As pointed out by our chairman, this workshop aims at being prospective, but for this introductory talk, its seems important to see where we are and where we come from. Optical fibre sensors started in the late seventies with a strong worldwide growth of R & D activity in the eighties.

Fibre-optic monochromatic interferometers have the significant advantage to measure displacements, fibre strain, and other physical parameters using secondary transducers, with extreme resolution and large dynamic range. In order to maintain their performance in hostile environment, they can be constructed as remote, electrically passive sensors. In a critical survey of components, architecture, and applications of fibre-optic interferometric sensors and sensor networks, their practical results and specific problems are discussed.

The ability to make distributed measurements on extended structures is of increasing importance. For example, the measurement of strain distribution on aircraft operating close to their performance limits, the distribution of temperature in boilers, pressure vessels, high voltage transformers etc.,

Optical fibre current and voltage sensors for power industry have needed about 20 years of devleopment time to gradually emerge at the market. The advantageous potential separation is confronted with an expectation of high reliability and low costs.

Optical fiber sensors have been developed for more than two decades and are now in practical use for many different applications. Their advantageous characteristics, such as high sensitivity, immunity to electromagnetic interference, small size, environmental stability, and multiplexing capability, make it possible to measure new physical parameters and to place the sensors in new environment

The process of embedding an optical fiber into a host medium is often accompanied with high pressure and high temperature. It is expected, therefore, that during that process significant birefringence will be induced into the embedded fiber

Rare earth doped fibres have made a significant impact upon the development of effective optical communications systems. The authors and others have extensively explored the use of these rare-earth doped materials in fibre optic high temperature probes, to enable measurements over a wide range

This paper presents the performance of a TPD FO hydrophone with Hydrostatic Pressure Compensation. In particularly a comparison with a conventional piezo hydrophone system is discussed.

Several industrial applications require precise microdisplacement measurements. Optical intensity modulated sensors are very suitable to meet these needs because they are simple and cost-effective. Many have been presented that monitor one-dimension displacement in the direction of the optical axis of the system.

Optical time domain reflectometry (OTDR) is a very useful tool used in optical fibre communications and in sensor networks. The cost of an OTDR instrument prohibits sometimes its use in fibre optic sensor networks. Desforges et al presented a scheme that allows the monitoring of 10 to 50 on/off microswitches along a fibre in industrial environments using retroreflected light.

Fluorescence lifetime based sensors have long since proven their advantages in several measurement fields, including thermometry[l]. Inherent stability to the source intensity fluctuations and possible reference-free design give them a unique position among optical sensors. However, certain issues, such as experimental design (measurement type, dynamic range) and signal processing to decode information from the fluorescence lifetime, still have to be addressed

In recent years, fibre Bragg gratings (FBG) have shown an enormous potential for strain sensing in smart structures and composite materials [1]. However, temperature sensitivity of FBG can lead to significant limitations in their practical application.

The shape of a structure which is known to deform in one-dimension only can be measured using a single optical fibre with one or more sensing elements multiplexed down its length. However, to monitor the shape of a structure that can deform in three-dimensions the full vector strain, or strain field, is required. To achieve this a minimum of three fibres, embedded in a non-collinear geometry, is required.

Compliant FPI-sensors were used to measure mortar deformation at very early ages with high strain resolution. An appropriate design of alternative coatings to achieve reliable bonding between fibre sensor and cement matrix is described.

We describe the use of a four-core optical fibre as the basis of a sensor capable of measuring the angle through which the fibre is bent in two dimensions. The intended application of the sensor is in measuring the shape of flexible structures.

Our aim is to investigate the use of distributed feedback (DFB) fiber lasers [1] as acoustic sensors. In this paper we will discuss the various contributions to the frequency shifts that make such sensing possible, and compare the theoretical results with preliminary experimental results.

The real-time measurement of the vibration of a point in a large vibrating object is an application that is often encountered in industry. Many laser based point vibration measuring devices have been proposed. All have their advantages and disadvantages and which one is used is determined by the application conditions.

Speckle pattern interferometry allows full-field, quantitative measurements to be made on nonspecular surfaces [1], To measure the deformation of a test object, two phase-referenced speckle patterns are recorded by a camera, one before and one after deformation

Molecular absorptiometry is a fast, selective and sensitive method for the determination of the most part of lanthanides and actinides ions. Separation steps of uranium, plutonium, and fission products on the nuclear fuel reprocessing are realised by a liquid-liquid extraction using pulsed columns. Kinetics are slow enough to allow the process to be controlled by liquid chromatography analyses.

The optochemical sensor network: uses side-polished optical fibre elements with wavelength multiplexed fibre-pptic Bragg gratings. The refractive index of the overlay material near to the surface of the polished fibre influences the propagation constant of the guided fibre mode and, thereby, decides the spectral position of the Bragg reflection. The sensor network can be applied for on-line measurement of spatial material distributions and for process control in chemical and biochemical technology.

The measurement of the concentration of stock solutions, dilutions, oils, and water-soluble industrial fluids is of interest in many quality control industrial processes in order to check the concentration stability and abnormal ageing effects. Off-line refractometers, such as the Abbe type, which offer a resolution of 0.2%, are commonly used.

The success of radiotherapy relies on the on-line monitoring of the dose of radiation to which the tumour and its adjacent tissues are exposed. Conventional thermoluminescence dosimeters provide only off-line monitoring, since they determine the radiation dosage after completion of the exposure.

Sediments, microbial mats, biofilms and other microbial communities are characterized by steep gradients of physical and chemical parameters. Fibre optical microsensors, microoptodes, that we developed over the last three years have become powerful tools to investigate and measure these parameters with a sufficient spatial resolution and with a minor disturbance of the micro-environment in natural systems.

Established sensors for fine scale measurements in natural environments are based on electrochemical measuring principles for e. g. oxygen and pH. The preparation of such electrochemical sensors is, however, a time consuming process.

A simple fibre sensor for continuous monitoring of refractive index variations of liquid mixtures is described. The principle of this sensor, based on the excitation of a surface plasmon at a metal/dielectric interface, has been descibed in previous articles. In this paper it is shown that this set-up, which uses monochromatic incident light, can work as a refractive index variation sensor either in a range between 1.36 and 1.40 when using a single silver layer or in a range shifted down to 1.33 when coating silver by a thin TiO2 adaptative layer obtained by sol-gel process.

Ophthalmic drug research and ocular diagnostics is hampered by an inability to perform continuous sampling of the aqueous humour contained within the anterior chamber of laboratory animal or human eyes. Direct sampling of the anterior chamber by paracentesis is technically problematic and is associated with the use of local or general anaesthesia.

Over the last four years, the authors have been involved in research in the broad area of optoelectronic and optical fibre chemical and biomedical sensing. The research projects have differed quite considerably in their applications and the technologies

A new multianalyser tensiograph approach to concentration measurements of pure protein solutions has been devised. Much work has been done over a long period using tensiometers and other surface analysis methods on proteins, enzymes and complex surface active molecules.

Fibre optic sensors may be described as either 'intrinsic' or 'extrinsic' according to whether the fibre itself forms part of the sensing medium or merely acts as a waveguide [1], One considerable attraction of the intrinsic type is the possibility of developing a spatially extended, position sensitive sensor system.

A number of important gases in the context of environmental and safety issues possess absorption lines in the near-IR region of the spectrum between 1 and 2µm. These include gases such as carbon monoxide, carbon dioxide, hydrogen sulphide and methane. The availability of low cost communications fibre and components such as connectors and couplers make this spectral region attractive for the development of fibre sensor networks for continuous monitoring of trace gases

The recent development of the in-fibre Bragg grating sensor (FBG) with its unique ability to detect temperature and strain and ease with which large numbers of such sensors, deployed remotely, can be multiplexed, has lead to the possibility of monitoring the structural integrity of major capitol items such as buildings and bridges.

The correlation DTS is based on correlation technology and Raman scattering concept. First let us know something about correlation and Raman scattering.. A. Correlation technique A correlation DTS launches an optical direct Pseudonoise(PN) sequence to probe the fibre. By integrating a returning anti-stokes sequence from the fibre, we can get the temperature information.

Optical interferometry is widely used for high accurate measurement and two-beam interferometry is one of the well-used techniques. Due to the nature of the Cosine response of an interferometer, a signal processing technique is necessary to obtain the measurand.

Bookham Technology has developed a unique manufacturing technology called ASOC™ which employs low-loss silicon-on-insulator (SOI) rib waveguides combined with interfaces for waveguide-to-fibre coupling and hybridised optical sources and detectors.

Stimulated Brillouin scattering is a unique parametric interaction which offers a simultaneous sensitivity to temperature and strain. Distributed sensing over 50 km with a spatial resolution in the meter range has been demonstrated.

A major development during the last two years has been the deployment of the first optically amplified high bit rate (> 5 Gb/s) and long haul (TAT 12/13, TPC 5) optical transmission links. A further parallel development over the last few years has been the design, and implementation upto the demonstrator stage, of large scale optically amplified high bit rate fibre communication networks [1,2].

Tapered optical fibres are used to design couplers, wavelength division multiplexers [1], near field scanning optical microscopy [2], just to mention a few. Moreover, and due to its strong transmission dependence to external medium the tapered fibre may also be used to sense distinct parameters such as temperature, humidity, PH, etc.

Fringe-counting sensors can usually resolve optical pathlength changes of one or one half wavelength, depending on the interferometer used. Recently, a fiber-optic fringe-counting sensor has been proposed, which may resolve a small fraction of a wavelength [1].

Optical fibre interferometric strain sensors embedded into structures offer a very accurate and robust method for shape measurement [1]. Many schemes have been demonstrated in which strain and/or temperature in a structure are inferred from monochromatic optical phase delay [2].

Extrinsic Fabry Perot Interferometers (EFPI) Sensors have been extensively used for the monitoring of strain and temperature into smart materials and structures. For these applications, the Fabry-Perot cavity used is usually formed by an air gap of few tens of microns located between the extremity of an input single-mode fiber and the reflective extremity of another fiber, either single-mode or

Optic fibre sensors and especially polarimetric ones provide high accuracy and sensitivity. They are insensitive to electromagnetic perturbations. The simulation of an angular position polarimetric sensor using telecom single-mode optic fibre as a transducer showed a thermal dependence [Mane 95], [Mane 96].

Optical fiber current sensors are of considerable interest to the electric power industry. Particularly attractive features as compared to conventional current transformers include inherent galvanic isolation of the sensor head from ground potential, less sensitivity to electromagnetic interference, smaller size and weight and higher safety.

Under the Composite Hull Embedded Sensor System (CHESS) program, which is a co-operative program run jointly by FFI and NRL, a drop test with a composite sandwich plate has been performed [1]. The plate was designed to have similar mechanical properties to a bottom panel in the Norwegian Navy’s new fast patrol boat (MTB).

There is considerable demand in the field of turbomachinery research to make in-situ measurements of temperature, heat flux, and pressure in large-scale flow rigs. This is driven by the desire to increase engine efficiency and reliability by improving our understanding of the flow regimes within compressors and turbines.

An interesting and increasingly popular method of building steel and concrete composite bridges involves the use of a large steel based structure called a box- girder. These massive structures, which have dimensions on the order of 5m x 5m x 150m with wall thickness sometimes exceeding 5 cm, are assembled by welding together many shorter (e.g. 5m x 5m x 5 m) box-girder pieces near a bridge building site.

The use of computational fluid dynamics (CFD) to model the temperature and pressure distributions which drive complex thermodynamic processes in gas turbine systems contributes to more cost efficient turbine design and development.

We report on a new type of optical extensometer for strain measurement in geotechnical and civil engineering applications. The system key elements are Fiber Bragg Gratings (FBG) embedded in glassfiber reinforced polymer (GRP) rockbolts. In order to monitor rock deformations in tunnels, a prototype sensor rockbolt was designed. First measurements have been made to demonstrate the characteristics of the sensor system.

A range of reports and most significantly several surveys of commercial optical fibre sensor technology have been carried out and published in recent years. In 1988 ERA Technology Ltd issued a report to the Optical Sensors Collaborative Association (OSCA) in the UK on a world-wide survey of manufacturers in the field and in 1994 this work was extended in a further document adding to the data available though a report based on interviews (mostly in the USA) and a questionnaire to major manufacturers

The reliability of rotating machines such as electrical generator is critical to the overall reliability and operation ofelectrical power plants. The very high cost ofthese machines, makes it necessary to improve the lifetime of a wide set of currently installed hydrogenerators around the world and avoid costly maintenance.

Optical fibre sensors have many attributes that make them attractive for diagnostics in gaseous electronics systems involving electrical discharges and plasmas. These systems often use high voltages and generate electromagnetic noise, so that optical fibres have advantages over the more conventional electric and magnetic probes used to measure discharge parameters.

All-fiber current sensor based on the Faraday effect has significant advantages over the conventional current sensors, including a high electric insulation, an immunity to electromagnetic interference, a wide dynamic range, a small size and a low cost.

This paper describes the design and development of an optical hydrophone array for a seabed application. Optical hydrophones have been under development in a number of countries [1] as alternatives to piezoelectric based sensors, and the technology has now reached the stage where arrays with significant numbers of sensors can be constructed and deployed in realistic (and frequently hostile) environments.

This paper deals with the design, testing results and practical application of a new type of optical voltage transformer (OVT) . It's different from the exist OVTs . The high voltage (beyond 110KV) is directly applied on the electrooptical crystal (Bi4Ge3012) sensor, without the divider. And a new type of the silicon rubber insulator, SF6 gas filled , is employed for high voltage insulation. Its precision is ±0.2% from 80% to 120% of the rating voltage, between -10°C and +40°C. All parts of the OVT are developed according to the requirement of products.

Fiber Bragg gratings (FBG) offer an attractive method of strain sensing owing to their fiber-based, wavelength encoded operation. In this paper we present a novel passive narrowband interrogation method for FBG strain measurements

There is a need for the assessment of the safety of ultrasound for medical applications [1,2] due to the trend towards increasing output powers from diagnostic ultrasound equipment and the widening use of high intensity ultrasonic fields in a range of therapeutic applications.

Many different schemes of Bragg grating based quasi-distributed and multiplexed sensors have been reported.1 Most of them utilize wavelength division multiplexing and detect the resonant wavelength for sensor interrogation

Multiplexed FBG strain sensors are currently deployed for the monitoring and analysis of structural loading worldwide. One remaining issue is the separation of the strain-induced wavelength shift from that induced by temperature changes.

The all-fibre Mach-Zehnder interferometer (FMZI) is an optical instrument capable of high-resolution phase-analysis. Constructed from a pair of 2x2 couplers spliced back-to- back, FMZIs dispense with the alignment problems of their bulk-optic counterparts, and offer the versatility of easily-implemented heterodyne phase-modulation and dual-output detection.

A new method for synthesis of fiber gratings with advanced characteristics is proposed. The method is based on an optimizing genetic algorithm, and facilitates the task of weighting the different requirements to the filter spectrum. A classical problem in applied physics and engineering fields is the inverse problem. An example of such a problem is to determine a fiber grating index modulation profile corresponding to a given reflection spectrum. This is not a trivial problem, and a variety of synthesis algorithms has been proposed [ 1 ]-[3]. For weak gratings, the synthesis problem of fiber gratings reduces to an inverse Fourier transform of the reflection coefficient. This is known as the first-order Born approximation, and applies only for gratings for which the reflectivity is small. Another solution to this problem was found by Song and Shin [2], who solved the coupled Gel’fand-Levitan-Marchenko (GLM) integral equations that appear in the inverse scattering theory of quantum mechanics. Their method is exact, but is restricted to reflection coefficients that can be expressed as a rational function. An iterative solution to the GLM equations was found by Peral et. al. [3], yielding smoother coupling coefficients than the exact method. Their algorithm is converging relatively fast, and gives satisfying results even for high reflectivity gratings. However, when specifying ideal, unachievable filter responses, it is desirable to have a weighting mechanism, which makes it easier to weight the different requirements. For example, when synthesizing an optical bandpass filter, one may be interested in weighting linear phase more than sharp peaks, because the dispersion may be a more critical parameter. The iterative GLM method does not support such a mechanism in a satisfactory way.

Fibre Bragg grating has become the most attractive intrisic fibre sensor in recent years for various reasons [1-4]. One of the major advantage of this type of sensor is attributed to wavelength encoded information provided by the Bragg grating when affected by the mensurand. Since the wavelength is an absolute parameter, signal from a Bragg grating may be processed such that its information remain immune from power fluctuations along the optical path

The use of optical fibres as sensing elements for electric current measurement has been developed by several methods such as those utilising magnetic field to generate the Faraday effect, magnetomotive force to make fibres bend, magnetostrictive material bonded on a fibre to constrict or lengthen the fibre, and heating effect to change the fibre’s length and refractive index

FBGs are especially useful for structure monitoring applications because their small physical cross-section and the mechanical strength of the optical fiber. However, the monitoring of large and complex structures often requires a very large number of sensors and high sampling rate.

Fiber optic sensors are being used in many biomedical applications. In particular, their dielectric nature makes them more suitable than thermocouples for temperature measurement in an environment of high electromagnetic field such as that used for hyperthermia treatment [1].

The use of Bragg gratings for measurement of pressure, strain and temperature has been the subject of considerable research over the last decade. Techniques for temperature/strain discrimination are summarised in Reference 1 and often involve either a specialised interrogation system or a dual grating approach

Fibre optic hydrophones have been under development for twenty years, and have attained similar performance to the more conventional piezoelectric based transducer. However, the recent development of fibre Bragg grating (FBG) sensors makes possible an alternative approach to optical hydrophones, which offers the advantages of small sensor size and very simple manufacture

A new technique is presented for active distributed fiber sensing for interrogating structural integrity and environmental monitoring using an innovation in low power integrated compact tunable fiber optic laser capability.