Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – Process of manufacturing optical fibers – waveguides – or...
Patent
1997-01-10
1999-12-21
Hoffmann, John
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
Process of manufacturing optical fibers, waveguides, or...
65402, 264 124, 264 127, C03B 3714
Patent
active
060033401
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to fiber optical strain sensors and in particular the manufacture thereof.
BACKGROUND
Optical sensors for various mechanical quantities have the obvious advantage of being insensitive to electrical interference. Strain sensors or gauges based on optical components and in particular on different kinds of optical fibers are thus suitable for measurements in the most varying environments. Also secondary mechanical quantities such as pressure, temperature, fill level and similar quantities can be measured by means of such sensors. For a strain sensor comprising a suitably designed optical fiber, further the signal can be transferred from the place of measurement to a monitoring unit through a portion of the optical fiber itself, what gives a smaller sensitivity to interference compared to electrical signal transmission.
PRIOR ART
In the patent U.S. Pat. No. 5,132,529 for Jonathan D. Weiss and the article "Fiber-Optic Strain Gauge", Jonathan D. Weiss, in Journal of Lightwave Technology, Vol. 7, No. 9, September 1989, p. 1308 and following pages, a fiber optical strain sensor is disclosed having ends 19a and 19b (the reference signs refer to the patent) rigidly attached to a substrate and a portion 16 which is not fixed and is provided with microbends. One end of the fiber is connected to a light source 13 and the other end is connected to a light detector 15. Alternatively one end can be connected to both the light source and the detector and the other end be provided with a reflector.
Further a method and a device are described for producing microbends in the optical fiber (FIGS. 2 and 3). The method comprises that the fiber is placed between two electrically heatable plates 29a and 29b provided with "forming ridges" 39, whereafter the plates are pressed against each other, so that permanent microbends are created. Preferably, plastics of optical quality is used as a material in the fiber but also commercial glass fibers of optical quality or other conventional fibers can be used.
SUMMARY
It is an object of the invention to provide simple methods, e.g. using standard apparatus, for producing fiber optical strain sensors and gauges from commercially available optical fibers.
It is another object of the invention to provide fiber optical strain sensors and gauges which, in a simple way and using standard apparatus, can be manufactured from commercially available optical fibers.
These objects are achieved by the invention, the characteristics of which are set out in the appended claims.
In order to obtain a permanent introduction of microbends in an optical fiber intended to be used as a strain sensor an optical fiber is first rigidly attached in two chucks in a fiber splicing machine, the chucks being not aligned with each other, after which the fiber is heated locally, at a cross-section thereof, by means of the electric arc of a fiber welding machine or a laser, whereby a permanent microbend is induced at the heated place of the fiber. A movement of the chucks into a state where they are not aligned can also be made during the heating, the chucks then being initially aligned. In a method for obtaining a microbend of the core in an optical longitudinal cavity fiber the longitudinal hole is closed by a local heating of the fiber, the closed state of the cavity inducing changes of the refractive index and also in most cases a microbend of the core.
Generally, an optical fiber is produced having varying transmission properties for light propagating in the fiber at different strain conditions of the fiber. The fiber can then have a region, in which is created when it is exposed to a mechanical stress, in particular a tensile stress or a compressive stress or a bending stress, a local disturbance or a local change of the refraction index adjacent the fiber core. The region can in the preferred case comprise a microbend of the core of the fiber. In the production of such a region the fiber is heated locally over a small region having an extension in the l
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Borak Georges
Kull Martin Carl Johan
Hoffmann John
Telefonaktiebolaget LM Ericsson
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