Perfect Circular Polarization Research Articles

High-Sensitivity Polarization Sensitive Optical Coherence Tomography Based on Numerical Correction for Perfect Circularly Polarized Light

Polarization sensitive optical coherence tomography (PSOCT) makes use of the birefringence information of the sample to compensate for the lack of internal tissue-specific contrast in conventional optical coherence tomography (OCT). Circularly polarized light is always used as an incident beam in PSOCT, but it is difficult to have perfect in practice. The manual calibration method of circularly polarized light suffers from the problems of complicated calibration operation and lack of stability. This study proposes a simple method to enhance the imaging of PSOCT without altering the system. A numerical calibration of circularly polarized light can be implemented using the original system setup, ensuring that the system’s complexity remains unchanged. Enhancements in imaging quality can be achieved through an algorithmic analysis of the captured interference fringe data. This calibration is applied in the field map of interference data before being quadrature-assembled. Notably, the proposed approach achieves high sensitivity in PSOCT. The birefringence image shows a more obvious layered structure. Improvements in the signal-to-noise ratio (SNR) were demonstrated for chicken breast, pork, and beef imaging at about 20 dB.

Perfect circular polarization of elastic waves in solid media

Elastic waves involving mechanical particle motions of solid media can couple volumetric and shear deformations, making their manipulation more difficult than electromagnetic waves. Thereby, circularly polarized waves in the elastic regime have been little explored, unlike their counterparts in the electromagnetic regime, where their practical usage has been evidenced in various applications. Here, we explore generating perfect circular polarization of elastic waves in an isotropic solid medium. We devise a novel strategy for converting a linearly polarized wave into a circularly polarized wave by employing an anisotropic medium, which induces a so-far-unexplored coupled resonance phenomenon; it describes the simultaneous occurrence of the Fabry-Pérot resonance in one diagonal plane and the quarter-wave resonance in another diagonal plane orthogonal to the former with an exact 90° out-of-phase relation. We establish a theory explaining the involved physics and validate it numerically and experimentally. As a potential application of elastic circular polarization, we present simulation results demonstrating that a circularly polarized elastic wave can detect an arbitrarily oriented crack undetectable by a linearly polarized elastic wave.

Polarization of electromagnetic pulses

We show the impossibility, for localized and exact solutions of the Maxwell equations, of perfect circular polarization in a fixed plane, or perfect linear polarization along a fixed direction. A measure of polarization of electromagnetic pulses is obtained by analogy with that useful in monochromatic radiation, and its limitations discussed. Using oscillatory solutions of the free-space Maxwell equations, for which all components of the electric and magnetic fields satisfy the wave equation, we construct explicit examples of TE pulses which are linearly polarized with an azimuthal electric field, TE+iTM pulses approximately linearly polarized along the propagation direction, and also approximately circularly polarized pulses. The latter have perfect circular polarization on the propagation axis.

Perfect Chirality with Imperfect Polarization.

Unidirectional (chiral) emission of light from a circular dipole emitter into a waveguide is only possible at points of perfect circular polarization (C points), with elliptical polarizations yielding a lower directional contrast. However, there is no need to restrict engineered systems to circular dipoles, and with an appropriate choice of dipole unidirectional emission is possible for any elliptical polarization. Using elliptical dipoles, rather than circular, typically increases the size of the area suitable for chiral interactions (in an exemplary mode by a factor ∼30), while simultaneously increasing coupling efficiencies. We propose illustrative schemes to engineer the necessary elliptical transitions in both atomic systems and quantum dots.

Selective excitation of four-wave mixing by helicity in gated graphene.

Gapless Dirac fermions in monolayer graphene give rise to an abundance of peculiar physical properties, including exceptional broadband nonlinear optical responses. By tuning the chemical potential, stacking order, and photonic structures, the effective modulation of nonlinear optical phenomena in graphene has been demonstrated in recent years. Here, we demonstrate that optical helicity can be used as an extra tuning knob for four-wave mixing in gated graphene. Our results reveal the helicity selection rule for four-wave mixing in monolayer graphene, revealing nearly perfect circular polarization. Corresponding theoretical interpretations of the helicity selection rule that are also applicable to other nonlinear optical processes and materials are presented.

Planar Achiral Metasurfaces-Induced Anomalous Chiroptical Effect of Optical Spin Isolation.

Planar chiral structures respond differently for oppositely handed incident light, and thus can produce extraordinary chiroptical effects such as circular conversion dichroism (CCD) and asymmetric transmission (AT). Such chiroptical effects are powerful tools to realize the fundamental principle of optical spin isolation, which leads to a plethora of applications such as optical conversion diodes, chiral imaging, and sensing. Here, we demonstrate the chiroptical effects of simultaneous CCD and AT through meticulously designed single-layered achiral nanofins. Our metamolecule consists of four achiral hydrogenated amorphous silicon (a-Si:H) nanofins that are carefully oriented and optimized to exhibit considerable CCD and AT. The device demonstrates a circular conversion dichroism of 55% and an asymmetric transmission of 58% at a wavelength of 633 nm. Right-hand circularly polarized light (RHCP) is completely absorbed, while left-hand circularly polarized light (LHCP) is transmitted with a polarization conversion, making it a perfect circular polarization wave isolator with negligible backscattering (due to low reflectance). This unique design and its underlying working mechanism are described comprehensively with three different techniques. These methods validate the proposed design and its methodology. For practical applications such as imaging, the proposed design realizes the Pancharatnam-Berry (PB) phase, achieving a 0-2π phase coverage for transmitted circular polarization. For the proof of concept, a metahologram is designed and demonstrated by employing the achieved full-phase control. The measured response of the fabricated metadevice not only validates the CCD and AT but also exhibits a simulated polarization conversion efficiency of up to 71% and measured efficiency up to 52%, comparable to state-of-the-art metahologram demonstrations.

Conditions for perfect circular polarization of high-order harmonics driven by bichromatic counter-rotating laser fields

Recently, studies of high-order harmonic generation (HHG) from atoms driven by bichromatic counter-rotating circularly polarized laser fields have received considerable attention for this process could be a potential source of coherent circularly polarized extreme ultraviolet (XUV) and soft-x-ray beams in a tabletop-scale setup. In this paper, we address the problem with molecular targets and perform a detailed quantum study of the ${\mathrm{H}}_{2}{}^{+}$ molecule in bichromatic (${\ensuremath{\omega}}_{0}, 2{\ensuremath{\omega}}_{0}$) counter-rotating circular polarized laser fields where we adopt wavelengths (790 and 395 nm) and intensities ($2\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.28em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$) reported in a recent experiment [K. M. Dorney et al., Phys. Rev. Lett. 119, 063201 (2017)]. Here, we demonstrate appropriate conditions to produce perfectly circular polarized harmonics. The calculated radiation spectrum contains doublets of left and right circularly polarized harmonics which display perfect circular polarization with use of the trapezoidal pulse shape, and substantial deviations from perfect circular polarization with use of the sine-squared pulse shape. We also study in detail short- and long-cycle counter-rotating circularly polarized driving pulses with a time delay between the two driving fields, ${\ensuremath{\omega}}_{0}$ and $2{\ensuremath{\omega}}_{0}$. These time delayed circularly polarized driving pulses are applied to H atoms and ${\mathrm{H}}_{2}{}^{+}$ molecules, and in both atomic and molecular cases we conclude a zero time delay corresponds to the highest HHG intensity for short pulses. For longer pulses there are no distinct differences in HHG intensities between the zero and nonzero time delays if the latter are within a few optical cycles of the fundamental frequency.

A W-Shaped Antenna With Spatial Polarization Variation for Direction Finding

A compact impedance-matched W-shaped antenna is presented that can radiate a perfect circular polarization (CP) at its boresight and distinct polarization states at different propagating directions in the far-field. The antenna structure consists of a horizontal dipole, a vertical dipole, and two elliptical loops connecting the adjacent arms of the dipole elements. The arc length and geometry of the loops are designed to produce the perfect CP at the boresight of the antenna. Using a single feed point, the antenna has an isotropic radiation pattern and is capable of producing distinct polarization states in different directions except for the plane of the antenna. Also, the symmetrical polarization characteristics with respect to the axes of the antenna symmetry are shown in the same propagating direction. This ambiguity of polarization can be resolved by using a pair of the proposed antennas operating at slightly different frequencies as a transmitter and triad dipoles to realize an azimuth-polar direction finding system. To demonstrate the validity of the antenna design, an antenna structure operating at 2.58 GHz is fabricated over a ground plane and measured. The measured radiation pattern shows the perfect CP at the boresight and 6.2% for the 3 dB axial ratio bandwidth.

Low Loss Transmission Circular Polarizer for KU Band Application

Low loss transmission circular polarizer is proposed for Ku band applications. The designed structure consists of two closely cross metallic strips which are based on FSS for 15.25 GHz and 15.28 GHz applications. The right hand circular polarization (RHCP) and left handed circular polarization (LHCP) are obtained at 15.25 GHz and at 15.28 GHz. The transmission loss through polarizer is important issue for high frequency applications. Due to transmission loss, new techniques are required to reduce the transmission loss of transmitted wave and achieve perfect circular polarization. Meanwhile, low loss transmission has been achieved by using dual layer of strips to obtain perfect circular polarization at certain mentioned resonant frequencies. Theoretically, it is found that the outgoing waves through polarizer are perfect circular polarization at the distinct frequency ranges.

Wideband and low axial ratio circularly polarized antenna using AMC-based structure polarization rotation reflective surface

AbstractThis paper investigates a wideband and low axial ratio circularly polarized (CP) antenna, which is composed of a monopole on a novel polarization rotating reflective surface (PRRS) based on a corner-truncated artificial magnetic conductor (AMC) structure. By adjusting the dimensions of truncated corner properly, the PRRS has two polarization rotation (PR) frequency points. Then, a large PR band of 18% (5.55–6.65 GHz) can be achieved with two adjacent PR frequency points coming together. The profile of the newly PRRS is only0.04λ0. With corner-truncated AMC-based PRRS loading, a measured impedance bandwidth of 1.8 GHz (5.4–7.2 GHz) and the 3 dB axial ratio bandwidth of 1 GHz (5.55–6.65 GHz) could be obtained by the monopole antenna and validated by measurements. The values of AR were well below 1 dB at most of the CP region, which show a perfect CP performance. Moreover, the proposed antenna has exhibited a large axial ratio beamwidth in both the xoz- and yoz-planes and a peak gain of 6.1 dBic within the operational bandwidth.

Cavity-based linear-to-circular polarization converter.

This paper presents a polarization converter to convert a linearly polarized (LP) incident wave into an outgoing circularly polarized (CP) wave. It is constructed by a 2D array of thin cavities, with each cavity etched with three slots. The front slot is used to couple the LP wave into the cavity, while the backside orthogonal slots are utilized to couple the field out of the cavity with the same amplitude and 90° out-of-phase; subsequently, a CP wave is formed at the other side of the converter. As a proof-of-concept, a sample of the proposed converter is fabricated and measured in the microwave regime. Eventually, a perfect CP wave is demonstrated after the LP wave passes through the converter. The proposed linear-to-circular polarization converter features an extremely low insertion loss of around 0.1 dB and a high polarization conversion efficiency of 0.97.

DESIGN OF CIRCULARLY POLARIZED OMNIDIRECTIONAL BIFILAR HELIX ANTENNAS WITH OPTIMUM WIDE AXIAL RATIO BEAMWIDTH

In this paper, design and analysis of omnidirectional single feed circularly polarized, wide axial ratio beamwidth resonant side-fed bifllar helix antennas that do not require a ground plane is presented. The simulation and measurement results show that side-fed helix antennas of various radii gives near perfect circular polarization (CP) almost over the whole sphere except at and around nulls, at a certain turn angle by properly proportioning the area of loop (A) with the product of pitch (‰) and radianlength (l) of helix. Helix antennas with smaller radii give axial ratio (AR) close to one at higher values of turn angle with lower value of resonant input impedances but CP is less sensitive to inaccuracy in turn angle. However helix antennas with larger radii results in AR close to one at lower values of turn angle and provides better values of input resistance but its AR is more sensitive to variations in turn angle. The simulated results show that the polarization solid angle beamwidth (for AR • 3dB) varies from 3:96… to 4… steradian. The gain and 3dB beamwidth of the antennas are 2dBi and 90 - respectively. The polarization bandwidth varies from 34% to 65%. The simulated results are verifled by experimental measurements.

Design on a broadband circularly polarized slot antenna

AbstractIn this article, a novel broadband circularly polarized (CP) slot antenna is proposed and fabricated, in which, a simple perturbation configuration with a narrow rectangular slot etched near the square slot is used for perfect CP operation. Through simulating and testing, the broad impedance bandwidth of 57.6% (VSWR < 2.0) and the 3‐dB axial ratio bandwidth of 50.2% are achieved. This slot antenna will be widely used in communication field. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1912–1915, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25337

Analysis on Fabry-Perot Interferometer using Cholesteric Liquid Crystal

Optical characteristics of a Fabry-Perot interferometer using cholesteric liquid crystal (CLC) are analyzed rigorously based on electro-magnetic wave equations. Being different from the conventional Fabry-Perot interferometer, the minimum cavity length for resonance is a quarter of wavelength, not half of wavelength. When the refractive indices of the CLC mirrors and material inside the cavity are the same, perfect circular polarization resonance with high finesse is obtained for the incident circularly polarized light.

Spin-resolved electron spectroscopy of the xenon N4,5 O2,3O2,3 Auger lines

The spin polarization of the Xe N4,5 O2,3 O2,3 Auger lines was measured after ionization by circularly polarized synchrotron radiation of 93.8 eV photon energy. The circularly polarized radiation was produced by converting the linearly polarized light from a conventional undulator by a Mo/Si transmission multilayer acting as a quarter-wave plate. Nearly perfect circular polarization was obtained. In the framework of the two-step model of Auger decay the orientation of the primary hole states 4d-1 2D3/2 and 4d-1 2D5/2 can be derived from the spin polarization of the 1S0 Auger lines. Furthermore, the intrinsic parameters for all lines in this Auger group corresponding to the other 5p-2 final states are determined and compared with theory.

Undulators at HiSOR – a compact racetrack-type ring

A compact racetrack-type 700 MeV storage ring (HiSOR) has been constructed at Hiroshima Synchrotron Radiation Center (HSRC). As the ring was planned for synchrotron radiation research on science and technology using VUV to X-rays up to 5 keV with limited size and cost, the ring was designed (i) to realize a high magnetic field (2.7 T) using conventional dipole magnets for higher critical energy, and (ii) to include two straight sections for insertion devices. A linear undulator (25-300 eV) and a new-type helical/linear undulator were installed at the two straight sections. The latter undulator consists of upper and lower jaws, as in a planar undulator; each jaw consists of one fixed magnet array at the centre and two magnet arrays on both sides. By longitudinal displacement of the side magnet arrays, the phase between the vertical and horizontal magnetic fields, and therefore the polarization (right- or left-circular, elliptical, linear) can be selected. The helical/linear undulator gives almost perfect circular polarization at 4-40 eV in the helical configuration without changing the phase of the magnet arrays, as well as linearly polarized light at 3-300 eV in the linear configuration.

Circularly polarized microstrip antenna with a single feed

A novel circularly polarized (CP) microstrip antenna with a single coaxial feed is introduced. The antenna consists of two layers, each radiating fields which at the zenith are perpendicular to each other with 90/spl deg/ phase difference. The CP bandwidth is substantially higher than that of the previously reported CP microstrip antennas with two nearly degenerate modes. In principle, a perfect CP radiation is feasible without the input impedance mismatch. The CP design procedure is independent of the feed location.

Synthesis of circular polarization with nonresonant slots in the narrow wall of a rectangular waveguide

AbstractFor a planar array antenna consisting of stacked slotted waveguides a circular polarization created by a slot pair on the narrow wall is proposed. The pair configuration satisfying the circular polarization condition is theoretically determined. It is necessary to accurately obtain the mutual coupling between slots. A formulation for the coupling is given as a boundary value problem. We first derive simultaneous integral equations for the aperture electric field in each slot. Next, solving these equations numerically, we find the effect of mutual coupling quantitatively. In the formulation process, the wall thickness of the waveguide is considered, unlike other analyses, which neglect the thickness. It is found that the effect of finitely thick walls is not negligible. To confirm the validity of the pair arrangement determined by the present analysis, experiments are performed with WRJ 3 waveguides for the S band and an almost perfect circular polarization of axial ratio 0.98 (−0.2 dB) is obtained.