Bias voltage control of a Mach-Zehnder optical modulator in an optical transmitter

摘要

The optical transmitter comprises a light source (2) which inputs continuous optical signal and a driving circuit (4) which inputs driving signal to an optical modulator (3) of Mach-Zehnder type. A photo coupler separates (5) a part of the output of the optical modulator (3). A photo diode (6) converts this part into electric signal. A band-pass filter (7) and a pre-amplifier (8) extract a frequency component of the driving signal contained in the electric signal. A mixer (9) conducts synchronous detection between the driving signal and the extracted frequency component. Finally, a bias voltage control circuit (12) controls a bias voltage based on a result of the phase comparison.