Sub-30 nm 2D Perovskites Patterns via Block Copolymer Guided Self-Assembly for Color Conversion Optical Polarizer.

Despite the remarkable advances made in the development of 2D perovskites suitable for various high-performance devices, the development of sub-30 nm nanopatterns of 2D perovskites with anisotropic photoelectronic properties remains challenging. Herein, a simple but robust route for fabricating sub-30 nm 1D nanopatterns of 2D perovskites over a large area is presented. This method is based on nanoimprinting a thin precursor film of a 2D perovskite with a topographically pre-patterned hard poly(dimethylsiloxane) mold replicated from a block copolymer nanopattern consisting of guided self-assembled monolayered in-plane cylinders. 1D nanopatterns of various 2D perovskites (A'2 MAn -1 Pbn X3 n +1 ,A' = BA, PEA, X = Br, I) are developed; their enhanced photoluminescence (PL) quantum yields are approximately four times greater than those of the corresponding control flat films. Anisotropic photocurrent is observed because 2D perovskite nanocrystals are embedded in a topological 1D nanopattern. Furthermore, this 1D metal-coated nanopattern of a 2D perovskite is employed as a color conversion optical polarizer, in which polarized PL is developed. This is due to its capability of polarization of an incident light arising from the sub-30 nm line pattern, as well as the PL of the confined 2D perovskite nanocrystals in the pattern.

Radial Alignment of Carbon Nanotubes via Dead-End Filtration.

Dead-end filtration is a facile method to globally align single wall carbon nanotubes (SWCNTs) in large area films with a 2D order parameter, S2D , approaching unity. Uniaxial alignment has been achieved using pristine and hot-embossed membranes but more sophisticated geometries have yet to be investigated. In this work, three different patterns with radial symmetry and an area of 3.8 cm2 are created. Two of these patterns are replicated by the filtered SWCNTs and S2D values of ≈0.85 are obtained. Each of the radially aligned SWCNT films is characterized by scanning cross-polarized microscopy in reflectance and laser imaging in transmittance with linear, radial, and azimuthal polarized light fields. The former is used to define a novel indicator akin to the 2D order parameter using Malu's law, yielding 0.82 for the respective film. The films are then transferred to a flexible printed circuit board and terminal two-probe electrical measurements are conducted to explore the potential of those new alignment geometries.

The Impact of Carbon Nanotube Length and Diameter on their Global Alignment by Dead-End Filtration.

Dead-end filtration has proven to effectively prepare macroscopically (3.8 cm2 ) aligned thin films from solutionbased single-wall carbon nanotubes (SWCNTs). However, to make this technique broadly applicable, the role of SWCNT length and diameter must be understood. To date, most groups report the alignment of unsorted, large diameter (≈1.4 nm) SWCNTs, but systematic studies on their small diameter are rare (≈0.78 nm). In this work, films with an area of A = 3.81 cm2 and a thickness of ≈40 nm are prepared from length-sorted fractions comprising of small and large diameter SWCNTs, respectively. The alignment is characterized by cross-polarized microscopy, scanning electron microscopy, absorption and Raman spectroscopy. For the longest fractions (Lavg = 952 nm ± 431 nm, Δ = 1.58 and Lavg = 667 nm ± 246 nm, Δ = 1.55), the 2D order parameter, S2D, values of ≈0.6 and ≈0.76 are reported for the small and large diameter SWCNTs over an area of A = 625 µm2 , respectively. A comparison of Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory calculations with the aligned domain size is then used to propose a law identifying the required length of a carbon nanotube with a given diameter and zeta potential.

Noninvasive Non-Contact SpO2 Monitoring Using an Integrated Polarization-Sensing CMOS Imaging Sensor.

BACKGROUND: In the diagnosis and primary health care of an individual, estimation of the pulse rate and blood oxygen saturation (SpO2) is critical. The pulse rate and SpO2 are determined by methods including photoplethysmography (iPPG), light spectroscopy, and pulse oximetry. These devices need to be compact, non-contact, and noninvasive for real-time health monitoring. Reflection-based iPPG is becoming popular as it allows non-contact estimation of the heart rate and SpO2. Most iPPG methods capture temporal data and form complex computations, and thus real-time measurements and spatial visualization are difficult. METHOD: In this research work, reflective mode polarized imaging-based iPPG is proposed. For polarization imaging, a custom image sensor with wire grid polarizers on each pixel is designed. Each pixel has a wire grid of varying transmission axes, allowing phase detection of the incoming light. The phase information of the backscattered light from the fingertips of 12 healthy volunteers was recorded in both the resting as well as the excited states. These data were then processed using MATLAB 2021b software. RESULTS: The phase information provides quantitative information on the reflection from the superficial and deep layers of skin. The ratio of deep to superficial layer backscattered phase information is shown to be directly correlated and linearly increasing with an increase in the SpO2 and heart rate. CONCLUSIONS: The phase-based measurements help to monitor the changes in the resting and excited state heart rate and SpO2 in real time. Furthermore, the use of the ratio of phase information helps to make the measurements independent of the individual skin traits and thus increases the accuracy of the measurements. The proposed iPPG works in ambient light, relaxing the instrumentation requirement and helping the system to be compact and portable.

Transmissive Polarizer Metasurfaces: From Microwave to Optical Regimes.

Metasurfaces, a special class of metamaterials, have recently become a rapidly growing field, particularly for thin polarization converters. They can be fabricated using a simple fabrication process due to their smaller planar profile, both in the microwave and optical regimes. In this paper, the recent progress in MSs for linear polarization (LP) to circular polarization (CP) conversion in transmission mode is reviewed. Starting from history, modeling and the theory of MSs, uncontrollable single and multiple bands and LP-to-CP conversions, are discussed and analyzed. Moreover, detailed reconfigurable MS-based LP-to-CP converters are presented. Further, key findings on the state-of-the-arts are discussed and tabulated to give readers a quick overview. Finally, a conclusion is drawn by providing opinions on future developments in this growing research field.

Design of Ultra-High Extinction Ratio TM- and TE-Pass Polarizers Based on Si-Sc0.2Sb2Te3 Hybrid Waveguide.

The selective polarizers play an important role in silicon-based integrated circuits. The previous polarizers based on silicon waveguides have the defects of large scale and low extinction ratio. In this work, TM- and TE-pass polarizers only 10 µm long were developed based on phase-change material of Sc0.2Sb2Te3 (SST) hybrid silicon waveguide, where several SST bars with a varied distance was designed. Because of the excellent characteristics of the refractive index of the material, ultra-high extinction ratios (ERs) were achieved. A 3-D finite element simulation was carried out to optimize the structure of the polarizers, and the distribution of light field, as well as the transmission behavior of TE and TM modes in the two polarizers, was further demonstrated in detail. When the SST is crystalline, the unwanted mode can be attenuated, while the wanted mode can pass through with low loss. Compared with the GST-based polarizers, the proposed ones achieved high extinction ratios of ~43.12 dB (TM-pass one) and ~44.21 dB (TE-pass one), respectively; at the same time, ILs for the wanted modes could be negligible. The design of high-performance polarizers paves a new way for applications of all-optical integrated circuits.

Broadband and Incident-Angle-Modulation Near-Infrared Polarizers Based on Optically Anisotropic SnSe.

Optical anisotropy offers an extra degree of freedom to dynamically and reversibly regulate polarizing optical components, such as polarizers, without extra energy consumption and with high modulating efficiency. In this paper, we theoretically and numerically design broadband and incident-angle-modulation near-infrared polarizers, based on the SnSe, whose optical anisotropy is quantitatively evaluated by the complete dielectric tensor, complex refractive index tensor, and derived birefringence (~|Δn|max = 0.4) and dichroism (~|Δk|max = 0.4). The bandwidth of a broadband polarizer is 324 nm, from 1262 nm to 1586 nm, with an average extinction ratio above 23 dB. For the incident-angle-modulation near-infrared polarizer, the high incident angles dynamically and reversibly modulate its working wavelength with a maximum extinction ratio of 71 dB. Numerical simulations and theoretical calculations reveal that the considerable absorption for p light and continuously and relatively low absorption of s light lead to the broadband polarizer, while the incident-angle-modulation one mainly arises from the blue shift of corresponding wavelength of p light's minimum reflectance. The proposed novel design of polarizers based on SnSe are likely to be mass-produced and integrated into an on-chip system, which opens up a new thought to design polarizing optical components by utilizing other low-symmetry materials.

Low-Loss Broadband Transverse Electric Pass Hybrid Plasmonic Fiber Polarizers Using Metallic Nanomaterials.

Metals were for decades perceived as devoid of interesting optical properties that could be harnessed for optical components and devices. However, with the development of accurate nanofabrication techniques and precise control over architectural parameters, metals can be structured and characterized on the nanoscale. Metallic plasmonic nanomaterials exhibit a number of unique structural and optical properties, which offer the potential for developing new types of plasmonic devices. Here, we demonstrate a low-loss broadband polarizer based on a hybrid plasmonic fiber structure using metals as polarization-selective absorption materials. The polarization mechanism, design, fabrication, and characteristics of the plasmonic polarizers are investigated theoretically, numerically, and experimentally. The theoretical analysis predicts that the polarization-selective absorption with insensitivity to wavelength enables hybrid plasmonic fibers to function as broadband polarizers. Numerical simulations give the comparison of the polarization-selective absorption of various metallic nanomaterials (Ag, Au, In, Al, Cr) and show that aluminum is regarded as the optimum absorption material for the plasmonic polarizer. Experimental results show that through precise control over geometrical parameters, this device is capable of offering a high polarization extinction ratio (PER) of over 40 dB and a low insertion loss (IL) of less than 1.3 dB in the wavelength region of 810.1-870.0 nm. Compared with commercial birefringent-crystal-fiber polarizers, the plasmonic fiber polarizer has a better PER and IL bandwidth. These merits, combined with a compact and robust configuration, enable the plasmonic polarizer to have great potential in a broad range of applications.

Dual-Channel Stopped-Flow Apparatus for Simultaneous Fluorescence, Anisotropy, and FRET Kinetic Data Acquisition for Binary and Ternary Biological Complexes.

The Stopped-Flow apparatus (SF) tracks molecular events by mixing the reactants in sub-millisecond regimes. The reaction of intrinsically or extrinsically labeled biomolecules can be monitored by recording the fluorescence, F(t), anisotropy, r(t), polarization, p(t), or FRET, F(t)FRET, traces at nanomolar concentrations. These kinetic measurements are critical to elucidate reaction mechanisms, structural information, and even thermodynamics. In a single detector SF, or L-configuration, the r(t), p(t), and F(t) traces are acquired by switching the orientation of the emission polarizer to collect the IVV and IVH signals however it requires two-shot experiments. In a two-detector SF, or T-configuration, these traces are collected in a single-shot experiment, but it increases the apparatus' complexity and price. Herein, we present a single-detector dual-channel SF to obtain the F(t) and r(t) traces simultaneously, in which a photo-elastic modulator oscillates by 90° the excitation light plane at a 50 kHz frequency, and the emission signal is processed by a set of electronic filters that split it into the r(t) and F(t) analog signals that are digitized and stored into separated spreadsheets by a custom-tailored instrument control software. We evaluated the association kinetics of binary and ternary biological complexes acquired with our dual-channel SF and the traditional methods; such as a single polarizer at the magic angle to acquire F(t), a set of polarizers to track F(t), and r(t), and by energy transfer quenching, F(t)FRET. Our dual-channel SF economized labeled material and yielded rate constants in excellent agreement with the traditional methods.

Polarization Selectivity of the Thin-Metal-Film Plasmon-Assisted Fiber-Optic Polarizer.

The interaction between light and metallic nanostructures leads to many impressive achievements and has a wide range of applications. The thin-metal-film plasmon-assisted fiber-optic polarizer is one of the essential applications. However, the polarization mechanism and the transmitted polarization of the plasmon-assisted polarizer have given rise to controversy over the past decade. Which of the polarizations is preferentially transmitted through the polarizer? The transverse electric polarization or the transverse magnetic polarization? Here, special emphasis is placed upon the polarization mechanism and the transmitted polarization of thin-metal-film plasmon-assisted fiber polarizers. We first investigate the polarization mechanism of the polarizers theoretically and numerically. Furthermore, a novel approach is proposed to demonstrate the transmitted polarization in the plasmon-assisted fiber polarizers experimentally. We demonstrate that the polarization mechanism is based on the polarization selective absorption of the metallic material, and the transverse electric polarization is the only transmitted polarization of the metallic plasmon-assisted polarizer. Moreover, the plasmon-assisted polarizer can offer a high polarization extinction ratio (33.1 dB) and a low insertion loss (1.1 dB) at room temperature and have excellent temperature stability in the range of -48 to 82 °C. Experimental results agree well with our theoretical and numerical analyses. The findings clarify the confusion about the polarization mechanism and the transmitted polarization of metallic plasmon-assisted fiber polarizers over the past decade, providing new ground for the exploration of polarization-sensitive optical systems, with good potential applications in the fields of optical sensors, plasmonic lasers, coherent optical communications, and biosensor systems.

Designing 3D Digital Metamaterial for Elastic Waves: From Elastic Wave Polarizer to Vibration Control.

Elastic wave polarizers, which can filter out linearly polarized elastic waves from hybrid elastic waves, remain a challenge since elastic waves contain both transverse and longitudinal natures. Here, a tunable, digital, locally resonant metamaterial inspired by abacus is proposed, which consists of 3D-printed octahedral frames and built-in electromagnets. By controlling current in the electromagnets, each unit cell exhibits three digital modes, where the elastic waves have different characteristics of propagation under each mode. A variety of waveguides can be formed by a combination of the three modes and desired polarization can be further filtered out from hybrid elastic waves in a tunable manner. The underlying mechanism of these polarizer-like characteristics is investigated through a combination of theoretical analysis, numerical simulation, and experimental testing. This study provides a means of filtering out the desired wave from hybrid elastic waves, and offers promise for vibration control of particle distribution and flexible structure.

Medicinal Plants As Natural Polarizers of Macrophages: Phytochemicals and Pharmacological Effects.

Macrophages are one of the crucial mediators of the immune response in different physiological and pathological conditions. These cells have critical functions in the inflammation mechanisms that are involved in the inhibition or progression of a wide range of diseases including cancer, autoimmune diseases, etc. It has been shown that macrophages are generally divided into two subtypes, M1 and M2, which are distinguished on the basis of their different gene expression patterns and phenotype. M1 macrophages are known as pro-inflammatory cells and are involved in inflammatory mechanisms, whereas M2 macrophages are known as anti-inflammatory cells that are involved in the inhibition of the inflammatory pathways. M2 macrophages help in tissue healing via producing anti-inflammatory cytokines. Increasing evidence indicated that the appearance of different macrophage subtypes is associated with the fate of diseases (progression versus suppression). Hence, polarization of macrophages can be introduced as an important venue in finding, designing and developing novel therapeutic approaches. Albeit, there are different pharmacological agents that are used for the treatment of various disorders, it has been shown that several natural compounds have the potential to regulate M1 to M2 macrophage polarization and vice versa. Herein, for the first time, we summarized new insights into the pharmacological effects of natural compounds on macrophage polarization.

Transmit-Array, Metasurface-Based Tunable Polarizer and High-Performance Biosensor in the Visible Regime.

There are two types of metasurfaces, reflect-array and transmit-array,-which are classified on the basis of structural features. In this paper, we design a transmit-array metasurface for y-polarized incidence which is characterized by having a transmission spectrum with a narrow dip (i.e., less than 3 nm). Furthermore, a tunable polarizer is achieved using linear geometric configurations, realizing a transmittivity ratio between x- and y-polarized incidence ranging from 0.031% to 1%. Based on the narrow-band polarization sensitivity of our polarizer, a biosensor was designed to detect an environmental refractive index ranging from 1.30 to 1.39, with a factor of sensitivity S = 192 nm/RIU and figure of merit (FOM) = 64/RIU. In the case of a narrow-band feature and dips in transmission spectrums close to zero, FOM* can have a value as large as 92,333/RIU. This unique feature makes the novel transmit-array metasurface a potential market candidate in the field of biosensors. Moreover, transmit-array metasurfaces with lossless materials offer great convenience by means of detecting either the reflectance spectrum or the transmission spectrum.

Complex Nanoscale-Ordered Liquid Crystal Polymer Film for High Transmittance Holographic Polarizer.

A special design of a complex-ordered liquid crystal polymer film is developed into a holographic polarizer. The holographic polarizer shows over 90% transmittance, which provides a simple solution to make LEDs polarized. Furthermore, the holographic polarizer exhibits intensity and polarization maintenance properties, which could be further developed for photonics applications.

Metal nanoparticle dispersion, alignment, and assembly in nematic liquid crystals for applications in switchable plasmonic color filters and E-polarizers.

Viewing angle characteristics of displays and performance of electro-optic devices are often compromised by the quality of dichroic thin-film polarizers, while dichroic optical filters usually lack tunability and cannot work beyond the visible part of optical spectrum. We demonstrate that molecular-colloidal organic-inorganic composites formed by liquid crystals and relatively dilute dispersions of orientationally ordered anisotropic gold nanoparticles, such as rods and platelets, can be used in engineering of switchable plasmonic polarizers and color filters. The use of metal nanoparticles instead of dichroic dyes allows for obtaining desired polarizing or scattering and absorption properties not only within the visible but also in the infrared parts of an optical spectrum. We explore spontaneous surface-anchoring-mediated alignment of surface-functionalized anisotropic gold nanoparticles and its control by low-voltage electric fields, elastic colloidal interactions and self-assembly, as well as the uses of these effects in defining tunable properties of the ensuing organic-inorganic nanostructured composites. Electrically tunable interaction of the composites may allow for engineering of practical electro-optic devices, such as a new breed of color filters and plasmonic polarizers.

Aligned Layers of Silver Nano-Fibers.

We describe a new dichroic polarizers made by ordering silver nano-fibers to aligned layers. The aligned layers consist of nano-fibers and self-assembled molecular aggregates of lyotropic liquid crystals. Unidirectional alignment of the layers is achieved by means of mechanical shearing. Aligned layers of silver nano-fibers are partially transparent to a linearly polarized electromagnetic radiation. The unidirectional alignment and density of the silver nano-fibers determine degree of polarization of transmitted light. The aligned layers of silver nano-fibers might be used in optics, microwave applications, and organic electronics.