Multilevel Monte Carlo sampling on heterogeneous computer architectures

Monte Carlo (MC) sampling is the standard approach for uncertainty propagation in problems with high-dimensional stochastic inputs. Various acceleration techniques have been developed to overcome the slow convergence of MC estimates, such as multilevel Monte Carlo (MLMC). MLMC uses successive approximations computed on levels, models with different levels of accuracy, and computational cost to reduce the estimator variance. MLMC analytically determines the number of samples required on each level to achieve a given accuracy at minimal cost. We propose an extension of the original MLMC theoretical framework for modern, heterogeneous computer architectures in which accelerators (GPUs) are available and, therefore, samples can be distributed on both different levels and different compute units (CPUs and GPUs). We derive the optimal sample allocation for the proposed MLMC extension by solving a convex optimization problem. We apply the MLMC extension to a stochastically heated channel flow to provide insight for a study on the design of concentrated solar energy receivers. We demonstrate for the stochastically heated channel flow that the proposed MLMC extension leads to considerable total cost reduction (up to 86%) compared to MLMC using only GPUs.Peer ReviewedPostprint (author's final draft

Experimental Demonstration of Stokes Space Equalization for Space Division Multiplexed Signals

In this letter we experimentally validate, for the first time, the Stokes space algorithm (SSA) equalizer for space division multiplexing (SDM) transmission systems. We introduce the frequency domain (FD)-SSA and FD least-mean square (FD-LMS) algorithms, and evaluate their performance for different frequency offsets by computer simulations. Our simulations show that FD-SSA is insensitive to the frequency offsets, not requiring carrier frequency estimation (CFE) before equalization (pre-CFE) or carrier phase estimation (CPE) inside the loop (L-CPE). Our experimental results confirm that FD-SSA presents the same performance as FD-LMS, where the required digital signal processing (DSP) stack for FD-SSA is simpler compared to the FDLMS

LCoS SLM Study and Its Application in Wavelength Selective Switch

The Liquid-Crystal on Silicon (LCoS) spatial light modulator (SLM) has been used in wavelength selective switch (WSS) systems since the 1990s. However, most of the LCoS devices used for WSS systems have a pixel size larger than 6 µm. Although there are some negative physical effects related to smaller pixel sizes, the benefits of more available ports, larger spatial bandwidth, improved resolution, and the compactness of the whole system make the latest generation LCoS microdisplays highly appealing as the core component in WSS systems. In this review work, three specifications of the WSS system including response time, crosstalk and insertion loss, and optimization directions are discussed. With respect to response time, the achievements of liquid crystal material are briefly surveyed. For the study of crosstalk and insertion loss, related physical effects and their relation to the crosstalk or insertion loss are discussed in detail, preliminary experimental study for these physical effects based on a small pixel LCoS SLM device (GAEA device, provided by Holoeye, 3.74 µm pixel pitch, 10 megapixel resolution, telecom) is first performed, which helps with predicting and optimizing the performance of a WSS system with a small pixel size SLM. In the last part, the trend of LCoS devices for future WSS modules is discussed based on the performance of the GAEA device. Tradeoffs between multiple factors are illustrated. In this work, we present the first study, to our knowledge, of the possible application of a small pixel sized SLM as a switching component in a WSS system.This work has been supported by the EC through H2020 project ROAM (Grant No. 645361 www.roam-project.eu)

Next Generation Flexible and Cognitive Heterogeneous Optical Networks:Supporting the Evolution to the Future Internet

Optical networking is the cornerstone of the Future Internet as it provides the physical infrastructure of the core backbone networks. Recent developments have enabled much better quality of service/experience for the end users, enabled through the much higher capacities that can be supported. Furthermore, optical networking developments facilitate the reduction of complexity of operations at the IP layer and therefore reduce the latency of the connections and the expenditures to deploy and operate the networks. New research directions in optical networking promise to further advance the capabilities of the Future Internet. In this book chapter, we highlight the latest activities of the optical networking community and in particular what has been the focus of EU funded research. The concepts of flexible and cognitive optical networks are introduced and their key expected benefits are highlighted. The overall framework envisioned for the future cognitive flexible optical networks are introduced and recent developments are presented

Polarimetric and diffractive evaluation of 3.74 micron pixel-size LCoS in the telecommunications C-band

Liquid-crystal on Silicon (LCoS) microdisplays are one of the competing technologies to implement wavelength selective switches (WSS) for optical telecommunications. Last generation LCoS, with more than 4 megapixels, have decreased pixel size to values smaller than 4 microns, what increases interpixel cross-talk effects such as fringing-field. We proceed with an experimental evaluation of a 3.74 micron pixel size parallel-aligned LCoS (PA-LCoS) device. At 1550 nm, for the first time we use time-average Stokes polarimetry to measure the retardance and its flicker magnitude as a function of voltage. We also verify the effect of the antireflection coating when we try to characterize the PA-LCoS out of the designed interval for the AR coating. Some preliminary results for the performance for binary gratings are also given, where the decrease of modulation range with the increase in spatial frequency is shown, together with some residual polarization effects.Work supported by Ministerio de Economía, Industria y Competitividad (Spain) (FIS2014-56100-C2-1-P and FIS2015- 66570-P) and by Generalitat Valenciana (Spain) (PROMETEO II/2015/015). This work has been supported by the EC through H2020 project ROAM (Grant no: 645361 www.roam-project.eu )

TREND towards more energy-efficient optical networks

International audienceWith one third of the world population online in 2013 and an international Internet bandwidth multiplied by more than eight since 2006, the ICT sector is a non-negligible contributor of worldwide greenhouse gases emissions and power consumption. Indeed, power consumption of telecommunication networks has become a major concern for all the actors of the domain, and efforts are made to reduce their impact on the overall figure of ICTs, and to support its foreseen growth in a sustainable way. In this context, the contributors of the European Network of Excellence TREND have developed innovative solutions to improve the energy efficiency of networks. This paper gives an overview of the solutions related to optical networks

A Study of Connection Management Approaches for an impairment-aware Optical Control Plane

Abstract. Transparent optical networks need novel connection management approaches to take into account the presence of physical impairments in lightpath provisioning. Two main schemes are emerging from literature when considering how to introduce impairment-aware mechanisms in a distributed optical control plane like GMPLS. A well-known approach is based on extending the routing protocol to compute an optically-feasible light-path. Lately, a new approach is emerging which keeps the routing protocol unmodified while leveraging on signaling protocol extensions to find the proper lightpath for the incoming connection request. The aim of this paper is to prove that the signaling-based approach has several advantages compared to the routing-based one, in term of scalability and robustness especially when link information changes are frequent in the network. Simulation results show that a signaling-based approach is much more robust to inaccurate information about network status, therefore it is a suitable approach for considering physical impairments in dynamic optical networks

Experimental Demonstration of a Cognitive Optical Network for Reduction of Restoration Time

This paper presents the implementation and performance evaluation of a cognitive heterogeneous optical network testbed. The testbed integrates the CMP, the data plane and the cognitive system and reduces by 48% the link restoration time. This paper presents the implementation and performance evaluation of a cognitive heterogeneous optical network testbed. The testbed integrates the CMP, the data plane and the cognitive system and reduces by 48% the link restoration time

Nonlinear impairment compensation using expectation maximization for dispersion managed and unmanaged PDM 16-QAM transmission

In this paper, we show numerically and experimentally that expectation maximization (EM) algorithm is a powerful tool in combating system impairments such as fibre nonlinearities, inphase and quadrature (I/Q) modulator imperfections and laser linewidth. The EM algorithm is an iterative algorithm that can be used to compensate for the impairments which have an imprint on a signal constellation, i.e. rotation and distortion of the constellation points. The EM is especially effective for combating non-linear phase noise (NLPN). It is because NLPN severely distorts the signal constellation and this can be tracked by the EM. The gain in the nonlinear system tolerance for the system under consideration is shown to be dependent on the transmission scenario. We show experimentally that for a dispersion managed polarization multiplexed 16-QAM system at 14 Gbaud a gain in the nonlinear system tolerance of up to 3 dB can be obtained. For, a dispersion unmanaged system this gain reduces to 0.5 dB