Mode birefringence in a single-mode elliptic optical fiber

Mode birefringence of an elliptic fiber is described by a formula valid in the case of a small ellipticity of the core and an arbitrary difference between the refractive indices of the core and cladding. This formula is derived using approximate vector solutions of the Maxwell equations for two dominant orthogonally polarized modes. It is shown that there are considerable changes in the mode birefringence due to changes in the parameters of the single-mode regime. A study is made of the difference between the group velocities of the dominant modes. It is shown that the ranges of the parameters of a single-mode elliptic fiber in which the mode birefringence is maximal and the intermode dispersion minimal overlap near the limit of the singlemode regime. A comparison is made with the published results.