Wire-grid Polarizer Research Articles

P‐68: Student Poster: A Miniaturized Polarization‐multiplexed Dual‐plane Head‐mounted Display System for Augmented Reality

A dual‐plane head‐mounted display system based on polarization‐multiplexing is proposed. A metal wire grid polarizer is employed to separate the two orthogonal polarizations to different optical paths due to its excellent polarization‐selective characteristics within large angle and spectrum ranges. System parameters including the curvatures of the reflective mirrors and the aspheric lens have been optimized to achieve good image quality within a field of view of ~ 50 degrees at different focal depths. Our system could provide correct depths for full‐color 3D images, so that the vergence‐accommodation conflict and visual fatigue problems could be solved.

An Interlaced Grid Dual-Band Dual-Polarized Bandpass FSS With a Large Band Ratio

Based on an interlaced grid arrangement, a dual-band dual-polarized bandpass frequency selective structure (FSS) with a large band ratio (BR) is proposed in this letter. The FSS is assembled from vertical layers arranged along <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> - and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> -directions, and the vertical layers arranged along the two orthogonal directions are polarization independent. The grating structures printed on the vertical layers form a higher frequency passband, and by having additional wire-grid polarizers with a high-pass response, a lower frequency passband is formed. The proposed interlaced grid FSS is a combination of two square grid FSSs. Since the distance between adjacent vertical layers is smaller than that of the square grid FSS, the proposed FSS has a wider bandstop response to achieve the design of a large BR. The measured results show that for both TE and TM polarizations, the center frequencies of the two passbands are 2.5 GHz and 15.5 GHz, respectively, with a corresponding BR of 6.2.

Simulation of Resonant Cavity-Coupled Colloidal Quantum-Dot Detectors with Polarization Sensitivity

Infrared detectors with polarization sensitivity could extend the information dimension of the detected signals and improve target recognition ability. However, traditional infrared polarization detectors with epitaxial semiconductors usually suffer from low extinction ratio, complexity in structure and high cost. Here, we report a simulation study of colloidal quantum dot (CQD) infrared detectors with monolithically integrated metal wire-grid polarizer and optical cavity. The solution processibility of CQDs enables the direct integration of metallic wire-grid polarizers with CQD films. The polarization selectivity of HgTe CQDs with resonant cavity-enhanced wire-grid polarizers are studied in both short-wave and mid-wave infrared region. The extinction ratio in short-wave and mid-wave region can reach up to 40 and 60 dB, respectively. Besides high extinction ratio, the optical cavity enhanced wire-grid polarizer could also significantly improve light absorption at resonant wavelength by a factor of 1.5, which leads to higher quantum efficiency and better spectral selectivity. We believe that coupling CQD infrared detector with wire-grid polarizer and optical cavity can become a promising way to realize high-performance infrared optoelectronic devices.

Design of the cross-polarization scattering diagnostic on the HL-2A tokamak

A new cross-polarization scattering (CPS) diagnostic has been developed on HL-2A, which aims to measure the local magnetic fluctuation inside the plasma. It is based on the scattering of an incident microwave beam into the perpendicular polarization by magnetic fluctuations. The CPS diagnostic has been designed in the Q-band (33–50 GHz), which consists of the electronic system, quasi-optical, and polarization rejector. The ray-tracing code is used to simulate the propagation of the probe and scattered rays. To test the performance of the quasi-optical system, a 3D test platform is built and detailed test results are shown. Two methods are developed for polarization rejector on HL-2A: wire grid polarizer and dual-polarized horn antenna (DPHA). The laboratory test result shows that the polarization rejection of both methods is better than 30 dB, which meets the needs for magnetic fluctuation detection. In the future, the CPS diagnosis will be used to study the electromagnetic turbulence behavior in the high-performance plasma of the HL-2A tokamak.

Use of wire grid polarizers with liquid crystal display for large-volume stereolithography

Spatial light modulators that use liquid crystal devices (LCDs) to pattern ultraviolet light for vat polymerization suffer from a few limitations: limited range of wavelengths that can be patterned, low damage threshold for incoming light, and low efficiency of light transmission. A monochrome LCD can more efficiently transmit useful wavelengths of light for stereolithography (365–405 nm) than a color LCD, but it still contains two absorptive film polarizers that suffer from the aforementioned limitations. Wire grid polarizers reflect rather than absorb the blocked polarizations of light, resulting in a higher intensity damage threshold. They can also polarize lower wavelength light that is limited only by the wire pitch. This research investigates the effects of replacing an LCD’s film polarizers with wire grid polarizers to enable polarization and patterning of high intensity UV light, resulting in shorter curing times and the ability to print a wider range of stereolithography feedstocks.

300 mm Large Area Wire Grid Polarizers with 50 nm Half-Pitch by ArF Immersion Lithography

The large area wire grid polarizers (LA-WGPs) with 50 nm half-pitch were fabricated using ArF immersion lithography overcoming the limit of the shot field size. To realize the 50 nm line and space patterns on a 300 mm wafer, a zero-distance stitching process that connects the shot fields is suggested. To compensate for mutual interference between the shot fields which is called the local flare effect (LFE), the shot field arrangement is changed with optical proximity correction (OPC). Using a master wafer produced by the suggested method, 300 mm large-area WGPs were fabricated by the nano-imprint process. The WGPs have more than 80% transmittance in the visible light region, and the possibility of performance improvement can be confirmed depending on the number and method of the etch process.

Patterned achromatic elliptical polarizer for short-wave infrared imaging polarimetry

Short-wave infrared (SWIR) imaging polarimetry has widespread applications in telecommunication, medical imaging, surveillance, remote-sensing, and industrial metrology. In this work, we design, fabricate, and test an achromatic SWIR elliptical polarizer, which is a key component of SWIR imaging polarimetry. The elliptical polarizer is made of a patterned linear polarizer and a patterned optical elliptical retarder. The linear polarizer is a wire grid polarizer. The elliptical retarder is constructed with three layers of nematic phase A-plate liquid crystal polymer (LCP) films with different fast axis orientations and physical film thicknesses. For each LCP layer, four arrays of hexagonal patterns with individual fast-axis orientations are realized utilizing selective linearly polarized ultraviolet (UV) irradiation on a photo-alignment polymer film. The Mueller matrices of the optical filters were measured in the wavelength range 1000 nm to 1600 nm and compared with theory. Our results demonstrate the functionality and quality of the patterned retarders with normalized analyzer vector parameter deviation below 7% over this wavelength range. To the best of our knowledge, this work represents the first polymer-based patterned elliptical polarizer for SWIR polarimetry imaging applications.

A high-performance terahertz back-reflections blocker based on wire grid and metasurface quarter-wave plate

Terahertz back-reflections blocker is a kind of device that effectively isolated the harmful reflected waves in an optical system, and plays an important role in the applications of terahertz transmission and communication. In this paper, a high-performance terahertz back-reflections blocker based on the metal wire grid polarizer and metasurface quarter-wave plate is demonstrated. By designing the metasurface with high-efficiency polarization conversion and low loss, the maximum blocking efficiency reaches 50.7 dB at 1.51 THz, and the blocking efficiency bandwidth of 20 dB reaches 280 GHz in the experiment. The combination of a metasurface quarter-wave plate and a wire grid polarizer is simple in construction and has low requirements for the operating environment, such as no magnetic field, low temperature and other conditions. Moreover, the ultra-thin nature of the metasurfaces makes this high-efficiency and low-loss back-reflections blocker have broad application prospects in the field of THz integrated on-chip systems.

Fabrication influences on a miniaturised stokes polarimeter consisting of stacked nano-optical wire grid polarizer and retarders

The polarization properties of light can be fully controlled with nano-optical wire grid polarizers and artificial birefringent grating structures. We demonstrate an integrated polarimeter based on stacked layers of such elements. However, the optical performance of such elements is fundamentally limited and may be further altered by deviations arising from the fabrication processes. In this contribution we investigate the influences on the polarimetry performance for such a device.

Enhancement in the extinction ratio of a wire grid polarizer in the mid-wavelength infrared range via hot electron diffused cold-annealing

Theoretical and experimental investigations were performed on the fabrication and polarization property enhancement of a single-layer Au grating serving as a wire grid polarizer (WGP) in the mid-wavelength infrared (MWIR) range. Femtosecond laser (FSL) annealing was performed to overcome the performance limitations of the WGP fabricated by nanotransfer printing (NTP), and the results were compared with those of the conventional thermal annealing methods using scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. Consequently, the extinction ratio of the WGP annealed with FSL reached up to 1378 (∼31 dB) in the 3–5 μm wavelength range, which corresponds to a 2.18-fold improvement over the non-annealed WGP. This result suggests that it is possible to manufacture MWIR WGPs at a low cost and over large areas through a simple NTP and FSL annealing process, ultimately yielding WGPs with improved performances.

Terahertz linear polarizers fabricated using magnetorheological fluid

In this work, we fabricated a metacomposite using magnetorheological fluid, in which Fe nanoparticles dispersed in silica gel spontaneously aligned under a magnetic field to form chain-like grids, thus working as a wire-grid polarizer. A single-layer polarizer was fabricated by mixing silica gel, silicone oil, high-purity spherical Fe powder with about 100 nm in diameter, followed by spin-coating and curing the mixture under a uniform magnetic field to form a solid matecomposite layer on a Teflon substrate. The polarizer was characterized by terahertz time-domain spectroscopy, showing good anisotropy and polarizing characteristics. Its performance was improved by multiple-layer stacking. The extinction ratio and degree of polarization of a five-layer polarizer are above 20 dB and 0.95 respectively in a frequency range of 0.8–2 THz.

Introduction of a 3 × 4 Mueller matrix decomposition method

A Mueller matrix can completely characterize the polarimetric properties of a medium, where the parameters of depolarization, retardance and diattenuation can be obtained by decomposing a Mueller matrix with existing decomposition methods. The introduction of polarization sensitive cameras with integrated wire-grid polarizers has allowed for the fast acquisition and analysis of four linear states within a single snapshot. Moreover, these cameras provide the opportunity to capture a reduced 3 × 4 Mueller matrix with the acquisition of generated states polarization in the illumination arm. In order to measure and characterize samples using a reduced 3 × 4 Mueller matrix, a 3 × 4 decomposition algorithm is introduced. This new algorithm is compared and validated against established 4 × 4 decompositions. The validation of this algorithm is shown using a previously reported Mueller matrix of polyacrylamide phantom, and experimental Mueller matrices of quarter-wave plates, silicone phantoms and a skin model sample. The 3 × 4 decomposition compares well to established decompositions and is capable of characterizing the samples based on the calculation of depolarization, retardance and orientation.

Polarization modeling and predictions for DKIST, part 8: calibration polarizer spatial variation impacts

Astronomical spectropolarimeters require high accuracy polarizers with large aperture and stringent uniformity requirements. In solar applications, wire grid polarizers are often used as performance is maintained under high heat loads and temperatures over 200°C. DKIST is the NSF’s new 4-m aperture solar telescope designed to deliver accurate spectropolarimetric solar data across a wide wavelength range, covering a large field of view simultaneously using multiple facility instruments. Polarizers at 120 mm diameter are used to calibrate DKIST instruments but vary spatially in transmission, extinction ratio, and orientation of maximum extinction. We combine new spatial and spectral metrology for polarizers and retarders to simulate the accuracy losses with field angle and wavelength caused simultaneously by spatial variation of several optical parameters including beam decenter from misalignments. We also present testing of a new crystal sapphire substrate polarizer designed and fabricated to improve DKIST long wavelength calibrations. We assess spatial thickness variation of sapphire and fused silica wafer substrates using spectral interference fringes.

Wire grid polarizer-based cyclic shearing interferometer with polarization phase shifting

Imaging of transparent phase samples using a wire grid polarizer (WGP)-based shearing interferometer is demonstrated. The proposed setup employs a WGP as a beam splitter in a triangular cyclic interferometer setup, so that the two counterpropagating beams are rendered linearly polarized in orthogonal directions as they emerge from the interferometer. These sheared waved fronts are made to pass through the phase sample. The magnitude of shear is affected by controlled angular shifts of one mirror about the reference X and Y axes. For each of these directional shears, the polarization phase shifting is implemented so as to generate a three-dimensional phase pattern, which is digitally combined and integrated to yield the sample phase. The proposed setup is robust, sufficiently tolerant to ambient vibrations, and shows very encouraging experimental results.

Polarization analysis of random THz lasers

By varying the geometrical filling factor from 8% to 12% and the hole radius from 3 to 5 µm, we investigate the interference pattern of a set of surface emitting, electrically pumped random lasers (RLs) at terahertz frequencies employing a surface pattern of random holes, studying the polarization of the emitted modes, the spectral emission, and the power extraction. By funneling the laser beams onto a wire grid polarizer, we demonstrate spectral reshaping of the RL emission and of the far-field profile, achieving highly collimated emission (5° × 3° angular divergence) and a spectral coverage of 340 GHz with up to 11 random lasing modes. The polarization analysis of the far-field and spectral characteristics of the laser offer an interesting tool to investigate the complex behavior of quantum cascade RLs, providing a route to engineer the emission of RLs in more detail.

A finite element model of terahertz substrate-based wire-grid polarizer

Using the finite element approximation of electromagnetic wave propagation problem in frequency domain analysis, we have developed and implemented a finite element model of a terahertz substrate-based wire grid polarizer in a form of unit cell. The proposed polarization unit cell is considered as a waveguide with a specific boundary condition. The model is implemented by the COMSOL software system as a ready to use tool for terahertz polarizers design or refinement. Simulation results show an excellent agreement with known experimental and simulation data.

High-volume rapid prototyping technique for terahertz metallic metasurfaces.

Terahertz technology has greatly benefited from the recent development and generalization of prototyping technologies such as 3D printing and laser machining. These techniques can be used to rapidly fabricate optical devices for applications in sensing, imaging and communications. In this paper, we introduce hot stamping, a simple inexpensive and rapid technique to form 2D metallic patterns that are suitable for many terahertz devices. We fabricate several example devices to illustrate the versatility of the technique, including metasurfaces made of arrays of split-ring resonators with resonances up to 550 GHz. We also fabricate a wire-grid polarizer for use as a polarizing beam splitter. The simplicity and low cost of this technique can help in rapid prototyping and realization of future terahertz devices.

Комбінований числово-аналітичний метод параметричного проєктування тера¬герцового підкладкового поляризатора на підставі дротяних сіток

Розглянуто комбінований числово-аналітичний метод параметричного проєктування підкладкового поляризатора терагерцового електромагнітного випромінювання, побудованого на підставі дротяних сіток. Здійснено літературний огляд порівняльних характеристик можливих конструкцій поляризаторів різних типів та описано перевагу конструкцій на підставі дротяних сіток. Наведено огляд матеріалів, що використовують для виготовлення відповідних поляризаторів для різної довжини хвилі випромінювання. Проаналізовано методи, що застосовують для розрахунку характеристик і параметрів поляризаторів на підставі дротяних сіток. Розроблений числово-аналітичний метод параметричного проєктування базується на аналітичному розрахунку ефективних антивідбивних характеристик конструкції елементарної комірки поляризатора. У межах методу розроблено скінченно-елементну модель поляризатора, реалізовану за допомогою програмного забезпечення COMSOL Multiphysics, що дає змогу уточнити характеристики конструкції елементарної комірки і можливості для їх розширення за допомогою числового моделювання методом скінченних елементів задачі поширення електромагнітних хвиль у цій конструкції в частотній області зі специфічними граничними умовами, що сукупно дає наукову новизну. Отримані результати моделювання добре узгоджуються з відомими експериментальними результатами та тісно корелюють з результатами моделювання, що отримали інші наукові групи, що свідчить про адекватність та практичну цінність методу для завдань проєктування поляризаторів терагерцового випромінювання з антивідбивними, високопропускними, низьковтратними та надійними характеристиками. Окрім цього, завдяки використанню числової скінченно-елементної складової, запропонований метод досить просто розширити способом зміни геометрії елементарної комірки для дослідження таких перспективних об'єктів, як багатошарові поляризатори чи поляризатори на підставі складніших мета- чи композиційних матеріалів.

Low-reflective wire-grid polariser sheet in the visible region fabricated by a nanoprinting process

For the construction of next-generation optical products and systems, the evolution of polariser sheets is a necessary requirement. To this end, a low-reflective wire-grid polariser (WGP) sheet for the visible light region is demonstrated, the nanowires of which consist of a sintered body of silver nanoparticle ink. The nanowires are formed by a nanoprinting process using a thermal nanoimprint method and ink filling. This process makes it easier to achieve multiple wafer-scale productions without using sophisticated equipment compared to conventional WGP nanofabrication techniques, which typically employ lithography and elaborate etching processes. The optical characteristics are controlled by the shape of the printed nanowires. A WGP sheet with a luminous degree of polarisation of 99.0%, a total luminous transmittance of 13.6%, and a luminous reflectance of 3.6% is produced. Its low reflectance is achieved through the uneven surface derived from the sintered body of the nanoparticle ink, and the shape of the bottom of the nanowire is derived from the tip shape of the mould structure. Furthermore, the printed WGP sheet has the durability required for the manufacturing of curved products, including sunglasses. The optical structures made of nanoparticle ink using this nanoprinting process have the potential to significantly contribute to the development of fine-structured optical elements with unprecedented functionality.

Experimental study of terahertz radiation driven by femtosecond ultraintense laser

Powerful terahertz (THz) radiation sources are crucial to the development of THz science. High-energy strong-field THz pulses have many significant applications such as in the ultrafast control of matter and the THz-driven electron acceleration. In recent years, ultraintense laser-plasma interactions have been proposed as a novel approach to strong-field THz generation. In this paper, the experimental results are presented about the generation of THz radiation from a solid foil irradiated by a 10-TW femtosecond laser pulse. The THz energy as a function of laser energy and defocusing amount is studied. It is found that both the THz energy and the laser-to-THz conversion efficiency increase nonlinearly with the laser energy increasing. At maximum laser energy ~270 mJ, the measured THz pulse energy is 458 μJ, corresponding to a laser-to-THz energy conversion efficiency of 0.17%. No indication of saturation is observed in the experiment, implying that a stronger THz radiation could be achieved with higher laser energy. By simultaneously monitoring the backward scattered laser light spectrum, it is qualitatively understood that the observed THz radiation as a function of laser energy and laser defocusing distance is closely related to the electron heating mechanisms at different laser intensities. The THz spectrum and polarization are characterized by using different band-pass filers and a wire-grid polarizer, respectively. The THz radiation covers an ultrabroad band ranging from 0.2 THz to 30 THz, and shows a radially polarized distribution. By fitting the measured THz spectrum with the theory of coherent transition radiation, the THz pulse duration is inferred to be about 30 fs. At the THz focal spot of ~1 mm in size, the THz field strength is evaluated to be 3.68 GV/m. Such a strong-field THz source will enable the study of extreme THz-matter interactions.