Seb Savory

University of Cambridge | Cam · Department of Engineering

Topology Bench is a comprehensive topology dataset designed to accelerate benchmarking studies in optical networks. The dataset, focusing on core optical networks, comprises publicly accessible and ready-to-use topologies, including (a) 105 georeferenced real-world optical networks and (b) 270,900 validated synthetic topologies. Prior research on r...

Ultra-wideband systems expand the optical bandwidth in wavelength-division multiplexed (WDM) systems to provide increased capacity using the existing fiber infrastructure. In ultra-wideband transmission, power is transferred from shorter-wavelength WDM channels to longer-wavelength WDM channels due to inelastic inter-channel stimulated Raman scatte...

We propose a data-driven erbium-doped fiber amplifier (EDFA) gain model utilizing Gaussian process regression (GPR). An additive Laplacian and radial-basis function kernel is proposed for the GPR and was found to outperform deep neural network (DNN) methods while additionally providing prediction uncertainty. Performance is measured using mean abso...

Recently several machine learning methods have been proposed to estimate the SNR, based on launch data and other system factors. These data-driven methods typically require a large number of datasets for training and generally are not interpretable. In this paper, we propose an alternative approach that requires less data and is interpretable, spec...

We demonstrate 200 Gb/s bidirectional coherent PON solutions using a simplified optical network unit (ONU) over 19 km of field-installed fiber. The ONU receiver is a single-polarization heterodyne detector with either a balanced or a single-ended photodetector and the transmitter is based on dual-polarization electro-absorption modulated laser (EML...

A simple single-polarization heterodyne optical network unit (ONU) receiver with Alamouti-coding based polarization diversity at the optical line terminal (OLT) side is a promising solution for passive optical networks (PON) beyond 50 Gbps. The special equalizer required for data recovery of such system has been demonstrated for 200 Gbps PON downst...

Future passive optical networks (PONs) for ${200}\;{\rm Gb/s/}\lambda$ 200 G b / s / λ , and beyond, pose a significant technological challenge. The use of coherent technology in access networks provides a great solution based on concepts from mature technologies to achieve the speeds needed for very-high-speed PON (VHSP). In this paper, we provide...

We present a fast and accurate physical layer model assisted by a neural network to maximize the throughput for ultra-wideband systems. The proposed approach significantly saves computation time and keeps the same precision.

Graph representation learning on real-world optical core networks outperforms edge prediction heuristics by 10 times, achieving up to 93.4% accuracy on BT(UK), COST(EU), and CORONET(USA) by learning from 10% training data.

We demonstrate 200 Gb/s/ λ bidirectional coherent PON solution with simplified ONU on field installed fiber. We achieve 30.5/37 dB power budget for the downstream transmission with single-ended/balanced photodiode and 30.1 dB for the upstream transmission.

We experimentally demonstrate 200 Gb/s/ $\lambda $ upstream coherent passive optical network (PON) using polarization division multiplexed (PDM) pulse amplitude modulation 4-level (PAM4) signal with coherent detection. The 50 GBaud PDM-PAM4 is generated using a low cost C-band electro-absorption modulated laser (EML), polarization-division multipl...

We present a novel methodology for optimizing fiber optic network performance by determining the ideal values for attenuation, nonlinearity, and dispersion parameters in terms of achieved signal-to-noise ratio (SNR) gain from digital backpropagation (DBP). Our approach uses Gaussian process regression, a probabilistic machine learning technique, to...

Performance optimization literature in optical networks predominantly consists of single objective optimization studies while often in practice multiple performance goals are to be met. This study addresses this issue with a generalized reinforcement learning (RL) model for parameter optimization in optical networks in the presence of multiple perf...

We experimentally demonstrate 200 Gb/s/ $\lambda $ downstream transmission for a passive optical network (PON) with a minimal coherent receiver at optical network unit (ONU). The low complexity receiver required at the cost-sensitive ONU employs heterodyne detection and requires a single photodiode, a 3-dB optical coupler and a local oscillator, a...

We experimentally investigate a simple fiber nonlinearity pre-compensation technique for 200 Gbps PON downstream using a simplified coherent receiver. A power budget improvement of 1.0 dB is achieved for 50 km reach in C-band.

Digital coherent transceivers have developed to the stage that they can monitor the physical state of an optical network and thus are capable of generating data to build measurement-informed physical layer models. After reviewing the measurement capabilities of coherent transceivers, we discuss different modeling approaches including physics-based...

In this paper, a nonlinearity-tolerant sphere shaping is proposed based on the parallel bisection structure. Compared to enumerative sphere shaping (ESS), the bisection-based sphere shaping (BS-SS) can achieve a lower average energy and rate loss at the same blocklength by selecting all preferential sequences. The nonlinearity-tolerant BS-SS (BS-SS...

The recent evolution of passive optical network standards and related research activities for physical layer solutions that achieve bit rates well above 10 Gbps per wavelength ( $\lambda$ λ ) is discussed. We show that the advancement toward 50, 100, and ${{200}}\;{\rm{Gbps/}}\lambda$ 200 G b p s / λ will certainly require a strong introduction of...

Increased global traffic puts tough requirements not just on fiber communications links but on the entire network. This manifests itself in multiple ways, including how to optimize wavelength routing around the network, how to maximize the benefits arising from fine-control DSP with increasingly accurate real-time monitoring, and how to best deploy...

We propose a novel application of reinforcement learning (RL) with invalid action masking and a novel training methodology for routing and wavelength assignment (RWA) in fixed-grid optical networks and demonstrate the generalizability of the learned policy to a realistic traffic matrix unseen during training. Through the introduction of invalid act...

In this letter, a bidirectional symmetric 100 Gb/s/ $\lambda $ coherent passive optical network (PON) scheme with a simplified optical network unit (ONU) transceiver is proposed and experimentally demonstrated. In the proposed scheme, the downstream signal is generated in a dual-polarization coherent transmitter with Alamouti-coding at the optical...

Maximized information rates of ultra-wideband (typically, beyond 100~nm modulated bandwidth) lumped-amplified fiber-optic communication systems have been thoroughly examined accounting for the wavelength dependencies of optical fiber parameters in conjunction with the impact of the inelastic inter-channel stimulated Raman scattering (SRS). Three st...

We present a methodology for the estimation of optical network physical layer parameters from signal to noise ratio via history matching. An expensive network link simulator is emulated by a Gaussian process surrogate model, which is used to estimate a set of physical layer parameters from simulated ground truth data. The a priori knowledge assumed...

We demonstrate 100- and 200-Gb/s/λ line-rate PON downstream transmission considering Alamouti-coded 16QAM signal with a single-polarization heterodyne receiver. The power budget is experimentally evaluated for both single-ended and balanced detection considering 25 km reach.

Optical networks generate a vast amount of diagnostic, control and performance monitoring data. When information is extracted from this data, reconfigurable network elements and reconfigurable transceivers allow the network to adapt both to changes in the physical infrastructure but also changing traffic conditions. Machine learning is emerging as...

While the capacity of the next-generation access network is expected to be 100 Gb/s and beyond, coherent optics is going to be a logical choice for the physical layer as the currently used intensity-modulation/ direct-detection technology will fail to meet the required power budget of such high line-rate systems. In this article, we present an over...

In this paper, a new method for the separation of noise categories based on Four-Wave Mixing is presented. The theoretical analysis is grounded in the Gaussian Noise model and verified by split step simulations. The noise categories react differently to the introduced perturbations, by performing a set of perturbations the behaviour of the differen...

We present a framework for enhancing Gaussian process regression machine learning models with a priori knowledge derived from models of the transmission physics in optical networks. This is done by framing the regression problem as multi-task learning, in which both the measured data and targets derived from a physical model of the system are used...

In this paper, a new technique for measuring transceiver noise, skew, and for the detection of uncompensated transceiver impairments is introduced. A Frequency domain notch or notches are applied at the transmitter, allowing an estimate of the Signal-to-Noise and Distortion Ratio (SNDR) at different stages over the transmission chain. The proposed...

The management of wavelength routed optical mesh networks is complex with many potential light path routes and numerous physical layer impairments to transmission performance. This complexity can be reduced by applying the ideas of abstraction from computer science where different equipment is described in the same basic terms. The noise-to-signal...

In this paper, a new method for the separation of noise categories based on Four-Wave Mixing is presented. The theoretical analysis is grounded in the Gaussian Noise model and verified by split step simulations. The noise categories react differently to the introduced perturbations, by performing a set of perturbations the behaviour of the differen...

In this paper, we discuss a new technique for measuring transceiver noise, skew, and for the detection of uncompensated transceiver impairments. The method consists on the introduction of frequency domain notch or notches at the transmitter, which allows to estimate of the Signal-to-Noise and Distortion Ratio (SNDR) at different stages over the tra...

In this paper, we discuss different nonlinear impairments in short-reach fibre transmission systems. Recent progress on the nonlinear digital signal processing techniques to mitigate such nonlinear impairments are summarized.

We demonstrate the suitability of extreme value statistics for the analysis of the extreme values of SNR time series data from a deployed network. Underlying theory, potential use cases and practical considerations are discussed.

A bidirectional symmetric 100-Gb/s/λ coherent PON with a simplified ONU transceiver is experimentally demonstrated. With only 3-dBm LO power at the ONU side, >30-dB power budget is achieved for both upstream and downstream with 50-km reach.

Perturbed spectra are modelled to estimate OSNR for a single channel amplified link. Perturbation-dependent nonlinear noise is separated from constant ASE noise using a set of propagated perturbed spectra. A least mean square fitting is used to estimate OSNR with standard deviation of 0.16 dB.

Extreme value theory provides a framework to assess rare but extreme events such as network outages or cycle slips. We present the theory of extreme value statistics and its application to optical fiber communication systems. © 2020 The Author

We propose a metric for MLSE-Viterbi differential decoding of complex modulation of directly modulated lasers (CM-DML) that reports SNR gains of 1.8 dB at BER=10−3 on a simulated PAM4 signal with a typical linewidth enhancement factor α = 4

Power fluctuations accumulate in ROADM–free space–switched networks. Thousands of randomized nonlinear transmissions demonstrate that capacity with an inventory of {5,10,15,20} dB gain amplifiers is within 10 % of optimal and triple that with {10,20} dB amplifiers over 1,000 km.

Digital coherent transceivers are a promising technology for future access networks, enabling self-calibration, increased sensitivity and the ability to mitigate channel impairments. We consider options for coherent access networks targeting 100 Gbit/s per wavelength channel.

Routing and wavelength assignment (RWA) algorithms must strike a balance between finding routes with high quality of transmission (QoT) and finding routes that will not interfere with allocating future traffic. Too much emphasis on the first will concentrate traffic along major routes causing congestion whilst too much emphasis on the second will c...

We demonstrate from a system design perspective that nonlinearity can be exploited to minimize the impact of system margins on system performance for both point-to-point links and elastic optical networks. A nonlinear interaction causes a 2 dB reduction in launch power to be reduced to $ \lt\!{0.25}\,\,{\rm{dB}}$ < 0.25 d B signal-to-noise ratio (S...

We consider the partially coherent additive white Gaussian noise channel (PCAWGN) in optical communications and review the derivation of the exact channel conditional probability model in a closed-form solution in polar coordinates. In addition, we derive a reduced-complexity approximation by replacing the Rician and Tikhonov distributions describi...

We compare three independent impairment abstractions of an installed fibre infrastructure. Abstractions agreed to within 1.3dB despite being obtained from different nodes using different terminal equipment. Validation using a DWDM virtual topology was within 1.4dB.

The required complexity of coherent technology has always been a show-stopper in optical access networks. Here, the recent compelling research activities in low-complexity coherent PONs are reviewed, and their feasibility for 50 Gb/s/λ is investigated.

Quantum key distribution (QKD), a technology that enables perfectly secure communication, has evolved to the stage where many different protocols are being used in real-world implementations. Each protocol has its own advantages, meaning that users can choose the one best-suited to their application, however each often requires different hardware....

Quantum key distribution (QKD), a technology that enables perfectly secure communication, has evolved to the stage where many different protocols are being used in real-world implementations. Each protocol has its own advantages, meaning that users can choose the one best-suited to their application, however each often requires different hardware....

Operators are pressured to maximize the achieved capacity over deployed links. This can be obtained by operating in the weakly nonlinear regime, requiring a precise understanding of the transmission conditions. Ideally, optical transponders should be capable of estimating the regime of operation from the received signal and feeding that information...

Digital coherent receivers employing Alamouti-coding are a promising solution for passive optical networks (PON) with downstream rates of 100Gb/s/λ. To reduce cost by utilizing high-volume photodiodes designed for 25Gb/s data-center applications, we consider 28-Gbaud 16-QAM modulation format detected with a single-polarization coherent receiver bas...

Digital coherent receivers employing Alamouti-coding are a promising solution for passive optical networks (PON) with downstream rates of 100Gb/s/λ. To reduce the cost by utilizing high-volume photodiodes designed for 25Gb/s data-center applications, we consider 28-Gbaud 16-QAM modulation format detected with a single-polarization coherent receiver...

We propose an adaptive sequential loading algorithm that approaches the ILP throughput. Of 2,000 network realizations tested, shortest path routing achieves >90 % of the maximum throughput in 341 cases c.f. 1,904 with the proposed algorithm.

A novel technique estimating ASE and non-linear SNR is presented. Our method is evaluated by simulations obtaining a std error of 0.23 dB for both ASE and non-linear SNR.

A dark fiber network was partially abstracted utilizing network monitors, prior information and a single probe channel. Validation employed 13x200Gb/s DWDM signals transmitted at the optimum launch power, with measured performance 0.2dB better than abstracted.

Distributed-phase-reference (DPR) systems were introduced as a method of decreasing the complexity of quantum key distribution systems for practical use. However, their information-theoretic security has only been proven when the added requirement of block-wise phase randomisation is met. Realisation of this with a conventional approach would resul...

The currently employed transceiver technology in optical network units is likely to be stretched when demand reaches multi-gigabit/s per subscriber level in access networks. Therefore, coherent-enabled access networks have become more attractive in recent years, as they offer high receiver sensitivity, inherent frequency selectivity, and linear fie...

It is predicted that demand in optical access networks will reach multi-Gb/s per user. However, the limited performance of the direct detection receiver technology currently used in the optical network units at the customers' premises restricts data rates/user. Therefore, the concept of coherent-enabled access networks has attracted attention in re...

High-speed broadband services require optical fibres in access networks, in which multiple subscribers are connected to service providers, to satisfy the continuously growing bandwidth demand. The primitive signaling scheme used in access networks enables the use of low-cost equipment but diminishes the bandwidth available to end-users. Thus, curre...

High-speed broadband services require optical fibres in access networks, in which multiple subscribers are connected to service providers, to satisfy the continuously growing bandwidth demand. The primitive signaling scheme used in access networks enables the use of low-cost equipment but diminishes the bandwidth available to end-users. Thus, curre...

Quantum key distribution (QKD) allows two users to communicate with theoretically provable secrecy by encoding information on photonic qubits. Current encoders are complex, however, which reduces their appeal for practical use and introduces potential vulnerabilities to quantum attacks. Distributed-phase-reference (DPR) systems were introduced as a...

Time-bin encoding is an attractive method for transmitting photonic qubits over long distances with minimal decoherence. It allows a simple receiver for quantum key distribution (QKD) that extracts a key by measuring time of arrival of photons and detects eavesdropping by measuring interference of pulses in different time bins. In the past, coheren...

Time-bin encoding is an attractive method for transmitting photonic qubits over long distances with minimal decoherence. It allows a simple receiver for quantum key distribution (QKD) that extracts a key by measuring time of arrival of photons and detects eavesdropping by measuring interference of pulses in different time bins. In the past, coheren...

We propose a modified DBP algorithm accounting for PMD. The accumulated PMD at the receiver is factorized into several PMD sections, and inserted into the DBP routine to distributively compensate for PMD, outperforming the conventional approach by 1.1 dB in SNR.

In this paper, we link the throughput gains, due to transceiver adaptation, in a point-to-point transmission link to the expected gains in a mesh network. We calculate the maximum network throughput for a given topology as we vary the length scale. We show that the expected gain in the network throughput due to transceiver adaptation is equivalent...

In this paper we link the throughput gains, due to transceiver adaptation, in a point-to-point transmission link to the expected gains in a mesh network. We calculate the maximum network throughput for a given topology as we vary the length scale. We show that the expected gain in network throughput due to transceiver adaptation is equivalent to th...

Digital coherent transceivers have revolutionized optical fiber communications due to their superior performance offered compared to intensity modulation and direct detection based alternatives. As systems employing digital coherent transceivers seek to approach their information theoretic capacity, the use of multilevel modulation formats combined...

Digital coherent transceivers have revolutionized optical fiber communications due to their superior performance offered compared to intensity modulation and direct detection based alternatives. As systems employing digital coherent transceivers seek to approach their information theoretic capacity, the use of multilevel modulation formats combined...

Digital backpropagation (DBP) is a promising digital-domain technique to mitigate Kerr-induced nonlinear interference. While it successfully removes deterministic signal–signal interactions, the performance of ideal DBP is limited by stochastic effects, such as polarization-mode dispersion (PMD). In this paper, we consider an ideal full-field DBP i...

Traditionally optical fiber nonlinearity is considered a limiting factor for transmission systems. Nevertheless from a system design perspective this nonlinearity can be exploited to minimize the impact of uncertainty on the system performance. A consequence of this is that it becomes beneficial to consider the uncertainty at the design stage, resu...

For the first time the modulation format dependence of nonlinear interference in long-haul optical fibre transmission is experimentally demonstrated for polarisation-division multiplexed 4, 16, 64 and 256-QAM.

Polarization-time block-coded OFDM-QPSK downstream channels are robustly detected using