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It is well known that geometrical or dielectric imperfections in conventional graded-index single-mode fibers depolarize light after a few centimeters. A slight improvement in the polarization performance of these fibers is achieved by introducing noncircularity in the core shape. This is evident from the measurements on borosilicate fibers with dumbbell shaped cores. This result is correlated with Marcatili's analysis, which shows that changing the core geometry, from square to rectangular, does not appreciably alter the difference in the propagation constants of the two fundamental modes with orthogonal polarizations. Thus, the noncircular geometry and the associated increase in stress-induced birefringence introduced during the manufacturing process alone are not sufficient to improve the polarization performance, and the enhancement of the anisotropic birefringence is necessary to achieve single-polarization fibers.

Publication costs assisted by Bell LaboratoriesThe chemical kinetics of the reactions which contribute to the modified chemical vapor deposition process of fiber waveguide fabrication have been studied by following the steady state reactant concentrations under a variety of experimental conditions. It was found that the reaction of SiCl4, GeCl4, POCl3, and SiBr4 with a large excess of 02 follows reaction kinetics which are first order. The kinetics of the reaction of BC13 with oxygen are more complex.

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