Numerical analysis of directional coupling in dual-core microstructured optical fibers

In this paper, we present a numerical analysis of the coupling coefficients in dual-core air-silica microstructured optical fibers with pi/6 symmetry. The calculations are based on an especially fitted application of the coupled mode theory for microstructured optical fibers. This method is compared with three other techniques, the supermode method, the beam propagation method and the equivalent fiber model, and is shown to be very computationally efficient. Our studies enable us to derive a formula linking the coupling coefficients to core separation according to the wavelength, the pitch and the hole diameter of the fiber structure.