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We present a low-cost transmitter based self-calibration for IQ time delay and frequency response using only low-bandwidth components. Sub-ps timing correction and frequency response correction enable transmission of 400GE, 66Gbaud DP-16QAM and 44Gbaud DP-64QAM.
We discuss several options for reducing power consumption of DSP used for coherent interfaces. These options are put in perspective with the needs of metro and data center interconnects for an overall optimized solution.
We demonstrate a new phase slip tolerant, multi-level coding scheme for 64QAM achieving 12.9 dB NCG with power dissipation less than 1W per 100G. Error free operation down to BER=10−15 and high slip tolerance is shown in a real-time experiment.
CFP2-ACO pluggables are used for the first real-time transmission of a lTb/s superchannel consisting of 4×40Gbaud 50GHz spaced DP-16QAM channels. Error free transmission is demonstrated over 6×104km of G.652 fibre with 92 neighbouring 100G channels.
We compare hybrid turbo differential decoding with other FEC-schemes that reduce the penalty usually associated with differential encoding applied for cycle slip mitigation. We discuss implementation aspects and show robust FEC-performance in nonlinear transmission experiments.
We experimentally investigate the cycle slip tolerance of an enhanced Turbo Differential Decoding algorithm in nonlinear transmission. Error-free post-FEC measurements using a 100G QPSK DWDM module show excellent tolerance against cycle slips without a differential encoding penalty.
We measure the impact of reflection induced multi-path interference on 32Gbaud PAM-2, 4 and 8. We show a good agreement with a Gaussian model and discuss system scenarios using standardised connectors.
We propose four strategies for TDHMF Tx operation. BER minimization permits PM-QPSK/PM-16QAM performance similar to PM-8QAM's. In TDHMF nonlinear propagation, predistortion and/or polarization interleaving enables the maximum reach predicted by GN-model.
Pilot-free coherent systems use blind carrier phase estimation (CPE) methods that inevitably generate cycle slips. We propose an enhanced CPE reducing the cycle slip probability low enough to enable turbo differential decoding.
A novel clock recovery architecture is presented that includes a feed-forward variable delay element. The architecture is resilient to channel distortion and achieves good performance with Nyquist pulse-shaped signals.
We present channel spacing measurements on a 28Gbaud CP-QPSK transmitter applying Nyquist-like signal shaping without using optical filters. This is enabled by a single sample per symbol digital-to-analog converter in combination with strong analog electrical filtering. OSNR performance is evaluated against a commercial real-time receiver.
We study the impact of stressors such as phase slips on the performance of LDPC codes with differentially encoded coherent DP-QPSK, comparing classical soft-decision decoding and iterative (turbo) differential decoding. We find that turbo decoding shows improved baseline performance but suffers from severely reduced phase slip resilience.
We present real-time measurements of the cycle-slip probabilities of a 100G DP-QPSK transceiver using a Viterbi-and-Viterbi carrier recovery. ASE and non-linear phase noise generated Poisson distributed slip events with mean probabilities between 10−12 to 10−3.
Structural design and functional blocks of a digital equalizer chipset is shown in a case study of two product generations. In addition, challenges from field applications and product solutions are presented.
A receiver using MLSE equalization is investigated in combination with a chirped transmitter in a 10Gbit/s field trial. Results show that the required OSNR at high CD and PMD can be decreased using appropriate chirp.
We compare the performance of MLSE-based receivers with parametric and non- parametric channel estimation methods and characterize their sensitivity against quantization, sampling jitter, and intersymbol interference (ISI) overload.
MLSE offers adaptive non-linear receiver-sided equalization for channels with memory. New areas of application considered are directly modulated DFB laser, D(B/Q)PSK, and duo-binary transmission systems. Reduced computational complexity is a new research area.
We have measured the performance of a 10 Gb/s receiver incorporating maximum-likelihood sequence estimation (MLSE) under conditions of severe polarization-mode dispersion (PMD). We find that certain trajectories of PMD evolution can lead to metastable states of receiver operation.
We review the basic electronic equalization techniques. We report new results of MLSE equalizers for combined chromatic dispersion and PMD. We show first results on the dynamic channel tracking performance of MLSE equalizers for PMD.
Improvements in silicon processing speeds have resulted in integrated circuits that can sample and digitally process 10 Gbit/s data. Signal processing techniques that have radically altered radio communication can now be applied to optical communications to improve tolerance to impairments such as chromatic dispersion and polarisation mode dispersion, as well as transmitter/receiver imperfections...
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