  We demonstrate ultrafast soliton-based nonlinear balancing of dual-core
asymmetry in highly nonlinear photonic crystal fiber at sub-nanojoule pulse
energy level. The effect of fiber asymmetry was studied experimentally by
selective excitation and monitoring of individual fiber cores at different
wavelengths between 1500 nm and 1800 nm. Higher energy transfer rate to
non-excited core was observed in the case of fast core excitation due to
nonlinear asymmetry balancing of temporal solitons, which was confirmed by the
dedicated numerical simulations based on the coupled generalized nonlinear
Schr\"odinger equations. Moreover, the simulation results correspond
qualitatively with the experimentally acquired dependences of the output
dual-core extinction ratio on excitation energy and wavelength. In the case of
1800 nm fast core excitation, narrow band spectral intensity switching between
the output channels was registered with contrast of 23 dB. The switching was
achieved by the change of the excitation pulse energy in sub-nanojoule region.
The performed detailed analysis of the nonlinear balancing of dual-core
asymmetry in solitonic propagation regime opens new perspectives for the
development of ultrafast nonlinear all-optical switching devices.
