Thermal-induced transverse-mode evolution in thermally guiding index-antiguided-core fiber.
The transverse-mode evolution in thermally guided (TG) index-antiguided-core (IAGc) fibers is numerically studied in this paper. With the finite-element method and thermal conduction equations, the fundamental mode evolution with a thermal load is investigated, and four evolution stages (i.e., the cladding-confined, quasi-cladding-confined, quasi-core-confined, and core-confined) are revealed. Thermal load thresholds corresponding to these stages are presented. Furthermore, the field evolutions of high-order modes also are investigated; the filling factors of these modes are discussed as well. The pertinent results can provide significant reference for designing TG IAGc fibers and understanding the thermal effect on the transverse mode of fibers involving the index-antiguided core.