Polarization Elements Research Articles

Polarization-selective dual-band infrared metamaterial perfect absorber

Abstract Metamaterial absorbers have significant effects and great potential for applications in a variety of important sciences and technologies, including infrared imaging, thermal emitters, electromagnetic shielding, and photodetectors. However, conventional absorbers with a single function are difficult to meet the growing demand of devices, especially for the situations where the absorption and polarization are simultaneously required in infrared detection. If the polarization absorption function is realized by integrating absorption and polarization elements, it will lead to a large overall system size and slow response time. To solve this problem, we propose a dual-band polarization-selective metamaterial perfect absorber, whose maximum absorptions at resonant wavelengths of λ1=2.824μm and λ2=7.622μm are 99.99% and 99.88%, respectively. The absorber exhibits strong polarization sensitivity, absorbing TM-polarized incident light and reflecting TE-polarized incident light at the two resonant wavelengths. The extinction ratios of the absorber at the two referred resonant wavelengths are 90.9 and 142.7, respectively. The proposed absorber would be beneficial for infrared polarization detection and imaging.

Analysis of interference fringes in a long-wave infrared full Stokes polarimeter based on rotating waveplates

In the long-wave infrared (LWIR, 8–15 µm) band, the interference effect of polarization elements becomes an issue in polarimetry due to defects in the anti-reflective coatings. The paper describes an analysis and optimization method for the rotating-waveplates-based Stokes polarimeter, to eliminate interference fringes and improve polarization measurement accuracy in LWIR. An interference model was established based on the theory of polarized light and thin-film optics. Different modulation schemes were simulated and analyzed to obtain an optimized Stokes polarimeter, reducing the instrumental polarization to less than 1E-3. Furthermore, experimental validation was conducted by the Accurate Infrared Magnetic Field Measurements of the Sun (AIMS) telescope. The result shows that the instrumental polarization was less than 2E-3, consistent with the simulation.

Programmable generation of counterrotating bicircular light pulses in the multi-terahertz frequency range

The manipulation of solid states using intense infrared or terahertz light fields is a pivotal area in contemporary ultrafast photonics research. While conventional circular polarization has been well explored, the potential of counterrotating bicircular light remains widely underexplored, despite growing interest in theory. In the mid-infrared or multi-terahertz region, experimental challenges lie in difficulties in stabilizing the relative phase between two-color lights and the lack of available polarization elements. Here, we successfully generated phase-stable counterrotating bicircular light pulses in the 14–39 THz frequency range circumventing the above problems. Employing spectral broadening, polarization pulse shaping with a spatial light modulator, and intra-pulse difference frequency generation leveraging a distinctive angular-momentum selection rule within the nonlinear crystal, we achieved direct conversion from near-infrared pulses into the designed counterrotating bicircular multi-terahertz pulses. Use of the spatial light modulator enables programmable control over the shape, orientation, rotational symmetry, and helicity of the bicircular light field trajectory. This advancement provides a novel pathway for the programmable manipulation of light fields, and marks a significant step toward understanding and harnessing the impact of tailored light fields on matter, particularly in the context of topological semimetals.

Advanced Transparent Glass‐Ceramics via Laser Anisotropic Nanocrystallization

AbstractTransparent glass‐ceramics, merging the attributes of both glass and ceramics, have diverse applications in ballistic protection, armor materials, dentistry, light‐emitting diode, and optical domains. A limitation of conventional methods for glass‐ceramic fabrication is their inadequacy in precisely controlling the morphology of crystallization, consequently constraining their prospective advancements in diverse areas. Here, a method that facilitates precise control over the formation and growth of polarization‐dependent nonperiodic anisotropic nanocrystals, with a short axis ranging from 15 to 280 nm, in Li2O‐Al2O3‐SiO2 (LAS) glass is proposed. The method utilizes the principles of near‐field anisotropy between light and matter, building upon the classical nucleation‐growth model of glass crystallization. Notably, the glass‐ceramics possessing laser‐induced nanocrystals within the Rayleigh size regime showcase an impressive 99.7% transmittance in the visible and near‐infrared wavelengths. Additionally, the glass‐ceramics with non‐periodic anisotropic nanocrystals macroscopically exhibit form‐birefringence properties, thus enabling transparent optical applications, such as polarization elements, geometric phase elements, and multi‐dimensional optical data storage. This work opens up new avenues for morphological manipulation of nanocrystallization, with potential applications in optics, nanophotonics, functional glass‐ceramics, and high mechanical performance devices.

A Concept for a Multipurpose Time-of-Flight Neutron Reflectometer at Compact Neutron Sources

The design of a time-of-flight neutron reflectometer proposed for the new generation of compact neutron sources is presented. The reflectometer offers the possibility to use spin-polarized neutrons. The reflectometer design presented here takes advantage of a cold neutron source and uses neutrons with wavelengths in the range of 2–15 Å for the unpolarized mode. In general, due to tight spatial restrictions and the need to avoid moving parts inside the beam channel, a multi-channel collimator guide and reflective neutron guide are used for the first section of the instrument. This enables definition of the desired wavelength band and easy selection of one out of three different Q-resolutions. A low background for the collimator system and the reflectometer is ensured by employing a tangential beam channel and an in-channel sapphire filter. The second section is the time-of-flight (TOF) system, which uses a double-disk neutron chopper followed by polarization elements, the sample environment and the neutron detector system. Monte Carlo simulations and neutron beamline intensity measurements are presented. The design considerations are adoptable for neutron sources where space is limited and sections of the instrument are in a high-radiation environment.

Stacked Polarizing Elements for Controlling Parameters of Surface Relief Gratings Written in Photosensitive Materials.

Photosensitive materials are widely used for the direct fabrication of surface relief gratings (SRGs) without the selective etching of the material. It is known that the interferometric approach makes it possible to fabricate SRGs with submicron and even subwavelength periods. However, to change the period of the written SRGs, it is necessary to change the convergence angle, shift a sample, and readjust the interferometric setup. Recently, it was shown that structured laser beams with predetermined, periodically modulated polarization distributions can also be used to fabricate SRGs. A structured laser beam with the desired polarization distribution can be formed with just one polarizing optical element-for example, the so-called depolarizer, a patterned micro-retarder array. The use of such stacked elements makes it possible to directly control the modulation period of the polarization of the generated laser beam. We show that this approach allows one to fabricate SRGs with submicron periods. Moreover, the addition of q-plates, elements effectively used to generate cylindrical vector beams with polarization singularities, allows the efficient formation of fork polarization gratings (FPGs) and the fabrication of higher-order fork-shaped SRGs. Full control of the parameters of the generated FPGs is possible. We demonstrate the formation of FPGs of higher orders (up to 12) by only adding first- and second-order q-plates and half-wave plates to the depolarizers. In this work, we numerically and experimentally study the parameters of various types of SRGs formed using these stacked polarizing elements and show the significant potential of this method for the laser processing of photosensitive materials, which often also serve as polarization sensors.

Tunable ultraviolet laser based on intracavity third harmonic generation of external cavity surface emitting laser

Ultraviolet laser has high frequency, short wavelength, large single-photon energy, and high spatial resolution, and has wide applications in many fields such as fine processing, life sciences, and spectroscopy. In this work, a wavelength tunable ultraviolet laser based on intracavity third harmonic generation from an external-cavity surface-emitting laser is reported. The W-type resonant cavity of the laser is composed of a distributed Bragg reflector (DBR) at the bottom of the gain chip, three plane-concave mirrors, and a rear plane mirror. On the arm containing the gain chip, a birefringent filter is inserted at the Brewster angle as the polarization and wavelength tuning element, which can also narrow the linewidth of the fundamental laser to a certain extent. A type-I phase-matched LBO crystal is placed on the beam waist between the folding mirrors M2 and M3 to convert the 980 nm fundamental laser into 490 nm blue light, and a type-I phase-matched BBO crystal is inserted in the beam waist near the rear mirror to produce a 327 nm ultraviolet output from the remained 980 nm fundamental laser and the frequency-doubled 490 nm second harmonic. Before the BBO crystal, a half-wave plate at 980 nm is employed to change the polarization of the fundamental laser, so as to meet the type-I phase-matching condition of the used BBO crystal. Owing to the larger nonlinear coefficient of the type-I phase-matched BBO crystal, and its obviously higher transmittance at 327 nm wavelength than the usually used LBO crystal, the output power is obtained to be 538 mW at 327 nm ultraviolet wavelength, corresponding to a conversion efficiency of 1.1% from pump light to ultraviolet laser. The experiment is performed under conditions of 15 ℃ temperature, 47 W absorbed pump power, 5 mm-length LBO and 5 mm-length BBO crystals. By using a 2 mm-thick birefringent filter as the tuning element, 34.1 nm tuning range of the 980 nm fundamental laser, 14.3 nm tuning range of the 490 nm second harmonic, and 8.6 nm tuning range of the 327 nm third harmonic are obtained. The ultraviolet laser exhibits good beam quality as well as acceptable power stability with the maximum power fluctuation less than 2% within 4.5 h.

Controllable multi-polarization laser beam generation and manipulation in a cylindrical cavity

The manipulation of spatial and polarization attributes in vector laser beams can be intricately controlled through a variety of methodologies including spatial light modulators, q-plates, optical cavities, and mode-selective coupling. Among these techniques, optical cavities exhibit notable merits as they enable the targeted amplification of desired polarization elements with significant efficiency and stability. This research article introduces a direct methodology to generate multiple polarized laser beams, leveraging a cylindrical laser cavity housing a birefringent c-cut Nd:YVO4 gain crystal. This technique facilitates the creation of Hermite-Gaussian modes exhibiting distinct polarization states. By exploiting specific geometrical arrangements involving optical Z-mode and W-mode, the degenerate laser cavity facilitates the concurrent production of numerous distinguishable elliptically and linearly polarized beams, obviating the necessity for supplementary optical components. Notably, this approach provides advanced control over the polarization of resulting beams through precise adjustments of pumping offset and cavity length. The polarization states are subjected to quantitative scrutiny through phase retardation analysis. This investigation introduces an innovative avenue for the generation of coherent multi-beams, thereby propelling progress across a wide spectrum of scientific and technological domains.

Polarization aberration analysis and suppression of an infrared remote sensing optical system based on a digital micro-mirror device

The off-axis polarized infrared remote sensing imaging system based on a digital micro-mirror device (DMD) is capable of obtaining super-resolution images and enhancing the acquisition of target details. Polarization aberrations can reduce system resolution and affect target detection accuracy, it is more obvious in infrared imaging optical systems with small F-numbers and large incidence angles. It is complex to analyze and suppress the inherent polarization aberrations of infrared optical systems. To address this challenge, we propose a simplified polarization analysis method to get the aberration coefficients by using the specific pupil’s aberration value. The ray sampling rate of simplified method is 0.02 times that of traditional method, and the accuracy is almost unchanged. A method using weak polarization elements to suppress polarization aberrations is developed. Compared to the values before suppression, there is a reduction of more than 50% in diattenuation and retardance under different wavelength and fields. The shift of PSF centroid reduces over 55%, and the ellipticity of PSF decreases over 40%. Furthermore, the implementation of this technique has resulted in 28% improvement in the accuracy of measuring the degree of linear polarization (DoLP) of the optical system.

About Some Aspects of Use of Optical Sensors for Monitoring the Aquatic Environment

Multi-channel polarization optical technology is increasingly used for prompt monitoring of water systems. Optical devices during the assessment of water quality determine the intensity of light through the studied aquatic environment. Spectrophotometric devices measure the spectrum of weakening of light through the aquatic environment. Spectroellipsometric devices receive spectra in vertical and horizontal polarizations. The presented article develops an adaptive optical hardware and image system for monitoring water bodies. The system is combined. It consists of 2 parts: 1) automated spectrophotometer-refractometer, and 2) adaptive spectroellipsometer. The system is equipped with a corresponding algorithmic and software, including algorithms for identifying spectral curves, databases and knowledge of spectral curves algorithms for solving reverse problems. The presented system is original since it differs from modern foreign systems by a new method of spectrophotometric and spectroellipsometric measurements, an original elemental base of polarization optics and a comprehensive mathematical approach to assessing the quality of a water body. There are no rotating polarization elements in the system. Therefore, this makes it possible to increase the signal-to-noise ratio and, as a result, improve measurement stability and simplify multichannel spectrophotometers and spectroellipsometers. The proposed system can be used in various water systems where it is necessary to assess water quality or identify the presence of a certain set of chemical elements.

Hot‐Electron Driven Ultrafast Optical Polarization Conversion with Graphene‐Loaded Metasurface

AbstractThe switching speed of light polarization plays a crucial role in determining the upper‐limit bandwidth of applications like optical communications and laser microscopy. However, conventional polarization elements based on macroscopic anisotropic crystals like birefringent crystals and chalcogenide glasses are either static or restricted by the low switching time of about hundreds of picoseconds. Here, a femtosecond‐scale all‐optical polarization controlling method is proposed through engineering the excited hot electrons in a graphene‐loaded metasurface. Remarkably, a giant polarization orientation from left‐handed polarization (LCP) to right‐handed polarization (RCP) in the Poincaré sphere (≈80° rotation) is realized within only 200 fs in the mid‐infrared. With pumping, the dedicated polarization‐sensitive design allows the metasurface to exhibit a consistent resonance blueshift as the transient increase of the hot‐electron temperature in graphene for y‐polarized incidence. This polarization conversion approach features a giant modulation range and enables the reflected light to be dynamically and arbitrarily modulated into RCP, LCP, and linear states at femtosecond timescale. A few logic operations “AND”, “OR”, “NAND”, and “XOR” based on this method are also demonstrated by monitoring the normalized Stokes parameters. It is believed that this work may find practical application in next‐generation signal‐processing systems with large capacity.

Troubleshooting spectral artifacts from biplate retarders for reliable Stokes spectropolarimetry.

Polarimetry is generally used to determine the polarization state of light beams in various research fields, such as biomedicine, astronomy, and materials science. In particular, the rotating quarter-wave plate polarimeter is an inexpensive and versatile option used in several single-wavelength applications to determine the four Stokes parameters. Extending this technique to broadband spectroscopic measurements is of great scientific interest since the information on light polarization is highly sensitive to anisotropic phenomena. However, the need for achromatic polarizing elements, especially quarter-wave plates, requires special attention in their modeling. In this study, we implemented a rotating retarder spectropolarimeter for broadband measurements using a commercially available quasi-achromatic biplate retarder over the visible range. Here, we present a comprehensive approach for troubleshooting this type of spectropolarimeter through the observation of artifacts stemming from the standard single-plate retarder model. Then, we derive a more suitable model for a quasi-achromatic retarder consisting of a biplate junction. This new biplate model requires knowledge of the intrinsic dispersive properties of the biplate, namely the equivalent retardance, fast axis tilt, and rotatory angle. Hence, in this study, we also show a self-consistent methodology to determine these biplate properties using the same polarimeter apparatus so that accurate Stokes parameters can be determined independently. Finally, the comparison of data generated with the standard single-plate and new biplate models shows a significant improvement in the measurement precision of the investigated polarization states, which confirms that remodeling the retarder for reliable spectropolarimetry is necessary.

Wideband High-Efficiency Transmitarray Antenna Using Compact Double-Layer Dual-Linearly Polarized Elements

In this letter, we propose a wideband high-efficiency transmitarray antenna (TAA) consisted of compact double-layer dual-linearly polarized elements. By loading L-shaped branches and four vias, these elements achieve a low transmission loss and full phase shift in a wide frequency band. Then, an optimization method for calculating the wideband average element loss is introduced, which determines the element distribution on the transmitarray aperture. For verification, a TAA prototype consist of 400 elements is fabricated and measured. The peak gain and aperture efficiency measured at 12 GHz are 27.1 dBi and 52.5%, respectively. The measured 1-dB gain bandwidth is 20.4% and the minimum aperture efficiency achieved across the 1-dB gain bandwidth is 33%. The results reveal that the proposed TAA exhibits the advantages of flat gain bandwidth, high aperture efficiency, low profile, and low cost, endowing it with the potential for conformal applications and the capability to reliably connect satellite links as a communication antenna.

Connecting the microscopic depolarizing origin of samples with macroscopic measures of the Indices of Polarimetric Purity

In this work we show how a specific set of three depolarizing observables, the Indices of Polarimetric Purity (IPP), P1, P2 and P3, are ideal metrics to study the depolarization characteristic of media. We simulate different depolarizing scenarios, based on different depolarizing origins, and we study the corresponding IPP values. The simulations are based on the incoherent addition of multiple elemental polarizing elements, as ideal polarizers and/or retarders with different specific characteristics (orientation, retardance, transmittance, etc.). Further depolarizing scenarios are also studied by including the effect of ideal depolarizers. We show for the first time how by analyzing depolarizing systems through IPP we unravel two different depolarizing origins: isotropic and anisotropic depolarization, with meaningful physical interpretation. The former, isotropic depolarization is related to pure scattering processes, and mainly connected with P3 observable. The later, anisotropic depolarization is originated by microscopic constituent elements showing polarimetric anisotropy (dichroic and/or birefringent elements with different characteristics) and anisotropic scattering produced by these elements, and mainly described by P1 and P2 observables. Both effects can be simultaneously observed in real samples and give us information of the processes that give rise to depolarization in light-matter interactions. The simulated results are experimentally validated by analyzing the depolarizing behavior, in terms of IPP, of diverse real samples with easy physical interpretation, and direct connection with simulations. The present study could be of interest in multiple scenarios, to further understand the depolarizing response of samples, and it can be of special interest for the study of biological tissues and pathologies, as they present important depolarizing behavior.

Dependence of Solar Cell ESD Voltage Threshold on Cover Glass Secondary Emission Properties

Spacecraft interacts with the charged particles of the space environment, leading to their electrostatic charging. This charging depends on the surface materials and their exposure to space. Thus, it is different for different parts of the spacecraft. This differential charging is particularly important on solar panels, which are composed of various polarized elements juxtaposed over small distances. This leads to strong electric fields ultimately leading to electrostatic discharges (ESDs), themselves being the onset of destructive secondary arcs. Hence, controlling the onset of ESDs is a key factor to prevent damages on spacecraft. Two ways are generally envisioned to act on the ESD onset: the geometry of the solar cells and the material electrostatic properties. In this article, the control of the ESD onset is tackled through the study of the effects of the cover glass secondary emission properties on the voltage threshold of solar cell ESDs. This study is conducted numerically with the spacecraft plasma interaction software (SPIS)-ESD software, as the natural variability of physical samples and the impossibility to have materials with controlled characteristics render the experimental study unpractical, if even feasible.

Harnessing disordered photonics via multi-task learning towards intelligent four-dimensional light field sensors

The complete description of a continuous-wave light field includes its four fundamental properties: wavelength, polarization, phase and amplitude. However, the simultaneous measurement of a multi-dimensional light field of such four degrees of freedom is challenging in conventional optical systems requiring a cascade of dispersive and polarization elements. In this work, we demonstrate a disordered-photonics-assisted intelligent four-dimensional light field sensor. This is achieved by discovering that the speckle patterns, generated from light scattering in a disordered medium, are intrinsically sensitive to a high-dimension light field given their high structural degrees of freedom. Further, the multi-task-learning deep neural network is leveraged to process the single-shot light-field-encoded speckle images free from any prior knowledge of the complex disordered structures and realizes the high-accuracy recognition of full-Stokes vector, multiple orbital angular momentum (OAM), wavelength and power. The proof-of-concept study shows that the states space of four-dimensional light field spanning as high as 1680=4 (multiple-OAM) times2 (OAM power spectra) times15 (multiple-wavelength) times14 (polarizations) can be well recognized with high accuracy in the chip-integrated sensor. Our work provides a novel paradigm for the design of optical sensors for high-dimension light fields, which can be widely applied in optical communication, holography, and imaging.

All fiber optic current sensor based on phase-shift fiber loop ringdown structure.

An all fiber optic current sensor (AFOCS) utilizing ordinary optical fiber is proposed and demonstrated, which is implemented with a phase-shift fiber loop ringdown (PS-FLRD) structure. The current-induced rotation angle is converted into a minute change in transmittance of the fiber loop, which can be obtained by measuring the phase shift. The current sensitivity is improved by allowing optical signals to traverse the sensing fiber repeatedly. The relationship between the current sensitivity, intrinsic phase shift, and initial transmittance of the fiber loop is numerically analyzed, and the tunable sensitivity is experimentally verified by adjusting the modulation frequency. An optimal current sensitivity of 0.8158°/A is experimentally obtained for the proposed sensor, and the minimum detectable current is at least 100 mA. The proposed sensor requires fewer polarization elements compared with the common type of fiber optic current sensor (FOCS) and has the characteristics of simple structure, high sensitivity, and ease of operation; it will be a promising approach in practical applications.

P‐2.30: Design and Fabrication of an Optical Path Folding Pancake Virtual Reality Head‐mounted Display

Metaverse has been going viral across the globe, and virtual reality head‐mounted displays (VR‐HMDs) as the basic infrastructure and entrance to cater to this evolution of social interaction are showing rapid development recently. Pancake optics based on optical path folding provides the feasibility of VR‐HMDs in the form of glasses and is wide recognition. The pancake system has become the current mainstream owing to its large exit pupil diameter (EPD), high resolution, novel compact, and lightweight. Owing to the use of polarization elements, the birefringence in the lens will change the polarization state of the light, resulting in uneven brightness and stray light, seriously reducing the optical performance of the system, so it is necessary to control the birefringence of the lens. In this study, we proposed a pancake system based on a 2.1‐inch LCD display which achieves 10 mm EPD at 11 mm, diagonal field of view (FOV) of 96°, overall length (OAL) of the system less than 20 mm, and support diopter adjustment from ‐7D to ‐1D. The residual birefringence of the lens can be effectively suppressed in four stages: 1) controlling the thickness ratio between the center and the edge of the lens during the optical design, 2) setting a reasonable position and size of the injection gate and cooling system during the mold design process, 3) adopting reasonable injection parameters during the precision injection molding process and 4) eliminating the birefringence of the lens with the lens annealing process. Ultra‐precision machining and correction of the mold cores have been employed to achieve high surface accuracy and low birefringence of the lens. The optomechanical design, assembly, and adjustment process are discussed. Finally, the prototype of the pancake system is experimentally tested, and the results demonstrate pretty well.

Simultaneously characterized Stokes parameters of a lightwave utilizing the tensor polarization holography theory.

Polarization is a natural property of a lightwave and makes a significant contribution to various scientific and technological applications, due to the different states of polarization (SoP) of a lightwave that may manifest distinct behaviors. Hence, it is important to determine the SoP of the lightwave. Generally, the SoP of a lightwave can be recognized by the Stokes parameters. In this paper, we proposed a novel method to simultaneously characterize the Stokes parameters of a lightwave, by employing the tensor polarization holography theory. This is done through merely a piece of polarization-sensitive material. Compared with the traditional method, this method requires only one measurement to obtain all the Stokes parameters, without using additional polarizing elements. The experimental result shows excellent agreement with the theoretical one, which confirmed the reliability and accuracy of the proposed method. We believe that this work may broaden the application field of polarization holography.

Polarization beam splitting in a Glan-Taylor prism based on dual effects of both birefringence and Goos-Hanchen shift

With the structure of biprism, polarization beam splitting in a Glan-Taylor polarizer was explored based on the birefringence and Goos-Hanchen shift. Due to the birefringence of the light in calcite crystal, the extraordinary light worked as the position calibration. As for the ordinary light, the propagated direction tilted noticeably due to the refraction as well as Goos-Hanchen effect at the prism-air interface of in the air gap. The Snell's law and stationary-phase approach were utilized for the calculation of the beam splitting between the two orthogonal polarization elements. By choosing appropriate incident angle and initial polarization, remarkable beam splitting was realized. With this configuration, the resolution with a magnitude of 10−5° and 10−3° was achieved for the response of the incident angle and polarization detection respectively.