Circular Polarization States Research Articles

On the line profile changes observed during the X2.2 class flare in the active region NOAA 11158

The solar active region NOAA 11158 produced a series of flares during its passage through the solar disk. The first major flare (of class X2.2) of the current solar cycle occurred in this active region on 2011 February 15 around 01:50 UT. We have analyzed the Dopplergrams and magnetograms obtained by the Helioseismic and Magnetic Imager (HMI) instrument onboard Solar Dynamics Observatory to examine the photospheric velocity and magnetic field changes associated with this flare. The HMI instrument provides high-quality Doppler and magnetic maps of the solar disk with 0.5″ spatial scale at a cadence of 45 s along with imaging spectroscopy. We have identified five locations of velocity transients in the active region during the flare. These transient velocity signals are located in and around the flare ribbons as observed by Hinode in the Ca II H wavelength and the footpoints of hard X-ray enhancement are in the energy range 12–25 keV from RHESSI. The changes in shape and width of two circular polarization states have been observed at the time of transients in three out of five locations. Forward modeling of the line profiles shows that the change in atmospheric parameters such as magnetic field strength, Doppler velocity and source function could explain the observed changes in the line profiles with respect to the pre-flare condition.

Breaking the diffraction-limited resolution barrier in fiber-optical two-photon fluorescence endoscopy by an azimuthally-polarized beam

Although fiber-optical two-photon endoscopy has been recognized as a potential high-resolution diagnostic and therapeutic procedure in vivo, its resolution is limited by the optical diffraction nature to a few micrometers due to the low numerical aperture of an endoscopic objective. On the other hand, stimulated emission depletion (STED) achieved by a circularly-polarized vortex beam has been used to break the diffraction-limited resolution barrier in a bulky microscope. It has been a challenge to apply the STED principle to a fiber-optical two-photon endoscope as a circular polarization state cannot be maintained due to the birefringence of a fiber. Here, we demonstrate the first fiber-optical STED two-photon endoscope using an azimuthally-polarized beam directly generated from a double-clad fiber. As such, the diffraction-limited resolution barrier of fiber-optical two-photon endoscopy can be broken by a factor of three. Our new accomplishment has paved a robust way for high-resolution in vivo biomedical studies.

Control of light polarization using optically spin-injected vertical external cavity surface emitting lasers

We fabricated and characterized an optically pumped (100)-oriented InGaAs/GaAsP multiple quantum well Vertical External Cavity Surface Emitting Laser (VECSEL). The structure is designed to allow the integration of a Metal-Tunnel-Junction ferromagnetic spin-injector for future electrical injection. We report here the control at room temperature of the electromagnetic field polarization using optical spin injection in the active medium of the VECSEL. The switching between two highly circular polarization states had been demonstrated using an M-shaped extended cavity in multi-modes lasing. This result witnesses an efficient spin-injection in the active medium of the LASER.

Ex Vivo Assessment of Carbon Tetrachloride (CCl4)-Induced Chronic Injury Using Polarized Light Spectroscopy

The liver performs various functions, such as the production and detoxification of chemicals; therefore, it is susceptible to hepatotoxins such as carbon tetrachloride (CCl4), which causes chronic injury. Thus, assessment of injury and its status of severity are of prime importance. Current work reports an ex vivo study for probing the severance of hepatic injury induced by CCl4 with polarized light over the spectral range 400-800 nm. Different concentrations of CCl4 were used to induce varying severity of hepatic injury in a rat model. Linear retardance, depolarization rates, and diagonal Mueller matrix elements (m22, m33, and m44), were successfully used as the distinguishing criterion for normal and different liver injuries. Our results show that linear retardance for injured liver samples with lower doses of CCl4 tends to increase when compared with normal liver samples, while samples injured at higher doses of CCl4 offer almost no retardance. Total, linear, and circular depolarizations follow decreasing trends with increased liver injury severity over the entire investigated wavelength range. Linear polarization states were observed to be better maintained as compared to circular polarization states for all samples. Furthermore, numerical values of diagonal elements of the experimentally measured Mueller matrix also increase with increasing doses of CCl4. Liver fibroses, change in transport albedo, and the relative refractive index of the extracellular matrix caused by CCl4 are responsible for the observed differences. These results will provide a pathway to gauge the severity of injury caused by toxic chemicals.

Design of a multipolarization reconfigurable microstrip array antenna using PIN diodes

ABSTRACTA multipolarization reconfigurable microstrip array antenna that can be used selectively for four polarizations [vertical polarization (VP), horizontal polarization (HP), right hand circular polarization (RHCP), left hand circular polarization (LHCP)] at the S‐band is proposed. To control the four polarization states, a single element consisting of four PIN diodes and a microstrip patch with a circular slot is need. The fabricated array antenna has a VSWR below 2 from 3.32 to 3.39 GHz for VP, from 3.30 to 3.375 GHz for HP, from 3.285 to 3.405 GHz for LHCP, and from 3.27 to 3.40 GHz for RHCP. The 3‐dB axial ratio bandwidth is wider than 19 MHz in the circular polarization states, and the cross‐polarization levels are higher than −20 dB in the linear polarization and −17 dB in the circular polarization, respectively. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:104–110, 2014

Circular polarization bandpass filters based on one-dimensional magnetophotonic crystals

The realization of circular polarization band pass filters based on defect mode splitting in one-dimensional magnetophotonic crystals (1D-MPCs) was investigated theoretically using the transfer matrix method. The analytical formulas of the resonance conditions are derived. The results reveal that for a specific repetition number of the microcavity type 1D-MPC structure, the defect mode splits into two completely separated modes, corresponding to right- and left-circular polarization resonances. It is shown that these modes have purely circular polarization states, which enables us to propose the structure as a single and dual channel circular polarization filter. Furthermore, the tuning properties of the considered structure under the variation of exterior magnetic field are studied.

Polarization-dependent Z-scan characterization for optical nonlinearity in pyran dye

Polarization-dependent Z-scan characterization is made for DCM (4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran) dye encapsulated in a polymer matrix (DCM/PMMA). A continuous wave Ar+ laser beam operating at ∼514 nm wavelength is employed as the source. The normalized transmittance for a linear, elliptical and circular polarization state of incident light with corresponding nonlinear refractive and nonlinear absorptive changes is studied. Intensity-dependent change in the refractive index (Δn) and change in the absorption coefficient (Δβ) with photoisomerization as well as two independent tensor components and of third order susceptibility (χ3) are reported. It is observed that nonresonant electronic nonlinearities dominate to give rise to an optical nonlinear response that can be exploited for use as optical switching.

Three Dimensional Chiral Metamaterial Nanospirals in the Visible Range by Vertically Compensated Focused Ion Beam Induced‐Deposition

Fabrication and characterization of chiral metallic nanospirals for application as metamaterials in the visible and near infrared range are described. The structures consist of platinum helicoidal three‐dimensional nanostructures realized by focused ion beam induced‐deposition, where the interaction with incident light can be controlled as a function of light circular polarization state and spectral region, showing a circular dichroism across a wide range of optical wavelengths. An accurate size control and nanometer resolution on the fabrication of the chiral structures are achieved by exploring substrate surface charge effects on substrates with different electrical properties and by studying and implementing an accurate scanning procedure for the nanostructure growth that allows compensation of the proximity and charge effects. Optical measurements carried out on the nanospiral arrays using a high spatial resolution setup show a transmittance difference of the right‐ and left‐circular polarized light near to 40%.

Precise, motion-free polarization control in Second Harmonic Generation microscopy using a liquid crystal modulator in the infinity space

Second Harmonic Generation (SHG) microscopy coupled with polarization analysis has great potential for use in tissue characterization, as molecular and supramolecular structural details can be extracted. Such measurements are difficult to perform quickly and accurately. Here we present a new method that uses a liquid crystal modulator (LCM) located in the infinity space of a SHG laser scanning microscope that allows the generation of any desired linear or circular polarization state. As the device contains no moving parts, polarization can be rotated accurately and faster than by manual or motorized control. The performance in terms of polarization purity was validated using Stokes vector polarimetry, and found to have minimal residual polarization ellipticity. SHG polarization imaging characteristics were validated against well-characterized specimens having cylindrical and/or linear symmetries. The LCM has a small footprint and can be implemented easily in any standard microscope and is cost effective relative to other technologies.

PIN 다이오드를 이용한 다중 편파 재구성 마이크로스트립 안테나

본 논문에서는 S-밴드에서 하나의 급전 회로로 4개의 편파(수직 편파, 수평 편파, 좌선회 편파, 우선회 편파)를 선택적으로 사용할 수 있는 다중 편파 재구성 마이크로스트립 안테나를 제안하였다. 제안된 안테나는 십자 슬롯과 원형 슬롯을 포함하는 정사각형 형태의 마이크로스트립 패치와 4개의 PIN 다이오드로 구성되어 있으며, 커플링을 통한 급전 방식을 이용한다. 각각의 PIN 다이오드에는 직류 전압을 인가하기 위한 바이어스 단이 있으며, 직류 전압의 인가에 따른 다이오드 ON / OFF 동작으로 편파를 재구성할 수 있다. 제작된 안테나는 수직 편파(3.17~3.21 GHz), 수평 편파(3.16~3.20 GHz), 좌선회 편파(3.08~3.19 GHz), 우선회 편파(3.10~3.20 GHz)에서 VSWR 2:1을 만족하며, 선형 편파에서는 20 dB 이상의 교차 편파 및 5 dBi 이상의 이득 특성을 갖고, 원형편파에서는 50 MHz 이상의 3 dB 축비 특성을 나타낸다. In this paper, a multi polarization reconfigurable microstrip antenna that can be used selectively for four polarizations(vertical polarization, horizontal polarization, right hand circular polarization, left hand circular polarization) at the S-band is presented. The proposed antenna consists of four PIN diodes and a microstrip patch with a cross slot and a circular slot and is fed by utiliting electromagnetic coupling between the microstrip patch and the feed line. The proposed antenna has a DC bias network to supply DC voltage to each PIN diode and the polarization can be determined by controlling the ON /OFF states of four PIN diodes. The fabricated antenna has a VSWR below 2 in the vertical polarization(3.17~3.21 GHz), the horizontal polarization(3.16~3.20 GHz), the left hand circular polarization (3.08~3.19 GHz), and the right hand circular polarization(3.10~3.2 GHz) frequency bands. The designed antenna has the cross polarization level higher than 20 dB, a gain over 5 dBi for the linear polarization states, and 3 dB axial ratio bandwidth wider than 50 MHz in the circular polarization states.

Dynamics of polarization singularities in composite optical vortices

We study the dynamics of polarization singularities in the superposition of two off-axis optical vortices with orthogonal polarization states. The motion of C points, states of circular polarization, is described by varying parameters such as separation distance, constant phase difference and topological charge. We analyze the zeros of the Stokes parameters and find analytical solutions for particular cases. The results could be used to realize an alternative method to measure the vortex topological charge.

X-ray Birefringence in highly Anisotropic Materials

Birefringence is the dependence of a material's refractive index on the direction of linear polarization. It induces a phase shift between two perpendicular polarization directions and thus couples linear and circular polarization states. Birefringence in x-ray absorption is as common as linear dichroism but is rarely discussed in the literature. We outline a mathematical framework for describing experiments on birefringence and illustrate the importance of the phenomenon with three examples.

Switchable holographic image splitter fabricated with dye-doped liquid crystals

Two electrically controllable holographic polarization gratings are spatially multiplexed to serve as an image splitter for further stereogram application. An external AC voltage is used to modulate the diffraction efficiency of the fabricated holographic image splitter for the switching of a 3D stereogram and a 2D plane image. The polarization grating was generated by two writing beams with orthogonal circular-polarization state in dye-doped liquid crystal films. With proper experimental arrangements, a quasi single order diffraction was obtained and the other non-zero order diffractions were suppressed in this presented polarization grating. This characteristic leads to a good image contrast ratio for a stereogram. Finally, a switchable stereogram system using circular-polarization beam as backlighting was demonstrated successfully.

Polarization Jitters Caused by Fiber Nonlinearity in PM Optical Communication System

The phenomenon of polarization jitters caused by fiber nonlinearity is investigated. A general formula about the polarization jitter is concluded in polarization multiplexing (PM) system based on two orthogonal linear polarization states when the best polarization correction is used. A 100 Gb/s PM system based on NRZ code is investigated by simulation, and the Stocks parameter about polarization jitter and Poincare sphere diagrams are got for different power and phase difference of two orthogonal polarized light. The results show that the polarization jitters will be suppressed when the combined PM signal is the linear or circular polarization state.

Strict Limit onCPTViolation from Polarization ofγ-Ray Bursts

We report the strictest observational verification of CPT invariance in the photon sector, as a result of γ-ray polarization measurement of distant gamma-ray bursts (GRBs), which are the brightest stellar-sized explosions in the Universe. We detected γ-ray polarization of three GRBs with high significance levels, and the source distances may be constrained by a well-known luminosity indicator for GRBs. For the Lorentz- and CPT-violating dispersion relation E(±)(2) = p(2) ± 2ξp(3)/M(Pl), where ± denotes different circular polarization states of the photon, the parameter ξ is constrained as |ξ|<O(10(-15)). Barring precise cancellation between quantum gravity effects and dark energy effects, the stringent limit on the CPT-violating effect leads to the expectation that quantum gravity presumably respects the CPT invariance.

Measurement of the polarization state of light using an integrated plasmonic polarimeter

AbstractPlasmonics has started to facilitate the replacement of bulky optical components in optical systems by compact nanometallic elements that perform the same function. This allows for a natural and very dense integration with electronic devices. In this vein, we present a silicon (Si) photodetector integrated with a set of plasmonic structures that can be used as either a broadband linear-Stokes polarimeter or a narrowband full-Stokes polarimeter capable of determining the complete state of polarization of a light beam. At a probe-wavelength of 830 nm, our experimental results show contrast ratios of 25 and 1.13 for orthogonal linear and circular states of polarization, in good agreement with simulations. The resulting device is lightweight, orders of magnitude smaller than conventional polarimeters, and mechanically robust. For these reasons, there promises to be a wide range of applications including polarimetric imaging and sensing.

Electron emission in the near-field of surface plasmons

Plasmon-enhanced photoelectron emission in the near-field region of gold nanostructures is reported. We show that, depending on the photon energy of the excitation light, the emission from the near-field region can be markedly stronger than from the plasmonic gold itself. Photoemission micrographs also indicate that the spatial confinement of the near-field emission is stronger than in the gold and that the near-field emission exhibits a strong sensitivity on the linear and circular polarization state of the excitation light. The results are explained in terms of work-function differences between the near-field region and the plasmonic material and an interaction between propagating and localized surface plasmon modes. We suggest that the circular polarization sensitivity of the near-field surface plasmon modes may open the way to generate spin-polarized electrons in a plasmon-induced photoemission process.

Polarization shaping of few-cycle terahertz waves

We present a polarization shaping technique for few-cycle terahertz (THz) waves. For this, N femtosecond laser pulses are generated from a devised diffractive optical system made of as-many glass wedges, which then simultaneously illuminate on various angular positions of a sub-wavelength circular pattern of an indium arsenide thin film, to produce a THz wave of tailor-made polarization state given as a superposition of N linearly-polarized THz pulses. By properly arranging the orientation and thickness of the glass wedges, which determine the polarization and its timing of the constituent THz pulses, we successfully generate THz waves of various unconventional polarization states, such as polarization rotation and alternation between circular polarization states.

Intra-cavity stimulated emissions of photons in almost pure spin states without imposed nonreciprocity

We propose a chiral Fabry-Perot cavity in which only the cavity modes in almost pure spin (circular polarization) states lase in the presence of gain. In absence of imposed nonreciprocal environments and time-reversal symmetry breaking of emitter states to favor the emission of circularly-polarized photons, only the resonance of modes with a specific spin orientation remains in the cavity. We demonstrate a prototype of the cavity using distributed Bragg reflectors and cholesteric liquid crystals. This reciprocal cavity may provide a method to control the angular momentum state of emitters based on stimulated emissions.

Spiral plasmonic nanoantennas as circular polarization transmission filters

We present simulation and experimental results for easily fabricated spiral plasmonic antenna analogues providing circular polarization selectivity. One circular polarization state is concentrated and transmitted through a subwavelength aperture, while the opposite circular state is blocked. The spectral bandwidth, efficiency, and extinction ratios are tunable through geometric parameters. Integration of such structures onto a focal plane array in conjunction with linear micropolarizers enables complete Stokes vector imaging, that, until now, has been difficult to achieve. An array of these structures forms a plasmonic metamaterial that exhibits high circular dichroism.