Modified widely linear filter for simultaneous multi-impairment compensation
We present a modified w idely l inear s ingle-tap b lind e qualizer f or t he joint multi-impairment compensation of polarization mixing, IQ Imbalance and transceiver phase noise, analyze its performance through simulation and experiments for 32Gbaud PM-16QAM transmission.
Geometric Parameter Extraction-based Receiver IQ imbalance correction for MQAM systems
We present a modulation transparent geometric parameter extraction method to compensate for the receiver IQ imbalance. We evaluate the algorithm's performance for various imbalance values for 32-GBd 16/64QAM signals in both simulations and through experiments.
Demonstration of 608 Gbps CO-OFDM Transmission using Gain Switched Comb
We experimentally demonstrate 608 Gbps CO-OFDM superchannel transmission over 25 km using optical carrier generated from an externally injected gain-switched comb source with linewidth ≈19 kHz. We show the BER performance is within the HD-FEC limit.
Widely Linear Filtering for Multiimpairment Compensation in Dispersion Managed mQAM Modulated Optical Systems
We propose a blind joint equalization algorithm for M-QAM signals based on a widely linear filtering approach. The proposed scheme jointly compensates for receiver IQ imbalance, receiver IQ skew, polarization mixing, carrier recovery, followed by transmitter IQ imbalance and skew. We first investigate the proposed scheme's tolerance to each of these impairments through numerical simulations for 32 GBd PM-16QAM and PM-64QAM signals and compare its performance with the conventional digital processing algorithms with and without IQ imbalance compensation. The proposed joint transceiver equalizer outperforms the conventional algorithms with a Q2 improvement of greater than 1 dB, and with improved tolerance to IQ imbalance. Further, with the proposed algorithm, we experimentally demonstrate the improvement in Q2 value with respect to conventional DSP for both PM-16QAM and PM-64QAM signals. We also show that the MSE convergence of the proposed joint equalizer is much faster than conventional DSP algorithms.
Pilot-free common phase error estimation for CO-OFDM with improved spectral efficiency
We propose an improved pilot free phase noise mitigation algorithm for CO-OFDM systems using weighted multi-level QPSK partitioning and Kalman filtering. Through extensive Monte Carlo simulations, we demonstrate an improvement in spectral efficiency of >6% in case of 200 Gbps single channel and 1 Tbps multi channel 16QAM CO-OFDM transmission with blind carrier phase estimation. We also experimentally demonstrate the performance of the proposed algorithm against the standard pilot aided algorithm for the transmission of 120 Gbps 16QAM CO-OFDM at different noise levels.
Adaptive Referencing Multitap Filter for TX-IQ Imbalance and Residual ISI Tolerance
We present a multi-tap filter for residual intersymbol interference correction which is tolerant to the transmitter IQ imbalance by adapting the reference constellation simultaneously. We evaluate the algorithm's performance for various imbalance values for 32-GBd 16QAM signals through experiments.
Dispersion and Nonlinearity Distortion Compensation of the QPSK/16QAM Signals Using Optical Phase Conjugation in Nonlinear SOAs
We experimentally demonstrate the simultaneous compensation of both dispersion and nonlinear effects in a 100 km optical fiber link using optical phase conjugation of a 21 GB aud QPSK and 16QAM signal with nonlinear SOAs. Error-free performance is recorded for a launched power of up to 12 dBm, without any digital signal processing to compensate for distortions due to chromatic dispersion and nonlinear effects in fiber. The performance is verified for operation across the C-band.
Optical Phase Conjugation Using Nonlinear SOA for Nonlinearity and Dispersion Compensation of Coherent Multi-Carrier Lightwave Systems
We study the use of nonlinear semiconductor optical amplifier (SOA) for generating optical phase conjugate towards compensation of distortions in short distance optical fiber transmission due to Kerr nonlinearity and chromatic dispersion in coherent multi-carrier lightwave signals. We experimentally demonstrate the effectiveness of the SOA-based phase conjugator to improve the link budget with a 100 km standard single mode fiber link for 20 GHz coherent OFDM signals, with QPSK and 16QAM modulations and a corresponding net bit-rate of 40 Gbps and 80 Gbps respectively. Mid-span spectral inversion scheme is employed where the optical phase conjugate is generated through a partially degenerate four-wave mixing process in a nonlinear SOA. We demonstrate a bit error rate performance within $2\times 10^{-2}$ for an average launched power of up to 12 dBm (9 dBm) for QPSK (16QAM) coherent OFDM signals, in a 100 km fiber link. We also investigate the possible improvement in link budget using numerical simulation for 16QAM and 64QAM CO-OFDM signals with the proposed scheme.
Pilot-free Bayesian Filter for Phase Noise Correction of 64QAM CO-OFDM Superchannel
We experimentally demonstrate the use of a pilot-free phase noise mitigation algorithm for a gain-switched comb-based 480 Gbps 64QAM CO-OFDM superchannel system using weighted-blind estimation and Bayesian filter with 18% potential improvement in spectral efficiency.
Carrier Phase Recovery Scheme Tolerant to Transmitter IQ Imbalance with Adaptive Constellation Referencing
We present a novel carrier phase recovery algorithm in the presence of transmitter IQ imbalance using a joint equalizer by performing gradient descent adaptation for phase tracking and simultaneously adapting the reference constellation. We test the efficacy of the proposed algorithm for 32 GBd QPSK and 16QAM signals.