POF has found wide use in multimode intensity-based sensor applications. The characteristics of POF, limit the link (sensor)length to a few tens of meters and the sensor operational temperature cannot exceed 80°C. However, when these limitations are not important, POF sensors can offer their most significant advantage over corresponding glass fibre sensors, and this is a significantly lower system cost. Following recent new developments in POF technology, such as fibre gratings and microstructured POF, one looks forward to new and more exciting POF sensor applications. The future of POF sensors is concluded as optimistic.

The propagation properties of microstructured optical fibers useful for sensing applications are reviewed. The interaction between light and sample can reach 95 % in singlemode hollow core fibers and examples of structures exhibiting such large overlap ratios are described. The generation of 300 nm and 700 nm flat continua of visible and IR light in a single highly nonlinear holey fiber, well suited for the detection of biological species by spectroscopy, is reported. The low temperature sensitivity of long period gratings and of the birefringence in holey fibers is attractive for sensors operating in varying environmental conditions.

Interactions between acoustic waves and optical modes both propagating along an optical fiber are reviewed for applications in tunable photonic sensory devices. Fiber design parameters in Brillouin scattering sensors, and acoustooptic tunable filters are discussed.

In this paper, we presents a comprehensive overview of novel long-period fiber gratings (LPFGs) fabricated by using the high-frequency CO₂ laser pulses technique for low-cost sensing. These LPFGs have not only better fabrication flexibility, better high temperature capability, much lower cost than those fabricated by the UV exposure method due to the use of relatively inexpensive CO₂ lasers and standard telecommunication fibers, but also a number of unique bend, transverse load and torsion characteristics due to the asymmetrical refractive index distribution on the cross-section of the fiber induced by high-frequency CO₂ laser pulses, offering greater potential for multi-parameter measurement.

In the paper some properties of optical fibers coatings applied in the chemical and biochemical sensors are presented. The special attention was focused to the surface properties and structure of sol-gel layers, but also the features of the polymer coatings are described.

We shortly review general reliability definitions and methods used for optical fiber components for telecommunication applications and attempt to discuss in how far these can be applied to fiber sensor components.

The bandstructure of photonic crystals offers intriguing possibilities for the manipulation of electromagnetic waves. During the last years, research has mainly focussed on the application of these photonic crystal properties in the telecom area. We suggest utilization of photonic crystals for sensor applications such as qualitative and quantitative gas and liquid analysis. Taking advantage of the low group velocity and certain mode distributions for some ~k-points in the bandstructure of a photonic crystal should enable the realization of very compact sensor devices. We show different device configurations of a photonic crystal based on macroporous silicon that fulfill the demands to serve as a compact gas sensor.

We survey attempts to accurately diagnose skin cancer in vivo and in real time through the use of optics and automatic computation without the intervention of the clinician. Although no system has yet been shown to have such a capability, commercialization of a variety of diagnostic aids has taken place. We describe our own research into the diagnosis of malignant melanoma, the most lethal form of skin cancer, based on the spectroscopy of diffuse white light reflectance collected with a single multimode fiber after delivery with a multimode fiber bundle. Our clinical study, which collected 82 melanomas and 277 lesions in total, highlights the complexity of this challenging application.

Scattered colorimetry, i.e., multi-angle and multi-wavelength absorption spectroscopy performed in the visible spectral range, was used to map three kinds of liquids: extra virgin olive oils, frying oils, and detergents in water. By multivariate processing of the spectral data, the liquids could be classified according to their intrinisic characteristics: geographic area of extra virgin olive oils, degradation of frying oils, and surfactant types and mixtures in water.

The use of semiconductor nano-particles as temperature probes in luminescence chemical sensing applications is addressed. Temperature changes the intensity, the peak wavelength and the spectral width of the quantum dots luminescent emission in a linear and reversible way. Results are presented that show the feasibility of implementing a self-referenced intensity based sensor to perform temperature measurements independent of the optical power level in the sensing system. Additionally, it is demonstrated that self-referenced temperature measurements in multiple points could be performed using reflection or transmission based optical fiber configurations.

The sensing properties of Langmuir-Blodgett (LB) films consisting of tangled Single-Walled Carbon Nanotubes (SWCNTs) used as sensitive nanomaterials for Volatile Organic Compounds (VOCs) detection have been investigated by using Quartz Crystal Microbalance (QCM) 10 MHz AT-cut quartz resonators, and standard Silica Optical Fiber SOF) based on light reflectometry at a wavelength of 1310 nm. The proposed detection techniques are focused on two key parameters in the gas sensing applications as mass change and complex refractive index change induced by gas molecules adsorption. Highly sensitive, repeatable and very fast responses of SWCNTs sensors to ethanol and ethylacetate, with concentrations in the range 10-500 ppm, have been observed. A good inter-relationship has been found between the two different transducers, showing a good correlation of the sensing mechanisms based on the change in the mass and optical properties of the chemosensitive nanomaterial for QCM and SOF sensors, respectively.

Palladium and its alloys show a high and selective affinity for hydrogen, resulting in a volume expansion. We report on development work using fibre Bragg gratings attached to palladium tubes to monitor strain resulting from hydrogen uptake. The technique is aimed at low concentration hydrogen monitoring where H₂ is the result of ageing of polymer materials.

Two fiber optic probes are combined for the simultaneous monitoring of colour and refractive index of a liquid. It is shown how, through modelling, the design can be adapted to cover different ranges in refractive index and light absorption.

Given the rapid aging of the world’s population, improvements in technology for automation of patient care and documentation are badly needed. We have previously demonstrated a 'smart bed' that can non-intrusively monitor a patient in bed and determine a patient's respiration, heart rate and movement without intrusive or restrictive medical measurements. This is an application of spatially distributed integrating fiber optic sensors. The basic concept is that any patient movement that also moves an optical fiber within a specified area will produce a change in the optical signal. Two modal modulation approaches were considered, a statistical mode (STM) sensor and a high order mode excitation (HOME) sensor. The present design includes an STM sensor combined with a HOME sensor, using both modal modulation approaches. A special lens system allows only the high order modes of the optical fiber to be excited and coupled into the sensor. For handling output from the dual STM-HOME sensor, computer processing methods are discussed that offer comprehensive perturbation analysis for more reliable patient monitoring.

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 along it. The original technology, "Brillouin Optical Correlation Domain Analysis: BOCDA" has been proposed and developed to analyze the distributed strain along the fiber by use of synthesis of correlation characteristics of continuous lightwave. Adopting this technology, "fiber optic nerve systems" with quite a high spatial resolution and measurement speed, have been established.

We present a sensing principle of the distributed fiber Brillouin strain and temperature sensor by coherent probe-pump technique that offers a new method to achieve centimeter spatial resolution with high frequency resolution. A combination of continuous wave (cw) and pulse source as the probe (Stokes) beam and cw laser as the pump beam have resulted in stronger Brillouin interaction of Stokes and pump inside the pulse-length in the form of cw-pump and pulse-pump interactions. We find that the coherent portion inside the pulse-length of these two interactions due to the same phase has a very high Brillouin amplification. The Brillouin profile originating from the coherent interaction of pulse-pump with cw-pump results in high temperature and strain accuracy with centimeter resolution, which has been verified by successfully detecting 1.5 cm out-layer crack on an optical ground wire (OPGW) cable.

A remotely pumped EDFA combined with Raman amplification was used to enhance the performance of spontaneous Brillouin intensity-based temperature sensor. A temperature resolution of 5.7°C, spatial resolution of 20m was achieved at 88km.

Very high time resolution of pulse timing drift sensor for long fiber skew monitor is demonstrated by using the 10-cc compact module which is used the cross-correlation and differential detection technique. The signal pulse timing drift value and direction are correctly measured even when the signal intensity is fluctuated. The sub-picosecond pulse timing drift through the long fiber delay line is detected by this module.

Frequency-modulated continuous wave (FMCW) measurements of Rayleigh backscattering and Fresnel reflection from 95-km fiber have been demonstrated by using a compact piezo-electrically-tuned sub-kilohertz-linewidth fiber laser. This technique enables ultra-long fiber fault location in optical transmission systems. The high sensitivity (over-80dBm) of the long-range backscatter measurements without using optical amplifier are benefit from the extremely long coherence length of the sub-kilohertz linewidth fiber laser, which has been estimated to be 210 km in air.

Brillouin intensity and frequency measurements achieved temperature and strain to be unambiguously resolved with resolutions of 3.5°C and 85 με at 50km. Frequency only measurements, achieved temperature or strain resolution of 1.7°C and 35 με at 100km.

We discuss the fundamental limits of fiber Bragg grating (FBG) wavelength metrology. High-accuracy wavelength measurements are critical for FBG strain sensors because a wavelength measurement uncertainty as small as 1 pm leads to an uncertainty of nearly 1 microstrain. We compare the measurement uncertainties for several common wavelength measurement systems, including tunable laser, optical spectrum analyzer (OSA), and interferometric. We show that when using an OSA it is difficult to achieve a measurement uncertainty better than 10 pm, and if the OSA is not accurately calibrated to a known wavelength reference, then the wavelength measurement uncertainty can be as large as 1 nm. We describe the uncertainties involved in determining peak and/or centroid wavelength from a measured data set. We also discuss calibration references for FBG sensor interrogation units. Wavelength references that are based on molecular absorption lines are often an excellent choice for FBG sensor calibration. However, some interrogation units require a wavelength reference unit based on narrow reflection lines rather than absorption lines. We investigated the application of athermally packaged FBGs as wavelength references, but we found that their wavelengths will drift with time and can undergo large jumps. We concluded that it is difficult to achieve stability better than 4 pm/year in athermally packaged FBGs.

We propse the application of sensors based on the intrinsic bend sensitivity of Bragg gratings inscribed in D-shaped fibers. The first example is a viscosity sensor, consisting of the D-shaped fiber with a sphere attached to the tip of the fiber. The force exerted on the sphere by the laminar flow of a fluid with unknown viscosity bends the fiber, and with this shifts the Bragg wavelength of the inscribed Bragg grating. The other one is a hydrogen senosr, which uses the influence of hydrogen on a palladium foil attached to the Bragg grating. The palladium foil, which is frictionally connected to the flat surface of the D-shaped fiber, is stretched under the influence of hydrogen and with this stretches/bends the fiber.

Long period gratings written into a standard optical fibre were modified by a femtosecond laser, which produced an asymmetric change to the cladding's refractive index resulting in a directional bend sensor.

This paper describes the application of fibre Bragg grating (FBG) sensors to measure strains at the outer surface of a mandible. The strains were correlated to identical ones obtained with a numerical finite element model. For this purpose, a synthetic mandible was used and 4 Bragg sensors were glued to the mandible. Strain patterns were assessed for different load configurations which included the forces of the masseter and temporal muscles and occlusion loads on different tooth (incisor, canine and molar). Overall the strains obtained using different measuring methods were identical, namely for the case of symmetric loading. When loading was non-symmetric, strain differences were observed at one sensor.

Using an ultrafast Ti:sapphire IR laser and a phase mask, fiber Bragg gratings (FBGs) with high thermal stability were fabricated in SMF-28 fiber for sensor applications and were subjected to long annealing tests at 1000 °C. FBGs that maintained more then 99.95 % reflectivity after several hundred hours at this temperature are demonstrated. The gratings perform well in cycling experiments up to 1000 °C and hysteresis in the wavelength response was not detected. The capability of this new type of FBG to be used for high temperature sensors is briefly discussed.

The monitoring of a complex industrial scale process is a challenging task, particularly when such a process is a large (100m³) industrial organic waste anaerobic digestion (AD) system. This paper describes the deployment of fibre optic based sensors for monitoring an AD process. To enable this complex process to proceed, a number of critical conditions must be set (e.g. temperature, pH etc.).Two novel fibre optic sensors have been developed for monitoring temperature and pH. These operate in a zone zero environment (highly explosive) and need to withstand vibrations and microbial activity and to operate over extended periods of time (months) with no or little servicing.

New techniques for introducing micro- and nanostructures in the core region of optical waveguides or fibers offer new opportunities to influence the propagation and coupling conditions of guided light. Such modifications include e.g. single mode conditions for optical fibers, the range of the numerical aperture, dispersion properties, mode shape, extended wavelength ranges or guiding with multiple cores. Although many developments were triggered by possible applications in communication technology, these new opportunities in functionality offer attractive chances also for new investigations into sensing with optical fibers.

The construction and operation of a DFB photonic crystal fibre laser produced in Er³⁺ core doped air-silica structured optical fibre is presented. Its potential in sensing generally is elaborated.

We report on a low-coherence interferometric scheme for the measurement of the strain and temperature dependences of group delay and dispersion in short, index-guiding, 'endlessly-single-mode', photonic crystal fibre elements in the 840 nm and 1550 nm regions. Based on the measurements, we propose two schemes for simultaneous strain and temperature measurement using a single unmodified PCF element, without a requirement for any compensating components, and we project the measurement accuracies of these schemes.

Bandgap guidance in photonic crystal fibers (PCF) is strongly selective spectrally and in this sense resembles guidance in fibers with Bragg gratings. The photonic band-edge shifts when the optical properties of the material in the fiber are affected by external factors such as strain, temperature, pressure, static fields, chemical vapour penetration etc. This analogy allows for the development of optical sensors with similar principle of operation as fibers with Bragg gratings, however with novel sensing characteristics. Here we study theoretically PCF filled with LC when material anisotropy plays a strong role in the creation of the bandgap.

In this paper we present results relative to Fiber Bragg Grating (FBG) photowritten in two kinds of Ge-doped microstructured optical fiber cores devoted to sensing applications. A cross-comparison between theoretical and experimental modal field patterns is carried out. We present the first values of spectral sensitivity of Bragg grating in relation to the refractive index of the substance inserted into the holes.

A fiber Bragg grating was written, using the phase mask technique, in a short length of Er³⁺:Yb³⁺-codoped fibre and its temperature and strain characteristics were investigated. Two of the three parameters of interest are associated with Bragg grating properties, namely the usual dip at the Bragg wavelength, λB, and an unexpected dip at ~2/3 λB that is the third harmonic of features within the grating having double the assumed periodicity. The third parameter is the fluorescence intensity ratio arising from a pair of transitions in Yb³⁺ ions. This arrangement consisting of three co-located sensors offers interesting possibilities for the simultaneous measurement of three parameters.

This paper summarizes nanostructured optical fiber sensors fabricated by molecular self-assembly chemistry. Strain, pressure, vibration and chemical sensors are described which are based on selfassembled fiber cores, claddings, distal endface coatings and free-standing membranes.

We demonstrate experimentally the optical control of the group velocity along an optical fibre using Stimulated Brillouin Scattering. We have achieved pulse delaying of 30 nanoseconds and group velocity exceeding the vacuum light velocity.

A high-speed MEMS swept-wavelength light source (SLS) for an FBG sensor system is proposed and demonstrated. It is basically a multi-mode external-cavity laser diode (LD), and consists mainly of an LD head, diffraction grating, and electromagnetically actuated MEMS scanning mirror. It has a linewidth of 0.03 nm, scan range from 1508 to 1582 nm, scan rate of 0.57 ms and output power of 10 mW. The heart of the MEMS SLS is the MEMS scanning mirror (8 x 6 mm) that changes the oscillation wavelength continuously and rapidly. The scanning mirror is actuated by electromagnetic force derived from a permalloy piece glued on the back of the mirror and a C-shape electromagnet. The MEMS SLS allows construction of a low-cost, simple and high-speed FBG interrogator system.

We have experimentally demonstrated a new compact surrounding refractive-index sensor using MMF-CSF-MMF structure. For refractive index range of 1.30 to 1.42, resolution of 9.68×10^-3 /nm and linear dynamic range of 20.5dB were obtained at λ=1310nm.

Optical low coherence reflectometry (OLCR) was used for the measurement of the local fiber Bragg grating (FBG) birefringence. The birefringence with resolution of 4μ10^-6 was determined directly from oscillations in the OLCR amplitude with a spatial resolution on the millimeter scale. Using OLCR phase in combination with inverse scattering algorithm the birefringence was retrieved with a high spatial resolution of 25 microns. The technique using OLCR amplitude was applied for measuring birefringence of a FBG under diametric loading.

We present an implementation of high-sensitivity optical chemsensors based on FBGs UV-inscribed in D-shape and multimode fibres and sensitized by HF-etching treatment, demonstrating a capability of detecting chemical concentration changes as small as < 0.5%.

This paper firstly presents a novel optical sensor technology developed to locate, from above ground, the lateral position of a buried dielectrically sheathed optical cable. Then, optical sensor methods for the distributed sensing and longitudinal positioning of time-varying acoustic disturbances are presented. It is hoped to present results of a novel field-trial capable OTDR based system in the verbal presentation.

We have developed a system for monitoring telecommunications tunnels to improve the reliability of telecommunication and to reduce maintenance costs through early damage detection. Core components of the system are a Brillouin optical time-domain reflectometer (BOTDR), which allows distributed and long-distance strain measurement, and optical fiber sensors installed in tunnels. Experimental results show that this system can detect tunnel deformation with a measurement error of 0.1 mm from a contraction of 1 mm to an elongation of 6 mm over a span of 10 km. The system used in practice at present is introduced.

Optical fibers are key components in telecommunication technologies. Apart from optical specifications, optical fibers are expected to keep most of their physical properties for 10 to 20 years in current operating conditions. The reliability and the expected lifetime of optical links are closely related to the action of the chemical environment on the silica network. However, the coating also contributes largely to the mechanical properties of the fibers. The aim of this work was to study the strength and the mechanical behaviour of the silica optical fibers in an acid environment. A container with ammonium bifluoride acid salt was plunged into hot water at different temperatures (55° and 75°C). This emitted acid vapors which attacked the optical fibers for a period of 1 to 18 days. An aging study was performed on silica optical fibers with standard polyacrylate coating and with hermetic carbon coating. A dynamic two-point bending bench at different faceplate velocities (100, 200, 400 and 800 μm/s) was used. For comparison, the same dynamic measurements were also carried out on non-aged fibers. After acid vapor condensation, salt crystal deposits on the fibers were displayed using an electron scanning microscope. These crystals became visible to the naked eye from the 7th day post exposure.

We have measured for the first time the shift of the Bragg wavelength and other parameters of fibre Bragg grating (FBGs) exposed to γ-radiation at different wavelengths up to a dose of 100 kGy. The results show that the FBG sensitivity to radiation increases from 820 nm to 1516 nm so that FBGs with higher Bragg wavelength, e.g. 1.55 μm, are good candidates for high dose radiation sensing: no saturation was observed up to 100 kGy and the measured wavelength shift was fairly independent on the radiation dose rate.

Distributed fibre optic sensors are being evaluated by the nuclear industry for monitoring purpose. We evaluate the radiation tolerance of distributed Brillouin sensors up to very high total gamma doses.

We propose a method to enlarge the measurement range for Brillouin Optical Correlation Domain Analysis system simplified with time-division pump-probe generation scheme. In this system, the pump and probe lightwaves, which are modulated in frequency with a sinusoidal waveform to localize the stimulated Brillouin scattering periodically, are additionally gated temporally to select only one localized position. We successfully measured distribution of fiber Brillouin gain spectrum over 250m measurement range with 8cm spatial resolution.

Fibre-optic sensors can show significant advantages against other sensor technologies when installed in the right application. We demonstrated successfully the use of fibre-optic current, temperature and strain sensors in power generators, power combustion turbines, and electric infrastructure and preventive maintenance for transportation systems. All solutions offer enhanced efficiency and availability of the units they were installed in.

The paper presents new results connected with the fibre-optic Sagnac interferometer (FORS-II) application for seismic rotation waves (SRW) investigation. Generally it is a fibre-optic rotational seismometer based on its resolution in the range of 4.27x10^-8 rad/s which can detect the SRW in the direct way. The paper presents the analyses of the experimental results obtained in Ojcow standard seismic observatory. The discussion presented in the paper shows a new aspect connected with physical fundamentals of the seismic rotation waves.

We show theoretically and experimentally that the use of an air-core photonic-bandgap fiber in a fiber-optic gyroscope can drastically reduce the noise and phase drift caused by Rayleigh backscattering as well as non-reciprocal and thermal effects.

We report experimental measurements of the strain and temperature sensitivity of the optical phase in a singlemode polymer optical fibre. These values were obtained by measuring optical path length change using a Mach-Zender interferometer.

In this paper a low coherence interferometric sensing method is presented. The magnitude of a small optical path length imbalance is monitored by measuring the wavelength dependence of the interferometer's output. The interferometer produces a spectral modulation, or interferogram, imposed on the background spectrum of the broadband light source used to illuminate the sensor. The interferograms are then recorded using a high-speed spectrometer and the small optical path imbalance is calculated by processing the interferogram in a computer using a Fast Fourier Transform (FFT). This sensing system has been configured to form the basis for an optical fibre voltage sensor. The system monitors the total retardance of a section of thermally poled twin hole silica fibre (sensing fibre). Transverse electric fields applied to the sensing fibre will then modulate its total retardance due to the polarisation dependence of the induced linear electrooptic effect. Experimental results for linearity, and an analysis of the methods used are presented.

A fiber-optic current sensor for direct currents up to 500 kA is presented. Applications include the control of the electrolysis process for the production of metals such as aluminum, copper, magnesium, etc. The sensor offers significant advantages with regard to performance and ease of installation compared to state-of-the-art Hall effect based current transducers. A novel scheme of a polarization-rotated reflection interferometer and fiber gyroscope technology is used to measure the magneto-optic phase shift. A new technique has been developed for packaging the sensing fiber in a flexible strip of fiber re-enforced epoxy for coil diameters up to several meters. The sensor can be installed without opening the current-carrying bus bars. Subsequent re-calibration is not necessary. Accuracy is within ±0.1% over a wide range of currents and temperatures.

Geodetect is an innovative geotextile-based monitoring system, developed for the measurement of strain and deformation of earthwork structures reinforced with geosynthetics. This paper presents the background and the results of the development and the practical experience acquired in real time jobs with this new technology.

Eight re-configurable, synchronized resonant cavity time-division-multiplexed FBG sensor interrogators provide 16,800 high-resolution measurements-per-second from 280 axially embedded strain sensors, for the analysis of vortex-shedding-induced vibration and bending in a composite oil riser pipe.

Distributed fiber optic sensing presents unique features that have no match in conventional sensing techniques. The ability to measure temperatures and strain at thousands of points along a single fiber is particularly interesting for the monitoring of large structures such as pipelines, flow lines, oil wells, dams and dikes. Sensing systems based on Brillouin and Raman scattering have been used for example to detect pipeline leakages, verify pipeline operational parameters, prevent failure of pipelines installed in landslide areas, optimize oil production from wells and detect hot-spots in high-power cables. The measurement instruments have been vastly improved in terms of spatial, temperature and strain resolution, distance range, measurement time, data processing and system cost. Analyzers for Brillouin and Raman scattering are now commercially available and offer reliable operation in field conditions. New application opportunities have however demonstrated that the design and production of sensing cables is a critical element for the success of any distributed sensing instrumentation project. Although standard telecommunication cables can be effectively used for sensing ordinary temperatures, monitoring high and low temperatures or distributed strain present unique challenges that require specific cable designs. This contribution presents three cable designs for high-temperature sensing, strain sensing and combined strain and temperature monitoring.

The leakage detection system based on the distributed fibre optical temperature measurement method is an analysing method for continuous detection and localization of leakages at pipelines in the steady and unsteady operation states according to the German rules for pipelines TRbF 301/TRFL which is valid in Germany since April 2003. The leakage detection system is useable under the precondition that there is a sufficient large temperature gradient between the leakage area and the unaffected environment. This can be caused by the medium itself or through a physical effect due to the leakage, e.g. gas expansion, evaporation. It's a very sensitive method, so also creeping leakages can be detected.

The paper describes a new method for the distributed measurement of isotropic pressure acting on an optical fibre. The method utilises backscatter polarimetry to measure the distribution of linear birefringence in a monomode side-hole fibre. The measurement is made with a spatial resolution ~1metre, in a time ~1 minute. The technique can be applied to the distributed measurement of fluid pressure, and is expected to have valuable application in the oil and gas industries. Extensions of the technique also will allow measurement of transverse and twist strains in extended structures.

In this paper we present how a miniature fiber optic pressure sensor based on micro-optical mechanical systems (MOMS) could solve most of the problems associated with fluidic pressure transduction presently used for triggering purposes in IABP therapy. The small size of the MOMS (0 550 μm) allows a positioning of the sensor directly at the tip of the intra-aortic catheter, exactly where the pressure should be monitored. With outstanding performances in terms of resolution and frequency fidelity, this absolute pressure sensor can precisely detect small pressure variations such as the dicrotic notch in the intra-aortic pressure waveform, which is used as a trigger point in IABP therapy. Such technology could probably help in the development of a less invasive therapy with reduced catheter size associated with reduction of vascular complications such as ischemia. The presented optical fiber sensor has intrinsic immunity to electromagnetic fields and noise perturbations. Furthermore, the patented white-light cross-correlation technology of the signal conditioner makes it immune to optical fiber binding and highly tolerant to optical losses. Such solution is extremely well adapted for in situ pressure monitoring in many medical applications.

An efficient multiplexing method for fiber Bragg grating sensors based on a broadband mode-locked laser source and interferometric interrogation is described. The system has the capability to interrogate several hundred fiber Bragg grating sensors on a single fiber, whilst achieving sub-microstrain resolution over bandwidths greater than 100 kHz. A demonstration system with 8 sensors is presented, which achieves strain resolutions less than 213 nε/Hz^1/2 up to 100 Hz.

We experimentally demonstrate a novel application of distributed fibre Raman amplification to a bus network for the wavelength multiplexing of optical sensors. Each sensor is uniquely identified by reflection from a fibre Bragg grating (FBG) and the distributed gain allows the number of sensors to be increased without using costly remote amplifiers. We show how the topology allows the received powers from the sensors to be equalised, even though only one Raman pump wavelength is used and we investigate how the performance depends on the launched pump power. The spectral filtering of the FBGs, combined with the distributed gain, jointly reduce the noise and we report measured signal to noise ratios.

Ordered arrays of nanometer-sized optical probes were developed on the distal face of coherent optical fiber bundles. The fabrication steps derived from SNOM probes methodology and allowed to produce high-density microarrays of nanoapertures with adjustable dimensions. The angular profile of the far-field intensity transmitted through the nanostructured arrays shows a diffracting behavior which is a function of the nanoaperture sizes. Nearfield optical behavior was thus established in an array format where each element is equivalent to a single nanoaperture. It means that each subwavelength aperture of the array is optically independent in the far-field regime. This analysis demonstrates its potential use as a near-field optical array. Since the initial architecture of the bundle is retained, the array format allows imaging a sample concomitantly at both nanometric and micrometric scales. Therefore such an array plays a bridging role between these 2 fundamental scales.

Doppler optical coherence tomography (OCT) can image tissue structure and blood flow at micrometer-scale resolution, with limited imaging penetration depth. We report a novel linear-scanning needle-based Doppler OCT system using angle-polished gradient-index or ball-lensed fibers. A prototype system using a 19-guage (diameter ~0.9 mm) echo-genic needle is constructed and demonstrates in vivo imaging of bidirectional blood flow in rat leg and abdominal cavity. To our knowledge this is the first demonstration of Doppler OCT through a needle probe in interstitial applications to visualize deeply situated microcirculation.

Optical coherence tomography (OCT) is a novel technique for noninvasive imaging based on low coherence interferometer. In order to get image with high resolution, the highly precise scanning and sample stages are essential. In this study, we develop a new optical fiber type of OCT with a commercial auto-focus device to simultaneously measure refractive index and thickness of a single-layer for demonstration. In order to diminish the measurement error resulting from the slight vibration of the sample or sample stage, we design an auto-focus device into the new OCT system. As compared to the conventional one, the new OCT setup is simpler and processes the data speedily. It is found that the conventional OCT with an auto-focus device would be extremely difficult in controlling stages.

A new high-performance, low-cost design for OCT imaging is presented. It involves an all-SMF autocorrelator topology. An imaging instrument complete with a scanning probe was constructed and evaluated confirming high performance imaging capability.

The applications of fiber optic sensors on board spacecraft and launchers are discussed based on the experience gained by several ESA funded R&D projects along with the experience of preparing the first spaceflight hardware demonstrations.

A fibre Bragg grating sensor system has been installed in a horizontal axis wind turbine and was successfully tested for already more than one year. We report the requirements, system design and realisation of the sensor system for continuous on-line load monitoring of the rotor blades, and provide examples of strain measurement results.

We describe the first application of multiplexed fibre Bragg grating strain sensors in a multicore fibre. Sets of gratings, acting as strain gauges, are co-located in the multicore fibre such that they enable the curvature to be measured. Multiple sets of these gratings allow the curvature to be measured at several points along the fibre. This sensor is configured to monitor displacement of concrete tunnel sections, and was demonstrated capable of displacement measurement with a resolution of ±0.1 mm over a range of several millimeters.

An array of fibre optic seismic intruder detection sensors has recently been tested by QinetiQ. The array consisted of a set of distributed cable sensors and accelerometers, each being interrogated by an interferometric effect. Both types of sensor were able to detect a person crossing over the array, and frequency analysis of the signals suggests ways in which automatic intruder detection could be achieved.

The disposal of high radioactive waste in underground repository sites is a complex and complicated topic due to the strong heat generation. At the Mont Terri URL (Underground Research Laboratory), which is located in a potential clay host rock in Switzerland, a special heater test is currently performed to investigate the heat impact on the clay behavior. A fiber optic measurement system has been developed in order to measure the temperature evolution around the heat sources that have a maximum temperature of 100°C as well as the induced rock deformation due to the thermal expansion of the clay. The system as well as some first results will be described.

Conventional heated wire anemometry in combination with distributed fiber optical temperature sensors based on fiber Bragg gratings offer the possibility of distributed flow measurements.

Index-guiding photonic crystal fibers (PCFs) with appropriate structural parameters support the fundamental and second order modes over a practically infinite wavelength range. The potential applications of such PCFs are discussed.

In this paper, we describe the use of a genetic algorithm and two thermally-modulated fiber Bragg grating's (FBG's) reflection intensity spectra for inversely extracting complete physical parameters. The fiber Bragg grating's complete parameters included the grating period, grating position, grating length, chirped direction, and refractive index modulation. In this study, a uniform and chirped fiber Bragg gratings are synthesized successfully in the experiment. The experimental results show that the complete parameter synthesis in grating period, grating length, refractive index modulation and various grating positions from a 10 mm length uniform FBG have been recovered accurately.

In a long period grating (LPG) made on a silica-based single material photonic crystal fiber (PCF), the effect of material dispersion on the resonance wavelength of the LPG is negligible. The resonance wavelength, the period and length of the LPG, and the diameter and pitch of the air -hole lattice of the PCF are found to obey a scaling law. Simulations show that the resonance wavelength has a non-monotonic dependence on the grating period and, for a particular grating period, there could exist dual resonance wavelengths and hence double transmission dips due to phase matching between the fundamental core mode and a cladding mode simultaneously at two wavelengths. This phenomenon may be explored for novel devices and sensor applications.

A Bragg grating in a two-mode air-silica structured PCF was written and its dependence with temperature and strain analyzed. The temperature and strain calibration curves for both modes are measured and found to be distinct.

A new index-guiding-holey-fiber is proposed for flexible modal birefringence control by introducing a fourlayered defect with central air hole, silica pedestal, germanosilicate ring, and silica clad. Effects of these parameters over birefringence are reported.

The strain and temperature responses of transmission dips at 2/3 of the Bragg wavelength in type I and IIA fiber Bragg gratings are presented. The existence of such dips is related to complex features that have been observed in microscope images of fiber Bragg gratings. The temperature and strain responses are as expected and demonstrate the suitability of using signals from both the Bragg wavelength and 2/3 of the Bragg wavelength for the simlutaneous and co-located measurement of strain and temperature, using a single light source.

The results of thermal tests of high-temperature Bragg gratings written in a nitrogen-doped-silica-core fiber are presented. The gratings were produced by the conventional technique using an ArF excimer laser and a phase mask at various exposure regimes. The possible physical mechanisms responsible for thermal decay of the gratings are analyzed. Based on the results obtained, high-temperature sensors of physical quantities have been developed. The sensors can withstand heating up to 900 °C.

Supercontinuum generation is shown for the first time in a tapered triangular structure photonic crystal fiber with two closely spaced zero dispersion wavelengths where dispersion becomes normal for all guided wavelengths at a certain distance along the taper. The numerical calculation shows an increased bandwidth and a reduced depletion of the pump source when the photonic crystal fiber is tapered. We simulate the propagation of 15 femtosecond pulse with a peak power of 80 kW centered at 808 nm. Both fiber and pump source are commercially available and the improved light source can be used for measuring techniques such as optical coherence tomography and spectroscopy.

The paper presents the latest experimental results on influence of temperature and external electrical fields on propagation properties of a photonic liquid-crystal fiber composed of a photonic crystal fiber infilled with a nematic liquid rystal characterized by either extremely low (of the order ~0.05) or relatively high (of the order ~0.3) material birefringence. The nematic liquid crystal was introduced into the micro holes of the photonic crystal fiber by the capillary effect. Due to anisotropic properties of the obtrained photonic liquid-crystal fiber, switching between different guiding mechanisms has also been demonstrated.

Technology and basic characterization of new kind of side hole optical fiber with silver layers in the holes named side metal pipe (SMP) optical fiber is presented. The static deposition method of silver layers of several hundred nm thickness from liquid phase was used. Polarization properties of the side metal pipe optical fibers were found.

Using high-intensity (100-500 GW/cm²) 264 nm laser radiation, we fabricated long-period fiber gratings in telecom and photosensitive fibers, studied their temperature sensing properties and demonstrated the effect of thermal recovery of a LPFG resonance peak.

Long period gratings in two types of photonic crystal fibre have been studied. The gratings display negligible temperature sensitivity but useful sensitivity to other measurands. Theoretical modelling suggests that unusual phase matching conditions apply.

Phase and spectral response characteristics of fibre Fabry-Perot interferometers (FFPI), formed between linearly chirped fibre Bragg gratings (FBG), were theoretically modelled using Rouard's method. The method models accurately the phase shift through a complex grating structure which the transfer matrix model is unable to achieve. The FBG FFPI cavities were modelled with variable free spectral range that was tailored further to provide strain insensitivity and strain enhancement by making the chirp parameter and cavity length satisfy the desired conditions at a given wavelength of illumination.

A wavelength tunable erbium-doped fiber ring laser dedicated to high-speed interrogation of Fiber Bragg Grating (FBG) sensors has been realised and characterized. A standard FBG is used as the output mirror whereas an intra cavity spectral filter formed by a π-phase-shifted FBG is implemented to narrow the output laser spectrum down to 0.5 pm. The emitting wavelength is tuned at 500 Hz over 3.6 nm by simultaneously straining both the standard and π-phase-shifted FBG with a piezoelectric actuator. An all-fiber Michelson interferometer is used to accurately determine the spectral scanning range. Bragg wavelength increments equal to 1.3 pm are resolved combining both wavelength referencing with an absorption gas cell and amplitude normalisation versus the laser output power. This instrumentation is designed to be embedded in a train cabin for making on-board strain and temperature measurements on pantographs with FBG sensors.

Nowadays development of optical networks causes significant grow of interest in reliable fiber connections. Although fiber splicing techniques are well known, the assessment of a joint quality still bases on the simple image processing estimation. In advanced applications such solution is not sufficient and more trustworthy method is needed. One of the promising techniques of reliable measurements is microinterferometric tomography which allows determination of three-dimensional refractive index distributions in phase isotropic microelements. Measurement bases on interferometric scan of the tested element. Contrary to the classical testing methods based on attenuation tests microinterferometric tomography analyses an inspected fiber with the beam passing perpendicularly to the fiber axis. Tomographic scans taken for numerous, well defined angular positions and further calculations result 3D map of the area with clearly seen splice zone. In this paper we propose the novel design of the integrated low-cost microinterferometric tomography setup (fig.1). The system is built as the waveguide Mach-Zehnder interferometer with reduced vibration sensitivity due to using the grating beamsplitter and recombiner. Additionally we present the details of design of microinterferometric tomography setup and the initial remarks on the possibility to fabricate it with Deep Lithography with Protons (DLP) - unique master prototyping technology of fabrication both micromechanical and microoptical elements in polymer material. We aim to take an advantage of compactness and reduced dimensions of the interferometer to implement it as the possible accessory of the commercial optical fiber splicer.

We present a numerical investigation of fundamental and higher order modes propagating in doped core birefringent holey fiber. The conditions for the co-existence of two competing light guiding mechanisms, their consequences on the mode propagation and the potentialities for Bragg grating applications with this are discussed.

We analysed spectral dependence of modal birefrincence and susceptibility to temperature and to strain in two birefringent photonic bandgap fibers. The birefringence in these fibers is induced by the elliptical shape of either the core or the cladding holes. We show that in one of the fibres, the sensitivity to temperature nad to strain reaches zero in the center of the photonic bandgap. Our calculation method is fully vectorial and based on a hybrid edge/nodal finite element approach.

This paper discusses direct focused ion beam (FIB) writing of microstructured photonic elements and sensors like apertures on tips of optical fibers, microlenses, or photonic crystals. Emphasis is mainly on the fabrication side.

Concave cone fabricated by chemical etching process similar to previous technique used to make fiber tips (convex cone) is presented. Typically, optical fibers are etched in a fluorhydric (HF) solution with a thin layer of oil floating on top of the HF. The present investigation shows that concave cone etched fiber (CCEF) can be obtained by following the beginning of etching process. Comprehensive measurements of the dependence of the width and height of taper angle of the concave cone are plotted. The results of this investigation have led to an optimum approach for fiber cores alignment that is suitable for use in connecting fibers for efficient coupling between single-mode fibers.

We demonstrate a novel wavelength division multiplexed polarimetric fiber laser sensor array for current sensing. A tunable Fabry-Perot filter is used for discriminating each sensor from the multiplexed signals, and a frequency demodulation technique based on a phase-locked loop circuit is applied for signal processing.

A key analog fiber-optic link parameter for RF and microwave antenna remoting is conversion gain or loss, which is a measure of the output RF power to the input RF power at the modulator. The link conversion loss can be minimized by using high-power lasers, modulators with low drive voltages, and sensitive photodetectors. It is highly desirable to achieve link gain without RF amplification. This has not been possible for broadband operation due to the required modulator drive voltages. This paper reports on the development of optical waveguide modulators that can achieve subvolt drive voltages to frequencies of approximately 20 GHz. Long interaction length, multipass LiNbO₃ serpentine modulators have been fabricated employing low optical loss compact 180° turns. A record minimum RF loss achieved with a novel bridge structure electrode and used in these high performance modulators is presented. These modulators when connected to conventional antennas, operate as optical fiber electric field sensors.

A long-period grating (LPG) coated with gelatin was developed as a high relative humidity (RH) sensor. The resonance dip or coupling intensity of the LPG spectrum varies with humidity while the resonance wavelength remains constant. The principle of operation of the sensor is based on the effect of an external medium, with higher refractive index than that of silica or cladding, on the LPG spectrum. Experimental investigations on the sensor yield a sensitivity of 1.2dB/%RH with an accuracy of ±0.25%RH, and a resolution of ±0.00833%RH. The LPG RH sensor also offers repeatability, hysteresis and stability errors of less than ±0.877%RH, ±0.203%RH and ±0.04%RH respectively. In addition to the characterization of the LPG RH sensor, further studies were conducted to determine the effect of grating periodicities on the sensitivity. Results show that higher-order cladding modes from smaller grating periods enable the sensor to achieve higher sensitivity to humidity. This method is proposed to be more cost effective as compared to more complex spectroscopic methods based on wavelength detection. This sensor can also help to solve problems in measuring high humidity with existing relative humidity measurement systems.

In order to develop a simple system for sensing taste substances, an optical method using polymer/lipid films doped with a voltage-sensitive dye and plastic optical fibers (POFs) has been studied experimentally. The several kinds of polymer/lipid blended membranes doped with rhodamine-B dye with a long hydrocarbon chain were used after transferring on to the glass substrate glued on the end surface of POF. Its fluorescence intensity around 600 nm showed different patterns for the taste substance solutions such as bitter, salty and "umami". These results and a principal component analysis gave the possibility of an optical fiber taste substance sensor.

We demonstrate a high sensitivity biosensor by fine tailoring mode dispersion and sensitivity of dual-peak LPGs using light-cladding-etching method. The etched device has been used to detect concentration of Hemoglobin protein in sugar solution, showing a sensitivity as high as 20nm/1%.

The use of Fibre Bragg Grating sensors to study the setting expansion of dental materials like resin based composites and gypsum is reported. Temperature and strain evolution during the hardening phase of the material are obtained.

The suitability of semiconductor nanoparticles to provide a reference signal in luminescence based chemical sensors is addressed. A CdSe-ZnS nanocrystal, with emission peak at 520 nm is used to provide a reference signal. Measurements of oxygen concentration, which are based on the dynamic quenching of the luminescence of a Ruthenium complex, are performed. Both dye and the nanocrystal are immobilized in a sol-gel matrix and are excited by a blue LED. Results are presented showing that the ratio between the reference and the sensor signals is highly insensitive to fluctuations of the excitation optical power. Preliminary results show that nanocrystals could be used to measure temperature and provide a reference signal.

Liquid hydrogen has been intensively used in aerospace applications during the past forty years and is of great interest for future automotive applications. Following upon major explosive risks due to the use of hydrogen in air, several studies were carried out in order to develop optical fibre sensors for the detection of hydrogen leakage. This communication is aimed towards the presentation of new sensors based on the use of Fibre Bragg Gratings (FBG) and Long Period Gratings (LPG). The sensing principle based on palladium-hydrogen interaction will be presented as well as experimental results with structures including FBG, LPG or in-series LPG. Detection parameters such as response time and sensitivity will be discussed versus temperature.

This study investigates the feasibility of acquiring fast optical response signals from the peripheral nervous system (PNS) and specifically to obtain knowledge about the sensory response of the median nerve through comparing electrophysiological responses with those obtained with a single photon counting system. Nerve potentials have been well studied so the primary purpose of this investigation is to better understand the conditions required for recording the optical analogue of this signal. Such action potential-correlated optical signals have been termed 'fast optical evoked responses' and their measurement in-vivo has hitherto proved fraught with difficulty. As yet measurement of these signals has been confined to evoked potential studies in the brain and so far there is no repeatable, confirmed procedure for their robust acquisition. In this work it is suggested that perhaps an easier route to acquire these elusive optical signals is through evoked potential studies centred on the PNS as opposed to the brain. Preliminary results suggest it is possible to correlate both data and draw important information from it although the most important contribution of this paper is the principle of directing the search for robust fast optical signals to the peripheral nervous system as opposed to the brain.

Metal-coated singlemode tapered optical fibers are demonstrated for high-resolution refractive index sensing. The fundamental fiber mode can excite the different hybrid surface plasmon modes supported by the semi-cylindrical metallic shell. The transmission spectrum of our devices exhibits multiple resonance peaks with either TE- or TM-polarized light. The number of resonance peaks as well their depth depend on the taper diameter and also on the external refractive index. Experimentally we have found that the first two or three resonance peaks are the most sensitive peaks to refractive index changes. We estimate that a resolution of about 2x10^-7 can be achieved with our sensors. Our devices can be used for high-resolution biosensing.

This paper presents recent progresses in the application of nanostructured optical fiber-based sensors for non-invasive, fast and reliable monitoring of respiratory airflow. Molecular-level self-assembly processing method is used to form multilayered inorganic nanocluster and polymer thin films on the distal ends of optical fibers to form such sensors. In order to optimize sensing performance, recent work has studies the synthesis process and the fundamental mechanisms for the change in optical reflection, specifically caused by exhaled air condensation on the coating surface. The physically small sensors fabricated by varying thin film chemistry, offer a full range of environmental relative humidity sensing from 0% to 100% with response times of microseconds, and mostly important, provide much higher sensitivity to breathing air, over 6 times larger than 100% relative humidity. The sensor performances in comparison with a medical nasal thermistor suggest such a thin film sensor an excellent device for advanced breathing airflow monitoring. All the features are appealing to clinical respiratory diagnosis and related sensor instrumentation design, and in good agreement with our analytical model.

The sensitive thin film elements based on bacteriorhodopsin in polymeric matrixes for the multichannel fiber-optical sensor system of measurement of chemical composition of gas mixtures are offered. It is shown, that modification of films compositions by the photosensitizing chemical additives changes the photocycle parameters and exhibits selectivity to the effect of various gases.

A photoacoustic sensor for the detection of ammonia using an EDFA-amplified semiconductor laser diode at 1532 nm is reported and for the first time a sub-ppb sensitivity of 0.6 ppb is demonstrated in the near infrared.

Different structures of photonic crystal fibers (PCF) have been investigated for application as intrinsic optical gas sensors. The fiber is used both as waveguiding structure and as sample containment. Advantages and drawbacks of solid core and hollow core PCF structures will be discussed. Theoretical assessment for the sensitivity of the investigated fiber types will be given. The calculated sensitivity of the solid core PCF will be reviewed using the fiber as methane sensor. A laser micro-drilling technology is used to perform first samples for quasi-distributed PCF chemical sensing.

The visible PL with broad peak at wavelength of λ=462 nm are observed from polished rice, flour and corn starch under illumination of ultra-violet (UV) light. PL peaking at λ=462 nm is excited effectively with UV light at λ=365 nm. Peak intensity is found to vary with the source and the breed of the rice specimens. PL images from rice also reveal the uniformity of the rice products. Two-dimensional images of PL, which reavealed the uniformity of rice under UV irradiation, are potentially useful for the evaluation and the quality control of the rice products.

Chemical absorption is investigated using the evanescent fraction of a whispering-gallery mode (WGM). An effective absorption path length of about 50 cm is obtained in methane sensing and about 100 cm in a liquid dye solution.

An optical fibre biosensor that uses an oxygen sensitive coating; Ruthenium complex [Dichlorotris(1,10-phenantroline)-ruthenium(II) hydrate], incorporated into an adhesive inorganic-organic hybrid polymer coating (ORMOCER) is described. The Ruthenium/ ORMOCER layer is used with optical fibres to form an extrinsic or intrinsic sensor. It can be applied to a microscope slide or lens to be interrogated by optical fibres, or form a cladding layer for an evanescent field optical fibre sensor. The Ruthenium complex is caused to fluoresce by a high brightness blue LED at 470 nm and the excitation light at 600nm is detected by a photomultiplier tube used as a photon counter, to measure fluorescence lifetime. The fluorescence is quenched by oxygen depletion within the layer, which can be linked to glucose by incorporation of suitable enzymes. The detection threshold is 0.7mg(O2)/litre, and the sensitivity is 70 ns/mg per litre.

We describe a compact, pulsed, broadband source for sensing using ASE from Er3+ doped fibre driven by an amplitudemodulated pump. Quiescent pumping halved rise time. The spectrum could be tailored with reflective fibre filters, eg. for C₂H₂ gas detection.

The Nuclear Factor kB is a transcription factor, ubiquitously expressed, involved in the regulation of a large number of genes and in a variety of human disease including inflammation, asthma, atherosclerosis, AIDS, septic shock, arthritis and cancer. The critical need for a simple and direct method to evaluate the quantity of active NF-kB in a biological sample can be addressed using a suitable and reusable biosensor. For this purpose, a novel method, using fluorescence resonance energy transfer (FRET), to detect the active form of NF-kB binding a specific DNA sequence has been developed. A single-stranded DNA (ssDNA) with auto-complementary sequence has been properly designed and synthesized. In order to evaluate FRET due to the DNA/protein binding interaction taking place between double-stranded DNA (dsDNA) immobilized in a capillary wall and NF-kB proteins, a highly sensitive FRET-based biosensor system developed in our laboratory was used. Preliminary results show that our system was capable of detecting the active form of NF-kB protein with a detection efficiency of about 90% and that the system has a good regenerability.

The fabrication and characterisation of Long Period Gratings in fibre tapers is presented alongside supporting theory. The devices possess a high sensitivity to the index of aqueous solutions due to an observed spectral bifurcation effect.

We report an experimental study of the response of a hydrogen sensor based on a palladium-coated tapered optical fiber, at different temperatures in the range [-30, 80]°C. The main features of the sensor's response have been correlated with the pressure-composition isotherms of the Pd-H system and its phase transitions. Moreover, heating of the palladium layer optically with an auxiliary laser diode, allows improving the sensor’s time response at low temperatures.

We will demonstrate the potential use of a 2 cm long 6° tilted Bragg grating for simultaneous refractive index and temperature sensing during the production process of sugar from sugarbeets. This sensor is easy to use and allows realtime measurements. Its accuracy falls within ± 0.1 % and ± 1°C for sugar concentration and temperature, respectively.

In order to satisfy increasingly stringent automotive emission control laws, it is necessary to develop sensors that are capable of quantifying exactly the pollutants entering the atmosphere. The development of a mid-infrared optical fibre based sensor suitable for the detection of automotive emissions is discussed in this paper. Mid-infrared spectroscopy is deemed suitable for the task as the fundamental absorption lines of the majority of the pollutant exhaust gases are in the mid-infrared region of the spectrum. This paper focuses on the monitoring of carbon dioxide gas as it has significant absorption in the mid-infrared.

We report on a recently developed highly sensitive instrument for label-free detection of biomolecules based on the principle of a Young interferometer. With this technology, biomolecular interactions can be detected in real-time without elaborate sample preparation using a planar waveguide as sensing element. The binding reaction of the antibody-antigen pair immunoglobulin G and protein G has been studied and an affinity constant of K=2.6*10⁷ M^-1 has been determined.

We investigate the sensing properties of the single-walled carbon nanotubes deposited onto cadmium arachidate buffer multilayer by acoustic and fiber optic sensors for VOCs detection, at room temperature. The carbon nanotubes are deposited by the Langmuir-Blodgett technique. The acoustic and optical sensors have been simultaneously exposed, in the same test cell, to individual VOCs of ethanol, methanol, iso-propanol, acetone, ethylacetate, toluene with different vapor pressures for comparing the sensitivity of the carbon nanotubes onto the several kinds of the sensors. Signals from different sensor types have been analyzed and processed by using pattern recognition techniques such as principal component analysis (PCA). The recognition and discrimination capabilities of the hybrid system are significantly improved when data fusion from acoustic and optical sensors is realized. To our knowledge, this is the first study reported of a combined hybrid integration of low- and high- frequency acoustic sensors with optical fiber sensors using nanostructured materials as single-walled carbon nanotubes for VOCs detection, at room temperature.

Based on measurements of different test gases at lowest concentrations and a spectral database including over 1000 UV vapor-phase spectra, the status of the research towards a fiber-based UV gas-analyzing equipment is reported.

This work presents an optochemical dosimeter for determining and discriminating nickel, copper, and cobalt ions in water that can be used as an early warning system for water pollution. An inexpensive fiber optic spectrophotometer monitors the sensor's spectral behavior under exposure to water solutions of heavy metal ions in the 1-10 mg/l concentration range. The Principal Component Analysis (PCA) method quantitatively determines the heavy metals and discriminates their type and combination.

A novel variation in optical correlation spectroscopy is presented. A semiconductor optical amplifier (SOA) is employed as the light source and an optical fibre delay line is used to achieve the 180° phase shift between the reference and measurement signals. The system was tested using acetylene (C2H2) gas. Absorption data from the HITRAN database is used to model the theoretical response of the system. Experimental results for the detection of various acetylene gas concentrations have been obtained and compared with theory.

Abstract: In this work, the use of non uniform thinned Fiber Bragg Gratings (ThFBGs) for the simultaneous measurements of temperature and refractive index is proposed. The proposed technique relies on the use of partial thinned FBG: along half of the grating length the cladding layer is partially or totally removed, while the remaining part is unchanged. The perturbation leads to a wavelength-splitting of the spectral response of the unperturbed structure in two separate peaks in dependence of the outer refractive index and the local temperature. The peak at lower wavelengths corresponds to the etched region and is dependent on the outer refractive index and the local temperature, while the peak at longer wavelength is related to the original structure and thus is dependent only on the local temperature. The simultaneous measurements of the Bragg wavelengths related to the two regions allow the accurate measurements of the refractive index and the temperature by using a single sensing element, simultaneously. Here, wet chemical etching in a buffered hydrofluoric acid (HF) solution was used for sensor fabrication. Experimental characterization for a 7.6 m etched cladding sensor is presented. The same approach can be used as key element for the development of sensors array for chemical sensing in practical applications.

In this work, a novel fiber optic sensor able to measure the concentration of organic analytes, in aqueous environment is presented. Long period gratings were selected as high sensitive refractive index transducers and syndiotactic polystyrene in the nanoporous crystalline form was used as sensitive polymeric layer due to its high sorption properties towards chlorinated and aromatic compounds. In particular, a thin semi-crystalline syndiotactic polystyrene film with crystalline nanoporous form was deposited along the sensing element by using dip-coating technique. Chemical detection has been carried out by measuring the wavelength shift and the amplitude change in the attenuation bands of the long period grating due to analytes sorption. Experimental results demonstrate the capability of the proposed sensor to detect very low concentrations (in the range of few ppm) of chloroform in water.

In this work, preliminary experimental results on the capability of a Metal Oxides (MOXs) based optical sensor to perform ammonia detection in water environments, at room temperature, are presented. Electro-spray pyrolisis technique has been used to deposit the SnO2 films on the distal end of standard Silica Optical Fibers (SOFs). Reflection spectra of the sensing probes have been measured in the range 1520-1620nm by using a tunable laser and an optical spectrum analyzer. Single wavelength reflectance measurements have been carried out to test the sensing performances for ammonia detection in the range 4-20 ppm. High sensitivity to the target analyte and fast response times have been observed. From the results obtained, a Limit Of Detection (LOD) as low as sub-ppm has been achieved.

A fibre-optic embedded sensor using a polymer-coated fibre Bragg grating (FBG) was developed and used to detect the ingress of moisture in concrete specimens of different porosity. Applications to structural health monitoring are discussed.

Fiber optic sensing requires the use of molecular probes such as fluorescent dyes or indicators that can be induced during analysis to produce a detectable spectral change. Spectroscopic techniques have long been applied to the determination of analytical and bioanalytical measurements using fiber optic sensors; however, relatively few studies have been reported utilizing near-infrared (NIR) absorbing chromophores. This longer wavelength region of the electromagnetic spectrum is more advantageous because of the inherently lower background interference and the high molar absorptivities of NIR absorbing chromophores. Low background interference is especially important in samples containing a complex matrix. The design and operation of an NIR probe are similar to that of conventional UV-visible probes. In principle optical fiber or other optical sensors can be made selective to a particular analyte. The selectivity will be determined primarily by the selectivity of the sensor dye and by the nature of the matrix entrapping the dye if the probe is non-covalently attached. This presentation discusses the development of different NIR dyes for fiber optic sensor applications. Examples are given for determining basic analytical properties, e.g., pH, metal ion concentration, and solvent hydrophobicity. Similarly, NIR dyes are very useful for bioanalytical probes (immunochemistry, etc.) as well.

We investigate the possible use as on-line dosimeters of commercially-available PMMA plastic optical fibres. The dose measurement is derived from the radiation-induced attenuation. A novel interrogation scheme based on a ratiometric technique is proposed for real-time dosimetry applications.

A photo-bleaching effect on radiation-induced transmission loss of fused silica core optical fibers was examined under ⁶⁰Co gamma-ray and 14 MeV fast neutron irradiation. In the visible wavelength range, radiation induced loss could be reduced by the photo-bleaching under the both irradiation. For using optical fibers in visible wavelength range such as a light guide and an image guide, the photo-bleaching is an effective technique to improve radiation resistance of optical fibers. In the meantime, a so-called microbending loss is generated by the radiations in the whole wavelength range. The microbending loss responded in a different way to the photo-bleaching between the both irradiation. The loss under the gamma-ray irradiation increased by the photo-bleaching, in contrast to its decrease under the fast neutron irradiation. It is considered that there will be multiple causes for the radiation enhanced microbending loss. Among the causes, that caused by modification of the reflection plane between the core/clad in optical fibers through the atomic displacement process can be reduced by the photo-bleaching. In general, it is concluded that the photo-bleaching technique is effective in improving radiation resistance of optical fibers under neutron associated and moderate flux radiation environments.

Dosimetry of ionizing radiation fields is playing a more and more essential role for safety and effective operation of nuclear systems. An optical dosimetry system composed of radiation resistant optical fibers and radioluminescence materials has several advantages over a conventional electric dosimetry system. Especially, in a nuclear fusion system, a real time diagnostics of intensity of radiation fields with a high time resolution is indispensable, where electromagnetic noises are surmount and it is hard to find engineering solutions to satisfy severe demands from plasma physics and engineering with conventional electric dosimetry system. Erbium oxide (Er₂O₃) is found to emit radioluminescence in an infrared region where radiation induced degradation of optical transmissivity of fused silica (SiO₂) core optical fiber is marginal. Also, an intensity of the radioluminescence of erbium oxide in an infrared region is found not to decrease with increase of the dose of ionizing irradiation. The optical dosimetry system with erbium oxide is applicable to dosimetry of intense ionizing radiation fields.

The sensitivities of type I and IIA fibre Bragg gratings written to different reflectivities in SMF-28 and B/Ge fibres to ionizing radiation up to 0.54MGy are investigated. The Bragg wavelength shows a small and rapid increase at the start of irradiation followed by either a plateau (type I) or a decrease (type IIA).

Three different fibre optic radiation sensor systems are described. Two are based on the radiation-induced attenuation increase of radiation sensitive doped fibres, whereas with the third system the Cerenkov light generated by relativistic electrons in radiation hard undoped fibres is detected. All three systems are successfully used for beam optimization and dose measurement at three German electron accelerators.

Commercial off-the-shelf (COTS) single-mode and multimode germanosilicate optical fibres are intended for use as part of control-command applications in the future Laser Megajoule facility. We evaluated their vulnerability to the radiative environment associated to this project by characterizing their transient radiation responses at infrared wavelengths (1064, 1310 and 1550 nm) after high dose rate exposure (> 10⁸ Gy/s). Our results showed that these COTS fibres exhibit very different transient responses (10^-9 s to 1 s after pulse) and permanent damages (times > 1s), depending on the wavelength of transmitted signal and on their compositions. Presented results could be used to define several choices to ensure the functionality of these applications for both shortest times after a shot (10^-9 to 10³ s) and during the whole LMJ lifetime (30 years).

We investigate a long distance temperature sensor with multichannel remote sensing functionality at a 50 km distance using Raman fiber laser based on multiple laser cavities based on FBG's and a tunable chirped FBG.

We introduce a Rayleigh Equivalent Criterion that unambiguously discriminates a stressed section which is smaller than the spatial resolution of a Distributed Brillouin Sensor. Under this criterion for the worst-case of any given sensing length, the minimum resolvable strain length is 0.50 the pulse length (w) with Brillouin frequency uncertainty of 15% or 0.85w with 2% frequency uncertainty which is smaller than the pulse length.

We applied axial and lateral stresses on a composite FRP/concrete column to produce earthquake like deformation. We monitored strain distribution with the Distributed Brillouin Sensor while the column was tested. We can correlate strain profile with column deformation and crack condition.

The temperature resolution of a fiber-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 on the Rayleigh signal. The amplitude fluctuations or coherent Rayleigh noise were investigated experimentally as a function of detection bandwidth, source bandwidth and spatial resolution and showed good agreement with theory.

A long-range and high-resolution reflectometry is proposed by synthesis of optical coherence function at region beyond the coherence length has been proposed. We discuss and simulate the principle of the reflectometry system. In basic experiments, the reflectivity distributions are successfully measured at the region beyond the coherence length with a spatial resolution of 19 cm and a measurement range of 1 km.

Because of the phase modulation (PM) and amplitude modulation (AM) of the probe signal from the electric optical modulator (EOM), the Brillouin gain/loss spectrum becomes asymmetric. The central Brillouin frequency is shifted from that of AM pulse. The maximum extinction ratio of the EOM is limited to ~29 cB for power splitting ratio of 51% to 49%. The PM also induces sub-peaks in the Brillouin spectrum due to the interaction of phonon field and AM/PM based probe beam. The sub-peaks is enhanced when the beat frequency of pump and probe beam is off from the Brillouin frequency.

We developed a strain measurement system based on optical frequency domain reflectometry and applied it to measuring strain distributions of a specimen in tensile tests. In the sensing region on the specimen, five FBG sensors of 6 mm gauge length or one of 100 mm gauge length was bonded and strain measurements were implemented with both configurations. By using the former configuration, we could successfully carry out accurate quasi-distributed strain measurements. The later allowed fully-distributed measurements for 100 mm at the high spatial resolution. Such performance of high resolution sensing can be applied to health monitoring of a structure which may have stress concentration. In this paper, we describe the principle of the measurement system and the results in the tensile tests.

A Brillouin optical time domain reflectometer (BOTDR) is a fiber optic strain distributed sensing system which can measure strain along arbitrary regions of an optical fiber. We have used this system for structural health monitoring of composite structures, such as racing yachts. Although the BOTDR is useful to measure strain distributions of a large area efficiently, it is difficult to accurately measure strain changing sharply within the length of the spatial resolution. The resolution depends on the width of the pulse light emitted from the BOTDR and it is 2 m for the pulse width of 20 ns. In this paper, we propose a new technique to improve the spatial resolution of a commercially available BOTDR in strain measurements. This technique is based on analysis of the Brillouin gain spectrum along a sensing fiber. We confirmed experimentally that the BOTDR using 20 ns pulse could measure strain which has a rectangular distribution of 0.3 m in the sensing fiber.

This paper reports on the design of a novel optical sensor for distributed measurement of water-content at discrete positions along a single fibre length embedded in low permeability media. Sensing is based on the characteristics of Brillouin scattering in optical fibres coupled with the characteristics of hydrophilic polymers used as transducers. Experiments with a water sensor prototype have demonstrated measurement of water-content up to 30%.Measured losses on the system indicate that mounting of hundreds of sensors over several kilometres of fibre is possible. Experiments involving swelling and drying of the polymers showed that the water-content measurements with the fibre-based sensor are fully reversible.

The distributed Brillouin scattering technique, using pulse width of 1ns, that is, one order of magnitude smaller than currently available in commercial applications of BOTDA, was successfully implemented and examined in laboratory environment by Bao et al. However, the two main problems prohibits its commercial use, namely, the measurement setting must be modified each time the measurements object is changed, and, furthermore, long-range measurements cannot be effectively carried out due to substantial increase in signal noise level with the measurement distance. This paper presents a new technique, which overcomes both of these problems, by introducing the pre-pump pulse in front of standard laser pulse. Theoretical analysis clearly demonstrates that the cm-order distributed sensing, independent of the fiber length, can be realized. Moreover, a quantitative analysis of strain measurement accuracy is also presented.

Optical fibers with improved hermeticity, strength and chemical resistance are presented. Specifically, we provide data demonstrating the resistance of carbon coated optical fibers to hydrogen (high partial pressures and temperatures) and acidic environments. As well we provide data and analysis indicating that carbon coated fibers with increased n-values provide long lifetimes under stressed conditions.

Using a short pulse (~ 1 ns) and a pre-injected CW beam as the probe beam in the pump-probe configuration of Brillouin-based distributed sensors, we develop a spectrum deconvolution method, which considers the location correlation of the strain distribution, to find the number of Brillouin peaks and their frequencies in the Brillouin profile and hence achieve accurate strain information at cm spatial resolution.

A distributed strain sensor based on Brillouin scattering has been employed to inspect localized pipe-wall buckling on a length of 2.58 m and diameter of 0.75 m steel pipe by measuring the axial strain distributions along the outer surface of the pipe. An optical fiber with 10 sections was laid along the longitudinal direction of the pipe. Both compressive load and bending load were applied on both end of tested pipe up to 2,013 and 300 kIPS respectively, to induce the localized pipe-wall buckling. The buckling locations comprising tension and compression of the pipe wall are found and distinguished using their corresponding strain distribution data. The compressive strains of - 4330 and - 6856 με measured by our distributed strain sensor on the bending load of 220 and 300 kIPS, respectively, at one location near buckling point, match the readings from strain gauge at the same location where the strain gauge attached. The tensile strain happened at different sides of the pipe are found too.

A quasi-distributed fibre optics polarimetric sensor has been studied both theoretically and experimentally. Theoretical results demonstrate the feasibility of such a sensor when a polarization-maintaining optical fibre has been properly designed. Two designs are proposed. Distributed detection of water has been demonstrated with a standard polarization-maintaining fibre whose cladding was locally removed by chemical etching.

A reconstruction algorithm employing an accurate modeling of the stimulated Brillouin scattering (SBS) interaction in a single-mode optical fiber, is experimentally demonstrated. Distributed temperature measureme nts are carried out by using a Brillouin optical frequency-domain analysis configuration. Reconstructions are carried out by fully taking into account the influence of the modulation of the acoustic wave involved in the SBS interaction. The sensor shows good accuracy in determining any temperature disturbances as narrow as 40 centimeters placed along the fiber.