Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1995-02-02
1997-06-24
Le, Que
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
25022718, 385 13, H01J 516
Patent
active
056419554
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a reconfigurable fiber-optic sensor.
Fiber-optic temperature or stress sensors have been the subject of numerous studies throughout the world. The field of intrinsic temperature or stress sensors has expanded particularly by virtue of the use of an optical fiber as the sensor (use of high-birefringence or polarization-maintaining optical fibers).
Production of optical sensors distributed along a birefringent fiber has made it possible to use N elementary sensors corresponding to N segments of sensor fiber. These various segments are defined by using coupling points serving as markers (delimiting these segments).
The production of coupling points on optical fibers has been studied for a long time, and today various production techniques are used, among which are: fiber and bonding the two portions after having rotated one of the fiber portions through an arbitrary angle. The main drawbacks of this method are the introduction of losses due to the reflections off the faces of the fibers and the control of the alignment and rotation of the fiber cores (diameter of the order of 5 .mu.m); fiber of chosen length is held at its ends and the fiber is rotated at one end, the other remaining fixed. A torsional stress is thus created. Using localized heating of the fiber, a polarization coupling point is thus produced. The drawbacks of this method are the use of a locally stripped fiber, a high-voltage generator and an electric arc in order to create the coupling point or points, and the irreversibility of the method of creating the coupling points; using a holographic method. The production of coupling points using this method is nowadays mainly studied by the BERTIN Company and many studies have concerned the production of index gratings in the fibers for sensor applications. The drawback of this method resides in its complexity of implementation, the need to use an additional high-power laser to produce the index gratings, and the need to employ a process for masking the fiber.
From the German Document DE-A-4,011,440, a fiber-optic temperature sensor is known, to which an element, which may be made of shape-memory alloy, applies a longitudinal stress deforming this fiber into a "U". This sensor enables only the measurement of a single temperature to be made and does not enable the location, where the stress induced by the measured temperature change has occurred, to be located precisely. In addition, the deformation produced by the SMA element is not reversible.
SUMMARY OF THE INVENTION
The subject of the present invention is a birefringent fiber-optic sensor such that one or more precisely-located coupling points may be formed on this fiber without damaging it or cutting it, without introducing losses, without having recourse to additional equipment, and all this as simply as possible, this sensor making it possible to perform, at several precisely-located points, measurements of stresses which may have different origins, the positions of the measurement points being able to be easily modifiable.
The sensor according to the invention, of the birefringent fiber-optic type, at least part of which acts as a sensor of a physical quantity manifested by a stress exerted on the fiber, this optical fiber interacting with a light source and an interferometric or polarimetric read device, includes an element made of shape-memory alloy arranged on the optical fiber, this shape-memory element being designed and taught so that when it is at temperatures lying on one side of the transition temperature of the constituent material it exerts virtually no stress on the fiber, and when it is at temperatures lying on the other side of the said transition temperature it exerts on the fiber a stress which can be measured by the said read device, and it is characterized in that it includes several elements made of shape-memory alloy which are distributed along the optical fiber and in that the stress that these elements exert on the fiber is a radial stress.
According to a
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Bonniau Philippe
Chazelas Jean
Turpin Marc
"Thomson-CSF"
Le Que
LandOfFree
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