arXiv subjects

Boon S. Ooi

Publications and source records attributed to Boon S. Ooi.

25 records · Page 2Linked to original sources

arXiv2019

OAM Mode Selection and Space-Time Coding for Turbulence Mitigation in FSO Communication

Free space optical (FSO) communications using orbital angular momentum (OAM) modes has recently received a considerable interest. Propagating OAM modes through free space may be subject to atmospheric turbulence (AT) distortions that cause intermodal crosstalk and power disparities between OAM modes. In this article, we are interested in 2x2 multiple-input multiple-output (MIMO) FSO coherent communication systems using OAM. We propose a selection criterion for OAM modes to minimize the impact of AT. To further improve the obtained performance, we propose a space-time (ST) coding scheme at the transmitter. Through numerical simulations of the error probability, we show that the penalty from AT is completely absorbed for weak AT and considerable coding gains are obtained in the strong AT regime.

eess.SP↗

arXiv2019

Communicating Using Spatial Mode Multiplexing: Potentials, Challenges and Perspectives

Time, polarization, and wavelength multiplexing schemes have been used to satisfy the growing need of transmission capacity. Using space as a new dimension for communication systems has been recently suggested as a versatile technique to address future bandwidth issues. We review the potentials of harnessing the space as an additional degree of freedom for communication applications including free space optics, optical fiber installation, underwater wireless optical links, on-chip interconnects, data center indoor connections, radio frequency and acoustic communications. We focus on the orbital angular momentum (OAM) modes and equally identify the challenges related to each of the applications of spatial modes and the particular OAM modes in communication. We further discuss the perspectives of this emerging technology. Finally, we provide the open research directions and we discuss the practical deployment of OAM communication links for different applications.

cs.IT↗

arXiv2018

Unified Statistical Channel Model for Turbulence-Induced Fading in Underwater Wireless Optical Communication Systems

A unified statistical model is proposed to characterize turbulence-induced fading in underwater wireless optical communication (UWOC) channels in the presence of air bubbles and temperature gradient for fresh and salty waters, based on experimental data. In this model, the channel irradiance fluctuations are characterized by the mixture Exponential-Generalized Gamma (EGG) distribution. We use the expectation maximization (EM) algorithm to obtain the maximum likelihood parameter estimation of the new model. Interestingly, the proposed model is shown to provide a perfect fit with the measured data under all channel conditions for both types of water. The major advantage of the new model is that it has a simple mathematical form making it attractive from a performance analysis point of view. Indeed, we show that the application of the EGG model leads to closed-form and analytically tractable expressions for key UWOC system performance metrics such as the outage probability, the average bit-error rate, and the ergodic capacity. To the best of our knowledge, this is the first-ever comprehensive channel model addressing the statistics of optical beam irradiance fluctuations in underwater wireless optical channels due to both air bubbles and temperature gradient.

cs.IT↗

arXiv2018

Accelerating vapor condensation with daytime radiative cooling

Vapor condensation plays a crucial role in solar water-purification technologies. Conventional condensers in solar water-purification systems do not provide sufficient cooling power for vapor condensation, limiting the water production rate to $0.4 L m^{-2} hour^{-1}$. On the other hand, radiative dew condensation, a technique used by existing radiative dew condensers, only works at nighttime and is incompatible with solar water-purification technologies. Here, we develop daytime radiative condensers that reflect almost all solar radiation, and can thus create dew water even in direct sunlight. Compared to state-of-art condensers, our daytime radiative condenser doubles the production of purified water over a 24-hour period. The integration of our daytime radiative condenser with solar water-purification systems can increase the water production rate in sunlight from $0.4 L m^{-2} hour^{-1}$ to more than $1 L m^{-2} hour^{-1}$.

physics.app-ph↗

arXiv2013

Electron irradiation induced reduction of the permittivity in chalcogenide glass (As2S3) thin film

We investigate the effect of electron beam irradiation on the dielectric properties of As2S3 Chalcogenide glass. By means of low-loss Electron Energy Loss Spectroscopy, we derive the permittivity function, its dispersive relation, and calculate the refractive index and absorption coefficients under the constant permeability approximation. The measured and calculated results show, to the best of our knowledge, a heretofore unseen phenomenon: the reduction in the permittivity of <40%, and consequently a modification of the refractive index follows, reducing it by 20%, hence suggesting a significant change on the optical properties of the material. The plausible physical phenomena leading to these observations are discussed in terms of the homopolar and heteropolar bond dynamics under high energy absorption.

cond-mat.mtrl-sci↗

arXiv2013

A possible approach on optical analogues of gravitational attractors

In this paper we report on the feasibility of light confinement in orbital geodesics on stationary, planar, and centro-symmetric refractive index mappings. Constrained to fabrication and [meta]material limitations, the refractive index, n, has been bounded to the range: $0.8\leq n(\vec r)\leq 3.5$. Mappings are obtained through the inverse problem to the light geodesics equations, considering trappings by generalized orbit conditions defined \emph{a priori}. Our simulation results show that the above mentioned refractive index distributions trap light in an open orbit manifold, both perennial and temporal, in regards to initial conditions. Moreover, due to their characteristics, these mappings could be advantageous to optical computing and telecommunications, for example, providing an on-demand time delay or optical memories. Furthermore, beyond their practical applications to photonics, these mappings set forth an attractive realm to construct a panoply of celestial mechanics analogies and experiments in the laboratory

math-ph↗

arXiv2012

Generation of J0-Bessel-Gauss Beam by an heterogeneous refractive index map

In this paper, we present the theoretical studies of a refractive index map to implement a Gauss to J0-Bessel-Gauss convertor. We theoretically demonstrate the viability of such device by solving the inverse electromagnetic problem. The computed conversion efficiency is 90%. The theoretical results, obtained from the beam conversion efficiency, self-regeneration, and propagation through an opaque obstruction; demonstrate that a 2D graded index map of the refractive index can be used to transform a Gauss beam into a J0-Bessel-Gauss beam. To the best of our knowledge, this is the first demonstration of such beam transformation by means of a 2D index-mapping which is fully integrable in silicon photonics based planar lightwave circuits (PLC). The concept device is significant for the eventual development of a new array of technologies, such as micro optical tweezers, optical traps, beam reshaping and non-linear beam diode lasers.

physics.optics↗