Fig. 1. Schematic diagram of Mth power algorithm for frequency offset estimation

Fig. 2. Schematic diagram of Mth power algorithm for phase difference estimation

Fig. 3. Schematic diagram of unwrapping phase ambiguity carrier synchronization algorithm

Fig. 4. DP-QPSK coherent optical communication simulation system

Fig. 5. Raw signal and carrier synchronization results of simulation system. (a) Raw signal; (b) X carrier synchronization result; (c) Y carrier synchronization result

Fig. 6. Carrier synchronization results of simulation signal under different frequency offsets. (a) 1.2 GHz; (b) 1.8 GHz; (c) 2.4 GHz; (d) 3.0 GHz

Fig. 7. Carrier synchronization results of simulation signal under different modulation rates. (a) 2 GBaud; (b) 5 GBaud; (c) 10 GBaud

Fig. 8. Variation of demodulation EVM value with phase difference under different frequency offsets

Fig. 9. Experimental setup of space coherent optical communication system

Fig. 10. Carrier synchronization results of experimental system signals with 2.3 GHz frequency offset under different modulation rates. (a) Raw signal; (b) 2 GBaud; (c) 5 GBaud; (d) 10 GBaud

Fig. 11. Carrier synchronization results of experimental system signals with 3.7 GHz frequency offset under different modulation rates. (a) Raw signal; (b) 2 GBaud; (c) 5 GBaud; (d) 10 GBaud