Chiral Fiber Research Articles

Basic study on controlling piezoelectric motion of chiral polymeric fiber

In order to control the bending motion of poly-L-lactic acid (PLLA) fiber, which is one type of chiral polymer, caused by its shear piezoelectricity upon applying electric field, we simulated the electric field distribution in the PLLA fiber by a finite-element method. As a result, we found that the electric field distribution depends strongly on the distance between the electrodes on the surface of the PLLA fiber. On the basis of the simulation results, we design some electrodes on the surface of the PLLA fiber. When we applied an electric field with a tangential component in the cross section perpendicular to the fiber axis, using one electrode, linear motion could be realized owing to its piezoelectricity. Furthermore, when we added a radial component of the electric field using another electrode, the motion could be changed from linear to elliptical.

Chiral nematic liquid crystals as an alternative filling in photonic crystal fibers

Chiral nematic liquid crystals (LCs) are very interesting materials to infiltrate photonic crystal fibers since they are characterized by unique optical properties such as selective Bragg reflection, circular dichroism and optical activity. In this letter first experimental results of chiral nematic LCs-infiltrated photonic crystal fibers are presented. Full Text: PDF

Consideration of chiral optical fibres

Circular birefringence is a property of chiral materials. In this work, we consider the use of chiral materials in optical fibres to produce circularly birefringent optical fibres and in fibres where a contrast in circular birefringence contributes to forming the waveguide. (t϶-menthyl methacrylate is also investigated as a possible material for the fabrication of such fibres.

Hamiltonian description of non-reciprocal light propagation in nonlinear chiral fibers

We introduce a novel type of a nonlinear optical isolator based on adiabatic time-irreversible mode conversion of a tightly confined core mode of an optical fiber into a loosely confined cladding mode of the same fiber. A simple model is developed, describing this device in terms of the time evolution of a driven nonlinear oscillator. Non-reciprocity is shown to be related to the combination of the phase space bifurcation and weak dissipation.

Guided modes in the chiral negative refractive index fiber

The novel characteristics of guided modes in the chiral negative refractive index fiber are investigated theoretically in this letter. We derive the characteristic equation of guided modes. Based on two types of chiral metamaterial parameters, we present the dispersion curves, energy flux, and power of guided modes. Some abnormal features, such as the existence of surface mode and dispersion curves with different shapes, intersection of dispersion curves of different guided modes, negative energy flux in the achiral cladding, and zero power at some normalized frequencies, are found in the chiral negative refractive index fiber.

Self-sorting chiral organogels from a long chain carbamate of 1-benzyl-pyrrolidine-3,4-diol

(3S,4S)-1-benzylpyrrolidine-3,4-diyl bis(dodecylcarbamate), a pyrrolidine ring bearing two long carbon chains connected by carbamate functionalities, is the origin of stable gels in both polar and apolar solvents. Several experimental and theoretical techniques (cryo-TEM, AFM, DSC, circular dichroism (CD), molecular mechanics calculations and CD simulations) were used to describe the formation and the characteristics of the chiral supramolecular structures and fibers constituting the gel. The chirality at both supramolecular and microscopic level depends on the configuration of the stereogenic centers of the pyrrolidine unit. The gels formed by the two enantiomers of the gelator and their mixtures display enantiomeric discrimination resulting in a self-sorting process. In fact, separate fibers of opposite helicity are obtained, which suggests this class of compounds has strong potential for realizing functionalized chiral architectures.

Guided and surface modes in chiral nihility fiber

Guided and surface modes in the chiral nihility fiber consisting of a chiral nihility metamaterial core with an achiral cladding have been investigated. The dispersion equations of guided and surface modes in the chiral nihility fiber and their cutoff frequencies are derived. Dispersion curves of guided and surface modes are presented and the effect of chirality parameter on dispersion curves is discussed in detail. Some novel propagation characteristics are found.

Controlled self-assembly of chiral gelator molecules into aligned fibers induced by nematic to smectic B phase transitions

Chiral bisoxalamide 1 shows remarkable gelling capacity of the nematic and smectic B liquid-crystalline phases of heptylcyclohexanecarboxylic acid ( HCCA). Chiral nematic-containing left-handed helical fiber bundles are formed if the gelator is present in amounts higher than 0.55 wt %. With lower amounts of 1, no nematic gel forms, however, a nematic to smectic B phase transition triggers instantaneous self-assembly of gelator molecules into aligned fibers. The latter liquid crystalline gel system represents an example of controlled self-assembly induced by a liquid crystalline phase transition.

Polarization properties of chiral fiber gratings

Recent experiments (Kopp et al 2007 J. Opt. Soc. Am. B 24 A48) have demonstrated that the polarization sensitivity of chiral fiber gratings depends strongly on the grating symmetry: double-helix fibers are polarization sensitive while single-helix fibers are not. A coupled-mode perturbation theory is developed and used to explain the polarization properties of chiral fiber gratings. Features of the transmission spectrum such as multiple dips in the spectrum and circular dichroism are also derived and attributed to chiral Bragg scattering of the core modes into the cladding modes of the fiber.

Chirofibers with helical windings – An analytical investigation

In this communication, the propagation characteristic of a chiral fiber having helical windings at the core–cladding boundary is analyzed in respect of the relative distribution of power over the sustained modes. The core and the cladding sections of the chirofiber are assumed to have different chirality admittance values while the helical winding pitch angle is considered to attain two particular values - 0 ∘ and 90°. It is observed that the introduction of helical structure leaves a dominant effect on the relative power distribution of the chiral fiber as the variations of the confinement factor with the allowed values of the propagation constants corresponding to different azimuthal modes exhibit much difference in nature for different values of the angle of pitch. It is noticed that the power confinement in the core is much higher when the pitch angle of the helix is effectively introduced by keeping the windings perpendicular to the propagation direction. Further, the property of mode degeneracy in chirofibers is also observed, which is reported to be of much significance when the helical structure remains parallel to the direction of propagation. A more profound mode degeneration characteristic is found for the chiral fiber with larger core dimension.

Simulation of non-isothermal draw and twist of a bi-component chiral glass fiber

A computational framework for computing taper and twist profiles for chiral fibers fabricated from heated bi-component drawn glass filaments is developed, with full coupling between the momentum and temperature fields in both the glass and the surrounding air. A method for solving the inverse problem, in which the takeup holder velocity is varied with a predefined program in order to obtain a desired taper shape, is developed and illustrated.

Electrically Controlled Piezoelectric Motion of Piezoelectric Chiral Polymeric Fibers

The electrically controlled piezoelectric motion of a fiber of poly(L-lactic acid) (PLLA), a type of chiral polymer, is investigated. Laser light was propagated into the PLLA fiber, and when the controlling electric field was applied to the fiber, the direction of the outgoing beam from the fiber changed owing to its piezoelectric motion. The change in direction was recorded using two charge coupled device (CCD) video cameras: one faces the tip of the PLLA fiber and the other is placed above the tip of the fiber. First, it was realized that the outgoing beam moved in a zigzag manner when we applied the ac voltage with high harmonic waves to the PLLA fiber. Furthermore, when a component parallel to the PLLA fiber axis of the applied electric field was generated, the trajectory of the outgoing beam changed from a straight line to an ellipse.

Piezoelectricity of chiral polymeric fiber and its application in biomedical engineering

Poly-L-lactic acid (PLLA), which is a type of chiral polymer, exhibits a high shear piezoelectric constant. To realize a higher shear piezoelectric constant, we spun PLLA resin into fibers. We succeeded in controlling the piezoelectric motion of a PLLA fiber by applying a dc voltage and ac voltage, similar to the control of a piezoelectric actuator. On the basis of this experimental result, we designed a catheter using a PLLA fiber (PLLA fiber catheter) and tweezers using a pair of PLLA fibers (PLLA fiber tweezers), controlled by adjusting the applied voltage. Then, using the PLLA fiber tweezers or catheter, we successfully picked up and removed small samples, such as a thrombosis in a blood vessel.

Electromagnetism and Absorptivity of the Modified Micro-coiled Chiral Carbon Fibers

Micro-coiled chiral carbon fibers are modified by nano-Ni. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to compare the composition and morphology of the unmodified and the modified fibers. The results show that electromagnetism parameters of the modified are different from those of the unmodified. After modification by nano-Ni, the micro-coiled chiral carbon fibers have decreased permittivity and electrical loss. The permeability and magnetic loss of the modified carbon fibers become larger than those of the unmodified ones. Moreover, the modification of unmodified chiral carbon fibers into the modified is much like changing hollow electric windings into those with magnetic cores inside. The modifier intensifies the cross polarization of the chiral carbon fibers and makes the permittivity and the permeability get closer to each other which improves the matching performance and enhances absorbability of coatings. In the range of 6-18 GHz, the reflectivity of the coating is 6-8 dB and the bandwidth is 12 GHz. The area density of the coating is below 3 kg/m2.

Single- and double-helix chiral fiber sensors

Copropagating core and cladding modes in optical fibers can be coupled by a grating with a period greatly exceeding the wavelength, since their propagation constants are similar. In contrast to conventional long-period gratings, in which the modulation is imposed by exposing a photosensitive core to ultraviolet light, we have created chiral long-period gratings with single- or double-helix symmetry by twisting optical fibers with nonconcentric or noncircular cores, respectively, as they pass through a short heat zone. The difference in symmetry between single- and double-helix gratings is manifested in their polarization properties. The use of these gratings as sensors of liquid level and temperature is demonstrated.

Synchronization of optical polarization conversion and scattering in chiral fibers

We demonstrate that polarization transformation and scattering in adiabatically twisted single-mode birefringent optical fibers is synchronized so that light in one evolving elliptically polarized mode is freely transmitted while orthogonally polarized light is scattered out of the fiber. Thus, linearly polarized radiation initially oriented along the fast axis of the untwisted fiber is transformed to circularly polarized light with the same sense of rotation as the twisted fiber and is scattered out of the fiber. When the fiber twist is first accelerated and then decelerated, the fiber becomes a broadband, low-insertion-loss, linear polarizer.

Liquid-filled hollow core microstructured polymer optical fiber

Guidance in a liquid core is possible with microstructured optical fibers, opening up many possibilities for chemical and biochemical fiber-optic sensing. In this work we demonstrate how the bandgaps of a hollow core microstructured polymer optical fiber scale with the refractive index of liquid introduced into the holes of the microstructure. Such a fiber is then filled with an aqueous solution of (-)-fructose, and the resulting optical rotation measured. Hence, we show that hollow core microstructured polymer optical fibers can be used for sensing, whilst also fabricating a chiral optical fiber based on material chirality, which has many applications in its own right.

Polarized Emission of Individual Self-Assembled Oligo(p-phenylenevinylene)-Based Nanofibers on a Solid Support

We have prepared 5 nm diameter, micrometer long tetra(p-phenylenevinylene) (OPV)-based nanofibers on a graphite surface. The fluorescence emission of an individual fiber shows a profound polarization over its entire length that directly corresponds to its orientation on the substrate. Quantitative analysis of the fluorescence polarization, including the depolarizing effect of the underlying graphite, evidences the high degree of organization within chiral fibers with the OPV molecules perpendicular to the fiber axis. The control of the internal order within self-assembled fibers, and the ability to measure it, is a crucial step to obtain uniform organic fibers that can be applied in nanosized electronics at room temperature.

Chiral fiber gratings.

Chiral gratings with double helix symmetry were produced by twisting glass optical fiber with a noncircular core cross section as it passed through a miniature oven. We observed polarization-selective transmission in chiral fibers with pitches of tens of micrometers. Two modes of optical interaction were differentiated. In chirallong-period gratings, dips in transmission were observed at wavelengths associated with scattering into distinct cladding modes mediated by the chiral grating. In chiral intermediateperiod gratings, a broad scattering band was observed. These gratings can be used to produce sharp or broad polarization-selective filters.

Self-assembled spiral nanoarchitecture and supramolecular chirality in Langmuir-Blodgett films of an achiral amphiphilic barbituric acid.

An amphiphilic barbituric acid derivative was found to form stable monolayers showing a clear phase transition at the air/water interface. It is interesting to find that the deposited Langmuir-Blodgett (LB) films of the compound showed circular dichroism (CD) although the molecule itself was achiral. AFM measurements on the transferred one-layer LB film revealed that spiral nanoarchitectures were formed. It was further found that the supramolecular chirality of the LB films was related to symmetry breaking at the interface. Hydrogen bonding and the pi-pi stacking between the neighboring molecules resulted in chiral fibers which formed the spiral structures. To the best of our knowledge, this is the first report on the chirality of the molecular assemblies and spiral nanostructures formed through the air/water interface by achiral molecules.