90°

1. 1 1 4 2 2 1 3 1 90° 90° LO LO LO 4 2 2 LO 90° 90° 3

2. Signal LO PBS Single-Polarization Downconverter II Single-Polarization Downconverter I

3. Σ Σ Down-converter Loop Filter Phase Estimator Signal LO + + + −

4. Slow Axis Signal PC RX PBS PBS Fast Axis Im Im Re Re

5. v I h −90°

6. Bit encoding Splitter Output DSP −90° −90° −90°

7.    OFDM TX OFDM RX O/E Down-Conversion+Sampling AddPrefix RemovePrefix P/S S/P MZ Channel IFFT FFT Length Npre Length Npre Size Nc Size Nc LO Receiver Transmitter  Channel 

8. +  −   PBS Sampler /DSP −90° PBS LO

9. t=mT p(t) t=mT Dual-PolarizationDown-Converter DigitalEqualizer p(t) t=mT p(t) t=mT p(t) LO Symbol Decision + − Σ

10. PBS PBS TXLaser LOLaser Channel MZ #1 MZ #2 Receiver FF Phase Estimator DigitalCoherent Receiver Soft Phase Estimator Signal LO Symbol Decision 

11. … … … … ■ □ ■ □ ● ● ○ ○

12. Dual-PolarizationDown-Converter DD DD DD DD Avg. Avg. LO Dual-PolarizationDown-Converter LO  

13. PBS OFDM TX #1 OFDM TX #1 MZ MZ Dual-PolarizationDown-Converter OFDM TX #2 OFDM RX #2 LO Soft Phase Est. Dual-PolarizationDown-Converter NLPNComp. Avg. Soft Phase Est. LO Symbol Decision  TED + − Loop Filter 

14. PBS Pol. Rotate −90°

15. +  − Dual-Polarization Down-converter     LO −90° −90° Single-Polarization Down-converter Single-Polarization Down-converter LO LO Ts Ts LPF LPF

16. Decision Decision Symbol Decision Soft Phase Estimator

18. DCF PBS PBS Dual-Pol. Down-Converter Digital Signal Processor LPF Pulse Carver DataModulation TX Laser LPF Channel LO Receiver Transmitter + + Digital Signal Processor Receiver Transmitter Channel