Showing papers on "Waveplate published in 2019"

Video-rate full-Stokes imaging polarimeter using two polarization cameras

Abstract: We show how to construct and calibrate a full-Stokes imaging polarimeter system by combining the video data from two separate polarization cameras with a nonpolarizing beamsplitter and a waveplate. As a result, this system can capture the full Stokes vector at each pixel for 3 megapixel images at up to 60 Hz. To demonstrate some of the advantages of measuring the s 3 Stokes vector component that is normally not measured in polarization cameras, we show three experiments: viewing three-dimensional glasses, detecting a scarab beetle in a natural environment via the circular dichroism of its shell, and mixing an optically active liquid with a neutral liquid.

Reconfigurable Terahertz Quarter-Wave Plate for Helicity Switching Based on Babinet Inversion of an Anisotropic Checkerboard Metasurface

Abstract: Dynamic helicity control with metasurfaces is essential for chirality-sensitive spectroscopy, data transmission, and sensitive measurements, but is challenging, as it requires deep modulation of light's polarization states. To conquer the challenge, this study leverages metallic checkerboards, the electromagnetic characteristics of which critically depend on the connection states. The authors establish a general guiding principle for realizing helicity switching with such structures, and implement a dynamic terahertz quarter-wave plate to that end. This approach paves the way to the effective use of light's spin degree of freedom.

Intracavity cylindrical vector beam generation from all-PM Er-doped mode-locked fiber laser.

Abstract: We demonstrate a practical method that is used to generate on-demand first- and higher-order cylindrical vector beams, in the 1550 nm band, directly from an all polarization maintaining mode-locked Er-fiber laser. On demand typical 1st order CVBs, including the radially and azimuthally polarized beams, can be easily achieved by properly adjusting the angle of a half-wave plate with respect to the fast axis of the vortex wave plate. The spatial beam mode can be flexibly switched with no disturbance on the time domain mode-locking output. The laser outputs the desired vector beams at 1571 nm with a spectral bandwidth at full-width at half-maximum of 32 nm. The mode-locked laser pulses have a repetition rate of 74.9 MHz. Moreover, the proposed method can be easily extended to create higher-order CVBs. Our research provides a convenient way to generate ultrafast pulses in highly flexible-controlled structured modes, which is essential for optical fabrication and light trapping applications.

Single-Layer Metasurfaces as Spectrally Tunable Terahertz Half- and Quarter-Waveplates.

Abstract: We propose a single-layer terahertz metasurface that acts as an efficient terahertz waveplate, providing phase retardation of up to 180° with a tunable operation frequency. Designed with the tight coupling of elementary resonators, our metasurface provides extraordinarily strong hyperbolicity that is closely associated with the distance between resonators, enabling both significant phase retardation and spectral tunability through mechanical deformation. The proposed concept of terahertz waveplates based on relatively simple metastructures fabricated on stretchable polydimethylsiloxane is experimentally confirmed using terahertz spectroscopy. It is believed that the proposed design will pave the way for a diverse range of terahertz applications.

Terahertz Quarter Wave-Plate Metasurface Polarizer Based on Arrays of Graphene Ribbons

Abstract: We propose a novel graphene-dielectric-based metasurface for manipulating the polarization of the incident light in the terahertz regime. The proposed structure comprised two orthogonally oriented periodic array of graphene ribbons (PAGRs) which are separated by a dielectric spacer and deposited on an Au-backed dielectric substrate. Based on the transmission line theory, an equivalent model with excellent accuracy is suggested for the proposed structure. By leveraging the simplicity of the model, we design a three-state quarter wave plate that is able to dynamically switch the polarization of the reflected wave to linear, right-, and left-hand polarizations while keeping the reflected amplitude remarkably high. Thanks to the simplicity of the model, the proposed structure can be easily used for designing other metasurfaces for light propagation control applications in imaging, sensing, and telecommunication.

Liquid-crystal-based magnetically tunable terahertz achromatic quarter-wave plate.

Abstract: Development of the wideband and tunable quasi-optic terahertz (THz) components is in high demand. In this work, we demonstrate a tunable achromatic quarter-wave plate (AQWP) for the THz frequency range. The phase retardation of this device can be set at 90° ± 9° from 0.20 to 0.50 THz. The operation range from 0.20 to 0.50 THz can be tuned to from 0.30 to 0.70 THz by introducing three nematic liquid crystals phase retarders, of which the birefringence can be magnetically tuned. The frequency-dependent phase retardation is in good agreement with theoretical predictions.

Multiple-Beam Interference-Enabled Broadband Metamaterial Wave Plates

Abstract: Metamaterials have generated considerable research interest in manipulating the polarization state of light, but many proposals suffer from narrow bandwidth or low transmission efficiency. Here researchers show that a classical multiple-beam interference mechanism can be used to modulate the phase dispersion of transmitted waves in metamaterials, which motivates a general strategy to achieve a broadband wave plate by independently controlling the phase dispersion for the two orthogonal polarizations. These findings can stimulate the production of high-performance broadband optical devices based on various metamaterials in different frequency domains, to impact applications in photonics.

Wideband sub-THz half-wave plate using 3D-printed low-index metagratings with superwavelength lattice

Abstract: High-index dielectric metasurfaces are rarely reported around 0.1-0.3 THz, as an extremely large etching depth is needed according to the millimeter-scale wavelength. In this work, we propose an easy solution to sub-THz wideband polarization control by utilizing 3D-printed low-index (n~1.5) metagratings. The metagrating with subwavelength lattice is shown as a very efficient half-wave plate (net polarization conversion of 87%) at 0.14 THz but showing noisy spectrum. The design with superwavelength lattice offers a smooth and wide bandwidth for linear polarization rotation. Study of the mechanism shows that the lattice size slightly above wavelength is a better choice for the low-index metadevice as it maintains high efficiency in the zero diffraction order and wide bandwidth due to the small mode dispersion. Such designs offer a feasible solution especially suitable for sub-THz polarization and phase control, complementary to the existing high-index dielectric and metallic metasurfaces.

Analysis of errors in polarimetry using a rotating waveplate.

Abstract: Modulation using a rotating waveplate is the most popular way in astronomy to obtain radiation polarization states and thus the physical condition of celestial bodies. Modulation error analysis of the rotating quarter-waveplate polarimeter is presented in this paper. In terms of geometric dimensions, three modulation error sources are analyzed: the waveplate axial error, waveplate rotation axis tip-tilt error (zenithal error), and position error of the waveplate fast axis (azimuthal error). The dispersion deviation, as another dimension of modulator error, is also studied in this paper. In theory, two factors affect the accuracy of polarization measurement using waveplate polarimetry: retardance $ \delta $δand fast axis position $ \theta $θ. The temperature property of the waveplate, which represents the axial error, the waveplate mounting tip-tilt error, which represents the zenithal error, and the wavelength-based retardance characteristic, which represents the dispersion property of the waveplate, belong to the retardance error. The motorized rotary stage home position error and the random sample rotating position error, representing the azimuthal error, belong to the fast axis position error. These factors will be analyzed in detail here. Based on these analyses, the maximum allowable upper limits for each error source under $ 1 \times {10^{ - 4}} $1×10-4 polarization measurement accuracy are presented. Also, feasible solutions are proposed to address these errors.

Demonstration of the broadband half-wave plate using the nine-layer sapphire for the CMB polarization experiment

Abstract: We report the development of the achromatic half-wave plate (AHWP) at millimeter wave for cosmic microwave background polarization experiments. We fabricate an AHWP consisting of nine A-cut sapphire plates based on the Pancharatnam recipe to cover a wide frequency range. The modulation efficiency and the phase are measured in a frequency range of 33 to 260 GHz with incident angles up to 10 deg. We find the measurements at room temperature are in good agreement with the predictions. This is the most broadband demonstration of an AHWP at millimeter wave.

Miniaturized Metalens Based Optical Tweezers on Liquid Crystal Droplets for Lab-on-a-Chip Optical Motors

Abstract: Surfaces covered with layers of ultrathin nanoantenna structures—so called metasurfaces have recently been proven capable of completely controlling phase of light. Metalenses have emerged from the advance in the development of metasurfaces providing a new basis for recasting traditional lenses into thin, planar optical components capable of focusing light. The lens made of arrays of plasmonic gold nanorods were fabricated on a glass substrate by using electron beam lithography. A 1064 nm laser was used to create a high intensity circularly polarized light focal spot through metalens of focal length 800 µm, N.A. = 0.6 fabricated based on Pancharatnam-Berry phase principle. We demonstrated that optical rotation of birefringent nematic liquid crystal droplets trapped in the laser beam was possible through this metalens. The rotation of birefringent droplets convinced that the optical trap possesses strong enough angular momentum of light from radiation of each nanostructure acting like a local half waveplate and introducing an orientation-dependent phase to light. Here, we show the success in creating a miniaturized and robust metalens based optical tweezers system capable of rotating liquid crystals droplets to imitate an optical motor for future lab-on-a-chip applications.

Classical Polarimetry with a Twist: A Compact, Geometric Approach

Abstract: We present an approach to classical polarimetry that requires no moving parts, is compact and robust, and that encodes the complete polarization information on a single data frame, accomplished by replacing the rotation of components such as wave plates with position along a spatial axis. We demonstrate the concept with a polarimeter having a quarter wave plate whose fast axis direction changes with location along one axis of a 2D data frame in conjunction with a fixed-direction polarization analyzer, analogous to a classical rotating quarter wave plate polarimeter. The full set of Stokes parameters is obtained, with maximal sensitivity to circular polarization Stokes V if a quarter wave retarder is used. Linear and circular polarization terms are encoded with spatial carrier frequencies that differ by a factor two, which minimizes cross-talk. Other rotating component polarimeters lend themselves to the approach. Since the polarization modulation spatial frequencies do not change greatly, if at all, with wavelength such devices are close to achromatic, simplifying instrument design. Since the polarimetric information is acquired in a single observation, rapidly varying, transient and moving targets are accessible, loss of precision due to sequential data acquisition is avoided, and moving parts are not required.

Designing a Broadband Terahertz Half-Wave Plate Using an Anisotropic Metasurface

Abstract: We design a multi-resonance metasurface at terahertz frequency, which can act as a polarization manipulator in the reflective mode. The proposed polarization converter consists of periodic unit cells and each unit cell has a resonator on the top surface. While a dielectric material forms the middle layer, a gold foil constitutes the bottom layer. The proposed polarization converter converts a linearly polarized terahertz wave into an orthogonal one for a wide range of operating frequencies. It provides a maximum conversion efficiency in the frequency range of 0.64–1.47 THz where the magnitudes of the cross reflection coefficients exceed 90%. The calculated relative bandwidth of the proposed converter is 78.67%. The phase difference of the reflected wave is between − 180∘ and 180∘ depending upon the operating frequency. Further, based on the detailed numerical results, we corroborate that the proposed device is robust against the variations in the structural parameters. The proposed converter maintains the conversion efficiency for various incident angles from 0∘ to 30∘. Besides, we also demonstrate the possibility of tuning the polarization conversion ratio by integrating silicon in the metasurface. The proposed metasurface may find potential applications in communications, antenna, and radar cross-section reduction technology.

Broadband waveplate operation by orthotropic metasurface reflector

Abstract: We present an anisotropic metasurface offering a simultaneous linear to cross-polarization conversion and linear to circular polarization conversion operations on large bandwidths of microwave frequencies. The proposed orthotropic structure consists of metallic bow tie shaped patches with embedded circular patches enabling diagonal structure symmetry. We demonstrate through numerical simulations and experiments that the metasurface can be used as a high efficiency linear to cross-polarization reflective converter within the two broad frequency bands of 7.48–10.55 GHz and 18.47–19.52 GHz with a polarization conversion ratio above 90%. Simultaneously, the designed metasurface acts as a circular polarizer for linearly polarized incident waves in triple frequency bands of 6.10–7.46 GHz, 10.55–18.42 GHz, and 19.60–22.39 GHz with an axial ratio below the 3 dB threshold. To the best of our knowledge, the second band from 10.55 to 18.42 GHz of circular polarization conversion “has the highest reported (to date) bandwidth of 54.3% for an axial ratio below 3 dB.” The designed metasurface remains angular stable up to 75 ° over most of the part of the above-mentioned operating bands for both transverse-electric and transverse-magnetic polarized wave incidences.

Simultaneous polarization transformation and amplification of multi-petawatt laser pulses in magnetized plasmas.

Abstract: With increasing laser peak power, the generation and manipulation of high-power laser pulses become a growing challenge for conventional solid-state optics due to their limited damage threshold. As a result, plasma-based optical components that can sustain extremely high fields are attracting increasing interest. Here, we propose a type of plasma waveplate based on magneto-optical birefringence under a transverse magnetic field, which can work under extremely high laser power. Importantly, this waveplate can simultaneously alter the polarization state and boost the peak laser power. It is demonstrated numerically that an initially linearly polarized laser pulse with 5 petawatt peak power can be converted into a circularly polarized pulse with a peak power higher than 10 petawatts by such a waveplate with a centimeter-scale diameter. The energy conversion efficiency of the polarization transformation is about 98%. The necessary waveplate thickness is shown to scale inversely with plasma electron density ne and the square of magnetic field B0, and it is about 1 cm for ne = 3 × 1020 cm−3 and B0 = 100 T. The proposed plasma waveplate and other plasma-based optical components can play a critical role for the effective utilization of multi-petawatt laser systems.

Classical polarimetry with a twist: a compact, geometric approach

Abstract: We present an approach to classical polarimetry that requires no moving parts, is compact and robust, and that encodes the complete polarization information on a single data frame, accomplished by replacing the rotation of components such as wave plates with position along a spatial axis. We demonstrate the concept with a polarimeter having a quarter wave plate whose fast axis direction changes with location along one axis of a 2D data frame in conjunction with a fixed-direction polarization analyzer, analogous to a classical rotating quarter wave plate polarimeter. The full set of Stokes parameters is obtained, with maximal sensitivity to circular polarization Stokes V if a quarter wave retarder is used. Linear and circular polarization terms are encoded with spatial carrier frequencies that differ by a factor two, which minimizes cross-talk. Other rotating component polarimeters lend themselves to the approach. Since the polarization modulation spatial frequencies do not change greatly, if at all, with wavelength such devices are close to achromatic, simplifying instrument design. Since the polarimetric information is acquired in a single observation, rapidly varying, transient and moving targets are accessible, loss of precision due to sequential data acquisition is avoided, and moving parts are not required.

Multifunctional super surface based on micro-nano half-wave plate

Abstract: The present invention designs a multifunctional super surface based on a micro-nano half-wave plate. The multi-functional super surface is composed of a substrate and a nano-brick array etched on thesubstrate, so that polarization regulation of linearly polarized light and phase regulation of circularly polarized light can be simultaneously implemented on the super surface; in the near field, high-resolution continuous gray image display can be implemented through the regulation of the polarization state, and the holographic image can be reproduced through the four-step phase regulation in the far field; and the two regulation modes are independent of each other and do not affect each other. The present invention provides a new method for information multiplexing, and the method can be widely applied to the fields of encryption display and information security.

Axially-offset differential interference contrast microscopy via polarization wavefront shaping.

Abstract: Sample-scan phase contrast imaging was demonstrated by producing and coherently recombining light from a pair of axially offset focal planes. Placing a homogeneous medium in one of the two focal planes enables quantitative phase imaging using only common-path optics, recovering absolute phase without halo or oblique-illumination artifacts. Axially offset foci separated by 70 μm with a 10x objective were produced through polarization wavefront shaping using a matched pair of custom-designed microretarder arrays, compatible with retrofitting into conventional commercial microscopes. Quantitative phase imaging was achieved by two complementary approaches: i) rotation of a half wave plate, and ii) 50 kHz polarization modulation with lock-in amplification for detection.

Temperature-responsive polymer wave Plates as tunable polarization converters

Abstract: A temperature-responsive polarization converter, which reversibly changes from a full-wave to a half-wave plate upon heating, is developed. The polymer wave plate has a controlled thickness and is based on a uniaxial aligned nematic semi-interpenetrating network coating containing a specific concentration of a non-crosslinked liquid crystal elastomer. Upon heating, the effective birefringence of the wave plate halves without changing the thickness. The function of the wave plate is demonstrated by sandwiching the tunable polarization converter between two identical right-handed circular polarized light reflective films with a wavelength around 770 nm. At low temperatures, this optical device reflects 50% of light at 770 nm, whereas at elevated temperature 81% is reflected. Such temperature-responsive optical devices have potential applications for both aesthetic purposes as well as energy saving windows.

Linear polarization grating combining a circular polarization grating with a special cycloidal diffractive quarter waveplate.

Abstract: We introduce and demonstrate a switchable novel linear polarization grating (LPG) consisting of a circular polarization grating (CPG) and a special cycloidal diffractive quarter waveplate (CQWP). The CQWP is developed that marvelously matches the polarization-state of beams passing through the CPG. Such an LPG is so polarization-sensitive that it can split an incident linear polarized beam into two proportionally controllable left- or right-handed circularly polarized lights. We establish rigorous simulation model based on finite element method to investigate near-field polarization-state distribution of CPGs. Furthermore, LPGs are demonstrated and the diffraction properties are obtained with simulation and Jones Matrix analysis. The combination of CPGs and CQWPs is achieved with polymerizable liquid crystal. The experimental results of deflection angle and polarization selectivity of LPGs are consistent with those of simulation.

Quarter-wave plate metasurfaces on electromagnetically thin polyimide substrates

Abstract: We experimentally demonstrate that electromagnetically thin polyimide substrates can mitigate substrate-induced detrimental effects to the performance of metallic metasurfaces. A planar quarter-wave plate for the microwave K-band is fabricated on a polyimide substrate of deep subwavelength thickness by means of standard photolithography. By properly selecting the combination of the polyimide thickness and the aluminum layer thickness of the metasurface, conversion from linear to circular polarization is achieved at the design frequency. The proposed approach is generic, and it can be applied to the fabrication of mechanically robust, flexible metallic metasurfaces, which are primarily designed to work in a free-standing configuration.

Simultaneous polarization transformation and amplification of multi-petawatt laser pulses in magnetized plasmas

Abstract: With increasing laser peak power, the generation and manipulation of high-power laser pulses becomes a growing challenge for conventional solid-state optics due to their limited damage threshold. As a result, plasma-based optical components which can sustain extremely high fields are attracting increasing interest. Here, we propose a type of plasma waveplate based on magneto-optical birefringence under a transverse magnetic field, which can work under extremely high laser power. Importantly, this waveplate can simultaneously alter the polarization state and boost the peak laser power. It is demonstrated numerically that an initially linearly polarized laser pulse with 5 petawatt peak power can be converted into a circularly polarized pulse with a peak power higher than 10 petawatts by such a waveplate with a centimeter-scale diameter. The energy conversion efficiency of the polarization transformation is about $98\%$. The necessary waveplate thickness is shown to scale inversely with plasma electron density $n_e$ and the square of magnetic field $B_0$, and it is about 1 cm for $n_e=3\times 10^{20}$ cm$^{-3}$ and $B_0=100$ T. The proposed plasma waveplate and other plasma-based optical components can play a critical role for the effective utilization of multi-petawatt laser systems.

Broadband Ultrathin Transmission Quarter Waveplate with Rectangular Hole Array Based on Plasmonic Resonances

Abstract: The control of the polarization states of light plays an important role in modern optical systems. However, traditional polarization manipulating devices often have narrow bandwidth and their large size makes it difficult for them to achieve miniaturization and integration of optical systems. This work presents an ultrathin quarter waveplate with a periodic silver film 2 × 2 rectangular hole array with a thickness less than λ/50. Numerical simulation shows that the waveplate can efficiently transform a circular polarized wave into a linearly polarized one at the center of 1550 nm, and its bandwidth is 525 nm. Furthermore, the quarter waveplate can efficiently invert linear polarization into circular polarization at 1550 nm, which ellipticity is near unit. With an array of small holes on a metal film to enhance transmission, this structure can increase the transmission to 0.44. The broadband quarter waveplate can be used in communication system and near infrared band system, and be integrated with other optical devices at nanoscale to achieve polarization operation, detection, and sensing.

High-power femtosecond cylindrical vector beam optical parametric oscillator.

Abstract: We report on high-power femtosecond cylindrical vector beam (CVB) generation from a Gaussian-pumped optical parametric oscillator (OPO). By introducing a half waveplate and a vortex half-wave plate of m = 1 to realize intracavity polarization modulation to the resonant Gaussian signal, the OPO could deliver broadband signal beam in CVB profile, i.e., radially and azimuthally polarized beam profile. The central wavelength of the generated CVB signals can be tuned continuously from 1405 to 1601 nm, while the corresponding pulse durations are all around 150 fs. A maximum average output power of 614 mW at 1505 nm is obtained. Moreover, our OPO cavity design can be extended to generate high order CVB by simply changing the vortex half-wave plate with different orders. Such a high-power CVB OPO configuration has the advantages of flexible control and wide tuning range, making it a practical tool for applications in super-resolution imaging, optical communication and quantum correlations.

0.02-wavelengths-thick transmission-type designer wave plate with high efficiency

Abstract: The thin thickness and the working efficiency are always two key problems for the transmission-type polarization converter. Here, we propose a planar C-band ultrathin (0.02 λ0 in the thickness) and highly efficient circular polarization converter in the transmission mode. The polarizer is composed of double layer surface structures printed on the both side of a single-layer substrate and the metallic layers are connected by a pair of through-via holes. The structure of the top layer is composed of a patch with a D-shape slot inside, and the bottom layer can be obtained by rotating the top layer with 180 degrees around the center. We demonstrate that the polarization converter can achieve transmission polarization conversions from right-handed circularly polarized (RHCP) incident electromagnetic (EM) waves to left-handed ones or from left-handed circularly polarized (LHCP) incident EM waves to right-handed ones in transmission mode. Transfer matrix and equivalent circuit theory and modeling are discussed to explain the conversion mechanism. The results show that the maximum cross-polarization efficiency of the polarizer working at 5.8 GHz is 94.6 %. This ultra-thin circular polarization converter is expected to be applied to wireless systems that require circular polarization diversity.

High-efficiency, broadband, and wide-angle all-dielectric quarter wave plate based on anisotropic electric and magnetic dipole resonances

Abstract: Metadevices based on dielectric nanostructure with excitation of electric and magnetic resonances have shown high efficiency for polarization control compared with conventional manipulation methods, as well as plasmonic structure metadevices. Since both the electric and magnetic dipole (MD) resonances can be precisely adjusted by optimizing geometric parameters of the resonators to meet the desired wavelength, this paper proposes an approach to implement the high transmittance metadevices operating at preferred wavelengths. By employing this method, we demonstrate an all-dielectric quarter wave plate (QWP) metasurface with high transmittance (>85%) and high polarization conversion efficiency (>0.88) in a broad telecom waveband. At the same time, conversion efficiency is nearly unaffected for incident angles within 75°. With features of high transmittance, wide angle, and invertible linear to circular polarization conversion, the all dielectric QWP can be a good replacement for plasmonic metasurface devices and offers a further step in developing polarization and phase manipulation metadevices.