Optical Fiber-based Sensors Research Articles

Polyvinylpyrrolidone-Capped Silver Nanoparticles for Highly Sensitive and Selective Optical Fiber-Based Ammonium Sensor.

Herein, aqueous ammonium sensing characteristics of polyvinylpyrrolidone (PVP) capped silver nanoparticles (Ag-NPs) coated optical fiber-based sensors are presented. The PVP-capped Ag-NPs were prepared using cold and modified polyol synthesis methods. Aqueous ammonium detection was carried out by the surface plasmon resonance (SPR) effect observed in the Ag-NPs coated optical fiber system. The effect of cold and modified polyol synthesis methods on optical sensing performance was studied. The optical fiber cladding was modified with PVP-capped Ag-NPs according to the standard protocol for sensing investigation. The probe sensing response was analyzed for varying concentrations of ammonium ions on red, green, and blue LEDs. The sensor characteristics, viz., sensing response, repeatability, calibration curve, and ambient light effect, were investigated for PVP capped Ag-NPs coated optical fiber-based sensor. The PVP capped Ag-NPs synthesized via the polyol synthesis method showed a detection limit of 48.9 mM, 1.33 mV/M sensitivity, and an excellent linear relationship (R2 = 0.9992) between voltage and ammonium ion concentration in the range of 0.054–13.4 M concentration. On the other hand, PVP capped Ag-NPs synthesized using the cold synthesis method showed a detection limit of 159.4 mM, a sensitivity of 0.06 mV/M, and a poor linear relationship (R2 = 0.4588) between voltage and ammonium ion concentration in the range of 0.054–13.4 M concentration. The results indicate that the PVP-capped Ag-NPs synthesized using the polyol synthesis method exhibit enhanced ammonium ion sensing compared to the cold synthesis method.

OPTICAL FIBER-BASED SENSORS AND THEIR RECENT APPLICATIONS IN SCIENCE AND ENGINEERING

OPTICAL FIBER-BASED SENSORS AND THEIR RECENT APPLICATIONS IN SCIENCE AND ENGINEERING

Compact breath monitoring based on helical intermediate-period fiber grating

Tiny and soft breath sensors offer unique capabilities in a continuous and long-term recording of vital physiological parameters for human health monitoring. Here, we propose an all fiber-optic breath sensor based on helical intermediate-period fiber grating (E-HIPFG) written in an elliptic core polarization-maintaining fiber. This E-HIPFG-based breath sensor shows ultrafast response time and recovery time, which are 34.46 ms and 41.34 ms, respectively. The response time and recovery time are three orders faster than the corresponding values of conventional optical fiber-based breath sensors with humidity-sensitive material. In addition, this sensor does not combine with any additional coating materials or fiber architectures, increasing the stability in a continuous and long-term detection for breath monitoring. The E-HIPFG sensor is insensitive to external influences, such as temperature, torsion and strain, endowing the possibility of stable detection in the moving body. Particularly, the temperature sensitivity of the sensor is 2.75 pm/°C, which is two orders lower than the corresponding value of previous reports. Due to its considerable stability, quick response, and insensitivity to external influences, the E-HIPFG-based breath sensor offers significant potential for long-term and compact breathing monitoring devices.

A method for the controllable fabrication of optical fiber-based localized surface plasmon resonance sensors

Optical fiber-based Localized Surface Plasmon Resonance (OF-LSPR) biosensors have emerged as an ultra-sensitive miniaturized tool for a great variety of applications. Their fabrication by the chemical immobilization of gold nanoparticles (AuNPs) on the optic fiber end face is a simple and versatile method. However, it can render poor reproducibility given the number of parameters that influence the binding of the AuNPs. In order to develop a method to obtain OF-LSPR sensors with high reproducibility, we studied the effect that factors such as temperature, AuNPs concentration, fiber core size and time of immersion had on the number and aggregation of AuNPs on the surface of the fibers and their resonance signal. Our method consisted in controlling the deposition of a determined AuNPs density on the tip of the fiber by measuring its LSPR signal (or plasmonic signal, Sp) in real-time. Sensors created thus were used to measure changes in the refractive index of their surroundings and the results showed that, as the number of AuNPs on the probes increased, the changes in the Sp maximum values were ever lower but the wavelength shifts were higher. These results highlighted the relevance of controlling the relationship between the sensor composition and its performance.

Sputtering Deposition of TiO2 Thin Film Coatings for Fiber Optic Sensors

Thin films of titanium dioxide (TiO2) and titanium (Ti) were deposited onto glass and optical fiber supports through DC magnetron sputtering, and their transmission was characterized with regard to their use in optical fiber-based sensors. Deposition parameters such as oxygen partial pressure, working pressure, and sputtering power were optimized to attain films with a high reflectance. The films deposited on glass supports were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Regarding the deposition parameters, all three parameters were tested simultaneously, changing the working pressure, the sputtering power, and the oxygen percentage. It was possible to conclude that a lower working pressure and higher applied power lead to films with a higher reflectance. Through the analysis of the as-sputtered thin films using X-ray diffraction, the deposition of both Ti and TiO2 films was confirmed. To study the applicability of TiO2 and Ti in fiber sensing, several thin films were deposited in single mode fibers (SMFs) using the sputtering conditions that revealed the most promising results in the glass supports. The sputtered TiO2 and Ti thin films were used as mirrors to increase the visibility of a low-finesse Fabry–Perot cavity and the possible sensing applications were studied.

Broadband Quantum Dot Superluminescent Diode with Simultaneous Three-State Emission.

Semiconductor superluminescent light-emitting diodes (SLEDs) have emerged as ideal and vital broadband light sources with extensive applications, such as optical fiber-based sensors, biomedical sensing/imaging, wavelength-division multiplexing system testing and optoelectronic systems, etc. Self-assembled quantum dots (SAQDs) are very promising candidates for the realization of broadband SLED due to their intrinsic large inhomogeneous spectral broadening. Introducing excited states (ESs) emission could further increase the spectral bandwidth. However, almost all QD-based SLEDs are limited to the ground state (GS) or GS and first excited state (ES1) emission. In this work, multiple five-QD-layer structures with large dot size inhomogeneous distribution were grown by optimizing the molecular beam epitaxy (MBE) growth conditions. Based on that, with the assistance of a carefully designed mirror-coating process to accurately control the cavity mirror loss of GS and ESs, respectively, a broadband QD-SLED with three simultaneous states of GS, ES1 and second excited-state (ES2) emission has been realized, exhibiting a large spectral width of 91 nm with a small spectral dip of 1.3 dB and a high continuous wave (CW) output power of 40 mW. These results pave the way for a new fabrication technique for high-performance QD-based low-coherent light sources.

Lead (Pb2+) ion sensor development using optical fiber gratings and nanocomposite materials

Research on compact, flexible optical sensors for water quality monitoring, specifically targeting heavy metal ion monitoring, has become extremely important due to the increasing number of water pollution incidents seen worldwide where such heavy metals are involved. Optical fiber-based sensors provide an excellent basis for creating new sensing solutions across a wide area, including for energy, healthcare, structural monitoring, defense and importantly here for environmental monitoring. An innovative, cost-optimized sensor solution to better heavy metal detection is proposed, by introducing a hybrid optical fiber grating sensor system based on concatenating a Long Period Grating (LPG) and Fiber Bragg Grating (FBG) for the concurrent detection of an important, specific heavy metal ion pollutant (in this case lead (Pb2+)). The approach uses the functionalization of an optical fiber grating with a chemically synthesized novel nanocomposite material (together with temperature sensing to allow such corrections to be applied). Such a method not only significantly enhances the system sensitivity (achieving 2.547 nm/nM), with a detection limit (0.5 nM), and high selectivity to the Pb2+ ions, but also mitigates the shortcomings of cross-sensitivity seen with many such sensors. Furthermore, in this work, the incorporation of a forward Artificial Neural Network (ANN)-based predictive algorithm has been incorporated to create an effective, well-calibrated system whose characteristics as an intelligent, highly sensitive system has been demonstrated in the detection of the sub-nanomolar concentration of Pb2+ ion in drinking water.

Strain sensing in underwater acoustics with a hybrid π-shifted FBG and different interrogation methods

Although Piezo-Electric Transducers (PZT) hydrophones are widely accepted and technologically mature in the field of Acoustic Emissions (AE) strain sensing underwater, optical fiber-based sensors are gaining more attraction due to their multiplexing capability, small size, high resolution, high sensitivity and immunity to Electromagnetic Interference (EMI). In this paper, we propose a hybrid Fiber Bragg Grating (FBG) system based on combining two apodized FBGs (AFBGs); named Nuttall and Cos8, separated by a pi-phase shift to apply it for underwater strain sensing. This combination results in optimum performance in terms of the reflection properties including high peak reflectivity, narrow Full Width at Half Maximum (FWHM), remarkable side lobes suppression, high roll-off rate, good Ripple Factor (RF) and high Detection Accuracy (DA) as well. In addition, an excellent multiplexing capability, high temperature and strain sensitivities and a stable operation over increased temperatures, strain and pressure levels (up to 250 °C, 1000 µstrain and 100 MPa) are achieved. Moreover, mechanical analysis and comparisons revealed that the Polymer Optical Fiber (POF) recorded the highest sensitivity among other fiber types and their coatings with a value of 1.43 pm/µstrain, making it applicable in the strain sensing in underwater acoustics. Furthermore, in this work, a detailed comparative study is performed between several types of interrogators targeting an optimum interrogator for the strain sensing application in underwater acoustics. The obtained results reveal that the linear edge absorption filter detection method achieves better results among the other types. But, unfortunately, when talking about the multiplexing capability, it shows a remarkable failure. Whereas, the Mach–Zehnder. Interferometry (MZI) comes in the second place with higher resolution range (103–104) with tunable sensitivity, fast measurement speed, good long-term stability, high multiplexing capability and medium cost. Accordingly, it could be applicable in the application understudy.

Recent Advances in Optical Fiber Enabled Radiation Sensors.

Optical fibers are being widely utilized as radiation sensors and dosimeters. Benefiting from the rapidly growing optical fiber manufacturing and material engineering, advanced optical fibers have evolved significantly by using functional structures and materials, promoting their detection accuracy and usage scenarios as radiation sensors. This paper summarizes the current development of optical fiber-based radiation sensors. The sensing principles of both extrinsic and intrinsic optical fiber radiation sensors, including radiation-induced attenuation (RIA), radiation-induced luminescence (RIL), and fiber grating wavelength shifting (RI-GWS), were analyzed. The relevant advanced fiber materials and structures, including silica glass, doped silica glasses, polymers, fluorescent and scintillator materials, were also categorized and summarized based on their characteristics. The fabrication methods of intrinsic all-fiber radiation sensors were introduced, as well. Moreover, the applicable scenarios from medical dosimetry to industrial environmental monitoring were discussed. In the end, both challenges and perspectives of fiber-based radiation sensors and fiber-shaped radiation dosimeters were presented.

Employing Remote Sensing, Data Communication Networks, AI, and Optimization Methodologies in Seismology

Seismology is among the intrinsic sciences that strictly affect human lives. Many research efforts are presented in the literature aiming at achieving risk mitigation and disaster management. More particularly, modern technologies have been employed in such a pivot. However, the day-to-day challenges and complexities of such natural science that face the stack holders still need more reliable and intelligent solutions. The solution can depend on a partial or integrated system of modern technologies. In this paper, we extensively survey the co-related modern technologies aiming to gather the major efforts exerted in this regard. It also outlines the desirability of seismology to modern technologies. Then, we present a detailed analysis of remote sensing and data communication networks (DCNs), which are considered the backend of seismic networks. Furthermore, for seismology, we depict both classical and non-classical approaches based on DCN principles, such as optical fiber-based acoustic sensors, social media, and the internet of things (IoT). Following that, a comprehensive description of the various optimization techniques utilized for seismic wave analysis and for prolonging network lifetime is offered. A description of the important functions that artificial intelligence (AI) can play in different fields of seismology is also included. Finally, we present some recommendations for stack holders to prevent natural calamities and preserve human lives.

A study of highly sensitive D-shaped optical fiber surface plasmon resonance based refractive index sensor using grating structures of Ag-TiO2 and Ag-SnO2

In this study, we propose a design and simulation of a highly sensitive surface plasmon resonance (SPR) based single-mode D-shaped optical fiber refractive index sensor in the near-infrared (NIR) region. It consists grating structure of silver coated with titanium dioxide (TiO2) and Tin dioxide (SnO2) layer on the core-cladding interface. With the help of the finite element method (FEM), the proposed optical fiber sensors are optimized with various geometrical parameters. Proposed optimized structures are investigated and various performance parameters are calculated. It is found that performance parameters enhance with TiO2/SnO2 coated on Ag grating structure at a particular thickness of TiO2/SnO2. Due to this more generations of surface plasmons take place on metal-metal oxide structures. We find the maximum sensitivity of 15.31 μm / RIU and 9.81 μm / RIU for Ag-TiO2 and Ag-SnO2 grating structure respectively which shows a better result in comparison to the other reported work. So proposed structure may have great potential to enhance the sensing ability of optical fiber-based sensors as compared to the other conventional SPR based optical fiber sensors.

Active Compensation of Radiation Effects on Optical Fibers for Sensing Applications.

Neutron and gamma irradiation is known to compact silica, resulting in macroscopic changes in refractive index (RI) and geometric structure. The change in RI and linear compaction in a radiation environment is caused by three well-known mechanisms: (i) radiation-induced attenuation (RIA), (ii) radiation-induced compaction (RIC), and (iii) radiation-induced emission (RIE). These macroscopic changes induce errors in monitoring physical parameters such as temperature, pressure, and strain in optical fiber-based sensors, which limit their application in radiation environments. We present a cascaded Fabry–Perot interferometer (FPI) technique to measure macroscopic properties, such as radiation-induced change in RI and length compaction in real time to actively account for sensor drift. The proposed cascaded FPI consists of two cavities: the first cavity is an air cavity, and the second is a silica cavity. The length compaction from the air cavity is used to deduce the RI change within the silica cavity. We utilize fast Fourier transform (FFT) algorithm and two bandpass filters for the signal extraction of each cavity. Inclusion of such a simple cascaded FPI structure will enable accurate determination of physical parameters under the test.

Optical Fiber Sensors for Ultrasonic Structural Health Monitoring: A Review.

Guided waves (GW) and acoustic emission (AE) -based structural health monitoring (SHM) have widespread applications in structures, as the monitoring of an entire structure is possible with a limited number of sensors. Optical fiber-based sensors offer several advantages, such as their low weight, small size, ability to be embedded, and immunity to electro-magnetic interference. Therefore, they have long been regarded as an ideal sensing solution for SHM. In this review, the different optical fiber technologies used for ultrasonic sensing are discussed in detail. Special attention has been given to the new developments in the use of FBG sensors for ultrasonic measurements, as they are the most promising and widely used of the sensors. The paper highlights the physics of the wave coupling to the optical fiber and explains the different phenomena such as directional sensitivity and directional coupling of the wave. Applications of the different sensors in real SHM applications have also been discussed. Finally, the review identifies the encouraging trends and future areas where the field is expected to develop.

A hybrid self-growing polymer microtip for ultracompact and fast fiber humidity sensing

A hybrid self-growing polymer microtip is firstly proposed and fabricated as an ultracompact fiber-tip Fabry-Perot interferometer (FPI) with enhanced figure of merit (FoM). The hybrid microtip FPI is based on a sharp polymer microtip grown on an ultraviolet (UV) cured polymer film at the fiber end, which has exhibited significant interferometric visibility with high fringe contrast up to 30 dB in the reflection spectra. Using this tiny FPI, an optical fiber relative humidity (RH) sensor with the enhanced FoM of ∼ 0.95/%RH was demonstrated, which is ∼30 times higher than the previous optical fiber-based humidity sensors, and the achieved sensitivity is high enough to perform real-time human breath observation. Furthermore, the humidity sensor exhibited excellent performance in monitoring human breath with fast response time of ∼ 0.6 s. This new type of photonic microtip RH sensing element has shown advantages of compactness, flexibility, fast-response and high sensitivity, which provides a promising platform for potential applications in environmental and biological RH sensing, especially in a restricted space environment.

Performance improvement of a glucose sensor based on fiber optic localized surface plasmon resonance and anti-aggregation of the non-enzymatic receptor

The performance of glucose sensors based on non-enzymatic receptors is often limited because of the aggregation of receptors and the resulting lowered binding efficiency. To improve the limit of detection (LOD) in glucose sensors, a polyoligomeric silsesquioxane (POSS) is introduced as a support to enhance the binding efficiency between glucose and non-enzymatic receptor. POSS support reduces the aggregation and partially grants orientation to ensure that non-enzymatic receptors can productively react with targets. The synthesized amine@POSS-aminophenylboronic acid (APBA) conjugate was immobilized on the surface of gold nanoparticles, which were fastened on the optical fiber. Optical fiber-based sensors using localized surface plasmon resonance (LSPR) enabled rapid detection, ease of handling, and remote sensing. After confirming the response characteristics to the refractive index, a suitable concentration of amine@POSS-APBA receptor was selected for the fabricated fiber optic sensor. Glucose detection was performed at various concentrations using non-enzymatic receptors with and without POSS support. The experimental results demonstrated that increased responses were observed in the designed method than when only the non-enzymatic receptor was applied. The LOD for glucose was quantified as 25.0 μM. We believe that improved glucose sensors based on fiber optic LSPR and POSS support has the potential to be applied to field detection in various fields, such as medicine, food safety, and the environment.

Tin Disulfide-Coated Microfiber for Humidity Sensing with Fast Response and High Sensitivity

Breath monitoring is significant in assessing human body conditions, such as cardiac and pulmonary symptoms. Optical fiber-based sensors have attracted much attention since they are immune to electromagnetic radiation, thus are safe for patients. Here, a microfiber (MF) humidity sensor is fabricated by coating tin disulfide (SnS2) nanosheets onto the surface of MF. The small diameter (~8 μm) and the long length (~5 mm) of the MF promise strong interaction between guiding light and SnS2. Thus, a small variation in the relative humidity (RH) will lead to a large change in optical transmitted power. A high RH sensitivity of 0.57 dB/%RH is therefore achieved. The response and recovery times are estimated to be 0.08 and 0.28 s, respectively. The high sensitivity and fast response speed enable our SnS2-MF sensor to monitor human breath in real time.

Back scattering method based-plastic optical fiber coupler viscosity sensors

Viscosity determination is necessary in variety of applications such as evaluation of environmental pollution, chemical analysis, and as a material quality assessment. Optical fiber-based viscosity sensors are interested since it has various advantages compared to conventional viscosity sensors such as free from electromagnetic interference, compact and could be applied in hazard environment. This study aims to study the performance of back scattering method based viscosity sensor using optical coupler. The sensor design consists of 2×2 plastic optical fiber coupler connected with un-cladded POF as sensor head (sensor A). Characterization was done by connecting 660 nm LED as light source to the one of the coupler branch and an Ocean Optic USB4000 spectrometer to the other branch as light detector. Meanwhile, the sensor head was immersed in glycerin solution. The glycerin solution concentration was varied for various concentration which are 40%, 50%, 60%, 70%, and 80%. Sensor head without the use of optical coupler was fabricated and characterized as comparison (sensor B). The results show that sensor A has a better performance compared to sensor B in terms of linear range. The sensitivity of sensor A is -0.88584 dB/mPa.s at working range of 8.765-57.265 mPa.s with a correlation coefficient of 95.72%.

Computational Modeling of Optical Fiber-Based Magnetic Field Sensors Using the Faraday and Kerr Magnetooptic Effects

Fiber-optic magnetic field sensors are attracting interest for applications in navigation, magnetic resonance, geophysics, space systems, power transformers, and generators, especially for harsh environments, at long distances, and for multiple monitoring points. This article presents a computational modeling for optical fiber-based magnetic field sensors using the magnetooptical Faraday and Kerr effects on the polar configuration. We propose two sensor profiles: one using a thin film of Fe and the other using a Ce:YIG layer. A simplified analytical model based on Fresnel equations is used to guide the numerical modeling built on COMSOL Multiphysics. The sensors’ design methodology is also presented, which optimizes the sensor operating range and sensitivity. The proposed sensor sensitivity, resolution, and operating range are presented and compared to others found in the literature. The results indicate the possibility of building high-resolution sensors for a restricted range of magnetic field intensities or a wide-operating range sensor.

Characterization of Temperature Response of Asymmetric Tapered-Plastic Optical Fiber-Mach Zehnder Interferometer

Temperature measurement is important in various applications; therefore, various temperature sensors have been developed. Due to its advantages, many optical fiber-based temperature sensors have been proposed. The wavelength modulation-based optical sensor is interesting due to high accuracy. However, the complex fabrication process and high cost limit the advantages of the sensors. Therefore, we proposed a simple and low-cost Mach Zehnder interferometer (MZI) sensor using step-index plastic optical fiber (SI-POF). Performance characterization of the sensor to temperature variation is presented. The sensor consists of two tapers at several distances, forming an interferometer. The first taper was designed to be steep to allow excitation of cladding modes, while the second taper was gradual to suppress power loss. Characterizations were done in terms of sensitivity, hysteresis, and repeatability by analyzing the output spectrums recorded by the spectrometer at various environment temperatures, 35oC to 85oC, with an increment of 10oC. The results showed that the sensor has a sensitivity of 0.0431 nm/oC and a correlation coefficient of 0.9965. Hysteresis of 6.9×10-3 was observed. In terms of repeatability, the sensor shows a maximum deviation, ±3oC, which was mainly resulted from the fluctuation of the oven temperature. Despite its high deviation, the sensor has advantages of simple fabrication, low cost, robust, and low power loss, which make it a good candidate for temperature sensors.

Highly sensitive tapered optical fiber coupler-based gas refractive index sensor enhanced by the Vernier effect

Aiming at the problem of the low sensitivity of conventional optical fiber-based gas refractive index sensors, an ultrasensitive tapered optical fiber coupler-based gas refractive index sensor enhanced by the Vernier effect is proposed and demonstrated. The birefringence property of the tapered optical fiber coupler allows it to support two passes of interferences in two orthogonal polarized states, and the superposition of these two interferences forms the Vernier effect. Theoretical analysis and numerical calculations indicate that, for the fiber couplers working in the gas medium when the waist width is within the range of 1.2 to 2.0 μm, the group birefringence difference between the even mode and odd mode equals zero. Thus the sensitivity toward the ambient gas refractive index can be enhanced significantly. To demonstrate these theoretical results, a tapered fiber coupler with a width of 1.6 μm and a length of 16.5 mm was fabricated, and ultrahigh sensitivities up to 22015.4 and −22690.0 nm / RIU were experimentally achieved. The proposed sensor has the merits of being easy to fabricate, having compact structure, and being cost effective. It has significant application prospects in the petrochemical and biomedical detection fields.