Optical waveguides – Optical fiber waveguide with cladding
Patent
1994-10-25
1997-11-18
Ngo, John
Optical waveguides
Optical fiber waveguide with cladding
385126, 385142, 385144, G02B 610
Patent
active
056895780
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a polarization-maintaining optical fiber, which can be used in a variety of optical fiber sensors or the like, to a method of production and to a connection method therefor, and to a light amplifier, a laser oscillator and a polarization-maintaining optical fiber coupler.
TECHNICAL BACKGROUND
Various polarization-maintaining optical fibers are conventionally known. FIGS. 22(a).about.(d) show representative examples of conventional polarization-maintaining optical fibers. The polarization-maintaining optical fiber in FIG. 22(a) is referred to as an elliptical core type. This elliptical core type polarization-maintaining optical fiber lifts the degeneracy of two orthogonal polarization modes by breaking the circular symmetry of an ideal fiber with a circular core, and is designed so that the propagation constant between the modes may differ, and so that polarization may be maintained.
FIGS. 22(b), 22(c) and 22(d) show polarization maintaining optical fibers of types referred to, respectively, as an elliptical cladding, a bow-tie, and a PANDA type. These polarization-maintaining optical fibers are designed to lift the degeneracy of two polarization modes by introducing stress, which is not circular symmetrical with respect to the center of the optical fiber, into the fiber. In the figures, the numeral 1 indicates a core, 2 indicates a cladding, 3 indicates a jacket and 4 indicates stress-applying parts.
The production technology for these polarization-maintaining optical fibers is disclosed in a number of publications, one example being J. Noda et al. "Polarization-Maintaining Fibers and Their Applications", Journal of Lightwave Technology, vol. LT-4, No. 8, August 1986, pp. 1071-1089.
As is clear from the disclosure in this publication, the production method for a conventional polarization-maintaining optical fiber is not easy, so that the fiber is an extremely special fiber and has not been widely used.
For example, for the PANDA type polarization-maintaining optical fiber, which is now most often used, a glass preform in the form of a rod with a core/cladding structure for a single mode optical fiber is first produced using the VAD method or the like. In another process, the glass rod which forms the stress-applying part is formed using the VAD method or the like. In order to make the coefficient of thermal expansion of this glass rod large, it is doped with boron oxide (B.sub.2 O.sub.3) in an amount close to 20% by weight. However, breakage occurs extremely easily in the quartz glass which has been doped with this much B.sub.2 O.sub.3 due to its thermal contraction. Accordingly, considerable care must be taken during this process.
Next, a pair of holes are drilled in the aforementioned core/cladding glass preform, and the glass rods which form the stress-applying parts are inserted into these holes. The PANDA type polarization-maintaining optical fiber is obtained by drawing the assembly as composed at this stage.
In the conventional rod-in-tube method, a method wherein, after inserting the rods in a tube, the whole assembly is heated and collapsed to be a unitary structure, is employed. However, when this method is applied for the aforementioned glass rods which include the stress-applying parts, the collapsed glass rod break when cooled.
As a result, even for the PANDA fiber, which is one of the most ordinary polarization-maintaining optical fibers, the production method is not easy, requires considerable time, and costs high.
Further, in this production method, the process of drilling a plurality of holes in the glass rods which form the claddings is bothersome and, moreover, requires a special hole drilling device. In order to lower production costs, a greater simplification of the production process is necessary.
Accordingly, a subject of the present invention is obtaining a polarization-maintaining optical fiber which can be easily produced and supplied at a low cost, and a production method therefor.
With regard to a polarization-maintaining opti
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Aikawa Kazuhiko
Himeno Kuniharu
Nozawa Tetsuo
Sawada Minoru
Suzuki Fumio
Fujikura Ltd.
Ngo John
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