Methods for crosstalk measurement and reduction in dense WDM systems

Abstract

We propose a scheme for the monitoring and reduction of crosstalk arising from the limited stop-band rejection of optical bandpass filters in dense WDM systems. The optical carrier at each wavelength is modulated with a subcarrier tone unique to that wavelength. The level of crosstalk from a given channel cain be determined by measuring the power of the corresponding; tone. Crosstalk from other channels can be cancelled in a linear fashion by weighting and summing the photocurrents of the desired channel and several adjacent interfering channels. Alternatively, in nonlinear crosstalk cancellation, decisions are made on the interfering signals, and these decision are weighted and summed with the photocurrent of the desired channel. For example, assuming an optical filter having a Gaussian passband, the channel density can be increased from 20 to 30%, depending on the number of adjacent channels ' detected. The signal-tointerference ratio can be increased by 10-20 dB and the system can achieve a BER < low9 under conditions where, without interference cancellation, the signal-to-interference ratio would be less then 10 dB.

Free-space-optical mobile ad hoc networks: Auto-configurable building blocks

“…For outdoors, fixed FSO communication techniques to remedy small vibrations [4,5], swaying of the buildings have been implemented using mechanical auto-tracking [2,6,17] or beam steering [29], and interference [16] and noise [26]. Similarly, for optical interconnects, auto-alignment or wavelength diversity techniques are reported to improve the misalignment tolerances in 2-dimensional arrays [9,10,12,14,19]. These techniques work only over small ranges (e.g.…”

Backscatter-induced crosstalk interference in urban optical wireless communication

“…An analytic expression is derived for the system bit-error-rate (BER) and a numerical example illustrates the detrimental effect of the backscattered light. Much research has been published dealing with crosstalk in optical communication systems 4,5 , particularly in WDM fiber networks, but, to the best of the authors' knowledge, the scenario investigated herein has not been treated in the professional literature. In the next section we elaborate on the communication scenario and in the following section we develop the mathematical model for the system BER, introducing concepts from lidar (light detection and ranging).…”

Performance analysis of low-frequency pilot-tone-based monitoring techniques in amplified wavelength-division-multiplexed networks

“…1,2 In addition, pilot tones have been used to monitor the optical powers and wavelengths of WDM signals, crosstalks between WDM channels, and optical paths in the optical cross-connects. [3][4][5][6] However, we recently pointed out that, when the lowfrequency pilot tones are used in amplified WDM networks, the performance of monitoring technique could be impaired by the slow dynamic property of the erbiumdoped fiber amplifier 7,8 ͑EDFA͒. In this paper, we report on a simple model to analyze the deleterious effect of slow EDFA gain dynamics on the pilot-tone-based monitoring technique.…”