OPTICAL TRANSMITTING APPARATUS, OPTICAL RECEIVING APPARATUS, AND OPTICAL COMMUNICATION SYSTEM COMPRISING THEM

摘要

PROBLEM TO BE SOLVED: To provide a configuration in which phase shifting, DC drift, and so forth can be appropriately controlled in an optical transmitting apparatus including a phase modulator.SOLUTION: A phase shift unit 12 provides a predetermined phase difference (for example, &pgr;/2) between a pair of optical signals transmitted via arms 21 and 22 constituting a data modulation unit 20. A low-frequency signal f0 is superimposed on one of the optical signals. A signal whose phase is shifted by &pgr;/2 with respect to a phase of the low-frequency signal f0 is superimposed on the other optical signal. A pair of the optical signals is coupled, and a part of which is converted into an electrical signal by a photodiode 3. A 2f0 component contained in the electrical signal is detected. Bias voltage provided to the phase shift unit 12 is controlled by feedback control so that the 2f0 component becomes the minimum.