| 摘要 |
<p>PROBLEM TO BE SOLVED: To make it possible to automatically execute control in such a manner that an optical extinction ratio may be obtained with simple constitution and to make it possible to obtain always constant output light by providing the above device with a peak detector, bias setting means for setting bias voltage in accordance with the output signal from the peak detector, etc. SOLUTION: The light signal outputted from a second output terminal 15b of an external optical modulator 2 is shifted in light frequency by a frequency shifter 9 and is delayed in an optical delay device 10, following which this signal is multiplexed with the light signal from a first demultiplexer/multiplexer 3a and is converted to an electric signal from the light signal in a PD 4 to generate a beat signal. This beat signal is amplified in a preamplifier 5 and is then selectively transmitted through a BPF 6 and is peak detected by the peak detector 7. The output signal from the peak detector 7 is sent to a bias setting circuit 8. The intensity of this output signal is always detected and the bias voltage to be impressed to the external optical modulator 2 is so set that the output intensity is set always at the minimum value.</p> |
