Reflectance Modulation Research Articles

The Use of FTIR Spectroscopy as a Tool for the Seasonal Variation Analysis and for the Quality Control of Polysaccharides from Seaweeds.

Macroalgae are a potentially novel source of nutrition and biologically active molecules. Proliferative species such as Eucheuma denticulatum, Solieria chordalis (red algae) and Sargassum muticum (brown alga) constitute a huge biomass that can be exploited. In this study, we focus on the extraction of polysaccharides from these three macroalgae species and the characterization of cell wall polysaccharides such as carrageenans, fucoidans and alginates by Fourier Transform Infrared spectroscopy with Attenuated Reflectance Module (FTIR-ATR). The comparison of purified extracts with commercial solutions of fucoidans, alginates or carrageenans shows a strong similarity between the spectra. It demonstrates that the methods of extraction that have been used are also suitable purifying technics. Moreover, it validates infrared spectroscopy as a quick, simple and non-destructive method for the accurate analysis of polysaccharides. The FTIR technique applied to samples collected at different periods of the year allowed us to highlight differences in the composition of fucoidans, alginates and carrageenans. Different classes corresponding to the season can be distinguished by statistical multidimensionnal analysis (Principal Component Analysis) showing that the structure of algal polysaccharides, related to bioactivity, depends on the period of harvest. FTIR results showed that S. chordalis and E. denticulatum possess a dominant type of carrageenan called iota-carrageenan. This type of carrageenan is in the majority when the alga is at maturity in its development cycle. During its growth phase, iota-carrageenan precursors can be detected by FTIR spectra, enabling a better control of the extraction and an application of these compounds in various economic sectors. When the alga E. denticulatum is in its juvenile stage, we found traces of kappa-carrageenan and nu-carrageenan polysaccharides in some extracts.

Tunable strong plasmon–exciton coupling based modulator employing borophene and deep subwavelength perovskite grating

Two-dimensional materials support deeply confined and tunable plasmonic modes, which have great potential for achieving device miniaturization and flexible manipulation. In this paper, we propose a diffraction-unlimited system (period ≈ λ/20) composed of borophene layer and perovskite grating to investigate the strong coupling between the borophene guiding plasmon (BGP) and perovskite exciton (PE) modes. The resonant energy of the BGP mode could be electrically tuned to match the energy of the PE mode, and a remarkable Rabi splitting is attained under zero-detuning conditions. The splitting energy could reach 230 meV due to the strong field enhancement provided by the BGP mode. Taking advantage of the proposed electrically tunable hybrid system, not only is the reflective amplitude modulation depth up to 99.9%, but the 1.76π phase range modulation is achieved. Furthermore, by increasing the distance between the borophene layer and perovskite grating, a passive parity-time symmetry breaking could be observed with the vanished energy splitting. Our results deepen our understanding of light–matter interactions at the sub-wavelength scale and provide a guideline for designing active plasmonic devices.

Hybrid electronic-photonic sensors on a fibre tip.

Most sensors rely on a change in an electrical parameter to the measurand of interest. Their direct readout via an electrical wire and an electronic circuit is, in principle, technically simple, but it is subject to electromagnetic interference, preventing its application in several industrial environments. Fibre-optic sensors can overcome these limitations because the sensing region and readout region can be spaced apart, sometimes by kilometres. However, fibre-optic sensing typically requires complex interrogation equipment due to the extremely high wavelength accuracy that is required. Here we combine the sensitivity and flexibility of electronic sensors with the advantages of optical readout, by demonstrating a hybrid electronic-photonic sensor integrated on the tip of a fibre. The sensor is based on an electro-optical nanophotonic structure that uses the strong co-localization of static and electromagnetic fields to simultaneously achieve a voltage-to-wavelength transduction and a modulation of reflectance. We demonstrate the possibility of reading the current-voltage characteristics of the electro-optic diode through the fibre and therefore its changes due to the environment. As a proof of concept, we show the application of this method to cryogenic temperature sensing. This approach allows fibre-optic sensing to take advantage of the vast toolbox of electrical sensing modalities for many different measurands.

Greatly Enhanced Resonant Exciton-Trion Conversion in Electrically Modulated Atomically Thin WS2 at Room Temperature.

Excitonic resonance in atomically thin semiconductors offers a favorite platform to study 2D nanophotonics in both classical and quantum regimes and promises potentials for highly tunable and ultra-compact optical devices. The understanding of charge density dependent exciton-trion conversion is the key for revealing the underlaying physics of optical tunability. Nevertheless, the insufficient and inefficient light-matter interactions hinder the observation of trionic phenomenon and the development of excitonic devices for dynamic power-efficient electro-optical applications. Here, by engaging an optical cavity with atomically thin transition metal dichalcogenides (TMDCs), greatly enhanced exciton-trion conversion is demonstrated at room temperature (RT) and achieve electrical modulation of reflectivity of ≈40% at exciton and 7% at trion state, which correspondingly enables a broadband large phase tuning in monolayer tungsten disulfide. Besides the absorptive conversion, ≈100% photoluminescence conversion from excitons to trions is observed at RT, illustrating a clear physical mechanism of an efficient exciton-trion conversion for extraordinary optical performance. The results indicate that both excitons and trions can play significant roles in electrical modulation of the optical parameters of TMDCs at RT. The work shows the real possibility for realizing electrical tunable and multi-functional ultra-thin optical devices using 2D materials.

OPTICAL PROPERTIES OF HgGaInS4 CRYSTALS

Luminescence, transmission, reflection, and wavelength modulation transmission and wavelength modulation reflection spectra of HgGaInS4 crystals were researched in the temperature range of 300-10 K. This article discusses the various features observed in the spectra of HgGaInS4 crystals. The dependence on temperature of the energy gap is shown. Spectra of wavelength modulation transmission have minima a1, a2, and a3, which vary with temperature and are caused by indirect transitions L-Г with phonon absorption and emission. Spectra of thicker crystals have more features caused by the same indirect transitions. The photoluminescence show a strong maximum at 2.43 eV, attributed to radiative recombination of free excitons. These various features have significant implications for the understanding of the electronic and optical properties of HgGaInS4 crystals.

Nanoelectromechanical Tuning of High-Q Slot Metasurfaces.

Nanoelectromechanical devices have been used widely in many applications across photonics, electronics, and acoustics. Their incorporation into metasurface systems could be beneficial in designing new types of active photonic devices. Here, we propose a design of active metasurfaces using a nanoelectromechanical system (NEMS) composed of silicon bars which operates under CMOS-level voltage and achieves phase modulation with wavelength-scale pixel pitch. By introducing a perturbation to the slot mode propagating between the silicon bars, the device operates in a high-Q regime, making the optical mode highly sensitive to mechanical movement. An over 12 dB reflection modulation is observed by full-wave simulation, and over 10% is achieved in the proof-of-concept experiment under CMOS-level voltage. We also simulate a device with 1.8π phase response using a bottom gold mirror. Based on this device, a 3-pixel optical beam deflector is shown to have 75% diffraction efficiency.

Deflecting and routing nematicons via orientation programmable liquid crystal array.

By designing a liquid crystal cell with comb electrode structure, the alignment modulation of nematic liquid crystal in the cell can be realized after the electric field is applied. In different orientation regions, the incident laser beam can deflect at different angles. At the same time, by changing the incident angle of the laser beam, the reflection modulation of the laser beam on the interface of the liquid crystal molecular orientation change can be realized. Based on the above discussion, we then demonstrate the modulation of liquid crystal molecular orientation arrays on nematicon pairs. In different orientation regions of liquid crystal molecules, nematicon pairs can exhibit various combinations of deflections, and these deflection angles are modulable under external fields. Deflection and modulation of nematicon pairs have potential applications in optical routing and optical communication.

Hybrid Reflection Modulation

Reconfigurable intelligent surface (RIS)-empowered communication has emerged as a novel concept for customizing future wireless environments in a cost- and energy-efficient way. However, due to double path loss, existing fully passive RIS systems that purely reflect the incident signals into preferred directions attain an unsatisfactory performance improvement over the traditional wireless networks in certain conditions. To overcome this bottleneck, we propose a novel transmission scheme, named hybrid reflection modulation (HRM), exploiting both active and passive reflecting elements at the RIS and their combinations, which enables to convey information without using any radio frequency (RF) chains. In the HRM scheme, the active reflecting elements using additional power amplifiers are able to amplify and reflect the incoming signal, while the remaining passive elements can simply reflect the signals with appropriate phase shifts. Based on this novel transmission model, we obtain an upper bound for the average bit error probability (ABEP), and derive achievable rate of the system using an information theoretic approach. Moreover, comprehensive computer simulations are performed to prove the superiority of the proposed HRM scheme over existing fully passive, fully active and reflection modulation (RM) systems.

31‐3: In‐cell touch supported novel reflective LCD mode Development

The novel display mode for in‐cell touch reflective LCDs was developed. The basic optical display performance in test cells was almost same as conventional VA. In addition, the touch performance of the prototype in‐cell touch reflective module (the simple modification of the transmissive) was equivalent to the conventional transmissive. The optimal panel design for this display mode is currently under development.

Broadband Mechanically Tunable Metasurface Reflectivity Modulator in the Visible Spectrum.

Reflectivity modulation is a critical feature for applications in telecommunications, 3D imaging and printing, advanced laser machining, or portable displays. Tunable metasurfaces have recently emerged as a promising implementation for miniaturized and high-performance tunable optical components. Commonly, metasurface response tuning is achieved by electro-optical effects. In this work, we demonstrate reflectivity modulation based on a nanostructured, mechanically tunable, metasurface, consisting of an amorphous silicon nanopillar array and a suspended amorphous silicon membrane with integrated electrostatic actuators. With a membrane displacement of only 150 nm, we demonstrate reflectivity modulation by Mie resonance enhanced absorption in the pillar array, leading to a reflectivity contrast ratio of 1:3 over the spectral range from 400-530 nm. With fast, low-power electrostatic actuation and a broadband response in the visible spectrum, this mechanically tunable metasurface reflectivity modulator could enable high frame rate dynamic reflective displays.

Six-channel programmable coding metasurface simultaneously for orthogonal circular and linear polarizations

Metasurfaces have intrigued long-standing research interests and developed multitudinous compelling applications owing to their unprecedented capability for manipulating electromagnetic waves, and the emerging programmable coding metasurfaces (PCMs) provide a real-time reconfigurable platform to dynamically implement customized functions. Nevertheless, most existing PCMs can only act on the single polarization state or perform in the limited polarization channel, which immensely restricts their practical application in multitask intelligent metadevices. Herein, an appealing strategy of the PCM is proposed to realize tunable functions in co-polarized reflection channels of orthogonal circularly polarized waves and in co-polarized and cross-polarized reflection channels of orthogonal linearly polarized waves from 9.0 to 10.5 GHz. In the above six channels, the spin-decoupled programmable meta-atom can achieve high-efficiency reflection and 1-bit digital phase modulation by selecting the specific ON/OFF states of two diodes, and the phase coding sequence of the PCM is dynamically regulated by the field-programmable gate array to generate the desired function. A proof-of-concept prototype is constructed to verify the feasibility of our methodology, and numerous simulation and experimental results are in excellent agreement with the theoretical predictions. This inspiring design opens a new avenue for constructing intelligent metasurfaces with higher serviceability and flexibility, and has tremendous application potential in communication, sensing, and other multifunctional smart metadevices.

Optical Properties of Electrochemically Gated La1−xSrxCoO3−δ as a Topotactic Phase‐Change Material

AbstractMaterials with tunable infrared refractive index changes have enabled active metasurfaces for novel control of optical circuits, thermal radiation, and more. Ion‐gel‐gated epitaxial films of the perovskite cobaltite La1−xSrxCoO3−δ (LSCO) with 0.00 ≤ x ≤ 0.70 offer a new route to significant, voltage‐tuned, nonvolatile refractive index modulation for infrared active metasurfaces, shown here through Kramers–Kronig‐consistent dispersion models, structural and electronic transport characterization, and electromagnetic simulations before and after electrochemical reduction. As‐grown perovskite films are high‐index insulators for x < 0.18 but lossy metals for x > 0.18, due to a percolation insulator‐metal transition. Positive‐voltage gating of LSCO transistors with x > 0.18 reveals a metal‐insulator transition from the metallic perovskite phase to a high‐index (n > 2.5), low‐loss insulating phase, accompanied by a perovskite to oxygen‐vacancy‐ordered brownmillerite transformation at high x. At x < 0.18, despite nominally insulating character, the LSCO films undergo remarkable refractive index changes to another lower‐index, lower‐loss insulating perovskite state with Δn > 0.6. In simulations of plasmonic metasurfaces, these metal‐insulator and insulator‐insulator transitions support significant, varied mid‐infrared reflectance modulation, thus framing electrochemically gated LSCO as a diverse library of room‐temperature phase‐change materials for applications including dynamic thermal imaging, camouflage, and optical memories.

Building school leaders’ instructional leadership capacity through virtual professional leadership learning communities

IntroductionResearch is still emerging on how to develop school leaders’ instructional capacity. We implemented research-based practices through virtual professional leadership learning communities (VPLCs) for building school leaders’ instructional capacity. We examined school leaders’ perceptions of (a) the effectiveness of the VPLC as a vehicle for improving instructional practices, (b) the essential components of an effective VPLC, and (c) school leaders’ instructional leadership practices through discussions within VPLC.MethodsThe participants of this study were 40 school leaders at the principal and assistant principal levels in elementary schools in the state of Texas. Based on the research purpose and design, multiple types of data were collected to explore participants’ perceptions and experiences of VPLC.ResultsBased on both qualitative and quantitative analyses of the data from questionnaires and interviews, we found that this VPLC allowed participants to share leadership research and resources and provided them with an avenue for collaborating and communicating with other school leaders. The results of the qualitative data revealed two major components that the participants thought a VPLC should provide based on their experiences in the program (a) community building through collaboration and (b) reflective modules and discussion.DiscussionAn SST explanation can potentially reduce some aspects of homophobia among both healthcare professionals and lay people. Also, worryingly, Chinese healthcare professionals, especially medical professionals, reported more homophobia than lay individuals These VPLCs were regarded as grounds for innovation, as participants worked together with other school leaders to find problems and determine creative and workable solutions focused on building instructional capacity in serving high-needs schools. Thus, school leaders can be supported through sustained, effective professional learning in communities of practice, or virtual professional leadership learning communities.

Rapid quality assessment of Gentianae Macrophyllae Radix based on near infrared spectroscopy and capillary electrophoresis.

The aim of this study was to establish a rapid quality assessment method for Gentianae Macrophyllae Radix (RGM) using near infrared (NIR) spectra combined with chemometric analysis. The NIR spectra were acquired using an integrating sphere diffuse reflectance module, using air as the reference. Capillary electrophoresis (CE) analyses were performed on a model P/ACE MDQ Plus system. Partial least squares-discriminant analysis qualitative model was developed to distinguish different species of RGM samples, and the prediction accuracy for all samples was 91%. The CE response values at each retention time were predicted by building a partial least squares regression (PLSR) calibration model with the CE data set as the Y matrix and the NIR spectra data set as the X matrix. The converted CE fingerprints basically match the real ones, and the six main peaks can be accurately predicted. Transforming NIR spectra fingerprints into the form of CE fingerprints increases its interpretability and more intuitively demonstrates the components that cause diversity among samples of different species and origins. Loganic acid, gentiopicroside and roburic acid were considered as quality indicators of RGM and calibration models were built using PLSR algorithm. The developed models gave root mean square error of prediction of 0.2592% for loganic acid, 0.5341% for gentiopicroside and 0.0846% for roburic acid. The overall results demonstrate that the rapid quality assessment system can be used for quality control of RGM. This article is protected by copyright. All rights reserved.

Response times of a degenerately doped semiconductor based plasmonic modulator

We present a transient response study of a semiconductor based plasmonic switch. The proposed device operates through active control and modulation of localized electron density waves, i.e., surface plasmon polaritons (SPPs) at degenerately doped In0.53Ga0.47As based PN++ junctions. A set of devices is designed and fabricated, and its optical and electronic behaviors are studied both experimentally and theoretically. Optical characterization shows far-field reflectivity modulation, a result of electrical tuning of the SPPs at the PN++ junctions for mid-IR wavelengths, with significant 3 dB bandwidths. Numerical studies using a self-consistent electro-optic multi-physics model are performed to uncover the temporal response of the devices’ electromagnetic and kinetic mechanisms facilitating the SPP switching at the PN++ junctions. Numerical simulations show strong synergy with the experimental results, validating the claim of potential optoelectronic switching with a 3 dB bandwidth as high as 2 GHz. Thus, this study confirms that the presented SPP diode architecture can be implemented for high-speed control of SPPs through electrical means, providing a pathway toward fast all-semiconductor plasmonic devices.

Joint RIS Grouping Design Assisted Generalized Quadrature Reflection Modulation

In this paper, a novel joint reconfigurable intelligent surface (RIS) grouping design assisted generalized quadrature reflection modulation (JGD-GQRM) scheme is proposed for a single radio frequency (RF) multiple-input multiple-output (MIMO) system. In JGD-GQRM, a limited number of RIS elements are spatially grouped, and the remaining reflection patterns are utilized for joint mapping to improve the reliability of the transmission. Moreover, it maps additional information bits by full reflection passive beamforming to improve the system's spectral efficiency (SE). In addition to the optimal maximum likelihood (ML) detector that has high computational complexity, a low-complexity sequential greedy detection (SGD) for JGD-GQRM is proposed. Simulation results show that the proposed scheme can achieve better bit error rate (BER) performance than the existing reflection modulation.

Five-state flexible dynamic windows

Flexible electrochromic (EC) devices are highly desirable in smart applications. Although flexible devices with up to three states have been demonstrated in previous work, the goal of EC device with characteristics of the multistate property, flexible compatibility, fast switching speed is still hard to achieve. In this work, we successfully developed a five-state flexible dynamic window (FFDW) based on Bi and Cu bimetal reversibly deposited system. This device possesses transparent state, gray state, black state, cupreous mirror state and silvery mirror state via a precise voltage control strategy. More excitingly, the phenomenon of two mirror states obtained in one device is firstly reported. This FFDW, which can be bended for more than 50 times, exhibits fast switching speed of 2.34 s for complete stripping and 11.12 s for tinting, with a more than 63% transmittance modulation range at black state and an over 60% reflectance modulation range at mirror state. Finally, we unveiled the mechanism accounting for the voltage-dependent rich optical states in details. Our findings are helpful for developing high-performance dynamic windows for application in smart homes, vehicles and wearable devices.

Arterial pulsation modulates the optical attenuation coefficient of skin.

Photoplethysmographic (PPG) signals arise from the modulation of light reflectivity on the skin due to changes of physiological origin. Imaging plethysmography (iPPG) is a video-based PPG method that can remotely monitor vital signs in a non-invasive manner. iPPG signals result from skin reflectivity modulation. The origin of such reflectivity modulation is still a subject of debate. Here, we have used optical coherence tomography (OCT) imaging to find whether iPPG signals may result from skin optical properties being directly or indirectly modulated by arterial transmural pressure propagation. The light intensity across the tissue was modeled through a simple exponential decay (Beer-Lambert law) to analyze in vivo the modulation of the optical attenuation coefficient of the skin by arterial pulsation. The OCT transversal images were acquired from a forearm of three subjects in a pilot study. The results show that the optical attenuation coefficient of skin changes at the same frequency as the arterial pulsation due to transmural pressure propagation (local ballistographic effect), but we cannot discard the contribution of global ballistographic effects.

Low-light image enhancement by deep learning network for improved illumination map

In the case of insufficient illumination conditions, the quality of the captured image is poor. At this time, increasing the brightness of the dark region of the whole image will inevitably aggravate noise pollution. Therefore, the ideal state of low-light image enhancement should be to make the dark areas brighter while not allowing the noise part to be enhanced as well. In this paper, we combine Retinex theory and convolutional neural networks to build a simple and effective model with three sub-modules: the decomposition module, illumination module, and reflection module, in which the decomposition module is used to decompose the input low-light image into illumination and reflection maps, the illumination module improves the feature extraction part of the simple convolutional layer used previously and constitutes a new feature extraction structure by Depthwise separable convolution, which makes up for the shortcoming that some dark areas are not well brightened and better adjusts the brightness of the illumination map, and the reflection module adjusts the texture details more clearly because it adds the illumination map as a reference. In this way, the original space is decoupled into two smaller subspaces to the extent that better results can be achieved. We demonstrate through extensive experiments the effectiveness of the design and its superiority over state-of-the-art techniques, especially in terms of robustness to severe visual defects and flexibility in adjusting luminance.

Investigating mechanisms of laser pulse-induced reflectivity modulations in photoacoustic remote sensing with a 10 million frames-per-second camera

Photoacoustic remote sensing has been recently developed as an all-optical imaging modality capable of imaging a variety of endogenous contrast agents label-free. Initially predicted laser pulse-induced refractive index perturbation-based interrogation beam reflectivity modulations have been found to be orders of magnitude smaller than those typically observed experimentally. In this report we utilize a 10 million frames-per-second camera to further investigate these predicted reflectivity modulations, while also exploring other potential mechanisms of laser pulse-induced reflectivity modulations. Laser-induced motion is demonstrated both laterally for gold wires suspended and submerged in air and water, respectively, and carbon fibers submerged in water, and axial motion is observed in gold wires submerged in a depth gradient of intralipid solution. This laser-induced sample motion is anticipated to cause reflectivity modulations local to the interrogation beam profile in microscopy set-ups. Non-motion-based maximum intensity modulations of 3% are also observed in gold wires submerged in water, indicating the presence of the originally predicted reflectivity modulations. Overall, these observations are important as they provide a widefield view of laser-pulse interactions unavailable in previous point scanning-based photoacoustic remote sensing microscopy configurations, where observed mechanisms occur on time-scales orders of magnitude faster than equivalent field of view point scanning capabilities.