Photonic liquid crystal fibers (PLCFs) have been studied for over a decade as an emerging field of sensing and telecommunication devices. Exciting properties of liquid crystals (LCs) infiltrating photonic crystal fibers (PCFs) can be additionally tuned by doping with various materials that are sensitive to external influences, such as an electric field or temperature. Among them, metallic nanoparticles (NPs) are gathering a great interest, due to their potential applications. NPs can be used to highly influence material properties of LCs as dielectric anisotropy, elastic constants, and viscosity. This may lead to many desirable effects, such as a decrease of the Fredericks threshold voltage or reduction of LC switching times. In this paper we doped a nematic LC with 2-nm gold (Au) and 8-nm silver (Ag) NPs, and infiltrated the prepared mixtures into photonic crystal fibers. We examined the influence of this doping in two different electric field systems, one with two flat copper electrodes, and second with four copper microelectrodes. Our results indicate that metallic NP (both Au and Ag) doping enhances sensitivity of the PLCF-based sensors to an electric field and decreases the threshold voltage. Additionally, due to smaller distances between the electrodes, the proposed four microelectrode system requires lower voltages to effectively tune the PLCF.
Experimental results on determination of optical parameters of monomer-doped liquid crystalline materials are
presented. Refractive indices, as well as propagation losses, have been particularly determined as a function of the
monomer concentration. Materials characterized in this way can be applied for fabrication of waveguiding structures
with use of the photo-polymerization process. Several factors, such as composition of the LC-monomer mixture and UV
illumination conditions, are needed to be taken under consideration when fabricating structures of satisfactory quality.
Importantly, their optical properties may be additionally tuned after fabrication what is in a huge advantage when
compared to waveguiding structures manufactured in other materials.
In this work we studied a newly reported class of nonlinear effects observed in 5CB liquid crystals doped with gold nanoparticles (GNPs). The size of the GNP was determined by direct TEM imaging and by X-ray scattering of the diluted NP solution. GNPs was coated by thiols with the ratio of mesogenic to n-alkyl thiols varying from 1:2 to 1:1. The research involved comparing properties of both undoped and doped 5CB (nematic LC) by infiltrating LC cell and microholes of the photonic crystal fiber (PCF) separately. In our experiment the PCF fiber type LMA-10 made by NKT Photonics as host material has been used.
Liquid crystals over the last two decades have been successfully used to infiltrate fiber-optic and photonic structures initially including hollow-core fibers and recently micro-structured photonic crystal fibers (PCFs). As a result photonic liquid crystal fibers (PLCFs) have been created as a new type of micro-structured fibers that benefit from a merge of “passive” PCF host structures with “active” LC guest materials and are responsible for diversity of new and uncommon spectral, propagation, and polarization properties. This combination has simultaneously boosted research activities in both fields of Liquid Crystals Photonics and Fiber Optics by demonstrating that optical fibers can be more “special” than previously thought. Simultaneously, photonic liquid crystal fibers create a new class of fiber-optic devices that utilize unique properties of the photonic crystal fibers and tunable properties of LCs. Compared to „classical” photonic crystal fibers, PLCFs can demonstrate greatly improved control over their optical properties. The paper discusses the latest advances in this field comprising PLCFs that are based on nanoparticles-doped LCs. Doping of LCs with nanoparticles has recently become a common method of improving their optical, magnetic, electrical, and physical properties. Such a combination of nanoparticles-based liquid crystals and photonic crystal fibers can be considered as a next milestone in developing a new class of fiber-based optofluidic systems.
The aim of this work is to create the regions of different effective refractive index in typical liquid crystal cell thanks to the polymer-stabilization. For this purpose typical liquid crystalline material, namely E7, has been combined with a small amount of the mixture of RM257 monomer and UV-sensitive activator, with percentage weight less than 10%. Thanks to the photo-polymerization process it is possible to obtain polymer-stabilized molecular orientation inside LC cell. In particular, periodic changes in spatial distribution of effective refractive index in LC layer have been achieved thanks to selective irradiation with UV light. Determination of suitable dose of both the monomer and UV-activator to be added to LC material, as well as of irradiation intensity and time, is essential and highly required to provide repeatable and good-quality periodic waveguiding structures. Eventually, functionality of the liquid crystal cells with distinguished regions of different molecular orientation, and in particular with combination of the planar and homeotropic alignment, has been experimentally tested by launching the near-infrared light beams of orthogonal linear polarizations. Thanks to the molecular reorientation induced by external electric field and/or by electromagnetic wave, it is additionally possible to control character of light propagation by electric bias and optical power, respectively. Proposed polymer-stabilized periodic waveguiding structures in liquid crystalline materials may find potential applications as functional elements and devices for LC-based integrated optics.
In great majority of the previous works devoted to photonic liquid crystal fibers (PLCFs) a photonic band-gap
propagation was investigated, since silica glass fibers' refractive index is lower than refractive indices of the most of
liquid crystals. In this work we focus on the electrical tuning of the index-guiding PLCFs based on host-fibers made from
multi-component glasses with enhanced value of refractive index. Impact of the electric field on the light propagation in
index-guiding PLCFs has been carefully studied and effective tuning of the phase birefringence, attenuation and
polarization dependent losses has been observed experimentally.
Similarly to liquid crystal displays technology in photonic liquid crystal fibers (PLCFs) a molecular orientation control
is a crucial issue that influences proper operation of PLCF-based devices. The paper presents two distinct
configurations: planar and radial escaped orientation of the LC molecules inside capillaries as well as methods of their
application to photonic liquid crystal fibers. Possibilities of LC orientation control influence both: attenuation and
transmitting spectra of the PLCF
The orienting method is based on creation of an additional orienting layer on the inner surface of the capillary or air
hole of the photonic liquid crystal fiber. Aligning materials used in the experiment are commercially available
polyimides SE1211 and SE130 which induce liquid crystal homeotropic and planar anchoring conditions. The orienting
layer increase an order parameter of the liquid crystal improving propagation properties and stability of photonic liquid
crystal fiber-based devices.
Photonic liquid crystal fibers (PLCFs) can be categorized in two principal groups: index guiding PLCFs and photonic
bandgap PLCFs. In this paper we focus on index guiding PLCFs in which effective refractive index of the
micro-structured cladding filled with liquid crystal is lower than refractive index of the fiber core. In such fibers
broadband propagation of light is observed and also effective tuning of guiding properties is possible (i.e. birefringence,
polarization dependent losses or attenuation tuning). Such fibers could be used for dynamic control of light in various
fiber optics systems, including optical fiber sensing setups.
Liquid Crystal Photonic Crystal Fibers (LC-PCFs) known also as Photonic Liquid Crystal Fibers (PLCFs) are advanced
specialty fibers that benefit from a combination of "passive" photonic crystal fiber host microstructures infiltrated with
"active" liquid crystal guest materials and are responsible for a diversity of new and uncommon spectral, propagation,
and polarization properties. This combination has simultaneously reinvigorated research in both fields of Liquid Crystals
Photonics and Fiber Optics by demonstrating that optical fibers can be more "special" than previously thought.
Simultaneously, photonic liquid crystal fibers create a new class of optical waveguides that utilizes unique guiding
properties of the micro-structured photonic crystal fibers and attractive tunable properties of liquid crystals. Comparing
to the conventional photonic crystal fibers, the photonic liquid crystal fibers can demonstrate greatly improved control
over their optical properties.
The paper describes basic physics including guiding mechanisms, spectral properties, polarization phenomena, thermal,
electrical and optical controlling effects as well as innovative emerging technology behind these developments. Some
examples of novel LC-PCFs highly tunable photonic devices as: attenuators, broadband filters, polarizers, waveplates,
and phase shifters recently demonstrated at the Warsaw University of Technology are also presented. Current research
progress in the field indicates that a new class of emerging liquid crystals tunable photonics devices could be expected.
The paper analyzes a modal structure of the guided modes in photonic liquid crystal fibers (PLCFs) by using numerical methods and presents experimental verification of the theoretical results. The theoretical analyses is based on numerical methods applied to find solution of the Helmholtz equation that describes possible forms of modal field propagating inside photonic crystal fiber (PCF) of defined geometry, as well as optical parameters. Numerical calculations based on the Finite Difference method were preformed for two different kinds of digitization of the PLCF structure (i.e. for using square and triangular lattice). Several boundary conditions applied in the case of analyzed lattices such as: constant, Dirichlet and semi-transparent condition were discussed. Input parameters of preformed simulations can be divided into two groups: physical and purely numerical. Physical parameters are: wavelength, number of capillaries, and spatial distribution of refractive index (in cross section of fiber surface). Numerical parameters are: type of used lattice, resolution of the lattice and the boundary condition. Numerical output is the value of effective refractive index and additionally shape of propagating mode field. In experimental part the measurements of numerical aperture (NA) were done in the way to find effective refractive indices of modes propagating in PCFs and PLCFs.
In this work we present experimental results of the influence of hydrostatic pressure on polarization and propagation properties of the photonic crystal fibers infiltrated with liquid crystals. Two ranges of Photonic Band Gaps (PBGs) were observed and hydrostatic pressure was found to narrow the PBGs and also to introduce changes in the state of polarization The results obtained suggest great potential of the LC-infiltrated photonic crystal fibers for prospective constructions of fiber optics pressure sensors.
In this paper the analyses of the linear and nonlinear light propagation in the photonic crystal fiber infiltrated with nematic liquid crystal is presented. Our theoretical investigations, carried out by using the finite difference beam propagation method, show the extreme importance of the discrete space representation aspect. The main aim of this work is to reveal that application of the triangular grid for the discretization of the analyzed structure of the photonic crystal fiber with the hexagonal symmetry gives more reasonable results than in the case of the standard square mesh utilization.