Fiber Core Research Articles

Chalcogenide dual-core all-solid anti-resonant fiber polarization beam splitter operating at 3 μm band

Abstract For the first time, we proposed a polarization beam splitter (PBS) designed based on chalcogenide dual-core all-solid anti-resonance fiber (AS-ARF) and simulated it numerically using the finite element method (FEM). Two large cladding tubes are introduced to divide the fiber core into fiber cores A and B. Mode coupling and energy exchange between the two fiber cores are enabled through the gap g between the two large cladding tubes. By adjusting the structural parameters of the AS-ARF, polarization beam-splitting ability and single-mode characteristics can be obtained. The influence of the position of the nested tube within the large cladding tube on the performance of the PBS is further investigated. The numerical results show that the beam-splitting lengths of the two proposed PBSs are 9.5 cm and 8.2 cm, respectively, and the polarization extinction ratios (PERs) are −55.98 dB and −41.35 dB at 3 μm. In the wavelength range from 2.98 μm to 3.03 μm, both PBSs can simultaneously achieve polarization beam-splitting and single-mode characteristics. The proposed chalcogenide-based dual-core AS-ARF is a suitable candidate for PBS in the mid-infrared 3 μm band.

SPR fiber optic sensor based on MMF-NCF doped with MgF2 for dual-parameter measurement of temperature and humidity

Dual-parameter temperature and humidity sensors based on optical fiber sensing have wide applications. Among various optical fiber sensors, surface plasmon resonance (SPR) sensors exhibit excellent sensing sensitivity. To address the bandwidth issue and expand the sensitivity, this paper proposes a multimode fiber-no core fiber (MMF-NCF) SPR sensor. The humidity channel covers an Ag/PVA composite film, while the temperature channel covers an Ag/MgF2/PDMS composite film. The MgF2 modulates the shape of the resonance curve, shifts the resonance curve towards the infrared direction and enhancing the sensitivity by 0.245 nm/oC. Compared with previous temperature and humidity detection ranges up to 20°C ∼ 100°C and 40% ∼ 100%, this has obvious improvement. The maximum sensitivities are -0.5683 nm/%RH and -3.259 nm/oC. The mean temperature sensitivity is -1.88877 nm/oC and the mean humidity sensitivity is -0.51249 nm/%RH. The polynomial fitting degrees reach 0.99914 and 0.99875, and FOM values are 2.715 × 10−2/oC and 4.735 × 10−3/%RH, which is expected to be in agriculture, food industry, such as biological implementation is widely used in production activities.

High Efficiency Butt-coupling of a 405nm Laser Diode to Hollow Core Fiber

High Efficiency Butt-coupling of a 405nm Laser Diode to Hollow Core Fiber

Long period fiber gratings in anti-resonant hollow core fiber

Abstract Long period gratings, based on anti-resonant hollow core fibers (AR-HCFs), are fabricated using a high-frequency CO2 laser pulse by carving periodic grooves. This device exhibits both axial strain and bending sensing characteristics. Benefiting from the low thermal sensitivity and radiation resistance characteristic of AR-HCFs, this grating can be utilized in extreme environments, particularly in the high-radiation environment, such as nuclear power plants and space shuttles. Additionally, due to the characteristics of AR-HCFs, including low latency, low dispersion, low nonlinearity, and high damage threshold, this device also serves for long-distance fiber communication and high-power laser pulse shaping.

Design of a Novel 31.5 THz Bandwidth Hybrid TDFA-HDFA at 2000 nm and Its Applications in Unregenerated DWDM Lightwave Transmission Systems

We report design and applications of a novel multi-Watt (> 1 Watt output power) 2000 nm band hybrid Thulium- and Holmium-doped fiber amplifier with record wideband 380 nm (31.5 THz) continuously operating bandwidth from 1720-2100 nm. We outline the theory, physics, and simulations behind this design, and show by comparison with previously published experimental results that the design presented is accurate to within ± 0.5 dB in saturated output power and ± 1.0 dB in small signal gain. Applications in future ~300-400 nm bandwidth wideband 2000 nm Pb/s DWDM lightwave fiber optical transmission systems spanning 10,000 km using new hollow core fiber designs are discussed. In particular, we demonstrate robust beginning-of-life optical signal to noise ratio (OSNR) and Q-factor margins for designs of 0.161 Pb/s DWDM unregenerated (without optical-to-electrical-to-optical or O-E-O electronic functions) all-optical transmission in the 2000 nm band over 10,000 km for representative terrestrial and submarine lightwave applications. We achieve a total capacity × distance product of 1608 Pb/s. km (1.61 Exabits/s. km) over a single one-core optical fiber for the 10,000 km system designs. Applications to designs of 40,000 km deployable unregenerated all-optical DWDM 0.124 Pb/s subsea lightwave transmission systems with 5.21 Exabit/s. km capacity × distance product are outlined. Received: 9 September 2024 | Revised: 10 December 2024 | Accepted: 26 December 2024 Conflicts of Interest The author declares that he has no conflicts of interest to this work. Data Availability Statement Exail Tm- and Ho-doped gain fiber specifications are openly available at https://cybel-llc.com/wp-content/uploads/2021/06/IXF-HDF-PM-8-125_edA-Ho-SC-doped-PM-fiber.pdf and https://cybel-llc.com/wp-content/uploads/2021/06/IXF-TDF-PM-5-125_edA-Tm-SC-doped-PM-fiber.pdf. Data of the component devices in Table 1 are openly available at https://retandassociatesllc.com/wp-content/uploads/2024/04/GSLEOP2022-Presentation-RET-v.11-08222022.pdf. Other data are available from the corresponding author upon reasonable request. Author Contribution Statement Robert E. Tench: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing - original draft, Writing - review & editing, Visualization, Supervision, Project administration, Funding acquisition.

Aspects of Influencing Factors in the Polishing of Plastic Optical Fibers

The interaction between the X-ray beam and the scintillating core of the optical fiber creates photons. The generated photons propagate through the fiber until the fiber end where they are captured by a solid state photon sensitive detector. This very sensitive detector converts generated photons into a low-level electronic signal that is amplified for later processing. For industrial, medical domains or for detection of contraband objects in custom control, flexible detectors can be built using 1 mm plastic scintillating optical fiber. The paper presents aspects related to the influencing factors of the optical fiber polishing process. Experiments related to the influencing factors of optical fiber polishing were performed. The results related to the influencing factors for cutting the optical fiber are presented. A proposal for plastic fiber cutting tool was given. The results related to factor of influence for polishing of plastic scintillating fiber were presented. In conclusion a possible technology for plastic scintillating fiber with 1 mm diameter is described.

Numerical optimization of anti resonant hollow core fiber for high sensitivity methane detection

This study presents an innovative methane gas sensor design based on anti-resonant hollow-core fiber (AR-HCF) technology, optimized for high-precision detection at 3.3. Our numerical analysis explores the geometric optimization of the AR-HCF’s structural parameters, incorporating real-world component specifications. The proposed design features a 65 diameter hollow core surrounded by seven silica rings. We achieved significant improvements in confinement loss and optical power distribution through progressive structural modifications. The optimized structure demonstrated a confinement loss of and over 95% optical power confinement in the hollow core. Our model predicts a relative sensitivity of , a response time of 5.4 s, and a theoretical detection threshold of 2.24 ppm. The limit of detection (LoD) was estimated to be 3.8 ppbv, and the normalized noise equivalent absorption (NNEA) coefficient was . The sensor response exhibited excellent linearity over its operating range, with an R2 value of 0.9917 in the critical concentration range. These findings highlight the potential of our AR-HCF-based methane sensor design for real-time gas monitoring applications.

Fiber optics-based surface enhanced Raman Spectroscopy sensors for rapid multiplex detection of foodborne pathogens in raw poultry

AbstractA new high-sensitivity, low-cost, Surface Enhanced Raman Spectroscopy (SERS) sensor allows for the rapid multiplex detection of foodborne pathogens in raw poultry. Self-assembled microspheres are used to pattern a hexagonal close-packed array of nanoantennas onto a side-polished multimode fiber core. Each microsphere focuses UV radiation to a photonic nanojet within a layer of photoresist on the fiber which allows the nanoantenna geometry to be controlled. Optimizing the geometry for the excitation layer generates electric field concentrations− referred to as a hotspot− within the analyte, thereby maximizing the Raman signal and improving the signal-to-noise ratio. The side polished configuration with a larger surface area has significantly better performance than the SERS sensor on the fiber tip. The use of additive manufacturing for the fiber polishing jigs as well as the sample testing compartment simplifies the sensor development and testing. Experimental results demonstrate a sensitivity range of 0.4–0.5 cells/ml achieved using raw chicken rinsates spiked with Salmonella typhimurium. Additionally, the sensor demonstrated its capability for multiplex and specific detection of Salmonella and E. coli O157:H7 with an optimal detection time of 10 min. The new sensor addresses a major global foodborne pathogen that poses significant public health concerns and can be readily adapted for the detection of other bacterial and viral pathogens such as E. coli O157:H7, Campylobacter, Listeria, and avian influenza and in other food products, e.g., dairy, beef, and produce, as well as clinical applications.

Stable Fabrication of Chitosan/Polycaprolactone (CS/PCL) Core-Shell Nanofibers by Electrospinning

Chitosan (CS), with its non-toxic and antibacterial properties, and Poly(ε-caprolactone) (PCL), known for its biodegradability and biocompatibility, are crucial materials in medical applications. This study proposed a solution utilizing electrospinning to manufacture fibers with nanometer-sized core-shell structures from these materials, with CS serving as the fiber core and PCL forming the shell. The influence of manufacturing technology parameters on fiber size and morphology was thoroughly researched and investigated. The solvent system used, Chloroform/Dimethylformamide (DMF), ensured complete solubility, viscosity control, conductivity, and proper solvent evaporation. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) results clearly demonstrated the morphology and internal structure of the nanofibers. The water contact angle (WCA) measurements of the fiber membrane showed almost no significant change over time, indicating strong hydrophobicity of the nanofibers. Additionally, the FTIR spectrum revealed distinct core-shell layers without any blending between them, while DSC analysis showed the thermal properties of fiber membranes. In summary, the electrospinning of nanofibers proved to be stable, producing thin fibers with an average diameter of approximately 400 nm. These findings are expected to significantly enhance the applicability of CS/PCL nanofibers across various fields, including healthcare and smart agriculture.

INVESTIGATION OF TUBERCULOSIS SENSING USING GRAPHENE COATED METAMATERIAL FIBER

Abstract Detection of tuberculosis (TB) is being showed a greater interest since it affects the
vital human organ (lungs). In this paper, a biosensor based on optical fiber sensing for
detecting TB is proposed. Here, a hollow core fiber protected with a graphene coated
metamaterial (MM) cladding is numerically investigated in the visible region using finite
element method (FEM). The analyte under test (mycobacterium TB affected haemoglobin) is
filled in the core and the change in refractive index is obtained to calculate the sensitivity.
Further, the proposed fiber is optimized by varying graphene thickness and concentration of
MM and investigated in terms of confinement loss, effective area, power confined to the core
and relative sensitivity. The proposed fiber reports an average relative sensitivity of 92.8%
depicting a power confinement of upto 97.7% and numerical aperture of 0.24. Performance
comparison with other designs is carried out in order to project the efficacy of the proposed
sensor. The obtained sensitivity enables the proposed sensor to be a suitable design in
detection of TB and can be employed in medical diagnosis.

High spectral-efficiency, ultra-low MIMO SDM transmission over a field-deployed multi-core OAM fiber

Space-division multiplexing (SDM) systems based on few-mode multi-core fibers (FM-MCFs) utilize both spatial channels (fiber cores) and modes (optical modes per core) to maximize transmission capacity. Unlike laboratory FM-MCFs or field-deployed single-mode multi-core fibers (SM-MCFs), SDM transmissions over field-deployed FM-MCFs in outdoor settings have not been reported. Therefore, concerns remain that environmental interference and cabling stress could worsen inter-core and intra-core modal crosstalk and impact the performance of SDM systems over FM-MCFs. In this paper, we demonstrate successful bidirectional SDM transmission over a 5-km, field-deployed seven ring-core fiber (7-RCF) with a cladding diameter of 178 μm. Our measurements show no significant differences in attenuation and mode coupling compared to pre-cabling conditions, confirming the fiber’s resilience to environmental disturbances and adaptability to cable deployment. Using the field-deployed 7-RCF, bi-directional SDM transmission is implemented, achieving spectral efficiency (SE) of 2×201.6 bit/(s Hz) which sets a new record in field-deployed fiber cables that is a tenfold increase over previous systems. Furthermore, these results were achieved using a small-scale 4×4 multiple-input multiple-output (MIMO) scheme with a time-domain equalization (TDE) tap number not exceeding 15. These results demonstrate the substantial potential of using SDM techniques to significantly enhance SE and expand capacity in practical fiber-optic transmission applications.

Magnetic field sensing with in-fiber cascaded Fabry-Perot interferometers (FPIs) using femtosecond laser direct writing

A magnetic field sensor made with femtosecond laser direct writing was built and characterized. The sensor makes use of the Vernier effect (VE) via a cascade of two Fabry-Perot interferometers (FPIs) with similar free spectra ranges (FSRs). The sensor cavity FPI 1 and the reference cavity FPI 2 are made by writing reflective surfaces directly onto the core of a single-mode fiber (SMF) with a femtosecond laser. FPI 1 is secured to a magnetostrictive material. A single FPI 1 has a sensitivity of 6 pm/mT in the 10–50 mT range, but two cascaded FPIs have a sensitivity of −117.1 pm/mT and an amplification of 19.5. The sensor’s temperature properties are studied, and cross-sensitivity to temperature is eliminated. This sensor is easy to fabricate, compact, simple, and structurally stable, making it highly promising for magnetic field sensing applications.

A Long Period Grating Sensor Based on Microtaper Eccentric Core Fiber

A Long Period Grating Sensor Based on Microtaper Eccentric Core Fiber

Nito “Core” Fiber-Reinforced Epoxy Composites: Enhancing Properties with NaHCO<sub>3</sub> Treatment

This study explores the use of sodium bicarbonate-treated Nito core fiber as a natural and eco-friendly alternative for fiber-reinforced composites to address the challenge of enhancing the mechanical properties of composite materials while also prioritizing environmental sustainability. Nito core fibers were treated with different concentrations of sodium bicarbonate, an economical and eco-friendly alternative to alkali treatment, to enhance its compatibility with various matrices. FTIR results showed that NaHCO3 treatment effectively removed and reduced some non-cellulosic components present in the Nito fiber such as hemicellulose and lignin. This resulted in the NaHCO3-treated fiber-epoxy composite showing better tensile strength and modulus of elasticity than the epoxy composite reinforced with untreated Nito fiber. The use of treated fiber, however, did not have a noticeable effect on the flexural strength and flexural modulus of the epoxy composite. The SEM images of the nito fiber-epoxy composites showed better fiber-matrix adhesion between the treated nito fiber and epoxy matrix. Thermogravimetric analysis (TGA) of nito fiber-epoxy composites shows that the thermal stability of the composite is mainly due to the presence of cellulose, which can also be enhanced by some lignin. This study, therefore demonstrates the potential of Nito ‘core’ fibers as a viable substitute for synthetic reinforcements that can contribute to the advancement of composite material technology that aligns with the global shift towards environmentally responsible manufacturing practices.

An investigation on the characteristics of core and inner cladding of few-mode double-clad optical fibers on the linearly polarised mode cut-off V-values

An investigation on the characteristics of core and inner cladding of few-mode double-clad optical fibers on the linearly polarised mode cut-off V-values

Research on center-assisted ring-core few-mode fiber with an eccentric circle for mode degeneracy separation in space division multiplexing

An eccentric-circle-assisted ring-core fiber (ECRF) structure is proposed to effectively separate spatial-degenerated linear polarization (LP) modes while maintaining birefringence at the 10−6 level, which provides more degrees of freedom in the design of few-mode fiber employment in space division multiplexing (SDM) systems. Our simulation analysis demonstrates that the effective refractive index difference (Δneff) between the spatially degenerate modes in this fiber falls within the range of (2.44−6.42)×10−4 at 1530–1565 nm, given the refractive index difference level typical of conventional fiber core and cladding. In addition, the polarization separation level for each mode is on the order of 10−6 and below. The design requirements of significant separation of spatial degeneracy and basically no separation of polarization degeneracy are achieved. Based on the characteristics of spatially degenerate mode in this fiber, we extend the regulation law for spatially degenerate mode separation of the LP m n mode groups in center-assisted ring-core fibers. In comparison to the existing center-assisted ring-core fiber structure, the ECRF can further reduce the fabrication difficulty and increase the feasibility of preparation.

A Coaxial Triboelectric Fiber Sensor for Human Motion Recognition and Rehabilitation via Machine Learning

This work presents the fabrication of a coaxial fiber triboelectric sensor (CFTES) designed for efficient energy harvesting and gesture detection in wearable electronics. The CFTES was fabricated using a facile one-step wet-spinning approach, with PVDF-HFP/CNTs/Carbon black as the conductive electrode and PVDF-HFP/MoS2 as the triboelectric layer. The incorporation of 1T phase MoS2 into the PVDF-HFP matrix significantly improves the sensor’s output owing to its electron capture capabilities. The sensor’s performance was carefully optimized by varying the weight percentage of MoS2, the thickness of the fiber core, and the CNT ratio. The optimized CFTES, with a core thickness of 156 µm and 0.6 wt% MoS2, achieved a stable output voltage of ~8.2 V at a frequency of 4 Hz and 10 N applied force, exhibiting remarkable robustness over 3600 s. Furthermore, the CFTES effectively detects human finger gestures, with machine learning algorithms further enhancing its accuracy. This innovative sensor offers a sustainable solution for energy transformation and has promising applications in smart portable power sources and wearable electronic devices.

Docosahexaenoic Acid-Infused Core-Shell Fibrous Membranes for Prevention of Epidural Adhesions.

Avoiding epidural adhesion following spinal surgery can reduce clinical discomfort and complications. As the severity of epidural adhesion is positively correlated with the inflammatory response, implanting a fibrous membrane after spinal surgery, which can act as a physical barrier to prevent adhesion formation while simultaneously modulates postoperative inflammation, is a promising approach to meet clinical needs. Toward this end, we fabricated an electrospun core-shell fibrous membrane (CSFM) based on polylactic acid (PLA) and infused the fiber core region with the potent natural anti-inflammatory compound docosahexaenoic acid (DHA). The PLA/DHA CSFM can continuously deliver DHA for up to 36 days in vitro and reduce the penetration and attachment of fibroblasts. The released DHA can downregulate the gene expression of inflammatory markers (IL-6, IL-1β, and TNF-α) in fibroblasts. Following an in vivo study that implanted a CSFM in rats subjected to lumbar laminectomy, the von Frey withdrawal test indicates the PLA/DHA CSFM treatment can successfully alleviate neuropathic pain-like behaviors in the treated rats, showing 3.60 ± 0.49 g threshold weight in comparison with 1.80 ± 0.75 g for the PLA CSFM treatment and 0.57 ± 0.37 g for the untreated control on day 21 post-implantation. The histological analysis also indicates that the PLA/DHA CSFM can significantly reduce proinflammatory cytokine (TNF-α and IL-1β) protein expression at the lesion and provide anti-adhesion effects, indicating its vital role in preventing epidural fibrosis by mitigating the inflammatory response.

Highly secure OFDM scheme based on multi-level masking and performance-enhanced key accompanying transmission.

In this Letter, we propose a highly secure OFDM scheme based on multi-level masking and performance-enhanced key-accompanying transmission. Our scheme exploits a four-dimensional hyperchaotic model and uses subcarriers and symbols to scramble the signal, thereby achieving chaotic encryption and enhancing system security. The dual-mode index technique is employed to conceal the key within the encrypted signal, enabling cooperative transmission of both the key and the signal. We conducted experiments that successfully transmitted a 28 Gb/s dual-mode QPSK (DM-QPSK) signal and a 42 Gb/s dual-mode 8QAM (DM-8QAM) signal over a 2-km stretch of 7-core fiber. The results demonstrated that our proposed key-accompanying transmission scheme did not compromise the system's transmission performance. Moreover, the key space of this scheme is as large as 10135, effectively ensuring system security. Under the received optical power corresponding to the bit error rate of 3.8 × 10-3, the minimum number of key repetitions in DM-8QAM that makes the key bit error rate zero is less than 9 times. This demonstrates that our proposed scheme effectively enhances the transmission performance of the key, achieving high-quality joint transmission of both the key and the signal.

Shape measurement using a multicore optical fiber sensor with asymmetric dual cores

Abstract Shape measurement using multicore optical fiber sensors has attracted more attention in many fields due to the good consistency of the fiber cores. Three symmetrically arranged cores in a multicore fiber are usually used to reconstruct shapes by calculating the bending vectors, which will not be achieved when one of the cores is damaged or occupied in actual application. A shape measurement method using a multicore optical fiber sensor with asymmetric dual cores is proposed in this paper. Based on the analysis of the principle of shape reconstruction and the geometric relationship of the asymmetric dual cores in the multicore fiber sensor, the bending vector is decomposed. The mathematical expressions for the bending curvature and orientation of the asymmetric dual cores are derived. The two-dimensional (2D) and three-dimensional (3D) shape reconstruction results in both finite element modeling simulation and shape measurement experiments based on optical frequency domain reflectometry have shown that the proposed method using a multicore fiber sensor with asymmetric dual cores is able to achieve shape measurement; its performance is comparable and even equivalent to the traditional method that uses three symmetrically arranged cores. In the experiment, the maximum relative errors of 2D and 3D reconstructed shapes are 2.653% and 5.139%, respectively. The proposed method, which only needs asymmetric dual cores in the multicore optical fiber sensor for shape reconstruction, will be conducive to solving the limitations of multicore optical fiber sensors in shape measurement applications.