Towards ultrafast sub-nanojoule solitonic nonlinear directional coupler based on soft glass dual-core photonics crystal fibers

We demonstrate narrow band spectral intensity switching in dual-core photonic crystal fibers made of highly nonlinear glass under femtosecond excitation. The fibers expressed dual-core asymmetry, thus the slow and fast fiber cores were unambiguously distinguished according to their dispersion profiles. The asymmetry effect on the dual-core propagation in anomalous dispersion region was studied both experimentally and numerically. The experimental study was carried out using femtosecond laser amplifier system providing tunable pulses in range of 1500 nm - 1800 nm. The obtained results unveiled, that it is possible to improve nonlinearly the coupling between the two waveguides by excitation of the fast fiber core. The results were obtained in regime of high-order soliton propagation and were verified numerically by the coupled generalized nonlinear Schrodinger equations model. The spectral analysis of the radiation transferred to the non-excited core revealed the role of effects such as third order dispersion, soliton compression and spectral dependence of the coupling efficiency. The simulation results provide reasonable agreement with the experimentally observed spectral evolutions in the both fiber cores. Under 1800 nm excitation, narrow band spectral intensity switching was registered with contrast of 23 dB at 10 mm fiber length by changing the excitation pulse energy in sub-nanojoule range.