Mohamed El-Darawy

Electronic Polarization Control Algorithms for Coherent Optical Transmission

In this paper, we review the nondata-aided constant-modulus algorithm (CMA) and a data-aided decision-directed algorithm (DDA) for polarization control and propose different extensions to both algorithms to improve their performance. The first extension to the CMA enables a common carrier recovery (CCR) through differential phase compensation (DPC-CMA). The second extension adapts the CMA for quadrature amplitude modulation signals (CMA-QAM). Both extensions can be combined to form a DPC-CMA for QAM signals (DPC-CMA-QAM). A new, modified DDA (MDDA) considerably increases polarization tracking speeds compared to the original DDA (ODDA). It is also usable for QAM signals. The algorithms are compared in simulations of QPSK and 16-QAM transmission systems. The results show that the DPC extension for the CMA in combination with CCR doubles laser linewidth tolerance and also the CMA-QAM triples polarization control speed compared to the standard CMA for QAM signals. The MDDA is 1.6-4 times faster than the CMA variants and is, at least when QAM signals are transmitted, more hardware-efficient.

Fast Adaptive Polarization and PDL Tracking in a Real-Time FPGA-Based Coherent PolDM-QPSK Receiver

Fast polarization changes of 40 krad/s and 6-dB polarization-dependent loss (PDL) are tracked in a 2.8-Gb/s real-time coherent quadrature phase-shift keying receiver. The tolerance against fast polarization changes and PDL is measured for different polarization control time constants. The sensitivity penalty of the receiver at a polarization change speed of 40 krad/s is 0.7 dB at bit-error rate (BER) of 1times 10-3, with a BER floor of 6.1times10-7. With an additional PDL of 6 dB, these figures become 1.7 dB and 9.6 times 10-6, respectively.

The robustness of subcarrier-index modulation in 16-QAM CO-OFDM system with 1024-point FFT.

We present in numerical simulations the robustness of subcarrier index modulation (SIM) OFDM to combat laser phase noise. The ability of using DFB lasers with SIM-OFDM in 16-QAM CO-OFDM system with 1024-point FFT has been verified. Although SIM-OFDM has lower spectral efficiency compared to the conventional CO-OFDM system, it is a good candidate for 16-QAM CO-OFDM system with 1024-point FFT which uses a DFB laser of 1 MHz linewidth. In addition, we show the tolerance of SIM-OFDM for mitigation of fiber nonlinearities in long-haul CO-OFDM system. The simulation results show a significant penalty reduction, essentially that due to SPM.

Differential phase compensated constant modulus algorithm for phase noise tolerant coherent optical transmission

We extend a non-data-aided constant modulus algorithm (CMA) by a differential phase compensation (DPC-CMA) and simulate its polarization demultiplexing performance in a digital coherent QPSK receiver against that of the standard CMA.

Fiber nonlinearity tolerance of SIM-OFDM in CO-OFDM transmission

We present the tolerance of subcarrier-index modulation OFDM which is a new method for mitigation of fiber nonlinearities in CO-OFDM transmission. Simulation results show a significant penalty reduction, essentially that due to SPM.

Hardware-Efficient Phase Estimation for Digital Coherent Transmission With Star Constellation QAM

In order to build optical transmission systems for 100 Gb/s and above on a single wavelength division multiplexing channel, transition from quadrature phase-shift keying (QPSK) to higher quadrature amplitude modulation (QAM) formats seems to be inevitable. Instead of the usual square constellation QAM, we focus on regular star constellation QAM formats and present a hardware-efficient phase-estimation algorithm that is suitable for all regular star constellations, together with preliminary simulation results.

Realtime 40 krad/s polarization tracking with 6 dB PDL in digital synchronous polarization-multiplexed QPSK receiver

Fast polarization changes of 40 krad/s (and 6 dB PDL) are tracked in a 2.8 Gb/s realtime coherent QPSK receiver with 0.7 dB (2.4 dB) sensitivity degradation.

Reduced sampling rate frequency domain CD equalization for 112 Gb/s PDM-QPSK

Frequency domain chromatic dispersion equalization is simulated for long-haul fiber transmission at 112 Gb/s. The received data is processed at a reduced fractional sampling rate of 1.6 samples per symbol with a 1.5 dB penalty.

Realtime phase tracking with multiplier-free barycenter approximation in digital synchronous QPSK receiver for coherent detection

A multiplier-free phase estimation algorithm for coherent QPSK detection is presented. The barycenter approach is modified by a selectivity mechanism that improves performance. In addition to recently published measurement results, theoretical derivations and simulation results are provided.

32-krad/s polarization and 3-dB PDL tracking in a realtime digital coherent polarization-multiplexed QPSK receiver

The tolerance against fast polarization changes and PDL of a digital coherent QPSK receiver is determined in a 2.8 Gb/s realtime polarization-multiplexed transmission experiment. The sensitivity penalty for polarization changes with a speed of 32 krad/s on the Poincare sphere is 0.5 dB.