Design of a High-performance Flat Reflector Antenna Based on Conformal Transformation Optics

In this paper, we design an implementable high-performance flat reflector based on conformal transformation optics. In the proposed 2-dimensional device, the rescaling refractive index approach is applied to overcome the sub-unit refractive index issue, resulting in an all-dielectric isotropic graded-index medium that is physically implementable. Rotating the permeability profile around the antenna axis yields the 3-dimensional profile of the flat reflector construction. The dielectric with continuous refractive index profile is split into eleven layers with a constant refractive index. The proposed antenna requires only dielectric layers with the permittivity of 1.1 to 3.8, making it realizable. Simulation results show that the proposed flat reflector can operate in wide frequency bandwidth. The simulated antenna gain is about 25.27 to 29.55 dBi in the 13-30 GHz frequency range with the side-lobe level below -15 dB. Design and simulation of the proposed antenna are done using COMSOL Multiphysics, and simulation results are validated with CST Studio Suite.

Optical one-dimensional waveguides in oxyfluoride glass fabricated by Helium Ion implantation

In this work, a one-dimensional waveguide is formed by virtue of the helium ion implantation in the oxyfluoride glass (OFG). The energy and the fluence of the ion implantation are 0.4 MeV and [Formula: see text] [Formula: see text], respectively. The m-line curve with the effective refractive indices of the modes was recorded by using the prism coupling system. The energy loss distribution and the refractive index profile were calculated by the stopping and range of ions into matter (SRIM)-2013 and the RCM, respectively. The light modal profile was measured by the end-facet coupling system. It suggests that the He[Formula: see text]-ion implanted OFG waveguides have the potential to act as integrated photonic devices.

A solution to the complement of the generalized Luneburg lens problem

Lenses are of interest for the design of directive antennas and multi-optics instruments in the microwave, terahertz and optical domains. Here, we introduce an optical problem defined as the complement of the well-known generalized Luneburg lens problem. The spherically symmetric inhomogeneous lenses obtained as solutions of this problem transform a given sphere in the homogeneous region outside of the lens into a virtual conjugate sphere, forming a virtual image from a real source. An analytical solution is proposed for the equivalent geodesic lens using the analogy between classical mechanics and geometrical optics. The refractive index profile of the corresponding inhomogeneous lens is then obtained using transformation optics. The focusing properties of this family of lenses are validated using ray-tracing models, further corroborated with full-wave simulations. The numerical results agree well with the predictions over the analyzed frequency bandwidth (10–30 GHz). This virtual focusing property may further benefit from recent developments in the fields of metamaterials and transformation optics.

Review of a Decade of Research on Disordered Anderson Localizing Optical Fibers

Nearly a decade ago, transverse Anderson localization was observed for the first time in an optical fiber with a random transverse refractive index profile. This started the development of a whole new class of optical fibers that guide light, not in a conventional core-cladding setting based on total internal reflection, but utilizing Anderson localization, where light can guide at any location across the transverse profile of the fiber. These fibers have since been used successfully in high-quality endoscopic image transport. They also show interesting nonlinear and active (lasing) properties with promising applications. This review will cover a brief history of these fibers with personal accounts of the events that led to their development in our research groups. It will then follow with recent progress and future perspectives on science and applications of these fibers.

Determination of the refractive index profile and surface topography of optically smooth objects using interference of optical vortices

In this paper, we present the results of the propagational dynamics of vortex beams in the scope of their possible applications for interferometric non-contact robust and precision optical surface profilometry with nanoscale longitudinal resolution. The result of coaxial superposition of the reference plane wave with singly charged vortex beams represents a dynamically changing intensity distribution. The nature of this changes, namely, rotational effects of intensity zeros, allows to determine directly the optical path difference which is introduced by the surfaces and internal structure of test object. We have proposed the experimental setup for examination of reflecting and transmitting objects.

Algorithm for optical characterization of dielectric gradient index nanofilm by surface plasmon resonance spectroscopy

A numerical algorithm for determining the refractive index profiles of gradient nanofilms is proposed. A physical justification for the necessity of using spectroscopic measurements in surface plasmon resonance sensing in addition to angular measurements for the unambiguous reconstruction of the shape of the gradient refractive index profile is given. The proposed approach can be effective for nanofilms made of dielectric materials transparent in the IR and THz range.

Effect of Geometry on the Electromagnetic Wave Transport Properties of Photonic Crystals: Comparison of Top-Flat and Top-Curved Refractive Index Profiles

In the current paper, we try to engineer the refractive index profile in a one-dimensional photonic crystal as a powerful tool to manage the electromagnetic wave transmission properties. For this purpose, we have compared four sinusoidal, rectangular, triangular, and saw-tooth refractive index profile types. In this way, we have used a transfer matrix method accompanied by the discretization of the spatial domain. This method can readily be applied to any arbitrary continuous refractive index profile. Then, we have tried to address the effects of different geometrical and physical parameters, including the photonic crystal length L, dielectric permittivity εd, number of layers and plasma density np, etc. on the light propagation through the mentioned photonic crystals. In the proposed two-layer plasma/dielectric photonic crystals we could observe acceptable ranges of Omni-directional photonic band gaps that their position width and their number can be regulated. We determine the most and least tunable systems.

Passive discrete lens for broadband elastic guided wave focusing

Elastic guided wave focusing is of great interest for applications such as vibroacoustic control, energy harvesting, or Structural Health Monitoring. Different strategies allow generation of this effect, GRadient-INdex devices in particular exploit medium with varying properties such as thickness to reproduce an adequate refractive index profile as in optics. The resulting continuous profiles have a curved geometry that can be hard to manufacture, and be difficult to integrate in a given design. The purpose of this paper is to propose a discrete design for a GRIN lens. It is composed of segments selected in number and thickness to give similar focusing effects as a continuous lens profile. The identified configuration is manufactured and bounded on an aluminium plate to evaluate the effective focusing performances. Numerical and experimental vibrometry results confirm that the proposed lens exhibits a fixed focal point over a broad frequency range. The discrete design overcomes fabrication issues encountered in continuous design, allowing for an easier integration in devices for elastic wave control.

PT-symmetry and supersymmetry: interconnection of broken and unbroken phases

The broken and unbroken phases of P T and supersymmetry in optical systems are explored for a complex refractive index profile in the form of a Scarf potential, under the framework of supersymmetric quantum mechanics. The transition from unbroken to the broken phases of P T -symmetry, with the merger of eigenfunctions near the exceptional point is found to arise from two distinct realizations of the potential, originating from the underlying supersymmetry. Interestingly, in P T -symmetric phase, spontaneous breaking of supersymmetry occurs in a parametric domain, possessing non-trivial shape invariances, under reparametrization to yield the corresponding energy spectra. One also observes a parametric bifurcation behaviour in this domain. Unlike the real Scraf potential, in P T -symmetric phase, a connection between complex isospecrtal superpotentials and modified Korteweg-de Vries equation occurs, only with certain restrictive parametric conditions. In the broken P T -symmetry phase, supersymmetry is found to be intact in the entire parameter domain yielding the complex energy spectra, with zero-width resonance occurring at integral values of a potential parameter.