Fiber Core Research Articles

Designing an OAM fiber with a two-layer seven-core structure to support 322 OAM-mode transmissions

In this paper, a two-layer seven-core structural fiber (TLSCSF) is proposed to support and improve the propagation of more orbital angular momentum (OAM) mode beams, thus increasing the transmission capacity and spectrum efficiency (SE) of an optical communication system. The TLSCSF is composed of seven sub-cores, each containing two inner and outer layers of core rings and a central air hole. The two core rings are prepared using two materials with different doping concentrations. The supported OAM modes can be propagated in the fiber core ring. A finite element method (FEM) is used to analyze the designed fiber, and the calculated results show that the TLSCSF can stably transmit 322 OAM modes without higher order radial modes in the wavelength range of 1.5∼1.6 um. The corresponding effective refractive index difference between two adjacent vector modes (HE/EH) is more than 10−4. The measured effective mode areas (Aeff) and the confinement losses (CL) of HE or EH modes are larger than 54 um2 and smaller than 10−10 dB m−1, respectively. Moreover, the calculated dispersion variations and the mode qualities are lower than 230 ps nm−1 km−1 and more than 90%, respectively. Finally, the 10ps walk-off lengths of all vector modes supported by TLSCSF at a wavelength of 1.55 um are also evaluated, where the measured results show that except for HE2,1 and EH1,1, all other modes achieve a 10ps walk-off length of the order of 103 to 105. Consequently, the TLSCSF can contributes to improving the channel capacity and SE by supporting 322 fundamental radial OAM modes with robust performances in an optical communication system.

Functionalising kapok fibre with lignin to enhance the structural and thermal performance of vacuum insulation panels

Kapok fibre has the advantage of low density, low porosity and low thermal conductivity, which make it an excellent substitute for fumed silica and environmentally-unfriendly synthetic polymers as core material of vacuum insulation panels (VIP). However, kapok fibre is hydrophobic, consequently, kapok fibre core materials made by conventional wet forming with weakly-bound fibres and large voids that shorten their service life. Lignin is a natural and sustainable material that has good hydrophilicity and small particle size to form nano-porous networks. Therefore, we herein present the incorporation of lignin in kapok fibre to generate a composite core material with hierarchical porous structure. Lignin functionalises the kapok fibre surface to make it hydrophilic and dispersible in water. Simultaneously, lignin enhances the mechanical properties and service life of core material by transforming its internal microstructure. The effective thermal conductivity of prepared VIP is below 6.00 mW/(m∙K), and after 28 days of accelerated ageing test without desiccant or getter, the effective thermal conductivity increases less than 5.00 mW/(m∙K). Interestingly, the addition of lignin also reduces radiative heat transfer in the VIP. So, lignin addition enables high-performance VIP to be produced. Moreover, as a natural material, kapok fibre is low-cost, environmentally-friendly, sustainable, and energy-efficient.

Management of dislodged crown using split cast metal post and core: A case report

Across diverse cultures, the practice of restoring lost tooth structure has endured through generations. It is widely understood that merely undergoing quality endodontic therapy is not sufficient to fully restore a severely weakened tooth with pulpal disease. Equally crucial is ensuring post-endodontic restoration followed by quality prosthetic rehabilitation. In instances where a tooth is extensively damaged, utilizing a post becomes the preferred course of action post endodontic treatment to preserve the core. The gold standard for the treatment of a severely compromised tooth is recognized as a cast post and core. In this case study, a previously treated maxillary first molar, which had a dislodged fiber post and core along with a porcelain-fused-to-metal (PFM) crown, underwent retreatment with a split cast metal post and core followed by a PFM crown.

Interfacing high numerical aperture metalenses with thermally expanded core fibers via 3D nanoprinting for advanced meta-fiber operation

This study introduces a novel meta-fiber design that combines single-mode fibers with thermally expanded cores and nano-printed high numerical aperture metalenses. These advanced meta-fibers feature enlarged mode field diameters, offering improved mechanical stability, reduced environmental sensitivity and simplified metalens design by minimizing wavefront curvature. The concept’s validity is confirmed through high numerical aperture metalenses, nanoprinted onto thermally expanded core fibers, demonstrating diffraction-limited focusing up to a numerical aperture of 0.9 in air and water. This innovative approach has potential applications in optical trapping, life science imaging, environmental sensing, and fiber-chip coupling in integrated photonics.

Micro-to-Nanoscale Characterization of Femtosecond Laser Photo-Inscribed Microvoids.

Fiber Bragg gratings are key components for optical fiber sensing applications in harsh environments. This paper investigates the structural and chemical characteristics of femtosecond laser photo-inscribed microvoids. These voids are at the base of type III fs-gratings consisting of a periodic array of microvoids inscribed at the core of an optical fiber. Using high-resolution techniques such as quantitative phase microscopy, electron transmission microscopy, and scattering-type scanning near-field IR optical microscopy, we examined the structure of the microvoids and the densified shells around them. We also investigated the high-temperature behavior of the voids, revealing their evolution in size and shape under step isochronal annealing conditions up to 1250 °C.

Ex vivo liquid core fiber photometry with high-resolution 3D printing

High resolution 3D printing emerges as an alternative to microfabrication due to its fine resolution along with one-step manufacturing. Thus, it is broadly used in many fields, such as biological and chemical applications. We introduce such a technique to the design of the optofluidic probe by integrating optics and microfluidics as an ex vivo liquid core fiber photometry. We build the optofluidic probes with various T-shapes and conduct the transmission measurements and the ray tracing simulations, where the results are comparable. Through the transmission and fluorescence measurements, we obtain optimized curl T-shape dimensions of 524 µm wide, ∼50 µm thick, and 350 µm long with longitudinal spaces between them of 260 um. Furthermore, a heightened level of complexity in structure, characterized by a feature size of 25 µm, is attained through the improvement process. We conclude the feasibility of this optofluidic system with two applications: the in vivo-like setting consisting of thyroid biopsy training phantom and human plasma and the ex vivo-like setting consisting of the mice brain slices stained with wheat germ agglutinin (WGA). This prototype is an important step of establishing a 3D printing optofluidic applications for various in vivo research.

High sensitivity fiber SPR sensor based on a spiral coarse cone structure.

A fiber SPR sensor can achieve rapid and portable detection of trivalent arsenic ions (As3+) in drinking water or food, but their sensitivity and detection limit need to be further improved and developed toward specific detection. This article proposed the implementation of the SPR sensor using a biased core fiber spiral coarse cone structure. The fine core of the biased core fiber was used to reduce the mode of transmitted light. By controlling the pitch of the spiral core to control the SPR incidence angle, a significant increase in the sensitivity of the fiber SPR sensor was achieved. Meanwhile, the harmless glutathione (GSH) was modified on the surface of the sensing gold film to achieve the specific detection of As3+. The experimental results indicate that the spiral coarse cone fiber SPR sensor proposed in this article has a detection sensitivity of 32.48 nm/ppb for As3+, with a detection limit as low as 0.011 ppb, meeting the detection requirements of the World Health Organization for As3+ in water, which provides a new feasible solution for fast, portable, and highly sensitive detection of metal ions in water and food.

Coaxial electrospinning synthesis free-standing Sn/TiO2 flexible carbon fibers with sheath/core structure for advanced flexible lithium/potassium-ion batteries

Flexible Sn/TiO2 carbon nanofiber (ST-NCF) composites were constructed by doping TiO2 into tin-based carbon nanofibers via coaxial electrospinning. Sn/TiO2 carbon nanofiber was directly used as an anode for Lithium-ion Batteries (LIBs) and Potassium-ion Batteries (PIBs), which show exceptional electrochemical performances. The layered sheath/core structure of the material lead to its good electrochemical properties, where the core Sn carbon nanofiber was encapsulated by the sheath layer of TiO2 nanoparticles. In addition to enhancing its electrical conductivity, the outer TiO2 and N-doped carbon fiber matrix also provide a buffer zone for volumetric strain during charging and discharging. The fiber core Sn and sheath TiO2 form a heterojunction interface on the two-dimensional tube surface, which increases the diffusion rate of ions and electrons. After 100 cycles, TiO2-NCF and ST-NCF-40%TBT (40% TBT indicates the percentage of TiO2 in shell solution to the total composition of shell spinning solution) show capacities of 386.6 mAh g−1 and 1336 mAh g-1, respectively, at 0.5A g-1. After 2000 cycles, ST-NCF-40%TBT in LIBs displayed a high capacity of 299 mAh g-1 at 10 A g-1. After 350 cycles at 1A g-1, the capacity of ST-NCF-40%TBT in PIBs is reserved at 307 mA h g-1. Due to the superior mechanical flexibility of ST-NCF-40%TBT films, it will be a promising anode candidate for flexible LIBs and PIBs.

Ptycho-endoscopy on a lensless ultrathin fiber bundle tip

Synthetic aperture radar (SAR) utilizes an aircraft-carried antenna to emit electromagnetic pulses and detect the returning echoes. As the aircraft travels across a designated area, it synthesizes a large virtual aperture to improve image resolution. Inspired by SAR, we introduce synthetic aperture ptycho-endoscopy (SAPE) for micro-endoscopic imaging beyond the diffraction limit. SAPE operates by hand-holding a lensless fiber bundle tip to record coherent diffraction patterns from specimens. The fiber cores at the distal tip modulate the diffracted wavefield within a confined area, emulating the role of the ‘airborne antenna’ in SAR. The handheld operation introduces positional shifts to the tip, analogous to the aircraft’s movement. These shifts facilitate the acquisition of a ptychogram and synthesize a large virtual aperture extending beyond the bundle’s physical limit. We mitigate the influences of hand motion and fiber bending through a low-rank spatiotemporal decomposition of the bundle’s modulation profile. Our tests demonstrate the ability to resolve a 548-nm linewidth on a resolution target. The achieved space-bandwidth product is ~1.1 million effective pixels, representing a 36-fold increase compared to that of the original fiber bundle. Furthermore, SAPE’s refocusing capability enables imaging over an extended depth of field exceeding 2 cm. The aperture synthesizing process in SAPE surpasses the diffraction limit set by the probe’s maximum collection angle, opening new opportunities for both fiber-based and distal-chip endoscopy in applications such as medical diagnostics and industrial inspection.

Amplification technology for spatial division multiplexing signals transmitted using multicore fibres

AbstractAmplification technologies needed for spatial division multiplexing (SDM) signal transmission have been reported, especially focusing on submarine systems, which have stricter requirements than terrestrial ones. As the first step of a large‐scale commercialisation, 2‐core un‐coupled (UC) fibre production has already been announced. However, optical amplifiers for SDM signals are still under investigation because SDM amplifiers have various architectural possibilities, depending on the requirements to be considered in designing systems. The multicore erbium‐doped fibre amplifier (MC‐EDFA) architecture is classified from the viewpoint of the number of erbium‐doped fibre (EDF) cores and its pumping method. Core pumped MC‐EDFA is more compatible with the conventional single‐core fibre (SCF)‐ based system and more mature than cladding pumped MC‐EDFA. However, cladding pumped MC‐EDFA has a unique feature of collective amplification of all cores in a single multicore fibre (MCF) and the potential of large‐scale integration of amplification cores in a single package. For a feasibility study, a C‐band 19‐core cladding pumped MC‐EDFA prototype is fabricated using a 19‐core isolator. A half volume of the equivalent conventional single‐core (SC‐) EDFA is successfully demonstrated. One unique feature of UC‐MCF is bidirectional (BD‐) transmission using a single UC‐MCF. Signal transmission direction can differ from core to core. This feature is useful for efficiently accommodating traffic of asymmetric communication data and expanding transmission capacity at a constant transmission distance. A C‐band 7‐core cladding pumped BD‐MC‐EDFA prototype is fabricated for the bidirectional MCF transmission line. Experimental results show transmission capacity was expanded by 17% using the prototype when bidirectional signal assignment was adapted. Towards practical use, optical components suitable for MC‐EDFA need to be developed to draw out potential advantages of SDM technologies.

Kenaf: Opportunities for an Ancient Fiber Crop

Hibiscus cannabinus (kenaf) is an annual fiber crop grown in warm seasons and known for its remarkable productivity; it has been cultivated worldwide for thousands of years as a fiber source. While every part of the plant can be utilized for some purpose, its primary significance lies in the diverse applications of its cellulosic fiber. Kenaf features a blend of long bast and short core fibers, rendering it suitable for various industrial uses. Initially utilized for cordage and livestock feed, kenaf’s applications have expanded over the last century to encompass its utilization as paper pulp, biocomposites, textiles, biomass energy, seed oil, filtration aids, industrial absorbents, and even as a component of potting medium or as a potential source of medicine. Although traditionally a niche crop, the discovery of its diverse applications positions kenaf for rapid expansion in production in the upcoming decades. This article aims to explore the manifold applications of kenaf, highlighting those with the greatest future potential and discussing those that hold promise for commercial-level application with additional research.

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.

Direct 3D-printed ring-resonator photonic circuit on a dual core fiber tip for remote sensing applications.

On-chip optical sensors using ring- and disk-resonators have many potential sensing applications, yet robust and efficient fiber-to-chip coupling and the differing form factor between the two pose deployment challenges. To resolve this, we 3D-printed a ring-resonator onto the tip of a dual-core fiber and demonstrate its use as a remote temperature sensor. The fiber-tip optical circuit is fabricated using direct laser writing (DLW) with two-photon absorption photopolymer material IP-Dip, forming micrometer-scale waveguide cores having a refractive index of 1.53 with a surrounding air cladding. We connect the two-fiber cores by a printed bus-waveguide, utilizing total internal reflection mirrors, allowing light launched into one core to be guided back to the other core. Furthermore, a DLW printed racetrack resonator evanescently coupled to the bus waveguide (Q ∼ 3000) imposes spectral dips on resonance wavelengths. Light sent down into one core is interrogated upon return from the second core, all from the distal end of the sensor. When the sensing end's temperature is varied, we find a sensitivity of 78 pm/K, due to the polymer's thermo-optic index variation. The ring-resonator could be functionalized for other sensing applications.

High sensitivity optical fiber temperature sensor based upon a polydimethylsiloxane filled Fabry-Perot interferometer

A high-sensitivity temperature sensor based upon an optical fiber Fabry-Perot interferometer (FPI) filled with polydimethylsiloxane (PDMS) is reported that employed a single mode fiber (SMF) and a hollow core fiber (HCF) to enhance the sensitivity. The sensing characteristics were investigated from 20 °C to 40 °C. The experimental results demonstrate that the sensor is sensitive to temperature due to the high thermal optical coefficient (TOC) and high thermal expansion coefficient (TEC) of PDMS, achieving a high sensitivity of 2.155 nm/°C. The designed sensor shows great potential for high-precision temperature sensing applications due to its high sensitivity, compact structure, and simple preparation.

Development Of An Endoscopic, Absorption Corrected And Calibrated OH Laser Induced Fluorescence Probe System for High Pressure Combustion Diagnostics

We present the design and preliminary results of an endoscopic OH laser-induced fluorescence (LIF) system that is capable of acquiring 1D-line measurements in high pressure combustion processes within large-scale test facilities. The system can be exploited to acquire line-of-sight OH-chemiluminescence images and absorption corrected absolute OH-species concentration from which additionally temperature distribution can be extracted in case of lean mixtures in chemical equilibrium. Different critical components, such as light guides for high power UV laser pulses and flexible UV image guides, were first tested and characterized in a laboratory setup. Optimization regarding pulse energy and beam quality led to the selection of an 1m long hollow core fiber for laser light delivery as a central element for the experimental setup despite high losses caused by bending the fiber. The image transfer is accomplished by a 7m long flexible UV image bundle, which is preferred to the use of a rigid borescope in harsh environments. We designed the endoscopic UV optics using readily available parts and achieved an approximated image resolution of 21.6 line pairs/mm. Additionally, post-processing methods, such as flat-field correction, can improve the image quality substantially and remove the pixilation effect of the fiber bundle structure nearly completely. To validate the complete system, probe-based qualitative OH-LIF measurements were performed in a well-known laminar flame of a matrix burner, which serves as a mock-up for anticipated applications in an industrial test environment with a technology readiness level (TRL) greater than 4. The final step consists of the integration of the miniaturized optics into a cooled probe system which protects the sensitive optics against the harsh environment of an aero-engine sector combustor. For this purpose, two probe systems were designed to include, on the one hand, the endoscope optics together with the fiber image bundle end tip and, on the other hand, the laser emitting and receiving system for performing an absorption measurement needed to quantify the recorded LIF signal.

Helical-sampled fiber Bragg grating inscribed by a femtosecond laser in a ring core fiber.

The inscription of a helical-sampled fiber Bragg grating (HSFBG) in a ring core fiber (RCF) using a low repetition rate femtosecond laser point-by-point technique is demonstrated. The reflection spectrum exhibits several peak groups attributed to the helical-sampled structure, with the wavelength interval between different groups determined by the helical pitch. Meanwhile, the number and spacing of the peaks within each group are dictated by the RCF. An investigation into the effects of helical pitch, helical radius, and grating length of the HSFBG on the reflection spectra is conducted. Furthermore, thermal annealing experiments demonstrate that this HSFBG can survive at the temperatures up to 800°C.

Bending analysis of textile reinforced concrete sandwich panels: Experimental and numerical evaluation

Textile reinforced concrete (TRC) is a combination of a cementitious matrix and a textile reinforcement that has good mechanical properties. This makes a highly promising composite material for a wide range of construction practices. One notable application of this innovative composite deals with the production of thin sandwich panels. Hence it is noteworthy to examine the control parameters (depth & number of layers) that affect the mechanical properties of TRC sandwich panels with chosen fibre meshes and core material.Initially, 24 different TRC panels were cast and modelled with varying depths (45 mm, 55 mm and 65 mm) and layers (3, 4, 5 and 6), incorporating two different fibre mesh reinforcements. The flexural behavior of these panels was studied both experimentally and numerically using ABAQUS software. The optimized control parameters was obtained from the results was TRC panel of 5 layers of Aramid fibre mesh having 55 mm depth.Further exploration focused on the effect of overall depth variation on the flexural behavior of TRC sandwich panels. A panel with Aramid fibre reinforcement and a calcium silicate board core, featuring a 55 mm overall depth, exhibited a remarkable 69.49 % increase in bending stress compared to a panel with a depth of 118 mm. These findings underscore the significance of optimized control parameters, showcasing the potential for enhancing the mechanical performance of TRC sandwich panels in construction practices.

Raman amplifier based on stimulated Raman scattering in a methane-filled hollow core fiber

This article reports on a single pass amplifier based on stimulated Raman scattering in a methane-filled negative curvature hollow core fiber (HCF) to transition 1.06 μm power to 1.54 μm. The researchers measured the highest average Raman power at a single frequency in a methane filled HCF to date of 4.92 W (246 μJ/pulse), with a high average quantum efficiency of 95.9%. A numerical model for the system was developed and shows good agreement with measured thresholds and efficiencies. Model results from a trade space study indicate configuration regimes necessary to maximize 1.54 μm power while avoiding power loss from the secondary shift.

Side-Opened Hollow Fiber-Based SPR Sensor for High Refractive Index Detection.

To facilitate the sensor fabrication and sensing operation in microstructured optical fiber-based surface plasmon resonance (SPR) sensors for high refractive index (RI) detection, we propose a special hollow fiber-based SPR sensor that comprises an opening on its body side and a thin gold layer coated on its outer surface. The analyte is able to flow into the hollow core through the side-opening to form new fiber core, with the Gaussian-like mode propagating in it. We investigate the sensing performance of the proposed sensor in a higher RI range of 1.48 to 1.54 at two feasible schemes: one is to only fill the fiber core with analyte (Scheme A), and the other is to directly immerse the sensor in the analyte (Scheme B). The results demonstrate that our sensor exhibits higher wavelength sensitivity at Scheme A with a maximum wavelength sensitivity of 12,320 nm/RIU, while a greater amplitude sensitivity was found at Scheme B with a maximum amplitude sensitivity of 1146 RIU-1. Our proposed sensor features the advantages of simple fabrication, flexible operation, easy analyte filling and replacing, enhanced real-time detection capabilities, high RI detection, and very high wavelength sensitivity and amplitude sensitivity, which makes it more competitive in SPR sensing applications.

Development of an optical fiber core sensor integrated with silver film for chloride ion measurement

This study introduced an optical fiber core sensor designed to measure chloride ions by removing the fiber's coating and cladding, allowing direct interaction between the fiber core and external solutions, thereby enhancing measurement sensitivity. Two types of fibers, plastic and quartz, were evaluated for their efficacy as sensors. Experimental results demonstrated that the fabricated plastic core fiber failed to accurately reflect alterations in external solutions onto the spectrum, making it unsuitable for sensor applications. Conversely, the quartz fiber core, when treated with chloroform to dissolve its cladding, exhibited superior performance due to its wider transmission wavelength range and higher durability. The integration of a silver film on the core further improved the sensor's sensitivity through surface plasmon resonance. The study also explored the impact of thin-film and thick-film formations on sensor performance, with the thin film providing rapid response times and the thick film offering enhanced durability. This advancement holds significant potential for applications in environmental monitoring and the early detection of chloride-induced corrosion in various structural materials.