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The results obtained for new dual-cladding optical fiber tapers surrounded by liquid crystal (LC) doped with Fe3O4 nanoparticles in a specially developed glass cell are presented. The created structures are sensitive to changes in refractive index values in the surrounding medium caused by modifying external environment parameters. In this investigation, cells are filled with nematic LCs 6CHBT and with the same mixture doped with 0.1 wt% and 0.5 wt% of magnetic nanoparticles (Fe3O4 NPs). The taper is made on a standard single-mode telecommunication fiber, stretched out to a length of 20.0 ± 0.5 mm, and the diameter of the tapers is approximately 15.0 ± 0.3 µm, with a loss lower than 0.5 dB @ 1,550 nm. Measurements are carried out in a wide range covering the visible and infrared ranges in two setups: 1) without a magnetic field, with steering only by voltage and 2) with an applied magnetic field. The presented spectrum results are divided into two ranges according to the parameters of optical spectrum analyzers: 350-1,200 nm and 1,200-2,400 nm. For all investigations, a steering voltage is chosen from the range of 0 to 200 V, which allows for establishing the influence of dopants on transmitted power and time response at different arrangements. Due to the sensitivity of LCs to temperature changes, this paper focuses on measuring at room temperature the effect of the magnetic field on propagation in a fiber optic taper. The proposed solution demonstrates the technology for creating advanced components as a combination of fiber optic technology, LCs, and nanoparticles. The presented results show the possibility of creating new sensors of various external factors such as magnetic or electric fields in miniaturized dimensions. [ABSTRACT FROM AUTHOR]

This paper presents a study of the influence of bimetallic layer covers of a tapered optical fiber surrounded by a low refractive index liquid crystal on the properties of light propagation in the taper structure. This research follows previous works on the effect of monometallic thin films (Au and Ag). In this case, the total thicknesses of the bimetallic layers were h = 10 nm, and the participation of gold and silver was equal. The films were deposited on one side of the tapered waist area. The liquid crystal cells were controlled with a voltage U from 0 to 200 V, with and without amplitude modulation at a frequency of fmod = 5 Hz. For the purposes of this research, spectral characteristics were obtained for a wavelength λ ranging from 550 to 1200 nm. Measurements were carried out at room temperature for three types of rubbed layers orientation—orthogonal, parallel, and twist in relation to the fiber axis. Obtained resonant peaks were compared with the previous results regarding the resonant wavelength, peak width, SNR, and maximum absorption. In the presented paper, the novelty is mainly focused on the materials used and their time stability, as well as corresponding changes in the technological parameters used. [ABSTRACT FROM AUTHOR]

The article presents a study of a hybrid structure based on the combination of a tapered optical fibre and gold nanoparticles dispersed in a liquid crystal material. Sensitivity to changes of the refractive index of the environment in which the structure is located, as well as the possibility of changing the refractive index of liquid crystals by external factors, such as temperature and electric field, were investigated. Electro- and thermally-induced changes of the refractive index of a liquid crystal through the rotation of a molecule director, which cause changes in the light propagated in a tapered optical fibre, were described. The most important issue in the article is to determine the influence of doping a liquid crystal with gold nanoparticles the concentration of which varies between 0.1 and 0.3 wt.%. The paper presents transmission measurements in a wide optical range depending on voltage, temperature, and frequency changes. Additionally, time courses of the obtained signal were measured. The study shows that the appropriate selection of nanoparticle concentration has a huge impact on the optical wave propagation. The experimental results show that the optical changes obtained for the investigated hybrid structure prefer it for use as an electrooptical switcher, filter, or sensor. [ABSTRACT FROM AUTHOR]

The paper presents the results of design, manufacturing, and characterization of a hybrid broad band in-line fiber-optic device. It uses nematic liquid crystal as cladding with electro-steering properties in a biconical optical fiber taper structure. Liquid crystal mixtures denoted as 6CHBT and E7 are designed for electric as well as temperature control of electromagnetic wave propagation in a broad wavelength range. The applied taper with 10±0.5 μm diameters has losses lower than 0.5 dB in whole investigated spectrum range. Three kinds of initial liquid crystal molecules' orientations (parallel, orthogonal, and twist) in relation to the light beam propagating in a taper were applied. The performance of a tuned cladding was studied at an electric field of the range of 0–190 V and the temperature range from 20°C up to 42°C and 59°C for 6CHBT and E7, respectively. The induced reorientation of liquid crystal molecules was measured at a broad wavelength range (550-1550 nm). [ABSTRACT FROM AUTHOR]

This paper is a continuation of previous work and shows the enhancement of the surface plasmon resonance effect in a tapered optical fiber device. The study investigated liquid crystal cells containing a tapered optical fiber covered with a silver nanolayer, surrounded by a low refractive index liquid crystal in terms of the properties of light propagation in the taper structure. Silver films with a thickness of d = 10 nm were deposited on the tapered waist area. Measurements were performed at room temperature; liquid crystal steering voltage U from 0 to 200 V, with and without any amplitude modulation with a frequency of f = 5 Hz, and the wavelength λ ranged from 550 to 1200 nm. A significant influence of the initial arrangement of liquid crystals molecules on light propagation was observed. Three types of liquid crystal cells—orthogonal, parallel, and twist—were considered. During the measurements, resonant peaks were obtained—the position of which can also be controlled by the type of liquid crystal cells and the steering voltage. Based on the obtained results, the best parameters, such as highest peak's width reduction, and the highest SNR value were received for twisted cells. In addition, the present work was compared with the previous work and showed the possibility of improving properties of the manufactured probes, and consequently, the surface plasmon resonance effect. In the presented paper, the novelty is mainly focused on the used materials as well as suitable changes in applied technological parameters. In contrast to gold, silver is characterized by different optic and dielectric properties, e.g., refractive index, extension coefficient, and permittivity, which results in changes in the light propagation and the SPR wavelengths. [ABSTRACT FROM AUTHOR]

The liquid crystalline filter exhibiting particular optical properties is presented. Their basis application is the multiresolution image analyzer based on a wavelet transform (WT). In co-operation with the phase shifter such a filter allows to rotate the polarization of the transmitted light. The resulted intensity distribution has been exploited as a tool to span the transmitted image onto the space of the circular Haar wavelets. It provides new possibilities in an optical signal processing. The analysis of the light transmission in considered filter as well as the wavelet space creation are also described. [ABSTRACT FROM AUTHOR]

Liquid crystal materials composed of mixed nematic compounds find broad use in liquid crystal displays and photonic applications. A ternary mixture formed from three different nematic compounds shows peculiar behavior such as tunable electro-optical properties dependent on the frequency of the driving voltage. The paper presents an analysis of the response time and phase retardation of a frequency tunable nematic liquid crystal mixture (under code name 5005). This material possesses high birefringence (Δn = 0.32 at 633 nm) as well as high dielectric anisotropy (Δε = 6.3 at 100 Hz). The unique property of the 5005 mixture is frequency-controlled phase modulation, as in a dual frequency liquid crystal, while dielectric anisotropy goes to zero instead of being negative at high frequencies. For each component of the mixture, details on mesomorphic properties and their role in the formulation of the mixture are reported. The 5005 mixture was characterized by multiple investigation techniques, such as temperature dependence dielectric anisotropy, transmittance measurements image polarizing microscopy, and UV stability. [ABSTRACT FROM AUTHOR]

This paper presents the influence of a thin metal layer deposition on the surface of a tapered optical fiber surrounded by a low liquid crystal, on light propagation inside the taper structure. In this research, three types of liquid crystal cells were under investigation: orthogonal, parallel, and twist. They differed by the rubbing direction of the electrodes in relation to the fiber axis determining the initial molecule arrangement inside the cell. Gold films with thickness d = 30 nm were deposited on the tapered fiber surface in the tapered waist area. Cells including a tapered optical fiber with no metallic layer were also examined and presented as a reference. All measurements were performed at room temperature for a different steering voltage U from 0 to 200 V, with and without any amplitude modulation with a frequency f = 5 Hz, and the wavelength λ range from 550 to 1200 nm. As a result, the resonant peaks were obtained, which depends on a liquid crystal cell type and steering voltage, as well. This paper shows the possibility of sensing the change of applied voltage by the constructed system. During measurements, additional effects as signal overlapping and intermodal interference were observed reducing measured voltage value. In the future, the improved, similar systems that will have a better response could be used as a sensor of factors to which liquid crystal (LC) will be sensitive, especially temperature and electric field. [ABSTRACT FROM AUTHOR]

It has been approximately 125 years since the Austrian scientist Friedrich Reinitzer in 1888 observed the curious behavior of the double melting points of cholesterol benzoate, a discovery that today is widely recognized as liquid crystal science. The authors reviewed recent advancements in adaptive LC lenses, introducing LC science and promising applications. Furthermore, novel applications of LC lenses were reviewed and the prospects and challenges of adaptive-focus LC lens technology were highlighted. [Extracted from the article]

Polarization is a very useful parameter of a light beam in many optical measurements. Improvement of holographic systems requires optical elements which need a diffused and depolarized light beam. This paper describes a simple monochromatic depolarizer based on a pure vertically aligned liquid crystal without pretilt. In this work we present an extended description of depolarizer by analyzing its electro-optic properties measured in spatial and time domains with the use of crossed polarizers and polarimetric configurations. Crossed polarizers set-up provides information on spatial and temporal changes of microscopic textures while polarimetric measurement allows to measure voltage and time dependence of degree of polarization. Three different thicknesses, i.e., 5 μm, 10 μm and 15 μm have been manufactured in order to analyze another degree of freedom for this type of depolarizer device based on a liquid crystals' material. Consideration of the light scattering capability of the cell is reported. [ABSTRACT FROM AUTHOR]

This paper presents results obtained for biconical tapered fibers surrounded/immersed in liquid crystal mixtures. The phenomenon of light propagating in the whole structure of a tapered fiber allows the creation of a sensor where the tapered region represents a core whereas the surrounding medium becomes a cladding. Created devices are very sensitive to changing refractive index value in a surrounding medium caused by modifying external environmental parameters like temperature, electric or magnetic field. For this reason, the properties of materials used as cladding should be easily modified. In this investigation, cells have been filled with two different nematic liquid crystals given as 1550* and 6CHBT (4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzoate), as well as with the same mixtures doped with 0.1 wt% gold nanoparticles (AuNPs). Optical spectrum analysis for the wavelength range of 550–1150 nm and time-courses performed for a wavelength of 846 nm at the temperature range of T = 25–40 °C were provided. For all investigations, a steering voltage in the range of 0–200 V which allows establishing the dopes' influence on transmitted power and time response at different temperatures was applied. [ABSTRACT FROM AUTHOR]

Liquid crystals act on the amplitude and the phase of a wave front under applied electric fields. Ordinary LCs are known as field induced birefringence, thus both phase and amplitude modulation strongly depend on the voltage controllable molecular tilt. In this work we present electrooptical properties of novel liquid crystal (LC) mixture with frequency tunable capabilities from 100Hz to 10 KHz at constant applied voltage. The frequency tunability of presented mixtures shown here came from composition of three different families of rodlike liquid crystals. Dielectric measurements are reported for the compounds constituting frequency-controlled birefringence liquid crystal. Characterization protocols allowing the optimum classification of different components of this mixture, paying attention to all relevant parameters such as anisotropic polarizability, dielectric anisotropy, and dipole moment are presented. [ABSTRACT FROM AUTHOR]