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CuInS2/ZnS core/shell quantum dots (CIS/ZnS QDs) dispersed ferroelectric liquid crystal (FLC) mixtures have been characterized for their application in electro-optical devices, energy storage, and solar cells. Physical properties of the CIS/ZnS QD-FLC (ferroelectric liquid crystal) mixtures have also been investigated with varying QD concentrations in order to optimize the critical concentration of QDs in mixtures. The presence of QDs breaks the geometrical symmetry in the FLC matrix, which results in a change in the physical properties of the mixtures. We observed the reduced values of primary and secondary order parameters (tilt angle and spontaneous polarization, respectively) for mixtures, which also depend on the concentration of QDs. The reduction of spontaneous polarization in QDs-FLC mixtures is attributed to the adverse role of flexoelectric contribution in the mixtures. The 92% faster electro-optic response and enhanced capacitance indicate the possible application of these mixtures in electro-optical devices and solar cells. Photoluminescence emission of pure FLC and QDs-FLC mixtures has been thermally tailored, which is explained by suitable models. [ABSTRACT FROM AUTHOR]

Effects of luminescent coupling are observed in monolithic 5V, five-junction GaAs phototransducers. Power conversion efficiency was measured at 61.6%±3% under the continuous, monochromatic illumination for which they were designed. Modeling shows that photon recycling can account for up to 350mV of photovoltage in these devices. Drift-diffusion based simulations including a luminescent coupling term in the continuity equation show a broadening of the internal quantum efficiency curve which agrees well with experimental measurements. Luminescent coupling is shown to expand the spectral bandwidth of the phototransducer by a factor of at least 3.5 for devices with three or more junctions, even in cases where multiple absorption/emission events are required to transfer excess carriers into the limiting junction. We present a detailed description of the novel luminescent coupling modeling technique used to predict these performance enhancements. [ABSTRACT FROM AUTHOR]

Detailed investigations of the quadratic nonlinear response of a series of new polyimides with covalently attached chromophore DR13 are performed by the Maker fringes method in the range of fundamental wavelength from 850 to 1450 nm. Polymer films with thickness of 100–400 nm were spin-coated on glass substrates and corona poled. For these materials, the maximum values of the second harmonic generation coefficients d33 are 80-120 pm/V. A red shift of the nonlinear response dispersion with respect to the linear absorption spectrum was observed for the DR13 chromophore. The temperature dependences of linear absorption and nonlinear coefficients d33 for studied structures are observed. It was found that the temperature changes of the absorption spectra lead to appreciable contribution to the value of the nonlinear coefficient d33. The demonstrated high temperature stability (up to 120 °C) of chromophore-containing polyimide thin films makes it possible to eliminate the degradation of their nonlinear optical properties in the future applications of such structures. [ABSTRACT FROM AUTHOR]

We examine the excitonic properties of layered configurations of low dimensional transition metal dichalcogenides (LTMDCs) using the fractional dimensional space approach. The binding energies of the exciton, trion, and biexciton in LTMDCs of varying layers are analyzed, and linked to the dimensionality parameter α, which provides insight into critical electro-optical properties (relative oscillator strength, absorption spectrum, exciton-exciton interaction) of the material systems. The usefulness of α is highlighted by its independence of the physical mechanisms underlying the confinement effects of geometrical structures. Our estimates of the binding energies of exciton complexes for the monolayer configuration of transition metal dichalcogenides suggest a non-collinear structure for the trion and a positronium-molecule-like square structure for the biexciton. [ABSTRACT FROM AUTHOR]

A new method for measuring spin currents is proposed, based on the linear electro-optic (Pockels) effect caused by the additional second-order nonlinear electric susceptibility (electro-optic tensor) generated by the spin currents. The non-zero elements of electro-optic tensor induced by spin currents in GaAs crystal are calculated, and the wave coupling theory of linear electro-optic effect is used to analyze the polarization change of a probe beam. The numerical results show that, for a linearly polarized probe beam with a frequency close to the band gap of GaAs crystal, its polarization rotation can be as large as 14 lrad under an applied electric field of about 350V/mm. This effect should offer an alternative detection method for spintronics. [ABSTRACT FROM AUTHOR]

In a silicon-on-insulator (SOI) waveguide corner mirror (WCM) structure, with the quantum process of a frustrated total internal reflection (FTIR) phenomenon and the time delay principle in the two-dimensional potential barrier tunneling process of a mass of particles, we derive an accurate physical model for the Goos-Hanchen (GH) shift of optical guided-mode in the FTIR process, and in principle match the GH shift jumping states with the independent guided-modes. Then, we propose and demonstrate a new regime of 1 × N digital optical switches with a matching state between the free-carrier dispersion (FCD) based refractive index modulation (RIM) of silicon to create a GH shift jumping function of a photonic signal at the reflecting interface and the independent guided-modes in the FTIR process, where a MOS-capacitor type electro-optic modulation regime is proposed and discussed to realize an effective FCD-based RIM. At the critical matching state, i.e., the incident of an optical beam is at the vicinity of Brewster angle in the WCM, a mini-change of refractive index of waveguide material can cause a great jump of GH shift along the FTIR reflecting interface, and further a 1 × N digital optical switching process could be realized. For a 350-500 nm single-mode rib waveguide made on the 220 nm CMOS-compatible SOI substrate and with the FCD effect based RIM of silicon crystal, a concentration variation of 1018-1019 cm-3 has caused a 0.5-2.5 μm GH shift of reflected beam, which is at 2-5 times of a mode-size and hence radically convinces an optical switching function with a 1 × 3-1 × 10 scale. [ABSTRACT FROM AUTHOR]

The societal impact of liquid crystals (LCs) in electrooptical displays arrived after decades of research involving molecular-level design of LCs and their alignment layers, and elucidation of LC electrooptical phenomena at device scales. The anisotropic optical, mechanical and dielectric properties of LCs used in displays also make LCs remarkable amplifiers of their interactions with chemical and biological species, thus opening up the possibility that LCs may play an influential role in a data-driven society that depends on information coming from sensors. In this article, we describe ongoing efforts to design LC systems tailored for chemical and biological sensing, efforts that mirror the challenges and opportunities in LC design and alignment tackled several decades ago during development of LC electrooptical displays. Now, however, traditional design approaches based on structure–property relationships are being supplemented by data-driven methods such as machine learning. Recent studies also show that computational chemistry can greatly increase the rate of discovery of chemically responsive LC systems. Additionally, non-equilibrium states of LCs are being revealed to be useful for design of biological sensors and more complex autonomous systems that integrate self-regulated actuation along with sensing. These topics and others are addressed in this article with the aim of highlighting approaches and goals for future research that will realise the full potential of LC-based sensors. [ABSTRACT FROM AUTHOR]

Integrated optical computing has the potential to enhance the computation abilities in terms of computing speed and power consumption during the post-Moore's law era. As one of the widely investigated approaches, electro-optic logic uses electro-optic switches as the building blocks to achieve complex functions. In this paper, we propose and experimentally demonstrate a multioperand electro-optic logic gate that contains multiple active regions in a single gate to further increase the versatility of gates. Thus, one gate can be controlled by several electrical inputs simultaneously. The ability of multioperand logic gates is thoroughly explored. The detailed comparison shows that the proposed gate can largely improve the circuit performance in terms of the area, latency, power, and insertion loss. We believe the multioperand logic gate has the potential to contribute to a more compact and power-efficient integrated optical computing system. [ABSTRACT FROM AUTHOR]

An attempt for specifying the concept of input effects has been made in the article in order more data to be systematized about them, to be specified the composition and their effect over the planning and functioning of electro-optical device. An analysis has been made, showing the impact of the input effects over the functionality of the electronic-optical device for measuring the position of distant objects according to angular coordinates. [ABSTRACT FROM AUTHOR]

Cholesteric liquid crystals with long pitch confined in homeotropic cells can be used to generate stable but distorted and localized liquid crystal structures exhibiting spherulitic textures, known as 'bubbles.' As these bubbles can be induced by an external electric field with a narrow range following the confinement ratio C=d/p ≈1 (d representing cell thickness and p representing cholesteric pitch), it is possible to obtain electrically controlled micro-lenses. Here we investigated the optical and electro-optical properties of such liquid crystal bubbles for creating an array of micro-lenses with electrically tunable focal length. [ABSTRACT FROM AUTHOR]

Deoxyribonucleic acid based gel solid electrolytes were prepared and their electric properties were characterized. Their ionic conductivity is in the range of 10-4-10-5 S/cm at room temperature and increases linearly in function of temperature, obeying an Arrhenius-like relationship. The present study, combined with the literature data, suggests that the electrical conduction mechanism in these membranes involve ion motion and/or charge hopping, promoted most likely by a significant interaction between the membrane components. The good conductivity results, as found here, together with the good transparency and good adhesion to the electrodes show that the DNA-based gel polymer electrolytes are very promising materials for application in various electrochromic devices. [ABSTRACT FROM AUTHOR]

It is shown that the formation of water at the surface of protonated LiNbO3 can lead to the precipitation of disordered phases, causing undesirable degradation of the electro-optic properties of the material. These structural defects are observed to increase the conductivity, which leads to a slow build-up of space charges, believed to be a key reason for voltage bias drifts in LiNbO3 electro-optic devices. Annealing under a controlled partial pressure of water vapor is shown to minimize such damage to the crystal lattice. An additional reverse exchange process is proposed that further improves the stability of the crystal and its electro-optic properties. [ABSTRACT FROM AUTHOR]

In order to estimate electro-optical response times, measurements of the transmitted light intensity through positive uniaxial nematic thin films in planar alignment have been performed. Very fast relaxation times were experimentally found for nematic samples aligned with conductive polymers, namely, polypyrrole doped with 5 types of anions having different molecular sizes and geometries. Using undoped polypyrrole alignment layers, slower electro-optical responses were obtained. Given that the improvement in the relaxation times is induced by the presence of the anions in the polypyrrole films, the increasing of the total restoring torque of the nematic molecules to the confining surfaces-responsible for the short relaxation times-is related to the charges accumulated at the nematic-conductive polymer interface. [ABSTRACT FROM AUTHOR]

We investigate the electro-optic properties and high-frequency relative dielectric constants of epitaxially grown lanthanum-modified lead zirconate titanate (PLZT) and polycrystalline barium titanate (BaTiO3) films in a high-frequency range of up to 40 GHz for designing a high-speed ferroelectric thin-film modulator. We also demonstrate a ferroelectric thin-film Mach-Zehnder-type waveguide modulator using the epitaxially grown PLZT film. The use of a composite structure with a low dielectric coefficient substrate and a buffer layer enabled of a ferroelectric thin-film waveguide modulator with 40-Gb/s operation. [ABSTRACT FROM AUTHOR]

Nanowires show a large potential for various electro-optical devices, such as light emitting diodes, solar cells, and nanowire lasers. We present a method developed to calculate the modal reflection and transmission matrix at the end facets of a waveguide of arbitrary cross-section, resulting in a generalized version of the Fresnel equations. The reflection can be conveniently computed using fast Fourier transforms once the waveguide modes are known. We demonstrate that the reflection coefficient is qualitatively described by two main parameters: the modal field confinement and the average Fresnel reflection of the plane waves constituting the waveguide mode. [ABSTRACT FROM AUTHOR]

We proposed a design of a tunable optical isolator. The electro-optic (EO) effects in periodically poled lithium niobate (PPLN) with a defect were studied. EO effects and second harmonic generation (SHG) allow three-wave coupling in this nonlinear optics process. A defect is inserted in an asymmetrical position in PPLN to break the reciprocity of the fundamental-wave transmission in two reversed propagating directions. We numerically demonstrated that the contrast of this optical isolator can be tuned from -1 to 1 by simply changing the external dc electric field. With EO effects, the position of the defect can be designed more flexibly maintaining a high contrast of the optical isolation. [ABSTRACT FROM AUTHOR]

Pb(ZrxTi1-x)O3 [x=0.52, PZT(52) near morphotropic phase boundary], tetragonal PZT(65), and rhombohedral PZT(20) thin films have been fabricated on different transparent substrates by radio frequency sputtering. The optical studies show that the band gap energies and refractive indices of the PZT thin films are crystal phase dependent. The largest electro-optic (EO) coefficient of 219.6 pm/V has been achieved by controlling the crystal phase of the PZT thin films. The linear EO coefficients of PZT(52) films on the (Pb0.86La0.14)TiO3-coated glass, indium tin oxides, and MgO substrates are also studied. Such study could contribute to the crystal phase and substrate dependent PZT films for electro-optic devices and multifunctional integrated circuits. [ABSTRACT FROM AUTHOR]

The CdGa2Se4 layers were grown by the hot-wall epitaxy method. From the absorption measurement, the band-gap variation in CdGa2Se4 was well interpreted using Varshni's equation. After the postannealing in various ambient, the behavior of point defects in CdGa2Se4 was investigated by measuring photoluminescence (PL). Point defects originating from VCd, VSe, Cdint, and/or Seint were classified as donor or acceptor types. Thus, the Ga in CdGa2Se4 did not form native defects because the Ga existed in the form of stable bonds in CdGa2Se4. Based on these PL results, we schemed out a band diagram of the recombination process in CdGa2Se4. [ABSTRACT FROM AUTHOR]

Planarly aligned cholesteric liquid crystals of short pitch were applied by the in-plane electric field. The reorientation of the director, increasing pitch, and flexoelectricity induce the change of transmission. The main effect in this research is due to the director reorientation along the electric field. The flexoelectricity deters the change in the birefringence induced by the dielectric response. The response was very fast for the effectively thin periodic boundary of the half-pitch of liquid crystal. The contrast ratio was more than 80 for red light and the response time was less than 0.1 ms for the experimental conditions. [ABSTRACT FROM AUTHOR]

In this paper we report the electro-optic characterization of two homologous series of low molar mass bimesogenic siloxane-containing liquid crystals. The materials used have two alkoxycyanobiphenyl mesogenic units with variable alkyl chain joined by a two- or five-siloxane moiety and all exhibit stable smectic A mesophases over wide temperature ranges (up to 100 °C wide). Due to their inherent ruggedness these materials have potential for use in polarizer-free, bistable, scattering display and storage devices. The bistable modes are at low and high frequencies. The low frequency mode (write) is a highly scattering focal conic texture resulting from electrohydrodynamic instabilities while the high frequency mode (erase) is a clear state due to dielectric reorientation of the material. Both modes are preserved upon removal of the applied electric field. We present threshold voltages as a function of temperature, frequency, and cell thickness and response times as a function of voltage for each of the bistable modes. We find reduced threshold voltages (5<=Vth<=12 V/μm) and response times that are strongly dependent on applied voltage (50 ms<=τ<=10 s). These operating conditions would suggest that these materials are particularly suitable for slow update, large area, low power information panels and displays. [ABSTRACT FROM AUTHOR]

ZnO thin films were epitaxially deposited on platinum/c-sapphire epitaxial layer using a radio frequency magnetron sputtering method. Xe, rather than Ar, was used as the sputtering gas. The leakage current as well as dielectric loss was suppressed upon use of Xe. Moreover, the full width at half maximum ω scan and surface morphology were improved by using Xe. These improvements are attributed to the fact that damage to the films during deposition using Xe is less than that upon the use of Ar. The electro-optical (EO) effect was evaluated by reflection configuration. ZnO films prepared with Ar showed no EO response. However, films prepared with Xe show a linear response of change in the birefringence with the electric field. The EO coefficient (rc) was evaluated as 0.2 pm/V. In order to reduce the leakage current and further improve the EO property, Mn was doped to the ZnO films prepared with Xe. As a result, the leakage current was eight orders of magnitude less than that of the undoped film. The dielectric loss was also reduced. Additionally, the frequency dispersion of dielectric loss was suppressed. Therefore, the space charge in the films is thought to be reduced by using Xe and doping with Mn. As a result of suppression of space charges, an rc of 2.2 pm/V was achieved. This value is close to that of the single crystal. [ABSTRACT FROM AUTHOR]

Responsivity measurements are reported for LiNbO3 electro-optic field sensors operated under applied electric fields at ac frequencies in the vicinity of the acoustic resonance values of the crystals. At these frequencies, piezoelectric effects dominate the sensor output. These resonance effects are well known and commonly considered parasitic. However, we propose their use as a sensitivity-enhancing mechanism for electric-field detection. We have found that our field sensors operated within these resonances responded linearly with the applied field strength and exhibited increases in their intrinsic sensitivities as high as 350 times larger than their normal, electro-optic values. Our modeling of the data suggests that the sensitivity enhancements are produced by the interplay between photoelastic shifts in the refractive indices and the physical vibration modes of the crystals. Aside from narrowband applications, these resonant enhancements can be exploited with fields at frequencies well beyond the narrow bandwidth of the acoustic resonance, if the fields are properly modulated. [ABSTRACT FROM AUTHOR]

The motion of highly dielectric polymer cholesteric liquid crystal (PCLC) flakes suspended in a host fluid can be controlled with an ac electric field. The electric field acts to induce a dipole moment on the flake due to interfacial, or Maxwell–Wagner, polarization. Theoretical modeling of PCLC flakes as oblate spheroids shows that the flakes will reorient to align one of the two major axes parallel to the electric field. The theory also supports the observed dependence of the particle reorientation time on the electric-field magnitude, frequency, and particle shape. A PCLC flake’s orientation determines its ability to reflect light of a specific wavelength and circular polarization. The ability to switch the position of PCLC flakes with an electric field has implications for electro-optic devices and display applications. [ABSTRACT FROM AUTHOR]

A Q-tensor method is used to model a grating-aligned zenithally bistable nematic device in two dimensions. The flexoelectrically driven switching between the two ground states is shown to occur through the creation and annihilation of pairs of defects, and the sign and magnitude of the voltage thresholds demonstrated to depend on the relative dielectric permittivity of the grating material. [ABSTRACT FROM AUTHOR]

The model of space-charge formation in photorefractive polymers due to Schildkraut and Buettner has been modified to include thermally accessible deep traps as well as shallow traps. The dynamic equations have been solved semiempirically using independent measurements of photoconductive properties to predict photorefractive dynamics. Dependencies of the dynamics on charge generation, mobility, trap density, acceptor density, ionized acceptor density, as well as their associated rates are examined. The magnitude of the fast time constant of photorefractive development is successfully predicted. The introduction of deep traps into the model has allowed us to qualitatively predict the reduction in speed due to deep trap filling and ionized acceptor growth. Experimental studies of photoconductivity and photorefraction (PR) in several polyvinyl carbazole photorefractive composites are carried out to demonstrate the applicability of the model. By choosing chromophores with different ionization potentials and by varying the chromophore concentrations, we investigate the influence of the chromophore ionization potential on the photoelectric and PR properties and reveal the nature of deep traps in the composites and their contribution to both photoconductivity and PR dynamics. Effects of plasticizer components are also discussed. [ABSTRACT FROM AUTHOR]

This article presents the results of an investigation of the electro-optical response for a hybrid twisted nematic (HTN) liquid crystal display. The device used both a hybrid alignment and a twisted director configuration. In comparison with the conventional twisted nematic mode, a faster response and a smaller operation voltage were obtained by using an appropriate amount of chiral dopant. The characteristics of the HTN cells were dependent on cell parameters such as the chemical nature of the polymer alignment layer, the cell thickness, the set twist angle, and the concentration of chiral dopant. Response times of 1.0 ms for turn-on and 16 ms for turn-off were achieved by the regulation of cell parameters. Computer simulations of the director configuration demonstrated that twist deformation plays an important role in the determination of the response characteristics. [ABSTRACT FROM AUTHOR]

Presents information on a study which proposed and demonstrated the design of an electrooptic polymer amplitude modulator. Technological steps for the fabrication of polymer-based devices; Concept of the polarization insensitive operation; Design and fabrication of the electrooptic polymer device; Conclusions.

From a diamino dicyano-phenylenevinylene skeleton a symmetrically di-salen dye was obtained and employed both as a dopant in non-emissive polymer matrixes and as building blocks in the preparation of a zinc self-assembly polymer. The new fluorophore C1 belongs to the class of the luminescent liquid crystals (LLCs). The molecule produces red emission in the crystalline phase and yellow luminescence in the nematic phase, which dramatically decreases in on-off switch mode after LC order was lost. Both C1 and its self-assembly zinc-based coordination polymer suffers a lot aggregation caused quench effect (ACQ). Conversely, thin films obtained by dispersion in polystyrene (PS) and poly(9-vinylcarbazole) (PVK) show remarkably enhanced fluorescence, reaching the noteworthy value of 77% Photoluminescence Quantum Yield (PLQY) for the PVK doped sample. Unlabelled Image • A fluorescent organic dye employable for optical and electrooptical devices was synthetized. • Cyano-phenylenevinylene (PV) derivatives are widely investigated fluorogens for emitting layers. • The dye was employed as dopant in polymer matrixes and in the preparation of a zinc coordination polymer. [ABSTRACT FROM AUTHOR]

The development of new organic simple and low-cost fluorophores is a current topic. To date innovative solutions include azo dyes because of the unique absorption behavior, but the azo group gives poor luminophores in the solid state. In order to produce a luminescent azo dye, we synthesized compound A2 , 4,4′-((1,1′)-(2,5-dimethoxy-1,4-phenylene)bis(diazene-2,1-diyl))dianiline, and its symmetrical Schiff-base derivative C2. The new compound C2 is a weakly luminescent fluorophore in the crystalline phase and when employed as building blocks in self-assembly of zinc (II) coordination polymer. Nevertheless, if used as a dopant in PS and PVK, C2 shows enhanced fluorescence and represents a good on-off naked-eye switch when dispersed in a room-temperature nematic polymer. PL azo dyes are very rare. We produced the symmetrical azo fluorophore C2 with considerable PL performances. The new fluorophore C2 is a yellow emitter weakly fluorescent in the crystalline phase but remarkably luminescent as a dopant in PS, PVK and in a LC matrix for on-off naked-eye PL switch. Unlabelled Image • A fluorescent azo dye employable for optical and electrooptical devices was synthetized. • Azobenzene fluorophores are investigated as emitters for LEDs and OLEDs. • The dye was employed as dopant in polymer matrixes and in the preparation of a zinc coordination polymer. [ABSTRACT FROM AUTHOR]

To deal with the registration of infrared and visible image with significant difference in contrast and large geometric distortion in electro-optical pod, a robust and fast registration method by using common structural features is proposed in this paper. First, to adjust the scales of input images, a geometric transformation model is built based on parameters of the cameras. Then, a global structural feature extraction strategy is developed by using phase congruency and significance ranking space. Those features are not only invariant to the scale and contrast but also embody the structural of the input images maximally and uniformly. Finally, to enhance the robustness to contrast, blurring, and incompleteness of structures, an adaptive feature matching method with kernelized correlation filter is presented. Experimental results demonstrate that the proposed method has better performance than several state-of-the-art methods in robustness and precision, and also confirm its validity in the real environment. [ABSTRACT FROM AUTHOR]

Measuring the transient voltages, including lightning or switching impulse overvoltage, is helpful for accident analysis of power system and insulation design. In this paper, a contactless transient voltage measuring system based on a metal-free integrated electro-optic electric field sensor was proposed, implemented, and tested. The lightning and switching impulse transients are proportional to the electric field they generate, and vice versa, enabling measurement of the transient voltage by measuring the associated electric field. The proposed method uses an electric field sensor to directly measure the field generated by the voltage without any capacitive coupling. In addition, a method to decouple the multiphase coupling was proposed. The performances of the measuring system were tested by simulation experiments and compared with that of a standard divider. The field data of the transient overvoltage on a 220 kV bus during the process of putting a capacitor voltage transformer into operation were given. The measurement results were found to coincide with the related physical process. [ABSTRACT FROM AUTHOR]

Microscale gas breakdown plays a critical role in microplasma generation for numerous applications and device lifetime for miniaturized electronics. This communication extends a previous investigation of pulsed breakdown morphology [G. Meng et al., Phys. Plasmas 25, 082116 (2018)] by providing further insight into the spatio-temporal dynamics of pulsed gas breakdown for different gap distances using an in-situ electrical-optical measurement method. Time-resolved sequential images and the corresponding photon number distributions are obtained to demonstrate the dynamic evolution of the breakdown channel morphology and the ionization intensity during breakdown development. For a 15 μm gap, breakdown transitions from a spot area on both electrode surfaces to a broad discharge region comprised of filamentary main breakdown channel (∼2.00 μm) and surrounding weak ionization area due to the local field enhancement. For a 2 μm gap, it transitions from a thin channel (∼1.09 μm) to a wider and uniform channel (∼2.14 μm) because the electric field is more uniform at smaller gaps. Interestingly, the main breakdown channel width at the instant of breakdown is independent of the gap width. For the 2 μm gap, field emission dominates the initial stage of breakdown and collision ionization (α process) dominates during breakdown development, while the Townsend avalanche dominates the breakdown process for the 15 μm gap. We apply a simple asymptotic theory to quantify the relative contribution of these phenomena and predict that breakdown will follow Paschen's law for gaps larger than 17.8 μm. [ABSTRACT FROM AUTHOR]

Abstract As well known, micro and nanosatellites are being proposed for a variety of space missions, due to the advantages offered in terms of flexibility, cost and development time-scales. They also allow the development of space missions based on distributed architectures, composed of a number of small platforms in coordinated flight. However, technological advancements are still needed to make micro and nanosatellite competitive with respect to larger platforms. In this paper, we explore the potentiality offered by hyper hemispheric lens for the development of miniaturized and multi-function sensors for use on board of micro satellites. Hyper hemispheric lens belong to the ultra-wide field-of-view optical objectives. Here a novel optics of this category is presented. Its field of view is 360° in azimuth (panoramic capabilities) and 135° for the off-boresight angle (hyper-hemispheric field). With such capabilities the lens may be exploited as a very-large field-of-view optics where moving parts can be avoided. This is of interest to space applications, in which devices with any moving part, representing a possible point of failure, shall be avoided or reduced to the minimum. A hyper hemispheric lens may, then, be adopted for electro optical devices in space satellite subsystems, such as star-, Sun- and Earth-sensors, or for monitoring the environment surrounding the satellite in the case of on-orbit servicing or active debris removal operations. Weight and cost budgets for small and micro satellites are also important parameters to determine their success. Hyper hemispheric lens may be kept quite compact in dimension and the need of a single imaging detector, for a so large field of view, strongly reduces costs. In this paper, we explore possible applications of a multi-purpose space device based on a hyper hemispheric lens on board of micro and nanosatellites. [ABSTRACT FROM AUTHOR]

Highlights • Compensate tracking boresight error by providing jitter for the signal light. • The electro-optic modulator (EOM) is used to provide jitter. • The EOM is used to estimate the boresight error. • The digital optical phase-locked loop is used. • The mixing efficiency and sensitivity of the communication system is well improved. Abstract A method for compensating the tracking boresight error by providing additional jitter for the signal light is proposed. The relationship between jitter angle and system performance is analyzed, which shows the sensitivity attenuation is within 0.1 dB when the angle is within 0.2–1.2 μrad. The optimal mathematical model of output power and compensation angle estimation is established. And the simulation results show the mixing efficiency of the coherent optical communication system is well improved. [ABSTRACT FROM AUTHOR]

Abstract The paper presents electrooptic properties of PDLC films obtained by photopolymerization-induced phase separation in different conditions and deposited on elastic substrates having different resistivity. The effect of the curing rate on the morphology of PDLC composite was confirmed. The faster is curing the lower is diameter of liquid crystal droplets and consequently switching voltages are higher and switching times are shorter. Choosing the proper liquid crystalline mixture for given polymer matrix one should take into account optical and dielectric properties, moreover solubility of mixture components in cured polymer matrix as well as their surface tension with respect to partly cured prepolymer. Both latter features can affect liquid crystal droplet shape and effective clearing point. It was shown that the resistivity of conducting layer of the elastic substrates can affect the morphology of the PDLC composite and consequently its electrooptic characteristics. Highlights • The effect of components properties on the PDLC morphology. • The effect of the resistance of conducting layer on the morphology and electrooptic properties of PDLC. • The reduction of the PDLC driving voltage. [ABSTRACT FROM AUTHOR]

Abstract We developed an alignment method for control of the polar pretilt angle at the boundaries of a liquid crystal (LC) layer in a continuous range 2–90° by introducing a low-density polymer network. The network was formed as a result of the electric field-induced segregation of a photo-reactive monomer added in concentrations of 0.5–1% to the LC host and subsequent in-situ UV-light-induced polymerization. LC director was "frozen" within a less than a micron-thick layer in the vicinity of the cell substrates at high average tilt angles anchoring the LC in the bulk similarly to a high-pretilt alignment layer. The resultant pretilt angle was determined by the voltage applied before and during polymerization and the duration of voltage application before UV-light exposure. The desired pretilt angle could be set over a small area of a sample which allowed for the fabrication of LC devices with spatially variable optical retardation. Using this method, we fabricated high-pretilt splay and bend LC cells, optically recorded converging lenses and bi-prisms with electrically controlled optical characteristics, and phase diffraction gratings with resolution better than 50 lines/mm. Highlights • We developed an effective method of pretilt angle control in nematic liquid crystal cells. • The paper includes our newest results on stabilization of high-pretilt bend structures in π-cells, the fastest display modes. • Our method of pretilt control eliminates a need for a photo-lithographically manufactured electrodes. • We present examples of an optically recorded lens, prism, and phase diffraction grating. • The optical elements demonstrate low light scattering, which allows for the commercial application. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we present a graphene-based plasmonic electro-optical multi-logic gate (MLG) operating at THz frequency. The designed MLG supports AND, XNOR, and NOR logic gates in a graphene-dielectric-metal structure, simultaneously. The propagation length of the surface plasmons (SPs), stimulated by a 27.35 THz incident TM wave, is about 62 times larger in ON state compared to OFF state. Simulation results by the finite difference time domain (FDTD) method show the minimum extinction ratio (ER) of 29.41, 97.38, and 29.40 dB for AND, XNOR, and NOR logic gates, respectively. Also, the minimum modulation depth (MD) is obtained 99.99% for XNOR and 99.88% for AND and NOR logic gates. The proposed MLG provides a high extinction ratio and ultra-compact logical block for using in digital processing circuits and THz applications. Highlights • Using graphene-dielectric-metal structure to stimulate the surface plasmons. • Supporting AND, XNOR, and NOR logic gates in a simple structure, simultaneously. • Having an ultra-compact footprint compared to the working wavelength. • Obtaining high extinction ratios and modulation depths for all three logic gates. [ABSTRACT FROM AUTHOR]

Thin films of WO 3 :H (~450 nm) were prepared on indium tin oxide (ITO) coated glass by reactive direct current magnetron sputtering at room temperature. The visible transmittance of the original state, and the X-ray photoelectron spectroscopy analysis of WO 3 :H films prove that H + ions have been introduced into the structure of WO 3 . Based on the optimized parameters of WO 3 :H thin film, the Glass/ITO/WO 3 :H/Ta 2 O 5 /NiO x /ITO electrochromic devices (ECDs) are prepared monolithically by magnetron sputtering. Different applied voltages of 1.0, 2.0 and 3.0 V were applied to the ECD for investigating its influence on the ECD's optical contrast and cycle life. Though the ECD can get a higher contrast about 42% at 550 nm under 3.0 V voltage, however, it will be destructed quickly. When the operating voltage is 2.0 V, the ECD has a stable cycle performance with the optical contrast of >30%. [ABSTRACT FROM AUTHOR]

High-resistance photosensitive crystals of Bi12SiO20 (BSO) doped with iron ions were studied. X-ray diffraction analysis reveals the compression of a unit cell in a BSO : Fe crystal with increasing impurity concentration. Electron paramagnetic resonance demonstrates a decrease in the intensity of the EPR signal when the BSO: Fe crystal is exposed to light that generates photocarriers. It is found that the characteristic time of the EPR signal decrease is close to the value of the Maxwellian relaxation time measured with the help of the longitudinal electrooptical effect. A physical model of the mechanism of optical charge exchange of magnetic iron centers is discussed, based on the statement that the nature of the crystal bonds of the iron ion with ligands without structural modification of the crystal lattice changes during the photogeneration of carriers. A physical model is proposed, according to which a trivalent Fe3+ ion transforms into a divalent state of Fe2+ with a change in the total spin from 5/2 to 2. The compression of the unit cell with increasing iron ion concentration in the framework of the model under discussion is due to the transformation of atomic orbitals upon replacement of silicon ions by iron ions. The transformation process affects the cells unoccupied by iron, which is proved by the absence of a bifurcation of X-ray reflections and indicates the long-range nature of the intracrystalline interactions in sillenites. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) thin film has in recent years emerged due to its unique physical, electrical and chemical properties. The microstructural and optical properties of nanocrystallite ZnO films fabricated using electrospinning and post-calcination, undoped and doped with aluminum, (AZO nanostructure films) were investigated in this study. The results indicated that the crystallized and monolithic AZO films comprised perfectly linked ZnO nanoparticles (NPs). Al incorporation deformed the lattice geometry ( a and c axis) and crystallite size of (002) plane, and led to formation of zinc vacancies and Al interstitial/substituted sites. Functional molecule groups and optical properties of pristine ZnO and AZO films were studied by far-FTIR, PL and UV–Vis techniques. Our findings showed that doping ZnO with Al resulted in the Zn-O bond shifting towards higher energy levels, and it polarized the visible lights more than pure ZnO thin films. Furthermore, the formation of the large concentration of point defects in sub-atomic structure of AZO (6 wt% Al) reduced the optical band gap energy of ZnO from the 3.4 e.V to 3.05 eV. The optical transmittance of AZO films was higher than 83% in visible light range. The electrical conductivity of ZnO film was improved by Al incorporation. The results of present work indicated that the electrospinning is a promising method to fabricate the nanostructured AZO films for use in electro-optical applications such as solar cells. [ABSTRACT FROM AUTHOR]

In this paper, the bimodal amplitude-and frequency modulation method of atomic force microscopy (AFM) is applied to investigate the residual oil film on KDP crystal surface after polishing and surface cleaning. The thickness map of residual oil film is obtained based on the relationship between the cantilever resonant frequency shift and the surface stiffness. The thickness maps measured by AFM and spectroscopic imaging ellipsometry methods are compared, and the results obtained by two methods are consistent. The measurement scheme extends the application of AFM technology to characterize the residual oil on the KDP surface quality quantitatively after polishing and surface cleaning. [ABSTRACT FROM AUTHOR]

Presents a study which examined the phenomenon of light propagation of birefringent medium with particular reference to the electro-optic crystal of Bi[sub 12]SiO[sub 20]. Electric field-induced linear birefringence for different crystal configurations; Polarization characteristics of the transmitted light; Measurement of the electro-optic coefficient.

Presents a study which developed an electro-optical technique to measure intense microwave. Principle of operation; Discussion of the proof-of-principle experiment; Data analysis.

Investigates the effects of asymmetric Fabry-Perot cavity structures on the switching dynamics of symmetric self-electro-optic effect devices made of AlxGa1-XAs/GaAs extremely shallow quantum wells. Response functions; Operating voltage and switching energies; Layer structure of a reflective-type optical modulator.

Presents a study which theoretically analyzed an electro-optical device consisting of a stack of undoped alternating layers of narrow- and wide-gap materials together with a series resistor under constant voltage bias. Operation of the device; Information on the Franz-Keldysh effect; Impact of the Kirchhoff's law for the electrical circuit of the device on the voltage drop; Mechanism for an effective operation of the devices.

Focuses on a study which investigated the dependence of electro-optic (e-o) effect in cubic materials on electric field distribution and light beam propagation direction. Derivation of the e-o effect in cubic materials using Nelson's approach; Methodology of the study; Results and discussion.