Blind nonlinearity equalization by machine learning based clustering for single- and multi-channel coherent optical OFDM

Fiber-induced intra- and inter-channel nonlinearities are experimentally tackled using blind nonlinear equalization (NLE) by unsupervised machine learning based clustering (MLC) in ∼46-Gb/s single-channel and ∼20-Gb/s (middle-channel) multi-channel coherent multi-carrier signals (OFDM-based). To that end we introduce, for the first time, Hierarchical and Fuzzy-Logic C-means (FLC) based clustering in optical communications. It is shown that among the two proposed MLC algorithms, FLC reveals the highest performance at optimum launched optical powers (LOPs), while at very high LOPs Hierarchical can compensate more effectively nonlinearities only for low-level modulation formats. FLC also outperforms K-means, Fast-Newton support vector machines, supervised artificial neural networks and a NLE with deterministic Volterra analysis, when employing BPSK and QPSK. In particular, for the middle channel of a QPSK WDM coherent optical OFDM system at optimum -5 dBm of LOP and 3200 km of transmission, FLC outperforms Volterra-NLE by 2.5 dB in Q-factor. However, for a 16-quadrature amplitude modulated single-channel system at 2000 km, the performance benefit of FLC over IVSTF reduces to ∼0.4 dB at a LOP of 2 dBm (optimum). Even when using novel sophisticated clustering designs in 16 clusters, no more than additional ∼0.3 dB Q-factor enhancement is observed. Finally, in contrast to the deterministic Volterra-NLE, MLC algorithms can partially tackle the stochastic parametric noise amplification

1THz-bandwidth polarization-diverse optical phase conjugation of 10x114Gb/s DP-QPSK WDM signals

Polarization diverse optical phase conjugation of a 1THz spectral-band 1.14Tb/s DP-QPSK WDM multiplex is demonstrated for the first time, showing a worst case Q2 penalty of 0.9dB over all conjugate wavelengths, polarizations and OSNR

Dual-band fiber optic parametric amplifier for bi-directional transient-sensitive fiber optical transmission links

We demonstrate an in-line polarization-insensitive fiber optic parametric amplifier (PI-FOPA) to simultaneously amplify burst and non-burst signals transmitted in opposite directions in C and L bands. The PI-FOPA provides >16 dB polarization insensitive net gain for signals which are 53 nm apart and counter-propagating in an extended reach link: an upstream bursty signal at 1533 nm and a downstream non-burst signal at 1586 nm. The PI-FOPA potential application as an in-line dual-band amplifier in transient-sensitive communication links is demonstrated by its employment in an extended reach access network with a symmetric 10 Gbps capacity

Experimental comparison of fiber optic parametric, Raman and erbium amplifiers for burst traffic for extended reach PONs

We experimentally compare the performance of a polarization-independent fiber optic parametric amplifier (FOPA), a discrete Raman amplifier and a commercial erbium doped fiber amplifier (EDFA) for burst traffic amplification in extended reach passive optical networks (PON). We demonstrate that EDFA and Raman amplifiers suffer from severe transient effects, causing penalty on receiver sensitivity >5 dB for traffic bursts of 10 Gbps on-off keying signal shorter than 10 µs. On the other hand, we demonstrate that FOPA does not introduce a penalty on receiver sensitivity when amplifying signal bursts as short as 5 µs as compared to a non-burst signal. Therefore, FOPA used as a drop-in replacement for an EDFA or Raman amplifier allows us to improve receiver sensitivity by >3 dB for short signal bursts. We conclude that FOPA allows substantially increased power budget for an extended reach PON transmitting variable duration bursts. In addition, we identify the maximum burst duration tolerated by each examined amplifier

Comparison of bit error rate estimation methods for QPSK CO-OFDM transmission

In this letter, we experimentally study the statistical properties of a received QPSK modulated signal and compare various bit error rate (BER) estimation methods for coherent optical orthogonal frequency division multiplexing transmission. We show that the statistical BER estimation method based on the probability density function of the received QPSK symbols offers the most accurate estimate of the system performance

Reduction of Nonlinear Intersubcarrier Intermixing in Coherent Optical OFDM by a Fast Newton-Based Support Vector Machine Nonlinear Equalizer

A fast Newton-based support vector machine (N-SVM) nonlinear equalizer (NLE) is experimentally demonstrated, for the first time, in 40 Gb/s 16-quadrature amplitude modulated coherent optical orthogonal frequency division multiplexing at 2000 km of transmission. It is shown that N-SVM-NLE extends the optimum launched optical power by 2 dB compared to the benchmark Volterra-based NLE. The performance improvement by N-SVM is due to its ability of tackling both deterministic fiber-induced nonlinear effects and the interaction between nonlinearities and stochastic noises (e.g., polarization-mode dispersion). An N-SVM is more tolerant to intersubcarrier nonlinear crosstalk effects than Volterra-based NLE, especially when applied across all subcarriers simultaneously. In contrast to the conventional SVM, the proposed algorithm is of reduced classifier complexity offering lower computational load and execution time. For a low C-parameter of 4 (a penalty parameter related to complexity), an execution time of 1.6 s is required for N-SVM to effectively mitigate nonlinearities. Compared to conventional SVM, the computational load of N-SVM is ∼6 times lower

Fibre optic parametric amplifier for high capacity burst-mode access networks

We compare performance of a polarization insensitive fiber optic parametric amplifier (PI-FOPA), a commercial erbium doped fiber amplifier (EDFA) and a discrete Raman amplifier (DRA) in a 50 km long-reach optical access network transmitting bursts of 10 Gbps signal with traffic density ranged from 5% to 97%. We demonstrate that for the same power budget the PI-FOPA allows for transmission of bursty traffic with density up to 97% while DRA and EDFA are limited to 30% and 15%, respectively. Alternatively, we demonstrate PI-FOPA to allow for 3 dB and 5 dB higher power budget than the DRA and EDFA, respectively, for the worst case scenario of 75% traffic density

Experimental demonstration of data-dependent pilot-aided phase noise estimation for CO-OFDM

We demonstrate a novel phase noise estimation scheme for CO-OFDM, in which pilot subcarriers are deliberately correlated to the data subcarriers. This technique reduces the overhead by a factor of 2

Exceeding the nonlinear-shannon limit using Raman laser based amplification and optical phase conjugation

We demonstrate that a combination of Raman laser based amplification and optical phase conjugation enables transmission beyond the nonlinear-Shannon limit. We show nonlinear compensation of 7x114Gbit/s DP-QPSK channels, increasing system reach by 30%

A cluster randomised trial of educational messages to improve the primary care of diabetes

<p>Abstract</p> <p>Background</p> <p>Regular laboratory test monitoring of patient parameters offers a route for improving the quality of chronic disease care. We evaluated the effects of brief educational messages attached to laboratory test reports on diabetes care.</p> <p>Methods</p> <p>A programme of cluster randomised controlled trials was set in primary care practices in one primary care trust in England. Participants were the primary care practices' constituent healthcare professionals and patients with diabetes. Interventions comprised brief educational messages added to paper and electronic primary care practice laboratory test reports and introduced over two phases. Phase one messages, attached to Haemoglobin A1c (HbA1c) reports, targeted glycaemic and cholesterol control. Phase two messages, attached to albumin:creatinine ratio (ACR) reports, targeted blood pressure (BP) control, and foot inspection. Main outcome measures comprised practice mean HbA1c and cholesterol levels, diastolic and systolic BP, and proportions of patients having undergone foot inspections.</p> <p>Results</p> <p>Initially, 35 out of 37 eligible practices participated. Outcome data were available for a total of 8,690 patients with diabetes from 32 practices. The BP message produced a statistically significant reduction in diastolic BP (-0.62 mmHg; 95% confidence interval -0.82 to -0.42 mmHg) but not systolic BP (-0.06 mmHg, -0.42 to 0.30 mmHg) and increased the odds of achieving target BP control (odds ratio 1.05; 1.00, 1.10). The foot inspection message increased the likelihood of a recorded foot inspection (incidence rate ratio 1.26; 1.18 to 1.36). The glycaemic control message had no effect on mean HbA1c (increase 0.01%; -0.03 to 0.04) despite increasing the odds of a change in likelihood of HbA1c tests being ordered (OR 1.06; 1.01, 1.11). The cholesterol message had no effect (decrease 0.01 mmol/l, -0.04 to 0.05).</p> <p>Conclusions</p> <p>Three out of four interventions improved intermediate outcomes or process of diabetes care. The diastolic BP reduction approximates to relative reductions in mortality of 3% to 5% in stroke and 3% to 4% in ischaemic heart disease over 10 years. The lack of effect for other outcomes may, in part, be explained by difficulties in bringing about further improvements beyond certain thresholds of clinical performance.</p> <p>Trial Registration</p> <p>Current Controlled Trials, <a href="http://www.controlled-trials.com/ISRCTN2186314">ISRCTN2186314</a>.</p