Experimental study on rainfall-induced slope failure monitoring using plastic optical fibers: signal characteristics and failure mechanism

Monitoring soil dry density by light intensity variation using plastic optical fiber technology

This paper proposes a temperature sensor based on surface plasmon resonance (SPR) technology utilizing a right-angle plastic optical fiber (POF). The sensor is fabricated by hot pressing the fiber to form two planar surfaces with a right-angle cross-section, on which Ag/PDMS composite films are deposited. Experimental results demonstrate that the sensor achieves a temperature sensitivity of up to -1.371nm/∘C within a broad temperature range from -40∘C to 96°C, which is superior to most existing fiber-optic temperature sensors. It also exhibits good repeatability and cycling stability during cooling/heating processes. The sensor is cost-effective and features a straightforward fabrication process, making it suitable for wide-range temperature-monitoring applications.

In this work, an innovative multi-resonant plasmonic cup-shaped platform was designed, developed, and combined with a bioreceptor layer to address two key issues in biosensing: the ultra-low limit of detection (LOD) and the ultra-wide detection range. A cup-shaped optical waveguide was utilized to achieve surface plasmon resonance (SPR) phenomena, exploiting a single fabrication step and featuring an integrated measurement cell, which enables easy integration into rapid and cost-effective point-of-care tests (POCTs). Changing the optical path in the cup-shaped waveguide, its peculiar geometry allows different plasmonic resonances to be triggered and monitored. To this end, as a proof-of-concept, three experimental configurations were explored and tested by simply changing the altitude from which light is launched/collected to/from the plasmonic cup-shaped waveguide through plastic optical fibers (POFs). For all three experimental configurations, the plasmonic cup-shaped sensor was first optically characterized to determine its bulk sensitivity. Then, after a functionalization procedure of the gold nanofilm with a bioreceptor layer specific for interleukin-1β (IL-1β) detection, the plasmonic cup-shaped biosensor was characterized to obtain the binding performance parameters. More specifically, the multi-resonant plasmonic biosensor demonstrated selective detection of IL-1β, an ultra-low LOD (at femtomolar concentration), and an ultra-wide detection range (about five orders of magnitude) using the same functionalized sensing area monitored differently. The experimental results reveal the potential of the SPR cup-shaped biosensor in terms of performance, versatility, and its ability to achieve a scalable and low-cost point-of-care device. • Innovative multi-resonant plasmonic cup-shaped waveguides for biosensing • Simple and low-cost plasmonic sensor chip with integrated measurement cell • Three experimental configurations to excite surface plasmon resonance phenomena • Binding tests for selective IL-1β detection are obtained as a proof-of-concept • Ultra-low limit of detection and ultra-wide detection range are demonstrated

The rapid and accurate detection of SARS-CoV-2 biomarkers remains a critical requirement for effective outbreak control and decentralized diagnostics. Although RT-PCR is the current gold standard, its reliance on centralized laboratories and long processing times limits its applicability in point-of-care settings. In this context, optical biosensing platforms based on surface plasmon resonance (SPR) offer attractive features, including label-free, real-time, and quantitative detection. This study explores the use of synthetic receptors for the highly sensitive detection of the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein. Specifically, soft molecularly imprinted polymer nanoparticles (nanoMIPs) were employed as synthetic receptors and integrated into a high-sensitivity, portable plasmonic platform based on a D-shaped plastic optical fiber (POF) SPR sensor. The nanoMIPs were selectively imprinted against the RBD, characterized by Dynamic Light Scattering (DLS), Isothermal Titration Calorimetry (ITC), and Scanning Electron Microscopy (SEM) to confirm nanoMIPs size, binding properties, and surface morphology. Next, the nanoMIPs were immobilized onto a gold-coated sensing surface, enabling enhanced specificity, affinity, and signal amplification compared to conventional biological recognition elements. The resulting RBD-SPR-nanoMIPs sensor demonstrated promising analytical performance, exhibiting high selectivity against potentially interfering proteins and an anticipated sensitivity suitable for RBD detection at femtomolar concentrations. The inherent stability of nanoMIPs suggests the potential for reusable SPR sensing platforms, paving the way for next-generation synthetic receptor-based plasmonic biosensors.

Abstract An H-shaped structure plastic optical fiber (POF) surface plasmon resonance (SPR) sensor was fabricated for dual-channel measurement of refractive index (RI) and temperature. The sensing region with an H-shaped side structure was created on the POF using a hot-pressing method, and a Ag film was deposited on both surfaces of the sensing region to excite SPR. A polydimethylsiloxane (PDMS) film was coated on one of the Ag surfaces as a temperature-sensitive medium, forming the temperature sensing channel, thus realizing dual sensing channels for RI and temperature. Experimental results show that within the RI range of 1.333 – 1.373 and temperature range of 10 – 60 °C, the sensor achieves an RI sensitivity of 1594 nm/RIU and a temperature sensitivity of -0.74 nm/°C. The sensor offers advantages of high sensitivity, compact structure, simple fabrication, low cost, and low crosstalk, making it highly promising for applications in biochemical sensing and biomedical fields.

Abstract This study examines the potential of light‐transmitting concrete to reduce energy consumption in building construction. A series of tests, including compressive strength and light transmittance assessments, were conducted, alongside modeling a residential building using building information modeling software. Light‐transmitting concrete samples were prepared using single‐mode optical fibers, plastic optical fibers, and waste‐tempered glass. The results demonstrated that light‐transmitting concrete with 1% volumetric single‐mode optical fibers achieved a 28‐day compressive strength of 39.2 MPa and 2% light transmission. Light‐transmitting concrete containing 5% volumetric plastic optical fibers also showed 5.88% light transmission and a 28‐day compressive strength of 44.89 MPa. The sample incorporating 14% by weight of broken tempered glass exhibited a compressive strength of 51.1 MPa with 1.15% light transmission. A two‐story residential building (1200 m 2 ) in Tehran was analyzed in the modeling phase, integrating light‐transmitting concrete blocks in a residential building, while solar panels are considered only as a complementary reference for contextual energy and economic evaluation. Energy analysis and return on investment calculations revealed that the optimal setup involved a combination of light‐transmitting concrete, conventional concrete, with an estimated return on investment period of 5.22 years. Finally, an economic analysis is performed to demonstrate how integrating a photovoltaic system can offset the higher initial cost of LTC blocks, reducing the payback period to a feasible range.

Molecularly imprinted polymers (MIPs) can be exploited to develop low-cost optical-chemical sensor configurations with several advantages via different sensing principles. In this work, two MIP-based plastic optical fiber (POF) sensors have been designed, realized, and tested for the selective detection of 4-chloro-2-methylphenoxyacetic acid (MCPA) herbicide in environmental monitoring, aiming to achieve two different detectable concentration ranges. In the first case, the MIPs pre-polymeric mixture was spun onto the surface plasmon resonance (SPR) area of D-shaped POF probes to achieve the detection of MCPA in a nano-to micromolar concentration range (7nM-1μM). A second type of POF-MIP sensor for detecting MCPA has been developed to demonstrate the capabilities of the MIP as the core of optical waveguides, enabling highly sensitive sensors with an intensity-based configuration. In particular, an extrinsic POF sensor scheme has been implemented via an optical-chemical chip based on two POFs connected via a MIP waveguide. The optical-chemical chip was achieved by filling a trench with two POFs at the end with the pre-polymeric mixture, followed by thermal polymerization. This intensity-based POF-MIP sensor can detect MCPA in a pico-to nanomolar concentration range (80 pM-10nM). Moreover, the same experimental setup can be used to monitor both POF-MIP chips, allowing for the detection of MCPA over an ultra-wide concentration range from 80 pM to 1μM.

Abstract This study presents a novel approach for uric acid detection using a balloon-like bent polymer optical fiber (POF) sensor. The sensor head was fabricated by integrating an unclad region with macrobending, creating a balloon-like structure that enhances evanescent wave interaction and improves sensing performance. The effect of bending radius on sensor response was systematically investigated, with radii varied from 1.5 to 2.5 cm, to identify optimal conditions. Experimental results revealed a strong linear relationship between transmitted intensity and uric acid concentration of 15-90 mg/dL. Optimal performance was achieved at a bending radius of 1.5 cm and an operating wavelength of 770 nm, delivering a sensitivity of 0.0028 (mg/dL)⁻¹, linearity of 0.8843, and a resolution of 3.61 mg/dL. Compared to other unclad and coated optical fiber designs, the proposed configuration offers a competitive combination of sensitivity, linearity, and detection range while maintaining simple fabrication and robust mechanical properties. These findings highlight the potential of bending geometry optimization as a practical approach to advancing low-cost, high-performance optical fiber biosensors for biomedical and environmental applications.

The development of a sensitive method for in situ monitoring of hydrogen peroxide (H2O2) released from living cells is crucial for disease diagnosis. In this work, we have fabricated a gold-coated optical fiber electrode (GOFE) for in situ monitoring of H2O2 released from living cells via transmitted electrogenerated chemiluminescence (ECL). The cylinder GOFE was fabricated by sputtering a conductive Au layer (∼100 nm) on the surface of the cylinder and the cross-section (one proximal end) of the plastic optical fiber, which was 2.4 cm in length and 2.0 mm in diameter. The prepared GOFE was further modified with luminol-conjugated gold nanoparticles (Luminol-AuNPs) on the proximal end as a transmitted sensing platform (abbreviated as Luminol-AuNPs/GOFE). Its proximal end was taken as the venue for sensing and ECL generation, while its distal end was taken as the readout spot for the ECL emission. Two detection modes, including transmission mode and nontransmission mode, were developed for ECL detection. The transmitted ECL intensity at the distal end via transmission mode was directly proportional to the concentration of H2O2 in the range from 50 μM to 1.0 mM with a limit of detection of 12.5 μM. Moreover, the developed Luminol-AuNPs/GOFE-based transmitted ECL method was successfully employed to monitor the release of H2O2 from living A549 cells in situ under lipopolysaccharide stimulation. This work presents a promising method for fabricating optical electrodes with favorable electroactive and transmittance properties for in situ and sensitive monitoring of biomolecules in different analytical applications.

ABSTRACT With the increasing number of users in local networks, the demand for high‐efficiency short‐distance data transmission has surged. Plastic optical fiber (POF) communication systems with high speed, bandwidth, and flexibility have been used as ideal technologies for last‐mile applications. However, visible‐light signal intensity attenuation and data quality degradation in POF transmission have become extremely severe owing to the continuously increasing number of network nodes in a finite space. In this study, polymer visible‐light fluorene‐doped waveguide amplifiers (FDWAs) are proposed for POF communication systems. Both intermolecular energy‐assisted and balanced transfer processes are realized between triarylsulfonium salt photoinitiators and fluorescent small‐molecule oligomers, based on the Förster resonance energy transfer mechanism. The FDWAs can be fabricated using a UV direct‐writing technique. The gain coefficients of 1.32 dB/mm at 532 nm green light and 0.83 dB/mm at 655 nm red light under 405 nm pumping light are obtained. The proposed technique is suitable for high‐density local POF network applications.

This paper presents a comprehensive multi-wavelength characterization of a humidity sensor based on an intensity-modulated U-shaped tapered plastic optical fiber (POF). The sensor exploits evanescent-wave interaction between guided light and the surrounding environment, enabling variations in relative humidity (RH) to modulate the transmitted optical power. A Mitsubishi SH4001 POF was manually tapered using fine-grade abrasive polishing to produce waist diameters of 500 µm and 600 µm, followed by bending into U-shaped structures with radii of 3 cm, 4 cm, and 5 cm. Light from light-emitting diodes (LEDs) at 470 nm, 530 nm, and 645 nm was launched into the fiber, and changes in output intensity were measured using a phototransistor and microcontroller-based signal acquisition system. Experimental results, obtained over 35–90 %RH, reveal a consistent inverse relationship between humidity and output voltage for all wavelengths. Among all configurations, the 645 nm wavelength paired with a 500 µm waist and 5 cm bend radius yielded the highest sensitivity of 0.0385 V/%RH and linearity of 98.74%. Comparative analysis demonstrates the significant influence of wavelength on evanescent-wave penetration depth and sensing performance. The findings confirm the suitability of tapered POF sensors as low-cost and robust alternatives for environmental humidity monitoring.

This study evaluates the neutron measurement and discrimination capabilities of a Eu:LiCaAlF<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> scintillator before and after coupling it to an optical fiber, and introduces a miniature Eu:LiCaAlF<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> fiber-coupled detector for reactor neutron measurement. Comprehensive Geant4 simulations were performed, and the results show that thinner scintillators effectively suppress high-energy gamma responses, thus improving the high n/γ discrimination capability. Experimental measurements were performed using a 0.8-mm-thick scintillator, both before and after its coupling to a 30-cm-long plastic optical fiber, in response to a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">252</sup>Cf neutron source and gamma sources. The detector exhibited a distinct peak response to thermal neutrons in both configurations, with an equivalent 1456 keV electron energy response. A miniature fiber-optic neutron detector was designed for monitoring the neutron flux in a zero-power research reactor. It featured a 0.6 mm × 0.6 mm × 0.6 mm Eu:LiCaAlF<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> scintillator coupled to a 1 m long quartz optical fiber with a 600 μm core diameter. The relative variation in neutron flux within the zero-power reactor was measured online during control rod movement. This measurement system was deemed to be adaptable for the measurement of thermal neutron flux up to 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> n/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>/s. Future research should focus on employing in-core extended optical fibers and detector arrays for internal, multi-point monitoring, with the aim of evaluating the system's long-term stability and reliability during continuous reactor operation to enable practical deployment.

In the context of ultra-low end applications such as smart homes, smart vehicles and Industrial Internet of Things (IIoT), the use of Plastic Optical Fibers (POFs) as communications backbone to enable the convergence of wireless and optical systems has emerged as a cost-effective and ruggedized solution. The transmission of standalone Narrowband IoT (NB-IoT) signals through large-core Step-Index POF (SI-POF) can be achieved by directly modulating a laser diode at the cost of introducing non-linear effects. In this work, the performance of a Radio-over-POF (RoPOF) link is enhanced by Digital Predistortion (DPD) using a memoryless polynomial approach whose complexity is reduced by scaling down the number of samples using a novel technique that preserves the data statistics by organizing the data into a number of clusters.

Human complex joint motion recognition based on plastic optical fiber wearable system

A plastic optical fiber humidity sensor for high-precision soil moisture monitoring: Design, validation, and unified modeling across soil types

High sensitive optical-chemical sensors based on optical fibers in a reflection scheme combined with C-shaped waveguides of MIP-microbeads.

Research on an abnormal respiration monitoring mattress based on a plastic optical fiber end-face coupling structure

Turbidity is an important water-quality parameter. Crucial for drinking water and industrial liquid. In this study, an extrinsic water turbidity sensor based on plastic optical fibre was proposed. The sensor detects suspended particles by measuring transmitted and 90°-scattered light experiments were conducted with NaCl concentrations between 10-100 g/l, corresponding to 1–16 NTU. Results show a strong correlation between the transmitted light and the 90°-scattered light, with a regression coefficient of 0.98. The limit of detection (LOD) and limit of quantification (LOQ) were 2.80 g/l (≈ 0.45 NTU) and 9.35 g/l (≈ 1.45 NTU), confirming high sensitivity. Optimum longitudinal distance between two coaxial fibres was found to be 10 mm providing a wider and more linear dynamic range while maintaining stability and reproducibility. These results demonstrates that the proposed sensor can accurately monitor turbidity in water with high sensitivity and reliable performance.

We present a graded-index (GI) plastic optical fiber (POF) that achieves significantly lower bit error rates (BERs) in high-speed data transmission using four-level pulse-amplitude modulation (PAM4), compared with standard silica GI multimode fibers (MMFs) in short-reach links based on vertical-cavity surface-emitting lasers. The GI POF features strong mode coupling associated with microscopic heterogeneities in the fiber core material, which effectively suppresses interferometric noise, particularly reflection noise. Experimental results demonstrate that the GI POF achieves BERs several orders of magnitude lower than those of silica GI MMFs in 53.125 Gb/s PAM4 transmission under identical optical return loss conditions, and maintains error-free operation (BER < 10-12) across a wide range of alignment conditions. The stability and robustness enabled by the GI POF can reduce reliance on externally implemented noise mitigation strategies, such as specialized transceiver optics, tight-tolerance connectors, and digital signal processing, thereby enabling cost-effective, energy-efficient, and low-latency optical interconnects.