The objective lens is a single element glass lens with one aspheric replicated surface and one flat surface. The manufacture of the aspheric surface by means of replication is suitable for high quality mass-production.

In this paper an overview is given of the PCVD process as applied for the large scale production of optical fibres for telecommunication. The specific merits and potentials of the process, such as the profile independent high deposition rate and excellent controllability are discribed. The current state of the art of the process, as it is used in the Eindhoven production unit, is a deposition rate of 1 g/min., a preform size equ'ivalent tO 28 km of fibre and a drawing speed of 4 m/s. Fibre characteristics are well within the requirements imposed by the telecommunication market. The PCVD process has also proven to be suited for the production of dispersion flattened singlemode fibres and high NA graded index fibres for short distance applications. For both fibre types the high refractive index differences obtained with fluorine doping are exploited. Depending upon the market demands all fibre types can be manufactured at the same productivity. Some trends are given towards further increase of productivity and reduction of fibre costs.

Technical and commercial factors important in assessing the impact of fibre optic sensors are considered, and concluded to be of especial importance for the military/aerospace/defence applications areas, Significant growth potential is anticipated, but previous work has not acknowledged the highly fragmented nature of the applications sectors, which are described, The current market for fibre optic sensors is compared with the electro-optics industry in Japan, and applications of electro-optic instrumentation in manufacturing, The work of the UK Optical Sensors Collaborative Association is described as a realistic response for the process/industrial sectors, It is concluded that the technology of fibre optic sensors has not progressed beyond user evaluation of early products, and in spite of the fragmented nature of the industrial and medical areas, growth potential in selected niches shows potential, The technology is particularly strong in the aerospace/defence sector,

Distributed optical-fibre sensors (DOFS) have many advantages for industrial use. The simultaneous acquisition of both the spatial and the temporal distribution of the measurand field allows increased monitoring capability and better understanding of system behaviour.

A new method of distributed fiber sensing is presented which uses a polarization maintaining fiber as the sensing fiber and a frequency modulated laser diode as the light source. The mode conversion caused in the fiber by a perturbation to be measured generates an optical beat signal in the forward travelling light. The magnitude and location of mode conversion can be real time detected from the amplitude and frequency of the beat signal, respectively.

This paper will describe techniques which should greatly reduce the signal averaging times required in conventional distributed Optical Time Domain Reflectometry (OTDR) sensor systems. The technique does not require coherent detection and spectral analysis as is currently used in FMCW or FMAMCW. A digitally generated pseudo-random noise sequence is modulated on to a light source and transmitted down an optical fibre. The received backscattered signal is then correlated (multiplied) with a delayed version of the transmitted sequence to evaluate the amplitude of the backscattered signal at a given point along the fibre. The average transmitted and received signal power is therefore increased allowing reduced signal averaging times or reduced peak laser powers to be used compared with conventional OTDR systems.

The paper describes the design, construction and testing of a fibre optic pressure sensor based on a reflecting Fabry-Perot etalon. The etalon comprised one fixed mirror and a second mirror designed to flex under the action of the pressure being monitored. A single multimode fibre was used to connect the passive, remote sensor to the transmitter/receiver section, and dual wavelength referencing was used to eliminate the effects of bending-induced attenuation in the fibre.

Experiments are performed toward the development of a fiber optic pressure sensor which uses the elasto-optic birefringence in a single-mode fiber. The 'side-hole' fiber-structure may be viewed as a PANDA-structure with open channels instead of the stress generating rods in its cross-section. The use of the side-hole fiber exploits the high reproducibility of silica serving as the elastic reference. By the side-hole geometry external hydrostatic pressure is converted into an anisotropic stress in the core region. Additionally, a stress concentration by a factor of 3 to 5 can be achieved by suitable choice of the geometry of the channels. In the experimental setup, the fiber is exposed in a pressure chamber directly to the pressure to be measured. The chamber is designed for a pressure range of 0 to 1000 bars.The induced birefringence is determined by passing a polarized laser beam through the fiber and by bi-directional counting the periods of phase delay between the two polarization-eigenstates of the fiber at the output. Thus, the sensor operates in an incremental mode. Using a fiber length of 10 cm, a pressure induced birefringence of 7.78 rad/(bar-m) was measured at a wavelength of 1300 nm. The resolution of optical phase evaluation is ni2, corresponding to a pressure resolution of approx. 2 bars. The overall accuracy of the sensor is better than ± 0.5% in the pressure range of 100-1000 bars where unambiguous phase evaluation was possible. Below 100 bars, in one fiber problems were caused near the point where the the birefringence vanishes. The experimental sensor-head is connected to the evaluation unit by a polarization-maintaining single-mode fiber, supplying the laser light, and three electrical leads for the detector signals. A version without any electrical lead to the sensor head is planned, in which the light source and the signal detectors are connected by optical fibers.

Micromechanical silicon cantilever structures of typical dimensions 1 mm x 80 μm x 5 μm have been excited by absorption of pulsed light from diode laser at 790 nm or a LED at 830 nm respectively. The excitation motion of the cantilevers was measured by means of a fiber-optic Michelson interferometer as well as a reflective multimode fiber optic pick up. In addition to the optical signal the electrical signal of a thin film piezoresistive transducer localized at the base of the cantilever has been measured. The optimal fiber position with respect to the cantilever was determined experimentally. At this position a signal to noise ratio of about 6 could be realized for the detected signal at 5 kHz bandwidth for optical power levels of 56 pW. Using a 125 μm diameter optical fiber this corresponds to an optical power density of 4.6 mW/mm2 which is below the critical value of 5 mW/mm2 suggested for explosive environments.

A fiber-optic pressure sensor and a fiber-optic force sensor based on a resonating mechanical structure are developed. The accuracy and reproducibility mainly depend on the characteristics of the mechanical structure. Both structures are optically excited and the readout transducer consists of a simple optical displacement sensor, hence we have an all-optic design with its specific advantages. Further, the mechanical structure can be batch fabricated and the optic links can then be integrated with the structure. Optical transfer functions have been measured. With the proposed arrangement we obtain a signal-to-noise ratio better than 30 dB having the advantage of frequency signal transmission. The prototypes of the fiber-optic pressure sensor and the fiber-optic force sensor show the feasibility of micromechanical structures in fiber-optic sensors.

An optical fiber displacement sensor, based on the light intensity modulation induced by the reflection and/or scattering of a target, is decribed. The optical head is constituted by two GRIN-rod lens ended fibers which make possible the sight of a target within a few millimeter sensing range. A description of the system and the experimental results are presented.

The development of optical methods for detection of ultrasound is important for the technology of non-contact Non-Destructive Evaluation of materials. Several optical methods are limited in their application by their sensitivity for ambient vibrations or their complexity. In this paper a Fiber Time Delay Interferometer is proposed which can be applied to the detection of pulsed ultrasonic vibrations. A practical instrument has been built with a detection limit of 2.10^-11m, determined with a detection bandwidth of 10 MHz. Results of experiments show that the method can be used for the detection of (artificial) sub-surface fatigue cracks, using pulsed ultrasonic excitation.

In the system described a pressure sensor and its'associated electronics are optically powered by a 20 mw laser and a photovoltaic cell via an optical fiber. The sensor is periodically interrogated and sends the measures obtained back to the central unit using an LED and a second fiber. The results obtained as well as the expected evolution will be described.

The operation of optically excited micro-resonator sensors is described in which internal feedback provided by an optical interferometer induces self-oscillation. Unmodulated light passes to the sensor through an optical fibre to maintain the oscillation, and modulated light is returned down the fibre with a frequency characteristic of the stress applied to the resonator.

The ultrasonic response of single mode fibers has been studied in the frequency regimes where the fiber is isotropic and anisotropic. Good agreement has been obtained between analytical and experimental results. Fiber optimization has been achieved by appropriate selections of fiber coatings which can maximize or minimize the fiber sensitivity. Finally, the air acoustic response of several sensing elements has been studied.

Twin-core, polarimetric and in-fiber Bragg grating temperature and strain sensors for point and distributed measurements are reviewed. New applications to the in-situ monitoring of polymer composites are reported including techniques for measuring stress waves, resolving principal stresses and determining flexural strain variations.

Absorption of 1.06pm radiation in neodymium-doped fibre and subsequent anti-stokes fluorescence is observed in neodymium-doped fibre at elevated temperatures. The increase in absorption is used as the basis for a distributed temperature sensor over the range 20-800°C. The temperature dependence of fluorescence at 940nm is used in an optical fibre point temperature sensor.

Passive multiplexing of a fiber optic temperature sensor network using spectral modulation encoding techniques in birefringent bulk materials is demonstrated. Various detection schemes are described and the consequences of the spectral dependence of optical properties for both transducer and demultiplexer are theoretically analyzed. The network organization choice is discussed and the first experimental evaluations of a breadboard network are reported (sensitivity, crosstalk, line losses effect).

Several principles for single or multipoint temperature sensing using optical fibers have been proposed but only few are able to give the continuous temperature profile along the way followed by the fiber. One of them, using Raman back scattering, was experimented in various materials and has a wide range but limited resolution, and needs a sophisticated equipment. We report here the experimentation of a new sensor concept based on the bend losses dependance on the temperature, induced by the variation of the refraction-index difference versus the temperature when organic material is used, as for example, in PCS fibers. Because of the sharp variation of the bend losses under strong curvatures, this sensor has a high sensivity (0,2°) over a wide range (at least -20° to +60°C). It is possible to shift this range by matching the radius of curvature. This principle can be applied in a single-point sensor (by measurement of the relative loss) or in a distributed sensor using the optical time reflectometry. It can give a high accuracy in the temperature profile or in the location of a temperature front, with a simple and available end-equipment. However, experiments have shown the non-negligible effect of the back-scattering enhancement and the reliability problems induced by a strong curvature. Various realizations of such a sensor are proposed.

An industrially realizable, hybrid, optical fibre temperature sensor has been built using a temperature dependent quartz resonator. It requires a minimum power of 110 μW; its resolution is 0.05% of span and its dynamic range, 36dB.

The development of a fiber optic interferometer for static temperature sensing in gas or steam flows and in steam turbines is reported. This paper contains informations from the initial motivations to the test procedures of the prototype. A Michelson interferometer single physical arm, combined with an active phase tracking heterodyne detection has been conceived. Tests of the semi-industrial prototype in a supersonic air pipe are described (resolution 0.5 K, dynamic 50 K). The design of an optical probe for steam turbine measurement is reported and an outline of future experiments of the optical system is given.

The paper reports on the feasibility of measuring temperature distribution in optical fibres using the optical Kerr effect. The basis of the proposed method is to inject a pump pulse into one arm of an optical fibre interferometer to cause a transient phase imbalance as a result of the optical Kerr effect. As the optical pulse and the interferometer interogating beams propagate in opposite directions, the magnitude of the optical Kerr effect as a function of distance along the fibre can be determined from the temporal variation of the detected signal. The results show that the temperature dependence of the optical Kerr effect appears to be substantially less than that reported for the electrical Kerr coefficients measured at low frequencies.

Presently there is considerable research interest in the development of all-fiber multi-sensor networks for use in arrays, and applications where a large number of different measurands are of interest (i.e., process control). A number of optical and opto-electronic multiplexing schemes have been developed for use with such networks in recent years. This paper will review this area of OFS technology and discuss some recent development in the multiplexing of interferometric sensors.

Fiber optic reflectance sensors, mounted on a gripper, have been constructed for a scara-type robot in the insertion of electronic components. The position of the gripper fingers, the distance to the object component, the edges, the orientation and the pin images are meas-ured and determined during the assembly process. The sensor consists of a transmitter (LED, 850 nm) and a receiver, (PIN-photodiode), which are equipped with different fiber optic measurement heads according the kind of application. The emitters and detectors are con-nected to optical fibers using mounts and SMA connectors. The position sensors of the gripper fingers are used to measure the distance between the gripper body and the fingers. The measurement range of the position sensor is 17 mm and the resolution is better than 50 pm using 100 Hz bandwidth. The measured position information is used to control the gripper dc-motor drive via a I/O controller. Proximity sensors mounted on the ejector are used to measure the distance to the object component and detect the edges. Based on measured scan profiles of components (capacitor, inductor) the edges can be determined. A typical transition range of an edge is < 2 mm giving a position resolution better than 50 pm. This edge information is used for orientation calculations. The separate pin image sensor station is used to measure the reflectance scan profiles of the pins of the component to determine the span of the component pin relative to the robot gripper. The xy-motion of the robot is used for scanning at a constant velocity. The position of the tip of the pin can be determined in the xy-plane to an accuracy greater than ± 50 μm. The realization of the sensors together with experimental results are presented.

The dual-wavelength interrogation of interferometric fiber-optic sensors is discussed. This approach can be used to alleviate the intrinsic ambiguity associated with the cosinusoidal output of interferometric systems. The application of this technique in temperature sensing and its use in the all-fiber gyroscope is reported.

A miniature, resonant, fiber-optic scanner driven by silicon detector photocurrent requires only 23μW to sequentially address each channel of a ten-bit optical encoder mask. The digital position code is transmitted twice each cycle to a remote readout, constituting a passive optical sensor, with multiplexing capability via its precise resonant frequency.

The precision of intensity modulated fiber optic sensor systems mainly is restricted by the damping characteristics of the analog fiber optical data link. Special encoding and referencing schemes are used to overcome this data link dependence. In this paper encoding and referencing principles for optical sensors are outlined and compared. Especially the two wavelengths referencing and the optical delay line processing techniques are discussed in more detail and results are presented.

A hollow glass tube is configured both as an oscillating cantilever and, by way of distortions of the tube walls, as a transducer of fluid pressure. Excitation of the vibration, whose frequency is a representation of pressure, and readout of the resultant motion, is carried out over long, multimode fibers. The excitation process is thermal via differential expansion effects between tube and a deposited layer. The device constitutes an all-optical, frequency-coded fiber pressure sensor.

We discuss the design, fabrication, and evaluation of waveguide electro-optic modulators in gallium arsenide for application to high-speed diagnostic systems. We focus specifically on high bandwidth, single event analog modulation, and radiation susceptibility of these devices.

A major limitation of current clinical diagnostic test technology is the inability to measure the reaction between a specific antibody and a sample analyte (antigen) without significant manipulation (e.g. washing steps). Evanescent wave methods using optical waveguides can address this problem. The current status of the area will be reviewed.

The design of a fibre optic probe for the fluorescence detection of photosensitizing drugs used in photochemotherapy is described. The probe is designed to use Raman scattering of the exciting radiation by water molecules to correct for the variable optical properties of in vivo sample volumes. In vitro tests of the probe in scattering and non-scattering media are reported, and the feasibility of obtaining quantitative data in vivo is discussed.

Two novel types of planar waveguide sensors for the chemical domain are introduced. Both are realized by thin film technologies. They consist of multilayered structures coated by a very thin organic overlayer that is able to absorb the species to be measured out of the environment. This absorbtion results in a change in its dielectric function. In the first sensor to be demonstrated this change is measured using a surface plasmon mode as a probe. In the second one the radiationless energy transfer from luminescent centres incorporated in one of the layers to the overlayer serves as a probe.

Fiber Optic intensity sensors based on the interaction between an external medium and t he evanescent wave of unclad and tapered multimode and single mode fibers have been developed to measure refractive index, temperature and liquid level. Here we describe an intensity bio-chemical fiber optic sensor (BCFOS) where absorption of t he evanescent wave by a dye-labeled solution is used to modulate, attenuate, t he intensity of t he signal in t he core of the fiber. The fabrication and performance is described for laboratory prototype sensors using etched multimode and tapered single mode fibers.

Fibre optic pH sensors, for use in acid-base titrations, have been developed which use two wavelengths, in one case from two LEDs and in the other an internally generated reference replaces one of the LEDs, to sense the change in absorption of an indicator dye and provide a reference channel. A description of the construction and calibrated response of these inexpensive sensing devices is given.

A miniature optode (diameter about 1 mm) was built with 200/280 all-silica fibers usable over long distances. The immobilized indicator is fixed on a cross-linked styrene/divinyl-benzene copolymer (XADZI). The sensors are constructed so that measurements can be taken either by absorption at many different points in the single optical fiber, or by reflection from the end of the fiber. A wide range of pH values are encountered with radioactive wastes, and experiments are performed either with bromophenol blue (3.0 to 6.0) or a double-indicator (thymol blue) between 0.8 and 3.2, and 9 and 13 pH, as well as other indicators. Lifetimes, reversibility and kinetics are considered. A new low-cost device is proposed for chemical process control and medical applications.

A hand-held automatic refractometer has been developed in cooperation with the Fraunhofer Institut fOr Physikalische Messtechnik in Freiburg, consisting of a fiber optic sensor and a microprocessor controlled measuring system. The refractometer is intended for routine measurements for carious kinds of liquids, especially under rough environmental conditions. The design of the refractometric sensor is based on a single, rigid multimode fiber. Additionally temperature and turbidity are measured., to allow the correction of the refractive index.

A new class of chemical sensors has begun to emerge which are based on the concept of using optically conducting fibre interfaced to a small transducer that varies its optical property with some chemical parameter of interest. This growing new technology which is generating a great deal of interest, can produce a series of optical fibre chemical sensors that can have many advantages in their application to process control, environmental and clinical analyses. Depending on the particular device, the optical property measured can he absorbance, reflectance, luminescence or scattering of light. This paper discusses some of the applications of this new kind of sensors for the detection and determination of gaseous chemical species.

A new technique has been developed which is capable of eliminating the effects of temperature, age, or any other parameter which can change the LED emission spectrum, from differential absorption sensors. This method was verified experimentally using a GaAs differential absorption temperature sensor.

Optical fiber sensors for the measurement of magnetic flux, current, voltage, temperature, lightning, wind and discharge, developed for the electric power industry, are described including their design considerations, typical performances and applications.

Optic sensors, forming a part of a fiber optic measuring system, are very attractive for use in the electric power industry. At KEMA a current sensor and a voltage sensor have been built for use in high-voltage measuring systems with data-registration by transient recorders. The voltage sensor consists of a Pockels cell situated near the test object connected to a light source and detectors in the control room by optical fibers. A crystal of bismuth-germaniumoxide was chosen as electro-optic material because of its superior characteristics in relation to unwanted optical effects. Different light sources and fibers were tested. The sensor was calibrated between -3 kV and +3 kV. The signal to noise ratio is in the order of 1000 for a wideband sensor (rise time 25 ns) and 25000 for a slow sensor (2 kHz bandwidth). Interference free measurements of HV breakdown demonstrate the capabilities of the optic voltage sensor. These sensors are now in use in research work on switchgear and in lightning tests.

In this paper, we discuss the all-fiber approach to current sensing for high voltage applications. We present different sensors, based on the Faraday effect, which allow to perform measurements without any contact or linkage between the fiber and the line. This is obtained by an accurate control of the bending birefringence in the sensing coil and by a proper design of its shape. Using a multimode laser diode and a polarization readout scheme,the typical sensitivity is 1A (rms), with a dynamic range up to three decades and a bandwidth of 10 KHz. These performances are adequate both for steady-state measurement and transient monitoring.

Several types of the fibre-optic magnetic field sensor by employing the magnetostriction for various purposes, are proposed and also realized. The minimum detectable field strength of the fibre-optic magnetic field sensor using conventional Mach-Zehnder interferometric configuration is improved to be the order of 10 0e, by sensitive metal glass material, by fibre-optic monomode coupler, and by computer data processing. The high sensitivity of this fibre-optic magnetometer will be useful in various applications. A small-sized and simple structure of the fibre-optic magnetostrictive sensor employing Michelson interferometer, instead of Mach-Zehnder interferometer, is also proposed and experimentally verified. This structure can be very small because it uses only one fibre coupler, but it is less sensitive due to the laser noise caused by the optical reflection. These types of the magnetic field sensor are usually used for a.c. magnetic field, because the biasing d.c. field must be applied to obtain the highest sensitivity. The d.c. magnetic field can be measured, however, by rotating the sensor, or applying a.c. biasing magnetic field. This magnetic field sensor for d.c. field with a.c. biasing field is also proposed and discussed. This type of the magnetic field sensor is usually used for measurement of the longitudinal (parallel to the fibre) field. But in practical applications, it is sometimes very important to measure the magnetic field in a narrow gap. A new type of the fibre-optic magnetic field sensor is designed to measure the transverse magnetic field. In this sensor, a transverse strain due to the magnetostriction is transformed into transverse strain through Poisson's ratio in the magnetostrictive material and is measured through the strain of the optical fibre. Many other variations of this fibre-optic magnetic field sensors are proposed. These sensors would be used as a cardiomagnetometer, gyroscope, magnetometer for the residual magnetization in rocks, and also in many other application fields.

Highly-elliptically birefringent fibres have been obtained by spinning a linearly-birefringent fibre during the draw. These fibres are particularly interesting for use in Faraday-effect fibre current monitors, since, in contrast with conventional fibres, they can be wound in small multi-turn coils and retain their sensitivity. We show that here the fibre output state of polarisation can be controlled to compensate for environmental perturbations using only one remote active element. Using a compact 80-turn fibre coil, currents up to 370 A rms have been measured, with a maximum sensitivity of 100pA rms Hz-.

A fiber-optic evanescent wave type fluorescence immunosensor was constructed. It is indicated which parameters determine the optical response to an immunoreaction. Furthermore, we discuss how this sensor in principle can be used to determine antigen-concentrations without relying on calibration-procedures.

A sensor for continuous monitoring of pH in seawater is presented. It is based on the conversion of the yellow (reduced) form of the indicator phenol red into the red (oxidized) form. The instrument is implemented using fibre-optic technology. The probe consists of a cell, containing the dye immobilized on a cross-linked styrene-divinylbenzene polymer Rotrix, placed on the tip of the optical fibre. The working range of the sensor is included within these bounds: 6< pH <9; 20.2e/bo<sai inity 35.2%4 5°C temperature 30°C. The design of the probes takes into account the influQnce of ionic strength and temperature and provisions are adopted to compensate for' their changes in working ranges specified above.

A low loss electromechanical scanner based on rotary motion is presented, which allows to address a number of optical fiber sensors by means of only one optical fiber connected to the detection and signal processing unit. To alleviate radial and axial tolerances and to reduce insertion losses, quarter-pitch graded index lenses are used. Details about design and experimental results are reported.

A novel method for measuring the voltage-microdisplacement correlation of a piezoelectric sensor has been devised. It is based on the multi-mode fiber-optic interferometry and the variation in the resonant frequency dv which can be affected by changing the cavity length of a laser with a piezoelectric sensor. Then the linearity of the PZT can be measured with a ultra-precision by counting the interfe.rometric fringes shifted. The experimental results have shown that this device permits to detecting the displacement of PZT as small as λ/240 when using a fiber 20m in length. The potential of fiber interferometry in measuring the ultra-microdisplacement is also discussed.

The possible role of optical fibres in implementing some of the robot's more important sensing functions are outlined. In particular, taking after the living being's nerves, it is suggested that optical fibre sensors can be used as the robot's nerves, permitting it the facility to see/touch/listen. Typical optical fibre sensors that might be used in robotics and the advantages/disadvantages of opticfioerisation in this context are discussed.

The paper analysis resolution of holographic reconstructive image of using the far field radiation emitted from incoherent multimode optical fiber bundle as the reference wave or illumination wave of object. It is demonstrated that if the coherence condition is satisfied, the point spread degree pr educed by mode dispersion is proportional to the distance, Zc, from reconstructive image to holofilm. Thus, when Z i.e. image-holograph, the resolution of re-image isn't nearly effected by the mode dispersion and the dimension of fiber cross-section, the experiment of deformation fringe with image-holograph is very well in accord with the theory expection.

Two basic techniques - multicrucible/extrusion and multirod-in-tube - of manufacturing of infrared transmitting and nonconventional, special-purpose /called later specialty/ optical fibres have been presented and compared. We are describing here our own technological facilities and methods. The paper addresses mainly the processes rather than materials. Ultimate developments of the technologies and equipment and future prospects are outlined. Several kinds of special purpose fibres are debated, some of their parameters given, indications concerning their applications are presented.

A sensor based on fluorescence quenching has been built to detect oxygen activity in gas and water. The sensor consists of a xenon flash bulb as a light source; an excitation wavelength band pass filter; a dichroic beam splitter; collimating and focussing lenses; a plastic clad silica (PCS) rod with the fluorophore immobilized at the tip of it; an emission wavelength band pass filter; a photomultiplier tube (PMT); a monitor PIN photodiode detector; and interface electronics to couple a computer to the rest of the sensor. The device demonstrates a reversible change in fluorescence quenching for changes in oxygen activity. The fluorescence signal seen by the PMT varies over a factor of 3, being highest at 0 oxygen activity and lowest at atmospheric oxygen activity. The device exhibits a 63 % response time of less than 1 second for gases and less than 10 seconds for oxygen dissolved in water. The noise floor of the sensor is approximately 1%. The present embodiment of the device was designed to allow the sensor to operate in the marine environment. The optical components, computer, batteries, and power supply circuitry are mounted on a rack that is enclosed in a pressure housing. The immobilized fluorophore is exposed to sea water. The light travels along the PCS rod, through a pressure seal, to the rest of the system. Present investigations are centered around long term stability of the fluorophore and constituents of the real ocean that will interfere with the quenching mechanism.

A novel fiber optic sensor based on the principle of induced Modal Power Distribution (MPD) changes among guided modes was investigated. This technique was found to be inherently more sensitive than other intensity type sensors and can be used to sense various phenomena, such as pressure, vibration and temperature.

The feasibility of using an emitting diode (LED or laser diode) as both light transmitter and receiver in a single-fibre reflective sensor system has been demonstrated. This arrangement may be used for remote sensing of frequency coded variables and for sensor time-domain multiplexing.

We describe a simple and inexpensive fiber optic thermal switch which gives an alarm if temperature exceeds a threshold determined by the material at the fiber end tip.The effect is based on the melting of suitable waxes where the back scattering of light vanishes when the critical threshold temperature is reached. The present device has many attractive features: it is uncomplicated, is based on a "solid state effect", is totally dielectric, and has an excellent long term stability.

Silicon is best known to the optical fibre sensor community as a detector material. However, its remarkable optical and mechanical properties and its ease of fabriation point to an increasing use of material in other contexts. This paper briefly reviews the principal mechanical and optical properties of silicon and describes applications as a mechanically resonant environmental sensor and as a waveguiding medium for evanescent wave devices. High quality, high yield fibre optic sensors fabricated using standard silicon processing techniques are likely to become available in the very near future.

A frequency shifter has been constructed which uses travelling acoustic flexure waves induced on a single birefringent optical fibre to produce coupling between the two orthogonal polarisation states. A scheme for determination of the axis orientation is described and an experimental technique for the measurement of the dispersion relation of the flexure waves is presented. Equations are given which enable the approximate value of the mode coupling constant κ to be found.

An all-fibre polarisation state controller, which overcomes the problems associated with the temperature dependence of the stress-optic coefficient in previously reported fibre devices is described. The controller consists of two short sections of linearly bire-fringent monomode fibre orientated with their eigenaxes at 450 with respect to each other. Polarisation control is achieved by applying axial strain to each fibre element using piezo-electric transducers. The system is demonstrated by generating polarisation states which are made to evolve along trajectories on the surface of the Poincare sphere.

The manufacture and characterisation of D shaped single mode optical fibres is described. Such fibres are found to have a strong dependence of cut off wavelength upon polarisation, yet have low intrinsic birefringence. The use of the fibres to make pressure and temperature sensors is described, and is compared to similar sensors made using standard circular fibres.

The design construction and operation of a thermally controlled optical fibre switch, based upon the lap/polish technique, is described in this paper. The lap/polish method allows access to the evanescent field in an optical fibre and coupling between two fibres can be controlled from zero to total power transfer by changing the refractive index of the oil in the coupling region. Such refractive index changes can be induced thermally by directly heating the matching oil at the interaction area, with forming heating elements close to the fibre core. Power coupling is then proportional to the current supplied to the electrodes. Results are presented showing the frequency response of tlio device.

An acoustic fibre phase modulator, operating up to a few MHz, is described which employs a piezoelectric plate in a squeezing action. A novel construction using two machined brass v-grooves results in a much reduced sensitivity to optical polarisation and the optimum groove angle is independent of the level of friction on the walls of each groove. A normalised birefringence of 0.04 was achieved at 1.5MHz, with a modulation efficiency of approximately 0.23 rad/Vrms., for a 2cm long device.

A single mode to multimode optical fibre coupler has been incorporated in a multimode recirculating delay line to produce variable transversal filter characteristics. The theory is outlined and experimental results for a polished and fused coupler are presented.

A special fiber for microbending applications was designed and fabricated. The coupling effects in the fiber are measured and discussed. The fiber was also used in a simple microbending sensor giving two output signals.