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

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

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

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

5. −90° h v I

6. −90°
Splitter
DSP
Output
Bit encoding

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

8. PBS LO 
−90°  + −
Sampler / DSP

9. Dual-Polarization Down-ConverterLO
p(t)
t=mT
Dual-Polarization Down-Converter
Digital Equalizer
Symbol Decision Σ + −

10. Digital Coherent Receiver
TX Laser
Receiver
Channel
MZ #1
PBS
MZ #2
LO Laser
Digital Coherent Receiver LO
Signal
FF Phase Estimator 
Symbol Decision
Soft Phase Estimator

11. … … ○ ● □ ■

12.  Dual-Polarization Down-Converter DD Avg. LO

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

14. PBS
−90°
Pol. Rotate

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

16. Soft Phase Estimator
Symbol Decision
Decision
Decision

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