Fig. 1. Diagram of PCTWO-UT-QPSK unrepeatered fiber communication system (inset i is transmitter DSP flowchart; inset ii is receiver DSP flowchart; inset iii is PCTWO-UT-QPSK signal frame structure)

Fig. 2. Receiver SNR varying with launch power and corresponding typical constellation diagrams. (a) Receiver SNR varying with launch power; (b) corresponding typical constellation diagrams

Fig. 3. System SNR penalty and PCTWO-UT gain under different transmission distances

Fig. 4. Nonlinear distortion and PCTWO-UT algorithm compensation at different signal rates

Fig. 5. Nonlinear distortion in fiber and PCTWO-UT compensation under different dispersion coefficients

Fig. 6. Raman-optimized unrepeatered optical communication system

Fig. 7. System link power distributions before and after Raman optimization

Fig. 8. Comparison of receiver constellation diagrams for two amplified link configurations. (a) EDFA; (b) Raman amplified link constellation diagram