Fiber Optic Sensor Research Articles

Realizing submeter spatial resolution for Raman distributed fiber-optic sensing using a chaotic asymmetric paired-pulse correlation-enhanced scheme

The sensing spatial resolution and signal-to-noise ratio (SNR) of Raman distributed optical fiber sensors are limited by the pulse width and weak Raman scattering signals. Notably, the sensing spatial resolution cannot exceed the order of meters at several kilometers sensing distances. To break through this physical bottleneck, a novel, to our knowledge, Raman scattering model based on paired-pulse sensing is constructed. The fundamental origins of the observed limited spatial resolution of conventional schemes are analyzed, and a chaotic asymmetric paired-pulse correlation-enhanced scheme for Raman distributed fiber-optic sensing is proposed and experimentally demonstrated. The proposed scheme uses a chaotic asymmetric paired-pulse as the sensing signal and extracts the light intensity information of each data point of the sensing fiber, which carries the random undulation characteristics of chaotic time series, based on the time-domain differential reconstruction method. This scheme overcomes the pulse width limitation of spatial resolution via correlation and demodulation, enhances the correlation characteristics between the temperature-modulated Raman scattered light field and detection signal, and improves the SNR. Finally, a sensing performance of 10 km, a spatial resolution of 30 cm, and an SNR of 6.67 dB are realized in the experiment. This scheme provides a new research idea for a high-performance Raman distributed optical fiber sensing system.

Experimental Verification of GFRP Bridge Deck Panels Using an Integrated Distributed Fiber Optic Sensing System

Experimental Verification of GFRP Bridge Deck Panels Using an Integrated Distributed Fiber Optic Sensing System

A Deep-Learning-Assisted Fiber-Optic Sensor Capable of Simultaneously Measuring Temperature and Vector Magnetic Field

A Deep-Learning-Assisted Fiber-Optic Sensor Capable of Simultaneously Measuring Temperature and Vector Magnetic Field

Hardware and Software Complex for Identification of Displacement Based on a Fiber-optic Sensor

The article deals with developing a hardware and software complex for identifying rock displacement in open pits. The complex allows for continuous measurement of several parameters and timely notification of personnel of mining enterprises engaged in underground and surface development. The software included in the complex is easy to use and allows changing the information interface. The complex collects, processes and analyzes data from fiber-optic sensors that monitor the geotechnical state of the edge massif. It is connected to fiber-optic sensors via optical conductors, which eliminates the use of the expensive copper cable. Fiber-optic sensors are intrinsically safe and explosion-proof, and are highly resistant to electromagnetic interference. The complex with fiber-optic sensors allows monitoring the geotechnical state of mine workings in open pits. The principle of operation of the complex is based on comparison of apertures and intensity of light spots using a high-resolution photodetector. It has been found that diffraction spots and their pixel pattern do not change in the absence of rock displacement of the edge massif. When a displacement occurs, the light wave that passes through the fiber-optic sensor changes its properties, which leads to changing the parameters of the light spot. After processing the data, the complex produces a numerical value of the displacement.

Applying Michelson-interferometer based optical fiber sensors for active control of road noise in a car

Active noise control (ANC) technology is a promising solution for reducing road noise in cars, where the quality of reference signals is critical for improving the performance. In this paper, an optical fiber sensor based on Michelson interferometer is proposed to obtain the vibration reference signal for active control of road noise in a car. First, the principle of this optical fiber sensor is introduced, then the feasibility of using optical fiber sensor for active control of sound radiation from a panel of an enclosure is verified, where the spectrum, coherence and impulse response of the optical fiber sensor are reported and compared with that of an accelerometer. Finally, the optical fiber sensor is applied in a car for active control of road noise and the simulation results based on the measured data are presented. The research demonstrates the potential of using the proposed optical fiber sensor for active control of road noise in a car by discussing its advantages and weakness.

Research on the Fabrication and Parameters of a Flexible Fiber Optic Pressure Sensor with High Sensitivity

In recent years, flexible pressure sensors have garnered significant attention. However, the development of large-area, low-cost, and easily fabricated flexible pressure sensors remains challenging. We designed a flexible fiber optic pressure sensor for contact force detection based on the principle of backward Rayleigh scattering using a single-mode optical fiber as the sensing element and polymer PDMS as the encapsulation material. To enhance the sensor’s sensitivity and stability, we optimized its structural design, parameters, and fabrication process and measured the fiber strain using an optical frequency domain reflectometer (OFDR). The results showed that the sensor achieved a high sensitivity of 6.93247 με/kPa with a PDMS concentration ratio of 10:1, a curing time of 2 h, and a substrate thickness of 5 mm. The sensor demonstrated excellent linearity and repeatability in static performance tests and was successfully used to monitor the plantar pressure distribution in real time. This flexible fiber optic pressure sensor can be developed via a simple fabrication process, has a low cost, and has high sensitivity, highlighting its potential applications in smart wearables and medical diagnostics.

Metal–semiconductor sulfide bilayer based SPR fiber optic sensors for the detection of methanol adulteration of ethanol using machine learning algorithms: an investigative study

Metal–semiconductor sulfide bilayer based SPR fiber optic sensors for the detection of methanol adulteration of ethanol using machine learning algorithms: an investigative study

(Invited) Development of Fiber-Optic Hydrogen Sensor Using Platinum-Supported Tungsten Trioxide-Silica Composite Film

A fiber-optic hydrogen gas sensor using a platinum-supported tungsten oxide-silica composite film was fabricated. This sensor utilizes the absorption of the evanescent field interaction in the hydrogen sensitive clad which was composed of WO3 and SiO2, coated on a silica core with sol-gel process. As a first step, transmission spectra of sensing film itself were measured. The transmittance of the sensitive film decreased in the range of wavelengths above about 500 nm after exposure to pure hydrogen, and the change in transmittance at 1300 nm was greater than that at 850 nm. Then, fiber optic sensor device was fabricated, and the amount of propagating light was measured. In the case of using the light source with a wavelength of 1300 nm, the sensitivity with respect to the hydrogen response was nearly twice and the response speed was faster, compared with those at 850 nm.

The Application of Distributed Fiber-Optic Sensing Technology in Monitoring the Loose Zone in the Floor of Stoping Roadway

The Application of Distributed Fiber-Optic Sensing Technology in Monitoring the Loose Zone in the Floor of Stoping Roadway

Experimental Study of Fiber-Optic Temperature Sensor Based on Dual FSIs

To improve the sensitivity measurement of temperature sensors, a fiber optic temperature sensor structure based on the harmonic Vernier effect with two parallel fiber Sagnac interferometers (FSIs) is designed, and theoretical analysis and experimental testing are conducted. The FSI consisting of two polarization maintaining fibers (PMFs) with lengths of 13.62 m and 15.05 m respectively is used to achieve the basic Vernier effect. Then by changing the length of one PMF to approximately i times that of the others, the FSI composed of two PMFs of 7.1 m and 15.05 m is used to achieve the first-order harmonic Vernier effect. Afterward, temperature sensing tests are conducted to observe the wavelength drift during temperature changes and ultimately achieve high sensitivity. The experimental results show that the temperature sensitivity of the sensor based on the first-order harmonic Vernier effect is −28.89 nm/°C, which is 17.09 times that of a single FSI structure (−1.69 nm/°C) and 1.84 times that of the sensitivity generated by the structure based on the basic Vernier effect (−15.69 nm/°C). The experimental results are consistent with the theoretical analysis. The structure proposed in this paper achieves drift measurement of 0.1 °C variation based on 1 °C drift, making the fiber optic temperature sensor applicable to related fields that require high precision temperature. The proposed temperature sensor has the simple structure, low production cost, high sensitivity, and broad application prospects.

Strain measurement of CFRP-Steel bonded joints using distributed optical fibre sensors

ABSTRACT Externally bonded carbon fibre reinforced polymer (CFRP) is widely employed for strengthening steel structures. The CFRP-steel bond behaviour is typically conducted using the single-lap joint (SLJ) and double-lap joint (DLJ) shear tests. This study utilizes advanced distributed optical fibre sensors (DOFS) to measure strains in CFRP-steel SLJs and DLJs, with a specific focus on examining the bending effect. An experimental investigation was conducted to verify the appropriate adhesive and fibre coating materials, achieving synergistic deformation between optical fibre sensors and adherends. The strain results reveal that PI-coated fibres bonded with epoxy resin enhance deformation compatibility. The CFRP strain distributions within the joints are accurately measured by DOFS, enabling the calculation of bending strain to assess joint bending effects. The observed strain aligns well with the finite element (FE) predictions. A more significant bending effect is observed in SLJs compared to DLJs, predominantly concentrated at the loaded end. It can be inferred that the SLJs are subjected to mixed-mode I/II loading in shear tests, and the DLJs appears to be mainly influenced by mode II loading. Additionally, the verified FE model demonstrates that the shear strain across the thickness of the adhesive layer exhibits significant variation at the bond ends.

In-line fiber optic optofluidic sensor based on a fully open Fabry-Perot interferometer

In-line fiber optic optofluidic sensor based on a fully open Fabry-Perot interferometer

Sensitivity-enhanced optical fiber sensor based on the Vernier effect for detection of ammonia in water.

A sensitivity-enhanced optical fiber sensor for the detection of dissolved ammonia in water based on the Vernier effect is proposed and demonstrated. The sensor comprises a sensing Fabry-Perot interferometer (S-FPI) and a reference Fabry-Perot interferometer (R-FPI) in parallel. The S-FPI is an open cavity fabricated by the dislocation welding of single-mode fiber(SMF), which is filled with a mixture of ultraviolet-curable resin NOA 170 and Oxazine 170 perchlorate (O17). The R-FPI is a sealed cavity, which is constructed by fusion splicing of SMF and hollow core fiber (HCF). The proposed sensor is based on the chemical reaction between the dissolved ammonia and O17. This chemical reaction alters the refractive index (RI) of the S-FPI, resulting in a wavelength shift of the reflected spectrum. The two interferometers exhibit a nearly identical free spectral range (FSR), thereby enabling the generation of the Vernier effect, which markedly enhances the ammonia sensitivity of the sensor. Experimental results indicate that the sensor sensitivity is 0.34 nm/ppm in the dissolved ammonia range of 5-40 ppm, which is approximately 9.1 times that of the single S-FPI. The proposed sensor exhibits both good repeatability and a short response time, in addition to selectivity for the detection of ammonia.

Fiber optic magnetic field sensor based on a magnetic-fluid-induced phase-shift FLRD

A magnetic field sensing system based on a phase-shift fiber loop ring-down (FLRD) technique and multi-mode interferometer (MI) coated with magnetic fluid (MF) is proposed and demonstrated. The MI is constructed by splicing a segment of no-core fiber between two sections of single-mode fibers, which is then immersed in MF to serve as a sensing head with the advantages of simple fabrication and specific magnetic sensitivity. Due to the magnetic refractive index tunable properties of the MF, the magnetic-field-dependent loss will be introduced in the fiber loop by the sensing head. Such magnetic-induced loss would be accumulated during the round trip of the optical carrier and reflected on the phase information of the modulated signal. The phase-shift changes with the applied magnetic field strength, enabling magnetic field sensing through phase-shift measurements. The sensing system is experimentally demonstrated and a sensitivity of 0.704×10−3deg/Gs in the linear region is achieved. Moreover, the stability and repeatability of the system are verified, leading to a promising method for magnetic field measurements.

Damage detection of Kevlar woven fabric using optical fiber multimode interferometer

Kevlar woven fabric is crucial for the lightweight design of aerospace structures due to its unique advantages. However, it is susceptible to damage during operation, making effective damage detection essential for ensuring structural reliability. Nevertheless, conventional sensors used for damage detection have limitations such as complex manufacturing processes and weight. To address this issue, this paper proposed a simple singlemode-multimode-singlemode (SMS) optical fiber sensor to collect vibration signals and construct a damage recognition model based on natural frequency in order to identify the size of damages in Kevlar woven fabrics. To achieve a highly linear and accurate sensor, a length determination criterion for multimode optical fiber segments based on quasi-image, notch, and transmission spectrum loss was proposed. An optical sensor was fabricated based on this criterion. The feasibility and sensitivity of the sensor for vibration signal measurement were verified by constructing a vibration signal measurement device. An experimental study was conducted to detect damage in Kevlar tapes, where the natural frequency changes measured by the SMS sensor were integrated with an optimized multi-variable gray model for damage size detection. The experimental results indicate that the estimated error in damage size is 0.71%. The damage identification system proposed in this paper offers a simple and cost-effective solution for measuring damage in flexible structures using fiber optic sensors.

A Study on Sensitivity Improvement of the Fiber Optic Acoustic Sensing System Based on Sagnac Interference.

A new pickup structure was introduced and modified to improve the resolution of the linear Sagnac optical fiber acoustic sensing system. The maximum strains corresponding to the material, diameter, wall thickness, and height of the pickups were analyzed by simulation. An aluminum cylinder with a diameter of 110 mm, a wall thickness of 3 mm, and a height of 120 mm was chosen as the basic pickup. A four-groove pickup with a vertical width of 80 mm and a horizontal width of 20 mm was introduced to improve the sensitivity of the system. The experiments showed that the average peak-to-peak sensitivity of the four-groove pickup increased by 215.54% to 106.806 mV/Pa. The improved pickup can be applied in areas to monitor the situation of invasion of the Sagnac optical fiber acoustic sensing system.

Application of acrylic plates as load cell for detecting strain and force in structures

This study presents the use of two superimposed transparent acrylic plates as a load cell for strain and force measurement. The gap between the plates behaves like an interferometer. When a monochromatic light beam is incident upon the gap, it interacts with the two air-acrylic interfaces, causing constructive and destructive interference. This phenomenon results in the formation of an interference pattern. Interferometers are devices used for high-precision measurements. In this work, the strain and force applied to an aluminum bar were precisely measured using two acrylic plates fixed to the bar. The experiments showed that the proposed method has a measurement range of 0–60[Formula: see text] and a resolution of 0.27[Formula: see text]. It is demonstrated that the proposed method offers a low-cost strain measurement technique with a wider measurement range compared to fiber optic sensors

Detection of tendon breaks in prestressed concrete structures using coda wave interferometry

AbstractTendon breaks significantly threaten the safety of prestressed concrete structures. Failure of embedded tendons does not necessarily indicate as surface cracks, demonstrating the need for early detection methods. This paper presents a novel ultrasound‐based approach for detecting and localizing tendon breaks using coda wave interferometry. Already few embedded ultrasonic transducers form a robust monitoring network able to detect subtle changes in the structure. To demonstrate the feasibility of detecting tendon breaks, a post‐tensioned concrete beam was fabricated at Ruhr University Bochum, Germany. A break of a centric and eccentric tendon was artificially created by drilling from the outside. Both were successfully detected and localized through characteristic changes in the ultrasound results without any evidence of damage on the concrete surface. Measurements with fiber optic sensors validate the ultrasonic findings and provide insights into the re‐anchoring behavior after tendon failure.

Experimental study towards the development of highly sensitive opto-mechanical sensors based on FSBS in telecom optical fibers.

The development of applications based on forward-stimulated Brillouin scattering (FSBS) in optical fibers has experienced a considerable increase in recent years, particularly in the area of fiber optic sensors. In this work, we present an experimental investigation to explore the limits of this physical mechanism in telecom optical fibers, whose results we think are of interest for the design of sensors in different areas. Specifically, we studied on the capability of the conventional probing method to detect FSBS in very short optical fibers, and the potential of FSBS to detect tiny diameter changes in the optical fiber. An experiment is presented that demonstrates the feasibility of FSBS as a physical mechanism to back the development of fiber optic sensors based on the mass microbalance concept.

Comparison of PMMA layers doped with methyl red and CdSe quantum dots for application in fibre optic

The paper presents a study of the luminescence properties in the visible spectral range of poly(methyl methacrylate) (PMMA) doped with organic dye-methyl red and CdSe quantum dots. The emission spectra of polymer-doped composite structures were investigated and compared with pure PMMA. Optical characterisation was carried out, focused on the measurement and analysis of excitation and luminescence spectra. Comparison of the spectroscopic characteristics of the developed materials allowed comparing the effect of doping on the luminescence properties of the obtained materials and considering their potential application as luminescent materials in fibre optic sensors.