Adaptive Filtering in Optical Coherent Flexible Bit-Rate Receivers in the Presence of State-of-Polarization Transients and Colored Noise

Ahmad Abdo,Claude D’Amours

doi:10.1155/2019/2938653

Ahmad Abdo, Claude D’Amours

Open Access

https://doi.org/10.1155/2019/2938653

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Abstract

In this article, we analyze the performance of adaptive filtering in the context of dual-polarization coherent optical flexible bit-rate transceivers. We investigate the ability of different adaptive algorithms to track fast state-of-polarization (SOP) transients in the presence of colored noise. Colored noise exists due to the concatenation of Wavelength Selective Switches (WSSs) and polarization dependent loss (PDL) which can be considered as spatially dependent noise. We consider the use of different modulation formats, and the practical limitation of error signal feedback delay in decision-directed adaptive filters is also taken into account. The back-to-back required signal-to-noise ratio (RSNR) penalty that can be tolerated determines the maximum SOP rate of change that can be tracked by the adaptive filters as well as the filter’s adaptive step size. We show that the recursive least squares algorithm, using the covariance matrix as an aggressive “step size,” has a much better convergence speed compared to the least mean squares (LMS) and normalized LMS (NLMS) algorithms in the presence of colored noise in the fiber. However, the three algorithms have similar tracking capabilities in the absence of colored noise.

Highlights

In this article, we analyze the performance of adaptive filtering in the context of dual-polarization coherent optical flexible bit-rate transceivers
We show that the recursive least squares algorithm, using the covariance matrix as an aggressive “step size,” has a much better convergence speed compared to the least mean squares (LMS) and normalized LMS (NLMS) algorithms in the presence of colored noise in the fiber
We investigate the performance of the LMS, normalized LMS (NLMS), recursive least square (RLS), and MMA algorithms for the adaptive filter in coherent receivers for dual-polarization optical signals in the presence of SOP transients, polarization dependent loss (PDL), and optical filters. en, we provide an overview of the main sources of SOP transients in optical links

Summary

Introduction

We analyze the performance of adaptive filtering in the context of dual-polarization coherent optical flexible bit-rate transceivers. E core operator in dual-polarization communication systems is the adaptive filter which performs equalization to correct the time-varying state-ofpolarization (SOP) as well as other linear channel impairments. Studying both the convergence and tracking performance of the adaptive filters used in this process is important in understanding the limitations of the system. We investigate the performance of the LMS, normalized LMS (NLMS), RLS, and MMA algorithms for the adaptive filter in coherent receivers for dual-polarization optical signals in the presence of SOP transients, PDL, and optical filters. We compare different adaptive algorithms by simulating their convergence speed and SNR penalty for different SOP transients’ speed. e main contributions of this paper are the following:

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