Fig. 1. Coherent receiving system based on digital signal processing

Fig. 2. Block diagrams of phase recovery algorithms. (a) VVPE algorithm; (b) BCPE algorithm

Fig. 3. Structure of parallel tree estimator

Fig. 4. BER performance versus E_b/N₀ using different phase estimation algorithms and partial constellation diagrams. (a) BER performance; (b1) constellation diagram of VVPE (E_b/N₀=2 dB); (b2) constellation diagram of BCPE (E_b/N₀=2 dB); (b3) constellation diagram of VVPE (E_b/N₀=7 dB); (b4) constellation diagram of BCPE (E_b/N₀=7 dB)

Fig. 5. Carrier phase estimation after unwrapping. (a) VVPE (E_b/N₀=2 dB); (b) BCPE (E_b/N₀=2 dB); (c) VVPE (E_b/N₀=7 dB); (d) BCPE (E_b/N₀=7 dB)

Fig. 6. Noise phase variance versus E_b/N₀ using different phase estimation algorithms

Fig. 7. Statistical distributions of noise phase. (a) E_b/N₀=2 dB; (b) E_b/N₀=7 dB

Fig. 8. BER performance versus Δν×T_s using different phase estimation algorithms

Fig. 9. BER performance versus average filter length using different phase estimation algorithms

Fig. 10. Experimental setup for 2.5 GBaud/10 GBaud QPSK system

Fig. 11. BER performance versus received optical power using different phase estimation algorithms. (a) Δν·T_s=4×10^-5; (b) Δν·T_s=1×10^-5

Fig. 12. Performance of fixed-point algorithm. (a) Comparison of the performance of fixed-point algorithm at different input signal bits under Matlab; (b) comparison of the performance of fixed-point algorithm between Matlab and Verilog