Circular Reflector Research Articles

A resonant circular polarization selective structure of closely spaced wire helices

AbstractA circular polarization selective structure (CPSS) reflects one handedness of circular polarization and transmits the other. We present a resonant CPSS consisting of closely spaced wire helices. Simulation results demonstrate that the design can operate over ±20° angle of incidence variation and has a bandwidth of about 10% at normal incidence. A suggested design case is presented, where the CPSS is implemented in a shared aperture circular polarization offset reflector antenna for satellite communication in the Ku band uplink of Australia at 17.3 GHz < f < 18.1 GHz.

Investigation of circular waveguide reflector feeds loaded with shaped dielectric rods

ABSTRACTCircular waveguides loaded with shaped dielectric rods are studied. The waveguide is entirely filled with a dielectric rod, extended from the waveguide aperture and conically shaped to modify the aperture distribution. Its performance as a primary feed is investigated, without and with quarter‐wavelength chokes, to improve sidelobe and backlobe levels. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1568–1573, 2015

Sum decomposition of Mueller-matrix images and spectra of beetle cuticles.

Spectral Mueller matrices measured at multiple angles of incidence as well as Mueller matrix images are recorded on the exoskeletons (cuticles) of the scarab beetles Cetonia aurata and Chrysina argenteola. Cetonia aurata is green whereas Chrysina argenteola is gold-colored. When illuminated with natural (unpolarized) light, both species reflect left-handed and near-circularly polarized light originating from helicoidal structures in their cuticles. These structures are referred to as circular Bragg reflectors. For both species the Mueller matrices are found to be nondiagonal depolarizers. The matrices are Cloude decomposed to a sum of non-depolarizing matrices and it is found that the cuticle optical response, in a first approximation can be described as a sum of Mueller matrices from an ideal mirror and an ideal circular polarizer with relative weights determined by the eigenvalues of the covariance matrices of the measured Mueller matrices. The spectral and image decompositions are consistent with each other. A regression-based decomposition of the spectral and image Mueller matrices is also presented whereby the basic optical components are assumed to be a mirror and a circular polarizer as suggested by the Cloude decomposition. The advantage with a regression decomposition compared to a Cloude decomposition is its better stability as the matrices in the decomposition are determined a priori. The origin of the depolarizing features are discussed but from present data it is not possible to conclude whether the two major components, the mirror and the circular polarizer are laterally separated in domains in the cuticle or if the depolarization originates from the intrinsic properties of the helicoidal structure.

Wide-band circular polarization-keeping reflection mediated by metasurface**Project supported by the National Natural Science Foundation of China (Grants Nos. 61331005, 11204378, 11274389, 11304393, and 61302023) and the National Natural Science Foundation of Shaanxi Province, China (Grant Nos. 2011JQ8031 and 2013JM6005).

In this paper, we show that circular polarization-keeping reflection can be achieved using reflective metasurfaces. The underlying physical mechanism of the polarization-keeping reflection is analyzed using a reflection matrix. A wideband circular polarization-keeping reflector is demonstrated using N-shaped resonators. Both the simulation and experiment results show that the polarization-keeping reflection can be achieved with a high efficiency larger than 98% over the frequency range from 9.2 GHz to 17.7 GHz for both incident left- and right-handed circularly polarized waves. Under oblique incidence, the bandwidth increases as the incident angle varies from 0° to 80°. Moreover, the co-polarization reflection is independent of the incident azimuth angles.

Electromagnetic field intensity distribution along focal region of a metallic circular reflector covered with a plasma layer

Theoretical analyses has been carried out to study the deviation of the electromagnetic field intensity distribution in the focal region of a long metallic circular reflector that contains a uniform cold collisional plasma layer on its surface. The electromagnetic field intensity expressions along the focal region have been obtained using Maslov’s method. Maslov’s method is systematic procedure, which combines the simplicity of ray optics and the generality of transform methods. The derived analytical field expressions in the focal region have been solved numerically. The reflected and transmitted field intensity distributions from the plasma layer along the focal point were examined. The effects of some physical parameters such as the plasma frequency, the thickness of plasma layer and the effective collision frequency on the transmitted field intensity distribution along the focal region are studied. The results are found to be in a good agreement with results obtained using Kirchhoff’s approximation.

Inverse problem for shape control of flexible space reflectors using distributed solar pressure

This paper investigates controlled elastic deflection of thin circular space reflectors using an inverse problem approach to non-linear thin membrane theory. When changing the surface reflectivity across the membrane, the distributed loads due to ambient solar radiation pressure can be manipulated optically, thus controlling the surface shape without using mechanical or piezo-electric systems. The surface reflectivity can in principle be modulated using uniformly distributed thin-film electro-chromic coatings. We present an analytic solution to the inverse problem of finding the necessary reflectivity distribution that creates a specific membrane deflection, for example that of a parabolic reflector. Importantly, the reflectivity distribution across the surface is found to be independent of membrane size, thickness and solar distance, enabling engineering of the reflectivity distribution directly during the manufacture of the membrane.

Ray Tracing Study to Determine the Characteristics of the Solar Image in the Receiver for a Scheffler-type Solar Concentrator Coupled with a Stirling Engine

This study presents the geometric aspects of the focal image for a Scheffler-type solar concentrator (STSC) using the ray tracing technique to establish parameters that allow the designation of the most suitable geometry for coupling the STSC to a Stirling engine of 3 kWe. The results of the ray tracing software are validated through thermographic images of the STSC solar concentration after modifying the image to establish the geometric areas with the highest temperature.When performing the simulations using the ray tracing software, we found that the most suitable solar image geometry has variations within an elliptical area of 14.25 cm2 on average with a circular aperture area reflector. While this result is appropriate, the geometry of the receiver would need to be modified to fit a Stirling engine. Finally, when validating the ray tracing results with the image provided by the thermography camera, it was found that the area tends to be elliptical but with an area greater than 36%; this result must be taken into consideration to improve the heat transfer by radiation at the receiver of the STSC.

Lateral Oxidation of AlAs for Circular and Inverted Mesa Saturable Bragg Reflectors

A model of the thermal oxidation kinetics that is based on the continuity equation is adapted to the fabrication of circular saturable Bragg reflector (SBR) mesa structures, as well as inverted mesa array structures. A comparison between theoretical calculations and experimental measurements shows good agreement, making the model a useful tool for the controllability of the structure-dependent oxidation process. The model is applied to the wet oxidation of buried AlAs layers for the fabrication of ultra-broadband, high index contrast, III-V/ AlxOy SBRs. The rate of oxidation is found to be dependent not only on the oxidation temperature, but also on oxidation time, mesa geometry, and AlAs layer thickness. The two distinct large-area SBR structures, the circular mesa and the inverted mesa, are fabricated.

Lasing in hybrid metal-Bragg nanocavities

We report room-temperature lasing from an optically pumped subwavelength-scale cylindrical InGaAsP pillar surrounded by circular Bragg reflectors on a metal substrate with a dielectric spacer layer. By taking advantage of wide in-plane photonic bandgaps and proper vertical antiresonances, three dielectric Bragg pairs produce a sufficient optical feedback capable of low threshold lasing from the fundamental TE011 mode. A large spontaneous emission coupling into the lasing mode is obtained from the cavity-enhanced Purcell effects and effective suppression of nonlasing modes.

A compact stacked Archimedean spiral antenna

This paper presents a compact linearly polarized double-arm Archimedean spiral antenna positioned between a circular reflector and a spiral parasitic element. The proposed design has a simulated gain of 10.6 dBi and an aperture reduction of 40% when compared to an equivalent half-wavelength dipole. Linear polarization has been maintained despite the spiral geometry of the antenna.

DESIGN OF A NIR-CONCENTRATOR SYSTEM INTEGRATED IN A GREENHOUSE

In this paper the design and development of a new type of greenhouse with an integrated filter for reflecting near infrared radiation (NIR) and a solar energy delivery system is described. Especially the optical parts as the spectral selective film, the properties of the circular reflector and the efficiencies of photo voltaic cells are studied. As a first measure, the spectral selective cover material, which prevents the entrance of NIR radiation, is investigated. It has to block up to 35% of the solar energy outside the greenhouse, which will reduce the needed cooling capacity. The second measure is the integration with a solar energy system. When the NIR reflecting coating is designed as a circular shaped reflector integrated in the greenhouse, the reflected solar energy of a PhotoVoltaic (PV) cell in the focus point delivers electric energy. With a ray tracing computer program the optimal geometry of the reflector was designed with respect to the collecting efficiency. The PV cells mounted in the focal point require cooling due to the high heat load of the concentrated radiation (geometric concentration factor of 30). The properties of different PV materials were investigated to find the optimal cell for this application. Cooled greenhouses are an important issue to cope with the combination of high global radiation and high outdoor temperatures. All parts are integrated in a 100m2 prototype greenhouse which will be applied for the proof of principle.

Focusing of electromagnetic field by a circular reflector coated with chiral medium

High frequency electromagnetic field expressions are analyzed for the focal region of a circular reflector coated with chiral medium. Maslov's method has been used for the study of focal region fields because geometrical optics is an approximate method and fails at the focal points. The effects of chirality parameter, thickness of chiral coating and permittivity of the medium on the focused fields are observed. It is concluded from the results that focused field strength increases with increase in chirality parameter, relative permittivity and thickness of the chiral coating.

On the directivity characteristic of an angle transducer in the reception mode

The acoustic path of an angle transducer is calculated in the reception mode in the geometrical-acoustics approximation. The comparison of the angles of propagation of transverse and longitudinal waves in the reception mode with the corresponding angles in the transmission mode shows their coincidence. It is established that the directivity characteristics of an angle transducer for transmission and reception are identical. The formula of the acoustic path for a flat-bottom circular reflector with different positions and orientations is obtained for the far-field zone of the angle transducer.

Optical thin-film linear polarization selector fabricated by oblique angle deposition

A linear polarization selector was made from a three-section sculptured thin film deposited using an oblique angle deposition technique. In this device, the circular Bragg reflector with a left-handed helical structure was sandwiched in between two quarter-wave plates with opposite in-plane birefringence. Within the Bragg regime, the normal incident S-polarized light on this device was reflected, whereas the incident P-polarized light was transmitted through it. The microstructure of the linear polarization selector was also examined by scanning electron microscopy.

Inverse Common-Reflection-Surface

SUMMARY The Common-Reflection-Surface (CRS) stack method is a powerful tool to produce high-quality stacked images of multicoverage seismic data. As a result of the CRS stack, not only a stacked section, but also a number of attributes defined at each point of that section, are produced. In this way, one can think of the CRS stack method as a transformation from data space to attribute space. Being a purely kinematic method, the CRS stack lacks amplitude information that can be useful for many purposes. Here we propose to fill this gap by means of a combined use of a zero-offset section (that could be a short-offset or amplitude-corrected stacked section) and common midpoint gather. We present an algorithm for an inverse CRS transformation, namely one that (approximately) transforms the CRS attributes back to data space. First synthetic tests provide satisfying results for the two simple cases of single dipping-plane and single circular reflectors with a homogeneous overburden, and provide estimates of the range of applicability, in both midpoint and offset directions. We further present an application for interpolating missing traces in a near-surface, high-resolution seismic experiment, conducted in the alluvial plain of the river Gave de Pau, near Assat, southern France, showing its ability to build coherent signals, where recording was not available. A somewhat unexpected good feature of the algorithm, is that it seems capable to reconstruct signals even in muted parts of the section.

Improvements in Optical Power and Emission Angle of Blue Light Emitting Diodes Using Patterned Sapphire Substrates with Low Threading Dislocation Densities

GaN blue light-emitting diodes (LEDs) with a peak emission wavelength of approximately 461 nm were fabricated on a c-face lens patterned sapphire substrate (PSS) and an unpatterened sapphire substrate (UPSS) by metal organic chemical vapor deposition (MOCVD). The crystal structure of an epitaxial GaN film was improved by using the PSS. The peak wavelengths with electroluminescence intensities of 462 and 464 nm were measured for PSS and UPSS LEDs using a 20 mA injection current. It was found that the electroluminescence intensity of the LEDs grown on the lens PSS was about 61% higher than that of the LEDs prepared on the UPSS. The emission angle of the PSS LED increased by 1.5 times compared with that of the UPSS LED. The luminous intensities of both LEDs increased similarly on both circular and square reflectors. The output power of the PSS LED was 33% greater than that of the LED UPSS. In addition, the reduction in full width at half maximum (FWHM) in the ω-scan rocking curves of GaN on the PSS suggested an improved crystal quality. These significant improvements in output power and emission angle resulted from the enhanced light extraction and the reduced threading dislocation (TD) density using the PSS method.

Increasing the coupling efficiency of a microdisk laser to waveguides by using well designed spiral structures

In this article, we optimize the coupling efficiency from a GaAs microdisk resonator into a single mode spiral waveguide. A classical microdisk resonator coupling light into a nonevanescent straight waveguide reaches a typical coupling efficiency of 67%. We show that the introduction of a spiral waveguide that works both as a waveguide and circular Bragg reflector can improve such efficiency to almost 90%. The same structure with the addition of a taper can couple up to 80% of the generated power into a slot waveguide.

On calculation of DGS diagrams of normal transducers for spherical and cylindrical reflectors

Formulas for the acoustic path were obtained and DGS diagrams were calculated in a general case and in a scalar approximation for a hollow spherical reflector positioned axially symmetrically relative to a normal transducer. The convergence of DGS diagrams to the asymptotic value determined by the formula for the far-field zone, the difference between them obtained using the reflection coefficients with exact and approximate accounting of the boundary conditions at the reflector, and the effect of a pulsed transmission-reception mode were studied. The DGS diagrams for a hollow circular cylindrical reflector (side drilled hole) were calculated using I.N. Ermolov’s method.

Linear polarization-discriminatory state inverter fabricated by oblique angle deposition

In this paper, we report a linear polarization-discriminatory state inverter made of three-layer sculpture thin film fabricated by oblique angle deposition technique. The first and third layers are quarter-wave plates of zigzag structure and the middle of them is a circular Bragg reflector of left-handed helical structure. It is found that the normal incidence of P-polarized light on this polarization-discriminatory state inverter becomes the S-polarized light at output, while the incident S-polarized light of wavelength lying in the Bragg regime is reflected. The microstructure of the linear polarization-discriminatory state inverter is also investigated by using a scanning electron microscope.

Calculation of the acoustic path for arbitrarily oriented reflectors of the flat-bottom-hole type of different shapes in the far-field zone of normal transducers

The Kirchhoff approximation is used to calculate the acoustic path for an arbitrarily oriented reflector of the flat-bottom-hole type, whose boundary is specified by the angular-coordinate-dependent distance from the center to the current point on the contour, in the far-field zone of normal circular transducers arbitrarily placed on the testing surface. The limiting values of the formula for the acoustic path coincide with those obtained earlier for an arbitrarily oriented circular reflector and a noncircular reflector with a surface parallel to the testing surface. Examples of calculations of the directivity characteristics of an elliptic reflector are presented.