Theory of dispersion loss nonlinearity and polarization mode dispersion simultaneous cancellation in WDM systems via optical phase conjugation

Abstract

Abstract Based on the theory of nonlinear Optics and phase conjugate Optics, We pointed out that in the WDM communications systems,most of effects, such as: chromatic Dispersion, loss, SRS, SPM, XPM, PMD as well as FWM can be eliminated by a device, OPC. We also showed that, for dispersion cancellation only needs the conjugated wave propagates same distance as signal wave does. However, for nonlinear effects cancellation the intensity adjustment are necessary , since they are depending on signal intensity inother channels or polarization direction. For random polarization mode coupling and FWM cancellation also need to meet the beat . condition.Keywords: dispersion, loss, SRS, SPM, XPM, PMD, FWM cancellation, OPC, WDM 1. Introduction The performance of Lightwave system is limited by many factors, the limitation of fiber loss and dispersionand their compensation are well known. The use of narrow channel spacing and high bit-rate in wavelength-division-multiplexed (WDM) system combined with high lunched powers will lead to signal distortion due tononlinear effects in fiber, such as Stimulated Raman Scattering (SRS), Cross phase modulation (XPM), four wavemixing (FWM) etc. Theoretical [1] and experimental [2] studies have [1-5] proved that the SRS crosstalk canseverely limit the performance of WDM systems. Meanwhile, XPM can introduce intensity distortion due tofrequency chirp [6], and the random coupling between polarization Modes also can distort the pulse waveform,FWM can create serious crosstalk. The idea of SRS crosstalk cancellation using mid-span spectra inversion wassuggested [3], and theoretically calculated [4]. The compensation of pulse waveform distortion due to dispersionand Kerr effect self-phase modulation (5PM) was demonstrated [7]. We are also concern about XPM, Polarizationmode dispersion (PMD) and FWM. Can they be cancelled by some measures? In this paper, we shall showtheoretically that the fiber loss, chromatic dispersion, SRS and SPM, XPM as well as PMD can be simultaneouslycancelled by optical phase conjugation (OPC), i.e. spectral inversion (SI).2. theoryFor studying the compensation of pulse waveform distortion due to chromatic dispersion and nonlinearityand PMD in fiber, we need to deduce the pulse propagation equations for a WDM system. Here we suppose that