Liquid Crystal Optical Fibers Research Articles

Liquid crystal optical fiber sensor based on misaligned core configuration for temperature and mixed volatile organic compound detection

In this paper, an optical fiber sensor based on cholesteric liquid crystal (CLC) is used for real-time monitoring of temperature and volatile organic compound (VOC) gas concentration. The sensor works based on a 2 × 2 multimode fiber coupler whose two output ports can respectively function as gas and temperature sensor probes. The former was realized by dislocation fusion of two multimode fibers (MMFs) coated with two CLCs, and the CLC reflection peak has a red shift with the increasing concentrations of acetone and tetrahydrofuran (THF) gas. The other MMF port has been fused with hollow capillary fibers (HCF). To eliminate the adverse effects of external temperature fluctuations, the enclosed CLC in the HCF will realize real-time temperature monitoring and temperature compensation. In addition, the sensor can also measure the dependence of the wavelength on the total gas concentration of different mixing ratios of acetone and THF, and distinguish the concentration of acetone and THF in the mixed gas.

Recent Progress in Liquid-Crystal Optical Fibers and Their Applications in Photonics

The aim of this paper is to review and demonstrate a recent progress in liquid-crystal optical fibers and their applications in photonics. The review starts from early works with classical optical fibers modified with liquid crystals and ends up with the latest achievements in the field of photonic liquid crystal fibers (PLCFs). Potential applications and future perspectives of PLCFs are shortly summarized.

On the conducting sheath double-helix loaded liquid crystal optical fibers

This work presents analysis of wave propagation in a rather new type of three-layer optical fiber wherein the outermost region being composed of radially anisotropic liquid crystal, and conducting sheath helix loadings exist at the core–inner clad as well as the inner clad–outer liquid crystal clad interfaces. The fiber structure offers two-way control on wave propagation through it. Focus is, however, made on the wave confinements in fiber due to the helix structures, as characterized by the respective pitch angles. Specific values of helix pitch angles at the two layer interfaces are taken into account, and the confinement patterns are analyzed. The dominant property of sheath helix structure over confinement patterns is quite an obvious fact. Clearly, the helix pitch angle greatly controls over the power confinement characteristics, which can be altered upon suitable adjustments of helical windings. Treatments have been made to illustrate the power patterns in all possible scenarios for critical pitch variations in each layer interface.

Linking the chemical speciation of cerium to its bioavailability in water for a freshwater alga.

Over the past decade, researchers have begun to use metals of the lanthanide family for numerous applications, including liquid crystal display (LCD) screens, optical fibers, and laser technology. Unfortunately, little is presently known about their bioavailability or the mechanisms by which they might cause toxicity. The present study focuses on cerium (Ce), one of the most widely used lanthanides, and on validating the biotic ligand model as a means to predict Ce bioaccumulation. Short-term exposures to Ce were performed using the unicellular alga Chlamydomonas reinhardtii, to better relate Ce bioavailability to its chemical speciation in solution. Maximum uptake fluxes (Jmax ) and affinity constants for the binding of Ce to the biological uptake sites (KS ) were established at pH 5.0 and pH 7.0. An apparent affinity constant of 1.8 × 10(7) M(-1) was observed at pH 5.0, with a larger value obtained at pH 7.0 (6 × 10(7) M(-1) ), albeit under conditions where equilibrium could not be confirmed. By evaluating Ce speciation using centrifugal ultrafiltration and single-particle inductively coupled plasma spectrometry, it could be concluded that very little (∼30%) Ce was truly dissolved at pH 7.0, with the majority of the metal being present in colloidal species. Speciation was also monitored by fluorescence to evaluate Ce complexation by natural organic matter (NOM). The presence of NOM decreased Ce bioaccumulation in line with free Ce concentrations. Finally, competition with calcium for the metal uptake sites was shown to result in a decrease in Ce uptake by C. reinhardtii.

Propagation through complex structured liquid crystal optical fibers

Wave propagation in optical mediums greatly depends on the materials of which the guides are composed. Among the other forms of optical mediums, liquid crystals are both inhomogeneous and optically anisotropic in nature, and exhibit strong electro-optic behavior, which allows alternation in their optical properties under the influence of external electrical fields. These features make optical fibers containing liquid crystals greatly useful for fabricating many optical devices for practical applications. As such, the analytical investigation of wave propagation through liquid crystal optical fibers, particularly a three-layer fiber with radially anisotropic liquid crystal material in the outermost clad section, remains interesting. The power confinement in the liquid crystal section of such fibers can be enhanced for these to be efficiently used in optical coupling and/or sensing applications. Furthermore, a control over the dispersion characteristics, and, hence, the confinement of power, in such fibers may be imposed by making the guide even more complex in the form of introducing a conducting sheath helix structure at the core-inner clad interface.

Lasing and waveguiding in smectic A liquid crystal optical fibers

We demonstrate a new class of soft matter optical fibers, which are self-assembled in a form of smectic-A liquid crystal microtubes grown in an aqueous surfactant dispersion of a smectic-A liquid crystal. The diameter of the fibers is highly uniform and the fibers are highly birefringent. They are characterized by a line topological defect in the core of the fiber with an optical axis pointing from the defect core towards the surface. We demonstrate guiding of light along the fiber and Whispering Gallery Mode (WGM) lasing in a plane perpendicular to the fiber. The light guiding as well as the lasing threshold are significantly dependent on the polarization of the excitation beam. The observed threshold for WGM lasing is very low (≈ 75μJ/cm(2)) when the pump beam polarization is perpendicular to the direction of the laser dye alignment and is similar to the lasing threshold in nematic droplets. The smectic-A fibers are soft and flexible and can be manipulated with laser tweezers demonstrating a promising approach for realization of soft photonic circuits.

A theoretical investigation of soliton induced supercontinuum generation in liquid core photonic crystal fiber and dual core optical fiber

The supercontinuum generation (SCG) in liquid core photonic crystal fiber (LCPCF) with versatile nonlinear response and the spectral broadening in dual core optical fiber is presented. The analysis is presented in two phase, phase I deals with the SCG in LCPCF with the effect of saturable nonlinearity and re-orientational nonlinearity. We identify and discuss the generic nature of the saturable nonlinearity and reorientational nonlinearity in the SCG, using suitable model. For the physical explanation, modulational instability and soliton fission techniques is implemented to investigate the impact of saturable nonlinear response and slow nonlinear response, respectively. It is observed that the saturable nonlinearity inevitably suppresses the MI and the subsequent SCG. On the other hand, the re-orientational nonlinearity contributes to the slow nonlinear response in addition to the conventional fast response due to the electronic contribution. The phase II features the exclusive investigation of the spectral broadening in the dual core optical fiber.

Evanescent Field Enhancement in Liquid Crystal Optical Fibers: A Field Characteristics Based Analysis

The paper presents the analysis of the electromagnetic wave propagation through liquid crystal optical fibers (LCOFs) of two different types—conventional guides loaded with liquid crystals (addressed as LCOFs) and those with additional twists due to conducting helical windings (addressed as HCLCOFs). More precisely, the three-layer optical waveguide structures are considered along with its outermost region being loaded with radially anisotropic liquid crystal material and the inner regions being made of usual silica, as used in conventional optical fibers. In addition to that, LCOF with twists introduced in the form of conducting helical windings at the interface of the silica core and the liquid crystal clad is also taken into account. Emphasis has been put on the power confinements by the lower-order TE modes sustained in the different sections of the LCOF structure. The results demonstrate useful applications of these guides in integrated optics as the power sustained in the liquid crystal section by the excited TE modes remains very high. In the case of twisted clad liquid crystal guides, descriptions are limited to the nature of dispersion relation only under the TE mode excitation, and corresponding to the cases of helix orientations being parallel and perpendicular to the optical axis.

TE and TM modes power transmission through liquid crystal optical fibers

Summary The paper deals with an analytical investigation of the power confinement factors in the different sections of a three-layer optical fiber with the outermost section as the liquid crystal. It is considered that the liquid crystal section has the radial anisotropy. The lower order TE and TM modes are considered, and the fields are evaluated by using Maxwell's equations. Plots are made of the power confinement factors for such liquid crystal fibers of various core dimensions, and it is found that, in all the cases, relatively higher amount of power is transmitted through the outer liquid crystal clad, which is attributed to the radial anisotropy of the section. Also, the distribution of power is fairly uniform over the considerable range of modal propagation constants. These features attract the usefulness of such liquid crystal fibers in the fabrication of coupling devices.

Thermometry and dosimetry of heat with specific reference to the liquid-crystal optical fiber temperature probe.

A temperature sensing probe was designed utilizing the unique optical properties of thermotropic liquid crystals. An electronic and fiberoptic system coupled to the sensor was used to monitor temperature-dependent interactions of light (660 nm) with the liquid crystal mixture. The probe is a nonmetallic, nonperturbing thermal sensor for continuous temperature measurements of biological specimens subjected to electromagnetic fields. The advantages and disadvantages of the Liquid Crystal Optical Fiber (LCOF) temperature probe are discussed along with some typical applications where accurate dosimetry and thermometry are important parameters in experimental studies.

Microwave-induced chronotropic effects in the isolated rat heart.

Continuous wave (cw) microwave irradiation at 960 MHz has caused bradycardia in isolated, perfused rat hearts maintained at 20°C. The observed bradycardia occurred at microwave dose rates that should have caused mild tachycardia in the heart based on the thermogenic properties of the irradiation. The observed bradycardia, moreover, exhibited neurologic features because atropinized hearts showed strong tachycardia during irradiation and hearts treated with propranolol showed significantly stronger bradycardia during irradiation than that seen without drugs. Use of the liquid-crystal optical-fiber (LCOF) temperature probe has shown, by calorimetric methods, that the microwave-induced bradycardia occurred at dose rates of 1.3 and 2.1 mW/g. We hypothesize that microwave energy interacts with the remaining portion of the autonomic nervous system within the heart to produce the observed chronotropic effects.

Microwave radiation alters peristaltic activity of isolated segments of rat gut

Irradiation (960‐MHz) of isolated post‐pyloric segments of rat gut at a specific absorption rate (SAR) of 1.5–5.5 W/kg caused an increase in peristaltic activity. A pressure transducer was used to monitor waveforms of muscle movements in a canulated section of intestine. The preparation was suspended in isothermal, aerated, modified Ringer's solution. Microwave radiation was applied with a parallel‐plate capacitor‐type radiator. The SAR was calculated from temperature measurements made with a liquid‐crystal optical‐fiber (LCOF) temperature probe. As reported previously, similar radiation applied to isolated turtle and rat heart caused bradycardia. These effects, in both the heart and gut, are thought to be neurally mediated by the release of transmitter substances by the autonomic nervous system (ANS). Generally, these effects can be modified by the addition of drugs that are effective at synapses within the ANS. In both the heart and gut, sympathetic and parasympathetic effects can be separated by the application of drugs that selectively block one or the other of the two divisions of the ANS.