Axisymmetric photonic structures with PT-symmetry

Copyright 2016 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.PT-symmetric structures in photonic crystals, combining refractive index and gain-loss modulations is becoming a research field with increasing interest due to the light directionality induced by these particular potentials. Here, we consider PT-symmetric potentials with axial symmetry to direct light to the crystal central point obtaining a localization effect. The axial and PT-symmetric potential intrinsically generates an exceptional central point in the photonic crystal by the merge of both symmetries. This particular point in the crystal lattice causes field amplitude gradients with exponential slopes around the crystal center. The field localization strongly depends on the phase of the central point and on the complex amplitude of the PT-potential. The presented work analyzes in a first stage 1D linear PT-axisymmetric crystals and the role of the central point phase that determines the defect character, i.e. refractive index defect, gain-loss defect or a combination of both. The interplay of the directional light effect induced by the PT-symmetry and the light localization around the central point through the axial symmetry enhances localization and allows higher field concentration for certain phases. The linearity of the studied crystals introduces an exponential growth of the field that mainly depends on the complex amplitude of the potential. The work is completed by the analysis of 2D PT-axisymmetric potentials showing different spatial slopes and growth rates caused by symmetry reasons.Peer ReviewedPostprint (published version

A New learning experience: voluntary preparatory course for the bachelor’s degree in engineering

This paper reports on a new experience carried out at school associated with the Technical University of Catalonia, Universitat Politècnica de Catalunya (UPC) in September 2010. The aim is to describe the organization, funding and results of a preparatory course in Physics for a bachelor's degree in Engineering. We assess the students’ opinions about the experience and whether it should be repeated. We also analyze the profile of the students who access this School, estimating their initial knowledge of physics. The results obtained provide solid evidence that 70% of new students coming from Vocational Education Schools do not meet the required minimums.Peer Reviewe

The conical scanner evaluation system design

The software design for the conical scanner evaluation system is presented. The purpose of this system is to support the performance analysis of the LANDSAT-D conical scanners, which are infrared horizon detection attitude sensors designed for improved accuracy. The system consists of six functionally independent subsystems and five interface data bases. The system structure and interfaces of each of the subsystems is described and the content, format, and file structure of each of the data bases is specified. For each subsystem, the functional logic, the control parameters, the baseline structure, and each of the subroutines are described. The subroutine descriptions include a procedure definition and the input and output parameters

Structured Meta-Mirrors for Beam Spatial Filtering

The work presents optical spatial filtering in reflection based on translationally invariant meta-mirrors. The meta-structure is generated by a thin grating presenting a transverse modulation of the refraction index on the sub-micron scale located in front of a mirror. We analyze the angular spectrum of the reflected waves for different types of structured meta-mirrors as well as the filtering effects of these meta-structures in reflected beams. The comparison between FDTD simulations of full Maxwell equations and different approximated models allows to determine the filtering contribution from the structured cavity and from Mie resonances associated to elements generating the grating.Peer ReviewedPostprint (author's final draft

Polarization-independent broadband bidirectional optical cloaking using a new type of inverse scattering approach

(c) 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.Since the advent of transformation optics a decade ago [1], the ability to achieve optical cloaking has become a matter of practical realization. However, so far extreme material requirements and large device areas have significantly posed an obstacle to realize compact cloaking schemes that are fully functional. Here, by taking a different approach and by following our recently developed general theorem to control the scattering behaviour of an arbitrary object on a specific demand [2], we show that nearly perfect bidirectional optical cloaking effect can be generated for any type of object with a given shape and size. Contrary to previous approaches, we reveal that such a method is always able to produce local refractive indices larger than one and that neither gain nor lossy materials are required. Furthermore, by means of numerical calculations, we demonstrate a highly tunable broad operational bandwidth of 550 nm (covering 650-1200 nm interval) and an angular aperture of 36° for both directions and polarizations. With these unprecedented features, we expect that the present work will hold a great potential to enable a new class of optical cloaking structures that will find applications particularly in communication systems, defence industry and in other related fields.Peer ReviewedPostprint (author's final draft

Non-Hermitian broad aperture semiconductor lasers based on PT-symmetry

In this paper we propose a novel configuration to regularize the complex spatiotemporal dynamics of broad area lasers into bright light beam. It has recently been shown that arbitrary non-Hermitian optical potentials based on local Parity-Time (PT-) symmetry may tailor and control the flow of light, due to the asymmetric mode coupling. We now provide a comprehensive analysis on how this can be applied to stabilize the emission from broad aperture semiconductor lasers. The mechanism relies on a non-Hermitian configuration of the laser potential achieved by simultaneous spatial modulation of the refractive index and gain-loss profiles. This allows concentrating the light into a bright and narrow output beam. We provide a numerical analysis on Vertical Cavity Surface Emitting lasers and Broad Area Semiconductor Lasers. The results indicate a significant intensity enhancement and concentration of the emitted stabilized beam. The proposed mechanism may be technologically achievable, and it is expected to be applicable to regularize the radiation of other broad aperture and microlasers, which typically emit quite random and irregular light patterns. Besides, the reported concentration effect is universal, and could be extended to random and quasi-periodic background potentials.Peer ReviewedPostprint (author's final draft

Slow light enabled wavelength demultiplexing

Photonic crystal waveguides supporting band gap guided modes hold great potential to tailor the group velocity of propagating light. We propose and explore different wavelength demultiplexer design approaches that utilize slow light concept. By altering the dielectric filling factors of each waveguide segment, one can show that different frequencies can be separated and extracted at different locations along the cascaded waveguide. Furthermore, to eliminate the inherent reflection loss of such a design, a composite structure involving a tapered waveguide with a side-coupled resonator is also presented. Such a structure features not only a forward propagating wave but also a backward propagating wave acting as a feedback mechanism for the drop channels. We show that by careful design of the waveguide and the resonator, the destructive and instructive interference of these waves can effectively eliminate the reflection loss and increase the coupling efficiency, respectively. Numerical and experimental verification of the proposed structures show that the targeted frequencies can be coupled out with low cross-talks and moderate quality factors, while maintaining a compact size. © 2016 IEEE.Peer ReviewedPostprint (published version

Self-collimation in PT -symmetric crystals

We predict the self-collimation phenomena (or equivalently, dynamical localization) in two-dimensional PT-symmetric complex potentials, where the complex modulation is considered in the transverse, longitudinal, or simultaneously in both directions. Nondiffractive propagation is analytically predicted and further confirmed by numerical integration of a paraxial model. The parameter space is explored to identify the self-collimation regime in crystals with different PT symmetries. In addition, we also analyze how the PT-symmetric potentials determine the energy distribution between spatial modes of the self-collimated beams.Peer ReviewedPostprint (published version

Self-collimation in 2D Complex P- and PT-symmetric systems

We predict the self-collimation phenomena (or equivalently, dynamical localization) in 2-dimensional P-symmetric and PT-symmetric complex potentials, with periodic modulations of both gain/loss and refractive index. Non diffractive propagation is analytically predicted and further confirmed by numerical integration of a paraxial model. The parameter space is explored to identify the self-collimation regime in crystals with different complex symmetries.Postprint (published version