Polarization-maintaining optical fibers with hollow circular pits

This paper gives a detailed investigation on the polarization-maintaining optical fibers with one hollow circular pit across the core-clad interface (single circular-pit fiber (SCF)), and two hollow circular pits across the core-clad interface (double circular-pit fiber (DCF)). The field problems are analyzed by the improved point matching method. Waveguide parameters of SCF and DCF which provide the largest modal birefringence, are investigated. It was found from numerical analysis that 1) the maximum modal birefringence B
max
for DCF is larger than that for SCF and 2) the value of
B_{max} = 4.49 \times 10^{-4}
has been attained for DCF when the refractive-index difference is 0.5 percent. Zero-polarization-mode dispersion can be realized at
V=V_{max}
, but cannot be realized just at
V = V_{max}
, where
V
is normalized frequency and V
max
is the value of
V
for B
max
. These results are quite reliable because a) the relative error of the modal birefringence computed by our method is less than 10
^-4
and b) this new method never produces ghost solutions.