Directional couplers operated by resonant coupling in all-solid photonic bandgap fibers

We have proposed directional couplers operated by resonant coupling in all-solid photonic bandgap fibers structure which consist of a cladding with an array of high-index rods in silica background, two cores formed by omitting two rods, and some defect rods introduced by reducing the diameter of the high-index rods between the cores. The resonant effect induced by the avoided crossing between core-guided supermodes and defect-guided modes significant decreases the coupling length. The directional couplers proposed in this paper are almost polarization independent and have potential application in realizing integrating all-fiber communication devices.