End Of Fiber Research Articles

Fullerene-Amyloid Complexes as Perspective Nanocomposites: Molecular Docking Studies

The molecular interactions between the amyloid fibrils from Aβ-peptide, insulin and α-synuclein and fullerenes of different sizes, including C20, C36, C60, C70, and C84, have been studied using the molecular docking approach. The fullerenes are found to bind to the loop or turn region of Aβ- and α-synuclein fibrillar assemblies, but reside at the end of insulin amyloid fibers, reflecting the lower affinity of carbon nanostructures to the latter aggregated protein. For all systems studied here, the fullerene binding to amyloid fibrils is size-dependent, with larger fullerenes exhibiting a higher binding affinity and a lower total energy of complexation. The analysis of side chain contacts highlights the pivotal role of van der Waals forces, specifically, alkyl and π-alkyl interactions, in the stabilization of the fullerene-amyloid complexes. The results obtained are discussed in terms of novel nanocomposite materials based on carbon nanoparticles and fibrillar proteins, as well as of the fullerene role in anti-amyloid therapy.

Repetition Frequency Control of a Mid-Infrared Ultrashort Pulse Laser

In this study, a method for controlling the repetition frequency of a mid-infrared ultrashort pulse laser with a central wavelength of 2.8 µm is developed. A ring cavity that is insensitive to the polarization state of the laser light emitted from the fiber end was constructed to stabilize the oscillation of the mid-infrared ultrashort pulse laser. More oscillation conditions for the ultrashort pulse laser based on nonlinear polarization rotation are found than the conventional method. To confirm that the pulse oscillation is mode-locked, ultrashort pulse oscillation was confirmed by an autocorrelator. The pulse repetition frequency of this robust ultrashort pulse laser was controlled. The control method was based on the phase-locked loop (PLL) control. A wedge window was inserted into the cavity and mounted on a linear stage driven by a piezoelectric transducer. By driving the piezoelectric transducer, the position of the wedge window changed, and the resulting optical path length also changed. The repetition frequency was controlled based on this principle. Optical path length control by the wedge window and temperature control provides an Allan deviation of approximately 1 mHz.

Fiber-Optic Sensor for Identifying Liquids and Determining Solutions Concentration

Fiber-optic sensors for identifying liquids and determining the concentration of solutions have been studied with the possibility of using various types of single-mode optical fibers produced by industry and widely used in optical cables and telecommunications to create sensors for identifying liquids and determining the concentration of solutions. To identify liquids with different refractive indices and determine the concentration of substances dissolved in water, the peak value of the reflectograms of the optical fiber located at the interface between the optical fiber core and the environment can be used as an information parameter. The value of the information parameter depends on the refractive index of the liquid in which one end of the optical fiber is located. The parameters of fiber-optic sensors for identifying liquids and determining the concentration of solutions were studied by optical reflectometry in different wavelength ranges of optical radiation with a duration of reflectometer probe pulses from 25 to 300 ns. It has been established that the fiber-optic sensor can operate at any wavelength of optical radiation corresponding to the transparency windows of the optical loss spectrum of the optical fiber. The influence of the length of the optical fiber between the recording device and the place where the concentration of a liquid solution is determined using a fiber-optic sensor was studied. The possibility of creating a fiber-optic sensor for determining the concentration of the liquid solutions based on optical fibers has been demonstrated.

Visualizing fiber end geometry effects on stress distribution in composites using mechanophores.

Localized stress concentrations at fiber ends in short fiber-reinforced polymer composites (SFRCs) significantly affect their mechanical properties. Our research targets these stress concentrations by embedding nitro-spiropyran (SPN) mechanophores into the polymer matrix. SPN mechanophores change color under mechanical stress, allowing us to visualize and quantify stress distributions at the fiber ends. We utilize glass fibers as the reinforcing material and employ confocal fluorescence microscopy to detect color changes in the SPN mechanophores, providing real-time insights into the stress distribution. By combining this mechanophore-based stress sensing with finite element analysis (FEA), we evaluate localized stresses that develop during a single fiber pull-out test near different fiber end geometries-flat, cone, round, and sharp. This method precisely quantifies stress distributions for each fiber end geometry. The mechanophore activation intensity varies with fiber end geometry and pull-out displacement. Our results indicate that round fiber ends exhibit more gradual stress transfer into the matrix, promoting effective stress distribution. Also, different fiber end geometries lead to distinct failure mechanisms. These findings demonstrate that fiber end geometry plays a crucial role in stress distribution management, critical for optimizing composite design and enhancing the reliability of SFRCs in practical applications. By integrating mechanophores for real-time stress visualization, we can accurately map quantified stress distributions that arise during loading and identify failure mechanisms in polymer composites, offering a comprehensive approach to enhancing their durability and performance.

In-situ temperature monitorization in oscillatory flow crystallizer using optical fiber sensors with a Bragg grating inscribed at the fiber tips ends

Optical fiber sensors were implemented to measure in-situ temperature variations in an oscillatory flow crystallizer operating in continuous. The sensors were fabricated by cleaved in the middle 8 mm-length fiber Bragg gratings, forming tips with a Bragg grating of 4 mm inscribed at the fiber ends. The geometry of the sensors fabricated, with a diameter of 125 μm, allowed the temperature monitorization of the process flow, inside the crystallizer, at four different points: input, two intermediate points, and output. The results revealed that the proposed technology allows to perform an in-situ and in line temperature monitorization, during all the crystallization process, as an alternative to more expensive and complex technology.

Various fiber optic microlenses fabricated using a large diameter splicing system

We developed and fabricated various types of microlenses on optical fiber end facets using a large diameter splicing (LDS) system and analyzed the obtained beam profiles. Numerical simulations support our experimental results.

Plastic Fiber Low Light Measurement Method

Paper describe researches performed to develop a method for checking the light transmission through plastic scintillating fiber. Such fibers are used in different industrial or research application but for our purpose are main components of a flexible detector. Such detector use photon scintillating signals read by higly sensitive detectors and special measures taken to get such sensitivity. We present in paper a method and algorithm developed for measurement of light transmission through plastic fiber when signals are at level of nW. We develop a stand to implement and verify this method. We use fibers with connectors at each fiber end. Fibers are previously polished at each end in order to allows to pass the signal through surface with low losses. Using the stand we perform measurements to analyse the feasibility of method. We present the results that demonstrate the feasibility of method. We succeed to measure signals at level of nW using special measures. Our results shows that method and stand can be used to measure low level signals through fibers. Using this method, it is possible to check the quality of plastic fiber polishing. A fiber with end surface well-polished allows to pass the signal at such low level (nW).

Self-oscillation of 3D trapped bubbles

In this study, we focus on the trapping and self-oscillation of microbubbles in ethanol using a low-power continuous-wave laser. The microbubble formation is achieved by heating of ethanol by light absorption (λ = 658 nm) at silver nanoparticles deposited on the distal end of a multi-mode optical fiber. Subsequently, a second low-power continuous-wave laser (λ = 1,550 nm) coupled to a single-mode optical fiber is used to trap the microbubble. To trap the microbubble, the red laser is turned off after its generation, and immediately the trapping laser is activated. The bulk light absorption at λ = 1,550 nm in ethanol modulates the surface tension of the bubble wall, creating a 3D potential well that effectively traps the bubble. Once the bubble is trapped, random variations in the bubble's radius led to instabilities in the trap, triggering the microbubble oscillation. The trapped bubble tends to oscillate along the light propagation between two points of quasi-steady-state equilibrium. These bubble oscillations result from the opposing competing forces: a changing-direction Marangoni force and drag forces and the upward buoyancy force. To explain the self-oscillation, we present a simple model that qualitatively describes the main features observed in the experimental data.

Optical fiber acoustic sensor with gold diaphragm based Fabry-Perot interferometer

This work proposes an optical fiber acoustic sensor using a Fabry-Perot interferometer (FPI), which consists of an optical fiber end face and a gold diaphragm with an effective diameter of 75 µm and a thickness of 20 nm. The sensor has contrast of up to 34 dB and achieves audible acoustic signal sensing over a broad frequency response range from 70 Hz to 20 kHz with a linear response to sound pressure. The minimum detectable sound pressure is 815.5 μPa/Hz1/2 at 70 Hz. The sensor made of a pure gold diaphragm has stable performance and can work consistently over a long period, promising to be applied as an optical microphone for real-time communication in some extreme environments.

Collinear optical links based on a GaN-integrated chip for fiber-optic acoustic detection.

This Letter reports a collinear optical interconnect architecture for acoustic sensing via a monolithic integrated GaN optoelectronic chip. The chip is designed with a ring-shaped photodiode (PD) surrounding a light-emitting diode (LED) of a spectral range from 420-530 nm. The axisymmetric structure helps the coaxial propagation of light transmission and reception. By placing this multiple-quantum wells (MQW)-based device and a piece of aluminum-coated polyethylene terephthalate (Al/PET) film on fiber ends, an ultra-compact acoustic sensing system is built. The sound vibrations can be simply detected by direct measurement of the diaphragm deformation-induced power change. An average signal noise ratio (SNR) of 40 dB and a maximum sensitivity of 82 mV/Pa are obtained when the acoustic vibration frequency changes from 400 Hz to 3.2 kHz. This work provides a feasible solution to miniaturize the sensing system footprint and reduce the cost.

NGHIÊN CỨU CHẾ TẠO MÔ ĐUN CHUYỂN HƯỚNG BỨC XẠ LASER BÁN DẪN GHÉP SỢI QUANG 650 NM ỨNG DỤNG TRONG QUANG TRỊ LIỆU VÀ QUANG SINH DIỆT KHUẨN

Currently, diode lasers in the red wavelength region, especially at 650 nm, are extensively utilized in phototherapy and photodynamic inactivation of bacterials by numerous research groups in the field of lasers for biomedical application. These devices offer exceptional advantages, such as their compact size, ease of design and integration, user-friendliness, and high safety for both operators and patients. Among these, fiber-coupled diode lasers provide an efficient solution for delivering radiation from the laser chip to the desired location. However, further optimization is still required for the fabrication technological development of these devices to meet specific application needs. This includes aspects like reducing manufacturing costs, improving component usability during operation, and meeting specialized usage requirements. To develop the technology for device fabrication, addressing the aforementioned demands, we conducted research on the design, fabrication, and characterization of fiber-coupled semiconductor lasers operating at a wavelength of 650 nm. The characterization results demonstrate that the manufactured devices can operate at maximal pumping current of 100 mA and under varying temperatures from 25oC to 40oC. Additionally, a radiation output orientation module has been designed and integrated at the end of the optical fiber to meet various demands in phototherapy and photodynamic inactivation of bacterials.

Sensing characteristics of the F-P cavity on the tip of a microstructured fiber

A Fabry-Pérot interferometer on the tip of a microstructured fiber and its sensing application was demonstrated. The microstructured side hole eccentric core fiber was fabricated using the drilling hole method. The fiber end face was polished to 45° which could reflect the light transverse to the fiber, utilizing the side wall of the air hole as the reflection surface. Sensing abilities of the interferometer were investigated in the experiment. It can work as a probe for liquid RI sensing by simply plunging the fiber tip into the solution being tested, in addition, it can become sensors for different parameters by filling functional materials into the air hole. An example of filling UV curable adhesive into the fiber to be a temperature sensor was demonstrated in the experiment. The sensing structure on the fiber tip shows the advantages of high linearity, easy fabrication and good reproducibility, as a sensor it is also convenient to operate.

Integration of knee-shaped self-written waveguides between optical fibers by direct illumination and tip to tip coupling

Optical transmission efficiency of self-written polymer waveguide has been investigated. The polymer couplers were fabricated from a photopolymerizable monomer system by direct illumination from two pre-aligned single mode fibers, and by butt coupling of two extended long polymer tips at the end of fibers. Regarding direct illumination, the writing beams exhibit quasi-solitonic behavior and both show a tendency to attract each other to be merged at the middle point where the droplet deposited between the aligned fiber. Optical transmission gives insertion loss of 4.3 dB and 5.7 dB with total knee angles of (5° and 10°) respectively. Polymer bridges with larger deviation angles were not formed, since the induced beams were not merged properly to form a decent waveguide. Therefore, long polymer tips were fabricated separately and then they were butt coupled at different knee-angles. Optical transmission efficiency was measured over broadband from Ultraviolet to Infrared (UV-IR). In the butt-coupling approach average loss of 1.7 dB, 5.4 dB, 8.6 dB, 10.4 dB and 14.6 dB at measured wavelength 1550 nm were obtained for 300 μm- 300 μm coupling tips corresponding to knee-angles of (0°,5°,10°,15°, and 20°) respectively.

Fibre and failure characterization in long glass fibre reinforced polypropylene by X-ray computed tomography

Long fibre reinforced thermoplastics (LFTs) have become important in recent years, due to outstanding mechanical properties (such as high strength, high stiffness, and excellent impact behaviour). Nevertheless, there is still a lack of knowledge regarding the failure micromechanics of LFTs. This publication focuses on the qualitative and quantitative analysis of influencing factors for failure initiation in long fibre reinforced thermoplastics. Existing and new methodologies are combined for detailed analysis of the local microstructure and micromechanical behaviour. In situ investigations of the LFT via X-ray computed tomography (CT) and subsequent fibre and mechanical characterization based on the volume data were performed. A measurement workflow for the decision on the scanning area before starting a scan series is suggested. The difficulties in fibre orientation analysis of long, curved fibres are revealed by a comparison of different evaluation approaches. Fibre straightness, fibre volume fraction, fibre orientation and fibre end accumulations are investigated in detail. Local strains are determined with digital volume correlation (DVC) and related to the true stress along the measured specimen length. The investigations showed that the test specimens do not necessarily break at the position of the smallest cross-section under uniaxial loading conditions. The failure behaviour of LFTs is strongly influenced by the local microstructure and thus the combination of various microstructural factors such as fibre bundles, fibre ends, local fibre volume fraction and orientation.

Corrosion behavior of steel fiber reinforced concrete under ambipolar stray current interference

This paper preliminarily discussed the influence of measured stray current (SC) with ambipolar characteristics on the corrosion behavior of steel fiber in simulated pore solution and concrete environment by means of corrosion morphology observation, weight loss experiment, electrochemical test, etc. In simulated solution, the results indicated that the influence of short-term SC on steel fiber was limited, while the addition of Cl- led to the weakening or even disappearance of the self-repairing ability of passivation film and accelerated the occurrence of pitting corrosion on the surface of steel fiber. For steel fiber reinforced concrete (SFRC) samples, the circuit loop was formed through the discrete steel fiber, and its resistance depended on the steel fiber content. Although the concrete provided finite protection, the SFRC suffered from severe corrosion under the combined effect of intense SC and Cl-, and the preferential corrosion site was the end of steel fiber.

Численное моделирование эволюции парового пузыря в условиях лазероиндуцированной кавитации

Based on the Lee vaporization-condensation model, numerical solutions were obtained that describe the process of growth and collapse of bubbles formed at the end of an optical fiber during laser heating. The simulation parameters are found for which the numerical solutions correspond to the observed experimental data. Using numerical modeling, the features associated with the dynamics of the growth-collapse of a cavitation bubble and the formation of heated jets are explained.

Improvement of response speed and precision of distributed Brillouin optical fiber sensors using neural networks

Distributed Brillouin optical fiber sensors can detect temperature and strain over long distances in standard single-mode fibers from the measurement of their Brillouin gain spectrum (BGS). However, the performance of these sensors is restricted by parameters such as the frequency scanning interval, average times of data acquisition, and Brillouin frequency shift (BFS) extraction time. Therefore, achieving high-precision real-time monitoring is challenging. In this study, we introduce a nonlinear interpolation deep neural network (NIDNN) to interpolate and denoise the BGS. Additionally, we propose a BFS extraction convolutional neural network (BFSECNN) based on depthwise separable convolution (DSC) to shorten the BFS extraction and training time. Both the simulation and experimental results show that the NIDNN and BFSECNN contributed to higher accuracy in BFS extraction and shorter data processing time. The sweep time of the distributed Brillouin optical fiber sensor with a 28.5-km length after using the NIDNN is 1/6 of the hardware sweep time of the 1-MHz interval, and the BFSECNN extraction time is 3.7 s. Moreover, combining the NIDNN with the BFSECNN reduced the BFS uncertainty by 5.3 MHz at the end of the optical fiber. Used individually or together, the proposed NIDNN and BFSECNN could improve the performance of existing distributed Brillouin optical fiber sensors without any hardware modifications.

Random Raman Fiber Laser as a Liquid Refractive Index Sensor

In this paper, a new concept of forward-pumped random Raman fiber laser (RRFL)-based liquid refractive index sensing is proposed for the first time. For liquid refractive index sensing, the flat fiber end immersed in the liquid can act as the point reflector for generating random fiber lasing and also as the sensing head. Due to the high sensitivity of the output power of the RRFL to the reflectivity provided by the point reflector in the ultralow reflectivity regime, the proposed RRFL is capable of achieving liquid refractive index sensing by measuring the random lasing output power. We theoretically investigate the effects of the operating pump power and fiber length on the refractive index sensitivity for the proposed RRFL. As a proof-of-concept demonstration, we experimentally realize high-sensitivity half-open short-cavity RRFL-based liquid refractive index sensing with the maximum sensitivity and the sensing resolution of–39.88W/RIU and 2.5075×10−5 RIU, respectively. We also experimentally verify that the refractive index sensitivity can be enhanced with the shorter fiber length of the RRFL. This work extends the application of the random fiber laser as a new platform for highly-sensitive refractive index sensing in chemical, biomedical, and environmental monitoring applications, etc.

Design for Hollow-Core fiber connector

This paper describes a newly developed butt joint type hollow-core fiber connector with protected fiber ends. It can typically realize nearly 0.5-dB insertion and 45-dB return loss without physical contact. It has been confirmed that the HCF connector is suitable for actual use because it maintains stable connection characteristics in mating cycles, and it can be cleaned with an ordinary connector cleaner.

Efficient laser emission at 1191 nm based on Ho3+-doped fluoroaluminate glass in a compact fiber configuration

Efficient laser emission at a wavelength of approximately 1.2 μm in Ho3+-doped AlF3-based glass fiber is reported for the first time. Lasing was achieved through in-band pumping at 1150 nm. The laser cavity's front-end feedback was facilitated by a (High reflectivity, HR) HR-FBG written in Corning HI1060 fiber, spliced to one end of the Ho3+-doped AlF3-based fiber. Fresnel's reflection of the gain fiber provided the other end feedback. The laser performance was characterized by different fiber lengths, and a 31 cm-long fiber achieved a maximum slope efficiency of 70.5 % and a maximum output power of 8.3 W. Furthermore, a series of (Low reflectivity, LR) LR-FBGs written in HI1060 fiber with different reflectivity values were used to replace the Fresnel reflection at the emission end of the gain fiber. The maximum slope efficiency was found to be 54.2 % for a LR-FBG with a reflectivity of 10 %. These results confirm that AlF3-based fiber can potentially serve as gain fiber for higher-power fiber lasers.