| 摘要 |
PURPOSE:To always obtain an excellent quenching ratio by monitoring a low frequency signal superimposed on a modulation current or a bias current of a laser diode and controlling a level of the signal to a specified level. CONSTITUTION:A clock signal is converted into a low speed rectangular wave by using a frequency divider circuit 13, a low frequency sine wave with a desired amplitude is generated by using a waveform equalization circuit 14 and an attenuator 15 and an optical output waveform having a prescribed envelope is obtained by superimposing the sine wave onto the bias current. The output waveform is reproduced as an electric signal waveform by a current voltage conversion amplifier circuit 16, and a clip circuit 17 eliminates an upper half of the waveform. A low frequency detection circuit 18 extracts the envelope from the signal, a 2nd capacitor 19 is used to smooth the envelope signal, a difference from a reference voltage is amplified by an error amplifier circuit 21 and the amplifier circuit 21 forms a feedback loop to control an output current of a current switch circuit 4. When a bias current of a laser diode 1 is set in the vicinity of an oscillation threshold current, an excellent extinction ratio is obtained. |
