Impact of Optical Phase Conjugation on the Nonlinear Shannon Limit

Abstract

Abstract:Compensation of the detrimental impacts of nonlinearity on long haul wavelength division multiplexed system performance is discussed, and the difference between transmitter, receiver and in-line compensation analyzed. The impact of system imperfections is also outlined.OCIS codes: (000.0000) General; (000.0000) General [8-pt. type] For codes, see http://www.osapublishing.org/submit/ocis/ IntroductionThe perception of the nonlinear Shannon limit [1] is currently seen as preventing the continued smooth (exponential) increase of optical transmission throughput, resulting in a predicted capacity crunch [2]. The focus of the research community on these issues has resulted in specific international discussion meetings [e.g. 3] and even significant inducement prizes [4]. One of the earliest proposals to compensate for nonlinear impairments in an optical transmission system was the use of optical phase conjugation (OPC) [5,6]. In an OPC system, the entire signal is phase conjugated after a certain length of a transmission system. If the signal is then propagated through an identical length, subject to certain symmetry conditions, nonlinear effects and even ordered dispersive effects are reversed. If the symmetry conditions are not met, then partial compensation of the impairments is still possible [7]. Following early work on direct detection systems [e.g. 8-10] which were severely constrained by nonlinearity, recent attention has focused on the digital signal processing capabilities enabled by nested Mach-Zhender modulators [11] and digital coherent receivers [12]. However, as we approach the nonlinear Shannon limit there is renewed interest in the direct compensation of nonlinear impairments. In this paper, we review recent progress in the use of optical conjugation for the mitigation of nonlinear impairments in both serial and parallel configurations, and estimate the extent to which each technique may enable transmission beyond the nonlinear Shannon limit.