Active Fiber Research Articles

Multifunctional Positive Electrodes for Structural Batteries

The rising demand for energy, coupled with the environmental consequences of CO2 emissions primarily stemming from the combustion of fossil fuels, has prompted the exploration of sustainable solutions for energy generation and storage. Specifically, the automotive industry is transitioning to electric-powered and lightweight vehicles equipped with batteries for generating and storing electric energy. The conventional lithium-ion batteries (LIB) offer high efficiency and energy density, however the presence of mono-functional material with no mechanical performance, liquid electrolyte, and hard protecting casing with poor load-bearing capability marks the battery dependent on inert structural components, which makes the battery bulky and limits its capacity.Structural battery composites, based on carbon fibre (CF), serve a dual purpose by not only storing energy but also acting as integral structural components, potentially replacing inert structural elements [1]. The integration of structural batteries into vehicles and aircraft offers additional power while significantly reducing weight, leading to a substantial enhancement in the overall energy efficiency of the vehicle [2,3].Nevertheless, there exist several challenges in realizing these structural battery composites. For instance, CF-based cathode composites face issues like low energy capacity and weak interfacial strength due to the inadequate adhesion of active materials to the CF surface. Additionally, the current manufacturing methods, such as blade or spray coating, rely on harmful organic solvents.To overcome these limitations, the concept of all-fibre structural batteries is introduced in the present work. In this approach, carbon fibre tows are utilized directly as the negative electrode, like graphite, while electrochemically active functional carbon fibres serve as positive electrodes and a two-phase solid-liquid electrolyte functions as the structural battery electrolyte (SBE). This essentially offers massless energy storage. The electrodes are manufactured using economically friendly, abundant, cheap, and non-toxic iron-based materials like olivine LiFePO4. Graphene, renowned for its high surface area and electrical conductivity, is incorporated to enhance the ion transport mechanism. Furthermore, a vacuum-infused solid-liquid electrolyte is cured to bolster the mechanical strength of the carbon fibres (CFs) and provide a medium for lithium-ion migration. Electrophoretic deposition is selected as a green process to manufacture the structural cathodes with homogeneous mass loading and pouch cells are employed to test the electrochemical performance of LiFePO4-based structural cathodes.

Electrochemically Activated Multifunctional Carbon Fibre Composites

A multifunctional lightweight material combines several functions in a single material entity able to simultaneously bear mechanical loads by acting as a carbon fibre composite component while providing one or more other functionalities at the same time, e.g. storing energy. Carbon fibres are particularly attractive as they can be used both as a high-performance structural material and as an active electrochemical material. Carbon fibres allow for ion insertion into their microstructure with capacities comparable to graphite and hard carbon used in state-of-the-art lithium-ion and other alkali-ion batteries [1]. Carbon fibres are electrically conductive and can therefore replace the conventional metallic current collector. Carbon fibres are thus in this context a truly multifunctional material. A piezo-electrochemical transducer effect (PECT) [2], has also been discovered in ion inserted carbon fibres. The PECT-effect, that mechanical load changes the electrochemical potential of ion-inserted materials, could be used for sensing, where a voltage change is related to the mechanical strain in the material. When carbon fibres are inserted with alkali ions, they expand in the axial direction [3]. This expansion could be used for making linear actuators with high forces or even to create shape-morphing materials [4]. Combing the PECT effect with the expansions allow for using carbon fibres in an electrochemical cell to harvest energy [5],[6]. Such functionalities could be combined with an inherent electrochemical energy storage (battery function) capability. Imagine a solid-state high-performance structural material that senses its own state, can change shape and harvest energy – that is stored in the material itself!In this work, we will show functionalities coming from alkali ion insertion in carbon fibres that goes beyond the battery function, and how these functions can be combined in a single device. The starting point for these concepts are so called structural batteries, which are hybrid and multifunctional composite materials able to carry load while storing electrical energy like lithium-ion batteries. In such a battery, carbon fibres are used as the load carrying material thanks to their excellent strength and stiffness properties, but also as the active negative electrode. They also include a multifunctional matrix system – a structural battery electrolyte (SBE), the material holding the fibres together to make a solid-state load carrying material, but which at the same time is ionically conductive and chemically stable in the voltage window used. It also includes a multifunctional positive electrode – a composite electrode based on conventional ion inserting materials like lithium iron phosphate (LFP) supported by electrochemically active carbon fibres for load carrying and electrical conduction. This can then also be used for inherent strain sensing in the material without any added mass or wiring. The material can also be made to shape-morph with electrical control at low voltages and harvesting energy by converting mechanical strain to electrical power.

Methodological comparison of laser stripping solutions with contemporary pulsed lasers for e-drive copper hairpins

The electric drives used in traction applications employ conventionally pure Cu bars bent to the required form, inserted in the stator and welded by a laser at the extremities. These extremities, which are referred to as Cu hairpins, should be stripped off from the electrically isolating polymeric enamel. Laser stripping is industrially used to remove the enamel from the Cu surface. Pulsed wave lasers are employed for the purpose with a large variety of solutions industrially available to the end users. The peculiar process may give way to material removal by surface heating for instance using infrared radiation (IR) or ultraviolet (UV) lasers or an indirect material expulsion via near-infrared (NIR) sources. Accordingly all major laser sources, namely CO2, active fiber, active disk, and Nd:YAG at different wavelengths, may be used for the purpose. Such laser sources possess very different characteristics regarding the pulse durations, power levels, and beam diameters. As newer laser system solutions are made available, the need for methods and experimental procedures to compare the process performance also increases. This work compares 7 different hairpin stripping solutions based on contemporary pulsed laser sources along with a detailed comparative analysis method. Initially, the 7 laser sources are used for hairpin stripping. The process quality is analyzed through surface morphology, chemistry, and the mechanical strength upon laser welding. Productivity and efficiency indicators are collected. Using the collected data, the work proposes system configurations for three different scenarios prioritizing quality, productivity, and cost.

Comparison of nail-holding performance of Pinus massoniana and Cunninghamia lanceolata dimension lumber based on round steel nails

In this study, the influence of the diameter of round steel nails, the guiding bores, and the wood sections on the nail holding performance of Pinus massoniana and Cunninghamia lanceolata dimension lumber was explored. The results showed that the nail-holding power of round steel nails mainly came from their friction with wood fibers, while the radial and tangential sections were also affected by the shearing action of wood fibers. The tangential section reached the largest nail-holding power, followed by the radial section and cross section. Greater wood density was associated with higher nail holding power. Under a large nail diameter, however, high-density wood was prone to plastic cracking, which influenced the nail holding power greatly. Prefabricated guiding bores could prevent plastic cracking in wood to some extent and improve the nail holding power of Pinus massoniana and Cunninghamia lanceolata dimension lumber when diameter of round steel nails was more than 3.0 mm. For Cunninghamia lanceolata characterized by low density and rigidity, the wood fiber was in close contact with the round steel nail and internal cracking could not be easily generated under a large diameter of round steel nails.

Modification of hydrophobic electrospun polyurethane fibers for efficient wound healing activity

The intricate process of wound healing demands an atmosphere that is conducive to quick healing. In this situation, creating biocompatible and antibacterial fibers may be a good choice. In this study, the unmodified polyurethane and polyurethane modified with cellulose acetate and rosemary oil were electrospun into fibers. These fibers were subsequently adsorbed using silver nanoparticles. The FE-SEM was used to characterize the fibers, revealing their defect-free morphology and the presence of nanoparticles on them. Additionally, the XRD findings demonstrated that silver nanoparticles were successfully incorporated into the spun fiber mats. The contact angle measurements indicated a decreasing behavior starting from 100.4±1° to 28.4±3° in the case of unmodified polyurethane and modified fibers. The antibacterial assay revealed that although unmodified fiber mats have negligible antibacterial action, the modified fibers exhibited considerable antibacterial activity against E. coli and S. aureus. In-vitro studies revealed that Human embryonic kidney 293T (HEK 293T) cell proliferation was enhanced on the surface of modified fibers compared to unmodified fibers. In conclusion, our research presents unique multifunctional fibrous scaffolds that are appropriate and optimal for wound healing applications.

Simulated Surface Electromyographic (SEMG) Signal Generation and Detection Model

Abstract For didactic purposes, the aim of this work was to improve a simulation model of surface electromyographic (sEMG) signal by taking into consideration the shortcomings of previously developed models. This model started with the simulation of the single fibre action potential (SFAP), then the model of the single motor unit action potential (MUAP), afterwards the imitation of the train of MUAP and finally the modellig of the resultant sEMG signal which is the sum of the MUAPs trains. SFAP simulation was based on: i) the description of the volume conductor model which is composed of four layers (bone, muscle, fat and skin), ii) the description of the electrodes shapes and sizes as well as spatial filters, iii) and the transmebrane current. The proposed model shows its effectiveness in the possibility of carrying out practical work by simulation on the modelling of SFAP, MUAP, MUAPT and the sEMG signal. The most important result of this model is that signal processing tools can be applied to analyze and interpret real-world phenomena such as the effects of physiological, non physiological and sensing system parameters on the shape of the simulated sEMG signal.

Experimental investigation of high-power broadband all-fiber nanosecond superfluorescent source

In this work, we demonstrate a broadband nanosecond superfluorescent fiber source (ns-SFS) with an average power of several hundred watts and an adjustable repetition frequency of 25 kHz–100 kHz. To figure out a suitable active fiber length for ns-SFS seed, the impact of active fiber length on the output spectrum of SFS is investigated theoretically and experimentally. The results indicate an evident redshift in the central wavelength of output spectrum with increasing fiber length. By scaling the power of the ns-SFS seed employing three amplifier stages, the maximum average power and pulse energy are obtained with a value of 463 W, 17.6 mJ, respectively. To the best of our knowledge, this work is the first demonstration of a broadband ns-SFS amplifier with output power exceeding hundred watt and pulse energy exceeding 10 mJ.

High peak-to-background-ratio solitons in a coherently driven active fiber cavity

We demonstrate that the peak-to-background ratio of driven solitons can be greatly improved by harnessing the cavity detuning. We use a driven fiber laser pumped below the lasing threshold to increase the finesse and excite solitons in a very wide range of detuning δ. When driving a 50 m long fiber cavity close to the anti-resonance condition (δ = π), we excite sub-800 fs solitons with a peak-to-background ratio close to 30 000. The experimental results are in good agreement with simple theoretical models describing the soliton peak power and the background power.

Does enforcing glenohumeral joint stability matter? A new rapid muscle redundancy solver highlights the importance of non-superficial shoulder muscles.

The complexity of the human shoulder girdle enables the large mobility of the upper extremity, but also introduces instability of the glenohumeral (GH) joint. Shoulder movements are generated by coordinating large superficial and deeper stabilizing muscles spanning numerous degrees-of-freedom. How shoulder muscles are coordinated to stabilize the movement of the GH joint remains widely unknown. Musculoskeletal simulations are powerful tools to gain insights into the actions of individual muscles and particularly of those that are difficult to measure. In this study, we analyze how enforcement of GH joint stability in a musculoskeletal model affects the estimates of individual muscle activity during shoulder movements. To estimate both muscle activity and GH stability from recorded shoulder movements, we developed a Rapid Muscle Redundancy (RMR) solver to include constraints on joint reaction forces (JRFs) from a musculoskeletal model. The RMR solver yields muscle activations and joint forces by minimizing the weighted sum of squared-activations, while matching experimental motion. We implemented three new features: first, computed muscle forces include active and passive fiber contributions; second, muscle activation rates are enforced to be physiological, and third, JRFs are efficiently formulated as linear functions of activations. Muscle activity from the RMR solver without GH stability was not different from the computed muscle control (CMC) algorithm and electromyography of superficial muscles. The efficiency of the solver enabled us to test over 3600 trials sampled within the uncertainty of the experimental movements to test the differences in muscle activity with and without GH joint stability enforced. We found that enforcing GH stability significantly increases the estimated activity of the rotator cuff muscles but not of most superficial muscles. Therefore, a comparison of shoulder model muscle activity to EMG measurements of superficial muscles alone is insufficient to validate the activity of rotator cuff muscles estimated from musculoskeletal models.

Pulse shaping, high average power narrow linewidth Er, Yb co-doped fiber amplifier

We demonstrate a high repetition rate, high average power narrow-linewidth fiber amplifier at 1.55 μm eye-safe waveband by using a very-large-mode-area active fiber doping Er and Yb, having a 60-μm-diameter core and a 600-μm-diameter inner cladding. A maximum average power reaches 16 W at a 10 kHz repetition rate for 600 ns pulses in the stimulated Brillouin scattering (SBS) free operation, which calculates to a 1.6 mJ pulse energy and 2.7 kW peak power. In addition, the peak power rises to 4.9 kW with 148 ns pulses at the onset of SBS. The signal peak is located at 1,551.15 nm with a 36 dB signal-to-noise ratio (SNR). In order to eliminate the pulse steepening, the pulse shaping technology using a triangular-like wave with a slower rising edge is applied on the input pulses. The half-width of the frequency-intensity spectrum from high-average-power fiber amplifier is about 1.02 MHz, approaching the Fourier transform limit.

Valorization of kidney bean (Phaseolus vulgaris L.) pod powder: Multifactorial optimization of gluten-free cake.

The lifelong gluten-free diet of celiac patients and gluten-intolerant people prevents their balanced diet mainly due to starch-rich products. The aim of this study is to determine optimum gluten-free cake formulation having kidney bean (Phaseolus vulgaris L.) pod powder as fat replacer of up to 50% and rice flour replacer of up to 30% using multifactorial optimization approach. Central composite design was used to determine optimum formulation. The use of kidney beans in gluten-free cake increased moisture, hardness, chewiness, L*, a*, b*, antioxidant activity, total phenolic content, and sensory evaluation scores (p < .05). The optimum gluten-free cake is rich in protein (5.89%), phenolic compounds (0.51 mg GAE/g), antioxidant activity (1.93 μmol TE/g), and total dietary fiber (4.43%) with improved sensory properties. The optimum gluten-free cake formulation prepared with kidney bean pod powder of 27.88% fat and 13.52% rice flour replacer provides higher specific volume, springiness, total phenolic content, antioxidant activity, and sensory analysis scores, and lower hardness and chewiness conditions. Gluten-free cake containing kidney bean pod powder as fat and rice flour replacer at optimum ratio is a new healthier alternative with reduced fat content and improved nutritional and sensory properties for celiac patients and gluten-intolerant people.

Nutritional Analysis of Raw, Cooked and Sprouted Cowpea Genotypes

Background: Four cultivars of cowpea NCK-15-01, NCK-15-05, NCK-15-08 and NCK-15-09 had been chosen for analysis in experiment. The raw cowpeas have been amassed from Pulse Research Station, Navsari Agricultural University, Navsari. Methods: After collection, samples were analysed under three exceptional processed states like raw, pressure cooking and sprouting. For the study the analysis of variance of the observed data was done using factorial complete randomized design (Factorial concept). The observations for every parameter had been taken with three repetitions. The critical difference at 5% level of the significance was worked out to compare the treatment means. Among the biochemical parameters some nutrient compositions like crude protein, albumin, globulin, prolamine, glutelin, total soluble sugar, crude fat, antioxidant activity, moisture content and crude fiber were analysed using standard methods. Result: The existing study found that, the cultivar NCK-15-09 contained maximum amount of albumin, prolamine, crude fat, antioxidant activity and crude fiber whereas NCK-15-08 showed highest quantity of crude protein and glutelin. NCK-15-05 had highest amount of globulin and NCK-15-01 is the richest cultivar for total soluble sugar, moisture content.The genotype NCK-15-09 confirmed the highest globulin content (4.84%) in sprouting treatment. Among the different cooking methods, the pressure cooking revealed highest crude protein (23.04%), albumin (3.93%), prolamine (4.04%), glutelin (5.41%), total soluble sugar (58.12 mg/g) and moisture content (12.25%). The highest crude fiber content was determined in sprouting (3.39%).

Changes in the structure and aggregation behavior of wheat glutenin and gliadin induced by the combined action of heat treatment and wheat bran dietary fiber

The effects of different levels of wheat bran dietary fiber (WBDF) on the structure and aggregation behavior of glutenin and gliadin during heating were studied. With increasing temperature, the tanδ value increased from 0.23 to 0.51 in the WBDF-glutenin system (P < 0.05) and decreased from 1.31 to 0.31 in the WBDF-gliadin system (P < 0.05). In the WBDF-gliadin system, the amount of free –SH increased from 0.46 to 5.18 μmol/g with increasing WBDF levels and temperature (P < 0.05). WBDF was involved in the rearrangement of the molecular forces of glutenin and gliadin during heating. WBDF enhanced the hydrophobic interaction between glutenin and gliadin at 25 °C and 60 °C, and weakened this interaction at 95 °C and 130 °C. Overall, WBDF addition had a greater effect than temperature for the induction of significant structural changes in glutenin and gliadin. This study provides a more comprehensive theoretical basis for the quality improvement of high-fiber flour products.

Abbreviated Score to Assess Adherence to the 2018 WCRF/AICR Cancer Prevention Recommendations and Risk of Cancer in the UK Biobank.

The World Cancer Research Fund (WCRF)/American Institute for Cancer Research (AICR) Cancer Prevention Recommendations are lifestyle-based guidelines which aim to reduce cancer risk. This study investigated, in the UK Biobank, associations between an abbreviated score to assess adherence to these Recommendations and the risk of all cancers combined and of 14 cancers for which there is strong evidence for links with diet, adiposity, and physical activity. We used data from 288,802 UK Biobank participants (mean age 56.2 years), cancer-free at baseline. An abbreviated version of the 2018 WCRF/AICR Score was calculated to assess adherence to five Recommendations on (i) body weight, (ii) physical activity, (iii) fruits, vegetables, and dietary fiber, (iv) red and processed meat, and (v) alcohol. Multivariable Cox proportional hazards models were used to analyze associations between the abbreviated score (range, 0-5 points) and cancer incidence, adjusting for confounders. During a median follow-up of 8.2 years (interquartile range, 7.4-8.9), 23,448 participants were diagnosed with cancer. The abbreviated score was inversely associated with risk of cancer overall [HR: 0.93; 95% confidence interval (CI): 0.92-0.95 per 1-point increment], and breast (HR: 0.90; 95% CI: 0.87-0.94), colorectal (HR: 0.86; 95% CI: 0.83-0.90), lung (HR: 0.89; 95% CI: 0.84-0.94), kidney (HR: 0.83; 95% CI: 0.76-0.90), pancreatic (HR: 0.86; 95% CI: 0.79-0.94), uterine (HR: 0.79; 95% CI: 0.73-0.86), esophageal (HR: 0.82; 95% CI: 0.75-0.90), stomach (HR: 0.89; 95% CI: 0.79-0.99), and liver (HR: 0.80; 95% CI: 0.72-0.90) cancers. Greater adherence to the Cancer Prevention Recommendations, assessed using an abbreviated score, was associated with reduced risk of all cancers combined and of nine site-specific cancers. Our findings support compliance to these Recommendations for cancer prevention.

Synergy between carbon fibers and copper-plated graphite on tribological performance of Cu-based composites

Various types of copper-based friction materials were prepared by blending different lubrication components in anticipation of improving the performance and reliability of high-speed train brake pads. The effects of copper-plated graphite (CG), carbon fiber (CF), MoS2 (MS), CG-CF (GF), and CG-MS (GM) on copper-based friction materials for high-speed braking were researched. The tribological properties were appraised on a pin-on-disk testing machine. The mechanical characteristics, micro morphology, element mapping, and tribo-layer were studied by the hardometer, densitometer, SEM, EDS, LSK, and XPS. GF sample has the best comprehensive performance. At 250–350 km/h, it exhibits the most consistent friction coefficient and lowest wear. Additionally, under water spray condition, the friction coefficient remains stable around 0.3 and the fluctuation range is the smallest. Through exploring the variations in element distribution, friction surface, section, and wear debris, the wear forms and mechanisms of materials were revealed. In addition, the synergistic action of copper-plated graphite and carbon fibers was elucidated.

THE EFFECT OF PHYSICAL ACTIVITY LEVELS AND FIBER CONSUMPTION ON BOWEL HABITS OF INDIVIDUALS AGED 40 YEARS AND OLDER LIVING IN RURAL AREAS

Bu çalışma kırsal bölgede yaşayan 40 yaş ve üzeri bireylerin fiziksel aktivite düzeyleri ve posa tüketimlerinin bağırsak alışkanlıklarına etkisini incelenmesi amacıyla yapılmıştır. Bu çalışma kırsal bölgede yaşayan 40 yaş ve üzeri kadın/erkek toplam 584 birey üzerinde yapılmış, kesitsel tipte bir araştırmadır. Değerlendirme için sosyodemografik bilgilerden, Bristol Gaita Skalası’ndan, Uluslararası Fiziksel Aktivite Anketi Kısa Formu (IPAQ)’ndan ve üç günlük besin tüketim kaydından oluşan bir anket formu uygulanmıştır. İstatistiksel analizlerde kullanılan başlıca testler; Ki-kare testi, Mann Whitney U testi, Kruskal Wallis testidir. Araştırmaya katılan bireylerin %17,5’i haftada üç kez veya daha seyrek dışkılama sıklığına sahiptir. Özellikle 70 yaş ve üzeri bireylerde, posa tüketiminin yetersiz olduğu ve dışkılama sıklığının haftada üç kez veya daha seyrek olduğu tespit edilmiştir. Günlük posa tüketimi ortancası 20,65 gram olup erkeklerin (21,9 gr) tüketimi kadınlardan (20,1 gr) daha fazladır (p&amp;lt;0,05). Bireylerin %26,9’unun inaktif olduğu belirlenmiştir. Fiziksel aktivite durumu ile dışkılama sıklığı incelendiğinde minimal aktif bireylerin günde bir kez dışkılama sıklığına sahip olduğu belirlenmiştir (p&amp;lt;0,05). Cinsiyet, ileri yaş, posa ve su tüketiminin az olması, fiziksel aktivite düzeyinin yetersiz olması bireylerin bağırsak alışkanlıkları üzerinde etkili olmaktadır. Çalışma belirli bir kırsal bölgede yaşayan bireyleri kapsadığı için daha geniş çaplı çalışmalara ihtiyaç vardır.

Experimental–Simulation Analysis of a Radiation Tolerant Erbium-Doped Fiber Amplifier for Space Applications

Research on optical amplifiers has highlighted how ionizing radiation negatively impacts the performance of erbium-doped fiber amplifiers (EDFAs), through the degradation of their gain. The amplitudes and kinetics of this degradation are mainly explained by the radiation-induced attenuation (RIA) phenomenon at the pump and signal wavelengths. In this work, the gain degradation of a radiation tolerant EDFA (exploiting a cerium-co-doped active optical fiber) induced by ionizing radiation up to 3 kGy (SiO2), at two dose rates, 0.28 Gy/s and 0.093 Gy/s, is studied through an experimental/simulation approach. Using a home-made simulation code based on the rate and power propagation equations and including the RIA effects, the radiation-dependent performance of EDFAs were estimated. The variations in the spectroscopic parameters caused by irradiation were also characterized, but our results show that they give rise to EDFA gain degradation of about 1%. To overcome the issue of overestimating the RIA during the radiation tests on the sole active rare-earth-doped fiber, a new RIA experimental setup is introduced allowing us to better consider the photobleaching mechanisms related to the pumping at 980 nm. A good agreement between experimental and simulated gain degradation dose dependences was obtained for two different irradiation conditions, thus also validating the simulation code for harsh environments applications.

Distantly related Alteromonas bacteriophages share tail fibers exhibiting properties of transient chaperone caps

The host recognition modules encoding the injection machinery and receptor binding proteins (RBPs) of bacteriophages are predisposed to mutation and recombination to maintain infectivity towards co-evolving bacterial hosts. In this study, we reveal how Alteromonas mediterranea schitovirus A5 shares its host recognition module, including tail fiber and cognate chaperone, with phages from distantly related families including Alteromonas myovirus V22. While the V22 chaperone is essential for producing active tail fibers, here we demonstrate production of functional A5 tail fibers regardless of chaperone co-expression. AlphaFold-generated models of tail fiber and chaperone pairs from phages A5, V22, and other Alteromonas phages reveal how amino acid insertions within both A5-like proteins results in a knob domain duplication in the tail fiber and a chaperone β-hairpin “tentacle” extension. These structural modifications are linked to differences in chaperone dependency between the A5 and V22 tail fibers. Structural similarity between the chaperones and intramolecular chaperone domains of other phage RBPs suggests an additional function of these chaperones as transient fiber “caps”. Finally, our identification of homologous host recognition modules from morphologically distinct phages implies that horizontal gene transfer and recombination events between unrelated phages may be a more common process than previously thought among Caudoviricetes phages.

Optical Reflection Induced by Flexural Acoustic Wave on Fiber Bragg Grating

Flexural acoustic waves can induce optical reflection peaks on one side of the Bragg wavelength in the reflection spectrum of a fiber Bragg grating, thus laying a cornerstone of active acoustic-optic fiber devices. The acoustically-induced refractive index distribution of FBG is deduced. The mechanism of forming acoustically-induced reflection peaks is investigated using mode coupling theory in vector mode presentation. A precise picture is depicted with the selection rules for mode coupling and observation of phase matching, such that the two-step and the three-step processes for acoustically-induced reflection peaks are identified with experimental confirmation. While the three-step coupling theory is discovered, our theoretical framework also refines the former scalar-mode two-step coupling theory. Empowering the theoretical prediction to perfectly match experiment, this work will facilitate the design and application of novel active fiber-optic devices based on acoustic-optic interactions.

Active Differential Fiber Coupled Plasmon Waveguide Resonance Sensor Based on the Mode Competition Effect

We proposed an active differential intensity (DI) fiber coupled plasmon waveguide resonance (CPWR) sensor based on the mode competition effect in the C-band, aiming to enhance the sensitivity. The sensing head is a fiber probe with a sensing layer of ITO/Au/ITO/TiO2 film, enabling the excitation of CPWR in the C-band. The narrow CPWR spectrum allows DI interrogation by tracking the intensity of light at two wavelengths. The fiber probe is inserted into a dual-wavelength fiber laser to adjust the intra-cavity loss at the two lasing wavelengths. By using the differential modulation of the reflectivity from the refractive index variations, the mode competition effect is triggered. The powers at two lasing wavelengths change oppositely, enlarging the power difference and then resulting in enhanced sensitivity. The average sensitivity is up to 5702 dB/RIUs, which is 10 times higher than that of conventional DI interrogation. The sensitivity enhancement mechanism based on the mode competition effect provides a new technical approach for enhancing the sensitivity of DI SPR sensors.