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Applied Mathematics Colloquium

Friday, September 16,  2005, 11:30 am
Cullimore Lecture Hall II
New Jersey Institute of Technology

Phase jitter in optical communication systems

C. J. McKinstrie

Bell Laboratories, Lucent Technologies

Abstract

In differential-phase-shift-keyed (DPSK) communication systems, information is encoded using the phase differences between neighboring pulses (solitons). For DPSK systems the error-free transmission distance is limited by phase jitter, in which power shifts caused by amplifier noise are converted into phase shifts by self-phase modulation. I will describe how to model the growth of phase jitter in constant-dispersion and dispersion-managed systems. I will also describe how cross-phase modulation augments the growth of phase jitter in multiple-channel (wavelength-division-multiplexed) systems. Phase jitter in any system can be reduced significantly by in-line phase conjugation, post-transmission phase-shift compensation or phase-sensitive amplification.

Phase jitter is governed by a pair of stochastic differential equations (SDEs) for the soliton power and phase perturbations. If these perturbations are small, one can model their growth using linearized SDEs, which produce Gauss probability-density functions (PDFs). However, system failures are caused by large perturbations that occur infrequently. For such perturbations the linearized equations (and the associated Gauss PDFs) are not valid. I will describe how to model power and phase jitter analytically, by using methods of statistical physics, and numerically, by making importance-sampled simulations based on the SDEs.