Conventional Fiber Research Articles

Advances in Photonic Crystal Fiber-Based Sensor for Detection of Physical and Biochemical Parameters—A Review

The promising properties of photonic crystal fibers (PCFs) have sparked the interest of a number of research organizations. Due to the PCF’s air holes, liquid or gas samples can be inserted into them. This permits a well-controlled interaction between confined light and sensing samples, enabling the development of novel sensing applications. That was never conceivable with conventional optical fibers. PCF applications in sensing fields can be divided into physical sensors and biochemical sensors based on the parameter being measured. Physical sensors measure pressure, temperature, refractive index (RI), curvature, vibration, torsion, electric field, and displacement, among other physical characteristics. Biochemical sensors can detect chemical and biological (such as antibodies, cells, bacteria, enzymes, viruses, nucleic acids, etc.) substances. The measurement of the chemical RI is a crucial component of biochemical sensors. Due to their close relationship with biosensors, chemical sensors are commonly referred to as biochemical sensors. This article covers the detecting capabilities of surface plasmon resonance (SPR)-based PCF biochemical and physical sensors in addition to a variety of ways to enhance their sensing capacities.

Collapsed photonic crystal fibre thermoluminescence dosimetry for external beam radiotherapy

In measuring exposure to ionizing radiation various detectors and techniques have been developed. Current investigation is of key TL dosimetric responses of Ge-doped collapsed photonic crystal fibre (PCF), a form offering the advantage of greater sensitivity compared to more conventional single-mode optical fibers. The PCF samples that have been studied herein have been used to obtain external photon beam percentage depth doses (PDD), elevated sensitivity being desirable in providing a basis for the capture of the range of doses. Using a linac operated at 6 and 10 MV, the results show a favourable comparison with ionization chamber values (typically to within 5%). Threshold dose, reproducibility, and dose-rate dependency have also been characterized.

Evaluation of a Novel Cuboid Hollow Fiber Hemodialyzer Design Using Computational Fluid Dynamics.

Conventional hollow fiber hemodialyzers have a cylindrical shell-and-tube design. Due to their circular cross-section and radial flow distribution and collection in the headers, the flow of blood in the header as well as in the hollow fiber membranes is non-uniform. The creation of high shear stress and high shear rate zones or stagnation zones could result in problems, such as cell lysis and blood clotting. In this paper, a novel cuboid hemodialyzer design is proposed as an alternative to the conventional cylindrical hemodialyzer. The primary motivation behind the proposed design is to create uniform flow conditions and thereby minimize some of the above-mentioned adverse effects. The most salient feature of the proposed design is a cuboid shell within which the hollow fiber membrane bundle is potted. The lumen of the fibers is fed from one side using a flow distributor consisting of embedded primary and secondary channels, while the fibers are drained from the other side using a flow collector, which also has embedded primary and secondary channels. The flow characteristics of the lumen side of the cuboid hemodialyzer were compared with those of a conventional hemodialyzer based on computational fluid dynamics (CFD) simulations. The results of CFD simulations clearly indicated that the flow of liquid within the cuboid dialyzer was significantly more uniform. Consequently, the shear rate and shear stress were also more uniform. By adopting this new design, some of the problems associated with the conventional hemodialyzer design could potentially be addressed.

Single-mode operation and spectral depuration by W-type Yb-doped fibers in Q-switched fiber lasers

We report a W-type fiber design for improving the beam quality and spectral purity of the Q-switched Yb-doped fiber lasers (YDFLs). Our W-type fiber exhibited higher losses in the high order modes (>100 dB/m) and lower losses in the fundamental modes (<0.1 dB/m). A 20/130 μm Yb-doped W-type fiber was fabricated by employing a modified chemical vapor deposition (MCVD) process and a solution-doping technique. The Yb-doped W-type fiber was examined in an acousto-optic Q-switched YDFL. A robust single-mode operation with a 1.19 M2 factor was obtained by optimizing the bending radii. The suppression of mixed mode four-wave mixing (FWM) and amplified spontaneous emission (ASE) was observed in the output spectral with an 18 dB signal to noise ratio (SNR) enhancement at 1064 nm and a 5.3 dB ASE inhibition ratio at 1030 nm. The Yb-doped W-type fiber exhibited enhanced beam quality and output spectra than the conventional Yb-doped step-type refractive index fiber. Therefore the W-type fiber suits the Q-switched fiber laser applications.

Orthogonal single-mode helical Bragg gratings created in fiber cladding for vector bending measurement.

We demonstrate a novel, to the best of our knowledge, two-dimensional vector bending sensor based on orthogonal helical Bragg gratings inscribed in the cladding of a conventional single-mode fiber (SMF). The helical cladding fiber Bragg gratings (HCFBGs) are created by using a femtosecond laser direct writing technology and a quarter-pitch graded index fiber (GIF) is used in front of the HCFBGs to diverge the core mode into fiber cladding. In contrast to the multimode resonance observed in conventional cladding Bragg gratings inscribed by using a femtosecond laser point-by-point (PbP) or line-by-line (LbL) technology, the proposed HCFBGs exhibit stable narrowband single-mode Bragg resonance. An HCFBG with a low peak reflectivity of -50.77 dB and a narrow bandwidth of 0.66 nm was successfully fabricated by using a lateral offset of 45 µm between the HCFBG and the fiber core axis. Moreover, two orthogonal HCFBGs were fabricated in the SMF cladding and used for vector bending sensing. Strong orientation dependence could be seen in omnidirectional bending measurement, exhibiting a maximum bending sensitivity of up to 50.0 pm/m-1, which is comparable to that in a multicore FBG. In addition, both the orientation and amplitude of bending vector could be reconstructed by using the measured Bragg wavelength shifts in two orthogonal HCFBGs. As such, the proposed HCFBGs could be used in many applications, such as structural health monitoring, robotic arms, and medical instruments.

Improving the interlaminar bonding and thermal conductivity of polymer composites by using split-radial mesophase pitch-based carbon fiber as reinforcement

Mesophase-pitch-based carbon fiber (MPCF) reinforced polymer (MPCFRP) have excellent properties such as high thermal conductivity and high modulus, but the significant anisotropy and surface inertness of MPCF result in the poor interlaminar thermal conductivity and interface bonding of MPCFRP, which greatly limits its application. To address this issue, MPCF-A with split-radial structure was prepared through fiber structure modulation. Compared with the conventional skin-core fiber (MPCF-B), the higher surface roughness and chemical activity of MPCF-A contribute to stronger mechanical locking and chemical bonding between fibers and resin, meanwhile open wedge crack and better graphite microcrystalline structure of MPCF-A play a positive role in increasing the contact points and reducing the phonon scattering in the heat transfer. Therefore, the interlaminar shear strength (40.7 MPa) and interlaminar thermal conductivity (2.09 W/(m·K)) of MPCFRP-A are 9.12% and 27.4% higher than those of MPCFRP-B, respectively, on the basis of the excellent in-plane thermal conductivity (322.8 W/(m·K)). This study provides a reliable guide to improve the interlayer performance of MPCFRP by tailoring the fiber microstructure.

Reflective structure for phase-shifted fiber Bragg grating.

A novel, to the best of our kowledge, reflective phase-shifted fiber Bragg grating (R-PS-FBG) structure composed of a conventional fiber Bragg grating (FBG) and a micromirror with an air gap between them is proposed. The R-PS-FBG may be regarded as consisting of a Fabry-Perot interferometer and a phase-shifted fiber Bragg grating (PS-FBG), and its reflection and transmission spectra are investigated numerically and experimentally for different mirror reflectances and gap widths. The R-PS-FBG can be implemented easily and could be used in optical spectrum filtering, wavelength tuning, and multiparameter sensing with better sensitivity and resolution.

Farklı Fiber Post Sistemleri ve Rezin Simanların Bağlanma Dayanımı: Deneysel Çalışma

Objective: The aim of this study was to compare the push-out bond strength (BS) of 2 different conventional fiber and glass fiber posts in the form of bundles by using 2 different resin cement and the fracture types formed accordingly. Material and Methods: Root canal treatment was applied to 48 extracted human premolars for the push-out test. The teeth were divided into 3 fiber post groups: Group 1: Biolight ST (conventional fiberpost), Group 2: RelyX (conventional fiberpost), Group 3: Biolight Plus (bundle post) according to the posts to be used for the push-out test. Each of the fiber post groups were divided into 2 subgroups according to adhesive cement [Core-X Flow, Build It FR] used in the cementation of posts (n=8). One mm sections were taken from the middle third of posts and the sections were subjected to a push-out test and the values were recorded. The samples were examined under a stereomicroscope and fracture types were determined. Results: No statistically significant difference was found between the groups according to the test results. When the fracture types were evaluated for all groups, there was no statistically significant difference in the result. Conclusion: The fiber post system in the form of bundles has similar properties with the conventional glass fiber post system in terms of BS.

Fusion splicing of hollow-core to standard single-mode fibers using a gradient-index bridge fiber

High-performance interconnection between hollow-core fiber and conventional solid-core fiber is of great significance for a lot of promising applications of hollow-core fibers. The current problems for high-performance hollow-core fiber/solid-core fiber interconnection mainly involve mode field mismatch of the two fibers and the complex splicing process. Subject of study. We study fusion splicing of anti-resonant hollow-core fiber with low loss (0.52 dB) and conventional single-mode fiber using a convenient graded-index bridge fiber. Purpose of the work. We aim to eliminate the mode field diameter mismatch between anti-resonant hollow-core fiber and single-mode fiber and simplify the mode field diameter adaptation method and process. Method. We employ a convenient graded-index bridge fiber approach, where a gradient index fiber is first spliced with the single-mode fiber, and the mode interference within the graded-index bridge fiber causes periodic enlargement and shrinkage of the mode field diameter. By precise cutting of the graded-index bridge fiber, the mode field diameter can be well controlled and made approximately equal to the mode field diameter of the anti-resonant hollow-core fiber. After mode field diameter adaptation, an optimized arc discharge fusion splicing procedure is applied for the anti-resonant hollow-core fiber/single-mode fiber fusion splicing. Main results. A fusion splicing loss of about 0.52 dB is achieved, which involves nearly 0.42 dB mode-field-diameter-mismatch-induced loss and about 0.1 dB fusion splicing loss that is caused by the deformation of the anti-resonant hollow-core fiber. Practical significance. The developed approach is convenient and cost-effective, which can benefit a lot of applications of anti-resonant hollow-core fibers in future telecommunications, fiber gas lasers as well as fiber-optic sensing.

Highly sensitive and stable probe refractometer based on configurable plasmonic resonance with nano-modified fiber core

A dispersion model is developed to provide a generic tool for configuring plasmonic resonance spectral characteristics. The customized design of the resonance curve aiming at specific detection requirements can be achieved. According to the model, a probe-type nano-modified fiber optic configurable plasmonic resonance (NMF-CPR) sensor with tip hot spot enhancement is demonstrated for the measurement of the refractive index in the range of 1.3332–1.3432 corresponding to the low-concentration biomarker solution. The new-type sensing structure avoids excessive broadening and redshift of the resonance dip, which provides more possibilities for the surface modification of other functional nanomaterials. The tip hot spots in nanogaps between the Au layer and Au nanostars (AuNSs), the tip electric field enhancement of AuNSs, and the high carrier mobility of the WSe₂ layer synergistically and significantly enhance the sensitivity of the sensor. Experimental results show that the sensitivity and the figure of merit of the tip hot spot enhanced fiber NMF-CPR sensor can achieve up to 2995.70 nm/RIU and 25.04 RIU⁻¹, respectively, which are 1.68 times and 1.29 times higher than those of the conventional fiber plasmonic resonance sensor. The results achieve good agreements with numerical simulations, demonstrate a better level compared to similar reported studies, and verify the correctness of the dispersion model. The detection resolution of the sensor reaches up to 2.00×10⁻⁵ RIU, which is obviously higher than that of the conventional side-polished fiber plasmonic resonance sensor. This indicates a high detection accuracy of the sensor. The dense Au layer effectively prevents the intermediate nanomaterials from shedding and chemical degradation, which enables the sensor with high stability. Furthermore, the terminal reflective sensing structure can be used as a practical probe and can allow a more convenient operation.

Coaxial electrospun nanofibers as drug delivery system for local treatment of periodontitis.

The aim of the present study was to prepare resorbable polylactide fibers for periodontitis treatment using coaxial electrospinning to optimize the release of metronidazole (MNA) by reducing the initial burst effect. Poly(L-lactide-co-D,L-lactide) (PLA) fibers mats with different distributions of metronidazole (MNA) were manufactured by coaxial electrospinning (COAX). By COAX spinning the central core of the fiber was enriched with 40% MNA (m/m), while the sheath of the fiber consisted of PLA only (test group). In contrast, fibers of the control group were prepared by conventional electrospinning with the same amount of MNA but with a homogenous drug distribution (HDD - homogenously distributed drug). The release of MNA was determined by analyzing aliquots from the fiber mats using UV-VIS spectroscopy. Agar diffusion tests were carried out to determine the antibacterial effect on periodontopathogenic bacteria. Biocompatibility was tested in direct contact to human gingival fibroblasts (HGF) for two days. The COAX mats showed a retarded drug release compared to the conventional HDD fibers. After 24h, 64% of total MNA was released cumulatively from the COAX fibers while 90% of the MNA was released from the HDD fibers (controls). The antibacterial effect of COAX fibers was significantly higher after 24h compared to the HDD fibers. Cell cultivation revealed significant higher numbers of vital cells among the COAX mats. COAX fibers showed improved sustained MNA release compared to conventional fibers and can be seen as potential drug delivery systems in local periodontitis treatment.

AFP tool path planning for manufacture of variable stiffness composites

Variable stiffness composites (VSC) demonstrate enhanced mechanical properties compared to conventional carbon fiber reinforced plastics (CFRP). Finite element analysis (FEA) is used to optimize layup directions, which need to be transformed into viable tool paths for automated fiber placement (AFP) processes. Manufacturing defects such as wrinkles, gaps, and overlaps should be handled. In this study, a novel path planning algorithm is developed for variable steering in AFP. The fiber directions are clustered and for each cluster a reference curve is fitted as B-Spline, where manufacturing constraints are considered. The proposed tool path planning approach is successfully demonstrated in a case study.

Improvement of isothermal characteristic of isothermal chamber by filling with graded copper foam

Due to the isotropy and high thermal conductivity of metal foam, a novel idea of isothermal chamber filled with graded copper foam (GCF) is developed to improve the isothermal characteristic of isothermal chamber. Firstly, an analytical effective thermal conductivity (ETC) prediction model of metal foam is proposed, with relative root-mean-square error (RRMSE) is 6.90%, which has higher ETC prediction accuracy than the semi-empirical models in the literatures. Secondly, the conventional porous random fiber bundle is replaced by the copper foam as the filler material to improve the isothermal characteristic, and this more accurate ETC prediction model of metal foam is used in the numerical simulation of the discharge process to determine the isothermal characteristic of isothermal chamber filled with homogeneous copper foam (HCF). Experiments are conducted to verify the results of simulation. Thirdly, the graded filling method is adopted to form an isothermal chamber filled with GCF, which enhance the heat transfer efficiency and further improve the isothermal characteristic. The results show that, compared with the conventional isothermal chamber filled with homogeneous porous random fiber bundle, the isothermal characteristic of the isothermal chamber filled with GCF is improved by 32.7%.

Double-Wire-Based Single Distributed Optical Fiber Strain Sensing Method in High-Temperature Environment

Optical strain sensors [optical fiber strain (OFS] based on optical frequency domain reflection (OFDR) are an optical sensor with great application value and the ability to achieve distributed detection. However, both the external ambient temperature and the strain contribute to the frequency shift of the Rayleigh scattering spectrum in the optical fiber during the measurement. This means that the problem of temperature compensation (TC) must be considered when detecting strain in the environment with temperature field, especially in high-temperature environment. In this article, a method of double-wire-based single optical fiber was proposed to aim at this problem, which makes one single fiber have two functions of TC and strain sensing at the same time. The contact strain sensing experiment was carried out on the conventional standard single-mode fiber (SMF)-128 polyimide-coated (PI) distributed OFS sensor (DOFSS) under high-temperature conditions (0 °C–300 °C). The TC for the strain measurement of optical fiber sensor-based OFDR was effectively realized by performing data fusion operation on the measurement results of TC and strain sensing, and the relationship between the temperature change rate and the compensation error rate (ER) was obtained. In addition, the noncontact fiber stretching sensing experiment under ultrahigh-temperature (50 °C–600 °C) conditions was carried out for the first time, which further verified the effectiveness of the method for the compensation of the fiber strain measurement error. Feasibility especially provides a simple and effective method for the application of strain measurement technology in high-temperature environment.

Comparative evaluation of bondingbetween composite relined fibre post and Conventional fibre post: an in-vitrostudy

Background:Fiber posts are widely used aesthetic material in restorative dentistry. These materials were introduced to overcome the inherent shortcomings of cast posts.Aim: This study aimed to evaluate and compare the pull-out bond strengthof fibre posts with relining and without relining.Materials and methods:Twenty maxillary canines were extracted and underwent endodontic treatment, involving the removal of their crown portion. Post-space preparation was performed, and the appropriate post size was selected. In Group 1, ten samples were coated with a layer of composite, reinserted into the post space of the canal, and then light cured outside the canal. The other ten samples (Group 2) were without relining. The fibre posts from both groups were cemented with RMGIC. The samples were mounted in tensile fixtures ofthe universal testing machine and subjected to a tensile load until the posts were debonded. The debonded samples were analysed using a stereo microscope for bond failure analysis. The obtained results were subjected to statistical analysis.Results:The mean pull-out force in group 1 and group 2 was 72.2100±8.56420 and 61.3700±11.00611, respectively. One way ANOVA analysis showed a significant difference in the pull-out force among the groups (P=0.043). In Group 1, 30% of the samples reported adhesive-2failures and 70% adhesive-1&amp;2 failures. But in Group 2, all samples were reported with adhesive-3 failures. Fisher’s Exact test displayed a significant difference in the type of bond failure between the groups (P=0.003).Conclusions:This study concluded that the coating of the fibre posts improves their tensile strength.

Evaluation of mechanical properties for stone mastic asphalt containing textile waste

Bitumen draining in stone mastic asphalt mixtures has become a potential problem. Due to the storage and laying temperatures as well as difficulties in providing the necessary compaction, the temperatures of the asphalt mix cannot be lowered to prevent or reduce drainage. In stone mastic asphalts, generally cellulose or mineral-based fibers are preferred to reduce draining down of bitumen. Conventional fibers commonly used in stone mastic asphalt increase pavement costs because they are expensive. The aim of this research is investigation of textile waste used to prevent bitumen drainage problem in stone mastic asphalt pavements instead of traditional fibers. Following the determination of the bitumen content, Marshall Stability tests, Schellenberg bitumen drainage test and Indirect Tensile Strength tests were conducted to evaluate the mechanical properties of the stone mastic asphalt mixtures in comparison to mixes containing textile waste. The results indicated that it is possible to produce stone mastic asphalt mixes with textile waste that exhibits similar mechanical properties mixes including cellulose fiber. Moreover, it was found that samples prepared with textile waste exhibits advantage in terms of cost compared to samples prepared with cellulose fiber.

Cylindrical vector beam generation from a passively mode-locked Raman fiber laser

We experimentally investigate cylindrical vector beam (CVB) generation from a passively mode-locked Raman fiber laser. The mode-locked Raman fiber lasers based on nonlinear polarization rotation (NPR), utilize the Raman gain resulted from the stimulated Raman scattering (SRS) effect in passive fibers, instead of stimulated emission amplification of active fibers in conventional mode-locked fiber lasers. With a mode-selective coupler (MSC) incorporated into the mode-locked Raman fiber laser, the generation of CVBs has been realized. In experiment, using a Raman pump source of 1454 nm, mode-locked CVB output with central wavelength of 1562 nm was obtained. The output polarization state can be switched between the radial and azimuthal polarization states, and the beam purity is above 90%. Due to the broadband Raman gain in optical fiber, the CVB output with the desired wavelength is available in principle by selecting a suitable pump source. This kind of flexible wavelength CVB Raman fiber laser may have potential applications in optical communications and fiber optics.

Ultrafine Carbon-Nanofiber-Reinforced Graphene Fiber Electrodes for Flexible Supercapacitors with High Specific Capacitance and Durable Cycle Stability

Graphene fiber-based supercapacitors (FSCs) are one of the most promising energy storage devices for flexible electronics. However, the electrochemical performance of conventional graphene fiber electrodes fabricated by wet spinning is still limited by the low specific surface area (SSA), mismatched pore size distribution, and considerable interface resistance. Herein, we developed a scalable method to produce hierarchical porous carbon nanofibers/graphene hybrid fibers (CNGFs) for flexible supercapacitor electrodes with high specific capacitance and durable cycle stability. For energy storage applications, both ion storage accommodation and rapid electronic transfer are required, which could be achieved by the ultrahigh SSA and exceptional conductivity of CNGF electrodes. Therefore, the electrodes of CNGF30 (hybrid fibers with 30% carbon nanofiber loading) exhibit excellent electrochemical performance in terms of the area of areal-specific capacitance (409.1 mF/cm2) and cycle stability (97.7% over 10 000 cycles). Moreover, the well-designed CNGF30 offers remarkable mechanical flexibility for assembled FSCs.

Seeing the strong suppression of higher order modes in single trench fiber using the S2 technique.

The single trench fiber (STF) is a promising fiber design for mode area scaling and higher order mode (HOM) suppression. In this Letter, we experimentally demonstrate the strong HOM-suppression in a homemade STF using the spatially and spectrally resolved imaging (S2) technique. This STF has a 20-µm core and its performance is compared to a conventional step-index fiber with almost the same parameter. Results show that the bending loss of the HOM in STF is 8-times larger than conventional fiber at a bend radius of 7 cm. In addition, when severe coupling mismatch is introduced at the input end of the fiber, the STF can keep the fundamental-mode output while the conventional fiber cannot. To the best of our knowledge, this is the first time to experimentally analyze the HOM content in an STF and compare its performance with that of a conventional fiber. Our results indicate the great potential of the STF for filtering the HOM in fiber laser applications.

A study of the fracture mechanisms of hybrid carbon fiber reinforced polymer laminates reinforced by thin‐ply

AbstractThe main stress component which creates delamination in bonded single lap joints with composite adherends is the transverse tensile stress. Therefore, the following study investigates the behavior of composite laminates (reference and hybrid laminates reinforced by thin‐ply) under transverse tensile loading. Texipreg HS 160T700 and NTPT‐TP415 were used as the conventional carbon fiber reinforced polymer (CFRP) and thin‐ply respectively. Hybrid composite laminates were studied using different amounts of thin‐ply, applied through the thickness. The manufactured laminates, of unidirectionally stacked construction, were tested under transverse tensile loading. Digital image correlation was performed to investigate the average peel strain distribution for the composite and to better understand the phenomena associated to the use of hybrid laminates. Experimental results show that the reinforced hybrid composite laminates, created using thin‐plies, present higher failure load compared to the reference conventional CFRP or thin‐ply laminates. This was found to be due to the higher ductility enabled by the presence of thin‐plies. Distributing a constant amount of thin‐ply through the thickness was found to increase the laminate transverse strength, as the thin‐ply laminates act as a barrier against crack propagation. A representative volume element was studied for each configuration since this numerical method brings the opportunity to investigate the studied configurations in microscale.