Electro-optical Measurements Research Articles

Chemical and physical properties of orthoconic liquid crystals: 2H NMR spectroscopy and molecular dynamics simulations.

In the field of chiral smectic liquid crystals, orthoconic antiferroelectric liquid crystals (OAFLCs) have attracted the interest of the scientific community due to the very high tilt angle, close to 45°, and the consequent optical properties. In the present study, the first 2H NMR investigation is reported on two samples, namely 3F5HPhF9 and 3F7HPhF8, showing the phase sequence isotropic-SmC*-SmCA* and the phase sequence isotropic-SmA-SmC*-SmCA*, respectively, when cooling from the isotropic to the crystalline phases. To this aim, the liquid crystals were doped with a small amount of deuterated probe biphenyl-4,4'-diol-d4. The trend of 2H NMR spectra versus temperature indicates the presence of very high values of the tilt of the deuterated probe in the antiferroelectric phase for both samples. The trend of the local order parameters and that of the tilt angle were compared with the results obtained for the same samples by means of different experimental techniques, namely X-ray diffraction and electrooptical measurements. Moreover, a computational study was performed on the sample labelled 3F5HPhF9 using fully atomistic classical molecular dynamics simulation of the orthoconic phase. The results obtained from the MD simulations show a very large molecular tilt of the molecules (about 42°) when packed in layers and this value is in very good agreement with experimental results. The present research aims to give additional clues about the molecular origin of the very peculiar high tilt angle of orthoconic liquid crystals in the antiferroelectric phase.

Measuring the Electro-Optical Kerr Effect Against the Background of Electro-Absorption Modulation in Liquids.

A new approach to the dynamic polarimetric method is proposed, which allows for the decoupling of electro-optical Kerr effect measurements from the electro-absorption effect in partially transparent liquids. The method is illustrated by using the results of engine oil measurements as a function of temperature and modulating field frequency. It was shown that the birefringence induced in the sample, the modulation of the ordinary wave transmission, and the modulation of the extraordinary wave transmission in the sample can be shifted in phase with respect to the square of the applied alternating modulating field. Each of these three phase shifts can depend differently on the temperature and frequency. Neglecting the influence of electro-absorption on electro-optical measurements in liquids or considering electro-absorption as an effect correlated in phase with induced birefringence may lead to significant measurement errors. This indicates that the Kerr constant and the electro-absorption coefficients for an alternating electric field should be considered as complex quantities instead of real values, as they have been traditionally. The proposed approach fills an important gap in measurement techniques described in the literature, which may provide erroneous results for measurements of the Kerr constant in partially transparent liquids including many industrially important liquids.

Compositional Optimization of Sputtered SnO2/ZnO Films for High Coloration Efficiency

We performed an electrochromic investigation to optimize the composition of reactive magnetron-sputtered mixed layers of zinc oxide and tin oxide (ZnO-SnO2). Deposition experiments were conducted as a combinatorial material synthesis approach. The binary system for the samples of SnO2-ZnO represented the full composition range. The coloration efficiency (CE) was determined for the mixed oxide films with the simultaneous measurement of layer transmittance, in a conventional three-electrode configuration, and an electric current was applied by using organic propylene carbonate electrolyte cells. The optical parameters and composition were measured and mapped by using spectroscopic ellipsometry (SE). Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) measurements were carried out to check the SE results, for (TiO2-SnO2). Pure metal targets were placed separately from each other, and the indium–tin-oxide (ITO)-covered glass samples and Si-probes on a glass holder were moved under the two separated targets (Zn and Sn) in a reactive argon–oxygen (Ar-O2) gas mixture. This combinatorial process ensured that all the compositions (from 0 to 100%) were achieved in the same sputtering chamber after one sputtering preparation cycle. The CE data evaluated from the electro-optical measurements plotted against the composition displayed a characteristic maximum at around 29% ZnO. The accuracy of our combinatorial approach was 5%.

Quantitative measurement of the flow depending nasal valve function by elastography with electro-optical distance sensors. A pilot study

Nasal valve function depends on the intensity of the inspiratory nasal airflow, the geometry of the nasal entrance and the mechanical properties of the lateral nasal wall. It is desirable to obtain objective information on the relation between flow and valve movement. In this study, the deflection of the lateral nasal wall and the inspiratory flow were measured on 30 healthy volunteers, aged 18 to 82 without a history of severe trauma or nasal surgery. Electro-optical distance sensors were housed under a full-face protective mask attached to an analogue inspiratory flowmeter. The mean values for normal breathing were assessed at 675 [cm3/s] for the bilateral flow and −0.57 mm for the total movement. With forced breathing, the mean values for the flow of both nostrils were found to be 1434 cm3/s and for the total movement −1.21 mm. Statistically significant differences between normal and forced breathing were found in all participants and in both sexes, but no significant correlation by age. Electro-optical distance measurement, representing a novel technical way for the ‘elastography’ of the nasal valve should be added to advanced 4-phase-rhinomanometers.

Enhanced forward emission by backside mirror design in micron-sized LEDs.

Tiny InGaN micro-LEDs (μ-LEDs) play a pivotal role in emerging display technologies, particularly augmented reality (AR) applications. Achieving both high internal quantum efficiency (IQE) and efficient light extraction efficiency (LEE) is essential. While wet chemical etching can recover the IQE after dry etching, it alters the pixel shape, impacting optical properties and reducing the LEE. In this study, we overcome this issue by fabricating 1 μm thin-film-based μ-LED emitter arrays with a metallic backside mirror deposited on a patterned dielectric material around the μ-LED mesa. This concave mirror can be straightforwardly integrated into a thin-film LED process chain, and it redirects photons within the μ-LED structure, enhancing the LEE in the forward direction. Electro-optical measurements show a 2.1-fold improvement in light output within the ±15∘ emission cone compared to μ-LEDs with vertical sidewalls. These findings hold significant implications for μ-LED projection displays, where maximizing the overall efficiency and directionality is critical.

The Status of Environmental Electric Field Detection Technologies: Progress and Perspectives.

The detection of electric fields in the environment has great importance for understanding various natural phenomena, environmental monitoring, and ensuring human safety. This review paper provides an overview of the current state-of-the-art technologies utilized for sensing electric fields in the environment, the challenges encountered, and the diverse applications of this sensing technology. The technology is divided into three categories according to the differences in the physical mechanism: the electro-optic effect-based measurement system, the MEMS-based sensor, and the newly reported quantum effect-based sensors. The principles of the underlying methods are comprehensively introduced, and the tentative applications for each type are discussed. Detailed comparisons of the three different techniques are identified and discussed with regard to the instrument, its sensitivity, and bandwidth. Additionally, the challenges faced in environmental electric field sensing, the potential solutions, and future development directions are addressed.

Molecular engineering controlled electric-optical performance of polymer dispersed liquid crystals

ABSTRACT In this work, the methods of doping different fluorine-containing monomers and fluorine-containing nanoparticles into the mixture were adopted to boost the electro-optical performance of PDLC films. The electro-optical measurements indicate the improved electro-optical performance of PDLCs through the introduction of MX-3 monomer, and the corresponded SEM results demonstrate the successful adjustment of surface morphology. Further doping F-Si@SiO2 nanoparticles into MX-3 monomer-modified PDLC system, the Vth and Vsat values are greatly reduced and reach lowest when F-Si@SiO2 content is 5 wt.%. The enhanced electro-optical property is due to the combined control of fluorine-containing MX-3 monomer and F-Si@SiO2 nanoparticles, the fluorine functional group can promote the uniform dispersion of nanoparticles; the existence of F-Si@SiO2 nanoparticles can regulate the anchoring effect on liquid crystal molecules in the polymer matrix, thus electric-optic characteristics of the PDLC materials are greatly enhanced.

Influence of chalcopyrite nanoplatelets on nematic phases of bend-shaped dimeric molecules: Phase diagram, birefringence, and reorientation transition

We investigated the influence of chalcopyrite (CuFeS2) nanoplatelets on the ordering of uniform and twist-bend nematic phases of achiral bend-shaped dimers, employing polarized optical microscopy, optical and electro-optical measurements. Specifically, aliphatic amine surface-functionalized hydrophobic chalcopyrite nanoplatelets were synthesized and characterized by XRD, TEM, and IR-vis-UV spectroscopy. Nanocomposites of the liquid crystal compound 1”,9”-bis(4-cyanobiphenyl-4'-yl)nonane (CB9CB) with the nanoplatelets were prepared. The study encompasses an assessment of the thermodynamic stability of the nanocomposites, constructing the corresponding phase diagram as a function of temperature and nanoplatelet mass fraction. Large phase temperature shifts were observed for minute mass fractions of NPs. Birefringence measurements were performed to investigate the orientational order parameter and the conical tilt angle's dependence on the mass fraction of the nanoplatelets and the temperature. Additionally, we measured a Fréedericksz-like reorientation transition voltage threshold and switching times as functions of the mass fraction and temperature. A huge increase of the voltage threshold was measured in the twist-bend nematic phase. The dependence of the viscoelastic coefficient ζ on NPls' mass fraction was investigated. The splay elastic constant of the helicoidal structure was estimated, using a coarse grain approximation, to be two orders of magnitude higher than in the uniform nematic phase. Finally, in the twist-bend nematic phase, the impact of temperature and nanoplatelets mass fraction on the hysteresis loop of the reorientation transition was investigated.

Electro-optic effect in thin film strontium barium niobate (SBN) grown by RF magnetron sputtering on SrTiO3 substrates

Ferroelectric strontium barium niobate (SrxBa1−xNb2O6 or SBN) is a material with high electro-optic (EO) response. It is currently of interest in low voltage silicon-integrated photonics (SiPh). We have grown strongly textured SBN films with x = 0.65 by radio frequency sputtering on (100)-oriented SrTiO3 substrates where grains with mixed (310) and (001) out-of-plane orientation form. For these mixed orientation films, we observed a maximum effective EO coefficient of 230 pm/V using a transmission EO measurement geometry that is responsive only to the in-plane polarization component coming from the (310)-oriented grains. We also demonstrate that by growing SBN on TiO2-terminated SrTiO3 substrates, we can obtain predominantly (001)-oriented SBN films with out-of-plane polarization. Transmission EO measurements on such (001)-oriented films show a reduced effective Pockels coefficient of 88 pm/V, which is consistent with the overall ferroelectric polarization becoming out-of-plane. This work shows that controlling substrate termination is effective in controlling the grain orientation of SBN films grown on top and that one can readily integrate SBN films on SrTiO3-buffered Si for use in SiPh.

Facile Growth of Zinc Oxysulfide Nano Thin Film-based Visible Light Photosensor by Hydrothermal Method

Zinc oxysulfide (ZnOS) nano-thin film has been deposited on a p-type silicon and glass substrate via the hydrothermal deposition method at a temperature of 200 °C. The crystallographic information and morphological analysis of zinc oxysulfide (ZnOS) thin film have been done by X-ray diffraction (XRD) patterns and field effect scanning electron microscopy (FESEM). The chemical composition investigation of the ZnOS thin film was done by energy-dispersive X-ray spectroscopy (EDX). Ultraviolet-visible (UV–vis) and photoluminescence (PL) spectroscopy have been utilized for optical analysis. The electrical and electro-optical measurements of ZnOS thin film have been carried out by I-V characteristics in the visible light environment with a power density of 30 mW cm−2. It was found that zinc oxysulfide (ZnOS) thin film illustrates the facile responsive photodetection under visible light. The ZnOS thin film has a response time of 1.46 s and a recovery time is equal to 1.32 s. The specific detectivity of the deposited thin film was found to be 3.81 × 108 Jones. The responsivity of the deposited thin film is found 7.08 × 102 mA W−1.

Effects of ion doping on the dielectric and electro-optical properties of chiral nematic liquid crystal

This study presents experimental findings pertaining to the use of the cationic surfactant cetyltrimethylammonium bromide (CTAB) as a dopant dispersed in cholesteric liquid crystal. The impact of the additive on the electrical and dielectric properties was investigated by dielectric spectroscopy. Compared with that in the pure counterpart, the dielectric relaxation frequency increased due to the added ions in the cholesteric liquid crystals impregnated with 0.01–0.5-wt% CTAB. Furthermore, by analyzing the dielectric spectra in a specific frequency range, the DC conductivity, ion density, and diffusion coefficient were calculated and compared. By fitting the experimental data into the Arrhenius equation, the activation energy was obtained as well. Our experimental results illustrated that all these physical properties were strongly dependent on the CTAB concentration and the temperature. This work also involved the electro-optical measurement in combination with the observation of optical texture. The ion addition provoked electrohydrodynamic flows in a surfactant-dispersed mixture, generating a homogeneous and transparent uniform lying helix state between two low-transmission optical states—the focal conic and dynamic scattering states. The operating frequency range of the dynamic scattering state was significantly broadened by the ionic dopant.

Extremely Weak Electro-Optic Kerr Effect in Methyl Silicone Oils.

The electro-optical properties of methyl silicone oils with viscosities ranging from 10 to 10,000 cSt have been studied extensively to verify their suitability as immersion liquids. Immersion liquids are often used in nonlinear optics to protect hygroscopic crystals from moisture, reduce multiple reflections, and protect against electrical breakdown. However, the lack of experimental data makes it difficult to select an optimal liquid that does not exhibit a significant electro-optical Kerr effect in the fringing electric field around the electrodes on the crystal. Electro-optical measurements were performed using an improved dynamic polarimetric method, which compensates for the measurement errors caused by inaccurate positioning of the electro-optical modulator's operating point on its transmission characteristics. The values of the Kerr coefficient ranged from -8.83 × 10-16 to -6.79 × 10-16 m V-2 for all oil samples, at temperatures from 25 to 80 °C and frequencies from 67 to 1017 Hz. These exceptionally low values, together with a low dielectric constant, very good transparency, and high chemical stability, make methyl silicone oils highly suitable as immersion liquids. The Kerr coefficient and other electro-optical coefficients increased with increasing temperature. This unusual result cannot be adequately explained by Buckingham's molecular theory of the Kerr effect.

Active Compensation Technology for the Target Measurement Error of Two-Axis Electro-Optical Measurement Equipment.

For two-axis electro-optical measurement equipment, there are many error sources in parts manufacturing, assembly, sensors, calibration, and so on, which cause some random errors in the final measurement results of the target. In order to eliminate the random measurement error as much as possible and improve the measurement accuracy, an active compensation technique for target measurement error is proposed in this paper. Firstly, the error formation mechanism and error transfer model establishment of the two-axis electro-optical measurement equipment were studied, and based on that, three error compensation and correction methods were proposed: the least square (LS)-based error compensation method, adaptive Kalman filter(AKF)-based error correction method, and radial basis function neural network (RBFNN)-based error compensation method. According to the theoretical analysis and numerical simulation comparison, the proposed RBFNN-based error compensation method was identified as the optimal error compensation method, which can approximate the random error space surface more precisely, so that a more accurate error compensation value can be obtained, and in order to improve the measurement accuracy with higher precision. Finally, the experimental results proved that the proposed active compensation technology was valid in engineering applicability and could efficiently enhance the measurement accuracy of the two-axis electro-optical measurement equipment.

Innovatively feasible wet incipient method for preparing Cu doped TiO2 nanocomposite: Electro-optical measurement supported by quantitative quantum and classical calculations

The Cu-doped titanium oxide (Cu/TiO2) nanocomposite was systematically prepared using the innovatively feasible incipient wet impregnation method. Notably, the samples were derived from the raw materials through water dilution only. The successful formation of the host anatase TiO2 phase was confirmed by the characteristic peaks observed in the acquired X-ray powder diffraction (XRD) spectrum, which displayed intense peaks attributed to Cu2+ scattering sites, indicating the formation of crystallite Cu/TiO2 nanostructures. Dielectric measurements revealed that Cu/TiO2 possesses a higher dielectric permittivity compared to undoped TiO2. The conductivity for both structures exhibited a decreasing trend with increasing temperature. Interestingly, the measured optical properties indicated that Cu/TiO2 exhibited the minimum energy gap and maximum refractive index. This was further validated by qualitative time-dependent density functional calculation on a stable structural model, which was confirmed through semi-empirical molecular dynamic calculations. Thus, we have demonstrated the capability of our innovatively feasible synthesis method to produce the industrially important Cu-doped TiO2.

Self-powered high-performance UV–vis–IR hybrid photovoltaic photodetector based on Epilobium angustifolium L. (Onagraceae)

Water-soluble Epilobium angustifolium (EA) extract was successfully coated on n-type Si single crystal by spin coating method to obtain EA/n-Si heterojunction device. UV–vis absorption and SEM analysis of the EA film were performed and the optical band gap was calculated as 2.71 eV. Electro-optical measurements of the fabricated device were performed and was found to give very good photoresponse in the UV–vis-IR regions. According to the experimental results, the EA/n-Si heterojunction showed not only high-performance photodetector properties but also self-driven properties under visible light as well as under UV and IR lights. At 150 mW/cm2 visible light, the device demonstrated excellent photovoltaic properties with Voc and Isc values of 0.40 V and 4.65 A, respectively. Under IR light, the responsivity, specific detectivity and NPDR reached 0.65 A/W and 1.41 × 1012 Jones, 4.23 × 108 W−1 respectively. Finally, a high-performance organic/inorganic photodetector in the broadband range has been successfully fabricated.

Exploring Quantum Dots Size Impact at Phase Diagram and Electrooptical Properties in 8CB Liquid Crystal Soft-Nanocomposites.

We explore the influence of functionalized core-shell CdSe/ZnS quantum dots on the properties of the host liquid crystal compound 4-cyano-4'-octylbiphenyl (8CB) through electrooptical measurements. Two different diameters of quantum dots are used to investigate the size effects. We assess both the dispersion quality of the nanoparticles within the mixtures and the phase stability of the resulting anisotropic soft nanocomposites using polarizing optical microscopy. The temperature-mass fraction phase diagrams of the nanocomposites reveal deviations from the linear behavior in the phase stability lines. We measure the birefringence, the threshold voltage of the Fréedericksz transition, and the electrooptic switching times of the nanocomposite systems in planar cell geometry as functions of temperature, mass fraction, and diameter of the quantum dots. Beyond a critical mass fraction of the dopant nanoparticles, the nematic order is strongly reduced. Furthermore, we investigate the impact of the nanoparticle size and mass fraction on the viscoelastic coefficient. The anchoring energy at the interfaces of the liquid crystal with the cell and the quantum dots is estimated.

Generation and characterization of ultrabroadband polarization-frequency hyperentangled photons.

We generate ultrabroadband photon pairs entangled in both polarization and frequency bins through an all-waveguided Sagnac source covering the entire optical C- and L-bands (1530-1625 nm). We perform comprehensive characterization of high-fidelity states in multiple dense wavelength-division multiplexed channels, achieving full tomography of effective four-qubit systems. Additionally, leveraging the inherent high dimensionality of frequency encoding and our electro-optic measurement approach, we demonstrate the scalability of our system to higher dimensions, reconstructing states in a 36-dimensional Hilbert space consisting of two polarization qubits and two frequency-bin qutrits. Our findings hold potential significance for quantum networking, particularly dense coding and entanglement distillation in wavelength-multiplexed quantum networks.

Electro-optical Kerr constant measurement of tellurite and chalcogenide glasses in the visible at 633nm and in the infrared at 3.39μm

We report the implementation of an optical bench to measure the electro-optical Kerr constant in bulk infrared glasses, especially for two different infrared glass families: tellurites and chalcogenides. We give a detailed description of the setup, including the specially designed Kerr cell. The samples preparation and the setup validation with a reference material are reported. Finally, we measure the Kerr constant of two compositions that we use as core glasses for the realization of hybrid fibers: 70 TeO2 – 25 ZnO – 05 La2O3 (mol. %) tellurite glass at 633 nm and 20 Ge – 60 Se – 20 Te (mol. %) chalcogenide glass at 3.39 μm. To our knowledge, this is the first measurement of electro-optical Kerr constant for a chalcogenide glass.

Short helix pitch ferroelectric liquid crystals induced in nematic matrix by chiral non-mesogenic dopants

We report the development of chiral smectic C (SmC*) ferroelectric liquid crystals (FLCs) obtained by mixing of a nematic liquid crystal (NLC) as a host and chiral non-mesogenic dopants. The NLC is a binary eutectic mixture of phenyl- and biphenyl-pyrimidines, while chiral dopants belong to homologous series of secondary dilactates with terphenyldicarboxylate core. The induction in the mixtures not only the cholesteric phase, but also the wide temperature range ferroelectric SmC* phase with the helix pitch p0≈100 nm and the spontaneous polarization Ps about 70 nC/cm2 has been confirmed by dielectric, optical, and electro-optical measurements. The developed FLC mixtures are highly efficient for the deformed helix ferroelectric liquid crystal electro-optical mode because the mixtures combine mechanical stability (or mechanical shock resistance) of NLCs and kilohertz switching frequency (due to short helix pitch) of FLCs. These FLCs can be used to create various photonic devices, such as generators of vortex light fields and field-sequential color displays.

Current-driven degradation dynamics in GaN/InGaN multi-quantum-wells UV photodetectors fabricated with a high-quality Al2O3 passivation film

The degradation dynamics in GaN/InGaN multi-quantum-wells (MQWs) ultraviolet photodetectors (UV-PDs) submitted to high current stress have been intensively investigated. To scrutinize the root mechanism for degradation, several electro-optical measurements have been performed. The obtained results imply that (i) the rectification ratio diminishes largely after stress treatment, suggesting that leakage current and resistive effects are improved; (ii) both open-circuit voltage (VOC), and short-circuit current density (JSC) decline sharply within the first few hours (<50 h) of stress, after that degradation rates for VOC, and JSC slow down when stress time increases to 340 h, suggesting the physical processes responsible for degradation are altered after certain stress time; (iii) the spectral responsivity (Rλ), particularly at 384 (peak value) and below 347 nm reduce due to stress, indicating generation of deep levels associated with donors in n-GaN, and formation of severe point defects within MQWs lower the value of Rλ, whilst worsening of p-GaN quality ruin the detection capability below 347 nm; and (iv) the photo-response time changes due to acute carrier trapping during stress. Finally, the collected results suggest that the combined effects of activation of initially inactive defects and worsening of metal/GaN interfaces degrade the performance of UV-PDs during stress.