Comparison of Bit-Loading DMT and Pre-Equalized DFT-Spread DMT for 2-km Optical Interconnect System

In this paper, we experimentally compared the performance of bit-loading discrete multi-tone (DMT) and pre-equalized discrete-Fourier-transform spread (DFT-Spread) DMT in intensity modulation with direct detection (IM/DD) system for 2-km optical interconnect for the first time. Pre-equalization is applied to compensate the high-frequency power fading in wideband communication system. However, it remains to be verified whether zero-forcing (ZF) channel estimation based complete pre-equalization can achieve the best performance for system with serious high frequency fading. In an IM/DD system with 120 Gbit/s data rate, we demonstrated that the bit error rate of DFT-Spread DMT signal with optimized quadratic curve fitting based partial pre-equalization outperforms ZF based complete pre-equalization after 2-km standard single mode fiber (SSMF) transmission. What's more, we experimentally compared the performance of pre-equalized DFT-Spread DMT and Chow-Cioffi-Bingham (CCB) algorithm-based bit loading DMT. The results show that the receiver sensitivity of pre-equalized DFT-Spread DMT is improved by 2.5 dB compared with CCB algorithm-based bit-loading DMT at hard decision forward error correction threshold of 3.8 × 10 -3 after 2-km SSMF transmission.