Publisher Summary Polarization mode dispersion (PMD) is a linear effect that can be compensated in principle. In an ideal circularly symmetric fiber, the two orthogonally polarized modes have the same group delay. However, in reality, fibers exhibit a certain amount of birefringence because of imperfections in the manufacturing process or mechanical stress on the fiber after manufacture. It is noted that fluctuations in the polarization mode and fiber birefringence produced by the environment lead to dispersion that varies statistically with time and frequency. PMD causes different delays for different polarizations and when the difference in the delays approaches a significant fraction of the bit period, it leads to pulse distortion and system penalties. Environmental changes— including temperature and stress—cause the fiber PMD to vary stochastically in time. PMD, illustrating the basic concepts, the measurement techniques, the PMD measurement, the PMD statistics for first- and higher orders, the PMD simulation and emulation, the system impairments, and the mitigation methods has been summarized in the chapter. Both the optical and the electrical PMD compensations are considered.

Polarization-Mode Dispersion

We propose and investigate a novel electronic dispersion compensation technique, in which signal precompensation is achieved using a dual-drive Mach-Zehnder modulator, driven by adaptive nonlinear digital filters. The results demonstrate effective compensation of over 13600 ps/nm, equivalent to 800 km of standard single-mode fiber, at 10 Gb/s.

Electronic dispersion compensation by signal predistortion using digital Processing and a dual-drive Mach-Zehnder Modulator

The performance of different electronic equalization and processing schemes for 40- and 10-Gb/s optical transmission over single-mode fiber (SMF) are discussed, from the point of their ability to compensate chromatic dispersion (CD) and polarization mode dispersion (PMD). In addition, the impact of fiber nonlinearity and modulation format on equalization is also investigated. The main objective of this paper is to present an overview and a comparison of the performances rather than a detailed explanation of the principles of the different equalization schemes. The equalizers which will be covered are analog equalizer (feedforward and decision feedback type), maximum likelihood sequence estimator (MLSE), electronic precompensation, coherent/intradyne detection with digital signal processing (DSP) equalization, DSP-based optical orthogonal frequency division multiplexing (OFDM), and turbo equalization.

Electronic Dispersion Compensation

We study numerically all-optical slow-light delays in room-temperature single-mode optical fibers induced by stimulated Brillouin scattering. We consider the propagation of a pulse through a cw-pumped Brillouin fiber amplifier, where the carrier frequency of the pulse is tuned near the Stokes resonance. Pulse delay and broadening of the Stokes pulse are studied in the small-signal and gain-saturation regimes. Pulse delay is shown to be limited by saturation of the Brillouin amplifier. In the small-signal regime, both time delay and pulse broadening increase with increasing gain. In the gain-saturation regime, both time delay and broadening decrease with increasing gain, and the pulse even achieves advancement. Time delay of more than one pulse-width is observed with modest pulse distortion, and over one pulse-width advancement can be obtained with larger pulse distortion in the gain-saturation regime.

https://www.phy.duke.edu/~qelectron/pubs/JOSAB22_2378.pdf

Numerical study of all-optical slow-light delays via stimulated Brillouin scattering in an optical fiber

A method and system of coherent detection of optical signals. The system utilizes a digital signal processor (36) to recover an incoming optical signal. The system employs a local oscillator (56), which does not need to be phase locked to the signal. The signal may be consistently recovered, even when the polarization state varies over time. Additionally, the signal may be recovered when it comprises two channels of the same wavelength that are polarization multiplexed together. In addition, any impairment to the signal may be reversed or eliminated.

Coherent optical detection and signal processing method and system

A transversal filter (TF) and a decision feedback equaliser (DFE) have been manufactured as integrated electronic circuits in SiGe technology suitable for 10 Gbit/s operation. Using these devices, electrical equalisers for implementation in optical receivers have been realised and the reduction in penalty induced by polarisation mode dispersion (PMD) has been experimentally analysed. A device consisting of the concatenation of a TF and DFE exhibits the lowest residual penalty, < 3 dB for a PMD with a differential group delay of < 80 ps.

PMD mitigation at 10 Gbit/s using linear and nonlinear integrated electronic equaliser circuits

At 10 Gbit/s a 3.3 dB reduction of the power penalty induced by the chromatic dispersion of an 127 km standard single-mode fiber (G.652) has been achieved (BER=10/sup -9/, PRBS 2/sup 23/-1) by processing the detected signal in the receiver with a nonlinear equaliser realized as SiGe integrated circuit.

Reduction of the chromatic dispersion penalty at 10 Gbit/s by integrated electronic equalisers

A system experiment is reported in which polarisation mode dispersion (PMD) and chromatic dispersion (CD) compensation was achieved using an SiGe IC linear equaliser, with a transmission rate of 100 bit/s over 95 km of standard single-mode fibre (DL=1600 ps/nm). Full equalisation was obtained, with a differential group delay (DGD) of <65 ps and a penalty reduction to 3.4 dB for DGD=100 ps.

R. Ballentin

Papers

PMD mitigation at 10 Gbit/s using linear and nonlinear integrated electronic equaliser circuits

Reduction of the chromatic dispersion penalty at 10 Gbit/s by integrated electronic equalisers

Electronic compensation of PMD and chromatic dispersion with an IC in 10 Gbit/s transmission system