arXiv subjects

Laureano Moreno-Pozas

Publications and source records attributed to Laureano Moreno-Pozas.

7 recordsLinked to original sources

arXiv2025

Simulador electromagnético eficiente para el diseño de rejillas de difracción débiles en guías dieléctricas

The significant growth of free-space optic communications and Light Detection and Ranging (LiDAR) is demanding gratings that emit highly collimated beams, i.e. with Rayleigh ranges of millimeters or even centimeters. Hence, weak-strength gratings, which radiate little amount of power per unit length, are needed. The main purpose of this work is to propose an efficient and accurate simulation tool to accelerate the design of weak-strength gratings required for these applications. To achieve this, we propose a simulator based on the classical perturbation method, which takes a circuit approach to the electromagnetic problem. Comparison with results obtained with a rigorous 2D full wave electromagnetic simulator (FEXEN) shows very good agreement with the advantage of decreasing simulation times by up to a factor $\times 16$

physics.optics↗

arXiv2025

Parabolic dielectric reflector for extreme on-chip spot-size conversion with broad bandwidth

Spot-size converters are key for efficient coupling of light between waveguides of different sizes. While adiabatic tapers are well suited for small size differences, they become impractically long for expansion factors around x100 which are often required when coupling integrated waveguides and free-space beams. Evanescent couplers and bragg deflectors can be used in this scenario, but their operation is inherently limited in bandwidth. Here we propose a solution based on a parabolic dielectric interface that couples light from a 0.5 um-wide waveguide to a 285 um-wide waveguide, i.e. an expansion factor of x570. We experimentally demonstrate an unprecedented bandwidth of more than 380 nm with insertion losses below 0.35 dB. We furthermore provide analytical expressions for the design of such parabolic spot-size-converters for arbitrary expansion factors.

physics.optics↗

arXiv2019

Extreme Eigenvalue Distributions of Jacobi Ensembles: New Exact Representations, Asymptotics and Finite Size Corrections

Let $\mathbf{W}_1$ and $\mathbf{W}_2$ be independent $n\times n$ complex central Wishart matrices with $m_1$ and $m_2$ degrees of freedom respectively. This paper is concerned with the extreme eigenvalue distributions of double-Wishart matrices $(\mathbf{W}_1+\mathbf{W}_2)^{-1}\mathbf{W}_1$, which are analogous to those of F matrices ${\bf W}_1 {\bf W}_2^{-1}$ and those of the Jacobi unitary ensemble (JUE). Defining $α_1=m_1-n$ and $α_2=m_2-n$, we derive new exact distribution formulas in terms of $(α_1+α_2)$-dimensional matrix determinants, with elements involving derivatives of Legendre polynomials. This provides a convenient exact representation, while facilitating a direct large-$n$ analysis with $α_1$ and $α_2$ fixed (i.e., under the so-called "hard-edge" scaling limit); the analysis is based on new asymptotic properties of Legendre polynomials and their relation with Bessel functions that are here established. Specifically, we present limiting formulas for the smallest and largest eigenvalue distributions as $n \to \infty$ in terms of $α_1$- and $α_2$-dimensional determinants respectively, which agrees with expectations from known universality results involving the JUE and the Laguerre unitary ensemble (LUE). We also derive finite-$n$ corrections for the asymptotic extreme eigenvalue distributions under hard-edge scaling, giving new insights on universality by comparing with corresponding correction terms derived recently for the LUE. Our derivations are based on elementary algebraic manipulations, differing from existing results on double-Wishart and related models which often involve Fredholm determinants, Painlevé differential equations, or hypergeometric functions of matrix arguments.

math-ph↗

arXiv2019

A Tractable Product Channel Model for Line-of-Sight Scenarios

We present a general and tractable fading model for line-of-sight (LOS) scenarios, which is based on the product of two independent and non-identically distributed $κ$-$μ$ shadowed random variables. Simple closed-form expressions for the probability density function, cumulative distribution function and moment-generating function are derived, which are as tractable as the corresponding expressions derived from a product of Nakagami-$m$ random variables. This model simplifies the challenging characterization of LOS product channels, as well as combinations of LOS channels with non-LOS ones. We leverage these results to analyze performance measures of interest in the contexts of wireless powered and backscatter communications, where both forward and reverse links are inherently of LOS nature, as well as in device-to-device communications subject to composite fading. In these contexts, the model shows a higher flexibility when fitting field measurements with respect to conventional approaches based on product distributions with deterministic LOS, together with a more complete physical interpretation of the underlying propagation characteristics.

cs.IT↗

arXiv2018

A New Approach to the Statistical Analysis of Non-Central Complex Gaussian Quadratic Forms with Applications

This paper proposes a novel approach to the statistical characterization of non-central complex Gaussian quadratic forms (CGQFs). Its key strategy is the generation of an auxiliary random variable (RV) that converges in distribution to the original CGQF. Since the mean squared error between both is given in a simple closed-form formulation, the auxiliary RV can be particularized to achieve the required accuracy. The technique is valid for both definite and indefinite CGQFs and yields simple expressions of the probability density function (PDF) and the cumulative distribution function (CDF) that involve only elementary functions. This overcomes a major limitation of previous approaches, in which the complexity of the resulting PDF and CDF prevents from using them for subsequent calculations. To illustrate this end, the proposed method is applied to maximal ratio combining systems over correlated Rician channels, for which the outage probability and the average bit error rate are derived.

cs.IT↗

arXiv2015

On Some Unifications Arising from the MIMO Rician Shadowed Model

This paper shows that the proposed Rician shadowed model for multi-antenna communications allows for the unification of a wide set of models, both for multiple-input multiple output (MIMO) and single-input single output (SISO) communications. The MIMO Rayleigh and MIMO Rician can be deduced from the MIMO Rician shadowed, and so their SISO counterparts. Other SISO models, besides the Rician shadowed proposed by Abdi et. al., are included in the model, such as the $κ$-$μ$ defined by Yacoub, and its recent generalization, the \mbox{$κ$-$μ$} shadowed model. Moreover, the SISO \mbox{$η$-$μ$} and \mbox{Nakagami-$q$} models can be seen as particular cases of the MIMO Rician shadowed. The literature already presents the probability density function (pdf) of the Rician shadowed Gram channel matrix in terms of the well-known gamma-Wishart distribution. We here derive its moment generating function in a tractable form. Closed-form expressions for the cumulative distribution function and the pdf of the maximum eigenvalue are also carried out.

cs.IT↗

arXiv2015

The $κ$-$μ$ Shadowed Fading Model: Unifying the $κ$-$μ$ and $η$-$μ$ Distributions

This paper shows that the recently proposed $κ$-$μ$ shadowed fading model includes, besides the $κ$-$μ$ model, the $η$-$μ$ fading model as a particular case. This has important relevance in practice, as it allows for the unification of these popular fading distributions through a more general, yet equally tractable, model. The convenience of new underlying physical models is discussed. Then, we derive simple and novel closed-form expressions for the asymptotic ergodic capacity in $κ$-$μ$ shadowed fading channels, which illustrate the effects of the different fading parameters on the system performance. By exploiting the unification here unveiled, the asymptotic capacity expressions for the $κ$-$μ$ and $η$-$μ$ fading models are also obtained in closed-form as special cases.

cs.IT↗