Aurenice O. Lima

A novel polarization diversity receiver for PMD mitigation

We present a novel polarization diversity receiver for mitigating polarization-mode dispersion (PMD). We show that with simple fixed optics and electronics we can significantly decrease the outage probability due to PMD and can achieve better performance than an electronic equalization solution using no diversity. By incorporating equalization into the diversity receiver structure, further performance improvements can be achieved and the intersymbol interference due to higher order PMD distortions can be reduced. We demonstrate the performance advantages of the proposed diversity receiver using importance sampling to accurately calculate the outage probability due to PMD.

Error estimation in multicanonical Monte Carlo Simulations with applications to polarization-mode-dispersion emulators

This paper shows how to estimate errors in multicanonical Monte Carlo (MMC) simulations using a transition-matrix method. MMC is a biasing Monte Carlo technique that allows one to compute the probability of rare events, such as the outage probability in optical-fiber communication systems. Since MMC is a Monte Carlo technique, it is subject to statistical errors, and it is essential to determine their magnitude. Since MMC is a highly nonlinear iterative method, linearized error-propagation techniques and standard error analyses do not work, and a more sophisticated method is needed. The proposed method is based on bootstrap techniques. This method was applied to efficiently estimate the error in the probability density function (pdf) of the differential group delay (DGD) of polarization-mode-dispersion (PMD) emulators that has been calculated using MMC. The method was validated by comparison to the results obtained using a large ensemble of MMC simulations.

A comparative study of single-section polarization-mode dispersion compensators

This paper shows how to use multiple importance sampling to study the performance of polarization-mode dispersion (PMD) compensators with a single differential group delay (DGD) element. We compute the eye opening penalty margin for compensated and uncompensated systems with outage probabilities of 10/sup -5/ or less with a fraction of the computational cost required by standard Monte Carlo methods. This paper shows that the performance of an optimized compensator with a fixed DGD element is comparable to that of a compensator with a variable DGD element. It also shows that the optimal value of the DGD compensator is two to three times larger than the mean DGD of the transmission line averaged over fiber realizations. This technique can be applied to the optimization of any PMD compensator whose dominant sources of residual penalty are both the DGD and the length of the frequency derivative of the polarization-dispersion vector.

Statistical analysis of the performance of PMD compensators using multiple importance sampling

In this letter, we evaluate the performance of fixed and variable differential group delay (DGD) polarization-mode dispersion (PMD) compensators as the first- and second-order PMD varies using multiple importance sampling. We show that importance sampling yields estimates of the average penalty with low variance over the entire region of interest of first- and second-order PMD. We also show that there is little advantage in using a compensator with a variable-DGD element and that the performance of a compensator that minimizes the residual DGD at the central frequency of the channel is considerably worse than a compensator that maximizes the eye opening.

Comparison of penalties resulting from first-order and all-order polarization mode dispersion distortions in optical fiber transmission systems

We compare the eye-opening penalty from a first-order polarization mode dispersion (PMD) model with that from an all-order PMD model in optical fiber transmission systems. Evaluating the performance by taking into account only first-order PMD produces a good approximation of the true eye-opening penalty of uncompensated systems when the penalty is low. However, when the penalties are high, this model overestimates the penalty for outage probabilities in the range of interest for systems designers, which is typically approximately 10(-5) to 10(-6).

Statistics of the system performance in a scrambled recirculating loop with PDL and PDG

We have demonstrated that with the loop-synchronous scrambling technique, the Q distribution of a recirculating loop closely resembles that of a straight-line system. By carefully choosing the scrambling rate, we show that slow scrambling at the transmitter improves the system performance and reduces the performance variation. We investigate the system performance for different polarization-dependent loss (PDL) levels and obtain excellent agreement between the experimental and simulation results. Our results show, for the first time, that the repolarization of the noise due to significant PDL causes an asymmetric Q-factor distribution.

System performance variations due to partially polarized noise in a receiver

We systematically investigate effects of partially polarized noise in a receiver. We introduce a relationship between the Q factor and the signal-to-noise ratio (SNR) that accounts for effects of partially polarized noise. We derive an expression for the distribution of the Q factor for a fixed SNR, and we validate our results by comparison to back-to-back experiments. We show that the system performance varies depending on the angle between the Stokes vectors of the signal and the noise as well as the degree-of-polarization of the noise. Highly polarized noise will cause a larger variation of the system performance.

Efficient computation of outage probabilities due to polarization effects in a WDM system using a reduced Stokes model and importance sampling

We propose a technique that uses Monte Carlo simulations with importance sampling and a reduced Stokes model to compute the probability density function of the Q factor and the outage probability for a channel in a long-haul wavelength-division-multiplexed optical-fiber transmission system due to the combination of polarization mode dispersion, polarization dependent loss, and polarization dependent gain. This technique allows us to compute outage probabilities as small as 10/sup -6/ at a fraction of the computational cost required by standard Monte Carlo simulations.

Performance characterization of chirped return-to-zero modulation format using an accurate receiver model

We derive an explicit relationship between the Q factor and the optical signal-to-noise ratio in optical fiber transmission systems for an arbitrary pulse shape using an accurate receiver model under the assumption that the noise is unpolarized. We also define the enhancement factor and two other parameters that explicitly quantify the relative performance of different modulation formats. We use this method to compare the performance of the chirped return-to-zero, return-to-zero, and nonreturn-to-zero modulation formats with a finite extinction ratio. The method that we propose can also be used as a tool for the design and optimization of optical receivers.

Modeling Receivers in Optical Communication Systems With Polarization Effects

The authors use a new receiver model to demonstrate that, in optical communication systems, the bit-error rate depends not only on the optical signal-to-noise ratio but also on the polarization states of the signal and the noise.