The worldwide market for fiber optic sensors, 1985 through 2000, is forecasted. The forecast is segmented according to geographic region, by application and by major sensor technology categories. Worldwide development programs are summarized. Blocks to market development are reviewed. Sensor and component cost trends are forecasted.

A fiber optic hydrophone is described, based on a dual in-line resonant cavity principle. The resonant cavities comprise all-polarization-preserving-fiber ring resonators which act as wavelength selective comb filters with a broadband source. Theoretical and experimental results on the hydrophone performance are presented.

We describe an experiment to visualize air flow separation in an aircraft air-intake. This experiment was realized in a large industrial wind-tunnel. It uses optical fibers to bring a laser beam into the model and an optical fiber endoscope to visualize images of the phenomenon. Some pictures showing changes of the air flow separation are presented for several aerodynamic conditions.

The fiber-optic voltage and current sensors applied for 84kV three phase type gas insulated substation (GIS) were tested in order to see the advantages of these sensors practically in adverse field condition. The application technologies and field endurance test results of the sensors are described in this paper.

A simple, inexpensive Laser Doppler Velocimeter (LDV) is described. The design has been optimised for hand-held machine vibration analysis and incorporates a laser diode and a single-mode optical fibre coupler. The laser diode acts as an integrated frequency-shifting light source and the vibration information is extracted by a pseudo-heterodyne technique.

Many types of integrated optic modulators can be made. The reasons of the choice of Mach-Zehnder modulator on LiNb03 are presented as also the achievement of high sensitivity. Some applications and different kinds of modulation are reviewed.

The paper reviews properties of distributed optical fibre sensors and techniques for passive multiplexing of multiple sensors on to a single optical fibre distribution network. A range of topologies for optical fibre networks associated with sensor multiplexing are discussed together with their limitations and advantages. These are then related to the modulation schemes of the light source and associated signal processing. The discussion covers pulse and FM schemes, sub-carrier modulation and synthetic pulse concepts.

The usefulness of optical fibre hydrophones, and their practicality in phased arrays, is critically dependent upon the technology and systems philosophy adopted for their implementation. Previous work has demonstrated the principles of pulsed ref lectometric techniques in this context, and modifications to the basic system have improved its performance in three respects: that of the acoustic design of the sensor, that of the optical loss budget, and that of the ambient noise performance. In the range of 100Hz to lkHz, the system noise has been reduced to below ambient sea noise under most conditions. The system has been demonstrated with 2.2km of fibre lead between the sensor head and the optical system, with no discernible loss of performance.

We propose a multisensor network where the refractive index modulators are distributed in cascade along the optical fibre. Reflections at fibre glass-monitoring medium interfaces provide a train of time multiplexed pulses. Backscattered radiation in the fibre serves as a reference channel for the individual sensors which can be designed for temperature, pressure, chemical composition measurements.

Because of their large information carrying capacity, optical fibers allow to create networks with a large number of terminals. This capability can be combined with the potential of optical fibers for sensing applications. These two characteristics lead directly to the concept of optical fiber sensor networks, which show promising for process control automation.

This paper presents a method of retrieving optical sensor data from an time division multiplexed (TDM) optical system. The total response may consist of overlapping sensor data which will occur due to the short optical delays. The method uses a straightforward deconvolution in the z-plane and allows the effects due to the distorsion of the optical signals by the optical network to be modelled.

A new type of stress location sensor is discussed in which the FMCW technique is used to detect the difference in propagation time between two optical paths in an optical fiber due to stress induced modal coupling. Two versions of the system are included, and experimental results are presented for each system.

Reported in this paper are novel fibre optic techniques for controlling the azimuth of a linearly polarised optical beam. Polarisation state control is implemented using piezo-electric and acousto-optic phase modulators. A pseudo-heterodyne signal processing scheme for polarimetry is described. Results from demonstration experiments of light scattering from a colloidal dispersion and the measurement of optical activity are presented.

The amplitude detection of the output of an intensity modulated sensor is replaced by the phase measurement of a radio-frequency modulated signal.

A new scheme of a fiber-optic sensor which permits the interferometric detection of slow time-dependent phenomena will be presented. Theoretical analysis and experimental results referring to a very-slow strain change will be reported together with the rejection capabi-lity of the unwanted perturbations.

An optical fiber temperature sensor utilizing a thermochromic transducer is presented. A time division multiplexing technique,used to obtain the sensing and the reference signals, allows the realization of a compact optoelectronic system. Technical data and experimental result are reported and discussed.

Temperature sensing is achieved via the temperature dependance of the absorption of the evanescent field of a polished single mode fiber embedded in an absorptive medium.

The average temperature of an environment has been measured using the anti-stokes Raman signal backscattered from a multimode fibre. Temperature measurements using less than 1mW of input laser power are accurate to 2°C over the range -200°c to 150°c.

The applications of the Fiber-Fabry-Perot (FFP) as demonstrated in the laboratory are shortly reviewed. The FFP has been used as optical spectrum analyzer, as a reference element for laser diode frequency stabilization, and as a sensing element for the measurement of temperature, mechanical vibrations, and electric and magnetic fields. A new FFP strain gauge sensor element is reported that is made from a gradient index fiber. Its main advantages are easy coupling between light supplying and signal transmission fibers to the FFP as well as a modular configuration of the FFP sensor. A signal evaluation method is described that identifies the sign of measurand change and allows for large intensity losses on the transmission module.

The temperature dependence behaviour of the microbend-induced birefringences of single mode fibers has been experimentally investigated. It is found that the temperature dependence of the microbend-induced birefringence of an elliptically jacketed fiber is much smaller than that of a non-polarization preserving fiber. In agreement with the theory, measurements show that the temperature dependence of the birefringence can be interpreted using the photoelestic effect of the fiber, and the corresponding stress on the fiber due to the microbending can be deduced from the experimental data.

A novel fibre optic temperature sensor which uses an internally generated fluorescence signal as an input intensity reference channel is constructed. The absorption changes of a sample of doped glass are monitored in the infra red region of the spectrum and a sensitive all optical thermometer is produced, tested over a wide temperature range from -60°C to +200°C.

The use of the evanescent wave coupling between a critically cut optical fibre and a glass plate is described. An experimentally demonstrated configuration is used to illustrate the principle in an analogue force/pressure sensor addressed by light from a He-Ne laser, and application to a non-intensity dependent measurement scheme is shown.

Fluorescence quenching is shown to be a viable method of measuring oxygen concentration. Two oxygen/optical transducers based on fluorescence quenching have been developed and characterized: one is hydrophobic and the other is hydrophilic. The development of both transducers provides great flexibility in the application of fluorescence to oxygen measurement. One transducer is produced by entrapping a fluorophor, 9,10-diphenyl anthracene, in poly(dimethyl siloxane) to yield a homogeneous composite polymer matrix. The resulting matrix is hydrophobic. This transducer is extremely sensitive to PO2 as a result of oxygen quenching the fluorescence of 9,10-diphenyl anthracene. This quenching is utilized in the novel method employed to measure the transport properties of oxygen within Ulf 2matrix. Results show large values for the diffusion coefficient at 25°C, D = 3.5 x 10-5 cm /s. The fluorescence intensity varies inversely with P02. The second oxygen transducer is fabricated by entrapping 9,10-diphenyl anthracene in poly(hydroxy ethyl methacrylate). Free radical, room temperature polymerization is employed. This transducer is hydrophilic, and contains 37% water. The transport properties of oxygen within this transducer are compared with those of the hydrophobic transducer. The feasibility of generalizing the oxygen transducers to a wider class of chemical sensors through coupling to other chemistries is proposed. An example of such coupling is given in a glucose/oxygen transducer. The glucose transducer is produced by entrapping an enzyme, glucose oxidase, in the composite matrix of the hydrophilic oxygen transducer. Glucose oxidase catalyzes a reaction between glucose and oxygen, thereby lowering the local oxygen concentration. This transducer yields a glucose modified optical oxygen signal. The operation of this transducer and preliminary results of its characterization are presented.

Fibre optical sensors allow the measurement of material properties in dynamic material testing which hithertoe seemed not possible. Their use in dynamic fracture mechanics proved very helpful for data acquisition at impact loaded specimen which in turn allows the design of nuclear reactor-components with extreme safety rquirements.

A simple Low cost position verification device, developed primarily for application in medicine is described. The design lends itself however to countless other applications particularly in civil and mechanical engineering. The resolution of the device depends on the diameter of the fiber optic used, the sophistication of the controlling microelectronics and optical collection system. In essence the device monitors any movement with respect to a basic reference frame defined by the beam of a helium/neon laser. The laser being attached to a remote structure which can be assumed to be fixed. A real-time positional display will enable the operator to correct for any unacceptable movement, or with a suitable feedback system this could be done automatically.

A flowmeter with a variable-area orifice has been investigated to measure low gas flows with low pressure drops in a pipe of internal diameter 150mm. A 'petal' construction is used with alternate fixed and flexible segments in a symmetrical arrangement about the axis of the pipe. A non-contacting optical fibre sensor is employed to monitor the deflection of a single petal as flow varies. Flows have been measured in the range 0.35 to 1.5ms-1 with a maximum pressure drop of 375Pa.

To overcome difficulties in measuring temperatures beyond 700°, or in places unapproachable by traditional techniques, an optical fiber is used to pick-up the corresponding temperature radiation. This radiation is sent to an optoelectronic system and split into two channels by an achromatic optical fiber coupler. Each of the two channels is defined by its specific spectral domain with the help of silicon photodiodes equipped with appropriated filters. Signals are then amplified and dicitized in order to be processed.

The level of drift produced by coherent backscatter in the optical fibre gyroscope is investigated. In particular the phase modulated minimum configuration system is considered and conclusions drawn concerning the optimum modulation frequency and the feasibility of incorporating a laser source in an inertial grade gyroscope. It is shown that the optimum modulation frequency is approximately one sixth of the eigenfrequency of the gyroscope and that at this point the backscatter is independent of the coupling ratio, environmental effects and rotation rate.

A new method for birefringence measurement in single mode optical fibre, using circularly polarised input light is described. Its usefulness is established through a detailed error analysis taking into account the performances of the optical components available on the market. The application of this method is demonstrated in an example.

The effect of birefringence induced in a single-mode fiber by a lateral force has been applied to measure the absolute value of static force or pressure with high resolution. A sensor configuration with an extended detecting surface has been investigated by means of calibrated weights. The sensor is sensitive to an incremental force of 2 x 10-3 N, independently of the length of the fiber. The maximum force applied was 10 N per centimeter of fiber lenoth.

A noncontact proximity sensor built with plastic multimode fibers is presented. The sensor is based on the measurements of the intensity variations of the light scattered by a mobile rough object illuminated with several focused beams. The intensity maxima obtained when the object is at the focal points are used for rapid detection of its presence and orientation.

Traditional instruments for spectral reflectance measurements consist of a broadband light source, a monochromator, a photodetector, a mechanical chopper, an analysing unit and a display. This equipment enables us to perform continuous reflectance spectrum measurements of an object. In many appearance measurement applications the reflectance at particular discrete wavelengths give adequate spectral information. Then the broadband light source and the monochromator can be replaced by narrow band light sources (e.g. a LED or a laser diode), which in industrial measurements have significant advantages: the possibility of electronic chopping, electrical and mechanical reliability and efficient connectability to optical fibres. With a view to the reguirements of industrial enviroments an eight channel spectrophotometer has been constructed. The equipment is composed of eight electronically chopped LED's, two photodiode detectors, a temperature controller, a fibre optic probe, a signal conditioning electronics, a microprocessor based controlling and analysing unit, a display and a plotter interface. The wavelengths of the semiconductor sources can be chosen from a commercial selection between 480 nm ... 1500 nm. The chopping of the channels is time multiplexed and the duration of one sampling sequence is 640 μs. Samples are taken syn-chronously from the emitted light pulses with the reference detector and from the light modulated by the object under test with the measurement detector. Before every light pulse, a "dark" sample is taken from the background irradiance to be reduced from the measurement signal. The microprocessor takes care of further signal processing, computation of the parameters and displaying of the results on the 8 x 4 digit display or on plotter curve. The influence of intensity variation of the emitters is eliminated by relative measurement and the consequences of temperature changes are minimized by stabilizing the temperature of the transmitters and receivers with a thermoelectric controller. The measuring end of the fibre optic probe is coaxial: The eight transmitting bundles from eight LEDs are bound together, randomly mixed and surrounded by the receiving bundle leading to the detector. A portion of each transmitting bundle goes to the reference detector for the measurement of the emitted light. The stability of the equipment and the measurement range for colour modulation detection are presented. The latter measurement is not dependent on the distance between the probe and the object. The colour measurement of different kinds of paper are presented as applications. Potential industrial applications could be, for example, the on-line colour measurement of paper on a paper machine or on a printing press and the in-line concentration measurements of various liquids at the same time.

The device presented is a void fraction measurement sensor, in two phase flows (liquid plus gas). The knowledge of the void fraction is essential to understanding the processes that takes place in heat exchangers. It is also an experimental checking tool when modeling two phase flows.

A fibre-optic dark-field micro bend sensor capable of detecting 80% of the power loss of the brightfield and with a sensitivity of 1.0 10-11 ml/√Hz has been constructed. It was found that the micro-bend loss was independent of the number of bends for 3 or more bends. The deforming device was transparent and a detector was attached to its end.

A fibre optic displacement sensor based on tracking the minima in the frequency response of a dual-fibre optical link is described. The sensor is based on multimode fibre technology and uses a LED source, and is insensitive to attenuation changes in the optical paths. The output is in the form of a frequency. Preliminary experimental results are given.

A fibre optic sensor for the measurement of strain is described, in which both the measurand induced changes in phase and polarisation state are simultaneously recovered. A sensor with inherently great resolution and wide measurement range is thus realised. The feasibility of a simultaneous measurement of strain and temperature is discussed and a sensor with intrinsic temperature compensation and measurement capability is described.

A novel, rugged, position sensing device, based entirely on commercially available multi-mode optical fiber components, is described. The operating principles, design and construction, and performance data obtained through deployment of the device in the hostile environment of a large hydro-electric generating unit, are presented.

The system described in this paper has been developed in response to a need to measure components of the dynamic displacement of a railway track relative to the sleeper. It embodies an array of two-wavelength optical fibre displacement sensors based on the Cambridge Consultants Ltd moving shutter principle. The sensors have been designed to operate over the frequency range DC to 3.5kHz with a resolution of lom over the displacement range 0-2mm. The distribution of the sensors over the track and sleeper enables combinations of orthogonal displacement components and linear tilts to be measured. The paper describes the detailed optical, mechanical and electronic design together with experimental results which demonstrate the immunity of the system to fibre noise, differential coupling losses, etc. Furthermore, preliminary structural displacement measurements are also presented.

A fiber optical strain gauge sensor for detection of respiration motion and heart beat rhythm has been developed in order to suppress motion artifacts in magnetic resonance images (MRI) by gating and triggering procedures. A photoelastic sensing principle has been used in this sensor. It has been adapted to optical fibers to achieve a remote evaluation of the optical signals. The sensor properties are discussed and first results on image quality improvements by the application of this optical sensor are presented for the case of 2 Tesla magnetic resonance imaging of the beating human heart.