In this work we, propose a tunable 2D-hydrid epsilon-near-zero (ENZ) platform in telecom windows. Taking advantage to the intrinsically ENZ of the Indium-thin-oxide (ITO) and exploiting the graphene capability to dynamically tune the plasmon polaritons we were able to adjust the cross-over frequency, where the epsilon vanishes, in four telecom bandwidth windows. Additionally, tunabilty can be achieved via electrical gating of the ITO leading to an interplay modulation of the surface plasmon polaritons at the graphene-ITO interface. Furthermore, a giant Purcell factor (PF) was observed at ENZ regimes. These results show how 2D-hybrid ENZ materials potentially find applications in multifunctional nonlinear nanophotonic systems such as ultrafast modulators, data processing and photonic quantum computers (QPCs).
Liquid crystal materials have interesting properties in Terahertz wave range. Specially 0.3 – 10.0 range is interesting looking from application point of view. The structure and rotational and vibrational oscillations of liquid crystal molecules have influence on physical properties of the material in this frequency range. Chosen liquid crystal materials with dielectric anisotropy parameters (Δε form 0 to more than 30) and optical refractive index (Δn from 0 to about 0.6) in THz range ware investigated. Firstly transmission, absorption and permittivity of chosen liquid crystal molecules were simulate. Influence ofdifferent terminal group like F, CN, NCS and quantity of benzene rings were compared. Relations between structure of molecules and absorption spectra were observed. These parameters were compared with experimental data. Some liquid crystal materials (single compounds and mixtures) obtained in Institute of Chemistry MUT with very high polarization coefficients more that 2000 nC/cm2 and relatively low loss were tested. Significant differences in their dielectric losses and dichroism have been obtained. Refractive indices and absorption parameters were characterized. Acceptable dynamic parameters from application point of view were received. This kind of liquid crystal samples can have application in tunable terahertz devices, like tunable phase shifter and gratings.
Nematic liquid crystals are promising dielectrics for tunable microwave devices due to their significant birefringence and
moderately low loss. Dielectric anisotropy or refractive index anisotropy of liquid crystal is one of the important
parameter for the design of variety of reconfigurable devices. In this work, transmission line method is used for the
broadband investigation of nematic liquid crystals in the frequency range of 1-10 GHz. For this purpose, a measurement
device is proposed with a tunable liquid crystal transduces based on an inverted microstrip structure section placed
between two segments of layered microstrip lines terminated by microstrip-coaxial line transitions. Measurements of the
scattering parameters of the device with standard liquid crystal 6CHBT as well as with a novel highly anisotropic
mixture W1825 have been conducted. Based on these measurements, a high effective refractive index anisotropy of 0.31
for the W1825 mixture compared to 0.12 for 6CHBT have been determined. These values are lower of 26% and 18%
than anisotropy of the refractive indices appointed by a resonator method for W1825 and 6CHBT, respectively. Progress
in highly anisotropic mixtures opens new low-cost liquid crystal applications in microwave devices.
I have investigated induced diffraction gratings recorded by light intensity pattern in pure and dye-doped nematic liquid crystals antraquinone dyes (0.1 - 1% w/w), sandwiched between two coating glass plates covered by ITO conductive and polyimide orientation layers (low-angle rubbing, tilt 1.5 - 2°) under dc electric field. In dye- doped nematic liquid crystals high diffraction efficiency approaching 20 % were measured. Fast optical grating formation with times constant ? of 2 ms were observed. The dependence of grating formation on strength of applied dc electric field, cell construction and liquid crystal parameters, configuration of light polarization and nematic director orientation have been reported. These effects are very useful for dynamic holography.
Our previous investigation regarding liquid crystal mixtures, used as a medium for dynamic holography, has proved the influence of addition of PVK (polivinylocarbazol) layer to the LC cell structure as a sensitivity amplifier [1]. This modification was very useful for bettering the dynamic properties of these modulators. In some cases (of LC Cells) we observe some kind of memory effect - holograms written before could be observed months after writing. We decided to examine different cells to determine CL Cell construction as rewritable holographic media.
A simple model describing location of Raman-Nath index grating photoexcited in a planar cell with photoconductive orienting layers is proposed. We believe that index grating vector is parallel to cell boundaries. One of the most important features resulting from this model is that the index grating spacing equals to projection of the exciting optical grating spacing on cell boundaries. The experimental study was carried out with 9 micrometer thick planar cell filled with nematic liquid crystal 6CHBT, activated by anthraquinone dyes. DC or square-wave AC field has been applied to the cell. Holographic gratings were recorded by two (signal + pump) or three (signal + 2 pumps) coherent p-polarized beams from He-Ne laser operating at 632.8 nm. The crossing angle between signal and pump beams and the sample tilting angle were chosen to satisfy "angular resonance". The tilting angle varied from 20° to 45°, high diffraction orders were observed up to angle 77°. Calculations on the basis of our model and experimental results are in good agreement. We also discuss and present explanation of the observed effects in geometry with 2 pump beams.
We report on asymmetric two-beam coupling and the ways of controlling it in liquid crystals cells with photoconducting polymer layers. The cells had one of the substrates covered with a photoconductive polymer layer, namely PVK, photosensitised with C60 to respond to visible light. Efficient gain was measured in 30 micron thick cells with two incident beams having the same intensity. We present a model of two-beam coupling gain based on the build-up and discharge of surface charge screening layers, spatially modulated due to the photoconductivity of doped PVK. The simulation of electric field distribution inside a liquid crystal cell for different two-beam coupling grating spacing showed different penetration of field into the liquid crystal bulk. The characteristics of dynamics, magnitude of two-beam coupling and the efficiency of diffraction were determined for different values of applied DC field, cell configuration and liquid crystals. We found that the direction of energy flow was determined just by the cell tilt and not by the DC field bias.
Dynamic optical reconstruction of digital binary holograms projected on optically addressed liquid crystal spatial light modulators with the use of computer driven multimedia projector is described. The high spatial resolution, sensitivity and full reversibility of manufactured spatial light modulators is achieved by the use of photoconducting PVK:TNF polymer layer serving as a transducer of incoming light intensity pattern into modulation of refractive index inside adjacent LC layer. Linearly polarized laser light reconstructs the phase holograms at the video-rate. The advantages and drawbacks of the presented system are discussed.
Dynamic optical data storage and other applications in the field of optical data processing would be enabled by the development of suitable nonlinear optical materials. In this paper we present an experimental investigation of the orientation photorefractive effect in nematic liquid crystal mixtures with different optical anisotropy and various cell construction layers.
A novel mechanism of photorefractivity in nematic LC cells is presented. Dynamic photorefractivity is based on temporal quasiperiodic modules excitation in the liquid crystal layer by applied external alternating electric field, and their reorientation due to charges induced by interference optical field on a surface of photoconducting orienting layer.
Photorefractive properties and possibility of guest-host effect application for real-time holography have been described. As the hosts isothiocyanate nematic liquid mixtures with positive dielectric anisotropy and as the guest antraquinone dyes were used. Enhancement of ultraphotorefractivity properties of these LC systems has been discussed. In dye-doped nematic liquid crystals high diffraction efficiency approaching 20% were obtained. Fast optical grating formation with a time constant τ of few ms have been observed. The results of our main investigations concentrated on the behavior of thin (5 ÷ 20 µm) cells with pure isothiocyanate nematic liquid crystal with high optical anisotropy (▵n > 0.35) and antraquinone doped have been presented. The dependence of grating formation on strength of applied dc and low frequency of ac electric field, configuration of light polarization and nematic director orientation were reported.
The performance of photorefractive hybrid panels made from photoconducting polymer ane nematic liquid crystal layers are reviewed and discussed. Their properties were studied under pulsed and cw illumination. The dynamic holography experiments with pulsed laser beams give information on the charge mobility in the thin photoconducting layers. The use of panels to visualize the phase objects introducing small distortions to plane wave front (such as e.g. turbulence of air) through the well-known Zernike filtering is also shown. The advantage of such nonlinear Zernike filter over conventional one is that no precise optical adjustment is necessary and the filtering is relatively easy to control by tuning the externally applied field to the modulator and/or varying the incoming light intensity.
The liquid crystal display dashboard for polish gliders PW-5 and PW-6 have been presented. The measuring flight parameters system and electronic scheme of the glider have been proposed, developed and tested. Laboratory investigations of the board flight parameters and their compatibility with standards have been described.
We report observation of the dynamic enhancement of photorefractive effect in dye-doped nematic liquid crystal in the presence of an applied ac electric field. The multi- wave mixing efficiency in a planar cell with photoconductive orienting layers has been increased by two orders.
Photorefractive properties and possibility of guest-host effect application for real-time holography have been described. Isothiocyanate nematic liquid mixtures with positive dielectric anisotropy as hosts while antraquinone dyes as guests were used. In dye-doped nematic liquid crystals high diffraction efficiency approaching 20% were obtained. Fast optical grating formation with a time constant (tau) of a few ms have been observed. The dependence of grating formation on strength of applied dc and low frequency of ac electric field, configuration of light polarization and nematic director orientation were reported.
The possibility of diffraction pattern generation in LC (Liquid Crystal) cells working as a dynamic write-read media was proven. Recording of holographic gratings formed by interfered He-Ne laser beams onto LC-cells with pure and dye-doped mixture have been investigated. The possibility of optoelectronic reconstruction of digitally stored microinterferograms allow us to adopt them in multimedia application. The hologram of virtual or real object was reconstructed by coherent illumination of optically addressed spatial light modulator (OASLM) containing holographic grating. The results obtained from LC cells of standard twisted nematic type were examined. As a result of examination of physical properties of nematic-type liquid crystal mixtures, new method of realization of LC cells were proposed. The experimental results of replacing TN cells with polivinylcarbazole (PVK) photosensitive layer cells have been discussed.
In this paper relation between the diffraction efficiency in LC dye doped cell in two wave mixing system and the applied voltage parameters had been described. The goal of this work was increase of diffraction efficiency using low frequency AC voltage. The LC cells used in the experiments were filled with pure and dye-doped liquid crystal mixtures. In this system we obtained diffraction efficiency increasing about five to eight times.
Electrohydrodynamic instabilities arising with a.c. electric field applied to planar-oriented cells filled with anthraquinone dye-doped multicomponent nematic mixture have been studied by diffraction methods. It has been found that c.w. He-Ne laser radiation of small power (~1 mW) exerts ordering effect on the LC layer domain structure. The ordered structure can persist in the presence of the same a.c. electric field for a few tens of minutes. The size of periodic optical irregularity has been calculated.
Liquid crystalline isothiocyanatocompounds have been investigated as components of mixtures for TN as well as STN displays. It was shown that mixtures with low viscosities and short response time can be formulated for both kind of display modes.
Mechanism of holographic dynamic grating recording in a thin cell with dye doped nematic liquid crystal under laser light has been proposed. Nematic liquid crystal with dye is sandwiched between two coating glass plates covered by ITO conductive and polyimide orientation layers. In this experiment, two interfering laser beams induced spatial modulation of refraction index and form interference pattern in the liquid crystal cell. The recording mechanism is linked with DC electric field driven reorientation of nematic director and induces the bulk photoconductivity of the system.
We have described the relation between LC parameters and induced diffraction gratings recorded by light intensity pattern in dye-doped nematic liquid crystals sandwiched between two coating glass plates covered with ITO conductive and polyimide orientation layers. In our investigations we used the LC cells containing planary oriented nematic mixtures (low-angle rubbing, tilt 1.5 - 2%) doped with the antraquinone dyes (0.1 - 1% w/w). Nematic liquid crystal mixtures with different electrooptical threshold, optical anisotropy, viscosity and conductivity have been investigated. The influence of resistivity, optical anisotropy of LC mixtures and polyimide layers on diffraction efficiency and other parameters have been discussed.
Induced by nanosecond pulses of second harmonic generation from Nd:YAG laser the hydrodynamical instabilities in planar- and twist-oriented layers of the nematic 6CHBT doped with anthraquinone dyes under dc electric field in the region above the Freedericksz threshold were revealed. The dependence of diffraction efficiency on voltage is characterized by the two maxima which are corresponding to the two types of EHD-instabilities that have two characteristic decay times, one of them is of the order of 100 ms and second one is equal to several milliseconds.
Self-diffraction of light on transient holographic index gratings has been measured in dye-doped twisted nematic liquid-crystal cells. The mechanism of gratings formation is connected with bulk photoconductivity which results in electric field induced torques causing local director axis reorientations. Time evolution of grating recording, voltage and polarization-configuration dependencies were examined. In the self-diffraction experiments the beam coupling effects were observed.
4-(trans-4-alkanoylcyclohexyl)cyanobenzenes and 4-alkyl 4- (trans-4-alkanoylcyclohexyl_benzoates have been synthesized and their viscosity, optical indices, dielectric and elastic constants have been measured.
An original idea of hydrostatic pressure monitoring based on a new kind of anisotropic fibers with a liquid crystalline core is presented. The liquid crystalline-core optical fiber giving a possibility of birefringence control unite the unique advantages of liquid crystals and quality of fiber technology what can be used for continuous pressure monitoring. Preliminary results of experimental studies of light propagation by optical fibers with liquid crystalline cores under hydrostatic pressure conditions are reported.
KEYWORDS: LCDs, Liquid crystals, Military display technology, Light sources and illumination, Optical filters, Solid state electronics, Crystals, Temperature metrology, Analog electronics, Visibility
The car dashboards we used were original construction. Liquid crystal display works on the twist-nematic effect with color filters. The central element of the dashboard is a digital speedometer. Other displays like tachometer, fuel and temperature gauge are analog. An electronic system assures cooperation with traditional car endowment. Isothiocyanate liquid crystal mixture assures wide range display operation -30 divided by 80 degree(s)C.
Multicomponent nematic mixtures formed from smectic components were described. Their physicochemical and electro-optical parameters (viscosity, threshold voltage, response times) were measured at different temperatures and discussed.
The investigations of some anthraquinone dyes in mixture with optical activity were presented. Their twist coefficients were defined. The comparison of electro-optical parameters with typical dichroic anthraquinone dyes were carried.
The guest-host effect permits us to eliminate at least one polarizer. This effect we apply to black and white displays. Our black and white mixtures were prepared with antraquinoe and azo-dyes and isothiocyanate LC. The optimization investigations of mixtures containing dyes admixtures were performed. The black and white displays for negative mode with the wide range of temperature (-30 divided by 85 degree(s)C) were constructed.
An influence of material constants such as elastic constants, electric permittivity constants, refractive indices, viscosity and concentration of optical dopants on the performance of STN displays are discussed. It is shown that mixtures containing as main components isothiocyanato and borodioxane compounds are speedily operating liquid crystalline materials and a high multiplexing level in this mode is obtained.
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