Gradient nonlinear Pancharatnam-Berry metasurfaces

We apply the Pancharatnam-Berry phase approach to plasmonic metasurfaces loaded by highly nonlinear multiquantum-well substrates, establishing a platform to control the nonlinear wave front at will based on giant localized nonlinear effects. We apply this approach to design flat nonlinear metasurfaces for efficient second-harmonic radiation, including beam steering, focusing, and polarization manipulation. Our findings open a new direction for nonlinear optics, in which phase matching issues are relaxed, and an unprecedented level of local wave front control is achieved over thin devices with giant nonlinear responses.close0

Engineering exotic linear and nonlinear electromagnetic responses using spatial and spatiotemporal modulation

Periodicity and modulation lie at the heart of modern electromagnetic, acoustic and mechanical engineering, dramatically altering the way in which waves interact with periodically structured media. The main idea driving the intense research into periodic systems is the fact that periodicity breaks the dependence on natural properties of constituent media and instead allows one to blend the responses of various materials and leverage their geometric shapes to obtain collective responses on demand. In the realm of electromagnetics, over the past two decades there has been an explosive surge of interest to artificially engineered time-invariant periodic structures thanks to numerous fascinating linear and nonlinear effects they enable. In this dissertation, I will present some transformative developments in the area of efficient nonlinear generation and wave mixing in thin 2D periodic structures based on multi-quantum-wells, as well as show the possibility to engineer to the great extent the dispersion topology of surface waves propagating along ideally thin conducting sheets with 1D spatial periodicity such as graphene ribbons. In parallel with the progress in obtaining desired responses in time-invariant periodic structures, significant progress is being made in applying temporal and synchronous spatial and temporal modulation to engage new degrees of freedom and extend the spectrum of achievable electromagnetic phenomena even further. In this dissertation, I will also show that spatiotemporal modulation applied to electronic networks holds a key to obtain ultrawideband and extremely compact delays far beyond those achievable in time-invariant systems. Spatiotemporal modulation also allows for all kinds of nonreciprocal devices to be seamlessly integrated in an electronic chip by overcoming the size and magnetic material incompatibility constraints. This fact holds a truly groundbreaking potential for future electronic devices and wireless systems by enabling their simultaneous transmit-and-receive operation. Finally, I will show that spatiotemporal modulation enables a direct translation of some of the most advanced and intricate concepts of condensed matter physics – topological insulators – to the realm of classical electronic circuits. Compared to standalone nonreciprocal devices, topologically-nontrivial electronic circuits provide an even larger toolbox to obtain various nonreciprocal functionalities by enforcing a wideband unidirectional transmission robust to defects and imperfectionsElectrical and Computer Engineerin

Faraday rotation due to excitation of magnetoplasmons in graphene microribbons

A single graphene sheet, when subjected to a perpendicular static magnetic field, provides a Faraday rotation that, per atomic layer, greatly surpasses that of any other known material. In continuous graphene, Faraday rotation originates from the cyclotron resonance of massless carriers, which allows dynamical tuning through either external electrostatic or magneto-static setting. Furthermore, the rotation direction can be controlled by changing the sign of the carriers in graphene, which can be done by means of an external electric field. However, despite these tuning possibilities, the requirement of large magnetic fields hinders the application of the Faraday effect in real devices, especially for frequencies higher than a few terahertz. In this work we demonstrate that large Faraday rotation can be achieved in arrays of graphene microribbons, through the excitation of the magnetoplasmons of individual ribbons, at larger frequencies than those dictated by the cyclotron resonance. In this way, for a given magnetic field and chemical potential, structuring graphene periodically can produce large Faraday rotation at larger frequencies than what would occur in a continuous graphene sheet. Alternatively, at a given frequency, graphene ribbons produce large Faraday rotation at much smaller magnetic fields than in continuous graphene. © 2013 American Chemical Society.This work has been partially funded by the Spanish Ministry of Science and Innovation under Contract MAT2011-28581-C02.Peer Reviewe

Nonlinear metasurfaces based on plasmonic resonators coupled to intersubband transitions

A nonlinear metasurface structure including a multi-quantum-well layer designed for a nonlinear response for a desired nonlinear optical process and an array of nanoantennas coupled to the intersubband transitions of the multi-quantum-well layer. Each nanoantenna in the array is designed to have electromagnetic resonances at or close to all input and output frequencies of a given nonlinear optical process. Nanoantennas allow efficient coupling of any incident and outgoing light polarizations to intersubband transitions. Nanoantennas may further provide significant field enhancement in the multi-quantum-well layer. As a result, the nonlinear metasurface structure can be designed to produce a highly nonlinear response for any polarization and angle of incidence of incoming and outgoing waves in a nonlinear optical process. Due to their very larger nonlinear response, efficient frequency conversion can be produced in these metasurfaces without the stringent phase-matching constraints of bulk nonlinear crystals.Board of Regents, University of Texas Syste

Quasielectrostatic Wave Propagation Beyond the Delay-Bandwidth Limit in Switched Networks

The delay-bandwidth limit implies a stringent trade-off between the time delay, bandwidth, and propagation distance of an electromagnetic signal. Here, we show that temporal modulation can overcome this constraint, enabling extremely broadband wave propagation with close-to-zero group velocity dispersion in switched multipath electronic networks. Contrary to time-invariant waveguides, in which wave propagation implies a delicate balance between electric and magnetic stored energies, in such modulated networks the stored energy is largely electrostatic in nature. We show that in this case the phase and group velocities become independent of the properties of their constituent elements, and they are controlled only by the modulation scheme. Based on these findings, we provide practical designs of deeply subwavelength CMOS-compatible reciprocal and nonreciprocal microwave components, such as delay lines, phase shifters, couplers, and circulators. The obtained results also explicitly show that temporally modulated systems are not bound by constraints of time-invariant systems and can achieve arbitrarily large delay-bandwidth products

Ultrathin nonlinear metasurfaces with continuous phase control at the nanoscale

We describe a novel class of ultrathin plasmonic metasurfaces able to provide nonlinear conversion efficiencies many orders of magnitude larger than any other nonlinear flat setup previously reported. This large efficiency is achieved over subwavelength thickness, avoiding the use of cumbersome phase matching techniques. In addition, we show how such metasurfaces can be designed to provide full control over the local phase of the generated signals, opening exciting prospects for creating nonlinear reflect- and transmittarrays able to tailor the emerging wavefronts at will, with direct application in light bending, focusing, and communication systems