相干光通信原理.ppt

Kerr nonlinearity: Refractive index depends on signal power In the absence of dispersion, nonlinear phase shift is proportional to instantaneous power Amplifier noise leads to uncertainty in phase shift – Nonlinear Phase Noise (NLPN) Partial compensation achieved by phase de-rotation: K.-P. Ho and J. M. Kahn, “Electronic Compensation Technique to Mitigate Nonlinear Phase Noise” Signal NLPN Compensator Phase de-rotation can reduce NLPN variance by a factor of four Nonlinear Phase De-rotation 50% of mean nonlinear phase shift Nonlinear phase noise compensation occurs first (since it requires knowledge of the received amplitude only) …Linear equalization follows …Carrier recovery performed at symbol rate Integrated Coherent Receiver Symbol Decision Dual-PolarizationDown-Converter LO FF. Carrier Recovery NLPNComp. FSE Rate M/KTs Rate 1/Ts 40 Gbit/s QPSK in one polarization over 3,060 km. All-Raman amplification, electronic NLPN compensation at receiver. Experimental Results ? Alcatel TX RX SMF DCF Nspan Transmission Link SMF: α = 0.2 dB/kmD = 17 ps/nm-kmγ = 0.0013 m?1W?1L = 80 km DCF: α = 0.6 dB/kmD = ?80 ps/nm-kmγ = 0.0053 m?1W?1L = 15 km EDFA: G = 12.5 dBF = 5 dB Nspan = 25 System Parameters Signaling: 50%RZ-QPSK, 1-pol.Rb = 20 Gbit/s Channel Model NLPN compensated yielded no performance gain compared to linear equalization only. Performance of Phase De-rotation Power Profile Distance Accumulated Dispersion 1 span Distance When there is (a) perfect dispersion compensation and (b) nonlinear effects are concentrated where local accumulated dispersion is small, zero-dispersion model of NLPN is a good model, so phase de-rotation works. In general when linear and nonlinear effects are coupled, they cannot be separately compensated. Power Profile Distance Accumulated Dispersion 1 span Distance Interaction between CD and Nonlinearity Backpropagation inverts the nonlinear Schr?dinger Equation In single polarization transmission, the receiver only needs