Electric heating – Microwave heating – Tunnel furnace
Patent
1980-01-23
1983-04-19
Lee, John D.
Electric heating
Microwave heating
Tunnel furnace
219121LE, 350 9620, G02B 5172
Patent
active
043803652
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
My present invention relates to an optical fiber having at least one of its end faces provided with a plano-convex microlens joined thereto with its flat side, as well as to a process for manufacturing such an optical fiber.
BACKGROUND OF THE INVENTION
The use of optical fibers as light-conducting means, long regarded as having a great future in numerous applications (telecommunications, links between computers, etc.), is currently experiencing a considerable expansion, notably by reason of the appearance on the market of low-loss fibers.
However, there still exist at present a certain number of problems which militate against the general use of optical fibers, a major one of which relates to the injection of light into the core of these fibers. It is in fact well known that optical fibers with planar end faces have a relatively narrow light-acceptor angle, so that in general these fibers can collect only a small fraction of the light beam to be injected, especially in the case of the beam emitted by strongly divergent light sources such as laser diodes since the core of the fiber can only accept those of the rays which arrive at an angle smaller than or equal to its acceptor angle. In other words, this inherent limitation of the optical fibers having planar end faces leads to the major drawback of relatively low efficiency of source-fiber couplings.
A number of solutions have already been proposed in attempting to improve this coupling efficiency; they are essentially based on the interposition of optical adaptor elements between the source and the fiber. Some of the solutions thus proposed consist in using independent optical elements located at a distance from the fiber and/or from the source (for example the use of a pair of orthogonal cylindrical macrolenses, or the use of a transverse fiber as a cylindrical microlens). However, the use of independent optical elements is fraught with the serious drawback that, by increasing the number of the elements forming the coupling system as a whole, it magnifies greatly the mounting and assembly problems of this coupling system and in particular the problems of high-precision positioning and alignment of the different elements relative to one another. This is the reason why, at present, the trend is towards the concept of optical elements integrated at the extremity of the fiber, so as to minimize assembly problems. The design of such integrated elements in turn raises a certain number of other problems concerning their manufacture and/or their integration with the fiber as well as the matter of their optical performance.
To realize such integrated elements, it has for example been proposed to join microlenses of semicylindrical shape to the extremities of the fibers. However, such a solution gives rise to serious problems in the manufacture of these semicylindrical microlenses as well as in the attachment of these microlenses to the fibers. In an attempt to remedy these drawbacks, it has accordingly been proposed to produce these microlenses directly on the extremities of the fibers, by using fusion methods. The microlenses thus produced on the fiber extremities, although easy to manufacture, yield only a rather mediocre optical performance, by reason of the slight curvatures obtainable in this manner whose control is moreover greatly limited by the differences in the melting temperature of core and cladding of the fiber. To avoid the above-mentioned problem, it has then been proposed to remove the cladding of the fiber by chemical attack before proceeding with the production of the microlens on the extremity of the core thus laid free. However, this solution is far from satisfactory inasmuch as the eventual increase in coupling resulting therefrom risks to be canceled out completely by the increase in optical losses inherent in the removal of the cladding.
Furthermore, it has been proposed to produce directly on the extremities of monomodal fibers cylindrical or hemispherical microlenses of ultra-small dimensions (radius below 5 mic
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Battelle (Memorial Institute)
Lee John D.
Ross Karl F.
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