| 摘要 |
<p>An optical fiber comprises a core and cladding having different refractive indices and forming a single-mode guiding region, the guiding region being located sufficiently close to the surface of the fiber, along a selected length of the fiber, to allow coupling to a guided wave. The outer surface of the fiber has a non-circular cross-section with a predetermined geometric relationship to the guiding region so that the location of the guiding region can be ascertained from the geometry of the outer surface. The guiding region of the fiber preferably has a non-circular cross-section defining two transverse orthogonal axes which, in combination with the different refraction indices of the core and cladding, permits the de-coupling of waves polarized along said axes, and the non-circular cross-section of the outer surface of the fiber preferably has a predetermined geometric relationship to the transverse axes of the guiding region so that the orientation of those axes can also be ascertained from the geometry of the outer surface. A directional coupler is formed by joining two such fibers so that at least a portion of a wave propagated through either guiding region is coupled into the other guiding region. There is also provided a method of making an optical fiber of the type described above by forming an optical preform having a core and a cladding with different refractive indices, the core being offset from the center of the preform and the outer surface of the preform having a non-circular cross-section with a predetermined geometric relationship to the core, and drawing an optical fiber from the preform with the drawing rate and temperature being controlled to produce a fiber with a cross-sectional geometry similar to that of the preform.</p> |
