69 research outputs found
Transient perturbative nonlinear responses of plasmonic materials
Recent investigations on optical nonlinearities of plasmonic materials
suggest their responses may be even beyond the usual perturbative description.
To better understand these surprisingly strong responses, we develop here a
simple but general approach to describe the nonlinear optical response of
plasmonic materials up to th perturbation order. We apply the approach to
understand spectral broadening occurring in resonant metasurfaces and
investigate the enhancement of high-harmonic generation from multiply-resonant
metasurfaces, predicting an over million-fold enhancement of higher harmonics.Comment: 6 pages, 2 figure
DeepTx: Deep Learning Beamforming with Channel Prediction
Machine learning algorithms have recently been considered for many tasks in
the field of wireless communications. Previously, we have proposed the use of a
deep fully convolutional neural network (CNN) for receiver processing and shown
it to provide considerable performance gains. In this study, we focus on
machine learning algorithms for the transmitter. In particular, we consider
beamforming and propose a CNN which, for a given uplink channel estimate as
input, outputs downlink channel information to be used for beamforming. The CNN
is trained in a supervised manner considering both uplink and downlink
transmissions with a loss function that is based on UE receiver performance.
The main task of the neural network is to predict the channel evolution between
uplink and downlink slots, but it can also learn to handle inefficiencies and
errors in the whole chain, including the actual beamforming phase. The provided
numerical experiments demonstrate the improved beamforming performance.Comment: 27 pages, this work has been submitted to the IEEE for possible
publication; v2: Fixed typo in author name, v3: a revisio
Demonstration of Optical Nonlinearity in InGaAsP/InP Passive Waveguides
We report on the study of the third-order nonlinear optical interactions in
InGaAsP/InP strip-loaded waveguides. The material
composition and waveguide structures were optimized for enhanced nonlinear
optical interactions. We performed self-phase modulation, four-wave mixing and
nonlinear absorption measurements at the pump wavelength 1568 nm in our
waveguides. The nonlinear phase shift of up to has been observed in
self-phase modulation experiments. The measured value of the two-photon
absorption coefficient was 15 cm/GW. The four-wave mixing conversion
range, representing the wavelength difference between maximally separated
signal and idler spectral components, was observed to be 45 nm. Our results
indicate that InGaAsP has a high potential as a material platform for nonlinear
photonic devices, provided that the operation wavelength range outside the
two-photon absorption window is selected
Using surface lattice resonances to engineer nonlinear optical processes in metal nanoparticle arrays
Collective responses of localized surface plasmon resonances, known as
surface lattice resonances (SLRs) in metal nanoparticle arrays, can lead to
high quality factors (~100), large local-field enhancements and strong
light-matter interactions. SLRs have found many applications in linear optics,
but little work of the influence of SLRs on nonlinear optics has been reported.
Here we show how SLRs could be utilized to enhance nonlinear optical
interactions. We devote special attention to the sum-frequency,
difference-frequency, and third-harmonic generation processes because of their
potential for the realization of novel sources of light. We also demonstrate
how such arrays could be engineered to enhance higher-order nonlinear optical
interactions through cascaded nonlinear processes. In particular, we
demonstrate how the efficiency of third-harmonic generation could be engineered
via cascaded second-order responses
HybridDeepRx: Deep Learning Receiver for High-EVM Signals
In this paper, we propose a machine learning (ML) based physical layer
receiver solution for demodulating OFDM signals that are subject to a high
level of nonlinear distortion. Specifically, a novel deep learning based
convolutional neural network receiver is devised, containing layers in both
time- and frequency domains, allowing to demodulate and decode the transmitted
bits reliably despite the high error vector magnitude (EVM) in the transmit
signal. Extensive set of numerical results is provided, in the context of 5G NR
uplink incorporating also measured terminal power amplifier characteristics.
The obtained results show that the proposed receiver system is able to clearly
outperform classical linear receivers as well as existing ML receiver
approaches, especially when the EVM is high in comparison with modulation
order. The proposed ML receiver can thus facilitate pushing the terminal power
amplifier (PA) systems deeper into saturation, and thereon improve the terminal
power-efficiency, radiated power and network coverage.Comment: To be presented in the 2021 IEEE International Symposium on Personal,
Indoor and Mobile Radio Communication
Thermal Control of Plasmonic Surface Lattice Resonances
Plasmonic metasurfaces exhibiting collective responses known as surface
lattice resonances (SLRs) show potential for realizing tunable and flat
photonic components for wavelength-selective processes, including lasing and
optical nonlinearities. However, post-fabrication tuning of SLRs remains
challenging, limiting the applicability of SLR-based components. Here, we
demonstrate how the properties of high quality factor SLRs are easily modified
by breaking the symmetry of the nanoparticle surroundings. We break the
symmetry by changing the refractive index of the overlying immersion oil simply
by controlling the ambient temperature of the device. We show that already
modest temperature changes of 10{\deg}C can increase the quality factor of the
investigated SLR from 400 to 750. Our results demonstrate accurate and
reversible modification of the properties of the SLRs, paving the way towards
tunable SLR-based photonic devices. On a more general level, our results
demonstrate how symmetry breaking of the surrounding dielectric environment can
be utilized for efficient and potentially ultrafast modification of the SLR
properties
Phase-Matched Second-Harmonic Generation from Metasurfaces Inside Multipass Cells
We demonstrate a simple and scalable approach to increase conversion
efficiencies of nonlinear metasurfaces by incorporating them into multipass
cells and by letting the pump beam to interact with the metasurfaces multiple
times. We experimentally show that by metasurface design, the associated
phase-matching criteria can be fulfilled. As a proof of principle, we achieve
phase matching of second-harmonic generation (SHG) using a metasurface
consisting of aluminium nanoparticles deposited on a glass substrate. The
phase-matching condition is verified to be achieved by measuring superlinear
dependence of the detected SHG as a function of number of passes. We measure an
order of magnitude enhancement in the SHG signal when the incident pump
traverses the metasurface up to 9 passes. Results are found to agree well with
a simple model developed to estimate the generated SHG signals. We also discuss
strategies to further scale-up the nonlinear signal generation. Our approach
provides a clear pathway to enhance nonlinear optical responses of
metasurface-based devices. The generic nature of our approach holds promise for
diverse applications in nonlinear optics and photonics
Polarized THG Microscopy Identifies Compositionally Different Lipid Droplets in Mammalian Cells
Peer reviewe
Nonlinear nonlocal metasurfaces
Optical metasurfaces have recently emerged as the game changer in light manipulation and opened up new perspectives in many subfields of optics and photonics. Recent developments in nonlocal metasurfaces, in which the nanoscale building blocks respond to the incoming light collectively rather than as individual objects, are especially promising for enhancing and controlling the nonlinear optical phenomena. In this article, we provide a brief overview of the basic principles of nonlocal metasurfaces in the context of their nonlinear optical functionalities. We discuss the origin and the regimes of the nonlocal response, covering the aspects of multiple scattering, radiation damping, quality factor, local-field enhancement, and temporal dynamics. Some important aspects are illustrated by computational examples. We also give our personal viewpoint on the selected ideas and research directions in nonlocal and nonlinear metasurfaces, including the role of spatial symmetry in nonlocal interactions, the effects of phase and momentum matching in frequency conversion, as well as the possibilities offered by new material platforms and novel concepts, such as bound states in the continuum, parity-time symmetry, and time-variant metasurfaces.publishedVersionPeer reviewe
- …