Anisotropic Optical Fibers Research Articles

Polarization Changes during a Lightning Strike: Isotropic Zones of Anisotropic Optical Fiber

Polarization Changes during a Lightning Strike: Isotropic Zones of Anisotropic Optical Fiber

SWAP and Fredkin gates for OAM optical beams via the sandwich of anisotropic optical fibers.

We study the propagation of circularly-polarized optical vortices of higher order topological charges ℓ ≥ 2 in a sandwich of multihelical - anisotropic - multihelical fibers on the basis of the Jones formalism for modes with orbital angular momentum. We demonstrate that such a system can operate as the all - fiber two - bit SWAP as well as universal tree - bit controlled-SWAP (Fredkin) gates over states of optical vortices, in which the mode radial number carries the control bit, while circular polarization and topological charge are the controlled bits.

Rigorous modeling of twisted anisotropic optical fibers with transformation optics formalism

In this study, we show that transformation optics formalism can be used to rigorously model a wide range of twisted anisotropic fibers, which could only be analyzed using perturbative methods. If the material anisotropy of fibers has an intrinsic origin or is induced by axially or helically symmetric physical factors, then they can be transformed into a form usable in rigorous two-dimensional (2D) modeling. We demonstrate the effectiveness of the proposed approach in 2D modeling of the propagation characteristics of first-order eigenmodes in twisted and spun fibers with high linear birefringence. We derive the equivalent electric permittivity tensors for such fibers in the helical coordinate system and study the evolution of the first-order modes toward vortex modes with increasing twist rate. The obtained results confirm that the proposed method can reveal phenomena that cannot be predicted by analytical approaches.

Radially anisotropic ring-core optical fiber: towards vector-vortex guided transmission using the full modal space

The radially anisotropic ring-core fiber with cylindrical birefringence is theoretically and numerically investigated as a novel platform for the transmission of vector-vortex beams with unique modal properties. First, we elucidate the parametric conditions where such fiber enables modal substitution in which either the donut-shaped azimuthal TE01 or radial TM01 mode replaces the normal Gaussian-like HE11 mode as the fundamental mode of the waveguide. We also demonstrate that it is possible to significantly engineer the waveguiding properties of the fiber via the addition of small radial birefringence (∼10−4) so as to make the (hitherto non-degenerate) TE0m and TM0m modes fully degenerate. The latter property is used to create stable vortex modes of high purity (>99%) with the newly degenerate modal pair – a feat not possible with standard few-mode fibers—all without affecting the co-propagating hybrid HE/EH modes that remain available as an independent basis set to produce vortex beams of similarly high purity. These new insights are relevant to the topical fields of mode-division multiplexing (MDM), structured light, fiber modelling and fabrication. With respect to MDM applications, the newly available vortex modes created with the degenerate TE/TM basis set can now be concurrently used with the more common vortex modes created via the HE/EH modal basis set.

OV-bearing modes with ℓ = 2 of twisted anisotropic optical fibres

We investigated the high-order mode structure of a weakly guiding twisted anisotropic optical fibre. An analytical solution of the vector wave equation for this case is presented. We obtained analytical expressions for the higher-order modes with an azimuthal number ℓ = 2 and their propagation constants of such a fibre, considering the mutual effect of linear anisotropy of fibre’s material, twisting, including torsional mechanical stress, and spin-orbital interaction. We showed that optical vortex beams with topological charge ±2 are the modes of the fibres considered.

Theoretical and Experimental Estimation of the Accuracy in Simultaneous Distributed Measurements of Temperatures and Strains in Anisotropic Optical Fibers Using Polarization-Brillouin Reflectometry

A model has been constructed for determining the effect of instrumental and calibration errors on the accuracy of a method for strain−temperature discrimination using polarization-Brillouin reflectometry based on measuring the Brillouin frequency shift in two polarization axes of an optical fiber. It is shown that the errors caused by the discrepancy of the calibration coefficients are negligible. The optimal hardware requirements for the reflectometer are determined. The experimental results of spectral scanning at the maximum resolution attainable in this study are in agreement with the results of computer simulation.

Design of germanium core with anisotropic metamaterial cladding optical fiber in mid-infrared range applications

A novel circular shaped metamaterial optical fiber with semiconductor core, metal/dielectric clad is numerically investigated. To surpass higher absorption loss and instability of noble metal, the core guiding medium of the fiber is comprised by crystalline germanium (Ge). The fiber is interrogated in terms of uniaxial permittivity, mode index, dispersion profile, effective area, nonlinearity, power fraction for different thickness (Cm = Cd, Cm > Cd, Cm < Cd) of Ag/Al2O3 using finite element method. In addition, it is shown how increased Ag/Al2O3 pair enhances optical properties especially for low loss which is reported as 0.025 dB/m with AMM cladding and 0.007 dB/m for layered cladding region. Hence, the proposed structure with comprising material is a promising candidate for mid-infrared applications.

Mechanically and Electronically Robust Transparent Organohydrogel Fibers.

Stretchable conductive fibers are key elements for next-generation flexible electronics. Most existing conductive fibers are electron-based, opaque, relatively rigid, and show a significant increase in resistance during stretching. Accordingly, soft, stretchable, and transparent ion-conductive hydrogel fibers have attracted significant attention. However, hydrogel fibers are difficult to manufacture and easy to dry and freeze, which significantly hinders their wide range of applications. Herein, organohydrogel fibers are designed to address these challenges. First, a newly designed hybrid crosslinking strategy continuously wet-spins hydrogel fibers, which are transformed into organohydrogel fibers by simple solvent replacement. The organohydrogel fibers show excellent antifreezing (< -80 °C) capability, stability (>5 months), transparency, and stretchability. The predominantly covalently crosslinked network ensures the fibers have a high dynamic mechanical stability with negligible hysteresis and creep, from which previous conductive fibers usually suffer. Accordingly, strain sensors made from the organohydrogel fibers accurately capture high-frequency (4 Hz) and high-speed (24 cm s-1 ) motion and exhibit little drift for 1000 stretch-release cycles, and are powerful for detecting rapid cyclic motions such as engine valves and are difficult to reach by previously reported conductive fibers. The organohydrogel fibers also demonstrate potential as wearable anisotropic sensors, data gloves, soft electrodes, and optical fibers.

Modelling of polarised optical frequency domain reflectometry of axially twisted anisotropic optical fibres

This paper presents a mathematical model that describes the influence of defects in an anisotropic optical fibre on its polarised frequency domain reflectograms. The model relies on the Jones matrix formalism. Calculated reflectograms are presented for a uniform axial twist of an optical fibre. As input data for simulation, we use real distributed optical parameters of the fibre determined by polarised light Brillouin reflectometry.

Symmetries and conservation laws of the Yao\u2013Zeng two-component short-pulse equation

This paper uses the Lie group method to analyze the symmetries of the Yao–Zeng two-component short-pulse equation which describes the propagation of polarized ultrashort light pulses in cubically nonlinear anisotropic optical fibers. Similarity reductions and exact solutions are obtained by constructing an optimal system of one-dimensional subalgebras. Moreover, the explicit solutions are constructed by the power series method and the convergence of power series solutions is proved. In addition, nonlinear self-adjointness and conservation laws of this system are discussed.

Inhomogeneously filled, cylindrically anisotropic metamaterial optical fiber

A theoretical study of a cylindrical anisotropic optical fiber filled inhomogeneously by an anisotropic metamaterial is carried out. Nanoporous alumina microtubes obtained recently by acid anodization techniques are physical manifestations of such optical waveguides. In these microtubes, the nanopores are aligned radially outward and the nanopore diameters vary radially, rendering the system inhomogeneous. By considering the radial variation of the nanopore size, a local permittivity tensor is obtained by a Maxwell-Garnett homogenization theory. The cylindrically anisotropic and inhomogeneously filled fiber is shown to support propagating modes of hybrid polarization character (EH or HE modes). The salient feature of this system is that the modal fields are extremely confined near the center of the waveguide due to the refractive inhomogeneity. The anisotropy plays a relatively minor role in the localization. The easy control over the dielectric anisotropy and the inhomogeneity made possible in the nanoporous alumina fiber makes it an attractive candidate for nanophotonic applications.

Study of the distributed H-parameter of an anisotropic optical fiber in a multi-layer coil of a fiberoptic gyroscope

An investigation has been performed on the distributed H-parameter in an anisotropic optical fiber with an elliptical strained shell in a multilayer coil of a fiberoptic gyroscope. Each fiber length is ~50 m and there are five layers. Studies have been carried out using three variants of coils. In the first variant, the layers were permeated by epoxy; in the second coil, the layers were permeated with silicon-based material; and, in the third variant, the coils were wound up without impregnation (using dry winding). The different influence of compressive mechanical stresses on the distributed H-parameter of the studied fiber has been observed depending on the variant of coil impregnation.

Visualization of fiber Bragg gratings of type II induced by radiation of an ArF excimer laser in an anisotropic single-mode optical fiber with an elliptical stress cladding

results in visualization of fiber Bragg gratings of type II recorded in birefringent single-mode optical fibers with an elliptical stress cladding with a high concentration of germanium dioxide are shown. Periodic structures of the induced refractive index are inscribed by a single pulse of an excimer laser with a working- gas mixture of ArF using the phase mask. Fiber Bragg gratings into anisotropic optical fiber were investigated by optical and scanning-probe microscopes. It is shown that single-pulse recording by ArF excimer laser creates in the fiber, both inside and on the surface of the quartz cladding, periodic structures, the spatial period of which corresponds to the period of the phase mask, optimized for the +1/–1 diffraction order.

The analysis of scattering interference pattern from the birefringent optical fiber with elliptical stress cladding

An experimental setup for observation of a scattering interference pattern from optical fibers is assembled. The dependence of scattering interference pattern from the anisotropic optical fiber with 4mol% of GeO2 in core on the stress applying ellipse position is studied experimentally. The anisotropic optical fiber with 4mol% of GeO2 in core was used for this study. The mathematical modeling and experimental data are in a good agreement. On its basis some recommendations for less time-consuming stressing ellipse orientation in specialty fibers used in fiber-optic interferometric sensors determination are made.

Efficiency of Bragg grating inscription by ArF excimer laser radiation depending on orientation of birefrin-gence axis of anisotropic optical fiber

Efficiency of Bragg grating inscription by ArF excimer laser radiation depending on orientation of birefrin-gence axis of anisotropic optical fiber

Effect of protective coating on random birefringence variations in anisotropic optical fibres in response to temperature changes

This paper examines for the first time the nature of an anomalous scatter in the birefringence beat length in an anisotropic silica fibre upon changes in its temperature. The effect has been studied by a conventional interferometric technique, using a spectrum analyser. The dispersion of the scatter in the beat length has been shown to be considerably higher at short fibre lengths, which is due to the effect of the protective coating. To interpret the observed effects, a physical model has been proposed which considers random centres, such as microbends, which form and disappear in the protective coating of the fibre in response to temperature changes. The random nature of such local centres may lead to unpredictable changes in the birefringence of anisotropic fibres and, hence, to changes in the sensitivity and accuracy of Faraday effect current sensors.

Impact study of anisotropic optical fibers winding with different tension value on the H-parameter invariance degree

Subject of Research. We have investigated the effect of anisotropic optical fibers winding with an elliptical sheath subjecting to stress on the H-parameter invariance degree. This type of optical fiber is used in the manufacture of fiber loop in fiber-optic gyroscopes. Method of Research. The method of research is based on the application of Michelson polarization scanning interferometer as a measuring device. Superluminescent diode with a central wavelength of 1575 nm and a half-width of the spectrum equal to 45 nm is used as a radiation source. The studies were carried out with anisotropic optical fiber with 50 m long elliptical sheath subjecting to stress. The fiber was wound with one layer turn to turn on the coil with a diameter of 18 cm, which is used in the design of fiber-optic gyroscope. The tension force of the optical fiber was controlled during winding on a special machine. Main Results. It was found that at the increase of tension force from 0.05 N to 0.8 H the value of H -parameter increases from 7×10-6 1/m up to 178×10-6 1/m, respectively; i.e. the coupling coefficient of orthogonal modes in the test fiber is being increased. Thus, it is necessary to consider the longitudinal tension force of fiber in the design and manufacture of the fiber-optic sensors of high accuracy class: the less the fiber winding power, the higher invariance degree of distributed H -parameter. The longitudinal tension force of anisotropic optical fiber with elliptical sheath subjecting to stress equal to 0.2 N is recommended in the process of designing fiber-optic gyroscopes. Practical Relevance. The proposed method of Michelson scanning interferometer is usable in the production process for quality determination of the optical fiber winding: no local defects, value controlling of fiber H -parameter.

Anisotropic metamaterial optical fibers.

Internal physical structure can drastically modify the properties of waveguides: photonic crystal fibers are able to confine light inside a hollow air core by Bragg scattering from a periodic array of holes, while metamaterial loaded waveguides for microwaves can support propagation at frequencies well below cutoff. Anisotropic metamaterials assembled into cylindrically symmetric geometries constitute light-guiding structures that support new kinds of exotic modes. A microtube of anodized nanoporous alumina, with nanopores radially emanating from the inner wall to the outer surface, is a manifestation of such an anisotropic metamaterial optical fiber. The nanopores, when filled with a plasmonic metal such as silver or gold, greatly increase the electromagnetic anisotropy. The modal solutions in such anisotropic circular waveguides can be uncommon Bessel functions with imaginary orders.

Twisted anisotropic fibers for robust orbital-angular-momentum-based information transmission

We study the light propagation in the twisted anisotropic optical fibers endowed with torsional mechanical stress by obtaining the analytical solution of the vector wave equation. We show that at certain interplay between fiber parameters optical vortex beams of topological charge $\ensuremath{\ell}=0,\ifmmode\pm\else\textpm\fi{}1,\ifmmode\pm\else\textpm\fi{}2,...$ become the modes of the fibers in question. To explain the splitting of the optical vortex propagation constants we introduce the notions of orbital birefringence and optical Zeeman effect. Moreover, we unveil that induced by torsional stress circular birefringence makes the vortex beams with the well-defined orbital angular momentum robust against small perturbations characterized by both constant and spatially varying orientation of a director. We believe that such fibers can be successfully utilized for the long-range robust transmission of information encoded in the light's orbital degrees of freedom.

Birefringence in anisotropic optical fibres studied by polarised light Brillouin reflectometry

Modal birefringence (the difference between the effective refractive indices of orthogonal polarisation modes) is one of the key parameters of anisotropic single-mode fibres, characterising their ability to preserve a linearly polarised state of input light. This parameter is commonly measured using short pieces of fibre, but such procedures are destructive and allow the birefringence to be determined only at the ends of long fibres. In this study, polarised light Brillouin reflectometry is used to assess birefringence uniformity throughout the length of an anisotropic fibre.