Cutoff properties of large-mode-area photonic crystal fibers

The cutoff properties of triangular photonic crystal fibers with different core dimensions have been deeply investigated. In particular, 7-rod core fibers, obtained by removing the air-holes belonging to the first ring, as well as the central one in the fiber cross-section, have been considered. A phase diagram which describes the regions of single-mode and multi-mode operation for these large mode area fibers has been calculated with two different approaches. Simulation results have demonstrated that, for a fixed air-filling fraction, triangular photonic crystal fibers with a wider silica core region are single-mode in a smaller wavelength range. As a consequence, also the endlessly single-mode region of 7-rod core triangular fibers is smaller than that of 1-rod core ones. However, by properly choosing low air-filling fraction and relatively small hole-to-hole distance, 7-rod core photonic crystal fibers can provide high effective area values, as well as single-mode operation, without the problem of leakage losses.