Methods and devices for power imbalance compensation and calibration of a coherent transmitter or transceiver are described. A pilot tone is combined with a digital data signal such that relative amplitudes of the pilot tone in each of four transmitted optical data channels may be detected by a pilot tone detector and used to calculate any power imbalances between I/Q phase channels and/or X/Y polarized channels of the transmitter. The pilot tone detector applies gain to the data signal of the transmitter to compensate for any calculated power imbalances. Because the pilot tone is combined with the digital data signal, its amplitude in each received channel is proportional to the data signal power of that channel.