The advancement of fibre optics in sensing has been inhibited in the last two decades by the lack of availability of suitable components. Whilst transduction principles have been fully explored, and some key applications (for example fibre optic gyroscopes) have moved forward, even the up-take of the ubiquitous fibre Bragg gratings as sensors is being inhibited by both practical and cost considerations. Optical sensors, it seems, can be created, but the means of extracting the information from them, building on the precision and systems advantages that fibre optics should bestow, has proved difficult. If sources, detectors and essential signal processing can be combined in such a way that, essentially, the benefits that fibre optics bestow in telecoms networks can be harnessed for sensing, then fibre optic sensing can truly be said to have realized its promise. Integrated optics modules employing silicon as both substrate and waveguide are being developed and deployed rapidly for telecommunications applications, through which they will become cost effective quite quickly. They have also been demonstrated as useful modules when employed in sensing systems as, for example, Sagnac and white light interferometers. In the latter form they have been employed to process signals in an optical system measuring the cylinder pressure in four-cylinder internal combustion engine. It is argued that this specific application, demanding as it is, illustrates the generic potential of such modules for broad application in many sensing situations.

This paper presents new measuring technology based on the application of Slow-Wave Structures (SWS). The use of SWS for RF-measurement transducers makes it possible quite efficiently to monitor and measure parameters of various industrial processes and materials. Difficulties arise when monitoring and measuring parameters of oil-liquids such as the conductivity or the continuity of flow. This is caused by the strong screening action of the monitored oil-liquid on electromagnetic field of the slowed wave in the helical sensitive elements (HSE). As the conductivity increases, the screening becomes even stronger, and this leads to a reduction in the sensitivity and measurement accuracy. The solution of such problems requires the creation and modeling of more complex designs of sensitive elements in which the screening action is weakened. Such an effect can be achieved by matching the field of a hybrid slowed wave to the medium being monitored, utilizing HSE based on layered magnetic and dielectric structures with a smooth variation of the electrodynamic parameters.

In order to improve the mechanic performance, the cure process mechanics are approached to find out the relationships among the viscosity history, void evolution and the ultimate mechanic property of the composite structure. A computer simulation program, on the base of resin flow model, thermal stress model, material model and void model, is developed to simulate the cure process, with which the cure process parameter is optimized to meet this challenge. The information of cure process, which mainly is the viscosity evolution and gel point, is obtained by fiber optic microbend sensor made specially. The reason to sensing and controlling the viscosity evolution is that it can represent the cure degree to some extent, besides, keep the viscosity at the lowest point as long as possible can reduce the void and keep appropriate fiber content in the ultimate composite structure. The data is processed by an expert system based on the computer simulation program, then the expert system give instruction to the temperature controller and pressure controller to regulate the cure process.

This paper presents results of a micromachined, SiC/sapphire pressure sensor designed for propulsive environments. The completed sensor is 3mm square with a sapphire fiber through the back of the sensor. Included are results from a high- speed fiber optic signal processing system combined with sapphire fiber for use in fluctuating, high temperature environments. The sensor is designed to be capable of operating at the extreme temperatures and pressures of the next generation engines including ramjet/scramjets. These conditions far exceed the capabilities of conventional metal and electronic sensors. Fiber optic sensors offer the ability to increase the temperature range of these devices by removing the electronics of conventional sensors from the hot zone. Unfortunately, these conditions also exceed the capabilities of silicon and silica optical fiber. In contrast, silicon carbide has excellent mechanical, thermal and chemical properties for use in such environments, while the high operating temperature and optical quality of sapphire fibers and the inherent immunity of optical fiber sensors to electromagnetic interference make their use of particularly advantageous. Sensors made from a combination of these materials would be able to operate in almost any propulsive environment and allow valuable insight into flow regimes where little previous data is available.

Reliable downhole communications, control and sensor networks will dramatically improve oil reservoir management practices and will enable the construction of intelligent or smart-well completions. Fiber optic technology will play a key role in the implementation of these communication, control and sensing systems because of inherent advantages of power, weight and reliability over more conventional electronic-based systems. Field test data, acquired using an array of fiber optic seismic hydrophones within a steam-flood, heavy oil- production filed, showed a significant improvement (10X in this specific case) in subsurface resolution as compared to conventional surface seismic acquisition. These results demonstrate the viability of using multiplexed fiber optic sensors for exploration and reservoir management in 3D vertical seismic profiling (VSP) surveys and in permanent sensor arrays for 4D surveys.

In the management of caverned fuel oil inventory, a strict rule of fire control has always been the first priority due to the special conditions. It is always a challenge to perform automatic measurement by means of conventional electrical devices for inspecting oil tank level there. Introduced in this paper is a fiber optic gauging technique with millimeter precision for automatic measurement in caverned tanks. Instead of using any electrical device, it uses optical encoders and optical fibers for converting and transmitting signals. Its principle, specifications, installation and applications are discussed in detail. Theoretical analysis of the factors affecting its accuracy, stability, and special procedures adopted in the installation of the fiber optic gauge are also discussed.

This paper describes how distributed temperature sensing (DTS) based on Raman Scattering is being used as an in-situ logging technique in oil and gas wells. Traditional methods of gathering production data to characterize oil and gas well performance have relied on the introduction of electric logging tools into the well. This can be an expensive process in highly deviated or horizontal wells and usually results in the well being shut-in with the loss or deferment of hydrocarbon production. More recently permanently placed pressure sensors based on CMOS technology have been used, but these systems do not easily deliver distributed measurements and reliability has been found to be poor.

Fiber optic sensors are becoming a well-established technology for a range of geophysical applications, and static pressure and temperature sensors in particular are now comparatively well developed. However, rather less attention has been paid to systems for measuring dynamic quantities such as acoustic and seismic signals. Furthermore, the very large multiplexing potential of fiber optic sensing systems has yet to be fully explored for geophysical applications. However, development of fiber optic sonar systems for military applications has proven the viability of large multiplexed arrays, and demonstrated advantages which include electrically passive arrays, long term reliability and the potential for operation in very deep ($GTR3000m) water. This paper describes the applications for large scale fiber optic sensing arrays in geophysical metrology. The main applications considered here are ocean bottom cables and streamers for marine seismic, and downwell seismic systems. Systems can require up to several thousand channels and the use of multi- component sensors, which include 3-axis geophones and hydrophones. The paper discusses the specific requirements for each application, and shows how these requirements can be met using a system approach based on time and wavelength multiplexing of interferometric sensors. Experimental and theoretical studies at DERA into the performance of highly multiplexed systems are also described, together with initial development work on fiber optic hydrophones and geophones.

A new production logging device has been field tested that uses innovative sensing technology to enable the direct detection and quantification of gas in multiphase flows. Four optical probes, deployed 90 degrees apart on the arms of a centralizer-like tool, measure the optical reflectance of the surrounding fluid. The probes are evenly spaced in the pipe cross section, and their orientation in space is accurately known through use of an integrated relative- bearing sensor. In gas-liquid mixtures, the optical signal reflected by the probe is used to determine gas holdup and a gas bubble count, which is related to gas flow rate. In addition, the individual sensor measurements are used to build an image of the gas flow in the well. These images are particularly useful in deviated and horizontal wells for better understanding the multiphase flow patterns and interpreting their inherent phase segregation occurring at such deviations. The new tool has been successfully field tested in wells throughout the world and the tool's capabilities are illustrated by example form both field and laboratory data sets. The new tool has been designed to detect the presence of gas, and hence its major application is to identify gas entries in oil/water wells or water/oil/condensate in gas wells. Because of its high sensitivity to minute amounts of gas, the tool can also be used to locate the bubble point when logging in the tubing. The introduction of optical sensing technology in this new tool represents an innovation in production logging. The provided data enable the direct detection and quantification of gas or liquid in multiphase mixtures, allowing the precise diagnosis of well problems and helping design of production enhancement interventions.

The measurement of the velocities of oil and water phases in the bore-hole of a producing well, together with volume fraction measurement, gives the flow rate of each fluid phase. Even though radioactive tracers methods provides a good velocity measurement, safety concerns and regulations makes their use unattractive. We propose a method of measuring fluid velocity using local optical fiber probes and tracer techniques. A fluorescence dye is injected into the bore-hole where it is mixed with the fluid of interest. An optical fiber probe is positioned down-stream from the point of injection detects the passage of the tracer with the flow. The time between injection and detection enables one to calculate the flow velocity for a given distance between injector and detector. The same local probes cold also be used for hold-up estimation. We describe laboratory experiments using a flow loop, fluorescence dye as tracer and an optical fiber probe. The dependency of the injection to detection distance to the flow mixing is observed. Best results for average velocity estimation can be achieved for long distances. Measurements at short distances are possible but some kind of flow model may be needed to interpret the results.

Fiber optic Bragg gratings packaged in long gage configurations are being used to measure static and dynamic strain in structures and structural models to monitor structural health and predict damage incurred from a seismic event. These long gage sensors are being used to experimentally verify analytical models of post-earthquake evaluation based on system identification analysis. This fiber optic deformation measurement system could play a significant role in monitoring/recording with a higher level of completeness the actual seismic response of structures and in non-destructive seismic damage assessment techniques based on dynamic signature analysis. This new sensor technology will enable field measurements of the response of real structures to real earthquakes with the same or higher level of detail/resolution as currently in structural testing under controlled laboratory conditions.

This paper introduces a new type of optical fiber voltage sensor with temperature compensation ability. The dual- light structure and operation of the sensor are discussed in great detail, and a series of test curves are given. The tests show that the dual-light channel voltage sensor has the ability of birefringence rejection and temperature compensation.

The basic concepts of temperature measurement in power transformers and underground power cables using fiber optic gratings are introduced. The economic benefits of continuous temperature measurements are discussed. The problems encountered in high density applications, i.e. using many sensors in the same power transformer, is identified as the resolution limitation due to comparatively large bandwidth of optical filters used. The deconvolution technique has been proposed as a possible solution to improve accuracy and resolution. The fundamental ideas are illustrated by giving results of a laboratory prototype using twelve measurement points. The prototype has a capacity to employ up to 30 gratings for each phase of a power transformer, connected to the same measuring unit using an optical multiplexer.