| 摘要 |
PROBLEM TO BE SOLVED: To allow an electric stage not to execute identification and regeneration and to suppress signal fluctuations due to an input signal light in both on/off states by converting the input signal light into an electric signal and applying the converted signal to a light source and an optical modulator whose modulation characteristic is set reverse to each other simultaneously. SOLUTION: A modulation signal is distributed into two, the one is given to a bias circuit 14, where a prescribed DC bias voltage Vb1 is superimposed on the signal and the resulting signal is fed to an EA modulator 15. The other is given to a bias circuit 17, where a prescribed DC bias voltage Vb2 is superimposed on the signal and the resulting signal is fed to a semiconductor laser (LD) 16. The DC voltage Vb2 is selected to be a voltage in excess of an oscillation threshold voltage of the LD 16, thus the LD 16 is oscillated and its output power is modulated by the modulation signal. In this case, the increase/decrease characteristic tendency of the modulated output power of the LD 16 is set reverse to that of the transmission rate of the EA modulator 15. Thus, the synthesized modulation characteristic of the LD 16 and the EA modulator forms a region where the output processor power is made constant regardless of the signal fluctuation due to an input signal light in both on/off states. |
