Experimental demonstration of low-complexity trigonometric-memory-polynomial decision-feedback equalizer for nonlinear compensation in IM/DD optical systems.

We propose a simple but high-performance trigonometric-memory-polynomial decision-feedback equalizer (TMP-DFE) to cope with the nonlinear distortions in intensity-modulation direct-detection (IM/DD) systems. The proposed method employs sine and cosine operations of received samples, which can be implemented by the efficient CORDIC algorithm using only additions and shifts, to fit odd- and even-order nonlinearities with the effect of different nonlinear orders adjusted by the nonlinear factor. We further propose TMP improved-weighted DFE (TMP-IWDFE) to reduce the error propagation probability of decision feedback. We experimentally evaluate the performance of the proposed schemes in a C-band Erbium-doped-fiber-amplifier-free 56-80Gbit/s four-level pulse-amplitude-modulation (PAM-4) IM/DD system over 30-50 km standard single-mode fiber (SSMF) transmission. The results show that TMP-DFE exhibits better bit error rate performance than Volterra decision-feedback equalizer (V-DFE), diagonally-pruned V-DFE (DP-V-DFE), and diagonally-pruned absolute-term V-DFE (DPAT-V-DFE) while only requiring real multiplications 20.04%, 43.25%, and 74.12% of these conventional schemes. TMP-IWDFE further improves the performance and is better than V-IWDFE, DP-V-IWDFE, and DPAT-V-IWDFE in terms of both performance and complexity. Therefore, the proposed schemes have great potential for high-performance and low-cost IM/DD optical transmission systems.