Enhanced Channel Equalizers for Adaptive Zero-Guard-Interval CO-OFDM Systems

We propose the design and implementation of frequency domain block least mean square and block recursive least square equalizers for adaptive zero-guard-interval (ZGI) coherent optical (CO) orthogonal frequency division multiplexing (OFDM) systems. We experimentally demonstrate the improvements in fiber nonlinear tolerance and channel estimation accuracy over conventional training symbol (TS)-based equalizers and data aided zero-forcing (ZF) equalizers, in single channel 112-Gb/s quadrature phase shift keying (QPSK), and 250-Gb/s 16 quadrature amplitude modulation (QAM) ZGI CO-OFDM systems. The transmission distance is increased by 20% and 7% for QPSK, and 53% and 35% for 16-QAM systems, compared with the TS-based and decision aided ZF adaptive equalizers, respectively. In addition, simulation results demonstrate the improved temporal tracking ability of the proposed algorithms over the previous ZF equalizer.