Instantaneous Differential Group Delay Research Articles

A Shared PMD and Chromatic Dispersion Monitor Based on a Coherent Receiver

We demonstrate a shared optical performance monitor utilizing a dual-polarization quadrature-phase-shift-keyed coherent single-ended receiver, with no optical filtering. The channel to be monitored is selected by tuning the local oscillator. The chromatic dispersion and instantaneous differential group delay of a channel can be read while 80 channels are simultaneously impinging upon the detector.

Performance of a 46-Gbps Dual-Polarization QPSK Transceiver With Real-Time Coherent Equalization Over High PMD Fiber

We report experimental results on the transmission performance of a coherent dual-polarization quadrature phase-shift-keyed (DP-QPSK) transceiver with real-time electronic equalization over fiber having 50-ps mean polarization mode dispersion (PMD). Both single-channel, single-span and multi-channel, multi-span measurements were performed over the high PMD fiber, which has near Maxwellian statistics for the differential group delay (DGD) as well as higher order PMD as expected for a long, mode-coupled fiber. Transmission of eighty channels was achieved over 8 times100 km of TrueWave Reduced Slope fiber plus distributed high PMD fiber, where individual channels had instantaneous DGD as high as 127 ps. The dependence of the OSNR penalty on the launch state of polarization was evaluated and found to be minimal, and the contribution of fiber nonlinearities to the transmission penalty was evaluated for two different per-channel launch powers. Finally, using a transceiver equipped with forward-error-correction, error-free transmission over the 800-km link was demonstrated over a 10-day period; during this time the DGD of the measured channel varied from 13 to 116 ps.

Distributed Polarization-Mode-Dispersion Measurement in Fiber Links by Polarization-Sensitive Reflectometric Techniques

We present a theoretical analysis showing how to measure the instantaneous differential group delay of an arbitrary subsection of a link, by means of a polarization-sensitive reflectometric measurement as, for instance, polarization optical time-domain reflectometry. Analytical predictions are supported and validated by preliminary experimental results.

Measurement of PMD tolerance in 40-Gb/s polarization-multiplexed RZ-DQPSK

We experimentally investigate the first-order polarization-mode dispersion (PMD) tolerance of two polarization-multiplexed (POLMUX) RZ-DQPSK signals at overall 40 Gb/s. The polarization demultiplexing is enabled by an automatic endless polarization stabilizer. Time-interleaving the two orthogonally polarized RZ-DQPSK signals minimizes the crosstalk due to the non-ideal polarization stabilization, while it represents the worstcase for the PMD-induced crosstalk. Bit-error rate measurements are performed both in back-to-back and after 25-km standard single-mode fiber. The PMD tolerance is evaluated as a function of the instantaneous differential group delay, introduced by a first-order PMD emulator. 40-Gb/s POLMUX RZ-DQPSK is more sensitive to PMD than single-polarization 20-Gb/s DQPSK, while it is more PMD-tolerant than 40-Gb/s NRZ-OOK. Besides, its chromatic dispersion robustness is similar to the single-polarization 20-Gb/s DQPSK. The combination of POLMUX and DQPSK is therefore very promising in view of transmission systems at high bit-rate.

Non-blocking PMD monitoring in live optical systems

A simple and non-blocking polarisation-mode dispersion (PMD) monitoring technique using coherent detection is demonstrated and applied to a 40 Gbit/s live fibre-optic system. The results demonstrated a clear correlation between the instantaneous differential group delay and the receiver Q-margin. It was also demonstrated that PMD-induced outage can be eliminated by an adaptive PMD compensator.

Study on the PMD impairment of optical multilevel DPSK systems and its mitigation methods

We examine the polarization-mode dispersion (PMD) impairment of optical multilevel differential phase-shift keying systems, and also its mitigation method by comparing the electrical equalization technique and the receiver bandwidth optimization. Analysis has been carried out with 40-Gb/s systems experiencing 0/spl sim/60 ps of instantaneous differential group delay, corresponding up to 240%/80% of bit/symbol transmission rate. Results show considerable improvement in the PMD tolerance for return-to-zero format for the optimized receiver bandwidth either with or without the electrical equalization. For nonreturn-to-zero, the bandwidth optimization alone does not significantly improve the system's PMD tolerances.

In-service measurements of polarization-mode dispersion and correlation to bit-error rate

We introduce a nondisruptive in situ polarization-mode dispersion measurement technique using the sidebands of working channels and show that it compares favorably with the standard Mueller matrix method. Using this technique, we observed time correlations between the instantaneous differential group delay and bit-error rate on a 1000-km field-installed 43-Gb/s transmission system.

PMD-induced impairments in polarization-interleaved WDM systems

Wavelength-division-multiplexing N /spl times/ 10 Gb/s systems with 12.5-GHz channel spacing should require polarization interleaving (PI). However, fiber PMD can alter PI, giving relevant limitations. We show how impairments are affected by the filtering effect of wavelength-sensitive multiplexers/demultiplexers. For the optimum configuration, an analytical equation relates to the signal Q factor to the instantaneous differential group delay of the link. Hence, PMD-induced impairments can be significantly lower than it was previously estimated.

Intrabit polarization diversity modulation for the mitigation of PMD effects

The authors propose and demonstrate a novel modulation format called intrabit polarization diversity modulation (IPDM) that helps to mitigate the deleterious effects of PMD on system performance. IPDM is a format in which the optical power in the first half of a nonreturn-to-zero (NRZ) bit time is transmitted in an orthogonal state-of-polarization (SOP) to the optical power in the second half of the bit time. At the receiver, a tunable polarizer is used to recover only one SOP. Given that both SOPs are launched at the transmitter, the probability of network outage due to PMD is considerably smaller. The use of this format limits the power penalty induced by first-order PMD to 3 dB, and the system sensitivity is independent of the fiber link's instantaneous differential group delay. In the presence of higher order PMD, the authors show a 4- and a 1-dB improvement in the average receiver sensitivity over conventional NRZ and RZ format, respectively, in terms of the 2% tail of the received optical power.

Differential group delay monitoring used as feedforward information for polarization mode dispersion compensation

A novel differential-group-delay (DGD) monitoring scheme that can provide feedforward information to facilitate the compensation of polarization mode dispersion (PMD) is demonstrated. Using a polarization scrambler at the beginning of the link, the instantaneous DGD can be monitored at the end of the link by using a second polarization scrambler followed by a fixed 0.8-dB polarization dependent loss (PDL) element or a polarizer. As the PMD value along the link increases, the instantaneous degree-of-polarization will decrease, thereby resulting in a decrease in the measured RMS power fluctuation value through the PDL element. The authors show instantaneous DGD monitoring of up to /spl sim/70 ps for both nonreturn-to-zero (NRZ) and return-to-zero data formats, and they demonstrate PMD compensation of a 10-Gb/s NRZ channel using the monitor output as part of the control feedforward signal.