Increase of the minor field component in stress-induced birefringent fibers, due to nonuniformity of stress

Analytical evaluations of the minor
x
-component of a LPO1 mode polarized along
y
-axis in strongly birefringent optical fibers are proposed, for weakly guiding step-index fibers. In the assumption where the
\bar{\bar{\epsilon}}
-tensor is everywhere diagonalized in
x-y-z
axes, it is shown that the anisotropy has little effect on the minor component and that the polarization ratio (E
x
power/E
y
power) remains within a few decibels from its value in an isotropic fiber. A considerably larger change can be predicted from a more realistic analysis of real birefringent fibers, taking into account the nonuniformity of the stress which produces the birefringence; this nonuniformity makes off-diagonal coordinates-dependent terms to appear in the
\bar{\bar{\epsilon}}
-tensor. A recent experimental report can thus be explained.