Research

In general terms our research is about applied electromagnetism/photonics. Main research lines are summarized below.

Theory and applications of exceptional points of degeneracy (EPDs)

We investigate the occurrence of EPDs in RF, microwaves, and optical structures (waveguides and cavities). And EPD is a special degeneracy condition where two or more eigenmodes of a system coalesce. Our goal is to exploit the physics associated to this very special degeneracy condition to conceive advanced and improved devices, like lasers, oscillators, amplifiers, sensors, switches, nonlinear effects, antennas, etc. We have generalize the concept of EPD to a variety of structures. Traditionally the concept of EPDs is associated to PT symmetry however we have shown that this is not necessary and actually several of our papers are not based on PT symmetry. We have also shown that EPDs do not necessarily occur in "non-Hermitian" systems, indeed we have found EPDs in several lossless and gainless structures. We have also demonstrated that EPDs can be induced in single resonators by applying a periodic time variation to one of the system components. So far we have shown that EPDs can be exploited in RF oscillators, electron beam devices, lasers, optical switches, antennas, RF and optical sensors, etc.

CMOS compatible optical leaky wave antennas (OLWAs) and devices, Sponsored by the National Science Foundation (Link)

We explore a new route to design highly directive SOI (silicon on insulator) / CMOS compatible optical antennas, employing leaky waves that require a single feed point to the waveguide and tunable periodic semiconductor perturbations that will lead to the controlled leaky radiation.

Note that having very small Si perturbations has the advantage to allow very fast electronic/optical control of the carrier generation, because carriers do not penetrate into the dielectric waveguide.

We have recently found the way to enhance the tunability control (that otherwise is limited, due to small Si perturbations) embedding the OLWA in a Fabry-Perot resonator or in a ring resonator. This research is done in collaboration with Prof. O. Boyraz (UC Irvine).

Electron beam devices, High power traveling wave tubes (TWTs) and BWOs

We are investigating new strategies to improve the interaction between electromagnetic slow waves and electron beams. For example we are considering a new class of slow ave structures whose (wavenumber-frequency) dispersion diagram exhibits exceptional points of degeneracy EPD), like stationary inflection point, or degenerate band edge, etc. We are investigating the interaction of electron beams with complex modal fields in waveguides. We are also investigating new concepts for pulse compression techniques. Our reserach is sponsored by the AFOSR and we collaborate with Prof. A. Figotin (UC Irvine, Dept. of Mathematics)

On-Chip Antennas and Highly Directive Antennas (Microwaves and Millimeter Waves)

We are interested in fully on-chip antennas at millimeter and sub-millimeter waves. We are also investigating hybrid solutions, where the radiator is composed of on-chip and off-chip components. We have investigated the use of metamaterials and high impedance surfaces directly on-chip, suing CMOS or Bi-CMOS technologies.

We are investigating practical implementations of Fabry-Perot cavity antennas at millimeter waves that exhibit high efficiency and high directivity. We are also developing theoretical tools to design such antennas. I collaborate with Prof. F. De Flaviis (UC irvine) for Fabry-Perot cavity antennas at 60 GHz and with Prof. D. Jackson (U of Houston) on fundamentals of radiation of these antennas. Fabrication of on-chip antennas has been done in collaboration with Prof. P. Heydari (UC irvine) and TowerJazz.

Imaging systems

We are interested in novel techniques. For example we are investigating a novel focal plane array at millimeter waves, developing the new concept of overlapping pixels. We are also investigating 'metamaterial approaches' analyzing and designing structures that exploit evanescent spectrum for better resolution. Our goal is to have a focal plane array on chip, with integrated front-end and antennas, to be developed in collaboration with Prof. P. Heydari (UC Irvine).

Metamaterials and Metasurfaces

We are studying various composite materials and their properties. In particular ENZ (epsilon near zero) metamaterials for field enhancement. Loss mitigation in metamaterials using gain. Homogenization methods. We have also dedicated a large effort in creating artificial magnetism (i.e., effective permeability different than unity), at microwaves, infrared, and optical frequencies.

Hyperbolic (or indefinite) metamaterials

These materials have the very interesting property that the otherwise evanescent spectrum excited by a scatterer actually becomes propagating, leading to a variety of interesting applications. Like super absorbers.

Field enhancement in composite structures

We are interested in two aspects of field enhancement: (1) for harmonic generation; and (2) for enhanced excitation and emission of molecules. We are investigating various strategies to obtain field enhancement, depending on the application.

Interactions with single dyes and optical nanostructures and nanoantennas

We are studying electromagnetic properties and modeling of single or collective dyes in presence of optical nanostructures.

Scattering and diffraction

High frequency methods, asymptotic methods, in frequency and time domain for ultra wide band modeling.

Page still under construction