Optical Fiber Research Articles

Exciton Dissociation and Recombination Afford Narrowband Organic Afterglow Through Efficient FRET.

Organic afterglow with long-persistent luminescence (LPL) after photoexcitation is highly attractive, but the realization of narrowband afterglow with small full-width at half-maximum (FWHM) is a huge challenge since it is intrinsically contradictory to the triplet- and solid-state emission nature of organic afterglow. Here, narrow-band, long-lived, and full-color organic LPL is realized by isolating multi-resonant thermally activated delayed fluorescent (MR-TADF) fluorophores in a glassy steroid-type host through a facile melt-cooling treatment. Such prepared host becomes capable of exciton dissociation and recombination (EDR) upon photoirradiation for both long-lived fluorescence and phosphorescence; and, the efficient Förster resonance energy transfer (FRET) from the host to various MR-TADF emitters leads to high-performance LPL, exhibiting small FWHM of 33nm, long persistent time over 10s, and facile color-tuning in a wide range from deep-blue to orange (414-600nm). Moreover, with the extraordinary narrowband LPL and easy processability of the material, centimeter-scale flexible optical waveguide fibers and integrated FWHM/color/lifetime-resolved multilevel encryption/decryption devices have been designed and fabricated. This novel EDR and singlet/triplet-to-singlet FRET strategy to achieve excellent LPL performances illustrates a promising way for constructing flexible organic afterglow with easy preparation methods, shedding valuable scientific insights into the design of narrow-band emission in organic afterglow.

Non-Destructive Methods for Assessing the Condition of Reinforcement Materials in Soil

A reinforced earth wall is a structure in which reinforcement materials are placed in an embankment to build a vertical or nearly vertical wall surface. Such walls have been widely used in roads and in developed land since around 1960. Reinforcement materials have a set service life of 100 years and fall into two types: steel and geosynthetics. To ensure long-term durability, steel reinforcement materials are plated, while geosynthetics are designed with a limit strength designed to resist fracture for 100 years under the conditions of a given load placed on the reinforcement materials. However, owing to the difficulty of assessing the condition of reinforcement materials in soil, this paper proposes solutions based on non-destructive methods. Specifically, it proposes a method of assessing the amount of strain through an embedded optical fiber in the case of geosynthetic reinforcement materials, or magnetic surveying to investigate the degree of corrosion in the case of steel reinforcement materials. This paper demonstrates that it is possible to non-destructively assess the state of either type of reinforcement material.

Highly-selective and temperature-compensated toluene sensor based on MOF-actuated optical WGM microresonator

This paper reports an optical fiber toluene sensor based on whispering gallery mode (WGM) microbottle resonator. The sensor includes a single-mode fiber (SMF)- no-core fiber (NCF)- SMF offset structure, which can be used as not only a coupler to couple light into the microbottle but also a multimode interferometer. The microbottle is formed by self-assembly of polydimethylsiloxane (PDMS) polymer doped with metal-organic framework (MOF) under the action of surface tension and gravity. The high specific surface area, suitable pore size, nitrogen-containing functional groups of MOF-Fe-PD and nonpolar groups on PDMS impart the high sensitivity and specific response of the sensor to toluene. When toluene is captured by the MOF and PDMS, the refractive index and volume of the cavity change, which affects the mode shift of WGM. According to test results, WGM of the sensor shows a linear sensitivity of 12.44pm/ppm with toluene concentration between 0 ppm and 337 ppm at room temperature, but it is affected by temperature crosstalk. While multimode interference dip is only sensitive to temperature, which can compensate for the mode shift of WGM caused by temperature change. Repeatability experiments show that the response and recovery time of the sensor are less than 70s. The method provides a toluene sensor with high selectivity, stable performance and simple preparation, which has potential environmental benefits and good industrial application prospects.

Measurement of electron and neutral particle densities using a two-color optical fiber interferometer.

A two-color homodyne Mach-Zehnder optical fiber interferometer is developed for the measurement of electron and neutral particle densities in a high-density capsule θ-pinch device. The interferometer leverages the disparate contributions of distinct particles to the refractive index across two discrete wavelengths of 1310 and 1550nm and incorporates the contributions of both electron and neutral particle densities to the phase shift in the plasma. The temporal evolutions of line-integrated electron and neutral argon densities are successfully measured by the interferometer. Comparing the electron density waveforms under various working gas pressures as well as the results obtained using the monochromatic and two-color measurements, it is inferred that the influence of neutral particle density can be neglected when measuring the electron density using a long-wavelength laser. Moreover, the maximum electron density is linearly correlated with the capacitor bank voltage for the θ-pinch device (5-9kV). Overall, the proposed interferometer is capable of simultaneously measuring the electron and neutral particle densities.

MSAACNN for intense noise suppression in DAS-VSP records

Distributed optical fiber sensor (DAS) is an emerging acquisition technique and has begun to be widely applied in seismic exploration owing to its advantages in acquisition and deployment. Nonetheless, DAS record has a low signal-to-noise ratio (SNR) due to the intense background noise. How to suppress the DAS background noise and increase the SNR of the DAS records has gradually become one of the hot issues in the field of seismic data processing. To solve the challenging tasks in intense DAS noise suppression, a multiscale sparse asymmetric attention convolutional neural network (MSAACNN) is proposed. The network uses dilated convolutions to expand the receptive field and map more feature information. Moreover, asymmetric convolutions are introduced to form an asymmetric unit, aiming to strengthen the feature extraction ability and realize the interaction between feature information of different scales. Finally, a pyramid attention module is used to enhance the primary features and improve the network denoising performance. The experimental results show that MSAACNN can effectively suppress the complex background noise in DAS records, compared with the traditional denoising methods and typical convolutional neural network (CNN) architecture. Additionally, the recovered signal components in the processing results are clear and complete, with significantly improved SNR.

R&D of Innovative Optical Fiber Facility Technologies

R&D of Innovative Optical Fiber Facility Technologies

MZI-based high intensity responsive sandwiched multi-layer fiber optic humidity sensor

This paper presents a multi-layer optical fiber humidity sensor based on dual-beam Mach-Zehnder interference (MZI) for optical intensity sensitivity. The sensor is fabricated using a large-scale axial offset fusion technique between a multimode fiber (MMF) and an offset hole two-core fiber (OHTC), making it suitable for agricultural and health monitoring applications. The 27 μm axial offset enables tilted light incidence, enhancing environmental sensitivity. With a single-cycle Graphene oxide (GO) coating of approximately 22 nm, the MMF-OHTC structure achieves high humidity sensitivity (0.39 dB/%RH) over the 25 %-80 % RH range with excellent linearity (R2≈0.99). The sensor exhibits stable, rapid response (2.52 s/0.46 s) and low temperature cross-sensitivity (0.06 %RH/°C). When combined with a hollow-core fiber Fabry-Perot interferometer (HCF-FPI), the system allows zero cross-talk simultaneous humidity and temperature measurements, expanding the potential applications of multi-layered structures in multifunctional detection systems.

Application of a Novel Disposable Flow Cell for Spectroscopic Bioprocess Monitoring

The evaluation of the analytical capabilities of a novel disposable flow cell for spectroscopic bioprocess monitoring is presented. The flow cell is presterilized and can be connected to any kind of bioreactor by weldable tube connections. It is clamped into a reusable holder, which is equipped with SMA-terminated optical fibers or an integrated light source and detection unit. This modular construction enables spectroscopic techniques like UV-Vis spectroscopy or turbidity measurements by scattered light for modern disposable bioreactors. A NIR scattering module was used for biomass monitoring in different cultivations. A high-cell-density fed-batch cultivation with Komagataella phaffii and a continuous perfusion cultivation with a CHO DG44 cell line were conducted. A high correlation between the sensor signal and biomass or viable cell count was observed. Furthermore, the sensor shows high sensitivity during low turbidity states, as well as a high dynamic range to monitor high turbidity values without saturation effects. In addition to upstream processing, the sensor system was used to monitor the purification process of a monoclonal antibody. The absorption module enables simple and cost-efficient monitoring of downstream processing and quality control measurements. Recorded absorption spectra can be used for antibody aggregate detection, due to an increase in overall optical density.

Silver nanoparticle-decorated reduced graphene oxide/ nanocrystalline titanium metal-organic frameworks composite membranes with enhanced nanofiltration performance and photocatalytic ability

Nanofiltration (NF) has garnered significant attention for removing persistent dyes from industrial wastewater. However, limited membrane separation efficiency and performance deterioration due to membrane fouling are the primary challenges hindering the broader application of NF technology. Herein, we developed high-performance silver nanoparticle-coated reduced graphene oxide/nanocrystalline MIL125(Ti) composite NF membranes (nAg-rGO/n-MIL), which feature self-cleaning capabilities through photocatalytic activity. This was achieved by intercalating nanocrystalline MIL-125(Ti) (n-MIL) metal-organic frameworks between graphene oxide (GO) nanosheets, followed by reducing the GO nanosheets and decorating them with silver nanoparticles (nAg) via UV exposure. The nAg-rGO/n-MIL demonstrated high water permeability (21.7 LMH/bar) and achieved excellent removal efficiencies for targeting dyes with relatively small molecular weights ranging from 300 to 500Da. Additionally, when operated in an NF system equipped with a UV side-emitting optical fiber, the nAg-rGO/n-MIL exhibited significantly reduced water flux decline and enhanced removal efficiencies, achieving up to 97.5% for methylene blue. Moreover, the nAg-rGO/n-MIL demonstrated high durability under the tested operating conditions, indicating its potential for long-term use in industrial applications. The GO composite membrane, with nanosized MOF-intercalated nanochannels and photocatalytic activity via nAg decoration and GO reduction, offers a promising solution to performance limitations and fouling issues in current nanofiltration membranes.

Speckle‐Insensitive Fractal Superconducting Nanowire Single‐Photon Detector Coupled with Multimode Optical Fiber (Laser Photonics Rev. 18(10)/2024)

Speckle‐Insensitive Fractal Superconducting Nanowire Single‐Photon Detector Coupled with Multimode Optical Fiber (Laser Photonics Rev. 18(10)/2024)

Critical-Layered MoS2 for the Enhancement of Supercontinuum Generation in Photonic Crystal Fibre.

Supercontinuum generation (SCG) from silica-based photonic crystal fibers (PCFs) is of highly technological significance from microscopy to metrology, but has been hindered by silica's relatively low intrinsic optical nonlinearity. The prevailing approaches of filling PCF with nonlinear gases or liquids can endow fibre with enhanced optical nonlinearity and boosted SCG efficiency, yet these hybrids are easily plagued by fusion complexity, environmental incompatibility or transmission mode instability. Here this work presentsa strategy of embedding solid-state 2D MoS2 atomic layers into the air-holes of PCF to efficiently enhance SCG. This work demonstrates a 4.8 times enhancement of the nonlinear coefficient and a 70% reduction of the threshold power for SCG with one octave spanning in the MoS2-PCF hybrid. Furthermore, this work finds that the SCG enhancement is highly layer-dependent, which only manifests for a real 2D regime within the thickness of five atomic layers. Theoretical calculations reveal that the critical thickness arises from the trade-off among the layer-dependent enhancement of the nonlinear coefficient, leakage of fundamental mode and redshift of zero-dispersion wavelength. This work provides significant advances toward efficient SCG, and highlights the importance of matching an appropriate atomic layer number in the design of functional 2D material optical fibers.

Temperature Effect on the Radioluminescence of Differently Doped Silica-Based Optical Fibers

Temperature Effect on the Radioluminescence of Differently Doped Silica-Based Optical Fibers

Spontaneous symmetry breaking and vortices in a tri-core nonlinear fractional waveguide

We introduce a waveguiding system composed of three linearly-coupled fractional waveguides, with a triangular (prismatic) transverse structure. It may be realized as a tri-core nonlinear optical fiber with fractional group-velocity dispersion (GVD), or, possibly, as a system of coupled Gross–Pitaevskii equations for a set of three tunnel-coupled cigar-shaped traps filled by a Bose–Einstein condensate of particles moving by Lévy flights. The analysis is focused on the phenomenon of spontaneous symmetry breaking (SSB) between components of triple solitons, and the formation and stability of vortex modes. In the self-focusing regime, we identify symmetric and asymmetric soliton states, whose structure and stability are determined by the Lévy index of the fractional GVD, the inter-core coupling strength, and the total energy, which determines the system’s nonlinearity. Bifurcation diagrams (of the supercritical type) reveal regions where SSB occurs, identifying the respective symmetric and asymmetric ground-state soliton modes. In agreement with the general principle of the SSB theory, the solitons with broken inter-component symmetry prevail with the increase of the energy in the weakly-coupled system. Three-components vortex solitons (which do not feature SSB) are studied too. Because the fractional GVD breaks the system’s Galilean invariance, we also address mobility of the vortex solitons, by applying a boost to them.

Integrative Approach to Fluorescence-Based Oxygen Sensing in Polymer Optical Fibers with Surface Plasmon Resonance

This study demonstrates a technique to enhance oxygen (O2) concentration measurement by combining surface plasmon resonance (SPR) and fluorescence-based sensor on polymer optical fiber (POF). The SPR was generated using silver (Ag) and the fluorescence was generated by organic dye. Three fluorescence dyes were used, Tris (4, 7-diphenyl-1, 10-phenanthroline) ruthenium (II) dichloride ([Ru(dpp)3]2+), platinum octaethylporphyrin (PtOEP) and 5,10,15,20-tetrakis (pentafluorophenyl) 21H,23H-porphine palladium (II) (PdTFPP). The sensor was tested in a gas chamber with different concentration level of O2. Sensitivity values for the fluorescence dyes for [Ru(dpp)₃]²⁺, PtOEP, and PdTFPP were 0.0099 a.u/%, 0.0343 a.u/% and 0.05 a.u/% respectively. When SPR was implemented, the sensitivity values for Ag/[Ru(dpp)₃]²⁺, Ag/PtOEP, and Ag/PdTFPP were 0.0589nm/%, 0.0345nm/%, and 0.118nm/% respectively. PdTFPP and Ag/PdTFPP exhibit highest sensitivity in each experiment. Therefore, the further analysis for the sensing performance of PdTFPP and Ag/PdTFPP were held. As a result, Ag/PdTFPP exhibits lower limit of detection (LOD), and limit of quantification (LOQ) with 3.054% and 9.254%, respectively, with higher R2 of 0.9971 and lower mean standard deviation of 0.174, compared to PdTFPP 16.496% and 49.988% respectively, with R2 of 0.9211 and higher mean standard deviation of 2.003. This improvement can benefit researchers and professionals in medical diagnostics, environmental monitoring, and industrial process control by providing a more sensitive and accurate method for measuring O2 levels.

Field investigations on the thermo-mechanical behavior of a partially activated energy pile in Miocene sediments

The City of Vienna, as one of the largest public clients in Austria, initiated a research project to determine the load-bearing behavior of various foundation elements in typical Viennese soils. Numerous large-scale tests were carried out on bored piles, micro piles, anchors, and jet grouted columns. In addition, two energy piles were installed in different soil layers to investigate their behavior under mechanical and thermal loading in each soil layer separately. This paper discusses the energy pile in the Miocene sediments, which consist mainly of silty fine sand and some sandy silt. The energy pile – fully instrumented with strain gauges, extensometers, heat gauges and optical fiber sensors – was loaded for two and a half months. The mechanical load was kept constant throughout the thermal cycles to determine the response of the pile to thermal loads. The measured temperature data were used in numerical back-calculations to determine the thermal parameters of the soil layers and the concrete. Based on the measured strain and deformation data, the deformation behavior of the energy pile due to the thermal load was investigated. Finally, a static pile load test was carried out on the energy pile and the results are compared with those of the conventional reference piles installed in the vicinity, which have not been subjected to thermal loading. The test demonstrated that, after several weeks of cyclic thermal loading, the energy pile exhibited more favorable load-deformation behavior compared to conventional reference piles.

Characterization and novel application of power over fiber for electronics in a harsh environment

Power-over-Fiber (PoF) technology has been used extensively in settings where high voltages require isolation from ground. In a novel application of PoF, power is provided to photon detector modules located on a surface at ∼ 300 kV with respect to ground in the planned DUNE experiment. In cryogenic environments, PoF offers a reliable means of power transmission, leveraging optical fibers to transfer optical power. PoF technology excels in maintaining low noise levels when delivering power to sensitive electronic systems operating in extreme temperatures and high voltage environments. This paper presents the R&D effort of PoF in extreme conditions and underscores its capacity to revolutionize power delivery and management in critical applications, offering a dependable solution with low noise, optimal efficiency (∼ 51%), and superior isolation.

Silica Multicore Microstructured Optical Fibers with Induced Twisting

Silica Multicore Microstructured Optical Fibers with Induced Twisting

Polarization-insensitive optical coherence tomography using polarization maintaining fiber with a simple optical configuration

Compensation of polarization-variance-related artifacts is required to steadily obtain high-quality optical coherence tomography (OCT) images at various experimental conditions. Since most OCT systems utilize optical fiber to transfer the light easily and a polarized light source, the polarization state is arbitrarily changed in every different condition. In this study, we proposed polarization-maintaining-fiber-based polarization-insensitive OCT (PM-PI-OCT) with a simple optical configuration and a simple compensation process. The proposed PM-PI-OCT is not only theoretically proved by mathematical derivations but also evaluated by quantitative analysis of various fiber twisting angles. Moreover, the applicability and robustness of the proposed PM-PI-OCT were proved by human retina imaging using the customized handheld probe. Our proposed polarization-insensitive OCT requires no pre-calibration, no post-processing procedure, and no computational load for implementation and is able to be applied to universal fiber-based OCT systems. We believe that our simple and robust polarization-insensitive OCT system is able to be applied to various existing OCT setups for polarization state variance compensation with high versatility and applicability.

Deep learning techniques for quality of transmission estimation in optical networks

A large body of research has recently examined the estimation of the quality of transmission (QoT) in optical networks with deep learning. This paper discusses a lightpath’s quality of transmission to design fiber-optic communication and networks using deep learning algorithms. We need different major estimation parameters for advanced optical fiber communication and networks, i.e., modulation formats, baud rate, and code rate. Currently, the quality of transmission for unspecified optical paths depends on different estimation techniques i.e., (1) analytical models estimating physical layer impairments (PLIs) and (2) margined formulas. This paper focuses on deep-learning techniques that can be applied to optimization and complex systems. The deep learning algorithms contain different classifiers that can simulate results and estimate the bit-error rate, and signal-to-noise ratio of unspecified optical paths with threshold values, traffic volume, and modulation format. We must train and test the datasets for various classifiers, and classification features using Korean network topology. The classifier accuracy and Area Under the ROC Curve (AUC) simulation results are carried out using MATLAB.

Design of an equal-power dual-peak Brillouin gain spectrum based on M-shaped optical fibers transitioning from ring to circular core for temperature and curvature sensing

Here we design a simple M-shaped optical fiber to generate equal-power dual Brillouin gain peaks, and numerically simulate bending loss-resistant temperature and curvature sensing. By investigating the M-shaped fibers transitioning from ring-core to circular-core, we examine the Brillouin gain spectrum evolution from a single peak to dual peaks and back to a single peak. During this fiber transition and spectral evolution, we find that the calculated Brillouin frequency shift (BFS) and Brillouin gain exhibit unique developments based on acoustic-optic coupling theory, providing a methodology for designing and optimizing a desirable Brillouin gain spectrum in M-shaped optical fibers. These theoretical advances enable the generation of equal-power dual peaks with an appropriate peak frequency interval for temperature and curvature sensing. Furthermore, by simulation, this sensor has temperature sensitives of 1.086 and 1.100 MHz/°C and curvature sensitivities of 453.6153 and 459.5102 MHz/cm, with resistance to bending loss. By comparison, we improve the curvature sensitivity by more than 1.5-fold and reduce the bending-induced birefringence by more than 2.5-fold. Overall, the proposed design has advantages in curvature sensitivity, is more resistant to bending loss, and suffers less bending-induced birefringence, offering a competitive option for Brillouin-based temperature and curvature sensors.