Design method for polarization‐maintaining optical fibers with zero total dispersion at two wavelengths

Abstract

The design method for the polarization‐maintaining optical fiber with two hollow circular pits across the core‐clad interface was investigated under the following two conditions: (1) the total dispersion for one of nondegenerated HE11 modes is zero simultaneously at the two wavelengths of 1.30 μm and 1.55 μm (the zero dispersion condition); and (2) the modal birefringence (=B) is maximum. The polarization‐maintaining optical fibers with hollow circular pits across the coreclad interface are the structure which can maximize the modal birefringence in angularly nonuniform refractive index profiles in the case where no dispersion is considered. To satisfy the conditions for (1) and (2), the relative index difference of the core and the clad Δ1, the normalized minimum distance between the core center and the pit periphery D [Δ(R0‐a3)/a1; R0; the distance between the core center and the pit center, a1: the core radius, a3: the pit radius], and the normalized pit radius (= a3/a1) are used as parameters. The principal results obtained in this paper are as follows. (1) If D is decreased, B also reduces since a3/a1 must also be decreased for the zero dispersion condition. (2) B can be maximized if two hollow pits are in contact with the core periphery (D = 1.0). (3) When Δ1 is 0.5 to 1.5 percent, the attained maximum value of B is 0.75 × 10−4 to 2.23 × 10−4.