Showing papers on "Circular polarization published in 2010"

Scalar and Tensor Holographic Artificial Impedance Surfaces

Abstract: We have developed a method for controlling electromagnetic surface wave propagation and radiation from complex metallic shapes. The object is covered with an artificial impedance surface that is implemented as an array of sub-wavelength metallic patches on a grounded dielectric substrate. We pattern the effective impedance over the surface by varying the size of the metallic patches. Using a holographic technique, we design the surface to scatter a known input wave into a desired output wave. Furthermore, by varying the shape of the patches we can create anisotropic surfaces with tensor impedance properties that provide control over polarization. As an example, we demonstrate a tensor impedance surface that produces circularly polarized radiation from a linearly polarized source.

Twisted split-ring-resonator photonic metamaterial with huge optical activity

Abstract: Coupled split-ring-resonator metamaterials have previously been shown to exhibit large coupling effects, which are a prerequisite for obtaining large effective optical activity. By a suitable lateral arrangement of these building blocks, we completely eliminate linear birefringence and obtain pure optical activity and connected circular optical dichroism. Experiments around a 100 THz frequency and corresponding modeling are in good agreement. Rotation angles of about 30 degrees for 205 nm sample thickness are derived.

Microstrip Patch Antennas

Abstract: Introduction Review of Some Background Materials General Formulation of the Cavity Model Characteristics of the Rectangular Patch Characteristics of the Circular Patch The Annular-Ring and the Equilaterial Triangular Patch Introduction to Full Wave Analysis of Microstrip Antennas Some Methods of Tuning the Resonant Frequencies of Patch Antennas Broadbanding Techniques Size Reduction Techniques Dual and Multi-Band Designs Dual Polarized Patch Antenna Designs Circular Polarization Microstrip Arrays

Asymmetric-Circular Shaped Slotted Microstrip Antennas for Circular Polarization and RFID Applications

Abstract: Novel asymmetric-circular shaped slotted microstrip patch antennas with slits are proposed for circularly polarized (CP) radiation and radio frequency identification (RFID) reader applications. A single-feed configuration based asymmetric-circular shaped slotted square microstrip patches are adopted to realize the compact circularly polarized microstrip antennas. The asymmetric-circular shaped slot(s) along the diagonal directions are embedded symmetrically onto a square microstrip patch for CP radiation and small antenna size. The CP radiation can be achieved by slightly asymmetric (unbalanced) patch along the diagonal directions by slot areas. Four symmetric-slits are also embedded symmetrically along the orthogonal directions of the asymmetric-circular shaped slotted patch to further reduce antenna size. The operating frequency of the antenna can be tuned by varying the slit length while keeping the CP radiation unchanged. The measured 3-dB axial-ratio (AR) bandwidth of around 6.0 MHz with 17.0 MHz impedance bandwidth is achieved for the antenna on a RO4003C substrate. The overall antenna size is 0.27λo × 0.27λo × 0.0137λo at 900 MHz.

Alignment, Rotation, and Spinning of Single Plasmonic Nanoparticles and Nanowires Using Polarization Dependent Optical Forces

Abstract: We demonstrate optical alignment and rotation of individual plasmonic nanostructures with lengths from tens of nanometers to several micrometers using a single beam of linearly polarized near-infrared laser light. Silver nanorods and dimers of gold nanoparticles align parallel to the laser polarization because of the high long-axis dipole polarizability. Silver nanowires, in contrast, spontaneously turn perpendicular to the incident polarization and predominantly attach at the wire ends, in agreement with electrodynamics simulations. Wires, rods, and dimers all rotate if the incident polarization is turned. In the case of nanowires, we demonstrate spinning at an angular frequency of ∼1 Hz due to transfer of spin angular momentum from circularly polarized light.

Radiation reaction effects on radiation pressure acceleration

Abstract: Radiation reaction (RR) effects on the acceleration of a thin plasma foil by a superintense laser pulse in the radiation pressure-dominated regime are investigated theoretically. A simple suitable approximation of the Landau–Lifshitz equation for the RR force and a novel leap-frog pusher for its inclusion in particle-in-cell simulations are provided. Simulations for both linear and circular polarization of the laser pulse are performed and compared. It is found that at intensities exceeding 1023 W cm− 2 the RR force strongly affects the dynamics for a linearly polarized laser pulse, reducing the maximum ion energy but also the width of the spectrum. In contrast, no significant effect is found for circularly polarized laser pulses whenever the laser pulse does not break through the foil.

Gold helix photonic metamaterials: A numerical parameter study

Abstract: We have recently shown that metamaterials composed of three-dimensional gold helices periodically arranged on a square lattice can be used as compact “thin-film” circular polarizers with one octave bandwidth. The physics of the motif of these artificial crystals is closely related to that of microwave sub-wavelength helical antennas in end-fire geometry. Here, we systematically study the dependence of the metamaterial’s chiral optical properties on helix pitch, helix radius, two-dimensional lattice constant, wire radius, number of helix pitches, and angle of incidence. Our numerical calculations show that the optical properties are governed by resonances of the individual helices, yet modified by interaction effects. Furthermore, our study shows possibilities and limitations regarding performance optimization.

Optical nanoprobing via spin-orbit interaction of light.

Abstract: We show, both theoretically and experimentally, that high-numerical-aperture (NA) optical microscopy is accompanied by strong spin-orbit interaction of light, which translates fine information about the specimen to the polarization degrees of freedom of light. An 80 nm gold nanoparticle scattering the light in the focus of a high-NA objective generates angular momentum conversion, which is seen as a nonuniform polarization distribution at the exit pupil. We demonstrate remarkable sensitivity of the effect to the position of the nanoparticle: Its subwavelength displacement produces the giant spin-Hall effect, i.e., macroseparation of spins in the outgoing light. This brings forth a far-field optical nanoprobing technique based on the spin-orbit interaction of light.

Experimental confirmation of miniature spiral plasmonic lens as a circular polarization analyzer

Abstract: A spiral plasmonic lens can focus circular polarization of a given handedness while simultaneously defocus the circular polarization of the opposite chirality, which may be used as a miniature circular polarization analyzer. In this letter, we experimentally investigated the plasmonic focusing properties of the spiral lens using a collection mode near-field scanning optical microscope. A single Archimedes' spiral slot with a single turn was etched through gold thin film as a spiral plasmonic lens. The plasmonic field at the focus of a spiral lens strongly depends on the spin of the incident photon. Circular polarization extinction ratio better than 50 is obtainable with a device size as small as only 4 times of surface plasmon wavelength.

Polarization demultiplexing in Stokes space

Abstract: A technique is demonstrated for polarization demultiplexing of arbitrary complex-modulated signals. The technique is based entirely on the observation of samples in Stokes space, does not involve demodulation and is modulation format independent. The data in Stokes space is used to find the best fit plane and the normal to it which contains the origin. This normal identifies the two orthogonal polarization states of transmission and the desired polarization alignment transformation matrix. The technique is verified experimentally and is compared with the constant modulus algorithm.

Radiation Reaction Effects on Radiation Pressure Acceleration

Abstract: Radiation reaction (RR) effects on the acceleration of a thin plasma foil by a superintense laser pulse in the radiation pressure dominated regime are investigated theoretically. A simple suitable approximation of the Landau-Lifshitz equation for the RR force and a novel leapfrog pusher for its inclusion in particle-in-cell simulations are provided. Simulations for both linear and circular polarization of the laser pulse are performed and compared. It is found that at intensities exceeding $10^{23} \Wcm$ the radiation reaction force strongly affects the dynamics for a linearly polarized laser pulse, reducing the maximum ion energy but also the width of the spectrum. In contrast, no significant effect is found for circularly polarized laser pulses whenever the laser pulse does not break through the foil.

325 GHz Single Layer Sub-Millimeter Wave FSS Based Split Slot Ring Linear to Circular Polarization Convertor

Abstract: A single layer, frequency selective surface based, sub-millimeter wave transmission polarizer is presented that converts incident slant linear 45° polarization into circular polarization upon transmission The polarization convertor consists of a 30 mm diameter 10 thick silicon reinforced metalized screen containing 2700 resonator cells and perforated with nested split ring slot apertures The screen was designed and optimized using CST Microwave Studio and predictions were validated experimentally by transmission measurements over the 250-365 GHz frequency range This frequency range is used for remote environmental monitoring and 325 GHz represents a molecular emission line for H2O The results obtained show good agreement between measured and modeled predictions The measured 3 dB axial ratio bandwidth was 1175%, measured minimum Axial Ratio was 019 dB and the measured insertion loss of the single layer screen was 338 dB

Microdrilling in steel using ultrashort pulsed laser beams with radial and azimuthal polarization

Abstract: A linear to radial and/or azimuthal polarization converter (LRAC) has been inserted into the beam delivery of a micromachining station equipped with a picosecond laser system. Percussion drilling and helical drilling in steel have been performed using radially as well as azimuthally polarized infrared radiation at 1030 nm. The presented machining results are discussed on the basis of numerical simulations of the polarization-dependent beam propagation inside the fabricated capillaries.

Highly tunable optical activity in planar achiral terahertz metamaterials

Abstract: Using terahertz time domain spectroscopy we demonstrate tunable polarization rotation and circular dichroism in intrinsically non-chiral planar terahertz metamaterials without twofold rotational symmetry. The observed effect is due to extrinsic chirality arising from the mutual orientation of the metamaterial plane and the propagation direction of the incident terahertz wave.

Millimeter-Wave Half Mode Substrate Integrated Waveguide Frequency Scanning Antenna With Quadri-Polarization

Abstract: A millimeter-wave frequency scanning antenna, which is capable of dynamically changing the state of polarization thereby providing four modes of operation, is investigated and synthesized in the half mode substrate integrated waveguide (HMSIW) technology. This antenna is a planar passive circuit and fabricated by the low-cost PCB process. It is able to operate in either linear or circular polarization (LP or CP), depending on the requirements of its specific application. A wide angular region can be covered by 3 dB beam-widths of the continuous scanning LP beams and CP beams varying the frequency. It has good performance validated by measurements and has nearly a half reduction in size compared with the substrate integrated waveguide (SIW) version. The axial ratios of CP modes are excellent in the main beam directions within whole frequency band of interest and the isolations between each channel are good as well.

Dynamic Hall Effect Driven by Circularly Polarized Light in a Graphene Layer

Abstract: We report the observation of the circular ac Hall effect where the current is solely driven by the crossed ac electric and magnetic fields of circularly polarized radiation. Illuminating an unbiased monolayer sheet of graphene with circularly polarized terahertz radiation at room temperature generates--under oblique incidence--an electric current perpendicular to the plane of incidence, whose sign is reversed by switching the radiation helicity. Alike the classical dc Hall effect, the voltage is caused by crossed E and B fields which are, however rotating with the light's frequency.

Spatially engineered polarization states and optical vortices in uniaxial crystals

Abstract: We describe how the propagation of light through uniaxial crystals can be used as a versatile tool towards the spatial engineering of polarization and phase, thereby providing an all-optical technique for vectorial and scalar singular beam shaping in optics. Besides the prominent role played by the linear birefringence, the influence of circular birefringence (the optical activity) is discussed as well and both the monochromatic and polychromatic singular beam shaping strategies are addressed. Under cylindrically symmetric light-matter interaction, the radially, azimuthally, and spirally polarized eigen-modes for the light field are revealed to be of a fundamental interest to describe the physical mechanisms at work when dealing with scalar and vectorial optical singularities. In addition, we also report on nontrivial effects arising from cylindrical symmetry breaking, e.g. tilting the incident beam with respect to the crystal optical axis.

Liquid-crystal micropolarimeter array for full Stokes polarization imaging in visible spectrum

Abstract: In this paper, we describe the design, modeling, fabrication, and optical characterization of the first micropolarimeter array enabling full Stokes polarization imaging in visible spectrum. The proposed micropolarimeter is fabricated by patterning a liquid-crystal (LC) layer on top of a visible-regime metal-wire-grid polarizer (MWGP) using ultraviolet sensitive sulfonic-dye-1 as the LC photoalignment material. This arrangement enables the formation of either micrometer-scale LC polarization rotators, neutral density filters or quarter wavelength retarders. These elements are in turn exploited to acquire all components of the Stokes vector, which describes all possible polarization states of light. Reported major principal transmittance of 75% and extinction ratio of 1100 demonstrate that the MWGP's superior optical characteristics are retained. The proposed liquidcrystal micropolarimeter array can be integrated on top of a complementary metal-oxide-semiconductor (CMOS) image sensor for real-time full Stokes polarization imaging.

Effect of Antenna Polarization Diversity on MIMO System Capacity

Abstract: The effect of circular polarization diversity on the capacity of a multiple-input-multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system is investigated based on channel measurements. In this letter, polarization reconfigurable U-slot antennas are incorporated in a 22 MIMO-OFDM demonstrator, and the channel measurements are conducted in both line-of-sight (LOS) and non-LoS (NLOS) indoor environments. Measured results show that transmit/receive antennas radiating different polarizations are able to improve the system capacity significantly compared to antennas with the same polarization in a LOS scenario, while the extent of the improvement is reduced in a NLOS scenario. Furthermore, the factors that can affect the system capacity in both scenarios are analyzed.

A Subwavelength Element for Broadband Circularly Polarized Reflectarrays

Abstract: A subwavelength element is presented for designing a circularly polarized (CP) reflectarray that converts the linearly polarized incident field of the feed into an outgoing circularly polarized field. To evaluate the performance of the designed element, a parametric study is carried out using Ansoft HFSS. Compared to the conventional near-resonant patch, the subwavelength one can realize a more similar behavior for the phase curves at different frequencies, leading to broader bandwidth. The phase shifts for both linear polarizations can be controlled by varying the x- and y-dimension of the element. A prime-focus reflectarray with this type of element has been designed and implemented, and a superior bandwidth performance has been verified, compared to a reflectarray with conventional ?/2 elements. The measured results show that the obtained 1-dB gain and 3-dB axial ratio bandwidths of the reflectarray with subwavelength elements can reach as large as 17% and 11%, respectively.

Virtually Shorted Patch Antenna for Circular Polarization

Abstract: This letter presents a new circularly polarized patch antenna with loaded shorting elements to achieve symmetric broadside radiation and size reduction. The loaded elements are parasitic to the driven patch, but are shorted to the ground plane. Conventionally, shorting pins or walls are a common technique for reducing the size of the antenna. However, deterioration in broadside radiation with high cross-polar level occurs. The proposed shorting elements provide a solution for size reduction of the radiating patch while maintaining good broadside radiation pattern. Since the radiating patch is effectively shorted to the ground at the operating frequency, it is designated as a virtually shorted patch antenna (VSPA).

Wideband Circularly Polarized E-Shaped Patch Antenna for Wireless Applications [Wireless Corner]

Abstract: A new technique to achieve a circularly polarized probe-fed single-layer microstrip-patch antenna with a wideband axial ratio is proposed. The antenna is a modified form of the conventional E-shaped patch, used to broaden the impedance bandwidth of a basic patch antenna. By letting the two parallel slots of the E patch be unequal, asymmetry is introduced. This leads to two orthogonal currents on the patch and, hence, circularly polarized fields are excited. The proposed technique exhibits the advantage of the simplicity of the E-shaped patch design, which requires only the slot lengths, widths, and position parameters to be determined. Investigations of the effect of various dimensions of the antenna have been carried out via parametric analysis. Based on these investigations, a design procedure for a circularly polarized E-shaped patch was developed. A prototype has been designed, following the suggested procedure for the IEEE 802.11big WLAN band. The performance of the fabricated antenna was measured and compared with simulation results. Various examples with different substrate thicknesses and material types are presented and compared with the recently proposed circularly polarized U-slot patch antennas.

Magnetic Doppler imaging of α2 Canum Venaticorum in all four Stokes parameters - Unveiling the hidden complexity of stellar magnetic fields

Abstract: Context. Strong organized magnetic fields have been studied in the upper main sequence chemically peculiar stars for more than half a century. However, only recently have observational methods and numerical techniques become sufficiently mature to allow us to record and interpret high-resolution four Stokes parameter spectra, leading to the first assumption-free magnetic field models of these stars. Aims. Here we present a detailed magnetic Doppler imaging analysis of the spectropolarimetric observations of the prototypical magnetic Ap star alpha(2) CVn. This is the second star for which the magnetic field topology and horizontal chemical abundance inhomogeneities have been inferred directly from phase-resolved observations of line profiles in all four Stokes parameters, free from the traditional assumption of a low-order multipolar field geometry. Methods. We interpret the rotational modulation of the circular and linear polarization profiles of the strong Fe II and Cr II lines in the spectra of alpha 2 CVn recorded with the MuSiCoS spectropolarimeter. The surface abundance distributions of the two chemical elements and a full vector map of the stellar magnetic field are reconstructed in a self-consistent inversion using our state-of-the-art magnetic Doppler imaging code INVERS10. Results. We succeeded in reproducing most of the details of the available spectropolarimetric observations of alpha 2 CVn with a magnetic map which combines a global dipolar-like field topology with localized spots of higher field intensity. We demonstrate that these small-scale magnetic structures are inevitably required to fit the linear polarization spectra; however, their presence cannot be inferred from the Stokes I and V observations alone. We also found high-contrast surface distributions of Fe and Cr, with both elements showing abundance minima in the region of weaker and topologically simpler magnetic field. Conclusions. Our magnetic Doppler imaging analysis of alpha 2 CVn and previous results for 53 Cam support the view that the upper main sequence stars can harbour fairly complex surface magnetic fields which resemble oblique dipoles only at the largest spatial scales. Spectra in all four Stokes parameters are absolutely essential to unveil and meaningfully characterize this field complexity in Ap stars. We therefore suggest that understanding magnetism of stars in other parts of the H-R diagram is similarly incomplete without investigation of their linear polarization spectra.

Wideband and High-Gain Composite Cavity-Backed Crossed Triangular Bowtie Dipoles for Circularly Polarized Radiation

Abstract: A composite cavity-backed antenna excited by crossed triangular bowtie dipoles is proposed and investigated for circular polarization (CP) applications. It is fed by a novel balun, i.e., a transition from a microstrip line to double slot lines, providing symmetrical electric field distributions at the feeding port. Measurements of an optimized antenna prototype show that it can achieve an impedance bandwidth of over 57.6% for SWR ≤ 2, a 3-dB axial-ratio bandwidth of 39%, a broadside gain of 8-10.7 dBi, and symmetrical radiation patterns over the whole operating band. The operating principles of the proposed antenna are analyzed carefully and found quite different from crossed thin-wire dipoles with very weak coupling. Problems in the feeding balun, greatly deteriorating the CP performance at the resonance, are clearly addressed and solved. Detailed parametric studies are given in the final part of this paper.

Polarization diffraction grating produced by femtosecond laser nanostructuring in glass

Abstract: We demonstrate polarization sensitive diffractive optical element fabrication by femtosecond direct writing in the bulk of silica glass. Modulation of the anisotropic properties is produced by controlling light-induced self-assembled nano-gratings.

Decomposition of radially and azimuthally polarized beams using a circular-polarization and vortex-sensing diffraction grating

Abstract: Both radially polarized and azimuthally polarized beams can be decomposed into linear combinations of circularly polarized vortex beams having opposite vortex charges. We show experimental evidence for this decomposition using a specially designed vortex sensing diffraction grating that generates multiple vortex patterns having different senses of circularly polarization in the different diffracted orders. When this grating is illuminated with a radially or azimuthally polarized beam, the grating separates the components into different diffracted orders. Experimental results are shown.

Display device with a transparent optical filter

Abstract: Optical filter which is adapted to prevent the reflection of external light and improve a signal level of a signal sent from a display device by preventing attenuation thereof, and which is further adapted to prevent a change in hue of an image and to improve the hue, contrast and brightness of an image, thereby enhancing visibility. First, a liquid crystal display device (1) outputs light which is linearly polarized light. First linearly polarizing plate (2) is mounted in the filter in such a manner as to be adjusted to an axis of polarization of the linearly polarized light. Namely, the light outputted from the liquid crystal display device (1) passes through the first linearly polarizing plate (2) without being changed. The light passing through the first linearly polarizing plate (2) is then changed by a first quarter-wave phase difference plate (11) into circularly polarized light so that the phase difference between extraordinary light and ordinary light is (1/4) of the wavelength. Subsequently, light passes through a transparent touch panel (12) and further propagates through a second quarter-wave phase difference plate (7). At that time, a phase difference therebetween is caused by (-1/4) of the wavelength of the light in which the phase difference of (1/4) of the wavelength has been caused. Thus, when passing through the touch panel(12), the light is changed into linearly polarized light. Then, the light, which has propagated through the transparent touch panel (12) and the second quarter-wave phase difference plate (7), passes through the second linearly polarizing plate (6).

Ultrabroadband optical circular polarizers consisting of double-helical nanowire structures

Abstract: Recently, it was demonstrated by Gansel et al. [Science 325, 1513 (2009)] that 3D single-helical metamaterials can serve as broadband circular polarizers in the IR range. In this study, we propose a structured metamaterial with double-helical nanowires to construct circular polarizers with boarder wavelength bands in the visible-light and near-IR regions. Using the finite-difference time-domain method, we confirmed that the circular polarizers with the double-helical structures have operation bands more than 50% broader than those of the single-helical structures.

A 3.5?mm Polarimetric Survey of Radio-loud Active Galactic Nuclei

Abstract: We present the results from the first large (>100 sources) 3.5 mm polarimetric survey of radio-loud active galactic nuclei (AGNs). This wavelength is favorable within the radio-millimeter range for measuring the intrinsic linearly polarized emission from AGNs, since in general it is only marginally affected by Faraday rotation of the electric vector position angle and depolarization. The I, Q, U, and V Stokes parameter observations were performed with the XPOL polarimeter at the IRAM 30 m Telescope on different observing epochs from 2005 July (when most of the measurements were made) to 2009 October. Our sample consists of 145 flat-radio-spectrum AGNs with declination >-30{sup 0} (J2000.0) and flux density {approx}>1 Jy at {approx}86 GHz, as measured at the IRAM 30 m Telescope from 1978 to 1994. This constraint on the radio spectrum causes our sample to be dominated by blazars, which allows us to conduct new statistical studies on this class of high-luminosity, relativistically beamed emitters. We detect linear and circular polarization (above minimum 3{sigma} levels of {approx}1.5% and {approx}0.3%) for 76% and 6% of the sample, respectively. We find a clear excess in degree of linear polarization detected at 86 GHz with regard to that at 15 GHz bymore » a factor of {approx}2. Over our entire source sample, the luminosity of the jets is anticorrelated with the degree of linear polarization. Consistent with previous findings claiming larger Doppler factors for brighter {gamma}-ray blazars, quasars listed in our sample, and in the Fermi Large Area Telescope Bright Source Catalog (LBAS), show larger luminosities than non-LBAS ones, but our data do not allow us to confirm the same for BL Lac objects. We do not find a clear relation between the linear polarization angle and the jet structural position angle for any source class in our sample. We interpret this as the consequence of a markedly non-axisymmetric character of the 3 mm emitting region in the jets. We find that intrinsic circular polarization is the most likely mechanism for generation of the circular polarization detected in our observations. Our new data can be used to estimate the 3.5 mm AGN contribution to measurements of the linear polarization of the cosmic microwave background, such as those performed by the Planck satellite.« less

Comparison of frequency-selective screen-based linear to circular split-ring polarisation convertors

Abstract: This study presents the use of periodic arrays of freestanding slot frequency-selective screens (FSS) as a means for generating circularly polarised signals from an incident linearly polarised signal at normal incidence to the structure Measured and simulated results for crossed, linear and various ring slot element shapes in single and double-layer polarisation convertor structures are presented for 10 GHz operation It is shown that 3 dB axial ratio (AR) bandwidths of 21% can be achieved with the one-layer perforated screen design and that the rate of change is lower than the double-layer structures An insertion loss of 034 dB can be achieved for the split circular ring double-layer periodic array, and of the three topologies presented the hexagonal split-ring polarisation convertor gives the lowest variation of AR with angle of incidence 18 dB/45° and 36 dB/45° for the single and double-screen FSS, respectively In addition, their tolerance to angle of incidence variation is presented The capability of the surfaces reported here as twist polariser or spatial isolator components has been demonstrated with up to -30 dB isolation between incident and re-reflected signals for the double-layer designs being measured