Specialty Fibers Research Articles

Comparison of the Sensitivity of Various Fibers in Distributed Acoustic Sensing

Standard single-mode telecommunication optical fiber is still one of the most popular in distributed acoustic sensing. Understanding the acoustic, mechanical and optical features of various fibers available currently can lead to a better optimization of distributed acoustic sensors, cost reduction and adaptation for specific needs. In this paper, a study of the performances of seven fibers with different coatings and production methods in a distributed acoustic sensor setup is presented. The main results include the amplitude–frequency characteristic for each of the investigated fibers in the range of acoustic frequencies from 100 to 7000 Hz. A single-mode fiber fabricated using the modified chemical vapor deposition technique together with a polyimide coating has shown the best sensitivity to acoustic events in the investigated range of frequencies. All of this allows us to both compare the studied specialty fibers with the standard single-mode fiber and choose the most suitable fiber for a specific application, providing an enhancement for the performance of distributed acoustic sensors and better adaptation for the newly aroused potential applications.

Large Range Curvature Measurement Using FBGs in Two-Core Fiber with Protective Coating

In this work, we propose a fiber Bragg grating (FBG)-based sensor for curvature measurements. Two gratings are inscribed through the protective coating in a specialty optical fiber using focused femtosecond laser pulses and point-by-point direct writing technology. One grating is inscribed on the central core adjacent to an air channel, while the other is inscribed on the eccentric core. The bending characteristics of the two-core fiber strongly depend on the bending direction due to the asymmetry of the fiber cores. A bending sensitivity of 58 pm/m−1 is achieved by the FBG in the eccentric fiber core over the curvature range of 0–50 m−1 . Temperature and humidity cross-sensitivity could be significantly reduced by analyzing the differences in peak shifts between the two gratings. The sensor features a large sensing range and good robustness due to the presence of its protective buffer coating, which makes it a good candidate for curvature sensing in engineering fields.

High-temperature resistant boron nitride-based coatings for specialty silica optical fibers

h-BN is well known for its thermal stability. h-BN coated silica optical fibers were manufactured. The coating solution is compatible with optical fiber drawing process, which allows the preparation of tens of meter of h-BN coated fibers. In addition, it is possible to use this coating material for the preparation of short length fiber samples in a post-production approach. Bentonite acts as a binder and allows the adhesion of h-BN to the silica optical fiber. The thermal stability of this protected optical fiber has been demonstrated over a short period of time (several hours) up to 900 °C and over a long period of time (1500 h) up to 800 °C in air. Moreover, the coated optical fiber can resist up to 1000 °C in neutral atmosphere (tested over 6 h).

Roadmap on specialty optical fibers

Abstract Optical fibers, long an enabling technology for telecommunications, are proving to play a central role in a growing number of modern applications, starting from high speed broad band internet to medical surgery and entering across the entire spectrum of scientific, military, industrial and commercial applications. Specialty optical fibers either special waveguide structure or novel material composition becomes heart of all fiber based advanced photonics devices and components. This rapidly evolving field calls on the expertise and skills of a broad set of different disciplines: materials science, ceramic engineering, optics, electrical engineering, physics, polymer chemistry, and several others. This roadmap on specialty optical fibers addresses different technologies and application areas. It is constituted by fourteen contributions authored by world-leading experts, providing insight into the current state-of-the-art and the challenges their respective fields face. Some articles address the area of multimode fibers, including the nonlinear effects occurring in them. Several other articles are dedicated to doped, plastic, and soft-glass fibers. Large mode area fibers, hollow-core fibers, and nanostructured fibers are also described in different sections. The use of some of such fibers for optical amplification and to realize several kinds of optical sources - including lasers, single photon sources and supercontinuum sources - is described in some other sections. Different approaches to satisfy applications at visible, infrared and THz spectra regions are also discussed. Throughout the roadmap there is an attempt to foresee and to suggest future directions in this particularly dynamic area of optical fiber technology.

Refractive insensitive directional bend sensor based on specialty microstructure optical fiber with dumbbell shape core

With the development of information society, more and more special occasions are calling for a wide range of sensors with special properties. In this work, a refractive index insensitive directional bend sensor is proposed based on a specialty microstructure optical fiber with dumbbell shape core, which works as a dual core fiber (DCF). Firstly, this specialty microstructure optical fiber with dumbbell shape core has been fabricated with self-pressurised drawing technique. Then, it has been constructed as a Mach-Zehnder interferometer (MZI) sensor. Consequently, its bend sensing characteristics has been investigated from both theory and experiment. The response of the proposed sensor to the bending evidently displays the directional dependence. In the bending along x direction, the interference peak wavelength is almost insensitive to the curvature. But the transmission is sensitive, which almost obeys the exponential function. Correspondingly, in the bending along y direction the wavelength almost linearly varies with curvature, giving out an averaged sensitivity of 2.44 nm/m−1 in the curvature range of 0–3.79 m−1. But the peak transmission fluctuates without typical principle. In addition, the response of the proposed sensor to the refractive index variation has been checked. It is found that the peak wavelength is almost insensitive to the change of refractive index from 1.33 to 1.45, and the peak transmission fluctuates without clear principle. All these results demonstrate that the proposed sensor has great potential for future internet of things (IoT) applications.

Orbital angular momentum mode multiplexing communication in multimode fibers

Vortex beams with orbital angular momentum (OAM) have infinite mode orthogonality, which can greatly boost communication capacity through mode-division multiplexing. However, current exploration of OAM beam transmission primarily focuses on free-space or specialty fibers limited by the OAM spiral phase wavefront characteristics. Due to the mode field phase sensitivity, these methods are constrained by turbulence interference and fabrication error tolerance, restricting transmission distance of OAM beam at practical application. Herein, we propose an OAM transmission scheme using commercial multimode fiber (MMF) exploiting the eigenmodes superposition theory. Leveraging linear superposition of HE and EH vector modes with ± (π/2) phase shift over MMF, OAM excitation and transmission can be supported with low interference. Simultaneously, due to the decreased demand for fabrication precision in the gradient core structure, the tolerance for machining errors is enhanced. As a proof-of-concept, we have demonstrated a multidimensional OAM multiplexing communication with 640-channel (4 OAM modes, 80 wavelengths and 2 polarization states) over a 5 km MMF, successfully transmitting QPSK-OFDM signals at a total rate of 15 Tbit/s. The system demonstrated OAM mode purity exceeding 65% and bit error rate (BER) below the forward error correction (FEC) threshold (3.8 × 10−3). Multiplexed OAM signals can be effectively transmitted in MMF over short to medium distances with acceptable mode crosstalk, while remaining compatible with wavelength and polarization dimensions, enabling the construction of multi-dimensional multiplexing local area networks.

Enhancing subsequent kraft fiber dewatering properties by using fiber polyamide-epichlorohydrin (PAE) treatment to prepare a dry pulp product,

The energy needed for the dewatering and drying of wet paper web represents around half of the energy consumption of papermaking processes. The present work examined whether the dewatering and drying of paper could be enhanced during a previous pulp drying process by pretreating the fibers with polyamide-epichlorohydrin (PAE). According to the hypothesis, the cured PAE restrains swelling and water absorption of water-wetted fibers by forming a fiber-bound, self-crosslinked polymer-network on the fiber surfaces. The hypothesis was tested by adding PAE to never-dried kraft pulp slurry followed by pulp thickening, drying, and final curing of the PAE-resin. After this, the PAE-treated fibers were dispersed in water, and their water retention values (WRV) and Shopper-Riegler values (○SR) were measured. The PAE pretreatments notably decreased the fibers´ WRV and ○SR, indicating improved water removal of paper web in the paper machine forming and drying section. Compared to chemical crosslinking pretreatments, which also can be used to decrease fibers WRV and ○SR-value, a notable advantage of PAE-pretreatment is milder required curing conditions of the PAE, which makes implementation of the method easier in practice. Due to decreased fiber-to-fiber bonding capability, the PAE-treated specialty fibers could take advantage especially as a bulking aid of paperboard, tissue, and absorbent materials.

Tilted Bragg grating in a glycerol-infiltrated specialty optical fiber for temperature and strain measurements.

In this Letter, we propose an in-line tilted fiber Bragg grating sensor for temperature and strain measurements. The grating is inscribed in a specialty optical fiber using tightly focused femtosecond laser pulses and the line-by-line direct writing method. Beside the central core in which the grating is produced, a hollow channel filled with glycerol aqueous solution significantly improves the sensitivity of the fiber cladding modes due to its high thermo-optic coefficient. We show that the temperature sensitivity of the core mode is 9.8 pm/°C, while the one of the cladding modes is strongly altered and can reach -24.3 pm/°C, in the investigated range of 20-40°C. For the strain measurement, sensitivities of the core mode and the cladding modes are similar (∼0.60 pm/με) between 0 and 2400 με. The significative difference of temperature sensitivity between the two modes facilitates the discrimination of the dual parameters in simultaneous measurements.

Advances in laser‐based manufacturing techniques for specialty optical fiber

AbstractAs demand for customized specialty fibers grows, standardized production methods face challenges. This article reviews industry standards and discusses potentially disruptive techniques that enable rapid prototyping and fabrication of optical fiber devices. Furthermore, we showcase laser powder deposition's (LPD) potential for additive manufacturing (AM) of customized glass structures. In the case of, for example, fiber preforms, although the feasible size is smaller than the industry standard, utilizing laser‐based manufacturing techniques for a small batch production presents an attractive avenue for rapid prototyping and expedites material and design optimization. In the realm of AM of glass, LPD offers numerous benefits, including minimal shrinkage, high densification, and the ability to tailor glass composition to achieve desired optical properties. The article reviews the latest achievements and highlights future directions in this technology.

Importance of Antimicrobial Finishes in Sportech: An Overview

Technical textiles are distinct from other types of textiles because their purpose is not to be aesthetically pleasing or decorative, but rather to have specific functional properties and technical performance.Textiles can be made to have unique functions by applying surface finishing agents and surface treatments, or by incorporating specialty fibers and polymers. Barrier, protection, improved comfort, medication, sensory, actuation, and shielding are a few examples of these functions.One of the biggest manufacturers of products in the Packtech, Clothtech, Hometech, and Sportech segments of technical textiles is India. The demand for these technical textile products has increased dramatically in India. It is anticipated that the technical textiles market will reach a valuation of $325 billion by 2025–2026, up from its current $260 billion. India’s technical textile market, currently valued at $22 billion, has come a long way. The government is determined to raise it to an incredible $40–50 billion within the next five years. The study thus explores the performance of specific Sportech producing segments of the Indian technical textile industry through production.Recently, there have been incidents all across the world thatrise in the number of people engaging in active sports. In the fiercely competitive realm of sports, there are now moreathletes in the professional ranks. Additionally, since sports directly contribute to maintaining their physical and mental fitness, people view them as an essential component of their daily activities. Global consumption of active sportswear has significantly increased in both quality and quantity.Moisture and heat management are the main concerns that must be met in a textile intended for sports applications in order to ensure proper thermophysiological and tactile comfort. Using specific fibers, yarns, and finishes, additional unique qualities are added to clothing while taking hygiene and health into consideration to create a comfortable fit.A thorough discussion has been held regarding the types of fabrics, finishes and recent advancements in sportech.

Enhanced transmission capacity through a specialty multi-channel topological optical fiber

We propose a multi-channel specialty topological fiber based on 1D periodic geometry which supports three coexisting and non-interacting topologically-protected robust light states in the mid-infrared wavelength range. Each channel comprises two topologically-distinct 1D periodic lattices that are characterized by the topological invariant, Zak phase. The interface between the trivial and the nontrivial lattices is made unconventional to provide a strong transverse confinement of the light state. Moreover, the observed multiple interface states exhibit robust simultaneous transmission of light through all the channels keeping in contact with each other with an inter-channel cross-talk of ∼−27 dB. Such highly stable, scatter-free, and robust interface states have the potential to increase the transmission capacity of the existing optical communication channels, and can eventually be utilized as an alternative platform via the space-division multiplexing schemes.

Graphene Oxide-Coated Mach-Zehnder Interferometer Based Ammonia Gas Sensor

The presence of high levels of ammonia in the bloodstream can lead to unconsciousness and convulsions, making it a prime example of dangerous air pollution. The presence of certain gases in our environment can be quite discomforting. In light of these concerns, we present a contemporary approach to designing and developing an exceptionally sensitive ammonia gas sensor. This sensor utilizes a substrate composed of single-mode fiber (SMF), photonic crystal fiber (PCF), and SMF to create a Mach-Zehnder interferometer (MZI). The sensing mechanism involves the immobilization of an Au and GO nanocomposite. In this setup, the region of interference between the waves of the SMF and the solid crystal fiber creates a collapse zone that is utilized to excite the core and cladding modes of the PCF. This innovative technique ensures remarkably rapid response and recovery times.The reusable probe showcased in this study displays significant potential for achieving rapid, highly accurate, and reproducible ultratrace ammonia detection. This introduces a novel avenue for conducting online measurements and environmental monitoring. The intersection point of the SMF and the solid crystal specialty fiber generates a collapse zone that effectively excites the core and cladding modes of the PCF, resulting in the promised rapid response and recovery times.The reusable probe exhibits the capability to swiftly detect ultratrace amounts of ammonia, boasting good selectivity, consistent characteristics, and sensitivities of up to 18.65 nm/ppm. This development opens up new possibilities for environmental monitoring and real-time measurements, offering improved insights into our surroundings.

Soft glass optical fiber characterization with X-ray computed microtomography

The high loss due to the presence of strong phonon resonances makes silica fibers unfit for applications in the mid-infrared spectral range. This has led to the development of specialty optical fibers, based on novel materials and manufacturing techniques. In some cases, the characterization of these new fibers by means of standard techniques may be challenging. Fiber manufacturers would strongly benefit from a tool, which is capable of checking the geometrical and optical properties of fibers (either after fiber drawing, or even in real-time, during the drawing process). Here, we propose and demonstrate that absorption contrast X-ray computed microtomography is a non-destructive technique, capable of characterizing both geometrical and optical properties of specialty optical fibers. We experimentally verified that the tomographic intensity profile in the fiber core has the same shape as the refractive index profile, which we determined via energy-dispersed X-ray spectroscopy. We tested step- and graded-index soft glass fibers, both purchased and made in-house. Owing to the presence of high atomic number elements, which provide higher X-ray cross-section, soft glasses were more suitable than silica for their characterization via X-ray computed microtomography.

Optical Fiber Alignment Aid with Image Processing on FPGA-based System

This paper introduces an innovative and efficient solution for achieving precise optical fiber alignment in fiber optic splicing applications. By harnessing the capabilities of FPGA-based real-time image processing, the system surpasses the required frame rate of 20 frames per second, ensuring swift and accurate alignment. With a verified resolution of approximately 1 pixel per µm, the system offers high precision suitable for various applications. Through advanced image processing techniques, the system calculates precise correction values for each frame, resulting in fast and accurate alignment of fiber cores and cladding. This unique feature enhances performance and adaptability, leading to substantial reduction in splice wastage. By integrating motorized alignment stages and guided machine vision, the system provides a robust and automated approach to fiber optic alignment. The FPGA-driven stepper motors enable precise and controlled fiber movements with micrometer-level step resolutions. The calculated correction factors effectively guide the alignment process, with deviations from actual results impressively low – a maximum of 12 µm in the Y correction factor and 7 µm in the X correction factor. This reliability makes the system a crucial component in any optical fiber splicing machine. Furthermore, the paper emphasizes the ability to handle specialty fiber alignment contributes significantly to cost-effective manufacturing of fiber optic components and modules. By ensuring precise and optimal fiber alignment, the system mitigates signal loss, leading to improved performance and reduced production costs.

Multi-parameter distributed fiber optic sensing using double-Brillouin peak fiber in Brillouin optical time domain analysis.

In this paper, we demonstrate a multi-parameter fiber sensing system based on stimulated Brillouin scattering in a double-Brillouin peak specialty fiber with enhanced Brillouin gain response. The amplitude level of the second Brillouin gain peak, which originated from the higher-order acoustic modes, has been improved with an approximately similar amplitude level to the first Brillouin gain peak from the fundamental acoustic mode. Compared to other multi-Brillouin peak fibers presented in the literature, the proposed fiber significantly reduces the measured Brillouin frequency shift error, thus improving strain and temperature accuracies. By utilizing the sensitivity values of the strain and temperature associated with each Brillouin gain spectrum (BGS) peak, a successful discriminative measurement of strain and temperature is performed with an accuracy of ±13 μɛ, and ±0.5 °C, respectively. The proposed double-Brillouin peak fiber appears to be a possible alternative to other multi-BGS peak fibers, for instance, large effective area fiber and dispersion compensating fibers, which are inherently accompanied by large measurement errors due to the weak Brillouin gain values originating from the higher-order acoustic modes. The demonstrated results show different strain and temperature coefficients of 47 kHz/µɛ, 1.15 MHz/°C for peak 1 and 51 kHz/µɛ, 1.37 MHz/°C for peak 2. Moreover, the enhanced BGS peak gains having nearly the same amplitude levels enable the discriminative measurement of strain and temperature. Such fibers in Brillouin interrogation eliminate the need for complex monitoring setups and reduce measurement errors. We recommend that for long-distance natural gas pipeline monitoring, where discriminative strain and temperature measurement is crucial, the proposed double-Brillouin peak fiber can be highly beneficial.

Phase encoded quantum key distribution up to 380 km in standard telecom grade fiber enabled by baseline error optimization

Phase encoding in quantum key distribution (QKD) enables long-distance information-theoretic secure communication in optical fibers. We present a novel theoretical model characterizing errors from various sources in practical phase encoding-based QKD systems, namely the laser linewidth, detector dark counts, and channel dispersion. This model provides optimized optical pulse parameters and less distortion in pulses, which eliminates system imperfections and leads to a reduced quantum bit error rate (QBER) for practical QKD scenario. This analysis is applicable to various fiber-based phase and time encoding protocols. In particular, we implement this to a differential phase shift (DPS) QKD scheme operating at a 2.5 GHz clock, which produces a secure key rate of 193 bits/s at a fiber length of 265 km and an unprecedented QBER < 1% up to 225 km length with standard telecom components. We show that by adjusting the quantum efficiency and dark count rates of detectors, proposed system can establish secure keys up to 380 km distance using standard telecom grade fiber with a QBER of 1.48%. Moreover, the system is compatible with existing optical fiber networks and capable of establishing a secure key exchange between two cities 432 km apart using ultra-low-loss (ULL) specialty fiber.

Amplified Spontaneous Emission from Optical Fibers Containing Anisotropic Morphology CdSe/CdS Quantum Dots Under Continuous Wave Excitation

Fiber laser field is typically dominated by rare earth ions as gain material in the core of a silica optical waveguide. Due to their specific emission wavelengths, rare‐earth‐doped fiber lasers are available only at few predefined wavelengths. However, quantum dots (QDs) are materials which show tunable emission with change in size and composition. Due to such tunability, QDs seem to be promising candidates for obtaining fiber lasers at a spectrum of wavelengths which is not possible using rare earth ions. To replace rare earth ions with QDs, it is of paramount importance that QDs show signatures of optical gain. Herein, the synthesis of asymmetric pod‐shaped CdSe/CdS QDs is reported, which demonstrate efficient gain on pumping. The intrinsic gain properties of the QDs are evaluated through transient absorption (TA) spectroscopy. Later, the exquisite QDs are used to fabricate specialty fibers from which amplified spontaneous emission (ASE) is obtained using continuous wave laser pump at room temperature. Finally, emission signal stability is checked by studying photobleaching and controlling the concentration of the QDs.

Caustic and enzymatic effects on dissolving pulp and its performance as specialty fiber

Abstract The aim of this study was to investigate an effective approach for improving the dissolving pulp properties for making specialty fiber. The caustic and enzymatic treatment of the properties of dissolving pulp was conducted by analyzing the macromolecular structure and chemical composition. The results showed that the enzymatic treatment was more effective on influencing the macromolecular properties, while the caustic treatment had more influence on structural changing, mainly cellulose crystal structure and crystallinity. Meanwhile, to maintain a higher purity and higher brightness, caustic treatment would be beneficial in comparison with enzymatic treatment. The performance of caustic treated sample was evaluated in regarding to chemical composition and acetylation reaction performance, using commercial pulp as reference. The competitive feature of treated sample suggested its potential in future application.

In situ growth of AuNPs with a nanocavity on the surface of optical fibre for development of SPR sensor

Gold nanoparticles (AuNPs) integrated within optical fibres show great potential as sensor materials in the field of sensing, utilizing the Surface Plasmon Resonance (SPR) principle. This study presents a straightforward, cost-effective, and replicable approach for producing permanent in-situ embedding of AuNPs with nanocavities on the surface of optical fibres. The process involves chemical vapour etching (CVE), followed by gold sputtering and isothermal heat treatment. The analysis conducted using High-Resolution Transmission Electron Microscopy (HRTEM) and Energy-Dispersive X-ray Spectroscopy (EDX), confirmed the presence of nearly spherical AuNPs embedded on the surface of the optical fibre, with an average diameter of 60 ± 5 nm. Additionally, the detection of two distinct plasmon absorption peaks at 567 ± 5 nm and 620 ± 5 nm using a Fibre Optic Spectrometer further validated the presence of AuNPs. To verify the existence of nanocavities surrounding the AuNPs, Field Emission Transmission Microscopy (FESEM) was employed, along with subjecting the AuNPs embedded fibre to three different NaCl solutions of varying concentrations. The results supported the presence of a nanocavity encapsulating the AuNPs. A proposed mechanism was put forth to explain the spectral behaviour resulting from the creation of the nanocavity. This specialty optical fibre is expected to have broad applications in the development of SPR-based chemicals and biosensors, as it facilitates close interaction between the AuNPs and analytes through the nanocavity surrounding the AuNPs on the fibre surface. The fabrication process demonstrated excellent repeatability, with strong adhesion of AuNPs to the optical fibre surface, and no leaching even after repeated use. Thus, we believe that this fabrication method is an exceptional technique for permanently incorporating AuNPs into various glass-based optical waveguide materials for SPR-based sensing applications.

Experimental demonstration of offset-induced sensitivity enhancement in SMS-based temperature and strain sensing

A simple, inexpensive, and high-sensitivity temperature and strain sensor based on a single-mode–multimode–single-mode (SMS) structure with core offset is developed and experimentally characterized. This sensor does not require specialty fibers and can be fabricated using a standard fiber fusion splicer. The dependencies of the temperature and strain sensitivities on the core-offset amplitudes at the input and output single-mode/multimode fiber boundaries are investigated. The results indicate that the maximum temperature and strain sensitivities are two times and eight times higher than those of the standard SMS structure, respectively. The limit of the sensitivity enhancement by core offset is also revealed.