Pure Polarization Research Articles

Radiation induced attenuation in pure silica polarization maintaining fibers

Radiation-induced attenuation (RIA) at λ = 1.55 μm is studied in polarization-maintaining (PM) pure-silica-core optical fibers of the Panda-type under γ-irradiation and upon pulsed-X-ray-irradiation. For the first time, the RIA spectrum is compared under γ-irradiation in a Panda and in a non-PM fiber drawn from the same preform before embedding the stress-applying rods. It is found out that the chief RIA origins in the near-IR range in both fibers are an extremely short-lived band centered at ~1 eV and the tails of the classical bands due to strain-assisted self-trapped holes (STHs) at 1.63 and 1.88 eV. The former band is found to be many times more intense in the Panda; the latter bands, somewhat more intense in the non-PM fiber. The ~1-eV band proved to be composed of two Gaussian sub-bands centered at 0.95 and 1.12 eV. Under γ-irradiation, the composite ~1-eV band is found to be photobleached virtually fully by 1.55-μm light of 5-mW power, which results in manifold reduction of the total RIA. Upon pulsed irradiation, RIA in Pandas at large post-pulse times (>1 ms–1 s) is found to fall off below the record low level demonstrated elsewhere by a non-PM pure-silica-core fiber. This fact is explained as being due to a smaller concentration of strain-assisted STHs in Pandas than in non-PM fibers. The concentration of strain-assisted STHs in Pandas is shown to increase with increasing the value of birefringence.

Rate-determining process in MISIM photocells for optoelectronic conversion using photo-induced pure polarization current without carrier transfer across interfaces.

Recently, we proposed a [metal|insulator|semiconductor|insulator|metal] (MISIM) photocell, as a novel architecture for high-speed organic photodetectors. The electric polarization in the S layer, induced by modulated light illumination, propagates into the outside circuit as a polarization current through the I layers, without any carrier transfer across the interfaces. In the present work, we examined the MISIM photocells consisting of zinc-phthalocyanine(ZnPc)-C60 bilayers for the S layer and Parylene C for the two I layers, to understand the fundamental aspects of the MISIM photocells, such as current polarity and modulation-frequency dependence. It was found that, in such devices, the current polarity was primarily determined by the polarization in the S layer, which was induced by the donor-acceptor charge-transfer upon illumination. Furthermore, the ON and OFF current, which appeared in the periods of illumination-on and -off, respectively, exhibited significantly different dependence on the modulation frequency. This was well-explained by an imbalance between a quick polarization in the S layer during illumination and its slow relaxation in the dark.

A multi-functional polarization convertor based on chiral metamaterial for terahertz waves

Abstract In this paper, a multi-functional polarization convertor for terahertz (THz) light composed of a bilayer wire-split-ring (WSR) structure chiral metamaterial (CMM) was proposed and investigated numerically. Simulation results indicate that when normal incident light is propagating along the – z axis direction through the proposed CMM structure, the y-polarization is converted to the left- and right-circular polarization (LCP and RCP) at 1.14 THz and 1.34 THz, respectively. Meanwhile, the x-polarization is converted to y-polarization in the frequency range of 2.19 – 2.47 THz. The further calculation results show that the proposed CMM structure can transmit a nearly pure circular polarization light with a polarization extinction ratio (PER) of over 30 dB and an orthogonal linear polarization light with a polarization conversion ratio (PCR) of over 90%. The mechanism of the polarization conversion properties is illustrated by the simulated electrical field and surface current distribution. Due to its excellent multi-functional polarization conversion properties, the proposed CMM is useful for the development of the integrated THz polarization manipulation devices.

Towards high-bandwidth organic photodetection based on pure active layer polarization

Organic photodetectors offer distinct advantages over their inorganic analogues, most notably through optical transparency and flexibility, yet their figures-of-merit still lag behind those of inorganic devices, and optimization strategies generally encounter a trade-off between device responsivity and bandwidth. Here we propose a novel photodetector architecture in which an organic photoactive semiconductor layer (S) is sandwiched between two thick insulating layers (I) that separate the semiconductor from the metallic contacts (M). In this architecture a differential photocurrent response is generated purely from the polarization of the active layer under illumination. Especially for an asymmetric MISIM design, where one insulating layer is a high-k ionic liquid IIL and the other a low-k polymer dielectric Ip, the responsivity/bandwidth trade-off is broken, since the role of the IIL in efficient charge separation is maintained, while the total device capacitance is reduced according to Ip. Thus the benefits of single insulating layer differential photodetectors (MISM) using either IIL or Ip are combined in a single device. Further improvements in device performance are also demonstrated by decreasing the series resistance of the photoactive layer through semiconductor:metal blending and by operation under strong background light.

Realizing High-Pulse-Energy Large-Angular-Momentum Beams by Astigmatic Transformation of Geometric Modes in an Nd:YAG/Cr4+:YAG Laser

An off-axis pumped Nd:YAG/Cr4+:YAG laser under different degenerate cavity conditions has been thoroughly studied to generate high-pulse-energy geometric modes for further beam transformation. Because of the employment of Nd:YAG gain crystal provides a flexible choice of cavity length to achieve efficient passively Q-switched (PQS) operation, various PQS geometric modes with stable spatial structures are generated. Moreover, it is experimentally confirmed that the output energy and peak power of the PQS geometric modes can easily reach up to over 100 μJ and 10 kW with fairly stable pulse trains in pure linear polarization. By using an astigmatic mode converter (AMC) to transform the planar geometric modes into the circular geometric modes, various high-energy vortex beams with large angular momentum and diverse phase structures are successfully realized to offer a promising light source for further application. The propagation evolution of the transformed geometric modes through the AMC was also analyzed theoretically to offer useful insights for the formation of the geometric vortex beams.

The Polarizations of Gravitational Waves

The gravitational wave provides a new method to examine General Relativity and its alternatives in the high speed, strong field regime. Alternative theories of gravity generally predict more polarizations than General Relativity, so it is important to study the polarization contents of theories of gravity to reveal the nature of gravity. In this talk, we analyze the polarization contents of Horndeski theory and f(R) gravity. We find out that in addition to the familiar plus and cross polarizations, a massless Horndeski theory predicts an extra transverse polarization, and there is a mix of pure longitudinal and transverse breathing polarizations in the massive Horndeski theory and f(R) gravity. It is possible to use pulsar timing arrays to detect the extra polarizations in these theories. We also point out that the classification of polarizations using Newman–Penrose variables cannot be applied to massive modes. It cannot be used to classify polarizations in Einstein-æther theory or generalized Tensor-Vector-Scalar (TeVeS) theory, either.

Spin- and valley-dependent negative magnetoresistance in a ferromagnetic MoS2 junction with a quantum well

We studied the spin and valley transports and magnetoresistance effect in a ${\mathrm{MoS}}_{2}$ junction with a quantum well inserted between the gate voltage and the ferromagnetic ${\mathrm{MoS}}_{2}$, which can apply generally to other transition metal dichalcogenides with the same crystal structure. In the absence of a quantum well, the broken inversion symmetry and spin-orbit coupling for ${\mathrm{MoS}}_{2}$ could give rise to a fully spin- and valley-polarized conductance for the parallel configuration, while there is no spin and valley polarization for the antiparallel configuration. The general condition of pure polarization and the position of resonant conductance are achieved. The magnetoresistance is positive and oscillates with the gate voltage. Dramatically, the presence of a quantum well can lead to the formation of spin-polarized quantum well states. As a result, the conductances for opposite spin and valley indices have a steady phase shift, making them oscillate in antiphase with the well width. Therefore, the high spin and valley polarization could be obtained for the antiparallel and parallel configurations. In particular, the spin-polarized quantum well states directly result in negative polarization and negative magnetoresistance.

Parametrization of 3 × 3 unitary matrices based on polarization algebra

A parametrization of 3x3 unitary matrices is presented. This mathematical approach is inspired on polarization algebra and is formulated through the identification of a set of three orthonormal three-dimensional Jones vectors representing the respective pure polarization states. This approach leads to the representation of a 3x3 unitary matrix as an orthogonal similarity transformation of a particular type of unitary matrix that depends on six independent parameters, while the remaining three parameters correspond to the orthogonal matrix of the said transformation. The results obtained are applied to determine the structure of the second component of the characteristic decomposition of a 3x3 positive semidefinite Hermitian matrix.

Electromechanically tunable metasurface transmission waveplate at terahertz frequencies

Dynamic polarization control of light is essential for numerous applications ranging from enhanced imaging to materials characterization and identification. We present a reconfigurable terahertz metasurface quarter-waveplate consisting of electromechanically actuated micro-cantilever arrays. Our anisotropic metasurface enables tunable polarization conversion cantilever actuation. Specifically, voltage-based actuation provides mode selective control of the resonance frequency, enabling real-time tuning of the polarization state of the transmitted light. The polarization tunable metasurface has been fabricated using surface micromachining and characterized using terahertz time domain spectroscopy. We observe a ~230 GHz cantilever actuated frequency shift of the resonance mode, sufficient to modulate the transmitted wave from pure circular polarization to linear polarization. Our CMOS-compatible tunable quarter-waveplate enriches the library of terahertz optical components, thereby facilitating practical applications of terahertz technologies.

Photoalignment-induced two-dimensional liquid crystal polarization structure via multi-beam polarization interferometry

A two-dimensional (2D) pure polarization pattern via four-beam polarization interferometry of circularly polarized beams is demonstrated both theoretically and experimentally. The polarization orientation of the interference pattern is recorded by an azobenzene photoalignment layer and transferred to liquid crystal (LC), enabling the fabrication of a 2D liquid crystal (LC) chiral structure. This structure behaves as a 2D LC polarization grating (LCPG) that can generate multiple polarization-selective diffraction beams of orthogonal polarization states with high efficiency. This 2D LCPG provides an effective way to distribute an optical signal into multiple receivers by both incidence polarization control and external electric field, therefore offering potential applications on multi-channel optical communication and information processing.

The polarizations of gravitational waves

The direct detection of gravitational waves opens a new window to probe the nature of gravity, and it brings us into the era of multi-messenger astronomy.Gravitational wave has no effect on the geodesics of a test particle, but it affects the relative motion between two nearby test particles.To measure gravitational wave and its polarizations, we need to study the geodesic deviation equation for two nearby test particles.Since only the electric part of the Riemann tensor $R_{i0j0}$ appears in the geodesic deviation equation and it has six independent components,there are up to six possible polarization states in general metric theories of gravity.In terms of the electric part of the Riemann tensor, the six polarizations are defined as follows.$\\hat{P}_+=-R_{x0x0}+R_{y0y0}$ corresponds to the “+ mode, $\\hat{P}_\\times=2R_{x0y0}$ denotes the “$\\times$ mode,$\\hat{P}_b=R_{x0x0}+R_{y0y0}$ corresponds to the breathing mode, $\\hat{P}_x=R_{x0z0}$ corresponds to the vector-$x$ mode,$\\hat{P}_x=R_{y0z0}$ represents to the vector-$y$ mode, and $\\hat{P}_l=R_{z0z0}$ denotes the longitudinal mode.For weak, plane and null gravitational waves, these six polarizations can be classified based on their properties under the Lorentz transformation.In Einsteins general relativity, the gravitational waves are tensor waves and there are “+ and “$\\times$ modes of polarization.In Brans-Dicke theory, in addition to the “+ and “$\\times$ polarization states, the scalar breathing mode also appears, and all these threepolarizations are transverse modes. In the most general scalar-tensor theory of gravity, the Horndeski theory,the massive scalar field excites both the breathing and the longitudinal modes, so in addition to the “+ and “$\\times$ polarizations,there exists a single mix state consisting of both the breathing and the longitudinal modes. In the massless limit,the longitudinal mode disappears andthe mix state becomes the pure transverse breathing polarization as that in Brans-Dicke theory. The nonlinear $f$($R$) theory of gravitycan be written as a scalar-tensor theory of gravity, so the polarization states in $f$($R$) gravity are the sameas those in Horndeski theory except that there is no massless limit in $f$($R$) gravity.In Einstein-Aether theory, due to the existence of the unit timelike vector field,the local Lorentz invariance is violated. The gravitational waves propagate with speeds different from the speed of light,and there are five independent polarization states,the “+ state $\\hat{P}_+$, the “$\\times$ state $\\hat{P}_\\times$, the vector$-x$ state $\\hat{P}_x$, the vector$-y$ state $\\hat{P}_y$ and themix state consisting of both the breathing and the longitudinal modes excited by the scalar field.In TeVeS theory, the local Lorentz invariance is also broken,so the gravitational waves in TeVeS theory propagate with speeds different from the speed of light.There are six polarization states in TeVeS theory,$\\hat{P}_+$, $\\hat{P}_\\times$, $\\hat{P}_x$, $\\hat{P}_y$ and twomix states excited by the two scalar fields. Each of the mix states consists of both the breathing and the longitudinal modes.Because gravitational waves have different polarization states for different theories of gravity, the measurementof polarizations is a powerful tool in probing the nature of gravity.

Effects of high pressure nitrogen annealing on ferroelectric Hf0.5Zr0.5O2 films

The effect of high-pressure nitrogen annealing at up to 50 atmospheres (atm) on Hf0.5Zr0.5O2 films at relatively low temperatures (450 °C) is analyzed using polarization-electric field curves, bipolar switching endurance measurements, grazing angle incidence X-ray diffraction, and piezoelectric force microscopy. Hf0.5Zr0.5O2 films annealed at 450 °C/50 atm have excellent characteristics, including remanent polarizations greater than 20 μC/cm2, a switching speed of 200 ns, and reliability, measured by sustained performance after 1010 bipolar switching cycles. The enhanced device features are attributed to the transition to the orthorhombic-phase from the tetragonal-phase of Hf0.5Zr0.5O2 at high pressure, which is also consistent with the results of “wake-up” analysis, and the variations of the pure polarization curves, extracted from the total displacement field under pressure.

Exploring vacuum birefringence based on a 100 PW laser and an x-ray free electron laser beam

Exploring vacuum birefringence with the station of extreme light at Shanghai Coherent Light Facility is considered. Laser pulses of intensity beyond 1023 W cm−2 are capable of polarizing the vacuum due to the ultra-strong electro-magnetic fields. The subtle difference of the vacuum refractive indexes along electric and magnetic fields leads to a birefringence effect for lights propagating through. The vacuum birefringence effect can now be captured by colliding a hard x-ray free electron laser (XFEL) beam with a high-power laser. The initial XFEL beam of pure linear polarization is predicated to gain a very small ellipticity after passing through the laser stimulated vacuum. Various interaction geometries are considered, showing that the estimated ellipticity lies between 1.8 × 10−10 and 10−9 for a 100 PW laser interacting with a 12.9 keV XFEL beam, approaching the threshold for todays’ polarity detection technique. The detailed experimental set-up is designed, including the polarimeter, the focusing compound refractive lens and the optical path. When taking into account the efficiencies of the x-ray instruments, it is found that about 10 polarization-flipped x-ray photons can be detected for a single shot for our design. Considering the background noise level, accumulating runs are necessary to obtain high confident measurement.

Low-Cost X/Ku/Ka-Band Dual-Polarized Array With Shared Aperture

This paper presents a novel tri-band (X/Ku/Ka-band) planar antenna array with dual polarizations and shared aperture. Compared with traditional dual-polarized arrays, the proposed array has advantages of low cost, low profile, and high integration. Three types of antennas resonating at different frequencies, including the perforated patch, stacked patch, and slim crosspatch, are innovatively interleaved in the same aperture. The crosspatch fed by proximity coupling is presented as Ku-band element for its advantages of compact size, high isolation, and pure polarization. The techniques such as series feed and reverse feed are utilized to implement the six feed networks in a compact size with reduced cross polarizations. Measured results agree well with the simulations, showing three operation bands at X-, Ku-, and Ka-bands with the bandwidths of 3.6%, 6.7%, and 5.3%, respectively. The antenna also exhibits excellent radiation performance with the cross-polarization discrimination over 25 dB at the three bands. To the best of the author’s knowledge, this is the first shared-aperture X/Ku/Ka-band dual-polarized antenna array reported, which is useful for potential synthetic aperture radar applications.

Demonstration of arbitrary temporal shaping of picosecond pulses in a radially polarized Yb-fiber MOPA with > 10 W average power.

High precision surface processing has an unmet demand for picosecond pulses with arbitrary temporal profiles in radial polarization states and at high average powers. Here, simultaneous spatial and arbitrary temporal shaping of chirped 10 - 100 picoseconds pulses is demonstrated with an Yb-doped fiber laser system generating an output power of more than 10 W at 40 MHz repetition frequency. The closed-loop control algorithm carves the pulses using a commercial, rugged, and fiberized optical pulse shaper placed at the front end of the system and uses feedback from the output pulse shapes for optimization. Arbitrary complex temporal profiles were demonstrated using a dispersive Fourier transform based technique and limits set by the system were investigated. Pulse shaping in the spatial domain was accomplished using an S-waveplate, fabricated in-house, to change the linearly polarized fundamental mode into a doughnut mode with radial polarization. This was amplified in a final-stage few-mode large-mode area fiber amplifier. Placing both temporal and spatial shaping elements before the power-amplifier avoids complex and potentially lossy conversion of the spatial mode profile at the output and provides an efficient route for power-scaling. The use of properly oriented quarter- and half-wave plates, which have both low loss and high power handling capability, enabled the output to be set to pure radial or azimuthal polarization states. Using commercial off-the-shelf components, our technique is able to immediately enhance the versatility of ultrashort fiber laser systems for high precision material processing and other industrial applications.

Polarizations of gravitational waves in f(R) gravity

We point out that there are only three polarizations for gravitational waves in $f(R)$ gravity, and the polarization due to the massive scalar mode is a mix of the pure longitudinal and transverse breathing polarization. The classification of the six polarizations by the Newman-Penrose quantities is based on weak, plane and null gravitational waves, so it is not applicable to the massive mode.

Cylindrical polarimetric phased array radar: Beamforming and calibration for weather applications

Future weather radar systems will need to provide rapid updates within a flexible multifunctional overall radar network. This naturally leads to the use of electronically scanned phased array antennas. However, the traditional multifaced planar antenna approaches suffer from having radiation patterns that are variant in both beam shape and polarization as a function of electronic scan angle; even with practically challenging angle-dependent polarization correction, this places limitations on how accurately weather can be measured. A cylindrical array with commutated beams, on the other hand, can theoretically provide patterns that are invariant with respect to azimuth scanning with very pure polarizations. This paper summarizes recent measurements of the cylindrical polarimetric phased array radar demonstrator, a system designed to explore the benefits and limitations of a cylindrical array approach to these future weather radar applications.

Pure circular polarization electroluminescence at room temperature with spin-polarized light-emitting diodes

We report the room-temperature electroluminescence (EL) with nearly pure circular polarization (CP) from GaAs-based spin-polarized light-emitting diodes (spin-LEDs). External magnetic fields are not used during device operation. There are two small schemes in the tested spin-LEDs: first, the stripe-laser-like structure that helps intensify the EL light at the cleaved side walls below the spin injector Fe slab, and second, the crystalline AlO x spin-tunnel barrier that ensures electrically stable device operation. The purity of CP is depressively low in the low current density (J) region, whereas it increases steeply and reaches close to the pure CP when J > 100 A/cm2 There, either right- or left-handed CP component is significantly suppressed depending on the direction of magnetization of the spin injector. Spin-dependent reabsorption, spin-induced birefringence, and optical spin-axis conversion are suggested to account for the observed experimental results.

Planar composite chiral metamaterial with broadband dispersionless polarization rotation and high transmission

We propose a planar composite chiral metamaterial (CCMM) by symmetrically inserting a metallic mesh between two layers of conjugated gammadion resonators. As the elaborate CCMM operates at off-resonance frequencies, it therefore presents low-loss and low-dispersion polarization rotation features. The results show that the proposed CCMM can achieve pure and dispersionless polarization rotation with efficient transmission for a linearly polarized wave within a broad bandwidth. This off-resonance CCMM overcomes the drawbacks of high transmission losses and highly dispersive polarization rotation that exist in the previous resonance-type chiral metamaterials and also exhibits more simplicity of fabrication than the three-dimensional CMMs. The intriguing properties greatly improve the performance of chiral metamaterials in controlling the polarization state of electromagnetic waves.

A study of geometric phase topology using Fourier transform method

Topological aspect of the geometric phase (GP) due to pure polarization projection is studied using the 2D Fourier transform (2D-FT) method. Projection of orthogonal polarization state results in a phase singularity in the 2D parameter space of ellipticity and orientation of polarization ellipse. Projection of its surrounding states results in an accumulation of GP in different amount that form a spiral structure. A half wave plate–quarter wave plate combination is used to generate different polarization states which are projected using a polarizer. The accumulated phase for each orientation of the wave plate is extracted from 2D-FT of the interferogram, obtained by interfering it with a reference beam in a Mach–Zehnder like interferometer.