The objective ofthis work was to demonstrate the feasibility ofusing fiber Optic Bragg grating sensors (BGS) to measure axial and bending strain in pipes. A special test section was used to characterize the performance ofthe BGS and compare the results with standard electrical resistance foil strain gages. Two sets of pipe strain tests were performed. In the first tests series, an optical fiber containing four BGS was used. The BUS were positioned along the pipe test section and directly attached to the outside surface ofthe pipe wall. In the second tests series, a second fiber was used and four BGS were encapsulated inside a stainless steel tube which was attached to the outside ofthe pipe wall. All tests were successfully completed and the results demonstrate that fiber optic Bragg grating sensors can be used in a practical configuration to measure axial and bending strain in pipes. The repeatability ofthe strain measurements was 2 microstrain in the first tests series and 6 microstrain in the second test series. The strain resolution was less than 1 microstrain. The test results also showed that as few as three BGS in one fiber can distinguish axial strain from bending strain.

In concrete curing process, the temperature and the volume of the structure, and the inner pressure/stress exerted on the rebars will change in a fashion that depends on the composition of the concrete mixture. The temperature, strain and pressure changes at various points of a 3m long concrete structure with a mixture of cement, water and aggregate were monitored over a period of several days. Fiber Bragg grating based sensors were used to monitor these parameters in vivo. These sensors were designed and optimized to measure the temperature, strain and pressure respectively.

A new demodulation technique for fiber Bragg grating based sensors is presented. The technique makes a use of pairs of low reflectance Bragg gratings forming a low finesse Fabry-Perot local sensor. The gratings in a pair have different sensitivity to a measurand, and overlapping of their reflectance spectra depends on the external influence. Demodulation is based on measurement of the degree of the grating’s spectra overlapping by means of energy of interference pattern in reflection spectrum of the interferometer. We demonstrate implementation of the proposed technique in experiments with axial strain and temperature measurements.

In-core temperature measurment is a critical issue for the safe operation of nuclear reactors. Classical thermocouples require shielded connections and are known to drift under high neutron fluence. As an alternative, we propose to take advantage of the multiplexing capabilities of FThre Bragg Grating (FBG) temperature sensors to perform the in-core temperature measurements. We first report on our irradiation experiments on multiplexed FBGs, written in different fibres, employed to measure the in-pile temperature of an air-cooled graphite-moderated nuclear reactor. For some FBGs the difference between the measurements and the readings of calibrated backup thermocouples was within the measurement uncertainty. In the worst case, the difference saturated after 30 hours of reactor operation at about 5°C. Afterwards, we irradiated multiplexed FBG sensors in our material testing nuclear reactor, evidencing the possibility to use FBG sensing technology for in-core monitoring of nuclear reactors with specific care and in well-specified conditions.

Optical fibers imprinted with a Bragg grating, a periodic change in the refractive index of the core of the fiber, can be used as strain gages in structural health monitoring. It is well known that fiber Bragg grating (FBG) structures can be applied as optical strain gages with very high sensitivity and reasonable accuracy. This application has been confirmed through numerous publications on the effect of axial loads on FBG structures. The FBG structure can easily be calibrated as an axial strain sensor. There are currently some trial applications ofthese optical strain gauges in bridge construction. However, using these FBG structures as embedded sensors has raised questions about sensor accuracy and measurements because of the Poisson's effect and/or application under multi-axial stress states. Therefore, the objective of this research was to study the effect of transverse loads on FBG structures for a better understanding of the interaction of the structure and the embedded Bragg fiber sensor output.

A high-resolution (sub micron accuracy) fiber optic coupled dual Michelson interferometer based instrument has been developed and is being utilized in a variety of process monitoring applications. The instrument includes both coherent and non-coherent light sources, custom application dependent optical probes and sample interfaces, a Michelson interferometer, custom electronics, a Pentium based PC with data acquisition cards and LabWindows CVI based application specific software. This paper describes the development of this instrument with special emphasis on applications development. The principles behind robust instrument design hardware, software and user interfaces are discussed.

Traditional white-light scanning interferometers utilize bulk optic components mounted on a mechanical scanning mechanism. Many emerging applications for these interferometers require fiber optic probes. By design, such fiber compatible instruments are expensive and are limited to slow scan rates. A new “all-fiber” design approach is presented, which reduces the cost of the design and enables higher scan rates.

Interferometer fiber optic gyros (I-FOGs) have already developed application in various field. TO have higher resolution, however, it is still required to reduce noices. Fluctuation of temperature distribution in sensing fiber coil is one of the dominant noise factor in FOGs. A countermeasure against the drift is specisl coil winding. To get superior performance, however, gyro output compensation with monitored temperature is still needed. In resonatoir FOG (R-FOG), on the other hand, the sensing fiber coil is very short. Then, it is expected that the drift can be reduced. In this paper, we derive an equation describing the drift due to the time variant temperature distribution for R-Fog. By using the equation we calculated the drift both in I-FOG and R-FOG, and compare them. It is shown that the drift in R-fog become much smaller than I-FOG when adopting a special coil winding.

We propose and demonstrate an interferometric technique for the high precision measurement of displacement, based on Hilbert transform processing of the interferometric signal. The experimental arrangement is that of a laser illuminated Michelson interferometer in which a mirror, mounted on the target under test, is a component mirror of the interferometer. The optical configuration retains the simplicity of the fringe counting arrangement. Using standard sampling electronics, we capture the high coherence interferogram for the target motion to be analysed. We process the sampled interferogram, using Hubert transform techniques to generate the complex analytic signal of the real valued interferogram. The phase of the complex signal is extracted, unwrapped, and converted to displacement information corresponding to each sampling instant. We have achieved a X/100 for the individual displacement measurements, for analysis of a 1OOOtm travel of the target. In all cases, the displacement data is readily processed to measure velocity and acceleration. We report on both bulk optic and fibre optic versions of the interferometer. We have applied the technique to the characterisation of the motion of translation stages, with the objective of assessing their potential efficacy in temporally scanned interferometers. We report on our measurements of the consistency of scan rate and on the degree of 'out-of-plane' motion of the stages.

We present experimental results that show the possibility of use an All-fiber Sagnac interferometer to compensate the transmitted spectrum of an optical signal. The compensation is achieved by selecting a wavelength and twisting both arms of the interferometer for that fixed wavelengths. We present a theoretical model that explain such behavior.

In this paper, an extremely small and laser Doppler sensor of low cost is presented. The sensor consists of a laser diode and of an optical system composed by two lenses in order to focus the laser light onto the target. The sensor measures velocity and it is based on the self-mixing effect that occurs in a semiconductor laser diode when the radiation generated inside the cavity is back reflected into the cavity. Velocity is calculated measuring the position of the frequency peak on the frequency spectrum of the Doppler spectrum generated by the photodiode present inside the laser diode when modulated by feedback light coming from the moving scattering particles. The laser Doppler self-mixing velocimeter has been statically calibrated, using a rotating disk covered with white paper. Authors report about the Doppler signal amplitude of the velocimeter as function of the characteristics and colour of the target surface. Dependence of the Doppler peak amplitude from the target distance and the angle between target and optical axis of the sensor are also reported. Results regarding dynamic characteristics of the sensor are reported and it is shown its capability to be used as a laser Doppler vibrometer.

A fiber optic dual Michelson interferometer for vibration measurement and analysis is presented in this paper. One of its main features is that it is operated in the homodyne mode allowing the detection of the direction of motion. The capability of the system in detecting periodic signals is described, through a comparison with a commercial laser vibrometer.

This paper discusses using the multi-pass techniques of cavity ring-down and intracavity spectroscopy (ICLAS) to increase the sensitivity of optical fibre gas sensors. An experimental fibre ioop system has been built with standard optical fibre components and a micro-optic cell. An erbium amplifier is included in the fibre loop. For the cavity ring-down the amplifier allows the fibre loop to mimic the high finesse cavities used for conventional, bulk optic ring-down by compensating for the system losses. The amplifier acts as the gain medium for the intracavity set-up.

This paper describes a novel multi-point fiber optic microsensor (optrode) based on dynamic luminescence quenching that is being developed for measuring oxygen leak detection for space applications. The sensor optrodes employ the quenching by oxygen of the fluorescence from a ruthenium complex. These optrodes were fabricated using Ruthenium-based fluorescent indicator immobilized in a porous glass rod placed at the end of multimode fiber. The light from a blue LED is launched into the optrode via a fiber optic bundle and used as the excitation source. The optrode's fluorescent emission intensity in the range of 0% to 10% oxygen is measured as a function of time. The measuring system is based on high reliability and low cost. The system consists of four units: 1) temperature compensated oxygen optrodes combined with a optical setup, 2) multipoint sensor communication fiber optic network cable, 3) digital/analogue optoelectronic signal processing unit with built-in micro controller for control of data acquisition and processing, and 4) a laptop computer for data display and storage. In testing, the sensor exhibited excellent response time and reversibility.

This paper describes progress in the development of a multi-point fiber optic micro sensor (optrode) based on a hydrogen gas sensitive chemistry immobilized in an optically transparent porous substrate. The hydrogen sensitive chemistry is fully reversible and has demonstrated a response to hydrogen gas in the range of 0% to 10% with a resolution of 0. 1 % and a response time of ?5 seconds measured at a gas flow rate of 1 cc/mm. The optical signature of the optrode in the visible spectrum varies proportionally to the local hydrogen gas concentration. The multi-point hydrogen sensing system uses temperature compensated hydrogen optrodes mounted at the tip of optical fibers. The hydrogen optrodes are distributed at multiple locations along a fiber optic cable-based network. A multi-channel optoelectronic sensor readout unit monitors the hydrogen and temperature response of the individual optrodes in real time and communicates this information via a serial communication port to a remote laptop computer.

The potential for intrinsic dosimetry with three different fibre types through the gamma ray radiation induced attenuation is investigated with respect to annealing, temperature dependencies, photo-bleaching and, to a limited extent, dose-rate. The radiation sensitivity of these three fibres covers an effective dose range of 0.1 Gy to 100 kGy which makes them suitable for a broad range of nuclear applications. With detailed analysis in both the spectral and temporal domain, it is shown that the long-term annealing effects can be suppressed by exploiting the stability of certain colour centres in the fibre core and adequate interrogation of the induced attenuation at a discrete set of wavelengths. Photo-bleaching is observed by employing a low power white light source (a few microwatts in the fibre) with Erbium doped fibres and when Germanium is added as a co-dopant with Phosphorous fibres. Temperature dependencies during irradiation and annealing are addressed from room temperature to 80 ?C. The Phosphorous and Erbium doped samples exhibit a reverse behaviour: the optical absorption increases with temperature.

It is demonstrated that optical coherence function can be synthesized into almost any arbitrary shape by stepwise spectral modulation of a laser source and synchronous phase modulation. In this presentation, the coherence function is synthesized experimentally into three forms, a scanning delta-function-like peak, a scanning peak with low side-lobes, and a standing triangle, respectively. The lasing frequency of a broadband tunable super-structure-grating distributed Bragg reflector laser diode (SSG-DBR-LD) is stepwise modulated. The spectral intensity is tailored with a semiconductor optical amplifier (SOA) to fit the spectral patterns required by correspondent coherence functions. The synthesized coherence functions are employed for distributed fiber optic stress sensing or stress locating. A polarization maintaining optical fiber (PMF) is used as the sensing element. When a stress is applied to the PMF, polarization mode coupling occurs; then an optical path difference between the two polarization modes appears due to their different propagation speeds. The optical path difference can be figured out by manipulating the coherence function. When using the coherence function of scanning peak, the coherence peak is moved to scan the detection range by the phase modulation; therefore, the stress distribution can be obtained. When using triangular coherence function, the detection range is set within a linear slope of the triangle, so the stress location is directly converted into the value of the coherence degree.

A fibre-optic system for the detection and location of hydrocarbon fuel spills with 2m accuracy over a total length of 10 km is presented. The sensor incorporates liquid-swelling polymers that transduce their swelling into a force on an optical fibre when activated. The standard Optical Time Domain Reflectometry (OTDR) technique is used to interrogate the sensor, which provides the possibility of locating target hydrocarbon fuels and chemicals at multiple positions along the sensor length. Response time of the sensor after exposure to the activating liquid is typically 30 seconds, dependent on the activating fuel. A brief explanation of the operational characteristics of the sensor and the underlying technology utilised in its operation is given. Swelling characteristics of the sensor polymer material in a range of hydrocarbon fuels and solvents is presented. Experimental test results using prototype sensors to detect simulated fuel spills at separate locations are then described. The ability to replace the polymer with materials that are sensitive to other liquids provides the possibility of sensing many other liquids using the same generic design.

The first wave of R&D on fibre optics in sensing applications lasted 20 years and is summarised. Safety related R&D has continued and the most recent results are presented. It has long been appreciated that a suitable component infrastructure for sensing has not yet been realised, and this is probably a significant part of the explanation for the relatively modest commercial impact ofthis technology at the present time. In the first wave, the significance of white light interferometry was identified, and the potential of silicon as a substrate for integrated optics was stimulated as much by communications as sensing needs. The important discovery of fibre Bragg gratings was made. Subsequent global efforts at commercialisation have been admirable, but are not yet major in business terms. Distributed sensing has rather plodded along, though some progress is being made. It is argued that we are now on the leading edge of a second wave of development in fibre optic sensing. The emphasis in this wave is not sensing principles but the adaptation and employment ofthe components and signal processing methods being facilitated by the huge wave of commercialisation in optoelectronics which is currently occurnng, primarily stimulated by the Internet explosion. For sensing systems it is judged that silicon ridge waveguide technology has the potential to create a standardised approach to optical sensing, in concept not dissimilar from the familiar standardised analogue electronic signal and transmission means (e.g. 4-20 mA).

Fiber Bragg grating (FBGs) are expected as sensor for monitoring of a large scale faculty because of their availability to measure multiparameter at many point along a fiber. In this study, we investgated the influence of radiation on the characteristic of FBGs that must be understand before applying FBGs to nuclear plant. FBGs written on fiber made from one perform with same condition were exposed to fast neutrons up to 1.7x1017n/cm2 or ?-rays up to 710KGy and their Bragg peak shift of 0.072nm anmd 0.027nm in the peak wavelength are observed in the maximum respective.

We describe a fiber optic voltage sensor with optically controlled sensitivity.The sensor operates at two widely separated wavelength (633nm and 976nm) one of whichis a control signal (976nm).We show that at a properly chosen wavelength of the control signal and of the phase-retarding element, variation of the control signal allow increase or decreases in the sensitivity of the sensor.A theoretical analysis of sensitivity as a function of the optical power of a control signal is presented. WE have demonstrated experimentally variation of the sensor ,s sensitivity from 0.01% to 0 per 1Vms of control power change in the range of 0÷7 ?W.

The increasing significance of a current state dependent maintenance and the demand for a reliability and an economical operation of power industry devices led to a discussion about monitoring and diagnosis possibilities for high-voltage (h-v) transformers which are one of the most important valuable network components. In the area of high field devices only the use of optical measurement techniques offers the possibility to supervise the characteristic measurands, e.g. critical temperatures or the occurance of Partial Discharges (PDs). Therefore a temperature detector based on Fiber Bragg Gratings (FBG) is presented, who allows a semi-distributed measurement at the active part of the h-v transformer. In this connection some points dealing with cost-effective signal processing units and details about a succesful integration of the sensing elements are investigated and the experimental results are shown. Partial discharges at transformers mainly occure in the insulating oil and on oil-surfaces. Hereby the quantity and amplitude of the PDs are relevant to the actual assessment of the transformer. To analyze the reason for occurrence of PDs it is necessary to localize and characterize the PD source. For on-line detection of PDs the measuring equipment must be placed into the oil. For this application a potential free experimental setup, based on a fiber optical system, for PD detection is described. By using a Mach-Zehnder-Interferometer for acousto-optic measurement the existence of PDs can be detected. By using fiber optical sensors for temperature and PD detection it is possible to watch the operating conditions of h-v transformers and avoid critical states.

Low loss coherent bundles can be used in the area of broadband infrared and thermal imaging. We have been able to extend the present hollow glass waveguide (HGW) technology to very small bore sizes, from 250 down to 50 ?m. HGWs with bore sizes from 50 to 320 ?m have been used to make flexible bundles. These bundles are then coated with Ag/AgI thin films using liquid phase chemistry techniques. The optical properties of these bundles were studied by FTIR spectroscopy. These bundles have relatively low loss in the wavelength range of 8 to 12 ?m.

Infrared laser delivery systems based on hollow fibers with an internal polymer layer has been developed. The system consists of a hollow fiber as the delivery medium, a launching coupler for effective coupling between the laser beam and the fiber, and a sealed hollow-fiber tip attached at the output end of the fiber. Fabrication process of the fiber and attachment of the delivery system is reported.

Leaky-type waveguides were fabricated using flexible hollow polymer tubing of bore sizes in the 840 to 3000 ?m range. The tubing used included polycarbonate, polyetherether ketone (PEEK), butyrate and polyimide. The losses for the 2000 ?m bore hollow polycarbonate waveguide were as low as 0.055 dB/m at 10.6 ?m. This is the lowest loss ever measured for a hollow waveguide. These waveguides exhibit a nearly flat spectral response from 3 to 16 ?m, so that they are well suited for broadband IR applications. The output beam profile for the small bore (840 ?m) waveguides is mainly single mode but, higher order modes propagate for the larger bore sizes. Bending the waveguides resulted in a highly multimode output for all the bore sizes.

A simple sealing technique for medical hollow fibers to protect the inner surface from debris or water scattered from targets is proposed. Hollow fibers are sealed with a film of fluorocarbon polymer that was selected from other polymers due to the low absorption and high mechanical strength. The transmission loss of the 20 mm-thick sealing film was 0.2 dB for Er:YAG laser light and the maximum energy density that is capable for the film was 47 J/cm2. We found no damage on the film after a continuous laser-delivery test and a radiation test in running water.

In some areas of fiber optic sensing, one can expect improvement in measurement accuracy and an expansion of the fields of application with the use of infrared transmitting fibers. Unfortunately, sensor development often fails due to a lack of suitable optical designs based on a thorough knowledge of fiber characteristics. This article provides an overview of infrared fiber sensors, describing what infrared fibers can do, which infrared fibers should be selected for what purposes, how the sensor system should be designed. Chronological tables are also shown for infrared fiber thermometry and spectroscopy.

In this contribution, the first application of the recently developed GaAs/AlGaAs quantum cascade lasers and hollow waveguides in gas sensing spectroscopy is demonstrated. A multimode GaAs/AlGaAs quantum cascade laser tuned to an emission maximum at 10.009 ?m is used to investigate a mid-infrared absorption of ethene at atmospheric pressure. The laser radiation is focused onto the entrance of a 434 mm long, gas-tight terminated hollow waveguide and it is collected after passing it. Well defined mixtures with ten different concentrations of helium and ethene are flushed through the waveguide. The radiation is analyzed using a Fourier-transform infrared spectrometer (FTIR) equipped with a mercurycadmium- telluride detector. The obtained discrete ethene spectrum is compared to a calculated spectrum finding a good agreement. A detection threshold of 250 ppm and a response time in the range of 100 ms have been obtained with the current setup.

The emerging demands of marine monitoring have initiated increased efforts to develop sensor systems capable of screening organic pollutants in seawater. The construction of a sensor system based on a Fourier transform infrared (FT-IR) spectrometer coupled to a mid-infrared fiber-optic sensor head to be used in a tow-body for underwater applications is part of the European Union project "SOFIE — Spectroscopy using Optical Fibers in the Marine Environment", aiming at the introduction of an entirely optical approach for in-situ ocean monitoring. The investigated analytes of this initiative include heavy metals, chlorinated hydrocarbons and aromatic hydrocarbons, which will be addressed using fiber-optic sensing schemes based on absorption (mid-infrared fiber-optic evanescent wave spectroscopy (MIR-FEWS), fluorescence, surface enhanced Raman scattering (SERS) and refractivity (surface plasmon resonance (SPR)). Since the system is modular, adaptation of existing techniques or the incorporation of new modules ensures the detection of further analytes. As part of this research project, a compact FT-JR based sensor system has been developed, reconstructing a Bruker Vector 22 FT-JR spectrometer. For the first time, a spectrometer was redesigned to fit into a submersible tube, with an inner diameter of 270 mm and an overall length of 1 100 mm. This approach proved capable of multi-component analysis in seawater, demonstrated for the example of various chlorinated hydrocarbons, as well as relatively low susceptibility to interfering parameters such as salinity and turbidity. First successful field test of the system integrated in a remotely operated vehicle corroborate the feasibility of this approach. With respect to the technological perspectives using miniaturized sensor components, a notable impact on this novel application area for MIR sensors can be expected.

A digital control system to draw fibers varying along the length from standard preform had been developed. It is possible to obtain bers with a necessary length dependence on the diameter with high accuracy. During the drawing process information about the current diameter is processed by digital control unit and compared with a calculated value. A control signal produced by the computer is passed to the drawing unit. Ada (ANSI-MIL-STD-1815A) has been choosen as programming language to develop the control system software. In particular the single mode bers with chromatic dispersion decreasing along the length (DDF) had been fabricated. Such bers are an attractive medium for optical signal processing and advanced communication systems. The DDF length may be in the range from several meters to several kilometers. The diameter deviation from the pre-arranged value is less than 0.2%.

The advantages of gallium lanthanum sulphide (GLS) based glass over other competing glasses for active and infrared applications are evident through its low-phonon energy, high rare-earth solubility, high transition temperature and non-toxicity. However this glass often devitrifies during fibre drawing due to a small separation between the crystallisation and fibre thawing temperatures. Improving GLS fabrication technology may hold the key to achieving practical optical waveguide devices. In this paper, we describe the cunent GLS research status, methods ofimproving glass purity and our directions toward alternatives to traditional fibre technology, in particular planar channel waveguides and holey or microstructured fibres.

The change in the absorption loss relative to room temperature of the IR-transmitting sulfur-based (As-S-Se) and tellurium-based (Ge-As-Se-Te) glass fibers in the temperature range of-110°C? T? 110°C was investigated. For the sulfur-based (As-S-Se) glass fibers, the change in loss relative to room temperature was slightly affected by temperature in the wavelength region of 1-5 ?m. For ? ? 6 ?m, the change in loss was mainly due to multiphonon absorption. For the tellurium-based (Ge-As-Se-Te) glass fibers, the attenuation increased significantly at T 40°C. This is mainly attributed to thermally activated free carriers associated with the semi-metallic character ofthe Te atom. For ? ? 4.2 ?m, the loss due to electronic and free carrier absorption was strongly affected by temperature. In the wavelength region of 5 - 11 ?m, the loss was mainly due to free carrier absorption. Beyond ?? 1 1 ?m, multiphonon absorption dominated the loss spectrum at T ? 60°C while free carrier absorption contributed mainly to the total loss at T 80°C.

Recent measurements are presented, using an improved, real-time, all-optical sensor for simultaneous measurement of dissolved oxygen and temperature. The sensor has a small Cr3+ - doped sapphire (ruby) thermal monitoring crystal mounted at the probe tip, to which is bonded a Ru2+-based oxygen-indicator membrane. The probe may be interrogated in real-time, using, for both temperature and oxygen monitoring, the same combination of blue LED, light source, optical filter set, photomultiplier detector and digital processor. The ruby crystal also provides a fluorescent intensity reference, for possible on-line self-testing of the interrogation hardware. By examining the relative intensities from ruby and the membrane, mechanical damage, detachment or photo-bleaching of the sensing membrane may also be recognised. Recent developments of our novel, Ti3+ - doped sapphire fluorescence-lifetime calibration probe are reported. These confirm that the fluorescence lifetime of the probe can be thermally controlled in a reliable manner. This calibration probe then allows multi-point calibration of Ru2+-chemical sensors.

Efforts have been underway for several years at AMI to develop a ribbon stacking method to fabricate infrared imaging bundles from chalcogenide glass fibers. Bundles have been formed drawing fibers from an As-Se-Te glass (Cl) and from As2S3 glass (C2). Fiber core diameter has been limited to 100 ?m or greater due to the low tensile strength of chalcogenide glasses. Glass cladding adds strength to the fiber but results in low active area (25-35%) and coarse images. Use ofunclad fiber increases packing density ( active area 50-70%,) and improves infrared camera images. Recently, a new As-Se glass, designated C4, was developed at AMI, that can be drawn into flexible fibers with core diameters of 50-60 ?m. Bundles formed from stacked ribbons ofunclad fiber produce infrared camera images markedly improved over previous bundles. Imagery using C4 bundles made with small core unclad fibers and a Cl bundle made with glass clad 140 ?m core fibers, are compared. Images for both bundles made using a low sensitivity 3-5?m camera are compared to those made using a very sensitive 3-5 ?m radiometer camera.

Chalcogenide glasses - Ge25Ga10S65 , Ge25Ga5As5S65 , As2S3 , As2S2Se , As25e3 — have been synthesized and doped with ions of rare earth RE3 , in the concentration range of 500 to 6000 wt.ppm. Special processing makes possible to reduce the hydroxyle content and to incorporate rare earth ions without phase separation. Various physical measurements, including photoluminescence have been implemented. Main observations and results may be summurized as follows: -OHgroup concentration could be lowered below 5x105 mol.% in pure chalcogenide glasses - Rare earth ions are introduced into sulfide glasses at concentrations ranging from 500 to 6000.ppm. Homogeneous and clear samples are obtained up to 3000wt.ppm Pr3+. - Clusters and defects are observed when RE and OH concentrations increases,. -Abackground photoluminescence in based glasses and it depends on temperature.

This paper reports a preliminary experimental investigation and characterization of an optical fiber based liquid level detection system for applications in aerospace industry. The sensor system is composed of a multiplexed array of point liquid probes. Two different designs of the probe were fabricated and tested. Probe tests were conducted in water/air and liquidlgas nitrogen environments. Response speed of the liquid probe was measured and compared experimentally with a Linear Variable Differential Transducer (LVDT). In addition, the multiplexing of multiple liquid probes using an OTDR device was successfully demonstrated. Finally, a novel liquid probe made by direct polishing the fiber tip is proposed, which may provide further miniaturization and performance improvements.