Plasmonic nanoantennas on Epsilon-Near-Zero Metamaterial substrates

The localized surface plasmon resonance (LSPR) is used for light confinement within sub-wavelength scale. The fields are localized and re-directed with the metal nanoantennas. The localization of electric field inside and outside of such a nanoantenna depends upon its shape, the metal, and substrate. Therefore, it is possible to tailor the resonant wavelength by changing the nanoantenna parameters. In this thesis, I have used epsilon-near-zero (ENZ) metamaterial as a substrate to dictate the LSPR of golden (Au) nanodisk (ND) antenna arrays. The hyperbolic metamaterial (HMM), which consists of metal and dielectric alternating layers, designed to have an effective permittivity (epsilon) close to zero. The ENZ substrate with almost zero index slows down the resonance shift of NDs which is known as "pinning effect". I have experimentally demonstrated the pinning effect, by comparing the transmission of ND antennas on glass to the transmission of NDs on HMM with ENZ wavelength at 684 nm. The NDs on HMM substrate have three times less spectral shift compare to the NDs on glass. The robust control of LSPR with ENZ metamaterial substrate can be applied in emission enhancing and beam steering

Nonreciprocal Metasurface with Space-Time Phase Modulation

Creating materials with time-variant properties is critical for breaking reciprocity that imposes fundamental limitations to wave propagation. However, it is challenging to realize efficient and ultrafast temporal modulation in a photonic system. Here, leveraging both spatial and temporal phase manipulation offered by an ultrathin nonlinear metasurface, we experimentally demonstrated nonreciprocal light reflection at wavelengths around 860 nm. The metasurface, with traveling-wave modulation upon nonlinear Kerr building blocks, creates spatial phase gradient and multi-terahertz temporal phase wobbling, which leads to unidirectional photonic transitions in both momentum and energy spaces. We observed completely asymmetric reflections in forward and backward light propagations within a sub-wavelength interaction length of 150 nm. Our approach pointed out a potential means for creating miniaturized and integratable nonreciprocal optical components.Comment: 25 pages, 5 figure

Spectral theory of electromagnetic scattering by a coated sphere

In this paper, we introduce an alternative representation of the electromagnetic field scattered from a homogeneous sphere coated with a homogeneous layer of uniform thickness. Specifically, we expand the scattered field using a set of modes that are independent of the permittivity of the coating, while the expansion coefficients are simple rational functions of the permittivity. The theory we develop represents both a framework for the analysis of plasmonic and photonic modes and a straightforward methodology to design the permittivity of the coating to pursue a prescribed tailoring of the scattered field. To illustrate the practical implications of this method, we design the permittivity of the coating to zero either the backscattering or a prescribed multipolar order of the scattered field, and to maximize an electric field component in a given point of space

Suppressing the spectral shift of a polarization-independent nanostructure with multiple resonances

Resonances are the cornerstone of photonic applications in many areas of physics and engineering. The spectral position of a photonic resonance is dominated by the structure design. Here, we devise a polarization-independent plasmonic structure comprising nanoantennas with two resonances on an epsilon-near-zero (ENZ) substrate in order to loosen this correlation to obtain less sensitivity to geometrical perturbations of the structure. Compared with the bare glass substrate, the designed plasmonic nanoantennas on an ENZ substrate exhibit a nearly three-fold reduction only in the resonance wavelength shift near the ENZ wavelength as a function of antenna length.publishedVersionPeer reviewe

Impact of surface roughness in nanogap plasmonic systems

Recent results have shown unprecedented control over separation distances between two metallic elements hundreds of nanometers in size, underlying the effects of free-electron nonlocal response also at mid-infrared wavelengths. Most of metallic systems however, still suffer from some degree of inhomogeneity due to fabrication-induced surface roughness. Nanoscale roughness in such systems might hinder the understanding of the role of microscopic interactions. Here we investigate the effect of surface roughness in coaxial nanoapertures resonating at mid-infrared frequencies. We show that although random roughness shifts the resonances in an unpredictable way, the impact of nonlocal effects can still be clearly observed. Roughness-induced perturbation on the peak resonance of the system shows a strong correlation with the effective gap size of the individual samples. Fluctuations due to fabrication imperfections then can be suppressed by performing measurements on structure ensembles in which averaging over a large number of samples provides a precise measure of the ideal system's optical properties

Longitudinal quantum plasmons in copper, gold, and silver

The propagation of plasmonic waves in various metallic quantum nanostructures have considered attention for their applications in technology. The quantum plasmonic properties of metallic nanostructures in the quantum size regime have been difficult to describe by an appropriate model. Here the nonlocal quantum plasmons are investigated in the most important metals of copper, gold, and silver. Dispersion properties of these metals and propagation of longitudinal quantum plasmons in the high photon energy regime are studied by a new model of nonlocal quantum dielectric permittivity. The epsilon near zero properties are investigated and the spectrum and the damping rate of the longitudinal quantum plasmons are obtained in these metals. The quantum plasmon s wave function is shown for both classical and quantum limits. It is shown that silver is the most appropriate for quantum metallic structures in the development of next generation of quantum optical and sensing technologies, due to low intrinsic loss

Plasmonics and metamaterials at terahertz frequencies

The research presented in this manuscript falls under the framework of metamaterials and plasmonics. It is mainly focused on applications at terahertz (THz) frequencies, a spectral band located between microwaves and infrared. Metamaterials are advanced materials able to synthesize electromagnetic properties hardly found in natural materials by means of engineering their meta-atoms. Metallic inclusions are commonly used in metamaterials design. At low frequency bands such as microwaves and millimeter-waves, metals behave fundamentally differently than at infrared and optics. Plasmonics sets the theory of the interaction processes between electromagnetic radiation and conduction electrons of metals at such high frequencies. The objective of this thesis is to devise, design, analyze and, whenever possible, experimentally realize and measure new metamaterials and plasmonics devices for free-space quasi-optical applications. Particularly, field concentrators in the form of advanced lenses and nanoantennas as well as advanced polarizing devices are targeted. The contributions presented here start from the specific theory of the field and the results are supported by numerical simulations, analytical calculations and/or measurements of real prototypes.Programa Oficial de Doctorado en Tecnologías de las Comunicaciones (RD 1393/2007)Komunikazioen Teknologietako Doktoretza Programa Ofiziala (ED 1393/2007

Epsilon-Near-Zero Grids for On-chip Quantum Networks

Realization of an on-chip quantum network is a major goal in the field of integrated quantum photonics. A typical network scalable on-chip demands optical integration of single photon sources, optical circuitry and detectors for routing and processing of quantum information. Current solutions either notoriously experience considerable decoherence or suffer from extended footprint dimensions limiting their on-chip scaling. Here we propose and numerically demonstrate a robust on-chip quantum network based on an epsilon-near-zero (ENZ) material, whose dielectric function has the real part close to zero. We show that ENZ materials strongly protect quantum information against decoherence and losses during its propagation in the dense network. As an example, we model a feasible implementation of an ENZ network and demonstrate that quantum information can be reliably sent across a titanium nitride grid with a coherence length of 434 nm, operating at room temperature, which is more than 40 times larger than state-of-the-art plasmonic analogs. Our results facilitate practical realization of large multi-node quantum photonic networks and circuits on-a-chip.Comment: 13 pages, 5 figure