Joint mitigation of laser phase noise and fiber nonlinearity for polarization-multiplexed QPSK and 16-QAM coherent transmission systems

Mohamed Morsy-Osman,David V Plant,Qunbi Zhuge,Lawrence R Chen

doi:10.1364/oe.19.00b329

Abstract

We propose the use of pilot-aided (PA) transmission, enabled by single-sideband-subcarrier modulation of both quadratures in the DSP-domain, in single-carrier systems to mitigate jointly laser phase noise and fiber nonlinearity. In addition to tolerance against laser phase noise, we show that the proposed scheme also improves the nonlinear tolerance of both polarization-division-multiplexed (PDM) QPSK and 16-QAM coherent transmission systems by increasing the maximum allowable launch power by 1 dB and 1.5 dB, respectively. The improved nonlinear performance of both systems also manifests itself as an increase in the maximum reach by 720 km and 480 km, respectively. Finally, when digital-to-analog converters (DACs) with lower bit resolutions are used at the transmitter, PA transmission is shown to preserve the same performance improvement over the non-PA case.

Highlights

Coherent detection combined with M-ary quadrature amplitude modulation (M-QAM) has emerged as a promising candidate in future optical transport systems because it meets the ever-increasing need for high spectral efficiency [1,2,3,4,5,6,7,8,9,10]
Laser phase noise (PN) can be mitigated by carrier recovery (CR) techniques with optical signal-to-noise ratio (OSNR) penalties depending on the transmitter (Tx) and receiver (Rx) laser linewidth-to-symbol rate ratio [13]
We propose the use of PA transmission in single-carrier (SC) systems to mitigate jointly both laser PN and fiber NL impairments

Summary

Introduction

Coherent detection combined with M-ary quadrature amplitude modulation (M-QAM) has emerged as a promising candidate in future optical transport systems because it meets the ever-increasing need for high spectral efficiency [1,2,3,4,5,6,7,8,9,10]. Enabled by high speed digital-toanalog converters (DACs) [11] and analog-to-digital converters (ADCs) [12] that can operate at speeds commensurate with optical line rates, a DSP-based coherent transceiver can pre-compensate or post-compensate transmission impairments by processing the in-phase and quadrature (I and Q) signals on both polarizations [3,4,5]. Other variants of BPS were more recently proposed in [18,19,20] to reduce the computational complexity while maintaining the excellent performance; these techniques are still quite complex and only mitigate laser phase noise and not fiber nonlinearity (NL) These NL impairments caused by fiber Kerr effect are still a problem in long-haul transmission systems since they limit the maximum allowable launch power, which in turn reduces the maximum achievable system reach. We show that PA transmission can still provide the same performance improvement when a DAC resolution of 4 or 5 bits is assumed

Proposed pilot-aided transmission system architecture and concept

Simulation results and discussion

Findings

Conclusion