arXiv subjects

Carlos Rios

Publications and source records attributed to Carlos Rios.

7 recordsLinked to original sources

arXiv2026

Photonic Theta Cavity: Engineering Bound States in the Continuum in Topological Resonators Beyond the Limitations of Near Field Coupling

The Theta Cavity is a unique topological resonator architecture which utilizes interferometric coupling to overcome fundamental design limitations associated with near-field evanescent coupling which currently dominates the design space for integrated photonics. The defining device physics is established by the mirror symmetric cross junctions which preserves efficient power transfer between a waveguide and ring resonator creating a strongly correlated phase relationship between the multiple paths. The unique mode selection physics allows for interference driven suppression of radiative pathways enabling strong cavity confinement and the emergence of Bound States in the Continuum (BICs). Analytical models reveal non-Hermitian optical band structure displaying non-trivial topological transitions between BIC and quasi-BIC modes that are robust to attenuation, temperature variations, and typical fabrication non-idealities, which is critical for overcoming intrinsic limitations associated with silicon based integrated photonics. The Theta Cavity architecture also circumvents limitations that arise from proximity requirements of the physical gap used in near-field coupled waveguides which enables a flexible design space for new devices. In this study, we demonstrate phase mediated long-range strong coupling of multiple ring resonators in the Nested Theta Cavity architecture showcasing band structure hybridization resulting in the formation of anti-crossing bandgaps, Dirac crossings, and Fano resonances. The photonic Theta Cavity architecture provides a scalable, topologically robust platform for engineering modes across a multidimensional parameter space with high resilience to perturbation and attenuation, enabling a new approach for the designing of integrated cavity devices.

physics.optics↗

arXiv2025

Reconstructing inflation in a generalized Rastall theory of gravity

We investigate the reconstruction of standard and generalized Rastall gravity inflationary models, using the scalar spectral index and the Rastall parameter expressed as functions of the number of $e-$folds $N$. Within a general formalism, we derive the effective potential in terms of the relevant cosmological parameters and the Rastall parameter for these gravity frameworks. As a specific example, we analyze the attractor $n_s(N) - 1 \propto N^{-1}$, first by considering constant values of the Rastall parameter to reconstruct the inflationary stage in standard Rastall gravity, and then by assuming a linear dependence on the number of $e-$folds $N$ to reconstruct the inflationary model in generalized Rastall gravity. Thus, the reconstruction of the potential $V(\phi)$ is obtained for both standard and generalized Rastall gravity inflationary models. In both frameworks, we constrain key parameters of the reconstructed models during inflation using the latest observational data from Planck.

gr-qc↗

arXiv2024

Reconstructing inflation and reheating in the framework of a generalized $\mathcal{F}(H)$ Friedmann equation

The reconstruction of an inflationary universe considering the parametrization of the scalar spectral index as a function of the number of $e-$folds in the framework of a modified Friedmann equation is analyzed. In this context, we examine the possibility of reconstructing the Hubble parameter together with the effective potential considering a modified Friedmann equation specified by $\mathcal{F}(H)\propto \rho$, where $\mathcal{F}(H)$ corresponds to an arbitrary function of the Hubble parameter $H$ and $\rho$ denotes the energy density associated with the matter in the universe. To reconstruct the background variables during the inflationary scenario, we develop a new methodology by expressing the spectral index in terms of the Hubble parameter and its derivatives. Thus, we obtain a general formalism for the reconstruction of the inflation, using the slow roll approximation together with the parametrization of the scalar spectral index as a function of the number of $e-$folds $N$. As specific examples, we consider the simplest attractor $n_s-1=-2/N$ together with different functions $\mathcal{F}(H)$, associated to the modified Friedmann equation, to rebuild the Hubble parameter and the effective potential in terms of the scalar field $\phi$. Additionally, we examine the reheating epoch by considering a constant equation of state parameter, in which we determine the temperature and the number of e-folds during this epoch, using the background variables found during the reconstruction of the different $\mathcal{F}(H)-$models studied. Besides, we constrain the different parameters associated with the reconstructed inflationary $\mathcal{F}(H)-$models during the epochs of inflation and reheating, using current astronomical data from Planck and BICEP/Keck results.

gr-qc↗

arXiv2024

Speed of sound and scalar spectral index: Reconstructing inflation and reheating in a non-canonical theory

In this article we analyze the reconstruction of inflation in the framework of a non-canonical theory. In this sense, we study the viability of reconstructing the background variables assuming a non-lineal kinetic term given by $K(X,\phi)=X+g(\phi)X^2$, with $X$ the standard kinetic term associated to the scalar field $\phi$ and $g(\phi)$ an arbitrary coupling function. In order to achieve this reconstruction in the context of inflation, we assume the slow-roll approximation together with the parametrization of the scalar spectral index $n_s$ and the speed of sound $c_s$ as a function of the number of $e-$folds $N$. By assuming the simplest parametrizations for $n_s-1=-2/N$ and $c_s\propto N^{-\beta}$ with $\beta$ a constant, we find the reconstruction of the effective potential $V(\phi)$ and the coupling function $g(\phi)$ in terms of the scalar field. Besides, we study the reheating epoch by considering a constant equation of state parameter, where we determine the temperature and number of $e-$folds during the reheating epoch in terms of the reconstructed variables and the observational parameters. In this way, the parameter-space related to the reconstructed inflationary model are constrained during the epochs of inflation and reheating by assuming the current astronomical data from Planck and BICEP/Keck results.

astro-ph.CO↗

arXiv2023

Reconstructing inflation and reheating in $f(ϕ)T$ gravity

The reconstruction of an inflationary universe in the context of one $f(ϕ)T$ gravity, in which $T$ corresponds to the trace of energy momentum tensor is studied. To realize this reconstruction during the inflationary epoch, we consider as attractor the scalar spectral index $n_s$ in terms of of the number of $e$-folds $N$, in the framework of the slow-roll approximation. By assuming a specific function $f(ϕ)$ together with the simplest attractor $n_s(N)$, we find different expressions for the reconstructed effective potential $V(ϕ)$. Additionally, we analyze the era of reheating occurs after of the reconstruction obtained during the inflationary epoch. In this scenario we determine the duration and temperature during the reheating epoch, in terms of the equation of state parameter and the observational parameters. In this context, the different parameters associated to the reconstructed model are restricted during the scenarios of inflation and reheating by considering the recent astronomical observations.

gr-qc↗

arXiv2019

Reconfigurable all-dielectric metalens with diffraction limited performance

Active metasurfaces, whose optical properties can be modulated post-fabrication, have emerged as an intensively explored field in recent years. The efforts to date, however, still face major performance limitations in tuning range, optical quality, and efficiency especially for non mechanical actuation mechanisms. In this paper, we introduce an active metasurface platform combining phase tuning covering the full 2$π$ range and diffraction-limited performance using an all-dielectric, low-loss architecture based on optical phase change materials (O-PCMs). We present a generic design principle enabling switching of metasurfaces between two arbitrary phase profiles and propose a new figure-of-merit (FOM) tailored for active meta-optics. We implement the approach to realize a high-performance varifocal metalens operating at 5.2 $μ$m wavelength. The metalens is constructed using Ge2Sb2Se4Te1 (GSST), an O-PCM with a large refractive index contrast ($Δ$ n > 1) and unique broadband low-loss characteristics in both amorphous and crystalline states. The reconfigurable metalens features focusing efficiencies above 20% at both states for linearly polarized light and a record large switching contrast ratio of 29.5 dB. We further validated aberration-free imaging using the metalens at both optical states, which represents the first experimental demonstration of a non-mechanical active metalens with diffraction-limited performance.

physics.optics↗

arXiv2019

Physics problems and instructional strategies for developing social networks in university classrooms

In this study, we explored the extent to which problems and instructional strategies affect social cohesion and interactions for information seeking in physics classrooms. Three sections of a mechanics physics course taught at a Chilean University in Coquimbo were investigated. Each section had a weekly problem-solving session using different sets of well and/or ill-structured problems (i.e., algebra-based and open-ended problems respectively), as well as instructional strategies for guiding the problem-solving sessions. Data was collected on networks of information seeking and perceptions of good physics students, during a problem-solving session. We used social network analysis (SNA) for constructing variables while conducting the study. Results suggest that the teaching and learning strategies to guide problem-solving of well and ill-structured problems yield different levels of social interaction among classmates, and significant levels of activity in seeking out information for learning and problem-solving. While strategies for guiding problem-solving lend to significant differences for network connectivity, well and ill-structured physics problems predict similar levels of social activity.

physics.ed-ph↗