Fiber Optic Sensors

This work presents a scheme for in situ monitoring of thin-film growth. A fiber-optic sensor based on Fabry–Perot interferometric technique has been established for the first time to monitor in situ growth of thin films. This was applied for determining thickness of cadmium sulfide (CdS) thin films during growth. The fabrication process of CdS film was carried out in 30 mM cadmium acetate and thioacetamide solution at 60°C temperature. The estimated thickness determined during the growth was verified by scanning electron microscopy. This study shows that in situ measurement of the thickness of thin films is feasible by this new technique, and a close match of the estimated thickness was achieved.

Calixarenes are interesting building blocks in supramolecular receptor design. They can be easily functionalized to give the desired guest binding and sequestration properties. We demonstrate here the use of simple alkylated calixarenes as novel NO 2 sensors. Upon reacting with gaseous NO 2 , alkylated calixarenes form stable calixarene-NO + (nitrosonium) complexes that have a deep purple color. This specific and selective formation of the colored complex was used to develop a fiber optic based colorimetric NO 2 sensor. Several alkylated calixarenes are used and tested as sensing materials. The calixarene compound was immobilized on a fine mesh silica-gel coated thin layer chromatography plate. The sensing plate was coupled with a fiber optic based photodetector. Gas samples were sampled in a manner where they impinged on the surface of sensing plate. The light transmission through the plate was continuously monitored. For a 5 min sample, the limit of detection was 0.54 ppmv with 1,3-alternate O-hexyl calix[4]arene (1a). There were no significant response differences between different conformations of calixarenes such as 1,3-alternate or cone. This chemistry can form the basis of a colorimetric sensor that relies on extant filter tape technology.

A new fiber strain sensor based on the Laser-Self-Mixing effect in Distributed Feedback Laser diodes is presented. Compared with existing fiber strain sensors based on Fiber Bragg Gratings, that are sensitive to local strain, our device achieves comparable sensitivity (~ 1 /le) distributed along the whole fib er length and requires a much simpler electronics. The sensor is based on the interferometric principle of the laser-self-mixing in the moderate feedback regime, whereby the fiber strain results in a variation of the optical path-length seen by the radiation reflected by the end facet of the fiber itself. Increasing or decreasing strain recognition is directly provided by the sign of the sawtooth-like fringes derivative.

Artur Dybko, Światłowodowy czujnik do pomiaru stężenia jonów hydroniowych, Praca dyplomowa magisterska, Instytut Podstaw Elektroniki, Politechnika Warszawska, 1990  (okładka, spis treści, dedykacja)
Wstęp,
Przegląd konstrukcji pH-metrów światłowodowych,
Wybór metody pomiarowyej,
Wyniki prac doświadczalnych,
Sugestie dalszych prac,
Dodatek chemiczny
Literatura.

An optical fiber sensor has been developed and applied to measure frequency of water waves based on wave induced polarization change of the light. The fiber sensor can accurately detect water wave frequency for regular and irregular waves. The optimum sag of sensing fiber to the sensor output's linearity has been studied. The agreement of the fiber sensor and wave gauge in frequency and time domain suggests that the fiber sensor has great potential for passive acoustic sensing and wave monitoring.

—Fiber optic sensors have become a mainstream sensing technology within a large array of applications due to their inherent benefits. They are now used significantly in structural health monitoring, and are an essential solution for monitoring harsh environments. Since their first development over 30 years ago, they have also found promise in security applications. Fibre Bragg grating (FBG) sensors are one of the most exciting developments in the field of optical fibre sensors in recent years. Compared with conventional fibre-optic sensors, FBG sensors have a number of distinguishing advantages. Significant progress has been made in applications to strain and temperature measurements. FBG sensors prove to be one of the most promising candidates for fibre-optic smart structures.This paper reviews all of the optical fiber-based techniques used in physical intrusion detection systems. This paper demonstrates with different setup the FBG sensor for intrusion detection.

The growing interest in the development of smart textiles for medical applications is driven by the aim to increase the mobility of patients who need a continuous monitoring of such physiological parameters. At the same time, the use of fiber optic sensors (FOSs) is gaining large acceptance as an alternative to traditional electrical and mechanical sensors for the monitoring of thermal and mechanical parameters. The potential impact of FOSs is related to their good metrological properties, their small size and their flexibility, as well as to their immunity from electromagnetic field. Their main advantage is the possibility to use textile based on fiber optic in a magnetic resonance imaging environment, where standard electronic sensors cannot be employed. This last feature makes FOSs suitable for monitoring biological parameters (e.g., respiratory and heartbeat monitoring) during magnetic resonance procedures. Research interest in combining FOSs and textiles into a single structure...

In this article a wearable belt that simultaneously measures the rates of the heartbeat and respiration using an into textile embedded single fiber Bragg grating (FBG) sensor is presented and realized. A miniature interrogator FBGT-600 from Redondo-USA has been used for the measurements. The measured signal has been processed and both the heartbeat and the respiration signals have been separated and visualized.The achieved data proved to be in-line with the common known values measured by other commercial available vital signs measurement systems.

Ryszard Romaniuk, Warsaw University of Technology, Tailored optical fibers technology, This report contains a comprehensive description of the basic and engineering, including some practical and application, aspects of tailored optical fibers (analysis, design, fabrication and measurements) such as signal transmission properties, optical signal transformation, fiber materials and fabrication processes, as well as real fiber characteristics and environmental sensitivities. Tailored optical fibers are defined here generally as the ones not designed directly for long-haul applications. Detailed data on the optical, thermal, chemical and mechanical properties of various fiber materials and optical filaments researched and measured by the author and his co-workers at Biaglass Co. are described. The fabrication processes of optical fibers are also described from the viewpoint of understanding what factors are important in the manufacture of special fibers. The modified multicrucible process (MMC), which has been co-developed by the author, is described in detail, as well as mosaic assembling technology, and hybrid ones – leading to very complex filamentary optical guiding structures. Brief review of fundamental kinds of studied tailored fibers, associated design problems and signal properties leads to a list of potential applications as photonic functional devices. Design algorithms to fulfill some of the application requirements and their theoretical background as well as hardware realization are described. The report contains also some practical information for tailored optical fibers users and photonic components, circuits and systems designers.

The health diagnosis of agricultural structures is critical to detecting damages such as cracks in concrete, corrosion, spalling, and delamination. Agricultural structures are susceptible to environmental degradation due to frequent exposure to water, organic effluent, farm chemicals, structural loading, and unloading. Various sensors have been employed for accurate and real-time monitoring of agricultural building structures, including electrochemical, ultrasonic, fiber-optic, piezoelectric, wireless, fiber Bragg grating sensors, and self-sensing concrete. The cost–benefits of each type of sensor and utility in a farm environment are explored in the review. Current literature suggests that the functionality of sensors has improved with progress in technology. Notable improvements made with the progress in technology include better accuracy of the measurements, reduction of signal-to-noise ratio, and transmission speed, and the deployment of machine learning, deep learning, and arti...

Phase holdups were measured in the riser section of a gas-liquid-solid circulating fluidized bed (GLSCFB). Electrical resistance tomography (ERT) as a non-invasive imaging technique, pressure transducers (PTs) and fibre optic probes were employed. Water was used as continuous and conductive phase, air as the gas phase and glass beads as solid nonconductive phases. ERT technique is based on conductivity measurement of the continuous phase (water in this study), which provides color-coded cross-sectional view of phases with a frequency of up to 250 images per second. The local conductivity measured by a number of electrodes located at the periphery of the plane was then further converted into a local phase concentration distribution based on Maxwell's relation. The results obtained by PTs, when combined with ERT results, were used to determine gas and solid holdups. Fibre optic probe was also employed to measure gas holdup independently. To measure gas and solid holdup, a model was introduced to exploit the fibre optic data in differentiating gas bubbles from solid particles in the riser. Radial profiles of the phase holdups were determined.

 Robotics is the branch of technology that deals with the design, construction, operation, and application of robots, as well as computer systems for their control, sensory feedback, and information processing.  These technologies deal with automated machines that can take the place of humans in dangerous environments or manufacturing processes, or resemble humans in appearance, behavior, and/or cognition.  Many of today's robots are inspired by nature contributing to the field of bio-inspired robotics.

Ryszard Romaniuk (Warsaw University of Technology), Praca stanowi wprowadzenie do wybranych zagadnień obecnego stanu wiedzy w zakresie teorii, technologii i zagadnień aplikacyjnych światłowodów kształtowanych. Jest przeznaczona dla studentów elektroniki i fizyki, doktorantów, inżynierów praktyków i pracowników naukowych, którzy pragną poznać, w aspektach podstawowych i stosowanych, tą stosunkowo nową i dynamicznie rozwijającą się dziedzinę fotoniki światłowodowej. Zamierzeniem autora jest, przy pomocy tej pracy, podjąć próbę rozszerzenia znajomości techniki światłowodów kształtowanych wśród szerszego kręgu inżynierów. W celu osiągnięcia tego zamierzenia przedstawiono wyczerpująco poszczególne zagadnienia teoretyczne, analityczne, projektowe, technologiczne, konstrukcyjne i aplikacyjne w kontekście fizycznym, chemicznym i technicznym starając się utrzymać pełną precyzję dyskusji naukowo-badawczej.
Technika światłowodów kształtowanych oferuje znacznie szerszy wybór narzędzi projektowania samego włókna optycznego i następnie wykonywanych z niego elementów i urządzeń światłowodowych, niż klasyczna technika światłowodów telekomunikacyjnych. Cena, którą płacimy za rozszerzenie swobody projektowania są znacznie większe straty jednostkowe światłowodów, gorsze właściwości mechaniczne i słabsza stabilność chemiczna. Świat praktycznych zastosowań włókien optycznych nie zdecydował jeszcze obecnie czy jest to cena warta zapłacenia. Niniejsza praca, poprzez szeroką analizę aktualnych problemów badawczych i technicznych, próbuje znaleźć kilka nowych przyczynków do takiej, ewentualnie pozytywnej, odpowiedzi. W najszerszym ujęciu, autor próbuje odpowiedzieć na pytania dotyczące „konkurencji” w zastosowaniach światłowodów telekomunikacyjnych i kształtowanych. Czy nominalne charakterystyki światłowodów kształtowanych predestynują je do zastosowań np. w trudnych warunkach środowiskowych w przemyśle, w technice wojskowej, motoryzacyjnej, lub fotonicznych systemach monitorowania stanu rozległych technicznych systemów municypalnych a także stanu środowiska naturalnego.

Fiber Bragg Grating (FBG) technology is used by several industries for a variety of applications. Fiber Bragg grating filters out selective wavelengths by reflecting them and transmitting others. It is done by altering the refractive indices inside the core of the fiber (PC Mag, Fibre Bragg Grating). The reflected wavelength is used for several measuring and sensing applications for physical parameters like temperature, vibration, electric current, strain, pressure and many more (Intech Open, A Guide to Fiber Bragg).

Structural Health Monitoring (SHM) can be understood as the integration of sensing and intelligence to enable the structure loading and damage-provoking conditions to be recorded, analyzed, localized, and predicted in such a way that nondestructive testing becomes an integral part of them. In addition, SHM systems can include actuation devices to take proper reaction or correction actions. SHM sensing requirements are very well suited for the application of optical fiber sensors (OFS), in particular, to provide integrated, quasi-distributed or fully distributed technologies. In this tutorial, after a brief introduction of the basic SHM concepts, the main fiber optic techniques available for this application are reviewed, emphasizing the four most successful ones. Then, several examples of the use of OFS in real structures are also addressed, including those from the renewable energy, transportation, civil engineering and the oil and gas industry sectors. Finally, the most relevant current technical challenges and the key sector markets are identified. This paper provides a tutorial introduction, a comprehensive background on this subject and also a forecast of the future of OFS for SHM. In addition, some of the challenges to be faced in the near future are addressed.

Monograph presents the results of development of fiber optic chemical sensors which are capable to measure series of admixtures in the air or water. Compared with conventional methods of chemical analysis, convenient miniature fiber optic sensors can be analyzed directly in one step and in any inaccessible places for long distance. These small devises permit avoid any pre-selection and preparation of samples. Due to such characteristics of the quartz fiber as corrosion resistance, spark and explosion, as well as the presence of a good fiber optic element base, such sensors are optimal for monitoring contamination stretches of the on-line mode. For example, the fiber optic sensor lines can encircle the perimeter of the plant, or ensure control shoreline of lakes, rivers and the sea. The book gives a comprehensive overview of the state of fiber-optic sensors, we set out to find new, innovative principles for the possibility of building a waveguide devices of this class, using a laser.

Optical Return Loss (ORL) is the total amount of light returned from an optical fiber relative to the injected light. ORL can adversely affect fiber optics systems which indirectly affects the quality of the fiber network. One of the effects of this loss (multiple reflections) contributes greatly to the noise levels at the optical detector. Optical Return Loss could be caused by intrinsic material scattering (Rayleigh scattering) and Fresnel reflection. This paper however, focuses on the investigation of ORL using an Optical Time Domain Reflectometer (OTDR) amongst Optical Continuous Wave Reflectometer (OCWR), Optical Low Coherence Reflectometer (OLCR), and Optical Frequency Domain Reflectometer (OFDR). The OTDR was able to establish the ORL in every portion of the fiber under test. An ORL average level of 72.54 dB was obtained over span length of 2.86709 – 2.868.11 km. This is beyond the acceptable tolerance level (32 dB) of both the transmission and receiving equipment suggesting serious problem with the links. By implication, ORL can be used to determine the overall efficiency or performance of a fiber plant.

A theoretical model for surface plasmon resonance (SPR) based tapered fiber optic sensor is proposed with three different taper profiles, namely, linear, parabolic, and exponential-linear. The effect of taper ratio and taper profiles on the sensor's performance is studied in detail and the design considerations for significantly enhanced sensitivity are reported. The study shows that the exponential-linear taper profile with high taper ratio provides the best performance. The physical reasons behind sensitivity enhancement due to taper ratio and taper profile are given, wherever required.

A review of optical fiber sensing demonstrations based on photonic crystal fibers is presented. The text is organized in five main sections: the first three deal with sensing approaches relying on fiber Bragg gratings, long-period gratings and interferometric structures; the fourth one reports applications of these fibers for gas and liquid sensing; finally, the last section focuses on the exploitation of nonlinear effects in photonic crystal fibers for sensing.

Keywords:
Coherent Detection, Local Oscillator, Sensitivity, Shot noise, Polarization Multiplexing.

Abstract:

The purpose of this project is to study the basis of optical coherent detection associated with digital signal processing and to design and implement such a receiver. The investigated coherent can be used to detect arbitrary complex modulation formats as it is capable of splitting polarization multiplexed signals and provides the real and imaginary parts of the optical field. After coherent detection, the signal is digitize to perform DSP in order to digitally obtain the clock from the signal received and compensate for the linear impairments that previously affected the signal. For that purpose the digital coherent receiver implemented is composed by three modules: the first module is a clock recovery that can obtain the clock signal from the received signal. A second module that, using Digital Signal Processing (DSP), is able to compensate Chromatic Dispersion (CD) and Polarization Mode Dispersion (PMD) using adaptive filters. These filters are programmed to use two kinds of adaptive algorithms: LMS and CMA, which can be previously selected. The third module is in charge of the phase noise estimation to compensate for the rotation that causes this impairment in the constellation sent. Two different architectures for phase noise estimation are compared. After designing the receiver in Matlab® we validate its functionality. For that we use the VPItransmissionMaker TM
tool in which we can simulate a realistic optical communication system, and, introducing our designed receiver model into the communication system
the receiver‟s capability to compensate CD, PMD and Phase Noise is studied. Furthermore, changing the optical communication system properties, we put the receiver ‟s robustness to test. We also change different configurations of the receiver and study how it influences the reception of the signal.

Optical fibers are transparent fibers, usually made of glass or plastic, for transmitting light. They are flexible strands roughly the diameter of a human hair. With the use of this latest technology, large amounts of data can be transmitted over long distances. During several years the optical fibers are used to broadcast light signals and audio signals, producing distortion-free sound. In addition, fiber optics is useful in medical procedures (for internal inspection of the body), automobiles, and aircraft.

AFIF SAIFUDDIN
10955005522

Date of Final Exam : 19 December 2013

Department of Electrical Engineering
Faculty of Science and Technology
State Islamic University of Sultan Syarif Kasim Riau
Soebrantas St. No. 155 Pekanbaru - Indonesia

ABSTRACT

Optical Fiber Channel has high capacity and high bit rate. Hybrid technology of Wavelength Division Multiplex and Gigabit Passive Optical Network will give rise to high bandwidth and high capacity network. Arrayed Waveguide Grating could be implemented as multiplexer and demultiplexer in order to acquire better performance. Channel spacing minimum, maximum number of fiber length, and maximum number of channel that could be implemented at model system was analised. Morevore, BER performance of AWG and WDM was be compared in this research. Based on simulation result, minimum channel spacing is 0.1 nm. Maximum number of optical fiber lengths that could be implemented is 90 km without repeter. In addition, the maximum number of channels that could be multiplexed is 64 channels. BER performance of AWG implementation as multiplexer and demultiplexer give better performance compared to WDM implementation.

Key Words : Arrayed Waveguide Grating, Wavelength Division Multiplex, Gigabit Passive Optical Network.

Most papers published on fiber optics and fiber optic sensors are so technical and the language is extremely complex that non experts in the field who wish to appreciate the basics of how these technologies work are thrown off when they pick a paper or a publication on the subject matter (in this case distributed fiber optic sensors) to read. This paper presents to the best of my knowledge in simple language, how distributed fiber optic sensors (BOTDA) work. We simplify the concepts of fiber optic communication, fiber optic sensors and then zoom in on distributed fiber optic sensors with Brillouin Optical Time Domain Analysis (BOTDA) sensors as a focus sensor to present the principles, theory and operation of distributed fiber optic sensors and their applications.

The fiber optic has been used not only in the communication system but also in leakage detection from the pipeline and the leakage monitoring for the dams as well. In several European countries such as Sweden, France, Germany, Switzerland and Austria, the leakage detection by fiber optic cable has been developed. With the measuring the temperature change surround the cable, it can indicate the location of the leakage point along the cable. One application of fiber optic for leakage detection is the Nam Ngum 2 dam, a CFRD in Lao PDR. Two cables were installed on the surface of the plinth; one of them has been heated for facilitating the temperature change. However, due to the limitation of usage fiber optic cable, the other geotechnical instruments are still needed for overall seepage monitoring.

Optical fiber sensor is evaluated for sinkhole detection under railway tunnels. Tests performed on a decametric structure equipped with embedded 110 m-cable interrogated by Brillouin-OTDR and OFDR showed great performances in accordance with finite-element calculations.

This article presents a three-layer index guided lead silicate (SF57) photonic crystal fiber which simultaneously promises to
yield large effective optical nonlinear coefficient and low anomalous dispersion that makes it suitable for supercontinuum
(SC) generation. At an operating wavelength 1550 nm, the typical optimized value of anomalous dispersion and effective
nonlinear coefficient turns out to be ~4 ps/km/nm and ~1078 W−1km−1, respectively. Through numerical simulation, it is
realized that the designed fiber promises to exhibit three octave spanning SC from 900 to 7200 nm using 50 fs ‘sech’
optical pulses of 5 kW peak power. Due to the cross-phase modulation and four-wave mixing processes, a long range of
red-shifted dispersive wave generated, which assists to achieve such large broadening. In addition, we have investigated
the compatibility of SC generation with input pulse peak power increment and briefly discussed the impact of nonlinear
processes on SC generation.

working life is normally needed to ensure its performance under expected applied loads. This usually involves investigation of cracking and damage due to applied loads, corrosion of steel, failure of bonds, excessive strain in concrete and reinforcing bars, critical deflection etc. The conventional techniques such as strain gauges, vibrating wires strain translucers, etc. have their own limitations. These sensors may not be functional and effective sensor throughout the life of structures. This being the position, the need of development of effective senor was being felt quite long. In recent years fiber optic based sensors have attracted considerable interest as non destructive structural health monitoring technique. In this research embedded fiber optic sensors are developed to monitor reinforced concrete beams. Embedded fiber optic sensor responded very well under the applied loads and any change in the intensity of light can be considered as a warning even before the cracks are visible on the outer surface. This characteristic of embedded fiber optic sensors can be used as a crack detection tools.

Providing a constant and perpetual energy source is a key design challenge for implantable medical devices. Harvesting energy from the human body and the surrounding is one of the possible solutions. Delivering energy from outside the body through different wireless media is another feasible solution. In this paper, we review different state-of-the-art methods that process " in-body " energy harvesting as well as " out-of-body" wireless power delivery. Details of the energy sources, transmission media, energy harvesting, coupling techniques and the required energy transducers will also be discussed. The merits and disadvantages of each approach will be presented. Different types of mechanisms have very different characteristics on their output voltage, amount of harvested power and power transfer efficiency. Therefore different types of power conditioning circuits are required. Issues of designing the building blocks for the power conditioning circuits for different energy harvesting or coupling mechanisms will be compared.

A single-mode non-adiabatic tapered optical fiber (NATOF) sensor was utilized for sensing the variation in refractive index (RI) with concentration of D-glucose in deionized water and measurement of the RI of amino acids (AAs) in carbohydrate solutions. This method showed a rewarding ability in understanding the basis of biomolecular interactions in biological systems. Due to high sensitivity, ease of application, low cost and real-time measurement, this method is more efficient in comparison with other techniques, such as calorimetric titration, NMR, UV absorption spectroscopy, x-ray crystallography, computer calculations, kinetic studies and chromatography data. The NATOF is fabricated by the heat pulling method, utilizing a CO 2 laser. The limit of detection of the NATOF was 55 ppm for a D-glucose concentration ranging from 0 to 80 mg ml −1 , and the limit of detection of the RI measurement corresponding to these concentrations in the range from 1.3330 to 1.3447 was 8.2 × 10 −6 as a refractometer sensor. The response of the NATOF shows that different kinds of interactions of various groups of AAs, such as L-alanine, L-leucine and L-cysteine with D-glucose, sucrose and water molecules, depend on functional groups in AAs such as OH, SH, CH 2 , NH + 3 and COO −. These results can be interpreted in terms of solute–solute and solute–solvent interactions and the structure making/breaking ability of solutes in the given solution. Such a study helps in the better understanding of the interactions occurring between AA molecules and entities present in biological matrices.

The last couple of decades had witnessed a steep rise in extensive research of optoelectronic and fiber optical communication fields, which resulted in applications focused initially in military, aerospace equipments, and later in health monitoring for medicine, heritage culture and various engineering fields. Health monitoring has attracted the effort of many engineers throughout the world and is fast emerging as a pioneering field. It is helping to improve world economy in two ways; first, directly by providing longevity to all the important structures and secondly, by prevention of untimely failure leading to loss of life and money. This field is very vast, consisting of traditional monitoring methods as well as smart system based methods. The fiber optics belong to finest class of smart materials, there are many types and classifications of fiber optics based on necessity, manufacturer and the end user. This paper, gives a complete over view of fiber sensing systems and their usefulness. In addition, it highlights some of the general fiber optics available in the market with selected examples.

Demand for online and real-time measurements techniques to meet environmental regulation and treatment compliance are increasing. However the conventional techniques, which involve scheduled sampling and chemical analysis can be expensive and time consuming. Therefore cheaper and faster alternatives to monitor wastewater characteristics are required as alternatives to conventional methods. This paper reviews existing conventional techniques and optical and fibre optic sensors to determine selected wastewater characteristics which are colour, Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD). The review confirms that with appropriate configuration, calibration and fibre features the parameters can be determined with accuracy comparable to conventional method. With more research in this area, the potential for using FOS for online and real-time measurement of more wastewater parameters for various types of industrial effluent are promising.

A fiber Bragg grating sensor for simultaneous static and dynamic strain detection is hereby presented. The principle of operation of the interrogator is based on direct intensity detection: a fixed-wavelength laser source is filtered through the sensing element, and the output power is detected with a photodiode. Multiple sensing for matched-wavelength gratings is performed by splitting the source into multiple channels. The exploitation of cheap components for optical telecommunications results in a low-cost hardware solution that matches several budget-constrained applications. The optical sensor is complemented by signal processing techniques (adaptive filters, spectral estimation, data modeling), capable of improving performances of the system without changing the optical layout.

We present the effect of epoxy bonding on strain sensitivity of fiber grating sensors. We show experimentally that, on average, sensors mounted onto aluminum plates by epoxy gluing both ends of the Bragg grating (epoxy free grating zone) display 16% more sensitivity to applied strain compared to those with epoxy covering the length of the grating zone (conventional method). We also show that in the conventional method, the epoxy layer contracts upon curing, forming an additional buffer that extends the breaking point of the sensor. Finally, adopting the conventional approach will also result in both spectral broadening and reduction in peak power of the reflected Bragg wavelength caused by the non-linearly distributed axial strain.

Sensors based on optical fibers use many principles to measure the required parameter. There are two basic types of fiber-optic sensors (FOS): Extrinsic-and Intrinsic-FOS. In this thesis an intrinsic FOS is designed to measure strain produced by a measurand. Alike the well known electrical strain gauges (ESG), a FOS is used to measure strain. The results are directly compared to the results given by the ESG and the theoretical calculations. The results are represented and discussed.

Brillouin fiber optic sensing is a promising technology for Structural Health Monitoring (SHM) whose diffusion is however at present reduced by the unavailability of proper sensor products and established installation techniques specifically aimed at the building industry. Due to its intrinsic distributed sensing capability, Brillouin systems can individually measure the deformation of any single segment of considerable lengths of single-mode fiber. In addition, Brillouin retains all the other typical advantages of Fiber Optic Sensors (FOS), such as harsh environment durability and electro-magnetic interference rejection. These advantages, especially considering that the required sensors are really low cost, make the system particularly attractive for periodical ("discontinuous") strain monitoring of unattended infrastructures that might be exposed to ageing and vandalism damages. Despite the high equipment cost, the technique can become economically convenient when the same initial investment can be amortized over a number of applications that can be monitored periodically using the same device. This work presents a comparison between two different Brillouin sensor installation techniques: Near-to-Surface Fiber (NSF) embedding and smart-FRP sensor bonding. Both systems have been experimented in the field on small Reinforced Concrete (RC) bridges subject to a diagnostic load test. The obtained results clearly highlight the advantages of the smart-FRP system, in terms of performance enhancements, installation cost, and time reduction.

Combining the functionalities of fiber Bragg gratings (FBGs) and microstructured optical fibers (MOFs) offers promising technological perspectives in the field of optical fiber sensors. Indeed, MOFs could overcome some of the limitations of FBGs in conventional fibers for sensor applications. The added value of MOFs stems from the ability to design an optical fiber in which an FBG acts as a sensor with a selective sensitivity, e.g. a sensor that is sensitive to directional strain but not to temperature. For this purpose we use a MOF with a phase modal birefringence on the order of 8×10 -3 . A FBG in this MOF yields two Bragg peak wavelengths, with a wavelength separation that depends on the phase modal birefringence of the MOF. We characterize these FBGs for transversal loads on a bare fiber and compare the results with simulated sensitivities. Then, we embed the sensor in a composite coupon and measure the response of the Bragg peak wavelengths as a function of the applied transversal pressure on the composite material. This allows drawing conclusions on the advantages of FBGs in MOFs for sensing applications.

The temperature resolution of a fibre-optic distributed temperature sensor based on taking the ratio of the temperature sensitive backscattered spontaneous Brillouin signal to the corresponding Rayleigh signal depends on the optical signal-to-noise of the receiver system and the amplitude fluctuations in the Rayleigh signal. The amplitude fluctuations or coherent Rayleigh noise have been investigated experimentally as a function of detection bandwidth, source bandwidth and spatial resolution and showed good agreement with theory.

h i g h l i g h t s " We monitor a concrete beam during a mechanical test with a fiber optic system. " The sensing system has a high strain sensitivity and a centimeter spatial resolution. " Fiber optic measurements were consistent with conventional sensors and modelling. " Externally bonded, embedded near and far from the rebars fibers showed same results. " The sensing system was able to detect cracks earlier than visual inspection.

Fiber Bragg grating sensors (FBGs) have gained rapid acceptance in aerospace and automotive structural health monitoring applications for the measurement of strain, stress, vibration, acoustics, acceleration, pressure, temperature, moisture, and corrosion distributed at multiple locations within the structure using a single fiber element. The most prominent advantages of FBGs are: small size and light weight, multiple FBG transducers on a single fiber, and immunity to radio frequency interference. A major disadvantage of FBG technology is that conventional state-of-the-art fiber Bragg grating interrogation systems are typically bulky and heavy bench top instruments that are assembled from off-the-shelf fiber optic and optical components integrated with a signal electronics board into an instrument console. Based on the need for a compact FBG interrogation system, this paper describes recent progress towards the development of a miniature fiber Bragg grating sensor interrogator (FBG-Transceiver™) system based on multi-channel integrated optic sensor (InOSense) microchip technology. The hybrid InOSense microchip technology enables the integration of all of the functionalities, both passive and active, of conventional bench top FBG sensor interrogators systems, packaged in a miniaturized, low power operation, 2-cm x 5-cm small form factor (SFF) package suitable for the long-term structural health monitoring in applications where size, weight, and power are critical for operation. The sponsor of this program is NAVAIR under a DOD SBIR contract.

This paper presents a method for the health monitoring of composite joints based on strain measurements using distributed embedded fiber Bragg grating (FBG) sensors. Secondary bonded woven E-glass/vinyl ester composite doubler plate joints were subjected to fatigue tension loading to induce stable crack propagation. A finite element (FE) model was developed to correlate experimental strain measurements prior to cyclic loading with the numerical predictions and to determine the sensitivity of the sensors to changes in longitudinal strain due to crack growth. Initial quasi-static tension tests demonstrated satisfactory correlation between the strains from the FBG sensors and FE predictions. The changes in longitudinal strain distribution during the fatigue tests were correlated with crack growth. A progressive shift in the strain distribution in the vicinity of the crack was observed. The experimental results demonstrated that a strain-based methodology can be utilized to detect crack propagation in this type of composite joints.