Ultra-Long-Haul WDM Transmission Using NANF Hollow-Core Fiber

Hollow-core fiber NANF prototypes have recently achieved lower loss and wider bandwidth than SMF. Theory predicts further progress may be possible. We investigate the potential impact of future high-performance NANFs on long-haul optical communication systems

Opportunities and Challenges for Long-Distance Transmission in Hollow-Core Fibres

Anti-resonant hollow-core fiber of the Nested Antiresonant Nodeless type (NANF) has been showing a steady decrease in loss over the last few years, gradually approaching that of standard Single-Mode Fiber (SMF). It already by far outperforms SMF as to non-linear effects, which are three to four orders of magnitude lower in NANF than in SMF. Theoretical predictions and experimental evidence also hint at a much wider usable bandwidth than SMF, potentially amounting to several tens of THz. Propagation speed is 50% faster, a key feature in certain contexts. In this paper we investigate the potential impact of possible future high-performance NANF on long-haul optical communication systems, assuming NANF continues on its current steady path towards better performance. We look at the system throughput in different long-haul scenarios, addressing links of various length, from 100~km to 4,000~km, and different NANF optical bandwidths, loss and total launch power. We compare such throughput with a benchmark state-of-the-art SMF Raman-amplified C+L system. We found that NANF might enable relative throughput gains vs.~the benchmark on the order of 1.5x to 5x, at reasonable NANF and system parameter values. We also study the problem of the impact of NANF Inter-Modal-Interference (IMI) on system performance and show that a value of -60~dB/km, close to the currently best reported values, is low enough to have no substantial harmful effect. We finally look at a more long-term scenario in which NANF loss gets below that of SMF and we show that in this context repeterless or even completely amplifierless systems might be possible, delivering 300-400 Tb/s per NANF, over 200 to 300~km distances. The system simplification and ease of wideband exploitation implied by these systems might prove quite attractive especially in densely populated regions where inter-node distances are modest. While several technological hurdles remain towards NANF systems becoming practical contenders, in our opinion NANF appears to have the potential to become an attractive and possibly disruptive alternative to conventional solid-core silica fibers

Optical phase-locked loop for coherent detection optical receiver

Lette

Accurate Closed-Form Real-Time EGN Model Formula Leveraging Machine-Learning over 8500 Thoroughly Randomized Full C-Band Systems

We derived an approximate non-linear interference (NLI) closed-form model (CFM), capable of handling a very broad range of optical WDM system scenarios. We tested the CFM over 8500 randomized C-band WDM systems, of which 6250 were fully-loaded and 2250 were partially loaded. The systems had highly diversified channel formats, symbol rates, fibers, as well as other parameters. We improved the CFM accuracy by augmenting the formula with simple machine-learning factors, optimized by leveraging the system test-set. We further improved the CFM by adding a term which models special situations where NLI has high self-coherence. In the end, we obtained a very good match with the results found using the numerically-integrated Enhanced GN-model (or EGN-model). We also checked the CFM accuracy by comparing its predictions with full-C-Band split-step simulations of 300 randomized systems. The combined high accuracy and very fast computation time (milliseconds) of the CFM potentially make it an effective tool for real-time physical-layer-aware optical network management and control

Performance evaluation of coherent WDM PS-QPSK (HEXA) accounting for non-linear fiber propagation effects

Coherent-detection (CoD) permits to fully exploit the fourdimensional (4D) signal space consisting of the in-phase and quadrature components of the two fiber polarizations. A well-known and successful format exploiting such 4D space is Polarization-multiplexed QPSK (PM-QPSK). Recently, new signal constellations specifically designed and optimized in 4D space have been proposed, among which polarizationswitched QPSK (PS-QPSK), consisting of a 8-point constellation at the vertices of a 4D polychoron called hexadecachoron. We call it HEXA because of its geometrical features and to avoid acronym mix-up with PM-QPSK, as well as with other similar acronyms. In this paper we investigate the performance of HEXA in direct comparison with PM-QPSK, addressing non-linear propagation over realistic links made up of 20 spans of either standard single mode fiber (SSMF) or non-zero dispersion-shifted fiber (NZDSF). We show that HEXA not only confirms its theoretical sensitivity advantage over PM-QPSK in back-to-back, but also shows a greater resilience to non-linear effects, allowing for substantially increased span loss margins. As a consequence, HEXA appears as an interesting option for dual-format transceivers capable to switch on-the-fly between PM-QPSK and HEXA when channel propagation degrades. It also appears as a possible direct competitor of PM-QPSK, especially over NZDSF fiber and uncompensated links

Application of the feature-detection rule to the negative selection algorithm

The Negative Selection Algorithm developed by Forrest et al. was inspired by the way in which T-cell lymphocytes mature within the thymus before being released into the blood system. The mature T-cell lymphocytes exhibit an interesting characteristic, in that they are only activated by non-self cells that invade the human body. The Negative Selection Algorithm utilises an affinity matching function to ascertain whether the affinity between a newly generated (NSA) T-cell lymphocyte and a self-cell is less than a particular threshold; that is, whether the T-cell lymphocyte is activated by the self-cell. T-cell lymphocytes not activated by self-sells become mature T-cell lymphocytes. A new affinity matching function termed the feature-detection rule is introduced in this paper. The feature-detection rule utilises the interrelationship between both adjacent and non-adjacent features of a particular problem domain to determine whether an antigen is activated by an artificial lymphocyte. The performance of the featuredetection rule is contrasted with traditional affinity matching functions, currently employed within Negative Selection Algorithms, most notably the r-chunks rule (which subsumes the r-contiguous bits rule) and the hamming distance rule. This paper shows that the feature-detection rule greatly improves the detection rates and false alarm rates exhibited by the NSA (utilising the r-chunks and hamming distance rule) in addition to refuting the way in which permutation masks are currently being applied in artificial immune systems.http://www.elsevier.com/locate/esw

A Simple and Effective Closed-Form GN-Model Correction Formula Accounting for Signal Non-Gaussian Distribution

The GN model of non-linear fiber propagation has been shown to overestimate the variance of non-linearity due to the signal Gaussianity approximation, leading to maximum reach predictions for realistic optical systems which may be pessimistic by about 5% to 15%, depending on fiber type and system set-up. Analytical corrections have been proposed, which however substantially increase the model complexity. In this paper we provide a simple closed-form GN model correction formula, derived from the EGN model, which we show to be quite effective in correcting for the GN model tendency to overestimate non-linearity. The formula also permits to clearly identify the correction dependence on key system parameters, such as span length and loss.Comment: This paper has been accepted for publication in the IEEE Journal of Lightwave Technolog