Circular polarization

About: Circular polarization is a research topic. Over the lifetime, 15201 publications have been published within this topic receiving 234418 citations.

A Design Technique Based on Equivalent Circuit and Coupler Theory for Broadband Linear to Circular Polarization Converters in Reflection or Transmission Mode

Abstract: A new approach to designing frequency selective surface (FSS)-based linear to circular polarization (LP–CP) converters is presented. It is based on the use of FSSs which exhibit dual diagonal symmetry, and a novel four-port equivalent circuit able to describe the electrical behavior of the cells for the two linear incident polarizations at the same time. The equivalent circuit allows the use of standardized branch line coupler theory to design LP–CP converters comprising a cascade of an arbitrary number of layers, whose synthesis includes the phase and makes it possible to achieve prescribed electrical conditions systematically. A full design procedure has been developed using the new approach and several designs in both transmission and reflection modes are presented and evaluated. It has been proven that single layer reflective converters exhibit large bandwidths as the two reflected field components are in quadrature independently of the frequency. One of these devices was designed and showed an axial ratio <0.2 dB within the band from 21.5 to 28.5 GHz. The reflective LP–CP converters designed was also manufactured and tested, and the measurements were used to validate the design procedure.

General relativistic polarized radiative transfer: building a dynamics–observations interface

Abstract: The rising number of polarized observations of relativistic sources necessitates a correct theory for proper model fitting. The equations for general relativistic (GR) polarized radiative transfer are derived starting from the Boltzmann equation and basic ideas of general relativity. The derivation is aimed at providing a practical guide to reproducing the synchrotron part of radio and submillimetre emission from low-luminosity active galactic nuclei (LLAGNs), in particular Sgr A*, and jets. A recipe for the fast exact calculation of cyclo-synchrotron emissivities, absorptivities, Faraday rotation and conversion coefficients is given for isotropic particle distributions. The multitude of physical effects influencing simulated spectra is discussed. The application of the prescribed technique is necessary to determine the black hole spin in LLAGNs. The observations of total flux, linear and circular polarization fractions, and electric vector position angle as functions of the observed frequency could substantially constrain the absolute value and orientation of spin.

All-silicon nanorod-based Dammann gratings

Abstract: Established diffractive optical elements (DOEs), such as Dammann gratings, whose phase profile is controlled by etching different depths into a transparent dielectric substrate, suffer from a contradiction between the complexity of fabrication procedures and the performance of such gratings. In this Letter, we combine the concept of geometric phase and phase modulation in depth, and prove by theoretical analysis and numerical simulation that nanorod arrays etched on a silicon substrate have a characteristic of strong polarization conversion between two circularly polarized states and can act as a highly efficient half-wave plate. More importantly, only by changing the orientation angles of each nanorod can the arrays control the phase of a circularly polarized light, cell by cell. With the above principle, we report the realization of nanorod-based Dammann gratings reaching diffraction efficiencies of 50%-52% in the C-band fiber telecommunications window (1530-1565 nm). In this design, uniform 4 x 4 spot arrays with an extending angle of 59 degrees x 59 degrees can be obtained in the far field. Because of these advantages of the single-step fabrication procedure, accurate phase controlling, and strong polarization conversion, nanorod-based Dammann gratings could be utilized for various practical applications in a range of fields. (C) 2015 Optical Society of America

Electric-field-induced differential scattering of right and left circularly polarized light

Abstract: The differential scattering of right and left circularly polarized light is a manifestation of optical activity. Both naturally optically active systems and fluids in a magnetic field parallel to the direction of propagation exhibit differential scattering. Although there is no electric analogue of Faraday's effect, a static electric field applied to a fluid perpendicular to the direction of propagation induces a difference in the scattered intensities of right and left circularly polarized light. The difference is linear in the field strength. It is determined by the effect of the field on the polarizabilities producing optical activity and is present in all matter, including monatomic gases. The classical theory of the scattering of electromagnetic waves is used in a formulation of the general theory of light scattering in an electric field. Results are given for some particular symmetries, including spherical, tetrahedral and dipolar molecules, and estimates of the magnitude of the effect are made.

Differential Scatter of Left and Right Circularlay Polarized Light by Optically Active Particulate Systems

Abstract: Because of the many heterogeneous systems which are of interest to the chemist and biochemist, the problems of distortions in circular dichroism patterns have been investigated. Specifically in this communication it is shown with a relatively well-characterized particular system (a suspension of α-helical poly-L-glutamic acid) that there is a measurable differential scatter of left and right circularly polarized light by suspensions of the optically active particles. This is a specific example of Perrin's assertion in 1942 (Perrin, F., J. Chem. Phys., 10, 415 (1942)) that the polarization characteristics of scattered light would differ depending on whether or not the scattering particle was optically active. Differential scatter is included with the concentration obscuring effects to demonstrate that distorted circular dichroism spectra on poly-L-glutamic acid suspension can be calculated with satisfying accuracy. The approach should be applicable to correcting the circular dichroism spectra for the many particles of biological interest, e.g., membranes, viruses, mitochondria, and insoluble proteins and polypeptides, and for small crystals in an effort to answer the crystal solution problem.