Towards Linearizing Fiber Links with Tailored Nonlinearity and Optical Phase Conjugation

The comparative effectiveness of different tailored nonlinearity schemes combined with optical phase conjugation (OPC) at the transmitter or receiver for improving the linearization of both unrepeatered and multi-span long distance fiber links is presented. Measurements show pre-distorting the signal in ∼60 km of standard fibers plus Raman amplification generally enables greatest compensation of the link's nonlinear distortion, however, a shorter ∼10 km long dispersion compensation fiber (DCF) is similarly beneficial and even superior for a Raman amplified unrepeatered fiber link. The DCF at the receiver also effectively replicates the main nonlinear distortion in 2000 km of dispersion-managed fiber (25×80 km spans) in only a fraction of the distance (0.5%) and extends the transmission reach by 56% from 16×80 km (1280 km) compared to no OPC in case of WDM 5×12 Gbaud dual polarization (DP) 16-QAM signals. This compares to ∼80% reach extension for predistortion in a 59 km Raman amplified fiber, which boosts the Q²-factor by 2.6 dB at 4.5 dB higher launch power compared to no OPC. The DCF also enables close to the ∼19% reach extension achieved for a 224 km unrepeatered fiber link via predistortion in Raman amplified fibers enabling 3.8 dB Q²-factor increase at 5 dB higher launch power for WDM 5×8 Gbaud DP 16-QAM signals. Transmitter side OPC is also shown to outperform the use of forward Raman amplification for unrepeatered links and calculations indicate that a DCF with same sign dispersion slope with wavelength as for the link can favor broadband wavelength insensitivity. Although a performance ceiling prevents further improvement from more optimally tailored nonlinearity as predicted by simulations, tailored nonlinearity combined with OPC outside the link still proves largely effective.