R. Khosravani

Time and frequency domain characteristics of polarization-mode dispersion emulators

We investigate both experimentally and theoretically a new technique to realistically emulate polarization-mode dispersion (PMD). We propose and demonstrate a PMD emulator using rotatable connectors between sections of polarization-maintaining fibers that generates an ensemble of high PMD fiber realizations by randomly rotating the connectors. It is shown that: (1) the DGD of this emulator is Maxwellian-distributed over an ensemble of fiber realizations at any fixed optical frequency; and (2) the frequency autocorrelation function of the PMD emulator resembles that in a real fiber when averaged over an ensemble of fiber realizations. A realistic autocorrelation function is required for proper emulation of higher order PMD and indicates the feasibility of using this emulator for wavelength-division-multiplexing (WDM) systems.

Comparison of polarization mode dispersion emulators

We analyze polarization mode dispersion (PMD) emulators comprised of a small number of sections of polarization-maintaining fibers with polarization scattering at the beginning of each section. Unlike previously studied devices, these emulators allow the emulation of a whole ensemble of fibers. We derive an analytical expressions and determine two main criteria that characterize the quality of PMD emulation. The experimental results are in good agreement with the theoretical predictions.

Polarization mode dispersion emulator

We investigate a new technique to realistically emulate polarization mode dispersion. We demonstrate that 15 sections of polarization-maintaining fiber with randomly rotatable connections emulates an almost ideal Maxwellian differential group delay (DGD) distribution, whereas fixed connections is inadequate.

Adjustable compensation of polarization mode dispersion using a high-birefringence nonlinearly chirped fiber Bragg grating

We demonstrate an adjustable polarization-mode-dispersion (PMD) compensator. The device uses a nonlinearly chirped fiber Bragg grating written into a high-birefringence photosensitive fiber. By mechanically stretching the grating, the device generates a time delay between different polarizations that is adjustable from 100 to 320 ps and is tunable over 2.3 nm. We demonstrate tunable PMD compensation of a 10-Gb/s signal that has an initial delay between the two polarization states of 127 or 302 ps.

Polarization-mode dispersion compensation in WDM systems

We demonstrate, both experimentally and numerically, polarization-mode dispersion (PMD) compensation in wavelength-division-multiplexing (WDM) systems without wavelength demultiplexing. Our technique improves the overall system performance by reducing the fading probability for the worst-performing channel at any given time. The effectiveness of our approach is based on the fact that, for moderate PMD, the probability that all channels are severely degraded at the same time is extremely small. A single-section PMD compensator reduces the 2% worst-case power penalty for a four-channel 10-Gb/s WDM system with /spl sim/42 ps average differential group delay from 9.6 to 5.3 dB.

System performance evaluation in terrestrial systems with high polarization mode dispersion and the effect of chirping

We evaluate the system power penalty for different modulation formats-nonreturn-to-zero (NRZ), return-to-zero (RZ), dispersion-managed solitons, and prechirped RZ-in the presence of polarization mode dispersion (PMD) for 10-Gb/s terrestrial systems. All orders of PMD are considered by simulating the fiber using the coarse-step method, and a statistical approach is used to estimate the occasional fading of the signals. We show that pulses with lower duty-cycles perform better in general, and the system performance is improved if appropriate prechirping interacts with the residual chromatic dispersion of the fiber.

Limitations to first-order PMD compensation in WDM systems due to XPM-induced PSP changes

We show both numerically and experimentally that the nonlinear phase change due to cross-phase modulation (XPM) induces a bit-pattern-dependent change in the state-of-polarization that translates to uncertainty in the principal states of polarization (PSP). This effect severely limits the effectiveness of first-order polarization mode dispersion (PMD) post-compensation and suggests the use of in-line compensation.

Comparison of different modulation formats in terrestrial systems with high polarization mode dispersion

We compare the performance of NRZ, RZ, dispersion-managed solitons, and pre-chirped RZ formats in the presence of high polarisation mode dispersion (PMD) for 10 Gbit/s terrestrial systems. Fiber nonlinearities and signal chirp interact with PMD-induced pulse distortion to generate clear trends in system power penalties. We show that chirped RZ pulses are more tolerant to high PMD values.

System impact of group-delay ripple in single and cascaded chirped FBGs

We experimentally show the system impact of group-delay ripple on system performance when considering a single fibre Bragg grating (FBG) and cascaded FBGs. We find that, for single gratings with different GD ripple, shorter pulse-widths can reduce the penalty induced by GD ripple, meanwhile, the impact of ripple becomes more and more serious as the data rate increases.

High-birefringence nonlinearly-chirped fiber Bragg grating for tunable compensation of polarization mode dispersion

We demonstrate a tunable polarization-mode dispersion (PMD) compensator using a high-birefringence nonlinearly chirped fiber Bragg grating (HN-FBG). Our device is capable of generating a 100 ps to 320 ps time delay between the polarization axes and tunable over 2.3 nm. For a 10-Gbit/s signal, we show that 170-ps tunability is realized by stretching the HN-FBG.