193,690 research outputs found
Optical forces between dielectric nanoparticles in an optical vortex
We report a study on the optical forces between a pair of dielectric particles, based on quantum electrodynamics. At a fundamental level these forces result from a stimulated scattering process which entails a virtual photon relay between the two particles. Results for a variety of systems are secured from a completely general analysis that accommodates a system with arbitrary dielectric properties (with regard to shape, frequency response etc.) in an optical field of arbitrary complexity. Specific results are obtained and exhibited for: (a) optical forces between nanoparticles, and specifically between carbon nanotubes; (b) the effects of optical ordering, clustering and trapping associated with twisted (Laguerre-Gaussian) laser beams
Optical Network Models and their Application to Software-Defined Network Management
Software-defined networking is finding its way into optical networks. Here,
it promises a simplification and unification of network management for optical
networks allowing automation of operational tasks despite the highly diverse
and vendor-specific commercial systems and the complexity and analog nature of
optical transmission. A fundamental component for software-defined optical
networking are common abstractions and interfaces. Currently, a number of
models for optical networks are available. They all claim to provide open and
vendor agnostic management of optical equipment. In this work, we survey and
compare the most important models and propose an intent interface for creating
virtual topologies that is integrated in the existing model ecosystem.Comment: Parts of the presented work has received funding from the European
Commission within the H2020 Research and Innovation Programme, under grant
agreeement n.645127, project ACIN
Using effective medium theories to design tailored nanocomposite materials for optical systems
Modern optical systems are subject to very restrictive performance, size and
cost requirements. Especially in portable systems size often is the most
important factor, which necessitates elaborate designs to achieve the desired
specifications. However, current designs already operate very close to the
physical limits and further progress is difficult to achieve by changing only
the complexity of the design. Another way of improving the performance is to
tailor the optical properties of materials specifically to the application at
hand. A class of novel, customizable materials that enables the tailoring of
the optical properties, and promises to overcome many of the intrinsic
disadvantages of polymers, are nanocomposites. However, despite considerable
past research efforts, these types of materials are largely underutilized in
optical systems. To shed light into this issue we, in this paper, discuss how
nanocomposites can be modeled using effective medium theories. In the second
part, we then investigate the fundamental requirements that have to be
fulfilled to make nanocomposites suitable for optical applications, and show
that it is indeed possible to fabricate such a material using existing methods.
Furthermore, we show how nanocomposites can be used to tailor the refractive
index and dispersion properties towards specific applications.Comment: This is a draft manuscript of a paper published in Proc. SPIE
(Proceedings Volume 10745, Current Developments in Lens Design and Optical
Engineering XIX, Event: SPIE Optical Engineering + Applications, 2018
Phase Noise Compensation for Nonlinearity-Tolerant Digital Subcarrier Systems With High-Order QAM
The fundamental penalty of subcarrier modulation (SCM) with independent subcarrier phase noise processing is estimated. It is shown that the fundamental signal-to-noise ratio (SNR) penalty related to poorer phase noise tolerance of decreased baudrate subcarriers increases significantly with modulation format size and can potentially exceed the gains of the nonlinear tolerance of SCM. A low-complexity algorithm is proposed for joint subcarrier phase noise processing, which is scalable in the number of subcarriers and recovers almost entirely the fundamental SNR penalty with respect to single-carrier systems operating at the same net data-rate. The proposed algorithm enables high-order modulation formats with high count of subcarriers to be safely employed for nonlinearity mitigation in optical communication systems
Multichannel Nonlinear Equalization in Coherent WDM Systems based on Bi-directional Recurrent Neural Networks
Kerr nonlinearity in the form of self- and cross-phase modulation imposes a
fundamental limitation to the capacity of wavelength division multiplexed (WDM)
optical communication systems. Digital back-propagation (DBP), that requires
solving the inverse-propagating nonlinear Schr\"odinger equation (NLSE), is a
widely adopted technique for the mitigation of impairments induced by Kerr
nonlinearity. However, multi-channel DBP is too complex to be implemented
commercially in WDM systems. Recurrent neural networks (RNNs) have been
recently exploited for nonlinear signal processing in the context of optical
communications. In this work, we propose multi-channel equalization through a
bidirectional vanilla recurrent neural network (bi-VRNN) in order to improve
the performance of the single-channel bi-VRNN algorithm in the transmission of
WDM M-QAM signals. We compare the proposed digital algorithm to full-field DBP
and to the single channel bi-RNN in order to reveal its merits with respect to
both performance and complexity. We finally provide experimental verification
through a QPSK metro link, showcasing over 2.5 dB optical signal-to-noise ratio
(OSNR) gain and up to 43% complexity reduction with respect to the
single-channel RNN and the DBP.Comment: 9 page
Experimental characterization of nonlocal photon fluids
Quantum gases of atoms and exciton-polaritons are now well-established theoretical and experimental tools for fundamental studies of quantum many-body physics and suggest promising applications to quantum computing. Given their technological complexity, it is of paramount interest to devise other systems where such quantum many-body physics can be investigated at lesser technological expense. Here we examine a relatively well-known system of laser light propagating through thermo-optical defocusing media: based on a hydrodynamic description of light as a quantum fluid of interacting photons, we investigate such systems as a valid room-temperature alternative to atomic or exciton–polariton condensates for studies of many-body physics. First, we show that by using a technique traditionally used in oceanography it is possible to perform a direct measurement of the single-particle part of the dispersion relation of the elementary excitations on top of the photon fluid and to detect its global flow. Then, using a pump-and-probe setup, we investigate the dispersion of excitation modes of the fluid: for very long wavelengths, a sonic, dispersionless propagation is observed that we interpret as a signature of superfluid behavior
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