LIGHT TRANSMITTER

摘要

PROBLEM TO BE SOLVED: To send out stable optical signals even when an operating point fluctuates in an MZ external modulator. SOLUTION: The MZ external modulator 12 intensity-modulates and outputs CM light inputted from a laser beam source 11 by input signals from which DC components are removed through a capacitor 13. A low frequency oscillation means 14 generates the low frequency signals of a prescribed frequency and an addition means 15 superimposes the low frequency signals to a bias voltage and applies it to the MZ type external modulator 12. The output optical signals (amplitude modulated optical signals) of the MZ external modulator 12 branched in a photocoupler 18 are converted to electric signals in an optic/electric conversion means 19, the DC components are removed in a DC component removal means 20, an envelope is detected in an envelope detection means 21 and the phase of the low frequency signals is compared in a synchronization detection means 22. An integration means 23 integrates the output signals of the synchronization detection means 22 and corrects the bias voltage to be applied to the MZ external modulator 12.