Fig. 1. Coherent detection system based on phase modulation

Fig. 2. Receiving principle of coherent detection system with different modulation frequency. (a) R_F=2R_S; (b) R_F=R_S

Fig. 3. Constellation diagrams of received signal with different Δf. (a) Δf=0 GHz; (b) Δf=3.5 GHz; (c) Δf=5 GHz

Fig. 4. Simulation block diagram of coherent detection system

Fig. 5. Frequency spectrum of received signal

Fig. 6. Influence of GSOP algorithm under different Δf on system BER

Fig. 7. Sensitivity penalty versus Δf for B2B transmission

Fig. 8. Influence of laser linewidth on BER. (a) Δf=0 GHz; (b) Δf=2 GHz

Fig. 9. Performance comparison based on EML and MZM systems with different Δf. (a) BER curve; (b) constellation diagram

Fig. 10. BER curves for different transmission distance. (a) Without Δf; (b) with Δf

Fig. 11. Performance comparison between our scheme and traditional coherent detection scheme. (a) BER curves for B2B transmission; (b) sensitivity penalty curves with different Δf

Fig. 12. BER performance of single PD receiving system under different LO optical powers

Fig. 13. BER performance of single PD and single BPD receivers