Optical waveguides – Optical fiber waveguide with cladding
Patent
1996-12-13
1999-03-16
Lee, John D.
Optical waveguides
Optical fiber waveguide with cladding
385 31, 385 47, 385147, G02B 616
Patent
active
058839976
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of producing an optical fibre reflector, a fibre reflector produced by means of the method and a use of the fibre reflector for verifying the function of an optical network.
BACKGROUND
Internal reflections in optical fibres have several applications, such as for sensor purposes and for verifying the function of a fibre optical network. Light transmitted in an optical fibre is reflected at the reflector and the reflected light can be detected.
Optical reflectors for generating internal reflections in optical fibres and methods for producing such reflectors are previously known from U.S. Pat. Nos. 4,892,388 and 4,400,056. However, the prior methods are rather complicated and there is thus a need for providing simple production methods for reflectors in optical fibres.
In the patent U.S. Pat. No. 5,210,801 optical components are disclosed constructed of flat wave guides or wave guides having rectangular cross-sections, where a cavity is arranged located adjacent a wave guide core, however never so located that the material of the wave guide core is located directly at the cavity. The production of the components is made by means of the conventional, process technological, relatively complicated and costly methods which are used for manufacturing electronic integrated circuits and optical planar circuits.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a simple method for producing internal reflections in optical fibres.
It is also an object of the invention to provide an optical fibre provided with an internal reflector for obtaining internal reflections in the optical fibre.
The objects mentioned above are achieved by the invention, the detailed characteristics of which are described below.
Thus, in a controlled way an air bubble, i.e. a small cavity, which in the main case is filled with air, is introduced in the core of an optical fibre by means of an etching or a welding procedure and thereby a broad band fibre reflector is obtained. The fibre end is first stripped, i.e. its exterior protective layer is removed, and is then cut in the conventional way for achieving an essentially flat end surface, that is located essentially perpendicularly to the longitudinal direction of the fibre end, after which, in the end surface thus formed, a pit or recess is made in the core region, i.e. in the region where the fibre core ends in the end surface. The pit can be produced by means of some mechanical method such as grinding or by treating the end surface with a laser beam for removing material at the suitable position. However, a chemical treatment is preferred, wherein the fibre end is etched with e.g. diluted hydrofluoric acid or a mixture thereof with similar substances such as ammonium fluoride. A recess is thereby produced, since the higher doped core is etched more rapidly than the cladding. The etched fibre end is then joined or spliced, in the preferred case welded, to a standard fibre having, in the preferred case, an essentially flat end surface, which is cut in the usual way and is essentially perpendicularly to the longitudinal direction of this fibre end, which results in an air bubble enclosed in the core. The magnitude of the reflectance can be changed by repeated heating operations in the same way as in welding over the spliced or joint region and/or by filling the bubble with another medium than air or by coating one of its walls with a suitable material, e.g. a metal.
Generally, an optical fibre has a fibre core and a cladding surrounding the core. In order to produce a reflector, a cavity is arranged in the optical fibre, which is in particular arranged in the fibre core. The cavity is generally completely surrounded by material of the fibre and is located so close to the core, that light which is introduced into and propagates along the fibre, will be disturbed significantly by the cavity, so that it is partly reflected. It is obtained by the fact that the fibre core material extends up to the cavity and in part
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Carlnas Torbjorn
Kull Martin
Ljungqvist Goran
Lee John D.
Telefonaktiebolaget LM Ericsson
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