Numerical analysis of polarization‐maintaining optical fibers with circular pits in a circular core

This paper proposes new optical fibers with angularly nonuniform index distributions featured by one circular pit in the core, two circular pits in the core, and noncoaxial W‐type distribution. The field problems are analyzed by the improved point‐matching method. Waveguide parameters of single circular‐pit fibers, double circular‐pit fibers, and noncoaxial W‐type fibers that provide the largest modal birefringence are investigated. It is found that (1) the maximum modal birefringence B max for single circular‐pit fibers and noncoaxial W‐type fibers is much larger than those for double circular pit fibers, (2) noncoaxial W‐type fibers exhibit larger modal birefringence than single circular‐pit fibers in the range Δ n < 1.8% (Δ n is relative index difference), and (3) the value B max of 1.7 × 10 −4 has been attained for Δ n = 0.42%. These results are quite reliable because (1) the relative error of the modal birefringence computed by our method is less than 10 −4 , and (2) this new method never produces ghost solutions.