arXiv subjects

Raúl de la Fuente

Publications and source records attributed to Raúl de la Fuente.

10 recordsLinked to original sources

arXiv2026

When Reflection and Transmission Amplitude Coefficients Exceed Unity: Evanescent Waves, Resonances, and Optical Modes

The reflection and transmission of propagating harmonic waves in linear optical systems have been widely discussed in the literature and are generally well understood. In passive systems involving only propagating waves, energy conservation constrains measurable quantities such as reflectance and transmittance, as well as the corresponding amplitude coefficients. However, when evanescent or damped waves are present, the reflection and transmission coefficients of the field amplitude may exhibit atypical behaviour, with the real or imaginary parts being much larger than one or even unbounded. In this study, we analyse this phenomenon in several simple optical configurations, including dielectric-metal interfaces, surface-plasmon-resonance prism couplers, plasmonic microcavities, step-index slab waveguides and prism-coupled waveguides. We demonstrate that these large amplitude coefficients naturally arise from extending reflection and transmission coefficients to evanescent or damped waves. On the other hand, they are not directly associated with measurable reflectance or transmittance and, therefore, do not conflict with energy conservation. Instead, they provide a useful formal description of resonant field enhancement, modal excitation and coupling processes in plasmonic and dielectric optical systems.

physics.optics↗

arXiv2026

Resonant optical tunnelling in planar three-layer photonic microstructures

We present a unified analytical framework for resonant optical tunnelling in three-layer photonic systems embedded in a transparent dielectric medium. Compact expressions for the transmission coefficient are derived using a generalized Fresnel-coefficient formalism, enabling us to distinguish between two fundamentally different tunnelling regimes determined by the nature of the waves supported in the core layer. When harmonic waves propagate within the core, resonances satisfy the conventional Fabry-Perot phase condition. In contrast, when evanescent or damped waves are supported, resonant tunnelling arises from an amplitude-matching condition governed by the magnitude of the composite reflection coefficient. This distinction leads to qualitatively different transmission characteristics and markedly different tunnelling behaviors. For clarity, transparent materials are treated first (including ideal metals), and the role of absorption is subsequently analyzed, revealing the transition from unitary resonant tunnelling to attenuated optical tunnelling. Angular-spectral maps illustrate the general features of each configuration and demonstrate that resonant tunnelling may occur in structures whose thickness exceeds several wavelengths. The results provide a consistent physical interpretation of resonant tunnelling phenomena in both dielectric and metal-dielectric multilayer systems.

physics.optics↗

arXiv2025

Coupled surface plasmon and resonant optical tunnelling in symmetric optical microcavities

A symmetrical structure consisting of a low refractive index dielectric layer between two metallic films, i.e. an optical cavity, surrounded by a semi-infinite dielectric medium of higher refractive index, forms an optical system capable of supporting both volume and surface resonances. The latter are associated with synchronized collective electronic oscillations in the inner surfaces of the two thin metallic films, called coupled surface plasmons. These oscillations are generated by an evanescent wave in the cavity and therefore the thickness of the cavity is limited to the micron range for visible radiation. Under suitable incident conditions, light propagating in the microcavity will resonate with these plasmonic oscillations and can be strongly transmitted into the surrounding medium. In this work, we establish a simple model of the transmission characteristics of the cavity and define resonance conditions that allow high transmittance even for inner dielectric layer thicknesses of various wavelengths. This phenomenon is an enhanced version of the optical process of frustrated total reflection between dielectrics analogous to quantum tunnelling effect. In the present situation, the phenomenon is more striking because it takes place in a system with two absorbing metal films which, under resonant conditions, favour a superior transmission.

physics.optics↗

arXiv2024

Enhancing Predictive Maintenance in Mining Mobile Machinery through a TinyML-enabled Hierarchical Inference Network

Mining machinery operating in variable environments faces high wear and unpredictable stress, challenging Predictive Maintenance (PdM). This paper introduces the Edge Sensor Network for Predictive Maintenance (ESN-PdM), a hierarchical inference framework across edge devices, gateways, and cloud services for real-time condition monitoring. The system dynamically adjusts inference locations--on-device, on-gateway, or on-cloud--based on trade-offs among accuracy, latency, and battery life, leveraging Tiny Machine Learning (TinyML) techniques for model optimization on resource-constrained devices. Performance evaluations showed that on-sensor and on-gateway inference modes achieved over 90\% classification accuracy, while cloud-based inference reached 99\%. On-sensor inference reduced power consumption by approximately 44\%, enabling up to 104 hours of operation. Latency was lowest for on-device inference (3.33 ms), increasing when offloading to the gateway (146.67 ms) or cloud (641.71 ms). The ESN-PdM framework provides a scalable, adaptive solution for reliable anomaly detection and PdM, crucial for maintaining machinery uptime in remote environments. By balancing accuracy, latency, and energy consumption, this approach advances PdM frameworks for industrial applications.

cs.LG↗

arXiv2024

Modelling resonant transmission in a Fabry-Perot/Surface-Plasmon microcavity

Coupled surface plasmons arise in the surfaces of a dielectric layer between two metallic media when a dim wave propagating in the dielectric generates resonant free charge oscillations at the interfaces. Here, we consider surface plasmon resonance in a Fabry-Perot type cavity with plane metallic mirrors and an inner dielectric medium, optically less dense than the outer surrounding dielectric medium. The experimentally observed transmission as a function of both the angle of incidence of light and the wavelength is well modelled by an elementary transmittance function from which resonance conditions are obtained both in the Fabry-Perot and Surface-Plasmon regime.

physics.optics↗

arXiv2024

Beneath and beyond frustrated total reflection: a practical demonstration

Frustrated total internal reflection is analyzed from an unusual point of view Unlike most similar works, incident angles are used here as the scanning variable, instead of the tunneled film thickness. The theoretical framework is presented defining our own normalized variables, better adapted to the problem at hand. A straightforward and captivating experiment, appropriate for undergraduate classroom demonstrations is also presented. The experiment involves measuring the reflection and transmission of light through a pair of prisms separated by an air or water layer, and the results are in fair agreement with theory.

physics.optics↗

arXiv2022

Fresnel coefficients, coherent optical scattering and planar waveguiding

One-dimensional optical waveguiding is revisited using the electromagnetic deduction of Fresnel formulas relating the incident, reflected, and transmitted waves on the abrupt interface between two different optical media. Throughout the paper, different optical configurations are analyzed from this perspective revealing that, in all cases, those solutions corresponding to waveguiding configurations share common features. These shared characteristics are: firstly, the guided modes always emerge as singular solutions of the associate coherent optical scattering problem and, secondly, the resonance condition that must be satisfied corresponds to the pole of the associated Fresnel Coefficients.

physics.optics↗

arXiv2021

Brewster angle as never seen before

In this paper we will discuss a demonstration we have been performing for years; not only with physics students from our university (Universidade de Santiago de Compostela), but also with high school students in some talks aimed at encouraging them to study science. It is related to Brewster's angle and its visualization in an ingenious way using a "loaded" LCD monitor. In some way, this experiment is a reverse version of what happens when a vampire faces a mirror and sees no reflected image of himself.

physics.ed-ph↗

arXiv2021

Accuracy of Refractive Index Spectroscopy by Broadband Interferometry

Uncertainties of refractive and group index in dispersion measurement by spectrally resolved white light interferometry are deeply analyzed. First, the contribution to uncertainty of the different parameters affecting both indices is identified. Afterwards, results are presented for a 1.5 mm thick fused silica sample over a broad spectral range, from 400 to 1000 nm, and the effects that mostly deteriorate the measurement accuracy are established. Finally, the different contributions are quadratically combined to determine the total uncertainty of the two indices.

physics.optics↗

arXiv2020

An Experimental and Computational Study on Material Dispersion of 1-Alkyl-3-Methylimidazolium Tetrafluoroborate Ionic Liquids

The material dispersion of the [Ckmim][BF4] (k = 2,3,4,6,7,8,10) family of ionic liquids is measured at several temperatures over a broad spectral range from 300 nm to 1550 nm. The experimental curves are fitted to a modified three-resonance Sellmeier model to understand the effect of temperature and alkyl chain length in the dispersion. From the parameters of the fitting, we analyze the influence that the different constituents of these ionic liquids have in the dispersion behaviour. In addition, a semi-empirical approach combining simulated electronic polarizabilities and experimental densities for predicting the material dispersion is successfully tested by direct comparison with the experimental results. The limitations of this method are analyzed in terms of the structure of the ionic liquids. The results of this work aim to increase our knowledge about how the structure of an ionic liquid influences its material dispersion. Understanding this influence is fundamental to produce ionic liquids with tailored optical properties.

cond-mat.soft↗