This PDF file contains the front matter associated with SPIE Proceedings Volume 10654, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Optical current and voltage sensors have become attractive alternatives to conventional instrument transformers in high voltage electric power transmission systems. The optical sensors offer important benefits such as small size and weight, enhanced performance, and constitute an important part of the transition to digital substations. The sensors must comply with stringent accuracy and reliability requirements. Commonly, substation applications demand accuracy to within ±0.2% over outdoor temperature ranges. Other aspects are insensitivity to shock and vibration and stray fields as well as life times in excess of 30 years. We review the technology of the sensors and present particular measures that were necessary to achieve the required performance. This includes the exploration of different sensing fiber types, inherent temperature compensation, accelerated life tests, and, in case of voltage sensors, adequate high voltage proof insulation and packaging. We discuss the integration of a current sensor into a circuit breaker and show results from a corresponding field test.

This paper presents an overview of past, present, and future uses of fiber optic sensors and systems in the power generation industry. The evolution of fiber optic sensors is discussed pertaining to monitoring of power generators.

Optical fiber technologies are very appropriate for using in high voltage equipment due to their excellent characteristics, mainly, immunity to electromagnetic interferences and electrical isolation. After the Smart Grid initiative, the focus for medium voltage (13.8 to 34 kV) smart meters leveraged the development of optical sensors for distribution application. This work provides a historical overview of optical technologies used in power quality monitoring, discussing technological, economics, standards and practical installation aspects. The sensors technologies analyzed in this work are the well-known optical Pockels cells and Faraday Effect, the fiber Bragg grating (FBG) and power-over-fiber (PoF).

Monitoring the dissolved gases and oil temperatures are the most responsive and dependable strategies of assessing the running state and health of power transformers. Novel fiber optic sensor approaches that minimize the footprint and cost of chemical sensors compatible with electrical asset insulation oil monitoring can ultimately allow the deployment on a broader range of power assets. Fiber optic sensor arrays based on nanocomposite thin films for simultaneous gas and temperature sensing at low temperatures have been fabricated. The performance of the sensor array was evaluated with two sensing elements comprised of Pd and Au nanoparticle incorporated SiO₂ thin films, which were deposited onto a coreless fiber by dip-coating in series and then fusion-spliced with two multimode fibers on either end. Such fiber optic sensor array showed monotonic responses over a wide range of H₂ at ambient conditions. A response of the localized surface plasmon resonance absorption peak of Au to changing temperatures from ambient to 110 °C was observed. Optical responses of H2 and temperatures showed opposite directions in transmission signals, which were evaluated by using principal component analysis (PCA). The resulting PCA score plot clearly shows discrimination between the characteristic signal of H₂ gas and temperature. In order to realize potential field deployment, the optical testing system employed low-cost components such as LEDs as fixedwavelength light sources and silicon photodiodes as detectors. The potential applications of such sensor arrays are dual-purpose gas and temperature sensing for on-site deployment in power transformers and other grid asset health monitoring.

Fluorescent fiber sensors fluoresce when light of various wavelengths is absorbed by the fiber. Fluorescent fiber sensors that fluoresce along the length of the fiber offer an advantage for detecting partial discharge (which generates UV and visible light), since light absorbed from any angle, along the entire length of the fiber, may be detected. However, other limitations have reduced the attractiveness of fluorescent fiber sensors for partial discharge detection, including short signal transmission range and constraints on fiber lengths due to high fiber attenuation, inability to pick up discharges internal to insulation, and the lack of multi-functional sensor capability. We describe the use of power over fiber as a means to enable multi-function sensors to be located near the source of partial discharge, and we explore the possibility of a hybrid power over fiber and fluorescent fiber sensor solution. This hybrid solution offers the potential to overcome the limitations of fluorescent fiber sensors. Furthermore, we expand the analysis to include the benefits of merging power over fiber with other fiber sensors. We find that new fiber sensor capabilities are created by combining these two technologies, and therefore enabling potential new applications, and market opportunities.

Two application examples of RFBG sensor arrays that are intended for high temperature profile measurements in chemical reaction vessels and in a gas turbine exhaust duct are described. The array for the chemical reaction vessel includes four sub-arrays with six measurement points each, distributed over a length of 2.3 m. By employing a largescale test facility, temperature profiles extending over 2.3 m with temperatures in the range of 200 °C to 500 °C were acquired with this RFBG array and an excellent agreement with thermocouple data was demonstrated. The second application reported is the measurement of the radial temperature distribution within the exhaust duct of a 7 MW gas turbine. Therefore, a three-point RFBG array was mounted radially in the exhaust gas stream and significant changes in the measured temperature gradient were observed when the engine was in idle or in full load operation mode. In addition to these field deployments of RFBG sensors, long-term annealing experiments at 450 °C in the research lab showed only a shift of the nonlinear temperature calibration curve without changing its shape, allowing recalibrations of RFBG sensor arrays at single temperature points. These examples demonstrate the suitability of RFBG based multipoint high temperature sensing for industrial applications.

Femtosecond Infrared (fs-IR) laser written fiber Bragg gratings (FBGs), have shown great potential for sensing in extreme environments. This paper presents the fabrication and deployment of two fs-IR laser written FBG temperature probes, for monitoring temperature gradients on the flame tube of a low emission burner, during a high pressure combustor test of an optically accessible combustor rig (OACR).

Results of this work include: contour plots of measured internal and exhaust temperature gradients, contrast of FBG measurements with thermocouple data, discussion of deployment strategies, as well as comments on reliability and other important considerations.

In this paper, a packaged FBG based optical fiber sensor written by femtosecond laser pulses in highly birefringent micro-structured optical fiber (MS-FBG sensor) is presented and validated for simultaneous pressure and temperature monitoring. The MS-FBG sensor is capable of separating the temperature information from pressure information without the need for an additional transduction mechanism and this with a negligible pressure-temperature cross-sensitivity. However, in order to use the sensor for downhole applications, a ruggedized sensor housing is required that not only offers mechanical protection to the fiber, but also provides pressure transfer from the well fluid to the sensing element without inducing an additional pressure-temperature cross-sensitivity. In this article, the design of the sensor housing is reported as well as the lab-scale validation up to a temperature and pressure of 150 °C and 700 bar, respectively.

As one of the most proven fiber optic sensors, novel fiber Bragg gratings are continually investigated to extend their roles in extreme environments. In this paper, a newly found “secondary Bragg grating” (SBG) is proposed. The presence of SBG occurs in the case of the type-IIa Bragg grating inscribed in small active fibers, where an additional resonance appears at the shorter wavelength. The SBG provides a variety of interesting characteristics, such as the dip integration, high temperature resistance and high reflectivity, showing promising potential in high temperature sensing.

Distributed Acoustic Sensing (DAS) is a technology with interesting features for real-time safety and security monitoring applications, and constitutes a steadily growing share of the optical fiber sensing market. Recently, the quantitative measurement of disturbances using DAS schemes based on Phase-Sensitive Time Domain Reflectometry (Φ-OTDR) has become a focus of investigation. In this contribution, we propose and experimentally demonstrate a stable homodyne phase demodulation scheme in a fiber optic Φ-OTDR sensor using a double pulse probe and a direct detection receiver. We show that a carrier for the distributed dynamic phase change induced by an external perturbation can be generated by selective phase modulation of one of the probing pulses. The local phase is then retrieved from the backscattering signal using a demodulation technique robust against light intensity disturbances, which have been limiting factors in existing phase demodulation schemes. In addition, the method is independent of the phase modulation depth and does not require computationally costly multi-dimensional phase unwrapping algorithms necessary when using I-Q demodulation in DAS, and is a suitable candidate for analogue signal processing. We demonstrate the capacity of the sensor to measure the distributed dynamic phase change induced by a nonlinear actuator generating a 2 kHz perturbation at a distance of 1.5 km with an SNR of ~24 dB. The demodulated multi-frequency response is also shown to be consistent with one obtained using a point senor based on an FBG and a commercial reading unit.

Distributed acoustic sensing (DAS) based on phase-sensitive optical time domain reflectometry (OTDR) is being widely used in several applications and attracting significant research interest. The main challenge in coherent detection-based phase-sensitive OTDR systems is the speckle-like background noise which impacts the detection performance and conventional techniques are not suitable for detecting weak vibrations under strong background noise. Recently, we proposed a temporal adaptive filtering (AMF) technique to reduce the background noise in phase-sensitive OTDR systems. The AMF method is based on linear filtering of the optical backscattered signals and the filter coefficients are computed from the observed data. In this study, after briefly reviewing the fundamental theory underlying the adaptive algorithm, we present the effectiveness and performance results of the AMF technique with the field tests. The impact of the diagonal loading level which is used to solve the ill-conditioning of the estimated noise covariance matrix is investigated. Performance dependence of the AMF technique on filter size and a comparison with the conventional trace averaging is presented. It is demonstrated that with the AMF technique, more than 10 dB of SNR values can be achieved without introducing additional optical amplifier stages in the DAS hardware. It is shown that intruder activities 25 m far away from a buried SMF-28 fiber underground can be detected with the proposed technique efficiently.

In this study, we present a direct detection distributed acoustic sensor based on phase-sensitive optical time domain reflectometer (φ-OTDR) with long sensing range and high signal-to-noise ratio (SNR), which is field-tested over a 50 kmlong fiber. Due to the random nature of Rayleigh backscattered light and fading phenomena, it is hard to characterize the performance of the system. For this reason, the performance of our sensor is specified in a statistical manner in which the mean SNR is determined using the histograms of the SNR. The SNR values are measured for identical acoustic signals in five different days, total of 48 hours and the SNR histograms are obtained for fiber distances of 100 m, 12 km, 21 km, 30 km, 40 km and 50 km. The system is field-tested using external disturbances that are generated from a 50-Hz vibrator. The SNR values are extracted from the power spectral density (psd) of the collected data over the monitored fiber span. Our results show that the φ-OTDR system exhibits a mean SNR of 22.5 dB at 50 km distance.

Optical fibers for telecommunications are designed to transmit light in a relatively benign and protected environment. The design aims to ensure minimal levels of attenuation, optical non-linearity, and other detrimental effects caused by external perturbations. However, for distributed sensing in harsh environments, the waveguide needs to be optimized as a sensing media and the coating on the optical fiber needs to provide mechanical protection at elevated temperatures. In this paper, we will review our work in three critical aspects of the optical fibers for sensing in harsh environments: waveguide design, coating thermal stability and mechanical strength at elevated temperatures.

This paper describes the design and performance of a new all optical fiber-coupled Fabry-Perot (FP) acceleration and vibration sensor. This device can be readily multiplexed with up to eight other sensors on a single interrogation channel, and an existing state of the art Fiber Bragg Grating (FBG) swept-wavelength interrogation system can be used to monitor the sensor response. The ease of multiplexing combined with passive operation leads to an effective solution for monitoring vibration at many different points across a wide area, with minimal cost of deployment. We will also describe tests of a fiber conduit security monitoring application.

Over the last 40 years the fiber optic sensor field has changed dramatically. This was driven in part by advances in optical components, optoelectronics, and semiconductors coupled with the emergence of fiber optic communication, compact disks, and DVD readers. This paper contains some illustrations on how key fiber optic sensors have evolved and are interrelated. These improved fiber sensor designs over time in combination with improvements in system components have allowed performance and cost improvements that have resulted in penetration into aerospace and defense, civil structures, oil and gas, electric power, and medical applications.

This paper presents an architectural design of a novel intelligent accelerometer sensor, constructed from a multi- mode fiber optic cable, and studied its performances. Experimental proofs are provided to demonstrate that as a multi-mode fiber deforms, variation in the shape and structure of speckle patterns will provide deterministic information for measuring the deformation parameters. We used a deep learning approach to analyze the shape of speckle patterns. A multilayer feed-forward convolutional neural network (CNN) has been used to utilize and classify images of speckle pattern into distinct pre-known classes of acceleration vectors. A pendulum setup is used for collecting repeatable and predictable sample data. The presented intelligent sensor is compared with a Micro Electromechanical Machine System (MEMS) accelerometer performances. Estimation of magnitude and direction of the acceleration vector in one plane of motion is achieved with high accuracy (over 97%), when the CNN was trained for 150 epochs. The results confirm that this novel accelerometer sensor performs as well as a MEMS accelerometer. With proper manufacturing, this novel fiber accelerometer has the potential to overcome the limitations associated with conventional accelerometer sensors, normally due to their physical characteristic, accuracies or performances. The potential sensor resulting from this research is expected to be simple, compact, and economically feasible. Moreover, the sensing approach can easily be generalized to measure other physical phenomenal including vibration and displacement.

Manganese is an important heavy metal element that influences nervous system. Detection of manganese in various mediums has thus attracted lots of attentions. Here we report a study on silver nanoparticles functionalized long-period fiber grating (LPFG) for manganese sensing. Silver nanoparticles (AgNPs) with a size in the range of 70nm10nm were synthesized with polyvinyl pyrrolidone (PVP)-glycol. The interplay between arginine, an agent that can cause aggregation of AgNPs, and Mn2+ leads to refractive index change in the AgNPs colloidal solution, thus a shift in the resonance wavelength of LPFG that is surrounded by the colloidal solution. A sensitivity of 0.2nm shift/10-6M was achieved using such strategy. We believe the integration of nanoparticles with LPFG represents a promising sensing strategy for more advanced applications important for not only environmental but also health science.

The unique capability of fiber-optic sensors over traditional sensors enables the use of fiber-optic sensing network to realize effective railway monitoring systems. An all-fiber sensing network has many advantages because optical fibers are small, immune from EMI, corrosion free, and has extremely low transmission loss. Interferometric fiber sensors such as fibre Bragg gratings, Fabry-Perot interferometers, and Sagnac loop interferometers can measure a multitude of different physical parameters including strain, acceleration, displacement, and vibration. These are intrinsic sensors and they offer an important unique advantage that the measurands are encoded in wavelength, providing very high signal fidelity. More importantly, it allow the realization of a truly integrated monitoring system, eliminating the need to integrate large number of different conventional monitoring systems, thus improving system maintainability and data manipulation. Railway systems in Hong Kong and Singapore are using fiber-optic sensing networks to switch from scheduled to condition-based and predictive maintenance to meet the rising expectations from passengers for better and more reliable services. The optical sensing networks are installed on in-service trains and rail tracks to monitor the health of tracks and trains, respectively. In addition to real-time monitoring functions that support the operation of the railway and condition-based maintenance, the system also continuously acquire massive amounts of train and track condition data to provide indispensable information for prognostic maintenance. The train condition monitoring system has successfully detected train structure problems that could cause serious accident. The optical fiber sensing systems installed have proven to be highly reliable and require minimal maintenance.

The focus of this paper is on the applications of fiber optic sensors for subsurface monitoring. Case studies on the deployment of multi-point fiber optic sensors for real-time monitoring of In-situ Thermal Remediation (ISTR) of contaminated lands will be reviewed. The adoption of fiber optic sensors for this type of application stems from unique features and technical capabilities unmatched by legacy electronic sensors; these features include low-loss remote sensing, the ability to work in harsh environments, immunity to electromagnetic interference, small size, and capability of integrated and distributed sensing.

Harsh environment sensor applications are becoming more accessible due to the implementation of single-crystal optical materials and devices. In particular, fossil energy applications like gas turbines or coal gassifiers require new, more robust sensing technologies compatible with modern control schemes. Fabricating common devices in sapphire or YAG fibers rather than standard fused silica can extend the operating temperature range significantly beyond the current state of the art. Here, we discuss configuration of our Laser Heated Pedestal growth (LHPG) system with a novel control algorithm that permits the growth of fibers with non-uniform diameters along the fiber’s length. This algorithm controls the molten zone height, laser power, and drawing rates simultaneously to reduce the mismatch between instantaneous diameter changes and current diameter. We detail the range of structural possibilities achievable using this control technique, and subsequently evaluate the spectral properties of as-grown devices like sapphire long-period gratings. Finally, we make recommendations regarding new single-crystal sensor devices which will be shown to maintain operational stability over a wide range of operating temperatures.

A very high-speed fiber Bragg grating sensing system has been used to characterize energetic materials in card gap and Russian DDT tests^1,2. This paper reviews the system capability of measuring the position, velocity, pressure, and temperature associated with energetic events. A readout system based on optical beam conditioning and high-speed detectors sends data from fiber Bragg grating sensors under extreme environments to a digital oscilloscope where events that occur on the order of a few nanoseconds can be resolved.

Fiber Bragg gratings (FBGs) are inherently sensitive to temperature and mechanical deformation. Coating and packaging the fiber by particular materials which are responsive to certain parameters can extend the range of sensing capabilities of FBG-based fiber optic sensors. In this study, a stimuli responsive polymeric material is developed to behave reversibly when exposed to environments with different pH concentrations. Protonation and deprotonation of acidic or basic pendant groups on the polymer cause a pH-dependent osmotic pressure difference which leads to the swelling and deswelling of the polymer relative to the external conditions. This propensity to swell can be translated into a strain which is detected by the FBG. In this work, the FBG section of a fiber optic is coated with a custom designed and nanostructured polymer materials. Various super porous polymers have been developed by tuning the micro and nanostructure of the custom-designed polymer to explore the relationship between the polymer mechanical properties and the strain induced on the FBG and investigate optimal formulations with sufficient sensitivity. It was observed that changing the concentration of porosity in the polymer leads to different time scales for swelling and consequently, sensor response time. The optimized super-porous polymer coated on the fiber showed a reversible response to pH over a wide range (3 to 8). The as-developed quasi-distributed FBG pH sensor cable can be used for real-time monitoring of chemical substances in harsh environments such as chemical and wastewater treatment plants, and also in smart greenhouses.

Rapid, accurate, and real-time measurements of ocean salinity are of great importance for a host of scientific, commercial and defense applications. We demonstrate a highly sensitive, fast-responding fiber-optic salinity sensor that integrates long-period fiber gratings (LPFG) with ionic strength-responsive hydrogel. Submicron-thick hydrogels were synthesized via layer-by-layer (LbL) assembly of partially quaternized poly(4-vinyl pyridine) (qP4VP) and poly(acrylic acid) (PAA), followed by chemical crosslinking of qP4VP and removal of PAA. Spectroscopic ellipsometry studies of hydrogels with 37% quaternized qP4VP revealed robust and reversible swelling/deswelling behavior of the coatings in solutions with different salt concentrations at pH 7.5. The performance of hydrogel-coated LPFG for the monitoring of sodium chloride solution in the salinity relevant range of 0.4 to 0.8 M was investigated. The swelling/deswelling process induced remarkable changes in the refractive index of the coating, resulting in robust shift in the resonance wavelength of LPFG. The hydrogel-coated LPFG exhibited a sensitivity of 7 nm/M with a response time less than 1 second. There is a linear correlation between the resonance wavelength shift and the salt concentration, making quantification of measured salinity straightforward.

Novel implementations of fiber Bragg gratings (FBG) and phase shifter in loop mirror configurations enable monitoring of environmental conditions at both terminals of the loop. These implementations allow accessing the sensed signals in both directions (east and west) at locations far from the sensing position using regular fiber transmission schemes. Optical light of a 1550 nm wideband LED diode (100nm) is launched into the fiber loop that has the FBG and phase shifter. The center wavelength of the FBG varies with changes of conditions affecting the grating such as temperature, pressure, stress and strain. As a result, the center wavelength of the generated continuous wave (CW) optical signal in the fiber loop mirror sensor shifts based on these conditions at the sensing location. Controlling the phase of the phase shifter determines the direction of the generated CW sensed signal to the transmission path or reflection path of the optical loop mirror. Numerical simulations were conducted, which demonstrated the operation of the fiber sensor design.

Fiber Bragg Grating (FBG) sensors may probe ultrafast changes in pressure caused by shock waves propagating in solid and liquid media impacted by high velocity projectiles. The FBG spectra are measured using an optical system comprising economically priced electro-optical components offering 5 nsec temporal resolution and 0.8 – 1.6 nm spectral resolution. We present results showing evolution of 5 kBar shock wave pressure in approx. 100 nsec, as well as the dependence of the FBG response on the physical length of the sensor (1mm and 0.1mm), and on the relative orientation between the FBG axis and the shock wavefront.

This presentation reports our findings in the fabrication and evaluation of nanostructured sapphire optical fiber (NSOF) for surface-enhanced Raman spectroscopy (SERS) sensing at elevated temperatures. Specifically, we systematically investigated the morphological stability and the mechanical properties of the anodized aluminum oxide (AAO) cladding of NSOF after cyclic thermal treatment at temperatures ranging from 1000°-1500°C with the pore diameter, interpore distance, as well as the cladding thickness as parameters. The cladding/sapphire fiber interface integrity due to possible mismatch in the coefficient of thermal expansion between AAO and sapphire fiber was also examined. We also immobilized Ag nanoparticles in the pore channels of AAO cladding for in-situ SERS measurements in a hot furnace. We will show that Ag nanoparticles confined in the nanoscopic pore channels of AAO exhibit much better thermal stability, compared with those on a planar substrate, making high-temperature harsh environment SERS sensing possible with NSOF.

This paper presents a characterization of ultrasonic generation from the sidewall of an optical fiber. Ultrasonic generation from an optical fiber could have broad applications, such as ultrasonic imaging, ultrasonic nondestructive test (NDT), and acoustic pyrometers and so on. There are many advantages of these fiber-optic ultrasonic transducers, such as small size, light weight, ease of use, and immunity to electromagnetic interference. This paper discusses two main factors that will influence the signal strength generated by the sidewall of the ultrasonic generator. The two factors are the thickness of the photoabsorption material and the optical energy emitted from the sidewall fiber. A 20 mm length fiber-optic sidewall ultrasonic generator was used for the characterization. Gold-nanocomposite materials were used as the photoabsorption material. A hydrophone was used to detect the ultrasonic signal. The ultrasonic time and frequency profile and the ultrasonic field distribution at the longitudinal section of this fiber-optic sidewall ultrasonic generator have been characterized in this paper.

We report the experimental performance and simulation of a multiwatt two-stage TDFA using an L-band (1567 nm) shared pump source. We focus on the behavior of the amplifier for the parameters of output power P_out, gain G, noise figure NF, signal wavelength λ_s, and dynamic range. We measure the spectral performance of the TDFA for three specific wavelengths (λ_s= 1909, 1952, and 2004 nm) chosen to cover the low-, mid-, and upper-wavelength operating regions of the wideband amplifier. We also compare the performance of the two-stage shared pump TDFA with a one stage shared pump amplifier. Experimental results are in good agreement with simulation.

Detection in chemical sensing which needs to be carried out in a specific controlled environment, becomes complex in multivariate environment. This complication is caused by chemical interference, sensor degradation or drifting of the signals with time. A minute drifting or overlapping of the signals affects the calibration, especially in the detection of sub-ppm level of concentration of any chemical species. The presence of other compounds can well interfere providing false positive readings, deterring calibration of the system in precise quantification of any compound. This problem is known to also happen in our optical fiber sensor for the detection of ammonia. A clad-modified polymer optical fiber sensor for ammonia detection is explored in this work where oxazine 170 per chlorate dye is used as a recognition element to detect ammonia. The sensor was tested in water media and the sensitivity of the sensor we found was 0.0006 ppm^-1cm^-2. However, the lower sensitivity causes significant overlaps in between signals corresponding to different concentrations. To resolve this problem, multivariate analysis method, such as principal component analysis (PCA) was explored to interpret the datasets for precision of measurement and classification of each concentration. PCA generates unique regression curve which represents each concentration of ammonia considering principle components. The significance of this research lies in its versatility dealing with the existing challenge of calibration of sub-ppm level measurement of any volatile compound, such as ammonia.

A dual modality fibre sensing system for simultaneous monitoring of temperature and acoustic disturbances in power cables is demonstrated. The system combines Raman OTDR (Optical Time-Domain Reflectometry) and Rayleigh phase- OTDR and is based on a single shared laser source. The performance of the system is demonstrated with absolute temperature measurements in heated fibre sections and detection of echoes from disturbance events. To the best of our knowledge, this is the first single-source simultaneous temperature and disturbance sensing in single-mode fibre. Finally, it is demonstrated that localised temperature variations and acoustic disturbances, such as cable strumming and strike, can be detected in an onshore 30 kV power cable.

Traditionally, metallic vessels have to comply with specific regulation rules (Pressure Equipment Directive from the European Parliament) involving periodic re-qualifications. However, for high pressure composite vessels, standards, and particularly non-destructive techniques, have to be developed, tested and validated. In this new frame, a research project has been set up for VECEP program (VEga launcher Consolidation and Evolution Preparation Programme) aiming at funding developments to set-up new control/monitoring techniques applicable to composite vessels, for both future regulatory and inspection needs. To reach the market, these techniques have also to be cost-effective in comparison with traditional ones. To monitor such vessels behavior and finalize the sensor system to the detection of structural defects, CIRA and AVIO have conducted R and D activities based on high resolution distributed strain profiles sensitivity analysis along single mode optical fibers. To elaborate this method, preliminary tests were carried out for testing different bonding agents and different surface finishing, on a set of representative coupon from composite overwrapped pressure vessels under bending incremental solicitation until reaching ultimate load. Additionally, their sensitivity, analyzed during the test, provided additional valuable data about structure integrity. A mechanical criterion based on OFDR (Optical Frequency Domain Reflectometry) differential strain profiles analysis was preliminarily implemented in order to evidence structural anomalies during the test.

Real-time temperature mapping that solves local overheating problems is important for obtaining an optimized thermal design for high-efficiency power transformers. Internal temperature monitoring of operating power transformers can also be leveraged for asset monitoring applications targeting at-fault detection enabling condition-based maintenance programs. However, transformers present a variety of challenging sensing environments such as high-levels of electromagnetic interference and limited space for conventional sensing systems in which to operate. Immersion of some power transformers in insulation oils for thermal management during operation and the presence of relatively large and time varying electrical and occasional magnetic fields make sensing technologies requiring electrical wires or active power at sensing locations highly undesirable. In this work, we investigate dynamic thermal response of a standard single-mode optical fiber instrumented on compact transformer cores by using an optical frequency-domain reflectometry scheme. Correlation between conventional temperature sensing methods and fiber-optic sensing results as well as trade-offs between spatial resolution and temperature measurement accuracy is discussed and spatially resolved real-time monitoring of temperatures in energized transformers is demonstrated.

Raman-based distributed temperature sensing (DTS) systems have found widely ranging commercial applications. For extended distance DTS measurement the spatial resolution is sometimes limited through pulse broadening caused by the intermodal dispersion of graded index multimode (GIMM) optical fiber. In this paper we describe the design, manufacturing and performance of a high bandwidth GIMM fiber, with bandwidth optimized at 1550 nm. Using this fiber, we demonstrate distributed temperature measurement with an extended distance of 32 km and spatial resolution of 3 meters. In comparison, the spatial resolution of an OM4 (bandwidth optimized for use at 850 nm) fiber typically used in temperature sensing over 32km is more than 10 meters.

We report an experimental study erbium-doped fiber laser for gas pressure detection in the L-band wavelength region by laser intracavity absorption spectroscopy. By using a high-birefringence fiber optical loop mirror as spectral filter within the ring cavity laser, the wavelength of the generated laser line is finely selected and tuned in a range of ~10 nm in order to select the wavelength where the gas absorption line is exhibited. Experimental results for detection of CO₂ pressure with absorption at 1573.2 nm are shown and discussed. The proposed fiber laser sensor exhibits reliability and stability for gas detection with absorption in the L-band such as CO₂, CO, and H₂S.

This paper presents a power over fiber (PoF) voltage and current sensor to be used in high voltage applications. The current sensor is based on a microelectronic hall sensor and the voltage sensor is based on a capacitive voltage divider. The measured signals are transmitted from the unit at high voltage to the unit at ground potential using an innovative pulse width modulation (PWM) multiplexed method. This technique is experimentally demonstrated by measuring voltages and currents up to 1.6 kV and 100 A, respectively.

Distributed fiber optic systems based on Brillouin Time Domain Reflectrometry BOTDR offer an exclusive solution for monitoring the load of large building structures such as buildings, bridges, tunnels, etc. Deformation measurements use special optical cables with added reinforcement element and a closer bond between cable jacket and fiber optic to achieve high sensitivity to mechanical deformation. Alternatively, cheaper standard optical fiber cables with single-fiber optic fibers are used. Alternatively, there is possible to use cheaper standard optical cables with single mode optical fibers. The paper deals with the analysis of the suitability of standard optical cables for the deformations measurement using a distributed BOTDR system. Several standard types of telecommunication optical cables were implemented into concrete beams and bent in a hydraulic press. The main result of this paper is the deformation sensitivities determination of optical cables for load measurement and the suitability analysis for embedding into the concrete beam with regard to long life.

Fiber optic Bragg gratings are among the most widely used fiber optic sensors. It uses in dangerous explosive environments thanks to the electrical passivity of the sensor itself, but also in applications with high electromagnetic disturbance. Maintaining immunity of the sensor to electromagnetic interference requires non-electrical encapsulation material. This paper describes the encapsulation of the FBG sensor on a plastic plate fixed by gluing to the monitored structure. The proposed FBG sensor is suitable for measuring deformations or vibrations of iron and concrete structures. Due to the material used, the FBG sensor keeps resistance to electromagnetic interference, humidity, and corrosion. The results show the almost equal sensitivity of FBG strain sensors mounted on a metal carrier when measuring very small deformations and vibrations. The proposed FBG sensor concept reduces the cost of its manufacturing by using a 3D printer to produce the plastic carrier.

Optical fibers can be used in many ways. In addition to telecommunication applications, they are increasingly used in sensory applications as well. The temperature measurement is one of many areas of using of optical fibers. The most commonly used are DTS (Distributed Temperature Sensor) also known as Raman optical time-domain reflectometry (OTDR). The using of fiber Bragg gratings (FBGs) is one of the other options. This paper describes our approach to temperature measurement using optical fibers, heat-sensitive materials and specialty products based on polydimethylsiloxane (PDMS) and other materials. The temperature sensor created by us can also be used in an unfavorable environment (chemical influences, etc.) in the temperature range up to approx. 400 K.

Optical fibers have many uses and in addition to communications applications for example in fiber-optic sensor applications. The area of pressure and vibration measurement is one of the many fields of applicability of optical fibers too. Very often, the fiber Bragg gratings (FBGs) is also used for medical applications. This paper describes our alternative approach to addressing this issue, based on standard optical fibers, special optical connections, PDMS-based products, and other materials. It is known that the vibrations of some machines can negatively affect the human body. The vibration detector created by us can find a use for indicative measurement of these negative vibrations of machines, especially in the frequency range up to about 100 Hz.

Nowadays optical fibers are used in many industries. In addition to the data transmission, many sensor applications with using some special optical fibers are expanding. Faraday's phenomenon is often used for detection of the magnetic field. The size of the deviation of the polarization plane of optical radiation passing through the optical fiber is evaluated in Faraday's phenomenon that occurs due to the influence of the external magnetic field. This paper describes our new approach to addressing this issue using standard telecommunication fibers, PDMS-based optical connections, specialty products and some magnetic field sensitive materials. Our detector of the magnetic field can find a use for simplified measurement of weak magnetic fields up to 0.3 T.

This article deals with the implementation of fiber-optic Bragg Grating Sensors signal processing methods for the detection of respiration rate, pulse rate, and body temperature. The sensed signals are influenced by a variety of interferences (motion artifact, environmental noise, etc.). Clinically relevant information is only available at certain frequencies, while the utilized optical sensor is able to cover relatively broad spectrum range. For real-world medical applications, the desired signal needs to be separated from the noise, which can often be other clinical information. This article introduces a virtual instrument for the extraction of clinically relevant information, such as respiration and heart rate, and body temperature. Frequency-selective filters were implemented in the proposed application. The functionality of the application was tested on real data using the FBGUARD and LabVIEW evaluation unit. The results were verified with commercially available devices and also statistically processed. Experimental results have shown that Fiber-Optic Bragg Grating Sensor signal processing is a key aspect of a successful incorporation of these sensors into clinical practice.

This article is focused on the advanced signal processing methods for third-generation sensors requirements. These sensors are based on the influence of a non-electric quantities on a light beam. This generation of sensors, also known as fiber optic sensors, is based on the principles of optoelectronics and integrated optics. These sensors are used in a variety of real-world applications such as biomedical engineering, industry 4.0, transportation, etc. In real-world applications, the signals sensed by these sensors are distorted by a variety of interference due to its sensitivity. We often encounter the problem that the useful information and the interference overlap in the spectral domain, therefore we cannot use conventional frequency selective filters. This article focuses on the implementation of adaptive filtering, Principle Component Analysis and Independent Component Analysis to reduce the interference in various application areas. The methods were tested on real data. This paper offers the comparison of the tested methods in different application areas.

This paper deals with methods for processing signals from an optical interferometer to monitor vital signs (Respiration Rate and Heart Rate). Optical interferometer signals are contaminated by variety of technical and biological artifacts (motion artifacts, hospital/patient-generated noise, etc.). Tested optical sensors are very sensitive, it therefore crucial to reduce such unwanted signals. In this article, a complex application for processing the signals from optical interferometer based on virtual instrumentation was developed. The experiments were conducted on data sensed by optical interferometer using a National Instruments card NI USB-6216 BNC and application in the LabVIEW environment. Frequency selective filters were tested in the experiments. The results obtained by using optical interferometer were statistically compared with the ECG and PCG reference. According to the results, optical interferometers are able to measure both the Respiration and Heart Rate under the given conditions. Unfortunately, the measurement is very difficult to replicate in the hospital environment, which is the primary reason why these methods are not used in clinical practice.

The publication describes the use of fiber-optic Bragg sensors in biomedical applications. Fiber-optic sensors are characterized by the immunity to electromagnetic interference (EMI) and by the electrical passivity. Currently, these types of sensors are increasingly being used in biomedical applications, for example, for measuring the temperature or the heart and respiratory rate of the human body. It is very important to encapsulate these types of sensors because encapsulation itself has a major effect on the sensor functionality. This publication describes a comparison of two materials - polymer polydimethylsiloxane (PDMS) and fiberglass (fiberglass is a composite material made up of glass fiber (fabric) and cured synthetic resin). The comparison was conducted by a series of laboratory experiments with ten volunteers with their written consent. Acquired data were compared by the Bland-Altman method.

The article describes the use of fiber-optic interferometer in the rail transport. We proposed a measuring sensor system based on the Mach-Zehnder interferometer. The basic tracked parameter of vehicles are detection (count of vehicles). The proposed system was tested in the real tram traffic. Altogether, 435 vehicles were detected with 100 % success. The basic advantages of the solution include immunity to electromagnetic interference (EMI) and the ability to remotely evaluate information about the traffic.

This article focuses on determining the attenuation properties and homogeneity of cylindrical waveguides made of specific polymer materials. Cylindrical waveguides were made from clear silicone rubbers based on polydimethylsiloxane (PDMS) - Sylgard 184 and RTV615. The mixture of PDMS and the curing agent was homogenized by means of an ultrasonic bath for two different frequencies (20 and 40 kHz) and for different time points (5, 10, and 20 minutes). Curing of the waveguides took place in a heat box at a constant temperature of 70 ° C ± 3 ° C. This procedure was applied to a total of 180 cylindrical waveguides with the same dimensions and diameter of the core. Attenuation dependencies were tested for two different light emitting diodes (LEDs) with central wavelengths of 470 and 625 nm. The analysis was conducted with respect to the use of PDMS in fiber-optic applications for its good mechanical and optical properties.

The authors focused on the problem of production and measurement parameters of optical couplers created from polymer polydimethylsiloxane (PDMS) for fiber-optic sensors. For the production of optical couplers, clear two-component elastomers Sylgard 184 and RTV 615 (manufacturer Dow Corning) was used. These elastomers offer a suitable combination of mechanical and optical properties. For the experiments, a total of 50 optical couplers were created. The effect of thermal aging on their transfer properties was analyzed. The thermal load was performed in a temperature box at 100 and 200 ° C under constant conditions for 48 hours. Measurements were made for a wavelength of 1550 nm and 1310 nm.

An approach is presented for measuring the dynamic variations in refractive index (RI) of Graphene Oxide (GO) based optical gas‐sensors [1‐ 3] upon their exposure to gases, using thin‐film interference method [4]. The approach is simple yet effective, and also is physically integratable into the sensing system, a required attribute for being able to measure the dynamically changing RI in response to the ongoing interactions with the analyte. The details can be found in our journal paper [5].

In the field of earthquake seismology, a new class of seismic wave has emerged that is associated with episodic tremor and slow-slip activity at tectonic plate boundaries. In order to detect and characterize these weak seismic waves, a high dynamic range optical sensor capable of remotely measuring minute displacements over a broad frequency range is being developed. The optical fiber Bragg grating sensor system is compact and inexpensive, and is well suited for collecting real-time data from remote sites deep underground within boreholes. A PZT mechanical vibration transducer simulates the small displacements created by a mechanical sensor’s response to the tremor. Low-frequency waveforms in the 1–20 Hz band are used to drive the PZT actuator. Stable detector output demonstrates optical sensor sensitivity to vibrational displacements less than 400 nm without using any digital filtering of the output signal.

FemtoFiberTec introduces the second generation of isotropic femtosecond point -by-point written FBGs with near zero polarization dependence in central wavelength and extremely low scattering loss . These features result in extremely precise static measurements required for accurate temperature monitoring and allow flexible sensor arrangement, also for large sensor assemblies and non-stationary installations.