Coherent and incoherent crosstalk in WDM optical networks

TLDR

Crosstalk in WDM optical networks arises when propagation delay differences in an OXC are smaller than the laser coherent time, producing coherent or incoherent interference that can cause power fluctuations and noise. The study aims to quantify the impact of coherent and incoherent crosstalk on optical signals in OXC nodes, derive analytical expressions, and propose a quantile-based approach to relax component specifications. The authors analytically model crosstalk contributions and use simulations to evaluate their statistical effect, introducing a quantile metric to reduce specification stringency. They determine component crosstalk specification limits for WDM networks of varying scales based on the proposed analysis.

Abstract

The impact of coherent and incoherent crosstalk on an optical signal passing through optical cross-connect nodes (OXC's) in wavelength division multiplexing (WDM) optical networks is studied, and the analytical expressions are given. Such crosstalk will be generated when the optical propagation delay differences of optical paths in an OXC do not exceed the coherent time of the lasers. While causing fluctuation of signal power, coherent crosstalk may cause noise or not, depending on the relationship between the optical propagation delay differences and the time duration of one bit of the signal. Incoherent crosstalk may cause very high noise power, because it can be a coherent combination of crosstalk contributions. The statistical impact of all crosstalk contributions on signal is studied by simulation, and the concept of quantile is proposed to relax the crosstalk specification requirement for components. The crosstalk specification requirements are then obtained for components used in WDM optical networks with different scales.