Vectorial wave analysis of side-tunnel type polarization-maintaining optical fibers by variational finite elements

Vectorial wave analysis of side-tunnel type polarization-maintaining optical fibers is presented using the vector -field finite-element method, which is applicable to the fibers having arbitrarily cross-sectional shape. First, to improve the accuracy of solutions, several techniques are investigated such as the zero-extrapolation method, curvilinear elements, and an improved virtual-boundary method. After checking the accuracy of solutions, the relation between the shape of the fibers and their polarization-mode properties, such as the axial propagation constants, the modal birefringence, the polarization-mode dispersion, and the magnetic-field distribution, is studied in detail. Also studied are the optical fields of side-tunnel fibers, which have never been investigated, and the mechanism for the phenomenon that the propagation constants of the fundamental modes come extraordinarily close to those of the first higher-order modes is clarified.