmitting the optical output of a DC level equivalent to the mean value of the optical output obtained during the transmission of an optical modulation signal when said modulation signal is cut off. CONSTITUTION:Diodes 7 and 9 and resistances 8 and 10 are added to an optical transmission circuit. When the transmission request signal is off, the voltage of a point A is set at (VOH+VOL)/2 by a power supply V through the diode 9 and resistances 8 and 10. Then a light emitting element 1 transmits the optical output of Pr/2 at a DC level, and a V1H/2 DC bias is produced at a preamplifier 5 of the reception side. When the transmission reception signal is turned on, the diode 9 is adversely biased. Then the output signal of a gate 3 is outputted to the point A, and the optical modulation signal is transmitted. Then the corresponding electric signal is outputted from the amplifier 5 and its bias is set at V1H/2 equal to the level obtained when the transmission request signal is off. Therefore the variance of the DC bias is eliminated, and no transient DC bias is produced to the reception signal output. |
