L.E. Nelson

Measurement of second-order polarization-mode dispersion vectors in optical fibers

A polarization-mode dispersion (PMD) measurement technique is described that allows the determination of second- and higher order PMD vectors in optical fibers. The algorithm, based on Muller matrices, requires the launch of only two polarizations per wavelength and uses large rotation angles as well as interleaving to attain low-noise high-resolution PMD data. It has been applied to fibers ranging from 2 to 40 ps in mean PMD.

Probability densities of second-order polarization mode dispersion including polarization dependent chromatic fiber dispersion

We describe experiments and simulation of second-order polarization mode dispersion (PMD) components in optical fibers with emphasis on polarization-dependent chromatic dispersion (PCD). Excellent agreement is found in comparisons of experimental, simulated, and theoretical probability densities. To our knowledge, these are the first such comparisons for the second-order PMD magnitude and the PCD.

Observation of PMD-induced coherent crosstalk in polarization-multiplexed transmission

We report wavelength-division-multiplexed (WDM) systems experiments with polarization multiplexing at 40 Gb/s per channel and 0.8 bit/s/Hz spectral efficiency designed to explore the worst case impairments caused by first-order polarization-mode dispersion (PMD) in the fiber. Both polarization-division multiplexing using two polarizations at each wavelength and polarization interleaving where adjacent channels have orthogonal polarizations were examined. Measured system penalties show that polarization multiplexing increases the PMD sensitivity by approximately a factor of five due to coherent crosstalk.

Polarization-mode dispersion impairment in return-to-zero and nonreturn-to-zero systems

Using 10-Gbit/s signals, amplitude modulated with either a return-to-zero (RZ) or a nonreturn-to-zero format (NRZ), we measured optically preamplified receiver sensitivity after distortion by polarization-made dispersion (PMD). RZ modulation was found to be more resilient to PMD than NRZ modulation.

Measurement of depolarization and scaling associated with second-order polarization mode dispersion in optical fibers

The Muller matrix method enables the low-noise, high-resolution measurement of second-order polarization-mode-dispersion (PMD) depolarization and related parameters required for systems modeling. We report experimental observations of second-order PMD statistical dependencies and scaling for fibers with mean differential group delay (DGD) ranging from 1.3 to 17.0 ps. Measurements of 10 different fibers confirm that the depolarization scales with the mean DGD while the polarization-dependent chromatic dispersion scales with the square of the mean DGD.

First-order PMD outage for the hinge model

System outage due to first-order polarization-mode dispersion of links obeying the hinge model is analyzed using outage maps. We find that some fraction of the wavelength-division-multiplexed fiber capacity does not meet any outage specification.

Resonances in cross-phase modulation impairment in wavelength-division-multiplexed lightwave transmission

Cross-phase modulation impairment resonances exist in wavelength-division-multiplexed lightwave systems when channels are spaced such that there occurs an integral number of bit walkthroughs per amplifier span. We have observed these resonances in transmission through 624-km standard single-mode fiber systems having amplifier span lengths of 40, 80, or 120 km. Q measurements of a 2.5-Gb/s five-channel system over 8/spl times/80 km with +7 dBm/channel predict on-resonance bit-error rates (BERs) that are several orders of magnitude higher than off-resonance BERs.

Receiver impact on first-order PMD outage

Simulation and measurement show that the robustness of a transmission system to first-order polarization-mode dispersion (PMD) depends on the combination of modulation format and receiver characteristics. For beat-noise limited receivers of typical bandwidth, return-to-zero has greater PMD tolerance than non return-to-zero coding.

Amplified spontaneous emission in pulse-pumped Raman amplifiers

We discuss amplified spontaneous emission (ASE) generated in Raman amplifiers that are counter-pumped with trains of pulses. Our experimental and theoretical results show that if the peak power of the pump pulses is too high, the ASE output from the amplifier can be significantly higher than that from a continuous-wave pumped amplifier providing the same gain. This effect places a lower limit on the duty cycle of pump pulses one can use for a given level of Raman gain. Furthermore, we report an additional ASE enhancement if there is insufficient walkoff between the pump pulses and copropagating ASE to average the effects of higher frequency pump intensity noise. As a result, less pump intensity noise can be tolerated when pulse-pumping a fiber having a zero-dispersion wavelength located midway between the pump and signal wavelengths.

Second-order PMD outage of first-order compensated fiber systems

Differential dispersion elements can model polarization-mode dispersion characteristics of fibers compensated to first order. We use these in a two-step method to calculate outage probabilities for compensated systems. In this approach, the dominant second-order penalty characteristics equal those of chromatic dispersion. They are determined by advanced receiver modeling and can be tested experimentally.