Millimeter-Wave Band Electro-Optical Imaging System Using Polarization CMOS Image Sensor and Amplified Optical Local Oscillator Source.

In this study, we developed and demonstrated a millimeter-wave electric field imaging system using an electro-optic crystal and a highly sensitive polarization measurement technique using a polarization image sensor, which was fabricated using a 0.35-µm standard CMOS process. The polarization image sensor was equipped with differential amplifiers that amplified the difference between the 0° and 90° pixels. With the amplifier, the signal-to-noise ratio at low incident light levels was improved. Also, an optical modulator and a semiconductor optical amplifier were used to generate an optical local oscillator (LO) signal with a high modulation accuracy and sufficient optical intensity. By combining the amplified LO signal and a highly sensitive polarization imaging system, we successfully performed millimeter-wave electric field imaging with a spatial resolution of 30×60 µm at a rate of 1 FPS, corresponding to 2400 pixels/s.

Circularly Polarized Vivaldi Antennas Integrated with Septum-like Polarizer.

In this paper, two orthogonally placed Vivaldi antennas with a septum-like polarizer to generate circular polarized (CP) waves are presented. Septum polarizers have garnered attention due to their simple structure and high quality of CP waves. While a typical septum polarizer has been applied to various types of waveguides, its applicability to the substrate integrated Vivaldi antenna is demonstrated here for the first time. A pulse train-shaped polarizer is used, which is placed on one of the two Vivaldi antennas. The contours of the polarizer are optimized using a genetic algorithm to provide an equal amplitude and 90° phase difference between the two orthogonal electric fields. In contrast to typical feed networks with a 90° phase shifter, any unwanted loss caused by an electronic circuit can be greatly mitigated. The antenna prototype was fabricated, and its radiation pattern and impedance matching were measured and compared to the simulated results.

Method of Directly Writing MPA on Photosensitive Surface of Detector Based on FIB.

The division of focal plane (DoFP) polarization detector has great potential for the development of aerospace polarimeters, but the existing commercial DoFP polarization detector cannot satisfy all the missions due to the diversity of satellite payloads. Here, we propose a method of directly writing a micro-polarizer array (MPA) on the detector surface based on focused ion beams (FIB) and fabricating a push-broom scanning DoFP polarization detector. The feasibility and low crosstalk of the solution were proved through testing, and the reasons for the low extinction ratio caused by oxidation were explained through characterization and numerical calculations. This scheme is not only applicable to DoFP polarization detectors but also provides ideas for the integration of other metasurface structures and detectors.

Circularly Polarized Organic Light-Emitting Diodes Based on Chiral Hole Transport Enantiomers.

The circularly polarized organic light-emitting diodes (CP-OLEDs) demonstrate promising application in 3D display due to the direct generation of circularly polarized electroluminescence (CPEL). But the chiral luminescence materials face challenges as intricated synthetic route, enantiomeric separation, etc. Herein, fresh CP-OLEDs are designed based on chiral hole transport material instead of chiral emitters. A pair of hole transport enantiomers (R/S-NPACZ) exhibit intense dissymmetry factors (|gPL|) about 5.0 × 10-3. With R/S-NPACZ as hole transport layers, CP-OLEDs are fabricated employing six achiral phosphorescence and thermally activated delayed fluorescence (TADF) materials with different wavelengths, in consistence with the generated CPEL spectra. The CP-OLEDs based on achiral red, green, and blue iridium(III) complexes exhibit external quantum efficiencies (EQEs) of 14.9%, 30.7%, and 14.1% with |gEL| factors of 8.8 × 10-4, 2.3 × 10-3, and 2.0 × 10-3, respectively. Moreover, the devices using achiral blue, blueish-green, and green TADF materials display EQEs of 24.1%, 17.9%, and 25.4% with |gEL| factors of 1.0 × 10-3, 3.6 × 10-3, and 2.2 × 10-3, respectively. As far as known, it is the first example of CP-OLEDs based on chiral hole transport materials, which act as the organic circularly polarizers and have potential to generate CPEL from achiral luminescence materials.

Si-Based Polarizer and 1-Bit Phase-Controlled Non-Polarizing Beam Splitter-Based Integrated Metasurface for Extended Shortwave Infrared.

Metasurfaces, composed of micro-nano-structured planar materials, offer highly tunable control over incident light and find significant applications in imaging, navigation, and sensing. However, highly efficient polarization devices are scarce for the extended shortwave infrared (ESWIR) range (1.7~2.5 µm). This paper proposes and demonstrates a highly efficient all-dielectric diatomic metasurface composed of single-crystalline Si nanocylinders and nanocubes on SiO2. This metasurface can serve as a nanoscale linear polarizer for generating polarization-angle-controllable linearly polarized light. At the wavelength of 2172 nm, the maximum transmission efficiency, extinction ratio, and linear polarization degree can reach 93.43%, 45.06 dB, and 0.9973, respectively. Moreover, a nonpolarizing beam splitter (NPBS) was designed and deduced theoretically based on this polarizer, which can achieve a splitting angle of ±13.18° and a phase difference of π. This beam splitter can be equivalently represented as an integration of a linear polarizer with controllable polarization angles and an NPBS with one-bit phase modulation. It is envisaged that through further design optimization, the phase tuning range of the metasurface can be expanded, allowing for the extension of the operational wavelength into the mid-wave infrared range, and the splitting angle is adjustable. Moreover, it can be utilized for integrated polarization detectors and be a potential application for optical digital encoding metasurfaces.

Chromatic Plasmonic Polarizer-Based Synapse for All-Optical Convolutional Neural Network.

Emerging memory devices have been demonstrated as artificial synapses for neural networks. However, the process of rewriting these synapses is often inefficient, in terms of hardware and energy usage. Herein, we present a novel surface plasmon resonance polarizer-based all-optical synapse for realizing convolutional filters and optical convolutional neural networks. The synaptic device comprises nanoscale crossed gold arrays with varying vertical and horizontal arms that respond strongly to the incident light's polarization angle. The presented synapse in an optical convolutional neural network achieved excellent performance in four different convolutional results for classifying the Modified National Institute of Standards and Technology (MNIST) handwritten digit data set. After training on 1,000 images, the network achieved a classification accuracy of over 98% when tested on a separate set of 10,000 images. This presents a promising approach for designing artificial neural networks with efficient hardware and energy consumption, low cost, and scalable fabrication.

Fluorinated graphene grating metasurface for terahertz dark state excitation.

We propose an original technique for the grating metasurfaces fabrication by low-power ultraviolet laser treatment of fluorinated graphene (FG) films with the focus on terahertz applications. The laser treatment reduces dielectric FG to its conductive counterparts, increasing DC conductivity to 170 S·m-1for treated areas. The electromagnetic response of the grating metasurfaces studied by THz time-domain spectroscopy in the 100 GHz-1 THz frequency range demonstrates enhanced resonant transmittance through metasurfaces. The intensity and position of transmittance peak could be tuned by changing the metasurface geometry, i.e. the period of the structure and width of the reduced and unreduced areas. In particular, the decrease of the reduced FG area width from 400 to 170µm leads to the shift of the resonance peak from 0.45 THz to the higher frequencies, 0.85 THz. Theoretical description based on the multipole theory supported by finite element numerical calculations confirms the excitation of the dark state in the metasurface unit cells comprising reduced and unreduced FG areas at resonance frequency determined by the structure geometrical features. Fabricated metasurfaces have been proved to be efficient narrowband polarizers being rotated by 50° about the incident THz field vector.

Highly Sensitive and Cost-Effective Polymeric-Sulfur-Based Mid-Wavelength Infrared Linear Polarizers with Tailored Fabry-Pérot Resonance.

Inverse-vulcanized polymeric sulfur has received considerable attention for application in waste-based infrared (IR) polarizers with high polarization sensitivities, owing to its high transmittance in the IR region and thermal processability. However, there have been few reports on highly sensitive polymeric sulfur-based polarizers by replication of pre-simulated dimensions to achieve a high transmission of the transverse magnetic field (TTM ) and extinction ratio (ER). Herein, a 400-nanometer-pitch mid-wavelength infrared bilayer linear polarizer with self-aligned metal gratings is introduced on polymeric sulfur gratings integrated with a spacer layer (SM-polarizer). The dimensions of the SM-polarizer can be closely replicated using pre-simulated dimensions via a systematic investigation of thermal nanoimprinting conditions. Spacer thickness is tailored from 40 to 5100 nm by adjusting the concentration of polymeric sulfur solution during spin-coating. A tailored spacer thickness can maximize TTM in the broadband MWIR region by satisfying Fabry-Pérot resonance. The SM-polarizer yields TTM of 0.65, 0.59, and 0.43 and ER of 3.12 × 103 , 5.19 × 103 , and 5.81 × 103 at 4 µm for spacer thicknesses of 90, 338, and 572 nm, respectively. This demonstration of a highly sensitive and cost-effective SM-polarizer opens up exciting avenues for infrared polarimetric imaging and for applications in polarization manipulation.

Broadband Circularly Polarized Conical Corrugated Horn Antenna Using a Dielectric Circular Polarizer.

In this paper, a broadband left-handed circularly polarized (LHCP) corrugated horn antenna using a dielectric circular polarizer is proposed. Circularly polarized (CP) waves are generated by inserting an improved dovetail-shaped dielectric plate into the circular waveguide. Compared with the traditional dovetail-shaped circular polarizer, the proposed improved dovetail-shaped circular polarizer has a wider impedance bandwidth and 3 dB axial ratio bandwidth. A substrate-integrated waveguide (SIW) structure is designed as a wall to eliminate the influence of fixed grooves on the circular polarizer. The simulated reflection coefficient of the dielectric plate circular polarizer is less than -20 dB in the frequency band from 17.57 to 33.25 GHz. Then, a conical corrugated horn antenna with five corrugations and a four-level metal stepped rectangular-circular waveguide converter are designed and optimized. The simulated -10 dB impedance and 3 dB axial ratio (AR) bandwidths of the circularly polarized horn antenna integrated with the polarizer are 61% (17.1-32.8 GHz) and 60.9% (17.76-33.32 GHz), respectively. The simulated peak gain is 17.34 dBic. The measured -10 dB impedance is 52.7% (17.2-27.5 GHz).

Grayscale Image Display Based on Nano-Polarizer Arrays.

Optical metasurfaces have shown unprecedented capabilities to control the two-dimensional distributions of phase, polarization, and intensity profiles of optical waves. Here, a TiO2 nanostructure functioning as a nano-polarizer was optimized considering that an anisotropic nanostructure is sensitive to the polarization states of incident light. We demonstrate two metasurfaces consisting of nano-polarizer arrays featured with different orientations, which can continuously manipulate the intensity distribution of the output light cell by cell according to Malus law and clearly display the detailed information of the target image. These metasurfaces have potential application in ultracompact displays, high-density optical information storage, and many other related polarization optics fields.

Technical note: Correcting angular dependencies using non-polarized components of Cherenkov light in water during high-energy X-ray irradiation.

OBJECTIVE: Dose distribution measurements of high-energy X-rays from medical linear accelerators (LINAC) in water are important for quality control (QC) of the system. Although Cherenkov-light imaging is a useful method for measuring the high-energy X-ray dose distribution, depth profiles have an underestimated dose at increased depths due to the angular dependency of the Cherenkov light generated in water. In this study, we use a linear polarizer to separate the majority of polarized components from the majority of unpolarized components of Cherenkov-light images in water and then use this information to correct for angular dependencies. METHODS: A water phantom, a cooled charge-coupled device (CCD) camera, and a polarizer were installed in a black box. Then, the water phantom was irradiated from the upper side with 6 or 10 MV X-rays, and the Cherenkov light generated in water was imaged with the polarizer axis at both parallel and perpendicular orientations to the beam. By using these images from the two orientations relative to the beam, we corrected the angular dependency of the Cherenkov light. RESULTS: By subtracting the images measured with the polarizer perpendicular to the beams from the images measured with the polarizer parallel to the beams, we could obtain images with only the polarized components. Using these images, we could calculate the images with non-polarized components that had similar depth profiles to those calculated with a planning system. The average difference between corrected depth profiles and those calculated with the planning system was less than 1%, while that between uncorrected depth profiles and the planning system was more than 8.3% in depths of water from 20 to 100 mm. CONCLUSION: We conclude that the use of the polarizer has the potential to improve the accuracy of dose distribution in Cherenkov-light imaging of water using high-energy X-rays.

Broadband Circular Polarizer Based on Chirped Double-Helix Chiral Fiber Grating.

We propose an all-fiber broadband circular polarizer based on leaky mode coupling and a phase-matched turning point (PMTP) in a chirped, double-helix, chiral, long-period, fiber grating (CLPG). The CLPG was coated with a material in which the refractive index was higher than that of the fiber cladding, enabling the coupling of the core mode to leaky modes to achieve a desired extinction ratio. The complex coupled-mode theory was employed to investigate the coupling mechanism and conditions under which the desired coupling efficiency could be achieved. Moreover, the PMTP in phase-matched curves, which resolved the conflict between the operating bandwidth and the grating pitch range of the CLPG and made a large bandwidth with a small grating pitch possible, was used in the design to achieve a compact structure. Finally, two broadband circular polarizers with an extinction ratio above 25 dB were simulated; one had a bandwidth of over 120 nm and a length of 3.5 cm, and the other had a bandwidth of over 300 nm and a length of 8 cm.

Ultra-Broadband and Compact TM-Pass Polarizer Based on Graphene-Buried Polymer Waveguide.

We report an ultra-broadband and compact TM-pass polarizer based on graphene-buried polymer waveguides. The characteristic parameters of the polarizer were carefully designed and optimized. The standard microfabrication processes were employed to fabricate the device. The presented polarizers exhibit high polarization-dependent transmission imposing a TE mode cutoff while leaving the TM mode almost unaffected. We experimentally demonstrated the polarizer that has an ultra-high extinction ratio of more than 22.9 dB and 41.9 dB for the monolayer graphene film placed on the surface of core layer and buried in the center of core layer, respectively, and as low insertion loss as ~4.0 dB for the TM mode with the bandwidth over 110 nm. The presented polarizer has the advantages of high extinction ratio, ultra-broadband, low cost, and easy integration with other polymer-based planar lightwave devices.

Control of Polarization Orientation Angle of Scattered Light Based on Metasurfaces: -90° to +90° Linear Variation.

Metasurfaces can be used to precisely control polarization state of the scattered light. Here, we present a metasurface-based terahertz device. On the one hand, it serves as a high performance linear polarization converter in transmission of over 80% power with weak reflection. It is capable of rotating linear polarization orientation angle with respect to x-axis continuously from -90° to +90° at 0.84 THz. On the other hand, it serves as a circular polarizer. It can transform a linear polarized wave into a circular polarized wave at 2.49 THz. The transmitted and reflected field are both circular polarized with 50% power. The proposed device with dual functionalities can be applied to modulate the polarization state of the signal in THz wireless communication.

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.

The Use of Natural Collagen Obtained from Fish Waste in Hair Styling and Care.

Chemically speaking, polymers are multi-molecular compounds that have specific physicochemical properties. Hair cosmetics utilize their ability to create a protective film and make the cosmetic formulation more viscous, which facilitates its application. Natural polymers are encountered in nature, but, in hair cosmetics, artificially modified ones are more often used. Unfortunately, artificially modified polymers are characterized by high resistance to biological factors, which creates an ecological problem. Another reason for a search for natural polymers is their milder action when compared to synthetic ones. One of the new sources of obtaining collagen is the waste connective tissue materials of aquatic animals-skins, spines, dorsal chords and scales, and swim bladders. These raw materials are most often disposed of in landfills, processed into fish meal, or destined for food for animals. The conducted research was aimed at proving the action of natural collagen in hair cosmetics as a substitute for synthetic polymers. In the patients using collagen laminate, it is possible to notice the complete elimination of excessive sebum production, restoration of the correct pH value, and reduction in skin inflammations.

Multifunctional Optical Device with a Continuous Tunability over 500 nm Spectral Range Using Polymerized Cholesteric Liquid Crystals.

We report that polymerization makes a robust, practically applicable multifunctional optical device with a continuous wavelength tunable over 500 nm spectral range using UV-polymerizable cholesteric liquid crystals (CLCs). It can be used as a circular polarizer generating an extremely high degree of circularly polarized light with |g| = 1.85~2.00. It can also be used for optical notch filters, bandwidth-variable (from ~28 nm to ~93 nm) bandpass filters, mirrors, and intensity-variable beam splitters. Furthermore, this CLC device shows excellent stability owing to the polymerization of CLC cells. Its performance remains constant for a long time (~2 years) after a high-temperature exposure (170 °C for 1 h) and an extremely high laser beam intensity exposure (~143 W/cm2 of CW 532 nm diode laser and ~2.98 MW/cm2 of Nd: YAG pulse laser operation for two hours, respectively). The optical properties of polymerized CLC were theoretically analyzed by Berreman's 4 × 4 matrix method. The characteristics of this device were significantly improved by introducing an anti-reflection layer on the device. This wavelength-tunable and multifunctional device could dramatically increase optical research efficiency in various spectroscopic works. It could be applied to many instruments using visible and near-infrared wavelengths.

Bottom-Up Synthesis of Helical Plasmonic Nanorods and Their Application in Generating Circularly Polarized Luminescence.

Chiral growth and chirality transfer associated with plasmonic nanostructures have rejuvenated the field of chirality. As the precise regioselective growth of inorganic crystals into chiral shapes at the nanoscale is extremely challenging, "bottom-up" synthesis of intrinsically chiral nanoparticles with structural stability is obviously attractive and important. With the thiolated bimolecular cosurfactants, we demonstrated a chemical strategy for the synthesis of intrinsically helical plasmonic nanorods (HPNRs) with strong and tailorable plasmonic circular dichroism (PCD) responses, deriving from the zwitterionic interactions between the -NH3+ and -COO- groups of the cysteine molecules (Cys). The influence of structural parameters of HPNRs on PCD responses was analyzed systematically by theoretical simulations. Among the different structural parameters, the pitch depth was found to have the greatest impact on the PCD signals, in agreement with the experimental results. Moreover, the obtained HPNRs with the strong, tunable, and stable chiroptical properties were found to be able to induce circularly polarized luminescence of achiral luminophores. Due to the generality of this effect, this chiral plasmonic nanostructure may have great potential for use in the fields of chiral sensors, chiral catalysis, and displays.

Dichroic Circular Polarizers Based on Plasmonics for Polarization Imaging Applications.

Dichroic circular polarizers (DCP) represent an important group of optical filters that transfer only that part of the incident light with the desired polarization state and absorb the remainder. However, DCPs are usually bulky and exhibit significant optical loss. Moreover, the integration of these kinds of DCP devices can be difficult and costly as different compositions of chemicals are needed to achieve the desired polarization status. Circular polarizers based on metasurfaces require only thin films in the order of hundreds of nanometers but are limited by their sensitivity to angle of incidence. Furthermore, few existing solutions offer broadband operation in the visible range. By using computational simulations, this paper proposes and analyses a plasmonic DCP structure operating in the visible, from 400 nm to 700 nm which overcomes these drawbacks. The resulting circular dichroism transmission (CDT) is more than 0.9, and the maximum transmission efficiency is greater than 78% at visible wavelengths. These CDT characteristics are largely independent of angle of incidence up to angles of 80 degrees.