Signal processing in any living being is much more complex than the one performed in artificial systems. Cortex architecture, although only partly known, gives some useful ideas to be employed in sensing technology. To analyze some of these structures is the objective of this paper. Among the points to be analyzed are the parallel transfer of information, the similarity of the different systems and the massive amount of data analyzed by physical techniques. As an example of these concepts, the possibility to transmit images in a parallel way will be reported.

Photonic crystal materials and waveguides have since their appearance in 1987 attracted very much attention from the scientific community. From being a more academia discipline, new components and functionalities have emerged, and photonic crystals have today started to enter the field of commercial devices. Especially the photonic crystal fiber (PCF) with its lattice of air holes running along the length of the fiber has matured, and the technology provides a large variety of novel optical properties and improvements compared to standard optical fibers. With respect to optical sensors, the photonic crystal structures have several important properties. First of all the wavelength-scale periodically-arranged material structures provide completely new means of fabricating tailored optical properties either using modified total internal reflection or the photonic bandgap effect. Secondly, the new materials with numerous micro- or even nano-scale structures and voids allow for superior mode control, use of polarization properties, and even more a the potential of close interaction between optical field and the material under test. The present paper will be using the example of the relatively mature photonic crystal fiber to discuss the fundamental optical properties of the photonic crystals, and recent examples of their use as optical sensors will be reviewed.

Recently developed fiber-optic technologies have provided new capabilities for high-resolution, minimally invasive diagnosis in clinical medicine. A variety of diagnostic techniques that leverage from components developed for the telecommunications industry enable sensitive optical detection of tissue characteristics such as scattering, absorption, perfusion, birefringence and flow. This presentation will review these technologies with emphasis on in vivo imaging and clinical applications.

After more than a decade of research, optical coherence tomography is in the early phases of establishing a niche as a medical imaging technology for routine clinical use. Far from tailing off, however, research activity is, if anything, on the increase. In this paper, we briefly and selectively review the current state-of-the-art in the more prominent areas of activity in the technology and its application. One is inevitably drawn to the conclusion that optical coherence tomography has much more to offer clinical practice than has yet been transferred.

We developed a miniature and high-speed optical spectrum analyzer (OSA) using Micro-Electro-Mechanical Systems (MEMS) technology. It consists of an engine, driving circuit, A/D converter, and PC. It has a wavelength accuracy of 10 pm, scan rate of 1.3 ms, and dynamic range of 33 dB. The heart of the MEMS-OSA is the MEMS scanning mirror (12 x 2 mm) that measures the spectrum continuously and rapidly. The scanning mirror is actuated by electrostatic force derived from electrodes integrated in the mirror. The driving voltage is about 200 V. This paper reviews the principal of the MEMS-OSA, design, performance, and application in a Fiber Bragg Grating (FBG) distortion sensor. This OSA permits measurement of applied distortion with a scan rate of 1.3 ms and an accuracy of ±2 μ Strain. It can measure distortion up to about 100 Hz, like the speed of an earthquake.

The acoustic fiber sensor arrays that have been developed over the past two decades for oil exploration and other applications can support hundreds of fiber hydrophones per fiber pair and exhibit exceptional properties, including shot-noise-limited sensitivities better than 1 μrad/√Hz, high stability, and dynamic ranges well in excess of 130 dB. This article reviews the main configurations reported to date, which are based on ladder architectures utilizing either Mach-Zehnder or Sagnac interferometric sensors and time-domain multiplexing. The emphasis is placed on their principles, performance characteristics, and relative advantages regarding such key issues as signal fading, polarization-induced fading, frequency response, sensitivity, and the number of sensors that can be multiplexed on a given pair of fibers.

We have been developing "fiber optic nerve systems" for "smart structures and smart materials," in which an optical fiber acts as sensor to measure distribution of strain and/or pressure along it. By embedding the fiber in structures and materials, such as buildings, bridges, aircraft fuel-tanks and pipe-lines, we can realize health monitoring function for these. We have created an original technology to analyze the distributed optical parameters along the fiber by use of synthesis of correlation characteristics of continuous lightwave. Adopting this technology, "fiber optic nerve systems," which have quite a high spatial resolution and measurement speed, have been established.

In this work, I examine the latest optic and fiber optic sensors designed for measuring chemical parameters and the prospects for their use in monitoring networks. The survey covers sensors described in the literature and commercially available sensors. In addition, I give an overview of the sensors developed under the European Union FP5 and those currently under development under the FP6.

A novel method for interrogating interferometric sensors, based on analyzing the characteristics of the light expelled from a tilted fiber Bragg grating and captured by a photodetector linear array, is presented in the paper. Also a novel algorithm for the recovery of the measured information is proposed and its performance explored. It belongs to the parametric frequency estimation methods and is an adaptation of the MUltiple SIgnal Classification (MUSIC) algorithm. Finally an insight to the possibility of interrogating multiplexed interferometric sensors is given.

Characterization of two simultaneous and co-located temperature-strain sensors based on FBGs and Er:Yb-codoped fiber has been performed. The sensors have demonstrated reasonable accuracies in the order of 0.4°C and 10 με over temperature and strain ranges of 20 - 150°C and 350 - 2500 με respectively.

We analyze the action of fire, causing degradation in a concrete cantilever beam using dynamic testing. The structure is instrumented with two fiber Bragg gratings (FBG) sensors. One of them is used to measure vibration and another one is used to measure temperature inside of the cantilever beam, while the beam is exposed to fire. The temperature in the cantilever beam increased until 150°C and a reduction in the strength of concrete can be observed through the modal analysis. A fiber Bragg grating interrogation system, based on tunable filter method, is used for the static and dynamic measurements during the experiments. That system has low cost and it is easy to assemble and maintain when compared to other available instruments.

This paper describes the laboratory tests and field trial on the Saint-Jean bridge (Bordeaux, France) of both FBG extensometers (long and short-gage) and associated instrumentation, in the context of its industrial transfer.

The sensor is based on a chirped fiber grating made in a fiber tapered by fusion. The grating has a metallic jacket and acts as sensor element by comparison with the second grating that provides a reference signal. The sensor is interrogated by measuring the power reflected by the two gratings. The system has an accuracy of 0.05°C over a linear operation range of more than 10°C that can be adjusted in the fabrication process.

An extrinsic optical fiber temperature sensor has been investigated and results are presented. A coating consists of a combination of two inorganic phosphors. Thermal quenching dominates the luminescent characteristics of one phosphor at temperatures in the range of interest while the other more stable phosphor is used as a reference. Ratios of their peak emission intensities are calculated and analyzed. The phosphor mixture is coated onto a Pyrex beaker. Boiling water is poured into beaker and the ratio is calculated as the temperature of the water descreases from 80°C to 30°C. Results show an increasing ratio for decreasing temperature. This paper describes the testing of the coating and its application, as part of a temperature sensor, for monitoring surface temperatures in electromagnetically harsh industrial environments.

In this work, the response of fiber Bragg gratings (FBG) subjected to longitudinal ultrasonic (US) field has been theoretically and numerically investigated. US field interaction has been modeled taking into account the direct deformation of the grating pitch combined with changes in local refractive index due to elasto-optic effect. Numerical results show that both broadband and narrowband FBG interrogation schemes can be used to detect US presence. In both schemes, sensitivity of the FBG response decreases when reducing the ultrasound wavelength below the grating length. US excitation has been also found to induce a FBG optical spectrum shape distortion for high power ultrasounds and US wavelengths comparable to the grating length. The results of this analysis provide useful tools for the design of grating based ultrasound sensors meeting specific requirements in terms of field intensity and frequency.

We have studied the effect of gamma radiation on Long Period Fiber Grating (LPFG) temperature sensors fabricated in a pure-silica fiber, using the arc discharge technique. The temperature sensitivity of the LPFGs remains unchanged by the irradiation.

Fiber Bragg Gratings (FBG) sensors embedded in composite insulators used for electrical high voltage applications have been studied. The study included the design of a new method for the manufacturing of composite insulators with optical fibers. The instrumented prototype insulators are intended to keep track of the mechanical and thermal stresses endured by the insulators in actual operating conditions. Optical characterization of the FBG sensors have been made using an erbium laser source and a spectrum analyzer. A 5kN strain resolution in a temperature range between -40°C and +60°C has been achieved using standard SMF-28 optical fibers.

We report experimental measurements of the reflection spectra of Bragg gratings inscribed in 4-core fibers under transverse loading. Broadening and splitting of the Bragg peaks from each core are observed as a function of load and fiber orientation.

A Fiber-Bragg-Grating based, advanced co-cured smart composite patch for the repair of metallic structures is proposed and demonstrated. Advantages include real time cure monitoring and long-term in-service structural integrity evaluation.

In this paper we review the sensing features of long period Bragg gratings and report on studies aimed at optimizing the sensitivities to various measurands by using different fiber geometries.

The curvature- or bend-sensing response of long-period gratings (LPG) UV-inscribed in D-shaped fiber has been investigated experimentally. Strong fiber orientation dependence of the spectral response when such LPGs are subjected to dynamic bending has been observed and is shown to form the basis for new vector sensors.

Very small point sensors for fluid pressure have extensive applications in aerodynamics and medical monitoring. We describe Fabry-Perot pressure sensors formed by laser machining of the end faces of single mode conventional and multicore fibers.

We demonstrate a fiber grating laser hydrophone that can measures ultrasound and temperature simultaneously. It can detect ultrasound with frequency up to 40 MHz and has advantage of ease of demodulation.

We use the time-dependent group delay response of a chirped fiber Bragg grating to measure the position and magnitude of the local pressure applied to the transducer. This paper presents ex-vivo experimental results.

A new downhole measurement technique has been proposed based on optical fiber Bragg grating (FBG) sensors for long-term monitoring of strain and its corresponding stress build-up in geological fault zones. Design and development of the present downhole sensor installation equipment have been demonstrated. Results from laboratory tests and from first field experiments in a research borehole at Trizonia island in the Gulf of Corinth area (Greece) have been reported.

The paper describes a sensor head for long-term high-precision measurements of very small deflections of a diaphragm used for pressure gauges. High precision deformation measurement is assured by using a fiber Fabry-Perot interferometer sensor; identification of zero-point changes, and thus, long-term stable measurement is achieved by a specially designed absolute interferometer sensor. Several fiber optic solutions based on fiber Fabry-Perot technique have been investigated to find out a reliable sensor design. The presented sensor design has reached prototype status and allows to measure unambiguously static deformations with high precision. In order to evaluate repeatability and possible changes of zero-point reference if the head has been disconnected, validation of the described pressure gauge has been started. This validation work includes calibration and enables to evaluate possible drift effects, and to identify mechanical or thermal hysteresis.

A sensing head for simultaneous measurement of temperature and strain is presented and analyzed. The proposed configuration is based on the combination of two Bragg gratings, written in different fibers and with different reflectivities, to form a single signature with a reflected step spectrum profile. By measuring the changes in the peak wavelength and spectral width of this signature, resolutions of 0.65°C/√Hz and ±2.55 με/√Hz were achieved for temperature and strain measurements, respectively.

Accurate and highly sensitive speed measurements have been successfully demonstrated by a self-aligned optical feedback velocimetry technique using the self-mixing modulation effect in a double-clad Er-Yb-doped fiber laser.

A simple optical fiber-based strain and pressure sensor has been fabricated using nanostructured self-assembled elastomeric free-standing thin film materials. The fabrication of the sensor material and a demonstration of the sensor performance are described.

Characteristics of plastic optical fiber (POF) as a distributed sensor are under test using a specially designed optical time-domain reflectometry (OTDR). Our system is capable for testing an ordinary POF of 1 mm in diameter up to about 120 m in length with the use of a photon counting detector. The OTDR responses are experimentally investigated for mechanical disturbance at one point along the POF such as small bending, axial strain, side loading and twisting deformation. We found that the POF sensing system can be applied for very large stain and has a memory effect due to the plastic deformation. Even after releasing the strain, we can observe the residual OTDR responses. This nature would serve a unique function as a distributed sensor which we can not achieve using silica-glass fiber system. Temperature effects on the OTDR results for POF are also studied and discussed.

A system for measuring liquid level in multiple tanks using optical fiber technology has been developed. Oil field service industry or any sector requiring liquid level measurements in inflammable atmospheres can be benefited from this intrinsically safe technology. Three different models considering various effects have been derived and tested on two prototypes. The first model use punctual emitters and divergence, the second model use finite emitters with paraxial approach, and the third model use a constant power rays distribution in the emitters using with each one of the rays the Snell's law, to take in count the optical aberrations. A Monte-Carlo method is used to fit the experimental data and obtain the models parameters. The simplest model is demonstrated to be accurate enough for a proper correlation between the experimental data and the fitted curve in a range of 2 m.

A partially embedded chirped fiber Bragg grating has been used to monitor the strain build up during non isothermal curing of a model thermoset resin. The particular feature of the spectra of a linearly chirped and strongly apodized fiber Bragg grating to encode position along the sensor has been used to simultaneously measure temperature and strain during the cure cycle of an epoxy based polymer. In particular, the embedded part of the grating allows the monitoring of temperature and processing strain while the rest of the sensor is sensible to temperature variation only. A new self temperature referenced sensor system has been successfully tested in an operative condition where usually thermomechanical loading are simultaneously active. The onset and progression of gelification as well as the temperature have been measured.

A fiber laser-based sensor system has been developed to measure wide range of temperatures (22 - 500°C) and strain (0 - 1200με) using a normal and a chirped grating as optical feedback elements and Er³⁺-doped fiber as gain medium.

A fiber-optic fluorescence-based sensing scheme for simultaneous measurement of a wide range of both strain (0 - 2000)με and temperature (20 - 600)°C has been demonstrated by using a grating with high reflectivity in an Sb-Er-Ge codoped silica fiber.

An intensity-referenced temperature-independent curvature measurement technique using a smart composite comprising two chirped fiber Bragg gratings is demonstrated. The two gratings are embedded on opposite sides of a composite laminate and act simultaneously as curvature sensors and as wavelength discriminators, enabling an unambiguous measurement of the composite radius of curvature.

A new sensing configuration is proposed for simultaneous measurement of strain and temperature that relies on a single long period grating written by the electric arc technique. The underlying principle is the azimuthal asymmetry induced by the electric arc fabrication technique, which results in a device with polarization dependent insertion loss sensitive to both temperature and strain. With the proposed configuration, resolutions of ±2.8°C/√Hz and ±13.9με/√Hz are obtained for temperature and strain measurements, respectively.

A possibility of applying a compact optical diagnostics to nuclear systems, such as detecting high energy neutrons in a nuclear fusion system and measuring a high-flux gamma-ray in a fission reactor with a wide dynamic range, has been studied, utilizing radiation resistant optical fibers and radioluminescent (radiation-induced luminescent) materials.

Irradiation test of pre-annealed optical fiber was carried out using gamma-ray and fast neutron source. Optical fiber has a good radiation resistance by the heat treatment and there are optimum temperatures changed by the kinds of radiation and the wavelength of transmission light. It is necessary to select the heat treatment temperature for developing the radiation resistance by the situation of the optical fiber.

The fiber-optic strain sensor based on Fabry-Perot air cavity, made inside single-mode fiber by simple micromachining technique is presented. The sensor features near-linear response, low transmission loss, low temperature dependence, easy fabrication and it can be applied in quasi-distributed networks by using standard OTDR interrogation.

We have studied the gamma dose-rate effect on the radiation sensitivity of a phosphorous doped optical fiber. The radiation sensitivity significantly increases with decreasing dose-rates.

Effect of the hot acid stripping of optical fiber polymeric coating on the dynamic and static fatigue is studied for assessing the impact of the stripping process on the life expectancy of embedded sensors.

The spectral properties of long period fiber gratings (LPFG) are modified when twisting is applied. Herein, results of applying torsion to UV-induced LPFGs are presented for comparing with others which have already been presented in literature and where the LPFGs are fabricated using different techniques. Both, the resonant wavelength and the peak attenuation of the resonance, have similar behaviors to those obtained by other authors. However, in spite of the fact that the values of sensitivity to twist rate are sensibly lower in the case of UV-LPFGs, its bigger mechanical strength lets them be subjected to higher twist rates, which could be useful in determinate applications.

The feasibility and advantages of smart bridge cable based on FBGs are discussed. And the sensing properties of FBGs installed in the cables under dead load are tested. The experimental results and practical applications show that the smart bridge cable is proper to be used in bridge cables transfer, construction control and long-term health monitoring.

A distributed temperature sensor based on spontaneous Raman scattering in a single-mode fiber is demonstrated. A brief theoretical description of the IOFDR technique for spatial resolution of the backscattered waves is given. Measurements on 16 km of SM fiber with spatial resolution of around 2m are presented. To the best of the authors' knowledge, this represents a new record for an IOFDR system. An accuracy of ±2K is achieved.

In this work we present a signal processing method applied to totally non-contact laser generated and detected acoustic waves for the estimation of the main elastic properties (Poisson ratio and Young's modulus) of structural materials.

We describe a novel method of damage location using ultrasonic Lamb waves detected by fiber Bragg gratings. The gratings are configured in a rosette configuration in order that the direction of an incoming wave may be determined. Location of holes was determined by finding the intersect point of the reflected ultrasound signals obtained from two rosettes. Accurate results are obtained when optimum geometries source transducers an fiber gratings are used.

We describe a novel optical acoustic detector based on a bias-controlled fiber Fabry-Perot interferometer. Broad bandwidth as 15 MHz ~ a few GHz and higher sensitivity than that of conventional systems were demonstrated. The minimum detectable phase was 4 x 10^-8 rad/Hz^1/2, which was 3 times larger than the quantum-limited value.

Interferometric sensing is used for vibrations inside power transformers. A probe with enhanced sensitivity is designed, obtaining synchronous multi-fringe outputs. This approach provides very high resolution demonstrated in the application, with a simple but powerful demodulation technique.

Lead-acid batteries are an energy storage system used in automotive sector, electric traction, communication remote control, etc. In all of this applications, and specially in remote control, is interested to know, among other variables, the electrolyte density. This measurement allow us to manage a battery or a set of batteries. In this work we present an optoelectronic sensor developed for the measurement of the lead-acid electrolyte density. The sensor has an optical emitter-receiver pair, two plastic optical fibers and the electronic circuit. One fiber is used like a reference in order to minimize the possible common mode errors, due temperature, power supplies, etc. The other fiber is the sensitive fiber and the measurements are taken with it, the functioning principle is an U bend configuration which allows losses due the refraction to the surrounding liquid, this losses depends on the liquid density (electrolyte density). Several tests were done with different conditions and different charging and discharging strategies, the results demonstrate the validity of this technique for the lead-acid electrolyte density measurement with a good stability in the time.

This work describes the use of a fiber Bragg grating sensor (FBG) to measure strains at a mandible surface caused by impact loads on a dental implant. The apparatus uses a tuneable optical filter reference scheme and is able to detect dynamic signals with frequency components up to 10 kHz. A dried cadaveric mandible with a dental implant, and a FBG placed on the outer surface was used. The results demonstrate the ability of the FBG as a biomechanical sensor.

A novel refractive index sensor has been presented which is characterized by the sensing part on the tip of the optical fiber. The principle of this sensor is based on surface plasmon resonance at the interface between gold and medium to be detected. In order to induce the evanescent wave interrogation, the proposed structure has been devised to deliberately leak the transmitted light into the cladding layer of the fiber by a mechanical cleaving and a thermal fusion splicing. The sensor response obtained from the spectral experiment exhibited availability in the use of spectral and optical intensity operation. The sensitivity for the case of spectral operation has achieved the values of 3.35*10^-4 and 4.99*10^-5 for 1.333 and 1.398 refractive index units, respectively.

CsI ionization radiation probes interrogated via a fiber optic transceiver link for monitoring medical procedures such as Intensity Modulated Radiotherapy, Brachytherapy and Nuclear Medicine are presented together with potential industrial, environmental and military applications.

This paper outlines the development of a dual hydrazine/nitrogen dioxide (HZ/NO₂) prototype fiber optic sensor utilizing an acid-base indicator that undergoes color changes depending on which gas is present. Bromothymol blue bromocresol green mixture (1/1) in hydrogel (1/1), produces a blue-green indicator for HZ and/or NO₂. The sensor was tested several times over a period of eight weeks and the response was cconsistent and proved the feasibility of dual HZ/NO₂ leak detection. Prototype sensor construction, the hardware, and the software of the electronic interrogator circuitry are briefly explained. The paper presents a summary of sensor response when exposed to 52 ppm and 18 ppm hydrazine and 400 ppm and 200 ppm nitrogen dioxide.

We have investigated the sensing properties of the carbon nanotubes deposited onto a cadmium arachidate buffered multilayer by acoustic sensors -- SAW and QCM -- and a reflectometric sensor system based on optical fiber for purposes of chemical detection of volatile organic compound (VOCs), at room temperature. The carbon nanotubes have been deposited by the molecular engineering Langmuir-Blodgett (L-B) technique onto a buffer multilayer of cadmium arachidate prepared monolayer-by-monolayer using the L-B technique as well. The sensing multilayered material has been prepared both onto a standard silica optical fiber configured in a reflectometer sensor system and onto acoustic sensors -- SAW and QCM -- configured as oscillators. The acoustic sensors and the optical sensor have been exposed simultaneously, in the same test chamber, towards different VOCs such as ethanol, methanol, iso-propanol, acetone, ethylacetate, toluene with different vapor pressures for comparing the sensitivity of the coating onto the different kinds of acoustic and optical transducers. Moreover, for the same type of transducer, acoustic or optical, the effect of carbon nanotubes onto the gas sensitivity is remarkably higher in all investigated cases.

Liquid hydrogen has been intensively used in aerospace applications during the past forty years and is of great interest for fuel cells technologies and future automotive applications. Following upon major explosive risks due to the use of hydrogen in air, previous studies were carried out in our laboratory in order to develop optical fiber sensors for the detection of hydrogen leakage. This communication is aimed towards a prototype optical fiber system designed for the detection of gaseous hydrogen leakage near the conecting flanges of the liquid hydrogen pipes on the test bench of the engine Vulcain of the rocket ARIANE V. Depending on the configuration, the prototype sensor provides a two-level alarm signal and the detection of gaseous hydrogen leakage is possible for concentrations lower than the lower explosive limit in air (between 0.1 and 4%) with alarm response times lower than 10 seconds in a wide range of temperatures between -35°C and 300°C. The sensing principle based on palladium-hydrogen interaction is presented as well as the detection system composed of an optical fiber probe and an optoelectronic device.

In this work, high sensitivity refractive index measurements have been experimentally demonstrated by using thinned fiber Bragg grating sensors. When cladding layer is reduced, significant changes in the effective refractive index occur due to external refractive index modifications, this means that consequent shifts in the Bragg wavelength are expected. Reduced cladding layer have been obtained by using wet chemical etching in hydrofluoric acid solutions. Experimental tests to prove sensor sensitivity induced by changes in the external refractive index have been carried out by using glycerine solutions with well known refractive indices. Obtained results agree with the numerical analysis carried out by using three layer fiber model. If the cladding layer is full etched resolutions of ≈10^-5 and ≈10^-4 for outer refractive index around 1.45 and 1.333, respectively, are possible. In addition, higher sensitivity and robustness could be achieved by using fiber Bragg grating sensors written in multimode graded index fibers as shown in a preliminary study here reported.

An optical fiber sensing system is investigated for measurement of exhaust emissions from an engine. This paper discusses the component infrastructure to conduct this task in the mid-infrared region and a sensing fiber and test system are proposed.

A novel fiber-optic sensor sensitive to glucose has been designed based on electrostatic self-assembly method. The polycation of the structure is a mixture of poly(allylamine hydrochloride) (PAH) and Prussian Blue, whereas the polyanion is well-known enzyme gluocose oxidase (GOx). The range of glucose concentration that can be measured is submilimolar and is located between 0.1 and 2 mM. Measures are based on a new detection scheme based on the slope of the change of signal produced by injection of glucose, yielding to a linear response. The sensor responses in a PH range between 4 and 7.4, which includes the physiological PH of blood. Some rules for esitmation of the refractive index of the material deposited and the thickness of bilayers are also given.

This paper reports on the use of rare earth doped optical fibers for the detection of low dose electron beams in radiotherapy applications. Neodymium and cerium doped singlemode fibers have been irradiated with 10 MeV electron beams and the losses induced by the radiation have been measured in the wavelength range 1200 - 1600 nm, the attenuation has a linear dependence with the applied dose and its order of magnitude is 0.001 dB per meter of fiber and cGy.

In the deep ultra-violet (DUV) and the mid infra red (MIR) regions of the spectrum, the so-called hollow core waveguide (HCW) is an alternative for light-delivery systems. In addition to efficient light transportation, the HCW can be used as an intrinsic sensor: due to the long path-length through the HCW the spectral absorption of the gas under test can easily be monitored. Within this study an experimental system for gas analysis was developed and the results are compared to those from IR absorption measurements, also using the HCW approach.

We present simultaneous electrochemical and waveguide surface plasmon resonance measurements demonstrating the electrochemically controlled desorption of a thiol monolayer from a gold electrode. Self-assembled thiol layers are used in biosensors to enable the attachment of lipids to the sensor. This work demonstrates the potential for development of the device for biological sensing applications. Simultaneous SPR electrochemical measurements are made during the thiol desorption and these results are discussed and compared to the results of a numerical simulation.

A 32-analyte integrated optical immunofluorescence multisensor system has been realized and tested for the first time. The sensor system is based upon bio/immuno-chemistry at the waveguide surface and fluoroimmunoassay in the evanescent fields of the optcal waeguides, to enable rapid, simultaneous and high-sensitivity fluorescence detection of up to 32 pollutants in water, and automatic regeneration for immediate reuse. The system has been demonstrated for estrone and a detection limit of 13 ng/L has been achieved.

An optical fiber sensor for the measurement of oxygen in gaseous environments, which is based on the quenching of the fluorescence of a ruthenium complex, is presented. The sensing chemistry is immobilized in a sol-gel based solid matrix that is coated on a tapered optical fiber probe. Oxygen measurement is performed both by phae and fluorescence intensity spectroscopy. Experimental results show that the fluorescence intensity and the lifetime depend both on oxygen and temperature. A scheme for simultaneous determination of the temperature and the oxygen concentration is proposed. Temperature measurement is performed using the excitation radiation and an absorption long pass filter. Preliminary results are presented which show a temperature measurement independent of oxygen and of optical power level.

Corrosion control in pipelines and wells is a critical issue in the oil industry. In this paper, we present an optical fiber sensing technique devoted to monitor one of the parameters involved in corrosion: the environment acidity. In the proposed technique, a transducer mechanically couples a fiber Bragg grating to a pH sensitive hydrogel. The possibility of determining pH values with resolution of 10^-2 in a range from 3 to 6 is evaluated and discussed.

We describe a sol-gel coated long-period grating sensor for detection of carbon dioxide. When carbon dioxide penetrates the porous glass matrix, it dissolves in the moisture forming carbonic acid, consequently interacting with the deprotonated dye.

Prion proteins are the infectious agents that cause Creutzfeldt-Jakob Disease (CJD) in humans. These proteins are particularly resistant to normal sterilization procedures, and the theoretical risk of prion transmission via surgical instruments is of current public and professional concern. We are currently investigating fluorescence methods for the detection of proteins on surfaces, with a view to developing an optical-fiber-based system for routine, online monitoring of residual protein contamination on surgical instruments, in hospital sterilization departments. This paper presents preliminary results on the detection of femtomole amounts of fluorescently labelled protein on surgical steel and discusses some of the problems involved in the detection of fluorescence from metal samples.

Innovative Polycrystalline IR-fibers (PIR-) from Silver Halide open a variety of promising fiber applications in 4-18 μm range. PIR-fibers coupled with IR-detectors enable unique flexible 2D & 3D IR-imaging, including IR-endoscopy with PIR-fiber bundles. FTIR- and other IR-spectrometers with PIR-fiber probes may be used for remote process molecular control, for in-vivo diagnostics of tissue and for pollution monitoring in liquid and gaseous phase in "finger-print" part of spectrum.

We have tested the viability of the Electrostatic Self-Assembly Method for the deposition of thin films on long period gratings in order to future developments of chemical sensors.

This paper proposes a novel fiber optic immunoassay biosensor based on the Fabry-Perot (F-P) interferometry. The PDMS dip coating and self-assembly monolayers coating are employed to prepare the fiber probes in the formation of F-P cavity and modification of the tip surface respectively. As the fiber probe inserting into the target solution, the immunoreaction will be introduced on the fiber tip. The covalent binding of the Rabbit IgG and Anti Rabbit IgG-Cy3 molecules on the fiber tip will contribute to the variation of the refractive index of interface as well as the reflectance. The interference spectrum will be shifted due to the reflectance variation. The time response is also implemented by taking the in-situ measurement of spectrum valley shift and the signal will reach the steady state within 15 minutes. Finally, the sensitivity of this immunoassay biosensor has also been demonstrated that the lowest detectable concentration of the target sample Anti Rabbit IgG-Cy3 is 10^-12 g/ml, which is lower than the detection limit of ELISA of 5*10^-11 g/ml. This fiber optic immunoassay biosensor will be applied in the brain resarch for in-vivo and in-situ monitoring the biochemical reactions of the neurocytes.

The development of optical fiber sensors and devices based upon Langmuir-Blodgett thin film overlays deposited onto side polished optical fibers and onto optical fibers containing long period gratings is described.

An Optical fiber based sensor system has been developed for the purpose of examining the color of food products online as they cook in a large-scale industrial oven. By classifying the color of each cooking stage it is possible to automatically determine if the food is cooked to an optimum perceived color. Developments have been made on previous work by the authors by further examining the internal color of the food and testing the repeatability of the system. Spectroscopic techniques are employed to determine the color and this signal is interrogated using an Artificial Neural Network.

Sensitive photoacoustic detection of methane with a fiber-coupled 1.65 μm laser is reported. A sensitivity of 0.18 parts-per-million (signal-to-noise ratio = 3) is achieved using a properly designed photoacoustic cell operating on its first longitudinal mode.

We present a comprehensive model of a CO₂ correlation spectroscopy based gas sensor. Predictions of the sensor response for typical fiber optic-coupled systems are made, taking into account effects of noise in detected signals.

A device for the measure of index of refraction of liquids in situ based on polymer optical fibers (POFs) was demonstrated. It consists in a sensor head of three passive POFs where two are coupled to two detectors and an electronic unit for the differential measure of signals. A differential operating principle is utilized to reduce noise such as light intensity fluctuation. The device was successfully checked measuring refraction index changes of the water with different concentrations of sugar, salt and alcohol.

We discuss the potential advantages of fiber lasers as sources for gas sensors in the near infrared. A number of challenges need to be met, particularly in regard to stable tuning, application of high sensitivity detection techniques and operation over an extended range of wavelength. Conventional loop cavities suffer from instabilities due to mode hopping and polarization drift. Some of these problems may be addressed through an alternative configuration using a short, polarization-maintaining cavity and a Faraday rotator mirror (the sigma fiber laser). Initial experiments conducted on the sigma fiber laser have investigated the gain that can be achieved through double pass operation as compared with the prediction of a theoretical model which takes into account the effects of amplified spontaneous emission. Several fiber laser designs are proposed for potential application to gas spectroscopy systems.

Methods for estimating the lifetime of reinforced concrete structures are being investigated with a fiber optic chemical sensor system, using a sol-gel as the matrix for the active material, for embedment in concrete for evaluation and testing. Results are presented on recent work.

An optical fiber, Fizeau configuration Optical Coherence Tomography (OCT) system is presented in this paper. The Interferometer is formed between the distal end of the sample-arm fiber and the sample itself. This ensures 'downlead insensitivity;' polarization variation is not a problem, as it is in the standard Michelson configuration. Path-length matching is performed by a secondary, bulk-optic scanning Mach-Zehnder interferometer. In this paper, we demonstrate the use of an optical circulator and balanced detection to permit optimum use of the light and maximize the signal-to-noise ratio.

Designs and simulations for a class of integrated photonic lightwave circuit spectrometers with low manufacturing tolerance are presented. The designs are applicable to all material platforms, including, but not limited to, silicon, glass, polymer, sol-gel, and gallium arsenide.

The nonlinear effect in a fiber-optic gyroscope has been measured with a single mode laser diode, a multi mode laser diode with an erbium-doped fiber amplifier and an erbium-doped fiber source. The experimental results confirm the estimations obtained from our improved theoretical treatment. The predicted dependency on the number of spectral lines and their power has been observed. The maximum phase error per power difference in the sensing coil is 1.3 μrad/μW corresponding to a rotation rate error of 0.3(°/h)/μW. The use of the multi mode laser diode reduces the errors by a factor of 5 according to its spectral shape. For the broadband erbium-doped fiber source the effect is zero within the error ranges. These theoretical and experimental results contradict predicted nonlinear gyro errors derived in literature.

We demonstrate interrogation of a single, high performance Mach-Zehnder interferometric sensor over a total of 166 km of single-mode optical fiber, using a remotely pumped EDFA and Raman amplification. A phase resolution less than 5 μrad/Hz^1/2 at 1 kHz is achieved.

We present a nonlinear highly birefringent microstructured fiber. The fiber has been fabricated adapting the fabrication method for microstructured fibers to the conventional one for elliptical-core fibers. Birefringence higher than 7 x 10^-3 is demonstrated.

The cut-off wavelengths of the two linearly polarized states in PCF can be designed by varying the diameters and pitch of the holes. Simulations show that single polarization operation over a range of up to 100 nm can be realized around 1.3 μm and 1.55 μm bands.

We report a multi-wavelength fiber laser with a semiconductor optical amplifier. The lasing wavelength of the laser can be adjusted from 1590 nm to 1645 nm by adjusting the round-trip cavity loss.

The polarization dependence of the linear electro-optic coefficient (LEO) in thermally poled twin-hole silica fiber has been characterized by two separate interferometric methods and the results compared. Firstly the magnitudes of the individual LEO values for the two separate polarization states of the thermally poled twin-hole silica fiber were measured and the difference in the LEO values was calculated by subtraction. Secondly a direct measurement of the difference was made using an interferometric technique by monitoring the total retardance of the birefringent poled twin hole fiber section while applying various electric fields to the internal electrodes. The second method, which directly measures the differential LEO, has strong potential as an interferometric method for the measurement of electric fields. The intended application is the measurement of line voltage in high voltage electricity distribution and transmission systems.

A novel watt-hour meter using optical sensor by single crystal and using electronic integral circuit is proposed and realized. This watt-hour meter is small, rugged and capable of running for long duration.

The radiation emitted by an optical fiber during heating due to an electric arc discharge was detected using a Cronin spectrometer. The fitting of the emission spectrum to the blackbody radiation, allowed the estimation of the temperature range attained by the fiber.

We present results of applying low coherence interferometry to gallery paintings. Infrared low coherence interferometry is capable of non-destructive examination of paintings in 3D, which shows not only the structure of the varnish layer but also the paint layers.

An ultra-compact single-mode six-wavelength DBR fiber laser, with potential as a source for multi-channel fiber sensors, is demonstrated. Pumped with a single 150 mW 980-nm diode laser, the average power is 5 dBm per line.

We propose a new structure for sensing variations in the refraction index independent of fluctuations in temperature. The scope of applications is very wide and can be used to detect electromagnetic, biochemical and even radiation changes. Also, it can be applied to the telecommunications field.

The fiber-optic Sagnac interferometer as an example of the point sensor is described in this paper. The described applications comprising a system for rotational tables' investigation, a system for measurement of vibrations with an amplitude of nanometer order of magnitude, devices for polarization parameters analysis and the rotational waves detector base on reciprocal condition of the Sagnac interferometer operation. Because the coherence phenomenon in this configuration occurs in any source of light, the polarization role in this configuration is emphasized. Basing on this approach the possibilities of practical use of the polarization influence on interference phenomenon for the mentioned above devices are mainly discussed.

We present and demonstrate a high-resolution absolute-distance measurement system based on multiple-wavelength interferometry. The information on a cavity length is obtained by sampling a fringe of its spectral response at different wavelengths. This is achieved by simultaneously tuning multiple fiber Bragg gratings. For a two wavelength system, an unambiguous measurement range of 262 μm was obtained with a resolution of 14.3 nm.

Design, experimental evaluation and performance of a tunable optical filter based on hybrid MOEMS is presented. The device meets the demodulation requirements for Fiber Bragg Gratings sensors reaching a repeatable tuning range over 400 pm.

For in situ monitoring of natural waters in respect of impurities miniaturized spectral analytical systems become more and more important. A case in point are nitrate impurities, which can be detected by absorption spectroscopy in the ultra violet (uv) spectral range between 200 and 350 nm. Using uv-transmitting optical fibers, a microoptical flow cell, a miniature polychromator and a deuterium light source, a miniaturized spectral photometer for nitrate detection has been developed. The spectral photometer is a key component in an automatic analyzer for in situ measurements in natural waters. To separate the nitrate absorption from the superposition of other uv-absorbing contaminations, for instance nitrite, carbonate and huminic acids, a multi-component analysis (MCA) software has been applied to the detected absorption spectra. The analyzer is suited for the permanent monitoring of nitrate, nitrite and carbonate in inland waters.

We present two novel multi-frequency techniques for absolute range measurement in interferometry. A comparison of these techniques with the method of excess fractions has been performed by computer simulation and experimental data is presented.

It has become a standard to use Shupe's nonreciprocity formula for calculating the thermally induced bias error in fiber gyroscopes. This effect is initiated by thermal waves propagating through the material. However, it seems as if it has not been recognized yet that elastooptical interactions in the fiber can also lead to a nonreciprocity effect. In this case it is not required that a thermal wave propagate through the material, a simple temperature change -- even if homogeneous -- would have the same effect. In this contribution, we demonstrate the nature of the effect and, based upon the standard architecture of a sensor coil assembly, report on calculations (including FEM) elucidating the origination of elastic stress leading to a nonreciprocity.

In this work we show dilute nitride (InGaAsN and GaAsN) based laser diodes and detectors grown by Molecular Beam Epitaxy as good candidates to be used in optical fiber sensors applications. The maturity of GaAs technology allow us to develop laser devices less expensive and complex than the present InP based diodes which exhibit limited performances. Laser emission up to 1.23 μm is achieved for these devices. In addition, a new generation of (In)GaAsN quantum well intersubband detectors is also presented. This structures can be tailored to operate in a very short interval of wavelengths (namely 0.4 to 1 μm) centered in the range between 1.3 and 2 μm with a responsivity around 3 mA/W. The excellent selectivity of these detectors make them suitable to be matched with the emission wavelength of the source, thus avoiding the interference of external light sources. Both devices can be tuned to work in the range of interest for optical fibers, giving rise to a number of potential applications including Er-doped optical amplifiers, and optical fiber sensors.

There are numerous types of fiber optic sensors and sensor systems that rely on the use of detector arrays to determine sensor output from returned optical signals. Spectrally modulating sensors such as those based on Bragg gratings and Fabry-Perot sensors based on white light interferometry are but two examples. One problem with such systems is often the resolution of the detector array. In this paper, experimental confirmation of a new technique is presented in which the signal from one or more sensors can be demodulated with high resolution. In the technique, the conventional detection system utilizing a linear detector array is replaced by a rotated 2-D digital camera. This results in a much higher sampling resolution than is obtained via linear sampling due to the "folding" of the detector array elements relative to the linearly varying parameter filter directly in front of the array. A theoretical description of the technique is given and its experimental validation is presented.

We demonstrate a Fourier Transform Spectroscopic approach to achieve high-resolution measurement of the structural detail of the reflected spectra from an infrared FBG grating array, with the inherent measurement capability over a wavelength range of 900 nm. Measurements on all gratings in the array are achieved in a single scan of the OPD, from an interferogram captured on a single InGaAs photodiode. We demonstrate the approach for measurements on standard gratings and in the case of a grating subjected to a nonuniform measurand. The OPD is referenced from a visible HeNe beam propagated on the array downlead, and we demonstrate the robustness of the measurement in the presence of the complex transverse modal structure of that reference beam.

We present a hybrid optical device for measurement of refractive index variation in a selfoc lens by the Talbot effect. The intrinsic nature of the device that combines a linear grating and an inhomogeneous medium permits to measure changes in the refractive index along the axis as a function of the position shift of the first self-image. Possible changes in the temperature during lens fabrication can be extracted from refractive index variation. The hybrid device has a refractive index sensitivity of ±7 x 10^-5 per nanometer of position shift of the first self-image.

Pump power-induced changes in the center wavelength of the attenuation band of the spectrum of long-period fiber gratings (LPG) writing in erbium doped fibers are experimentally checked. The pump tuning of the LPG is demonstrated.

Spin-coated layers of ZnPc and CuP have been used as chemically interacting materials for the detection of alcohols, amines, ketones, alkanes and pyridine for applications in food quality control. The UV-VIS variations obtained by the exposure of the sensing layers to the mentioned analytes in controlled atmosphere have been analyzed and compared with those deriving by a single thin film obtained by mixing the two metal complexes in an appropriate ratio. A multichannel monitoring of the main bands of the sensing layer due to the interaction with the analyte vapors became the basis to construct a set of independent sensors located on a single sensing element. The effects in the variation of the absorption bands of the blend system are compared with the variations in absorbance observed with the two sensing layers fabricated separately with each single compound. The interaction between the VOCs species and the heterogeneous sensing layer shows a different behavior in the responses respect to the results obtained with each single compound.

Nitride semiconductor devices have recently been developed for a number of electronic and optoelectronic applications, including amplifiers, light emitters and several kinds of sensors. In particular, ultraviolet detectors with a tailored spectral response can be achieved due to the direct wide bandgap of AlGaN alloys; on the other side, acoustic wave devices take advantage of the piezoelectric and elastic properties. In this work, we will describe the fabrication and characterization of a novel kind of optical detector, based on the interaction of surface acoustic waves and photocarriers. The response, which is linear with the incident optical power, can be controlled either by modifying the input power of the RF signal which creates the acoustic wave, or by tuning its frequency, in the latter case with a very high sensitivity. Several applications can be envisaged as a result of this synergy, such as imaging displays and electro-optical modulators.

A novel time-dependent Mueller-like formalism is used to optimize performance in fiber-optic sensing scenarios, where the RF envelope of the interrogating signal is distorted by PMD/PDL.

In this paper a theoretical prediction of a new kind of in-fiber devices is presented. They behave essentially like long-period Bragg gratings except for the fact that they are not permanent but volatile. This is because these devices are not formed by the UV-induced increment of the refractive index but by the twisting of a pristine HiBi fiber. This way, a long period fiber grating whose characteristics can be modified by changing the polarization of the incoming light is obtained.

Embedded fiber Bragg gratings (FBGs) are sensitive to changes of near strain fields in a composite host monolithic structure, typical of aircraft airframes. FBGs have been embedded in different configurations (a typical position is the skin -- stiffener interface in a monolithic structure) for detecting events associated to damage occurrence. Thus, it is possible to think in FBGs not only as strain sensors, in a classical load monitoring configuration, but as a part of a structural health monitoring (SHM) system in composite structures dimensioned following damage tolerance criteria.

An optical-fiber salinometer has been evaluated during a two-week measurement campaign in the Baltic Sea. The obtained results in three different tests are presented in comparison with those obtained with a standard electric CTD sonde commercially available.

An absolute displacement sensing system based on 'Channelled Spectrum' processing capable of simultaneous interrogation of FBGs and FOIS is presented where the role of the optical spectrometer is performed by a scanning Fabry-Perot Filter.

CPOTDR allows measurement of the distribution of the full polarization properties of a single-mode optical fiber. This paper describes the practical application of the technique to the measurement of transverse strain and physical displacement.

We present a new technique for simultaneous measurement of chromatic dispersion and Brillouin shift distribution along conventional, single-mode optical fibers used in telecommunications. It is based on performing Brillouin Optical Time Domain Analysis (BOTDA) over the four-wave mixing generated by two low-power pumps (< 10 mW). Unlike others, this technique can measure any arbitrary value of dispersion. With the use of this technique we have obtained consistent, high-resolution and low-noise measurements for both magnitudes. Our measurements indicate a certain correlation betwen the spatial distribution of both quantities, although the degree of correlation varies for the different manufacturers tested.

The approaches to the development of distributed networks, consisting of fiber optic measuring lines with integral sensitivity is considered. A problem of tomography reconstruction of scalar and vector physical fields parameters by this network signals is discussed.

We present a simple and low-cost device for monitoring fiber Bragg gratings sensors. A resolution of 1 pm is demonstrated. The device translates into a time interval the wavelength position of a spectral line.

This paper describes an application of Fiber Bragg Grating sensors devoted to both health monitoring of road bridge structures and traffic load monitoring. The ultimate aim of the application is the remote continuous monitoring of the structures, with real time acquisition of the dynamic and quasi-static deformations inferred by both the road traffic and the daily and seasonal thermal variations. A Fiber Bragg Grating network composed of 24 sensors has been installed on the bridge on the Po river of the 'A21 Torino Brescia' Italian Highway. The bridge is a concrete structure, and sensors are applied on various rebar components. The sensors were installed directly on the rebars, adopting a special technique specifically developed for permanent concrete embedding. An extensive data acquisition program is in progress with the aim of both health monitoring and in transit lorry weighing. Results are discussed and planned future work is presented.

The relative accuracy of temperature and strain determination using Brillouin frequency shift and power change in standard single-mode fiber and the frequency shifts of the two Brillouin peaks in large effective area fiber is reported.

We report on a novel method for simultaneous distributed measurement of the temperature and strain in an optical fiber based on spatially resolving the anti-Stokes signals of both the spontaneous Raman and Brillouin backscattered signals.

A theoretical investigation on two techniques for the interrogation of fiber Bragg gratings (FBG) is reported. We compare two methods for decoding the Bragg wavelengths of gratings: the Fast Fourier Transform (FFT) processing and a parametric frequency estimation method called MUSIC. Results demonstrate that the second technique has advantages over the first one.

A new interrogation system for a large number of strain sensors is presented. In the residential building sensor market some facts have to be dealt with: low cost, networks with a large number of sensors, reliability, passive devices, amongst others. We have accomplished all of these with the new interrogation system we are going to present.

The experimental validation of a numerical technique for temperature/strain sensing, based on frequency domain fiber-optic Brillouin measurements, is presented. In this technique both measurements and the signal processing are performed in the frequency domain. The algorithm is based on a harmonic expansion of the unknown profile, whose coefficients are determined by means of a multidimensional minimization. Preliminary results prove the validity of the proposed technique.

A fiber optical laser sensor is applied for online and in-situ concentration monitoring of volcano gases. This can help to better understand the mechanisms underlying volcanic activity and enable the establishment of novel warning systems.

The semiconductor laser diodes that are typically used in applications of optical communications, when working as amplifiers, present under certain conditions optical bistability, which is characterized by abruptly switching between two different output states and an associated hysteresis cycle. This bistable behavior is strongly dependent on the frequency detuning between the frequency of the external* optical signal that is injected into the semiconductor laser amplifier and its own emission frequency. This means that small changes in the wavelength of an optical signal applied to a laser amplifier causes relevant changes in the characteristics of its transfer function in terms of the power requirements to achieve bistability and the width of the hysteresis. This strong dependence in the working characteristics of semiconductor laser amplifiers on frequency detuning suggest the use of this kind of devices in optical sensing applications for optical communications, such as the detection of shifts in the emission wavelength of a laser, or detect possible interference between adjacent channels in DWDM (Dense Wavelength Division Multiplexing) optical communication networks.

Different optical fiber sensor configurations based on a LBL nano-technique will be presented. With this technique it is possible to fabricate different structures such as nano Fabry Perot interferometers, optical fiber gratings and any other one dimensional photonic bandgap structures that may be used either for sensing applications or for the implementation of other fiber optic devices. Some of the proposed fiber optic sensors have been fabricated and their main characteristics are their negligible temperature dependence, their fast response, the possibility of using low cost LEDs instead of lasers or even the possibility of operating at different wavelengths.

This paper presents the first optical fiber sensor gateway for integrating these special measurement devices in Home Automation Systems, concretely in those buildings that use the KNX European Intelligent Buildings Standard.

A new arbitrary distributed strain and temperature sensing method based on three fiber Bragg gratings with different reflection spectrums and combine genetic algorithm have been developed and simulated. This method uses three different fiber Bragg gratings: two are uniform fiber Bragg gratings and the other is chirped fiber Bragg grating.

Novel devices consisting of uniform-waist tapered optical fibers with a double layer (metal plus dielectric) deposition are presented and their properties in terms of optical transmission are studied. Excitation of surface plasmons in the metallic layers is experimentally shown. These devices can be used as basis for new sensors.

The two-dimensional shape of a multicore optical fiber is estimated from distributed strain measurements. The fiber's shape is calculated based on the local curvature of the fiber and assuming practical strain sensitivities.

In our previous papers we have introduced the Chirped-Pulsed Frequency Modulation technique (C-PFM); it has been used to allow the multiplexing capability of a multipoint Fiber Bragg Grating (FBG) sensor network. In this paper we report some preliminary experimental results, which confirm the theoretical analyses previously obtained. The innovative multiplexing approach, without to increase the complexity of the acquisition system, is able to address up to 10 independent sensing points on a single fiber. The C-PFM technique is based on the amplitude modulation of the emitted signal (pulsed) from the laser source by a chirped frequency signal and on the demodulation of the reflected signal by means of an adaptive filter (that is only a numerical elaboration). The experimental result are here shown and commented in order to define limitations and capabilities of the approach.

For the first time online temperature measurements with FBG temperature sensors on railway overhead lines could be demonstrated. All sensors measured successfully under outdoor conditions over a two year period. As a first experimental result the excess temperatures due to current load are small compared to ambient sources of temperature change. In the future this first result will be analyzed under different seasonal and current load conditions. Furthermore the modeling and first field test have demonstrated the possibility to acquire information about the interaction between OCL and current collector via optical strain gauges integrated into conventional current collector strips.

Over the course of the last few years, several readout techniques for fiber Bragg grating (FBG) sensors have been proposed. However, all of them suffer from specific restrictions concerning response speed, accuracy, sensor multiplexibility and cost. In the past, it was often assumed that diffraction grating spectrometers were suitable only for FBG applications with modest resolution. The achievable pixel resolution is nowadays in the range of several tens of pm. For FBG sensors with typical temperature coefficients of 5 pm/K and strain coefficients of 0.7 pm/με this resolution is not sufficient for the majority of applications. We present a discussion on different methods for the subpixel registration of FBG spectra and we introduce a novel detection algorithm: the linear phase operator technique (LPO). Even under extreme noisy conditions LPO ensures a significant resolution enhancement by a factor of three compared to conventional algorithms and is shown to be very efficient in its implementation. The efficiencies of several conventional algorithms and LPO is compared by simulations and by means of a test bench. With slight efforts LPO is adaptable to further applications like spectrometer based Fabry-Perot sensors and other sensors with CCD detectors.

Polarization state of the optical signal in erbium doped fiber is experimentally checked. Dependencies with the pump power, the input signal power and with the spectrum are reported.

Laser welding is being introduced in the aerospace industry due to its many advantages over traditional techniques. However, welding of parts with complex shapes requires precise control of the focal point of the laser in order to achieve full penetration over the entire seam. In this paper, we present an improved control system for real-time adjustment of the correct focal position, which is based on the monitoring of the light emitted by the process in two different spectral bands. The reported system has been optimized for use in a real environment: it is robust, compact, easy to operate, able to adjust itself to different welding conditions, materials and laser setups, and includes a direct connection to an external PC. Results from recent field trials on complex aerospace structures are provided.

Establishing and testing the performance of a monitoring system designed for long-term applications presents some challenges that do not always apply to other measurement instruments. The evolution of the main measurement parameters must be evaluated over long periods of time and the reliability and failure-rate must be estimated in a statistically sound procedure. When establishing testing procedures for any system it is important to achieve three goal: the procedures must be based on traceable international standards, the procedures must be reproducible by the system users or third-parties testing authorities and the tests should be applicable to different measurement systems to allow a fair comparison of the respective performances. This contribution describes the main procedures used to test the compliance of SMARTEC's SOFO system components to the published specifications. It also offers a general overview of some issues related to the testing of long-term system performances.

Injection locking of two DFB semiconductors opens new possibilities to generate effective signals for optical sensing, in order to reach better performances. Pure waveforms can be generated with qualities exceeding those obtained using external modulators.