Channel Parameter Estimation for Polarization Diverse Coherent Receivers (original) (raw)
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Automatic PMD Compensation by Unsupervised Polarization Diversity Combining Coherent Receivers
Journal of Lightwave Technology, 2000
A new automatic scheme to compensate the intersymbol interference caused by fiber polarization mode dispersion (PMD) is introduced. The proposed method makes use of the orthogonal polarization components by combining them through adaptive electronic filters, which are adjusted through a low-complexity unsupervised updating method. The simplicity of the proposed unsupervised method is its most critical feature in terms of enabling real-time and all-hardware implementation. Simulation results are provided for a fiber channel with 40 Gsymbols/s signalling rate and a mean DGD level greater than the symbol period, where it is demonstrated that the PMD can be effectively compensated with a 2 dB signal-to-noise ratio penalty relative to PMD-free channel. Turkey. His research interests are in computational prototyping of electronic and optoelectronic systems, numerical modeling and analysis, stochastic dynamical systems and their applications, and noise in nonlinear electronic, optical, and communication systems. The work he did with Bell Laboratories and CeLight is the subject of six patents. He has coauthored two books in the areas of nonlinear-noise analysis
Signal statistics in fiber-optical channels with polarization multiplexing and self-phase modulation
2011
Abstract In this paper, the statistics of received signals in a single-channel dispersion-managed dual-polarization fiber-optical channel are derived in the limit of low dispersion. The joint probability density function (pdf) of the received amplitudes and phases of such a system is derived for both lumped and distributed amplification. The new pdf expressions are used to numerically evaluate the performance of modulation formats over channels with nonlinear phase noise.
Journal of Lightwave Technology, 2009
Polarization division multiplexing (PDM) has been proposed as a scheme for increasing data rates in fiber optic communication systems. In the PDM scheme, the use of two orthogonal polarizations as alternative data paths is a promising approach in terms of doubling the information rate relative to conventional schemes. However, due to the severe distortion caused by the propagation medium, especially the Polarization mode dispersion (PMD), the development of receiver compensation methods are critical for the deployment of PDM based transceivers. This article proposes a receiver compensation method for high symbol rate fiber optic communication links, where the two data streams sent through orthogonal polarizations are mixed by the fiber channel not only in space but also in time. The proposed receiver algorithm adaptively recovers the original pair of data streams from their space-time mixtures. We also provide simulation results for an end-to-end fiber communication link to illustrate the performance of the proposed approach.
Simplified backpropagation equalization in WDM coherent polarization multiplexed systems
ICTON 2009: 11th International Conference on Transparent Optical Networks, 2009
The digital equalization of fibre impairments in coherent optical communications allows for ultimate limits of spectral efficiency to be achieved, while reducing the cost and complexity compared to optical based solutions. Digital backpropagation (BP) was proposed recently as a reduced complexity approach for jointly compensating linear and non-linear impairments in single polarization coherent optical systems. Furthermore, polarization division multiplexed quadrature phase-shift keying (PDM-QPSK) has emerged as a promising format to increase spectral efficiency. Here we assess the performance of the simplified backpropagation equalization in both single channel and multiple channel transmission in combination with polarization multiplexing for different dispersion map configurations. It is shown that polarization multiplexing induces a degradation in performance due to cross-phase modulation polarization scattering, the backpropagation algorithm still overperforming linear equalization.
Optimal Polarization Demultiplexing for Coherent Optical Communications Systems
Journal of Lightwave Technology, 2000
Spectrally-efficient optical communications systems employ polarization division multiplexing (PDM) as a practical solution, in order to double the capacity of a fiber link. Polarization demultiplexing can be performed electronically, using polarization-diversity coherent optical receivers. The primary goal of this paper is the optimal design, using the maximum-likelihood criterion, of polarization-diversity coherent optical receivers for polarization-multiplexed optical signals, in the absence of polarization mode dispersion (PMD). It is shown that simultaneous joint estimation of the symbols, over the two received states of polarization, yields optimal performance, in the absence of phase noise and intermediate frequency offset. In contrast, the commonly used zero-forcing polarization demultiplexer, followed by individual demodulation of the polarization-multiplexed tributaries, exhibits inferior performance, and becomes optimal only if the channel transfer matrix is unitary, e.g., in the absence of polarization dependent loss (PDL), and if the noise components at the polarization diversity branches have equal variances. In this special case, the zero-forcing polarization demultiplexer can be implemented by a 2 2 lattice adaptive filter, which is controlled by only two independent real parameters. These parameters can be computed recursively using the constant modulus algorithm (CMA). We evaluate, by simulation, the performance of the aforementioned zero-forcing polarization demultiplexer in coherent optical communication systems using PDM quadrature phase shift keying (QPSK) signals. We show that it is, by far, superior, in terms of convergence accuracy and speed, compared to conventional CMA-based polarization demultiplexers. Finally, we experimentally test the robustness of the proposed constrained CMA polarization demultiplexer to realistic imperfections of polarization-diversity coherent optical receivers. The PMD and PDL tolerance of the proposed demultiplexer can be used as a benchmark in order to compare the performance of more sophisticated adaptive electronic PMD/PDL equalizers.
Simplified Volterra Series Nonlinear Equalizer for Polarization-Multiplexed Coherent Optical Systems
Journal of Lightwave Technology, 2013
Starting from a previously proposed frequencydomain Volterra series nonlinear equalizer (VSNE), whose complexity evolves as O(N 3), with N being the frequency-domain block length, we derive a symmetric VSNE filter array formulation for polarization-multiplexed (PM) signals, whose full VSNE equivalent is up to 3× more computationally efficient, with zero performance penalty. By gradually reconstructing the third-order kernel from its column/diagonal components, the full VSNE can be reduced to a restrict set of N k frequency-domain filters, leading to O(N k N 2) complexity, associated with negligible performance loss. Finally, a simplified VSNE approach with invariant Kernel coefficients is proposed, delivering O(N k N) complexity at the expense of controlled performance penalty. The proposed array of symmetric VSNE filters significantly increases the scalability of the previous matrix-based VSNE, providing a more flexible balance between performance and complexity, which can be freely adjusted to match the available computational resources. Performing a direct comparison between the simplified VSNE and the widely used split-step Fourier method in a long-haul 224 Gb/s PM-16QAM transmission system, we demonstrate a reduction of over 60% in terms of computational effort and 90% in terms of equalization latency.
Journal of Lightwave Technology, 2000
Polarization division multiplexing (PDM) has been proposed as a scheme for increasing data rates in fiber optic communication systems. In the PDM scheme, the use of two orthogonal polarizations as alternative data paths is a promising approach in terms of doubling the information rate relative to conventional schemes. However, due to the severe distortion caused by the propagation medium, especially the Polarization mode dispersion (PMD), the development of receiver compensation methods are critical for the deployment of PDM based transceivers. This article proposes a receiver compensation method for high symbol rate fiber optic communication links, where the two data streams sent through orthogonal polarizations are mixed by the fiber channel not only in space but also in time. The proposed receiver algorithm adaptively recovers the original pair of data streams from their space-time mixtures. We also provide simulation results for an end-to-end fiber communication link to illustrate the performance of the proposed approach.