All-silica, large mode area, single mode photonic bandgap fibre with Fabry–Perot resonant structures

• We characterise the dispersion, loss and nonlinear properties of a PBG fibre by FEM.
• We introduce structural modifications which result in resonant dispersion functions.
• Using modified index regions, one can tailor the dispersion behaviour of the fibre.
• The modified cladding structures increase mode field area and reduce the fibre nonlinearity.
• Calculations demonstrate the nonlinear compression capabilities of the designed fibre.

All-silica, photonic crystal fibres consisting of a low index, silica core surrounded by higher index inclusions embedded in a silica matrix to form a photonic bandgap cladding were numerically analysed. The aim of the investigations was to modify the guiding properties of the fibre by introducing resonant structural entities. These structural modifications are realised by altering the refractive index of certain high index inclusions in the photonic crystal cladding resulting in mode coupling between the core mode and the mode propagated in the modified index region. This results in an increased effective core area of the fundamental core mode and consequently decreased nonlinearity as well as modified effective index compared to the effective index of the unmodified structure and resonant dispersion profile that can be used for pulse compression or optical delay purposes.