Optical Waveguide Theory

Increasing customer demand for durable and functional apparel manufactured in a sustainable manner has created an opportunity for nanomaterials to be integrated into textile substrates. Nanomoieties can induce stain repellence, wrinkle-freeness, static elimination, and electrical conductivity to fibers without compromising their comfort and flexibility. Nanomaterials also offer a wider application potential to create connected garments that can sense and respond to external stimuli via electrical, color, or physiological signals. This review discusses electronic and photonic nanotechnologies that are integrated with textiles and shows their applications in displays, sensing, and drug release within the context of performance, durability, and connectivity. Risk factors including nanotoxicity, nanomaterial release during washing, and environmental impact of nanotextiles based on life cycle assessments have been evaluated. This review also provides an analysis of nanotechnology consolidation in the textiles ...

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Nanotechnology in Textiles

Stimuli-responsive polymers (SRPs) are smart materials which can show noticeable changes in their properties with environmental stimulus variations. Novel functionalities can be delivered to textiles by integrating smart SRPs into them. SRPs inclusive of thermal-responsive polymers, moisture-responsive polymers, thermal-responsive hydrogels, pH-responsive hydrogels, and light-responsive polymers have been applied in textiles to improve or achieve textile smart functionalities. The functionalities include aesthetic appeal, comfort, textile soft display, smart controlled drug release, fantasy design with color changing, wound monitoring, smart wetting properties and protection against extreme variations in environmental conditions. In this review, the applications of SRPs in the textile and clothing sector are elucidated; the associated constraints in fabrication processes for textiles and their potential applications in the near future are discussed.

https://iopscience.iop.org/article/10.1088/0964-1726/21/5/053001/pdf

A review of stimuli-responsive polymers for smart textile applications

We report on a new class of polymer photonic crystal fibers for low-loss guidance of THz radiation. The use of the cyclic olefin copolymer Topas, in combination with advanced fabrication technology, results in bendable THz fibers with unprecedented low loss and low material dispersion in the THz regime.We demonstrate experimentally how the dispersion may be engineered by fabricating both high- and low-dispersion fibers with zero-dispersion frequency in the regime 0.5-0.6 THz. Near-field, frequencyresolved characterization with high spatial resolution of the amplitude and phase of the modal structure proves that the fiber is single-moded over a wide frequency range, and we see the onset of higher-order modes at high frequencies as well as indication of microporous guiding at low frequencies and high porosity of the fiber. Transmission spectroscopy demonstrates low-loss propagation (< 0.1 dB/cm loss at 0.6 THz) over a wide frequency range.

/pdf/bendable-low-loss-topas-fibers-for-the-terahertz-frequency-427i253lrq.pdf

Bendable, low-loss Topas fibers for the terahertz frequency range

We propose two designs of effectively single mode porous polymer fibers for low-loss guiding of terahertz radiation. First, we present a fiber of several wavelengths in diameter containing an array of sub-wavelength holes separated by sub-wavelength material veins. Second, we detail a large diameter hollow core photonic bandgap Bragg fiber made of solid film layers suspended in air by a network of circular bridges. Numerical simulations of radiation, absorption and bending losses are presented; strategies for the experimental realization of both fibers are suggested. Emphasis is put on the optimization of the fiber geometries to increase the fraction of power guided in the air inside of the fiber, thereby alleviating the effects of material absorption and interaction with the environment. Total fiber loss of less than 10 dB/m, bending radii as tight as 3 cm, and fiber bandwidth of ~1 THz is predicted for the porous fibers with sub-wavelength holes. Performance of this fiber type is also compared to that of the equivalent sub-wavelength rod-in-the-air fiber with a conclusion that suggested porous fibers outperform considerably the rod-in-the-air fiber designs. For the porous Bragg fibers total loss of less than 5 dB/m, bending radii as tight as 12 cm, and fiber bandwidth of ~0.1 THz are predicted. Coupling to the surface states of a multilayer reflector facilitated by the material bridges is determined as primary mechanism responsible for the reduction of the bandwidth of a porous Bragg fiber. In all the simulations, polymer fiber material is assumed to be Teflon with bulk absorption loss of 130 dB/m.

Porous polymer fibers for low-loss Terahertz guiding.

A method for fabricating a terahertz waveguide comprises forming a multilayer reflector formed of alternating layers of first and second polymer materials with distinct refractive indices, and defining with the multilayer reflector a hollow core through which terahertz radiation propagates. The corresponding terahertz waveguide comprises the multilayer reflector formed of the alternating layers of the first and second polymer materials with distinct refractive indices, and a hollow core defined by the multilayer reflector and through which terahertz radiation propagates.

Ferroelectric all-polymer hollow bragg fibers for terahertz guidance

We propose a porous polymer terahertz fiber with a core composed of a hexagonal array of subwavelength air holes. Numerical simulations show that the larger part of guided power propagates inside the air holes within the fiber core, resulting in suppression of the bulk absorption losses of the core material by a factor of ∼10–20. Confinement of terahertz power in the subwavelength holes greatly reduces effective refractive index of the guided mode but not as much as to considerably increase modal radiation losses due to bending. As a result, tight bends of several centimeter bending radii can be tolerated.

Low loss porous terahertz fibers containing multiple subwavelength holes

We report on the terahertz (THz) spectral characteristics of hollow-core THz Bragg fibers. Two types of high-index contrast Bragg fibers were fabricated: one based on the index contrast between a polymer and air, and the second based on the contrast between a pure polymer and a polymer composite doped with high-index inclusions. The THz transmission of these waveguides is compared to theoretical simulations of ideal and nonideal structures. Waveguide dispersion is low, and total loss measurements allow us to estimate an upper bound of 0.05 cm−1 for the power absorption coefficient of these waveguides in certain frequency bands. We discuss multimode regimes, coupling losses, fabrication difficulties, and how bending losses will ultimately be the discriminant between different THz waveguiding strategies.

/pdf/transmission-measurements-of-hollow-core-thz-bragg-fibers-4iptp2poln.pdf

Transmission measurements of hollow-core THz Bragg fibers

We outline the most recent technological advancements in the design, fabrication and characterization of polymer microstructured optical fibers (MOFs) for applications in the terahertz waveband. Focusing on specific experimental demonstrations, we show that polymer optical fibers provide a very flexible route towards THz wave guiding. Crucial incentives include the large variety of the low-cost and relatively low absorption loss polymers, the facile fiber preform fabrication by molding, drilling, stacking and extrusion, and finally, the simple fabrication through fiber drawing at low forming temperatures.

/pdf/polymer-microstructured-optical-fibers-for-terahertz-wave-45fwxcrj4u.pdf

Alexandre Dupuis

Papers

Porous polymer fibers for low-loss Terahertz guiding.

Ferroelectric all-polymer hollow bragg fibers for terahertz guidance

Low loss porous terahertz fibers containing multiple subwavelength holes

Transmission measurements of hollow-core THz Bragg fibers

Polymer microstructured optical fibers for terahertz wave guiding