Improving the Nonlinear Tolerance of Polarization-Division-Multiplexed CO-OFDM in Long-Haul Fiber Transmission

We present digital signal processing techniques and algorithms for improving the tolerance of polarization-division multiplexed (PDM) coherent optical orthogonal frequencydivision multiplexing (CO-OFDM) to fiber nonlinear effects, in both single-channel and wavelength-division multiplexed (WDM) transmission. 

For single-channel transmission, we discuss a selfphase modulation (SPM) compensation method that jointly processes two polarization components of a PDM CO-OFDM signal. For WDM transmission, we describe a novel OFDM channel estimation scheme that reduces the cross-phasemodulation (XPM) penalty among the WDM channels. 

The nonlinear tolerance improvements enabled by these signal processing techniques are quantified through numerical simulations for both dispersion-unmanaged and dispersionmanaged long-haul optical fiber transmission with 112-Gb/s PDM CO-OFDM wavelength channels.