Summary

My research interests focus on the general fields of plamonics, metamaterials and terahertz.

Plasmonics

The field of plasmonics is concerned with the science and engineering of optical interaction with the free electrons in metals and semi-conductors. It is meant to bridge the gap between the world of nanoscale electronics and microscale photonics, but it also holds promise in spectroscopy, imaging, quantum physics, nonlinearities, etc.

My current interest in plasmonics is on nanoantennas for harmonic generation and ultra-wideband spectroscopy.

Efficient frequency conversion is commonly accomplished at the macroscopic scale in inorganic birefringent crystals. However, nonlinear crystals are several wavelengths in size, polarization-dependent, and phase-matching limited, which hinder the development of chip-scale tuneable nonlinear optical materials. In addition, to trigger the non-linear process, high intensity sources are required. We envision that broadband nanoantennas designed to operate at the fundamental and harmonics can potentially path the way for efficient nonlinear nanodevices with high frequency tune-ability and lower source intensity needs.

Currently, performing surface-enhanced spectroscopy experiments from the visible to the infrared regions is done designing and fabricating multiple plasmonics structures, which is time consuming and prevents the development of integrated sensors for monitoring simultaneously multiple spectral fingerprint regions or probing random molecular species. Had we a single platform enabling field enhancement from visible to infrared, this problem would be solved. Hence, we propose the use of broadband/multi-frequency antenna designs like the log-periodic antenna to overcome this limitation.

Broadband log-periodic plasmonic nanoantenna

THG from a single ITO nanoparticle coupled to a nanoantenna

Achievements:

Simultaneous surface-enhanced fluorescence, Raman and infrared absorption spectroscopies using a single broadband nanoantenna

Effective χ⁽²⁾ from an only-metal nanoantenna of the order of nonlinear crystals

Third harmonic generation enhancements of up to 10⁶ folds compared to an isolated ITO nanoparticle, with an effective third order susceptibility up to 3.5×10³ nm²/V² and conversion efficiency of 0.0007%

Metamaterials

Metamaterials are artificial structures whose electromagnetic properties, represented by the electric permittivity and magnetic permeability, can be engineered by properly designing the building blocks (i.e. the repetitive sub-wavelength unit cell) to achieve extraordinary phenomena not observed easily in nature. This field has revolutionized the way we design and engineer new materials.

Great deal of research is being devoted to the underlying physics of metamaterials. However, my attention is focused on developing quasi-optical devices with a twofold objective: (i) demonstrate experimentally certain properties such as effective negative refractive index, and (ii) propose metamaterial-based devices competitive in some aspects with the current technology. In particular, I am very keen on metamaterial-based lenses and wave plates given their compactness and potential free-space matching.

Mmw metamaterial prism displaying negative refraction for Ey, and positive refraction for Ex

λ-thick zoned fishnet metamaterial lens working at 60 GHz

Achievements:

First experimental demonstration of negative refraction on the fishnet metamaterial (also known also as extraordinary transmission metamaterial or stacked sub-wavelength hole array metamaterial) via the prism experiment

Unveil the connection between the extraordinary transmission phenomenon and the fishnet metamaterial

Quasi-optical devices (lenses, polarizers, etc.) based on the fishnet metamaterial competitive with classical metallic quasi-optical devices

Terahertz

The terahertz frequency range (ca. 0.3 - 10 THz, i.e., λ = 30 μm - 1 mm) is particularly rich in spectral fingerprints. This includes  low energy  excitations  in  electronic  materials,  low-frequency  vibrational  modes  of  condensed phase  media,  and  vibration  and  rotational  transitions  in  molecules.  This region of the spectrum has been less explored than others until recently, due to the lack of efficient and compact THz sources and detectors. THz  technology  promises  significant applications  on  the  areas  of  security  (driven  by  the  global  concern  of personal  screening  in  public  places), medical  imaging and high-speed communication.

My activity in this field encompasses two disciplines:

Design of frequency selective surfaces for quasi-optical mesh filters, highly-confined surface waves and beam-shaping.

Near-field time-domain spectroscopy and imaging for device (e.g. waveguides) characterization and for the investigation of sub-wavelength dielectric particles.

Dispersion diagram of different pierced metals supporting THz slow waves. Bottom: CSRR-based broadband slow wave

Blind annular holes support highly confined surface waves at two different frequencies

Pulse propagation along a tapered parallel-plate waveguide

Achievements:

Unify the description of confined THz surface waves based on periodically pierced metals using the transverse resonance method for transmission lines/equivalent lumped networks.

Wideband highly-confined THz surface wave

Discuss for the first time the effect of TE_m,n modes on finite-parallel-plate waveguide 

International R&D projects:

1. Broadband THz surface waves, IE130803, funded by the Royal Society - International Exchange Grant, 10/11/2013-19/09/2014

2. Novel Antennas Based Upon Extraordinary Transmission Metamaterial Lenses, funded by European Office of Aerospace Research and Development (EOARD), US Air Force Research Laboratory and US Army Research Laboratory, 03/08/2010-02/08/2011

3. Metamaterials for Active Electronically Scanned Arrays, METALESA, A-1089-RT-GC, funded by European Defence Agency, EDA JIP-ICET, 2010-2012

4. Forecasts in Metamaterials with Extreme Parameters for Disruptive Antennas, Radomes, and Cloaking in Radar Applications, METAFORE, A-1036-RT-GC, funded by European Defence Agency, EDA JIP-ICET, 2010-2011

Spanish R&D projects:

1. Avanzando en Plasmonica y Metamateriales para Sensores y Comunicaciones, TEC2011-28664-C02-01, funded by the Spanish Government, 01/01/2012-31/12/2014

2. Analisis de prestaciones de metamateriales en aplicaciones volumetricas, funded by Tafco Metawireless, S.L., OTRI 2010024071, 03/06/2010-02/09/2010

3. Consolider Engineering Metamaterials, CSD2008-00066, funded by the Spanish Government, 2008-2012

4. Metamateriales: Estructuras Periodicas y Estructuras Sintetizadas para Microondas y Ondas Milimetricas, TEC2008-06871-C02-01, funded by the Spanish Government, 2009-2011

5. Metamateriales para Elementos Radiantes en Microondas y Milimetricas, TEC2005-06923-C03-01, funded by the Spanish Government, 2006-2008

6. Tecnicas de diseño de filtros compactos de microondas para front-ends de comunicaciones Ultra-Wide Band (UWB) mediante conectorizacion BGA (Ball Grid Array) compatible con tecnologia clasica de circuito impreso PCB (Printed Circuit Board), funded by the Navarre government, 2006-2007