A Reliable Joint MCMA and DD-LMS for Lite DSP in Short-Reach Self-Homodyne Optical Coherent Scheme

In this paper, we propose a highly convergent joint modified constant modulus and Decision-Directed least mean square (DD-LMS) algorithm for adaptive blind polarization demultiplexing in the elastic datacenter optical networks (EONs). We compare the proposed joint algorithm with traditional constant modulus algorithm (CMA) and modified constant modulus algorithm (MCMA), in terms of performance in 840-Gbit/s dual-polarization 64QAM Self-Homodyne detection (SHD) system. The simulation result shows that the proposed joint algorithm can not only simultaneously accomplish polarization de-multiplexing and phase recovery at low bit error rate (BER) level, but also simplify DSP and reduce power consumption.

I. Introduction

Future internet traffic tends to become dynamic, heterogeneous and unpredictable due to the rapid increase of high-speed optical network with various modulation formats and diverse bitrates [1]. Standardization body has reported 800-Gb/s and 1.6-Tb/s as the potential next bit-rate step [2]. Hence, according to the Ethernet roadmap [3], aggregate throughputs of optical pluggables need to be increased by 8- or 16-fold from the current commercially available speed of 100 Gb/s. Because of aforementioned drivers and present challenges, a plethora of transmission schemes have been proposed in the recent literature that bridge the gap [4]. Some systems used intensity modulation (IM) of semiconductor lasers, and the intensity of the optical signal transmitted through an optical fiber was detected by a photodiode [5]. The IM-Direct detection scheme has a significant advantage in that the receiver sensitivity is dependent neither on the carrier phase nor on the state of polarization (SOP) of the incoming signal [6], which randomly fluctuate in real systems. In the case of coherent receivers, it can restore full-field information on optical carriers, which enhances spectral efficiency.