The monitoring of fuel tanks and toxic liquid containers with embedded long optical fibers makes it possible to determine their condition and to detect probable environmental risks. We present here measurements of microbending loss in long, single-mode telecommunication fibers installed inside the walls of composite containers during the manufacturing process. The measurements were performed by the optical through power technique and using a commercial optical time domain reflectometer. The measurement data indicate that the optical sensing fibers can detect the end of the curing process in the composite and the occurrence of external loading likely to damage the structure.

A specially designed optical time domain reflectometer was used to measure the speed of propagation of rapidly running induced cracks along high density polyethylene pipes. Optical fibers were wound in a helical form around each pipe sample. Upon arrival, the propagating crack succesively broke and shortened the fibers; thereby the travel time of a reflected light pulse was reduced. The time dependent lengths of the fibers indicated the position of the edge of the crack. With this method crack speeds in the range of 100 m/s to 200 m/s were measured. The results agree well with those obtained by a conventional method. The fiber optical measurement even allowed to determine the form of the crack path.

A new active homodyne sawtooth fringe counting technique is described for eliminating the directional ambiguity in incremental readout of interferometric strain gauges. Results of quantitative strain measurements using unbalanced Michelson and capillary based instrinsic Fabry-Perot sensors agree reasonably well with the readout of a resistive strain gauge as well as with the theoretically predicted sensitivity.

This experiment presents the characterization of a medium birefringence single mode optical fiber within a composite, when submitted to radial strength. The system operation is based on elasto-optic effect, which induces birefringence in the optical fiber, modifying the polarization state of the guided light. The changes in the polarization state of the signal are converted into intensity variations and are detected by a silicon photodiode and analyzed using a microcomputer.

Fiber-optic sensors could offer advantages in the field of airport ground traffic monitoring: immunity to electromagnetic interference, installation without costly and time consuming airfield closures, and low loss, low noise optical connection between sensors and signal processing equipment. This paper describes fiber-optic sensors developed for airport taxiway monitoring and the first steps toward their installation in an experimental surface movement guidance and control system at the Braunschweig airport. Initial results obtained with fiber- optic light barriers and vibration sensors are reported. The feasibility of employing interferometric strain gauges for this application will be discussed based on sensor characteristics obtained through measurements of strain in an aircraft structure in flight.

Fiber Bragg gratings are attracting increasing attention as sensors for the measurement of strain, temperature, and pressure. They are equally important as wavelength selective reflectors for fiber, and to a lesser extent, semiconductor lasers. This paper describes results from a hybrid laser comprising of a semiconductor optical amplifier coupled to a Bragg grating, and investigates the characteristics of such a laser system as a discrete strain sensor.

In this paper, we present two new approaches of distributed optical fiber force sensors. The first approach relies on the optical Kerr effect which utilizes two lasers launched into a Hi-Bi fiber from the same end. A He-Ne laser provides a CW probe beam which is launched into fiber to excite two polarization modes with equal intensities. A Nd:YAG laser is used to provide a pulsed pump beam which excites one polarization mode. The polarization state of the CW beam changes when the pump beam propagates through the fiber, or when a force is applied to the fiber. Information regarding the intensity of the force and its position can be obtained using a data acquisition and analysis system. The second approach is based on the FMCW technique. In this case, a frequency modulated laser beam is launched into a Hi-Bi fiber with one polarization mode and reflected from the far end of the fiber by a mirror. When a force is applied to the fiber at any position, mode coupling will occur. By detecting the beat frequency produced by the two coupled mode beams, the intensity and the position of the force can be found. In this paper, the experimental results obtained from the two sensor systems are presented.

The application of a highly birefringent fiber polarization modulation technique for ellipsometric measurements on sol-gel thin films is described. The ability of the system to determine the ellipsometric parameters of thin films is demonstrated. The system is then used to monitor the ellipsometric parameters of thin films on exposure to a perturbing environment of humidity and pressure. The potential of the system for application in chemical sensor systems is indicated and discussed.

The laser system for control of building contour and deformation consists of two parts. In the illuminator laser beam is divided into some parts. One of these parts works as reference ray or plane, and directions of others may be changed by the task program at the same time. A traditional instrument, for example, a theodolite or a phototheodolite, may be used as the measurement station of the system. The system permits to ensure a very high accuracy is we want to pass from one to another building components.

The shearographic interferometry is employed as a nondestructive full field, optical testing and measuring method without contact. Fringes of contant strain (so called isotase, tasis (Greek) equals strain) can be observed in real-time on the surface of the investigated machine parts and structures of any material and are represented by the shearogram. Using shearography two states of deformation are recorded by doubly exposing a Holotest film in an ordinary camera or stored by an electronic image processing system. In the objective of the camera a shearing element is integrated or the lateral Michelson shearing interferometer is used. Rigid body motions of the object are not recorded. Local deformation irregulatrites caused by a defect under or on the surface of the specimen create strain concentrations; the homogeneous surrounding is poorly superimposed by an interference pattern. The shearogram shows dark and bright fringes which are the functions of the displaceemnt derivative. The holographic interferometry measures the out of plane deformations directly. Terms of the out-of-plane strain can be determined by the shearographic method as well as the in-plane strain fringes which are described in this paper.

A new stress/strain sensor for localized measurements in polymer based composites, has been developed and tested. The stress/strain dependent property is the frequency of the atomic vibrations of reinforcing fibers which can be proved with laser Raman spectroscopy. Measurements can be conducted in reinforcing fibers near the surface of laminates. For measurements in the bulk of composites, the exciting laser light has to be transported to the reinforcing fibers via an embedded fiber optic cable. The backscattered light is transmitted through the same fiber optic and is sent to the Raman spectrometer for analysis. The effect of the direction of the fiber optic cable with respect to the axis of the reinforcing fibers is examined. Finally, the relationships between the local fiber stress or strain obtained from the Raman sensor and the far field stress or strain measured conventionally, are established.

The analysis of realisibility and feasibility of small, lightweight noncoherent infrared LED rangefinder for mass application as a distance telemeter system for moving traffic objects are given. The proposed short-range rangefinder, suitable for measuring distances from fixed and moving objects, in the range from 1 m to 20 m, with significantly increased accuracy is presented in the paper. These measuring methods, with double referent mixing technique, improves the distance resolution when the phase measurement principle is applied. A phase difference still detectable is +/- 1/4, at symmetrically double frequency conversion from 0.5 MHz to 100 Hz, and enables distance resolution +/- 0.1 m. The detection process is completely independent of the signal amplitude. That means that the reflectivity of target does not disturb the distance measurement results. The possible applications are in traffic control and traffic safety systems as a proximity switch in contest of alarm systems. This paper describes the optimum characteristics of the rangefinder regarding the cost/performance parameter. The description of the method with analytical analysis and the results of experimental realization are also given. The discussion is presented as the experimental support of theoretical analysis.

Principles of optoelectronic detection method and extraction of EMP (electromagnetic pulse) parameters, using the magneto-optical Faraday rotation as a measuring principle and systems of optical fiber sensors and signal transmission lines, are described. This gives the opportunity for an unconventional application of fiber optic sensors as electromagnetic fiber square coil antennas for detection of EMP in extreme conditions.

A novel laser doppler sensor for measuring transverse vibration and angular velocity of rotating cylindrical objects is proposed. The sensor has a sensitivity to only one component of the transverse vibration and it is insensitive to other movements of the object. The optical structure of the sensor is based on two differential type laser doppler velocimeters. The principle of operation of the proposed sensor is theoretically described on the basis of laser doppler anemomentry and the general expressions for vibratory displacement and angular velocity is obtained. The block diagram of the signal processing system is proposed.

We consider the use of some superconductivity effects for estimating the vibration signal picked up by a probe in a controlled potential well. Sensitivity in excess of previously attained levels is achieved.

The use of fiber optic sensors for measuring and monitoring tasks on structure components and large civil structures will only be successful if one is attentive to a nubmer of conditions in this raw environment. Most of the tasks require a direct contact of the sensor element to the measuring object without any protecting barrier. Such a contact may always entail mechanical damages to the sensor surface and chemical attacks on the primary coating.

It is now well accepted that the increase of atmospheric greenhouse effect gases, particularly carbon dioxide, has an important impact on our climatic system, even if the true effect of the development of human industrial activities is not totally assessed. It is then necessary to have a good overall knowledge of the carbon dioxide cycle, and more particularly the fluxes exchanged the three CO₂ tanks: atmosphere, ocean, and continental biosphere. Since the ocean is the biggest carbon tank (60 times the atmosphere tank), it constitutes an important potenetial well for the atmospheric CO₂. However, the data available show an uncertainty of ca. 30% on the estimated flux. It is then important to assess the quantity of CO₂ at the surface of the ocean, and the corresponding atmosphere/ocean flux. The possible future atmospheric CO₂ concentration corresponding to different industrial emission scenarii can then be assessed. The method measurement of the CO₂ at the sea surface use spectro- photometry of a sensitive dye, housed in a tank which has walls immersed in the sea water. The spectro-photometer especially designed, patented, and build-up by IFP has been developed with special emphasis on high accuracy, rugged construction, ease of operation without maintenance, and calibration over a period of time of over one year. The leading idea was to have as few internal moving parts as possible by the use of fiber optics, and internal calibration by the use of internal reference channels. Ancillary data are also measured. Data is transmitted to the processing center via ARGOS. The equipment described is part of the EUREKA CARIOCA project (EU 819), supported by the French Ministere de l'Enseignement Superieur et de la Recherche (93 W 0011) and UK's DTI. The partners are: LODYC, LGE, INSU, SERPE-IESM (France), and Chelsea Instruments (UK).