Multimode Optical Fiber Sensor Research Articles

Surface Plasmon Resonance (SPR)-Based Multimode Optical Fiber Sensors for Electrical Transformer Oil Aging Detection

I In this study, optical fibers were designed and implemented as a chemical sensor based on surface plasmon resonance (SPR) to estimate the age of the oil used in electrical transformers. The study depends on the refractive indices of the oil. The sensor was created by embedding the center portion of the optical fiber in a resin block, followed by polishing, and tapering to create the optical fiber sensor. The tapering time was 50 min. The multi-mode optical fiber was coated with 60 nm thickness gold metal. The deposition length was 4 cm. The sensor's resonance wavelength was 415 nm. The primary sensor parameters were calculated, including sensitivity (6.25), signal-to-noise ratio (2.38), figure of merit (4.88), and accuracy (3.2). In the current study, the refractive index values of sucrose and water solutions at different concentrations, which were used as a calibration method, were calculated to be (1.346, 1.359, 1.382, and 1.39). It was found that when the refractive index of the sensitive medium increases, the length of the resonant wavelength increases due to the decrease in energy.

Multimode optical fiber strain monitoring for smart infrastructures

The in-service monitoring of civil infrastructures is an important task required to achieve their smart operation. This task requires the installation of sensors to continuously check and control the structures’ status in order to fulfil the demanded operating conditions and avoid the occurrence of malfunctions. This work presents an investigation of the use of multimode optical fiber sensors in detecting strain and vibration of infrastructures. The multimode fiber sensor is composed of a single mode – multimode – single mode concatenated fiber structure. To explore its practical application for strain monitoring, the sensor is used to measure the strain on a pressurized pipe and its performance compared with the well-developed fiber Bragg grating sensor. The detuning of spectral features of the multimode sensor transmission with increasing pipe pressure is found to have a good linearity (R2 ∼ 0.95) and is more sensitive to strain compared to that of the fiber Bragg grating.

Microfiber Optics Liquid Refractometer: The Effect of Taper Waist

A simple tapered multimode fiber (MMF) optic sensor is proposed and demonstrated as a refractometer for liquid samples application. The working mechanism of such device is based on the intensity modulated transmission of the tapered fiber when it is immersed in solutions with increasing refractive index. The tapered fiber is fabricated using heat-pulling method to achieve a waist diameter of 40, 50 and 75μm over the length of 18 mm. The performance of the tapered fiber with different waist has been evaluated on samples of ethylene glycol solution and glycerol. The obtained results show good correlation with the data provided by a commercial refractometer. The main advantages of this sensor are its enablement of miniaturization and simplification, ease to fabricate and handle while providing high accuracy measurement.

Characterization of single-mode multimode single-mode fiber optic sensors for steel rebar corrosion monitoring in NaCl and simulated concrete pore solutions

Single-mode multimode single-mode (SMS) fiber optic sensors are characterized for corrosion monitoring of steel rebars in NaCl and simulated concrete pore solutions. Three diameters of the multimode fiber (MMF) are considered including 125 µm, 90 µm, and 60 µm. Steel rebar specimens were first cast in epoxy resin and then polished to expose a rectangular section. The SMS fiber optic sensors are directly attached on the polished surface of the steel rebar and then immersed in solutions for corrosion monitoring. Two types of solution are prepared, including 3.5 wt.% NaCl solution and simulated concrete pore solutions. During the immersion tests, the corrosion evolution of the steel rebar was measured with open circuit potential and linear polarization resistance. The change of the transmission spectrum of the SMS fiber optic sensors is recorded with an optical spectra analyzer. The change of the characteristic wavelength is correlated with the corrosion-induced mass loss of the steel rebars. Results show that linear relationships are present between the corrosion-induced mass loss of the steel rebars and the shift of the characteristic wavelength of the SMS fiber optic sensors. The corrosion monitoring sensitivity of SMS fiber optic sensors increases with a decrease of the diameter of the MMF.

Sensing performance optimization by refining the temperature and humidity of clad engraved optical fiber sensor in glucose solution concentration

The experiments and performance of an evanescence wave-based plastic multimode fiber optic sensor to delineate their spectral and output power response in a glucose solution at room temperature and also at varying temperatures and humidity are described in this paper. In this study, the spectral transmission and the amount of transmitted intensity of the fiber when its morphology was varied both linearly and U-bent were examined. Furthermore, the effect of temperature was investigated by monitoring response both spectrally and electrically for linearly aligned clad removed fiber as a function of time at varying temperatures (20 °C, 25 °C, 30 °C, 40 °C). The sensors’ response towards various glucose concentrations (10–100 mM) was also determined under different relative humidity conditions (30 %, 40 %, 50 % 60 %), maintaining the temperature constant. Changes in the refractive index, surface morphology, temperature, and humidity of the sensing region had an impact on the light-transmission modes and sensitivity of the sensor. In summary, our study on the influence of temperature and humidity on glucose sensitivity can broaden the scope of optical sensing, thereby advancing the development of plastic fiber-optic-based evanescent wave sensors.

DETECTION OF ADULTERANT TRACES IN EDIBLE OIL BASED ON FIBER OPTIC SENSOR TECHNOLOGY

Low-cost multimode fiber (MMF) optic sensor for detection and determination of adulterant traces of palm oil in coconut oil is experimentally demonstrated. The fundamental principle of detection is the sensitive dependence of the wavelength shift on the refractive index changes of the surrounding medium of multimode fiber cladding. The transmission spectral changes due to variation of adulteration levels have been investigated. Building up of this low-cost multimode fiber optic sensor is helpful in prevention of adulteration. This technique has resulted in 20% adulteration for coconut-palm oil binary mixture

Enhanced Mach-Zehnder interferometer multimode–single-mode–multimode fiber optic refractive index sensor based on surface plasmon resonance

In this paper, an all-fiber Mach-Zehnder interferometer (MZI) sensor for refractive index (RI) measuring is presented, which is based on Multimode–Single-mode–Multimode (MSM) fiber. The effects of both reducing the radius of the sensing part and the surface plasmon resonance (SPR) on its efficiency are investigated. Increasing the interaction of high-order modes with external media, caused by etching the cladding layer of the single-mode fiber part, significantly improves the sensitivity. Both wavelength and intensity interrogation approaches are employed to study the Multimode–etched Single-mode–Multimode (MESM) fiber sensor. The intensity and the wavelength sensitivities for the RI measurement in the range of 1.428–1.458 are obtained as −2306.754 %/RIU and 1315.74 nm/RIU, respectively. Finally, the MESM-SPR sensor is proposed and characterized. Results exhibit high performance in the RI range of 1.333 to 1.357, in which the sensitivity of 1437.056 nm/RIU is achieved. The advantages like low cost, high sensitivity, and simple fabrication methods make these sensors promising devices for chemical, food industry, and biosensing applications.

Multimode optical fiber specklegram smart bed sensor array.

.SignificanceMonitoring the movement and vital signs of patients in hospitals and other healthcare environments is a significant burden on healthcare staff. Early warning systems using smart bed sensors hold promise to relieve this burden and improve patient outcomes. We propose a scalable and cost-effective optical fiber sensor array that can be embedded into a mattress to detect movement, both sensitively and spatially.AimProof-of-concept demonstration that a multimode optical fiber (MMF) specklegram sensor array can be used to detect and image movement on a bed.ApproachSeven MMFs are attached to the upper surface of a mattress such that they cross in a array. The specklegram output is monitored using a single laser and single camera and movement on the fibers is monitored by calculating a rolling zero-normalized cross-correlation. A image is formed by comparing the signal at each crossing point between two fibers.ResultsThe MMF sensor array can detect and image movement on a bed, including getting on and off the bed, rolling on the bed, and breathing.ConclusionsThe sensor array shows a high sensitivity to movement, which can be used for monitoring physiological parameters and patient movement for potential applications in healthcare settings.

Numerical and experimental study of a multimode optical fiber sensor based on Fresnel reflection at the fiber tip for refractive index measurement

This paper presents the numerical and experimental study of a multimode optical fiber (MMF) sensor based on Fresnel reflection at the fiber tip. Considering different modal power distributions (uniform mode distribution, gaussian and equilibrium mode distribution), the effective fraction of the incident light reflected at the interface between the end of the fiber and the surrounding medium is first calculated numerically with a ray model. Even when considering modal power distribution and non-normal incidence influence, simplifying assumptions such as normal incidence hypothesis can be made to facilitate experimental data exploitation, with a maximum error on the deduced medium refractive index of the 10-4 order. A statistical analysis of noise is then made, to study the influence of a random noise between 0.1% and 5% noise level: results show that the approximation error made by using normal incidence formula for a Fresnel sensor based on a MMF is significantly smaller than the repeatability error. These assumptions are then verified experimentally with two experimental setups by measuring the refractive index at 1550 nm of reference solutions (distilled water-isopropanol and distilled water-sodium chloride mixtures) with a Fresnel based on a multimode fiber, and a Fresnel based on single-mode fiber for comparison. Good agreement is found with refractive index values from the literature with a maximum relative difference of only 0.1%, and the maximum experimental uncertainties in this work is 1.1×10-4. Differences between refractive index measured with a Fresnel based on single-mode and multimode fiber are found to be in accordance with values from the statistical study.

CNT-based tapered optical fiber for ethanol remote sensing over 3-km optical fiber

Certain organic liquids like ethanol in water are considered hazardous and have an enormous environmental impact since it is toxic and classified as class I flammable liquids. Remote sensing with complex sensors is a common technique for detecting and tracking spillages of hazardous spillages. Most of the applied remote sensing methods suffer from location and control issues that force the user to be at the exact sensing spot during operation. The present work introduces a simple and highly sensitive tapered multimode optical fiber (TMOF) sensor coated with carbon nanotubes (CNT) for flammable liquids remote sensing applications. The new proposed sensor ability to transfer signals to a remote data collection center of about 3 km from the sensor location was investigated. Ethanol was utilized as the index solution to be tested in the present work. The proposed sensor was attached to 3 km multimode silica optical fiber and characterized towards different concentrations of ethanol in de-ionized water at room temperature. Various characterization techniques have investigated the detailed structural properties of the sensing layer. The experimental results demonstrated that the proposed remote sensor exhibits rapid response with recovery times of 8.7 s and 18 s, respectively, and relative absorbance of 26% upon exposure to 100% ethanol. The sensor attains an overall sensitivity of 1.3/vol% towards low ethanol concentrations in water (0.01–0.5%). Besides, the optical sensor manifests outstanding repeatability when exposed to another cycle of ethanol with concentrations of 20% and 40% in de-ionized water. The proposed optical remote sensor's superior performance via low cost and simple techniques indicates its high efficiency for ethanol detection in various industrial applications.

Modified fiber optic sensor for highly precise identification of mercuric ion (Hg2+) concentrations in aqueous solution

A fiber optic sensor for monitoring mercuric (Hg2+) ions in the aqueous sample have been developed based on modified cladding. To fabricate a D-shaped sensing zone onto the multimode optical fiber lengthwise polishing was utilized using a mechanical end and edge polishing system. The produced sensing region has dimensions of 10 mm × 125 μm × 62 μm (l × w × h). A 2 μm thin layer of Al2O3 nanoparticles sensitized with 4-(2-pyridylazo)-resorcinol was deposited onto the sensing element of multimode fiber optic sensor to make it sensitive and selective for Hg2+ ions. The analytical results demonstrate that the sensing device has a linear response for Hg2+ ions concentration over a range from 4 to 16 ppm along with a 4 ppm limit of detection in an aqueous sample at room temperature. The selectivity of the sensor is examined for the recognition of Hg2+ ions in presence of other cations such as zinc and/or lead ions up to 16 ppm in an aqueous solution. The main merits of this fabricated sensor are easy and safe installation, rapid response, enhanced linear response range, and better selectivity towards Hg2+ ions.

Embedded optical fiber link interferometer sensors for snapshot surface inspection using the synthetic wavelength technique.

Free-space optical measurement systems can have a direct impact on evaluation systems operational in propagation paths. During propagation via optical fibers, light suffers scattering or interference, causing some output signal loss with an uncertainty outcome. Therefore, this study aims to explore the instant decisions related to the use of single- and multi-mode fiber optics and how they affect the gathering of data from high-speed optical measurement instrument links. The study also seeks to address a number of design methodology aspects and the empirical outcomes related to a surface topography measurement sensor based on fiber optics capable of surface roughness or step-height measurement. The study suggests that the Fourier transform profilometry method (FTP) can overcome the disadvantages of optical metrology sensors (e.g., bulkiness, challenging set-up, high costs, and low speed). However, despite eliminating vertical height problems, the Fourier transform profilometry (FTP) did have some shortcomings for every outcome related to core variables, including the dispersive optical fiber link sensor. The synthetic wavelength method enabled the dispersive optical fiber link sensor to calculate the vertical step height of the selected sample (1 µm). There was improved step-height repeatability, with satisfactory from 20 to 18 nm outcome improvement range. Additional investigations are necessary to establish the compatibility of single- or multi-mode optical fiber sensors with particular instruments, especially those currently preferred for embedded metrology applications.

The Reinforced Optical Fiber Sensing with bilayer AuNPs/SiC for pressure measurement: Characterization and Optimization

A cladding modified multimode optical fiber sensor reinforced with bilayers Au:SiC is designed and fabricated for pressure sensing in this presented. The Au thin film was used to enhanced the sensitivity of the sensor while the SiC thin film has been investigated as the reinforced layer at the sensing part to measure the wide range of applied pressure. The data acquisition interrogated using an optical time-domain reflectometer (OTDR). The results showed that the performance of the optical fiber sensor coated with bilayers Au:SiC coating is significantly improved in the measurement of applied pressure at the sensing part. Additionally, the sensor coated with bilayer Au:SiC exhibits linear variation in the return losses measured from OTDR trace with the wide range of applied pressure compare to the sensor coated with Au thin film. Where the maximum value in the sensitivity is equal to 35% dB/um of the sensor coated with bilayers SiC:Au compared to the sensitivity of the sensor coated with Au which equal to 30% dB/um. The high performance showed in results demonstrating that the fabricated optical fiber sensor has the excellent potential application as a sensor to measure a wide range of applied pressure without deform the sensing part.

Monitoring of vital bio-signs by analysis of speckle patterns in a fabric-integrated multimode optical fiber sensor.

Continuous noninvasive measurement of vital bio-signs, such as cardiovascular parameters, is an important tool in evaluation of the patient's physiological condition and health monitoring. Based on new enabling technologies, continuous monitoring of heart and respiration rate, pulse wave velocity and blood pressure have been investigated, advanced and reflected in numerous papers published in recent years. In this paper, we introduce a new technique for noninvasive sensing of vital bio-signs based on a multimode optical fiber sensor that can be integrated into a fabric. The sensor consists of a laser, optical fiber, video camera and computer. Its operation is based on tracking of point-wise intensity variations on speckle patterns caused by interference of the light modes within the fiber subjected to deformation. The paper contains theoretical analysis and experimental validation of the proposed scheme. The main goal is to advance a simple low-cost sensor embedded in a cloth fabric to track changes in the cardiovascular condition of the wearer.

Fiber Optic Fabry-Perot Micro-Displacement Sensor Based on Low-Cost Polymer Film

This manuscript experimentally validates a thin-film polymer and multimode fiber optic interaction-based low-cost optical fiber displacement sensor. The sensing setup is operated by deflecting a commercially Mylar® polymer film using multimode optical fiber. The sensor exhibits a higher sensitivity of 24nm/μm and resolution of 41.6nm. The sensor's analyses also demonstrate good polynomial approximation, with a maximal adjusted square of R = 0.9801, and high stability, in which minimal power (0.4dB-Hour) and wavelength (<; 2nm-Hour) variations are observed. Moreover, thermal experiments prove that the sensor has lower temperature traits (0.05μm/°C), and this parameter can be distinguished considering the wavelength shifting direction. The simplicity of the scheme, as well as the cost of the elements involved, make this technique a reliable alternative to detect microdisplacements.

Comprehensive investigation of evanescent wave optical fiber refractive index sensor coated with ZnO nanoparticles

Abstract Combination of optical fiber and semiconductor metal oxide nanostructure provide a label-free refractive index (RI) sensor with an excellent limit of detection. ZnO NPs (nanoparticles) coated evanescent based multimode optical fiber sensor is established to detect different crude oil concentrations blended in diethyl ether. The efficacy of fabricated sensors with respect to wavelength shift and intensity changes is tested with different crude oil concentration from 0% (RI: 1.35) to 100% (RI: 1.47). By increasing the crude oil concentration, the maximum shift of ~10 nm towards lower wavelength is occurred. The signal in visible area originated from the electron–hole recombination at a deep level via singly ionized oxygen vacancies (VO+). Increasing the crude oil concentration leads to decreasing the transmission intensity up to 72% of its maximum value. Changes in refractive index of ZnO nanostructure from 2.671 to 2.726 with the change in oil concentration from 0% to 100% respectively, leads to different quantity of evanescent wave absorption taken placed. Different absorption rate and reflection angle in the cladding-ZnO interface are responsible for intensity modulation. The interaction of oxygen vacancies on ZnO surface, electron migration from donor media to the valance band and lowering the band-gap with decreasing the crude oil concentration are responsible for RI modification of ZnO. Therefore, an economic, high sensitive and multipurpose dual sensing scale has been proposed for crude oil detection.

Enhanced sensitivity of fiber optic evanescent wave absorption-based concentration sensor by shining a Bessel–Gauss beam and effect of fiber bending on the sensor response: a theoretical analysis

We present a theoretical perspective on the notion of a highly sensitive multimode fiber optic evanescent wave absorption-based sensor by exploiting a zero-order Bessel–Gauss beam to determine the concentration of sodium chloride (NaCl) from its aqueous solution. The phenomenon of excited waveguide modes inside the sensor structure has been assessed by using a classical wave-optic model. By harnessing the advantages of the Bessel–Gauss beam, the difference in transmitted output power is evaluated for various concentrations of NaCl, ranging from 0 to 360 g/L. To corroborate our theoretical predictions, the computer-aided simulation in Mode Solutions software has been performed on the proposed sensing configuration. In contrast to the conventional concentration sensor using Gaussian beam, the projected scheme yields a maximum 14.40-fold superior sensitivity of 0.072 dB / gL − 1 with a commendable sensing resolution of ∼0.013 g / L. Also, attention has been paid to the Bessel–Gauss beam shined U-bent fiber-optic absorption-based concentration sensor, where the sensor response has been numerically investigated for different bending radii, and it is concluded that the sensitivity can be enhanced appreciably by gently reducing the bending radius. Due to ultrahigh sensitivity, the present paradigm is very much alluring and evocative, establishing pivotal implication in chemical and biological sensing fields.

Ultrahigh-sensitive multimode interference-based fiber optic liquid-level sensor realized using illuminating zero-order Bessel–Gauss beam

A proposal toward the enhancement in the sensitivity of a multimode interference-based fiber optic liquid-level sensor is explored analytically using a zero-order Bessel–Gauss (BG) beam as the input source. The sensor head consists of a suitable length of no-core fiber (NCF) sandwiched between two specialty high-order mode fibers. The coupling efficiency of various order modes inside the sensor structure is assessed using guided-mode propagation analysis and the performance of the proposed sensor has been benchmarked against the conventional sensor using a Gaussian beam. Furthermore, the study has been corroborated using a finite-difference beam propagation method in Lumerical’s Mode Solutions software to investigate the propagation of the zero-order BG beam inside the sensor structure. Based on the simulation outcomes, the proposed scheme yields a maximum absolute sensitivity of up to 3.551 dB / mm and a sensing resolution of 2.816 × 10 − 3 mm through the choice of an appropriate length of NCF at an operating wavelength of 1.55 μm. Owing to this superior sensing performance, the reported sensing technology expedites an avenue to devise a high-performance fiber optic-level sensor that finds profound implication in different physical, biological, and chemical sensing purposes.

Fabrication and characterization of multimode optical fiber sensor for chemical temperature monitoring using optical time domain reflectometer

In this work, the optical fiber sensor system to measure the optical loss due to temperature variation of gasoline and toluene was papered. The optical fiber sensor was characterized using optical time domain reflectometer (OTDR). The sensor was a 50 cm multimode fiber with about 1–3 cm at its central region being partially unclad. The partial uncladding was carried out using chemical etching technique. The optical loss of sensor was measured when unclad part exposed to gasoline and toluene respectively at different temperature ranging from 25 °C to 60 °C. The optical loss of sensor increases in a step drop of OTDR trace as the temperature is increased. The rate of optical loss was estimated to be 0.01576 dB/°C and 0.02212 dB/°C for gasoline and toluene respectively.

A comparative study of nanocrystalline SiC thin films on multimode optical fiber sensors, synthesized via DBD-NTP and 150 MHz VHF-PECVD

In this study, nanocrystalline SiC films were successfully synthesized on the surface of multimode fiber (MMF) sensors using 150MHz very-high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) and dielectric barrier discharge nonthermal plasma (DBD-NTP) methods. The effects of the different utilized methods and various deposition times on the microstructure and chemical composition of the deposited SiC films were investigated For both methods, the SiC film thickness increased with increased deposition time. The dependency of sensitivity on the deposition time and thickness of SiC films was studied by investigating the effects of refractive index and temperature variation on the response of the MMF sensors. The SiC films deposited by 150MHz VHF-PECVD showed more uniformity and higher sensitivity compared to those deposited using DBD-NTP. Using VHF-PECVD with a deposition time of 1min yielded the lowest thickness (54.06nm) and therefore the highest sensitivity (0.0240dB/°C) for the SiC-deposited MMF sensors. Thus, the VHF-PECVD method may be a better option than DBD-NTP for the deposition of thin SiC films to improve the sensitivity of the MMF sensors.