Fig. 1. Schematic of experiment with the same length of signal fiber link and local oscillator link

Fig. 2. Constellations of three kinds of distortion. (a) I-Q gain imbalance constellation; (b) I-Q phase error constellation; (c) I-Q amplitude uneven distribution constellation

Fig. 3. Constellation of fiber links. (a) Unequal; (b) equal

Fig. 4. (a) Constellation with cluster analysis; (b) cluster centroid constellation

Fig. 5. Distorted constellations after DSP. Constellations of (a) I-Q gain imbalance signal, (b) I-Q phase error signal, and (c) I-Q amplitude uneven distribution signal processed reference to the standard constellation; constellations of (d) I-Q gain imbalance signal, (e) I-Q phase error signal, and (f) I-Q amplitude uneven distribution signaprocessed reference to the cluster centroid constellation

Fig. 6. Estimated values of distortion with different OSNRs. (a) Estimated values of I-Q gain imbalance coefficient; (b) estimated values of I-Q phase error

Fig. 7. Estimated values of I-Q amplitude uneven distribution with different OSNRs

Fig. 8. Constellations of recieved signal with (a) equal fiber link and (b) unequal fiber link

Fig. 9. Recovery constellations of (a) I-Q gain imbalance signal, (b) I-Q amplitude uneven distribution signals, and (c) I-Q phase error signal

Fig. 10. Estimated values and theoretical values of distorted signals in different circumstances. (a) I-Q gain imbalance signal; (b) I-Q amplitude uneven distribution signals