Design principles of multifiber resonant directional couplers with hollow Bragg fibers: example of a 3 x 3 coupler.
When several hollow photonic crystal fibers (HPCFs) are placed in proximity to each other, radiation-induced interfiber coupling between their core guided modes is observed. Under certain conditions coupling between the core modes of two touching collinear fibers can have a resonant increase via excitation of a low-quality intermirror cavity resonant state. Such coupling, however, decreases dramatically within the first micrometer of intermirror separation. Moreover, when fibers are touching, in the frequency domain a large number of accidental degeneracies with fiber surface and mirror states complicate the design of a stable 2 x 2 coupler. To alleviate these problems we consider coupling among three hollow Bragg fibers. When placed in the vertices of an isosceles triangle, even for a finite separation between fibers, triangular interfiber cavity forms a high-quality resonator that can be tuned via additional structural elements to a particular frequency of interest. Interfiber surface states are suppressed by keeping the fiber separation finite, thus allowing stable coupling conditions in a 3 x 3 HPCF coupler configuration.
Skorobogatiy
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Ecole Polytechnique de Montréal, Génie Physique, C.P 6079, succursale Centre-Ville Montreal, Québec H3C3A7, Canada. maksim.skorobogatiy@polymtl.ca