Fiber Design Research Articles

Anti-resonant hollow core fiber with excellent bending resistance in the visible spectral range

The development of wideband guided hollow-core anti-resonant fiber (HC-ARF) that covers the sensitive range of the human eye's visible spectrum is progressing rapidly. However, achieving low-loss wideband transmission with a small bending radius remains a challenging issue to be addressed. In light of this, we propose a novel, to our knowledge, HC-ARF with a nested double-semi-elliptical cladding structure in the visible spectral region. By employing finite element method simulations, we investigate the confinement loss, bending loss, and single-mode performance of this fiber design. The result shows that the confinement loss of this new fiber exhibits below 10−5 dB·m-1 across almost the entire visible band range, with a minimum loss of 1.55 × 10−7 dB·m-1 achieved for λ = 650 nm. Furthermore, this fiber demonstrates excellent resistance to bending and can maintain an ultra-low bending loss as low as 3 × 10−7 dB·m-1 even under extreme bending conditions with a radius of only 3 cm. Notably, its 3-dB bending radius reaches just 3.5 cm for λ = 532 nm. Additionally, it exhibits outstanding single-mode conductivity under various bending scenarios and achieves a high extinction ratio of up to 104 for higher-order modes after parameter optimization for specific wavelengths.

Progress in module design for membrane distillation

There have been tremendous advances in membrane distillation (MD) since the concept was introduced in 1961: new membrane designs and process configurations have emerged, and its commercial viability has been evaluated in several pilot-scale studies. However, its high energy consumption has hindered its commercialization. One of the most promising ways to overcome this obstacle is to develop more energy-efficient membrane modules. The MD research community has therefore developed diverse new module configurations for hollow fiber and flat sheet membranes that increase the thermal energy efficiency of MD by minimizing thermal polarization, increasing mass transfer across the membrane, and improving heat recovery from the condensed vapor. This review summarizes the progress made in the design of hollow fiber and flat sheet membrane modules for MD applications. It begins with a brief introduction to MD and its configurations before describing developments in module fabrication and highlighting key areas where further research is needed.

Design and fabrication of a tellurite hollow-core anti-resonant fiber for mid-infrared applications

The hollow core anti-resonant fibers (HC-ARFs) based on soft glass are in high demand for 3-6 µm laser delivery. A HC-ARF based on tellurite glass with 6 touching capillaries as cladding was designed and fabricated for the first time, to the best of our knowledge. A relatively low loss of 3.75 dB/m at 4.45 µm was realized in it. The effects of capillary number, core diameter, wall thickness of capillary, and material absorption loss on the loss of the HC-ARF were analyzed by the numerically simulation. The output beam quality was measured and the influence of bending on the fiber loss was discussed. The results of numerical simulation suggested that the theoretical loss of the prepared fiber can be reduced to 0.1 dB/m, indicating that tellurite HC-ARFs have great potential for mid-infrared laser applications.

Real-time polarization compensation method in quantum communication based on channel Muller parameters detection

Polarization drift in fiber and free-space optical links is a major factor in the dynamic increase of bit error rate in polarization-coded quantum key distribution (QKD) systems. A dynamic polarization compensation method applicable to both links is a challenge. Here we propose a universally applicable real-time polarization compensation method, that the Muller parameters of the optical links are first detected using a polarization detector, and then the optimal parameters of the controller are obtained by gradient descent algorithm. Simulation results indicate advantages over current methods, with fewer waveplates, faster speed, and wider applicability for various optical links. In equivalent experiments of both satellite and fiber optical links, the average polarization extinction ratio of 27.9 dB and 32.2 dB are respectively achieved. The successful implementation of our method will contribute to the real-time polarization design of fiber and free-space QKD systems, while also contributing to the design of laser-based polarization systems.

Utilizing Joukowsky transformation in the design of optical fiber for elliptical-to-circular mode conversion.

This study addresses the challenge of enhancing coupling efficiency between optical fibers and elliptical Gaussian beams emitted by semiconductor lasers, particularly in fiber communication systems. We introduce a method for fiber design utilizing the Joukowsky transformation to facilitate efficient mode transformation from elliptical to circular, thereby augmenting the coupling efficiency with both single-mode and multimode fibers. Theoretical analysis and numerical simulations demonstrate that the fiber with a structurally transitional core maintains high-efficiency mode transformation across various lengths, and its structure has been optimized accordingly. Additionally, our investigation reveals the designed fiber's ability to preserve polarization states, which could have significant implications in precision optical applications. The proposed design offers an approach to improving performance in optical communication systems, especially in wavelength-division multiplexing (WDM) transmission systems and fiber lasers.

A metasurface structure-assisted terahertz negative curvature fiber

Negative curvature fibers have the benefits of high bandwidth, low loss, and provide higher transmission performances. Birefringence of the fiber is particularly important, with potential application value in communication, imaging and other fields. In this paper, a metasurface structure-assisted terahertz negative curvature fiber is designed to improve the birefringence characteristic. This work breaks through the conditional design ideas, and theoretically analyzes the effect of adding gold microstructures in the cladding structures on the transmission characteristics of negative curvature fibers. The investigation results show that the birefringence of the designed fiber exhibits a significant increase in most frequency range between 1.75–2.4 THz compared to the results before adding gold microstructures. The maximum birefringence reaches as high as 0.00216 when the frequency is 2.175 THz and θ is 90°. Compared to the original frequency, the birefringence has increased by nearly an order of magnitude. The highest birefringence has been increased to 3.5 times. In addition, the influences of the gold microstructures on the confinement loss, waveguide dispersion, and effective mode field area are also investigated. This fiber provides a reference for the design of high birefringence terahertz fibers in the future.

High-performance Fabry-Perot fiber optic sensors from one-step laser side-polished platforms

A facile one-step non-contact process was developed for preparing the substrates for Fabry-Perot-based side-polished optical fiber sensors. A carbon dioxide (CO2) laser cladding removal technique was used to control the profile of the polished fiber surface and to introduce two reflective cavities. The substrates were characterized for a range of cavity lengths and their thermal response was studied. This device added a degree of freedom to the design of optical fiber based Fabry-Perot sensors and its potential was demonstrated by coating the substrate with polydimethylsiloxane (PDMS). The resulting sensors had a three-order of magnitude increase in sensitivity when compared to the substrate. The polished flat surface provided a route for the integration of novel materials for sensing applications, particularly those where polarization control was vital for light-matter interaction, for example, low dimensional materials such as graphene or MXene. The inherent simplicity, mechanical stability, and scalability of this approach are important steps for the realization of practical devices of this type.

Interfacial blending in co-axially electrospun polymer core-shell fibers and their interaction with cells via focal adhesion point analysis

Electrospun polymer scaffolds have gained prominence in biomedical applications, including tissue engineering, drug delivery, and wound dressings, due to their customizable properties. As the interplay between cells and materials assumes fundamental significance in biomaterials research, understanding the relationship between fiber properties and cell behaviour is imperative. Nevertheless, altering fiber properties introduces complexity by intertwining mechanical and surface chemistry effects, challenging the differentiation of their individual impacts on cell behaviour. Core-shell fibers present an appealing solution, enabling the control of mechanical properties of scaffolds, flexibility in material and drug selection, efficient encapsulation, strong protection of bioactive drugs against harsh environments, and controlled, prolonged drug release. This study addresses a key challenge in core-shell fiber design related to the blending effect between core and shell polymers. Two types of fibers, PMMA and core-shell PC-PMMA, were electrospun, and thorough analyses confirmed the desired core-shell structure in PC-PMMA fibers. Surface chemistry analysis revealed PC diffusion to the PMMA shell of the core-shell fiber during electrospinning, subsequently prompting an investigation of the fiber’s surface potential. Conducting cellular studies on osteoblasts by super-resolution confocal microscopy provided insights into the direct influence of interfacial polymer blending and, consequently, altered fiber surface and mechanical properties on cell focal adhesion points, bridging the gap between material attributes and cell responses in core-shell fibers.

Sustainable design and carbon-credited application framework of recycled steel fibre reinforced concrete

Waste tires pose significant environmental, health, and fire risks. Creative waste management solutions, including reuse, recycle and repurpose, are necessary to mitigate those impacts while enriching their valorisation. An innovative solution is the upcycling of recycled steel fibre (RSF) from waste tires to enhance strength and durability of concrete. This study thus experimentally examines dynamic and mechanical behaviours of high-strength concrete with varying proportions of RSF, from 0% to 1.2% by volume. The results reveal that high-strength concrete with 1.2% RSF exhibits the best improvement in strengths. In addition, the damping ratio, dynamic modulus of RSF concrete and SEM images confirm valorisation potentials of waste fibres. Via a robust critical lifecycle analysis, the new insights form a new sustainable design and carbon credited application framework for RSF. Our results portray that innovative recycling practices for end-of-life tires yield substantial environmental benefits, including a significant carbon emission reduction.

Design and Analysis of Multicore Fiber with High Bend Tolerance and Uniform Effective Area

Design and Analysis of Multicore Fiber with High Bend Tolerance and Uniform Effective Area

Coaxial Fibres Incorporated with Phase Change Materials for Thermoregulation Applications

Nowadays, the growing concern about improving thermal comfort in different structures (textiles, buildings, and pavements, among others) has stimulated research into phase change materials (PCMs). The direct incorporation of PCMs into composite materials can cause mechanical impacts. Therefore, this study focuses on the design of phase change coaxial fibres (PCFs), using commercial cellulose acetate (CA) or recycled CA obtained from cotton fabrics (CAt) as the sheath and polyethylene glycol (PEG) 2000 as the core, via the wet spinning method; the fibres vary in molecular weight, concentration and ejection velocity. The fibres were assessed for their optical, chemical, thermal, and mechanical properties. The presence of PEG2000 is confirmed in the core of the fibres. Thermal analyses revealed a mass loss at high temperatures, attributable to the presence of PEG2000. Notably, the fibres with CA (Mn 30,000) showed superior thermal and mechanical performance. The melting point of PEG2000 incorporated into these PCFs coincided with the melting point of pure PEG2000 (about 55 °C), with a slight deviation, indicating that PCFs were obtained. Finally, the results point to the application of the fibres in civil engineering materials requiring a phase change between 50 and 60 °C, providing promising prospects for their use in applications requiring thermoregulatory properties.

Investigation of hybrid chalcogenide photonic crystal fiber for MIR supercontinuum generation and optical communication

Abstract This study describes a wideband supercontinuum generation (SCG) in the mid-infrared range using a chalcogenide multi-material microstructured fiber design with significant non-linearity under optical communication. The fiber has a single core of As2Se3 and three rings of As2S5 rods arranged in hexagonal pattern in the AsSe2 cladding region. The reported PCF design has effective area and nonlinear coefficients as 59.4174 μm2 and 219.36 W−1 km−1 respectively at 5.3 μm pump wavelength. Additionally, it has a chromatic dispersion profile that is nearly zero and flattened over a large wavelength range of 5–15 µm, which is advantageous for broadband supercontinuum spectrum in the mid-infrared region. Specifically, with pulse width and pulse peak power of 200 fs and 10 kW, respectively, for a 100 mm fibre length, this research work illustrates the SCG that expands from 1000 nm to over 15,000 nm. These extremely nonlinear PCFs are robust contenders for applications that are nonlinear in nature, such as the generation of slow-light and supercontinuum.

Design of uncomplicated triangular core PCF for enhanced non-linearity applications

An innovative design of Photonic Crystal Fibre (PCF) for enhanced non-linearity applications using simulation with the Finite Element Method (FEM) is presented. The PCF is a kind of fibre optic waveguide that has air-holes along the entire length of the optical fibre, which exploits its exclusive features of being continuously single-moded and having a modifiable spot-size and dispersion properties for various linear and non-linear applications. This proposed triangular core PCF is made of silica material with a refractive index of 1.445 and features three large air-holes placed 120° apart in the core, each with a refractive index of 1.00. The air-holes have a pitch length of 6.03 μm and a radius of 2.86 μm, and the wavelength of operation is 1.55 μm. The proposed PCF design has a large diameter to pitch ratio (d/Λ) of up to 0.95, resulting in a reduced spot-size of just above 1.00 μm2. This indicates that the proposed triangular core PCF design could be used to enhance non-linearity applications. This study introduces a novel structure that simplifies construction by employing three strategically positioned large air-holes in the cladding, thus achieving the necessary properties for guiding light through the core. This streamlined approach overcomes complexities associated with previous designs from the literature, hence, offering a practical solution for effective light guidance while minimising construction difficulties. This inventive proposed PCF design can be fabricated using the Stack and Draw process or the slurry casting method.

Structure and properties of wet-spun nylon/graphene nanocomposite fibers

Due to an increasing demand for more portable and intelligent electronic devices, strong and flexible fibers which are also electrically conductive and thermally stable are currently on demand. Herein, wet-spun nylon/graphene nanoplatelets (GNPs) and nylon/reduced graphene oxide (rGO) nanocomposite fibers were fabricated in a range of filler loadings and the effect of the type of graphene employed and the presence/absence of ions absorbed into the fibers during coagulation on their structure, processing and properties was evaluated. The diameters were homogenous along the fibers and similar for identical loadings of both fillers. The increasing viscosities of the dopes with increasing filler loadings were, however, reducing progressively the processability of the systems, leading to increasingly thicker and more defective fibers. The nanocomposite fibers behaved as electrically percolated systems, with considerably lower percolation threshold found for the rGO based fibers relative to the GNPs based ones due to the higher aspect ratio of rGO relative to GNPs. The richer surface chemistry of the rGO flakes provided stronger filler–polymer interfaces, leading to a higher optimal loading and effective modulus relative to the GNPs system. Whereas the presence of ions from the coagulation bath did not affect the diameters, microstructure or electrical properties of the fibers, it was found to have an impact on their mechanical properties, thermal stability and melting and crystallization behavior. This knowledge is key to gain control on the design of nanostructured fibers with specific structure and properties that meet the requirements for particular applications in the field of multifunctional textiles.

Reverse engineering and analysis of microstructure polymer fiber via artificial neural networks: simplifying the design approach

Abstract Microstructure polymer fibers have been extensively researched for their applications in various fields. The design and simulation of these fibers have utilized time-consuming techniques like the finite-difference time-domain and finite element method to facilitate the process. This study proposes an optimal artificial neural network (ANN) for predicting the structural design required to achieve desired optical properties. The ANN model takes various optical properties, including confinement loss, effective index, effective mode area, and wavelengths, as inputs to predict fiber design parameters such as diameter and pitch. To address the challenge of skewed distributions, a data set with a Gaussian-like distribution for confinement loss was generated using a logarithmic transformation method, enabling effective training of machine learning models. Furthermore, the ANN model demonstrates its capability to rapidly predict unknown geometric parameters using only the core mode properties of a polymer fiber, achieving results in a significantly shorter time (3 ms) compared to the trial-and-error approach of finite element method simulation (15 s). The reverse engineering model achieves a mean square error of 3.4877 × 10−06 with five hidden layers. The ANN model not only offers ultrafast calculation speed but also delivers high prediction accuracy, thereby accelerating the design process of optical devices. The differentiation among the prediction result, target, and calculation result provides compelling evidence that the proposed approach is an effective methodology for designing microstructure polymer fibers.

Design and simulation of photonic crystal fiber for highly sensitive chemical sensing applications

Abstract Photonic crystal fibers (PCF) have demonstrated promising capabilities for liquid sensing applications owing to their distinctive optical properties. This work presents a numerical investigation of a PCF sensor optimized for discriminating water, ethanol, and benzene samples. In the proposed configuration, there are five concentric rings of air holes in the cladding arranged in a hybrid lattice structure, while the core contains only one air hole. The optical properties of the sensor, such as refractive index, power fraction, relative sensitivity, confinement loss, effective area, and nonlinearity, were assessed through a comprehensive analysis utilizing the full vector Finite Element Method within the COMSOL Multiphysics software. All these properties have been meticulously examined through numerical investigation across a broader range of wavelengths spanning from 0.8 to 2.2 µm. The suggested model has high sensitivity, minimal confinement loss, and an exceptional nonlinear coefficient value. At a wavelength of 1.3 µm, the suggested PCF exhibits greater sensitivity of 96.84, 98.12, and 100% for water, ethanol, and benzene, respectively, and nonlinear coefficients of 13.98 W−1 km−1 for water, 13.93 W−1 km−1 for ethanol, and 14.85 W−1 km−1 for benzene, with decreased confinement loss. The created model can be utilized in several research areas, particularly in chemical sensing and bio-sensing, as well as their respective applications.

Elephant Trunk Inspired Multimodal Deformations and Movements of Soft Robotic Arms

AbstractElephant trunks are capable of complex, multimodal deformations, allowing them to perform task‐oriented high‐degree‐of‐freedom (DOF) movements pertinent to the field of soft actuators. Despite recent advances, most soft actuators can only achieve one or two deformation modes, limiting their motion range and applications. Inspired by the elephant trunk musculature, a liquid crystal elastomer (LCE)‐based multi‐fiber design strategy is proposed for soft robotic arms in which a discrete number of artificial muscle fibers can be selectively actuated, achieving multimodal deformations and transitions between modes for continuous movements. Through experiments, finite element analysis (FEA), and a theoretical model, the influence of LCE fiber design on the achievable deformations, movements, and reachability of trunk‐inspired robotic arms is studied. Fiber geometry is parametrically investigated for 2‐fiber robotic arms and the tilting and bending of these arms is characterized. A 3‐fiber robotic arm is additionally studied with a simplified fiber arrangement analogous to that of an actual elephant trunk. The remarkably broad range of deformations and the reachability of the arm are discussed, alongside transitions between deformation modes for functional movements. It is anticipated that this design and actuation strategy will serve as a robust method to realize high‐DOF soft actuators for various engineering applications.

Confinement loss prediction in diverse anti-resonant fibers through neural networks.

In this work, genetic algorithm (GA) is employed to optimize convolutional neural networks (CNNs) for predicting the confinement loss (CL) in anti-resonant fibers (ARFs), achieving a prediction accuracy of CL magnitude reached 90.6%, which, to the best of our knowledge, represents the highest accuracy to date and marks the first instance of using a single model to predict CL across diverse ARF structures. Different from the previous definition of ARF structures with parameter groups, we use anchor points to describe these structures, thus eliminating the differences in expression among them. This improvement allows the model to gain insight into the specific structural characteristics, thereby enhancing its generalization capabilities. Furthermore, we demonstrate a particle swarm optimization algorithm (PSO), driven by our model, for the design of ARFs, validating the model's robust predictive accuracy and versatility. Compared with the calculation of CL by finite element method (FEM), this model significantly reduces the cost time, and provides a speed-up method in fiber design driven by numerical calculation.

A modified equally-spaced method (MEQS) for fibre placement in additive manufacturing of topology-optimised continuous carbon fibre-reinforced polymer composite structures

This study proposes a modified equally-spaced (MEQS) method for the path design of continuous fibres in additive manufacturing (AM) of topologically optimised composite structures. The MEQS method addresses the low fibre infill rate issue of the traditional Equally-Spaced (EQS) method by utilising the Offset method to generate looped printing paths around the internal cavities and gaps between continuous fibre paths. The developed MEQS method was first illustrated against EQS and Offset methods using an open-hole composite plate in which topology and material orientation were simultaneously optimised using the discrete–continuous parameterisation (DCP) method. Actual printing path-based finite element modelling showed that the MEQS method achieves a 25.32% increase in stiffness compared to the Offset method. Experimental testing of the additively manufactured open-hole composite plates showed that the MEQS method improves the stiffness and strength by 15.52% and 27.38%, respectively, compared to the Offset method. The proposed MEQS was further demonstrated through two other case studies by finite element modelling, showing that the stiffness of MEQS has increased by an average of 66.71% and 14.95% compared to EQS and Offset, respectively.

A grating-modified broadband D-type photonic crystal fiber polarization filter

In this paper, a D-type grating-modified broadband photonic crystal fiber polarization filter based on surface plasmon resonance is proposed. The asymmetric design of D-type photonic crystal fiber is helpful to achieve single-mode polarization filtering, and grating can increase the coupling between the core mode and the SPP mode and thus increase the constraint loss. From our simulation results, it can be seen that the applicable bandwidth range can easily reach 1 μm. At the communication wavelength of 1750 nm, the calculated constraint losses of x-polarized and y-polarized core modes are 4.2526 dB cm−1 and 1491.8 dB cm−1, respectively, and the crosstalk is up to 1292 dB. The proposed grating-modified of photonic crystal fiber has achieved good filtering effect in the near-infrared band, and even extended to the mid-infrared band.