Circular Polarization Filters Research Articles

Twisted hyperbolic van der Waals crystals for chip-scale full Stokes mid-infrared polarization detection

Abstract Investigating the polarization properties of light in the mid-infrared (mid-IR) spectrum is crucial for molecular sensing, biomedical diagnostics, and IR imaging system technologies. Traditional methods, limited by bulky size and complicated fabrication process, utilize large rotating optics for full Stokes polarization detection, impeding miniaturization and accuracy. Naturally occurring hyperbolic van der Waals (vdW) material based devices can address these challenges due to their lithography-free fabrication, ease of integration with chip-scale platforms and room-temperature operation. This study designs a chip-integrated polarimeter by performing multi-objective optimization for efficient exploration of the design parameter space. The spatial division measurement scheme used incorporates six precisely designed linear and circular polarization filters, achieving high extinction ratios exceeding 30 dB and transmittance surpassing 50%, with fabrication tolerance of film thickness up to 100 nm. The proposed device represents a significant advancement in polarimetric detection, providing a compact, cost-effective solution and opens new avenues for on-chip mid-IR polarimetric detection in next-generation ultra-compact optical systems.

Single-double-band switchable optical circular polarizers based on surface plasmon resonance.

A single-double-band switchable circular polarization filter based on surface plasmon resonance exhibits significant potential for applications in fields such as communication and sensing due to its adjustable, low-cost, and easy integration features. In this study, we propose a bi-layer rod nanostructure and use FEM simulation to study the transmission spectra of the structure. The results demonstrate that the structure exhibits both single- and double-band circular polarization filtering effects, which can be switched by varying geometric parameters such as the distance between the two layers and the width of nanorods. Furthermore, the filtering effects of both single- and double-band are highly dependent on the length of the nanorods, with average extinction rates reaching 486 and 2020/129, respectively; the operating bandwidths (defined as extinction ratio >10) can reach 170nm and 35nm/70nm, respectively. The underlying physical mechanisms are clarified by analyzing the electric dipole, magnetic dipole resonance modes, and induced chiral fields on nanostructures.

Large-area ultracompact pixelated aluminum-wire-grid-based metamaterials for Vis-NIR full-Stokes polarization imaging

The study of pixelated metamaterials that integrate both the functions of linear and circular polarization filters is rapidly growing due to the need for full-Stokes polarization imaging. However, there is a lack of large-area, ultracompact pixelated full-Stokes metamaterials with excellent performance, especially circular polarization filters with a high extinction ratio, a broad operating bandwidth, and a low-cost, high-quality, efficient manufacturing process, which limits the practical applications of pixelated full-Stokes metamaterials. In this study, we propose a universal design and fabrication scheme for large-area, ultracompact pixelated aluminum wire-grid-based metamaterials used in Vis-NIR full-Stokes polarization imaging. The aluminum wire-grid was designed as a linear polarization filter with an average linear polarization extinction ratio of 36,000 and a circular polarization filter with an average circular polarization extinction ratio of 110 in Vis-NIR. A large-area, ultracompact 320×320 pixelated aluminum wire-grid-based full-Stokes metamaterial was fabricated using nanoimprint lithography and nano transfer printing with the advantages of low cost and high efficiency. This metamaterial was used to achieve full-Stokes polarization imaging with errors within 8.77%, 12.58%, 14.04%, and 25.96% for Stokes parameters S0, S1, S2, and S3, respectively. The inversion errors of the compensated Stokes parameters can be reduced to 0.21%, 0.21%, 0.42%, and 1.96%, respectively.

High-performance full-Stokes polarization detection at exceptional point in a non-Hermitian metasurface

Polarization and its detection have attracted tremendous attention due to the rich information it provides and the practical applications it enables. Here, we propose a high-performance reflective pixelated metasurface with full-Stokes detection in the visible wavelength, which integrates both linear polarization (LP) and circular polarization (CP) filters on one platform. The system achieves a high extinction ratio for CP incidence in a non-Hermitian system, generated from the exceptional point (EP) effect. With integrated LP filters, full-Stokes detection can be obtained with accuracy and efficiency in real time. The EP-based innovation also promises other practical applications, such as polarization imaging technologies and optical computing.

Polarization-based optical characterization for color texture analysis and segmentation

• Hand-crafted texture characterization based on light polarization signatures. • Image segmentation relying on pixel based circular polarization signature. • Multispectral image (185 bands) with five total variation planes. • The Karhunen-Loeve transform and then k-means were applied to the 185 bands. • Superior segmentation accuracy (compared with classic k-means on RGB). Texture characterization is very useful for automatic analysis of object surface images for a plethora of applications in medicine, agriculture, industry or remote sensing. Various texture characterization techniques exist, from the classical Haralick descriptors, Gabor filters, local binary patterns to automatically-extracted features using machine learning models. We propose a new hand-crafted texture characterization technique, based on light polarization property, by deploying a circular polarization filter (rotated from 0° to 360° in steps of 10°) in the image acquisition process. The hypothesis is that different materials and surfaces will exhibit different polarization signatures defined as pixel values variation as a function of polarization angle. Such polarization signature is able to locally characterize texture as a consequence of light reflections captured in every pixel due to the texture intrinsic variations. We show the usefulness of our approach for surface/material classification for the purpose of color image segmentation of natural outdoor scenes.

Ruddlesden–Popper 2D Chiral Perovskite‐Based Solar Cells

In this work, 2D chiral perovskite is demonstrated, where the barrier molecules are the two enantiomers (R)‐(+)‐α‐Methylbenzylamine (R‐MBA) and (S)‐(‐)‐α‐Methylbenzylamine (S‐MBA). The chirality is manifested at high χ values and pure 2D structure measured by circular dichroism (CD) (where the perovskite general formula is ABX3 χ (S/R‐MBA)2PbI4, χ is the ratio of the barrier molecule to the small cation (A+)). The anisotropy factor (gabs) decreased by an order of magnitude when decreasing the χ value achieving 0.0062 for pure 2D. Ab initio many‐body perturbation theory successfully describes the bandgaps, absorbance, and CD measurements. For the first time, these quasi‐2D chiral perovskites are integrated into the solar cell. Using circular polarization (CP) and cutoff filter, the chirality effect from the solar cells photovoltaic response is able to be distinguished. It is revealed that at high χ values, the chirality affects the current density of the solar cell more than at low χ values while the open‐circuit voltage didn't change. These chiral 2D perovskite are new class of materials which open the way for polarized hybrid perovskite.

Highly Efficient Anisotropic Chiral Plasmonic Metamaterials for Polarization Conversion and Detection.

Plasmonic chiral metamaterials have attracted broad research interest because of their potential applications in optical communication, biomedical diagnosis, polarization imaging, and circular dichroism spectroscopy. However, optical losses in plasmonic structures severely limit practical applications. Here, we present the design concept and experimental demonstration for highly efficient subwavelength-thick plasmonic chiral metamaterials with strong chirality. The proposed designs utilize plasmonic metasurfaces to control the phase and polarization of light and exploit anisotropic thin-film interference effects to enhance optical chirality while minimizing optical loss. Based on such design concepts, we demonstrated experimentally optical devices such as circular polarization filters with transmission efficiency up to 90% and extinction ratio >180, polarization converters with conversion efficiency up to 90%, as well as on-chip integrated microfilter arrays for full Stokes polarization detection with high accuracy over a broad wavelength range (3.5-5 μm). The proposed design concepts are applicable from near-infrared to Terahertz regions via structural engineering.

High efficiency all-dielectric pixelated metasurface for near-infrared full-Stokes polarization detection

Pixelated metasurfaces integrating both the functions of linear polarization and circular polarization filters on a single platform can achieve full-Stokes polarization detection. At present, the pixelated full-Stokes metasurfaces mainly face the following problems: low transmission, low circular dichroism (CD) of circular polarization filters, and high requirements in fabrication and integration. Herein, we propose high performance ultracompact all-dielectric pixelated full-Stokes metasurfaces in the near-infrared band based on silicon-on-insulator, which is compatible with the available semiconductor industry technologies. Circular polarization filters with high CD are achieved by using simple two-dimensional chiral structures, which can be easily integrated with the linear polarization filters on a single chip. In addition, the dielectric materials have higher transmission than metal materials with intrinsic absorption. We experimentally demonstrated the circular polarization filter with maximum CD up to 70% at a wavelength of 1.6 μm and average transmission efficiency above 80% from 1.48 μm to 1.6 μm. Therefore, our design is highly desirable for many applications, such as target detection, clinical diagnosis, and polarimetric imaging and sensing.

Mueller matrix ellipsometry study of a circular polarizing filter

The authors introduce an ellipsometric data analysis strategy for a flexible polymeric circular polarizing filter consisting of a thin linear polarizer and quarter-wave plate sandwich. The circular polarizing filter is an inhomogeneous optical system exhibiting different optical responses depending on the propagation direction of light. If light enters from the linear polarizer, the transmitted beam is linearly polarized before entering the quarter-wave plate. The orientation of the quarter-wave plate is rotated 45° from the linear polarizer axis. The emerging light from the quarter-wave plate is circularly polarized. If light is circularly polarized and enters from the reserve side, the quarter-wave plate converts it into linearly polarized light. The following linear polarizer either transmits or absorbs the beam depending on the handedness of the original circular polarization. The optical response in the forward direction is utilized in photography to reduce unwanted reflections in the image. The optical response in the reverse direction is utilized in 3D eyeglasses, which consist of two orthogonal circular polarizing filters to separate the left and right images. Mueller matrix spectroscopic ellipsometry is used to observe the optical responses of a circular polarizing filter in both directions. The authors demonstrate data analysis procedures for individual layers to find the optical constants in a wide spectral range from 400 to 1700 nm. The circular polarizing filter measured in the forward direction enables ellipsometry to determine the included angle between the linear polarizer and the quarter-wave plate. The ellipsometric data analysis result is used to predict transmitted light intensity versus rotation angle (deg) with respect to any input polarization state.

Nature-inspired chiral metasurfaces for circular polarization detection and full-Stokes polarimetric measurements

The manipulation and characterization of light polarization states are essential for many applications in quantum communication and computing, spectroscopy, bioinspired navigation, and imaging. Chiral metamaterials and metasurfaces facilitate ultracompact devices for circularly polarized light generation, manipulation, and detection. Herein, we report bioinspired chiral metasurfaces with both strong chiral optical effects and low insertion loss. We experimentally demonstrated submicron-thick circularly polarized light filters with peak extinction ratios up to 35 and maximum transmission efficiencies close to 80% at near-infrared wavelengths (the best operational wavelengths can be engineered in the range of 1.3–1.6 µm). We also monolithically integrated the microscale circular polarization filters with linear polarization filters to perform full-Stokes polarimetric measurements of light with arbitrary polarization states. With the advantages of easy on-chip integration, ultracompact footprints, scalability, and broad wavelength coverage, our designs hold great promise for facilitating chip-integrated polarimeters and polarimetric imaging systems for quantum-based optical computing and information processing, circular dichroism spectroscopy, biomedical diagnosis, and remote sensing applications.

Chip-integrated plasmonic flat optics for mid-infrared full-Stokes polarization detection

Flat optics presents a new path to control the phase, amplitude, and polarization state of light with ultracompact devices. Here we demonstrate chip-integrated metasurface devices for polarization detection of mid-infrared light with arbitrary polarization states. Six high-performance microscale linear and circular polarization filters based on vertically stacked plasmonic metasurfaces (with total thickness <600 nm) are integrated on the same chip to obtain all four Stokes parameters of light with high accuracy. The device designs can be tailored to operate at any wavelength in the mid-infrared spectral region and are feasible for on-chip integration with mid-infrared (mid-IR) photodetectors and imager arrays. Our work will enable on-chip mid-IR polarimeters and polarimetric imaging systems, which are highly desirable for many applications, such as clinical diagnosis, target detection, and space exploration.

Producing true-color rainbows with patterned multi-layer liquid-crystal polarization gratings

We present the technical design of the art installation Rainbow Station, that projects a 40-m diameter true-color rainbow. The core technology is comprised of a patterned polarization grating that produces the rainbow with the correct shape and correct color order. We achieve an effective grating period as small as 1.55 µm, and obtain high diffraction efficiency over the entire visible spectral range thanks to a multi-layer liquid-crystal implementation. The -1 spectral order is suppressed by circular polarization filtering.

All-Fiber Circular Polarization Filter Realized by Using Helical Long-Period Fiber Gratings

A simple method to produce an all-fiber circular polarization filter is proposed and experimentally demonstrated, which is realized based on the utilization of two consecutively cascaded single-helix helical long-period fiber gratings but with opposite helicities (SHLPGs-OHs). The proposed SHLPGs-OH can be used as a circular polarizer as well as an equivalent half wave-plate, which enables us to turn a left-circular (right-circular) polarization light to a right-circular (left-circular) polarization one. As a concept-proof example, a polarization-converter with an extinction ratio (between the left- and the right-circular polarization light) of ~20 dB, insertion loss of ~10 dB, and a bandwidth of ~4 nm has been successfully demonstrated.

Chiral sculptured thin films for circular polarization of mid-wavelength infrared light.

Being an assembly of identical upright helices, a chiral sculptured thin film (CSTF) exhibits the circular Bragg phenomenon and can therefore be used as a circular polarization filter in a spectral regime called the circular Bragg regime. This has been already demonstrated in the near-infrared and short-wavelength infrared regimes. If two CSTFs are fabricated in identical conditions to differ only in the helical pitch, and if both are made of a material whose bulk refractive index is constant in a wide enough spectral regime, then the center wavelengths of the circular Bragg regimes of the two CSTFs must be in the same ratio as their helical pitches by virtue of the scale invariance of the frequency-domain Maxwell postulates. This theoretical result was confirmed by measuring the linear transmittance spectra of two zinc-selenide CSTFs with helical pitches in the ratio 1:7.97. The center wavelengths were found to be in the ratio 1:7.1, and the deviation from the ratio of helical pitches is explainable at least in part because the bulk refractive index of zinc selenide decreases a little with wavelength. We concluded that CSTFs can be fabricated to function as circular polarization filters in the mid-wavelength infrared regime.

Chiral All-Dielectric Metasurface Based on Elliptic Resonators with Circular Dichroism Behavior

We present the design of a new microwave all-dielectric chiral metasurface with circular dichroism behavior based on elliptic dielectric resonators (EDRs). During the design procedure, we have first optimized numerically the effects of the main design parameters such as the resonator’s size and orientation, as well as the size of the slot within them, on the metasurface transmission over the frequency band 10–20 GHz. Measurements on the final metasurface prototype have shown a large circular dichroism (Δ=0.61 and Δ=0.5) over two bands (17.55–17.61 GHz and 17.91–18.05 GHz) with ellipticities close to 45° which means that the developed device can be used as a circular polarization filter and circular polarizer at microwave frequencies.

Measurement of surface parameters of three-dimensional braided composite preform based on curvature scale space corner detector

Surface braiding angle and pitch length are two important parameters for characterizing and evaluating the performance of three-dimensional braided composite preforms. In this paper a new method based on an improved curvature scale space corner detector with adaptive threshold is proposed for measuring these parameters, with applications to three-dimensional, four-directional carbon-fiber braided composite preforms. First, the original image is acquired using a system employing ‘dome light source + CCD camera + circular polarizing filter’. Second, the original image is processed using Lab transform and BM3D (block-matching and 3D filter). Third, the corners are detected using an improved curvature scale space corner detector with adaptive threshold. Finally, the pitch lengths and surface braiding angles are measured from the detected corners. Experimental results show that the proposed method can achieve automatic measurement of the pitch length and surface braiding angle with smaller average errors relative to manual measurements compared with alternative schemes.

Intra-Minute Cloud Passing Forecasting Based on a Low Cost IoT Sensor-A Solution for Smoothing the Output Power of PV Power Plants.

Clouds moving at a high speed in front of the Sun can cause step changes in the output power of photovoltaic (PV) power plants, which can lead to voltage fluctuations and stability problems in the connected electricity networks. These effects can be reduced effectively by proper short-term cloud passing forecasting and suitable PV power plant output power control. This paper proposes a low-cost Internet of Things (IoT)-based solution for intra-minute cloud passing forecasting. The hardware consists of a Raspberry PI Model B 3 with a WiFi connection and an OmniVision OV5647 sensor with a mounted wide-angle lens, a circular polarizing (CPL) filter and a natural density (ND) filter. The completely new algorithm for cloud passing forecasting uses the green and blue colors in the photo to determine the position of the Sun, to recognize the clouds, and to predict their movement. The image processing is performed in several stages, considering selectively only a small part of the photo relevant to the movement of the clouds in the vicinity of the Sun in the next minute. The proposed algorithm is compact, fast and suitable for implementation on low cost processors with low computation power. The speed of the cloud parts closest to the Sun is used to predict when the clouds will cover the Sun. WiFi communication is used to transmit this data to the PV power plant control system in order to decrease the output power slowly and smoothly.

A Chiral Plasmonic Metasurface Circular Polarization Filter

Here, we demonstrate a proof of principle circular polarization filter based on a far-field interference effect using an array of pairs of simple nanoapertures. We demonstrate computationally and experimentally device performance which show good agreement and close to a 10% difference in transmission through the structure for left- and right-circularly polarized light. This ultracompact device could prove useful for remote sensing and advanced telecommunication applications.

Circular polarization bandpass filters based on one-dimensional magnetophotonic crystals

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

36.3: Effects of 3D Display System on Convergence and Accommodation

AbstractWe compared the circular polarizing filter method and liquid crystal shutter method. We were interested in comparing how these methods affect convergence and accommodation, when subjects viewed 3D images. The numeric values for convergence‐accommodation with the liquid crystal shutter were very close. However, in the case of the circular polarized filter method, there was discrepancy in the values of convergence and accommodation.