Solitonic spectral transformations in double core photonic crystal fiber

Abstract

Nonlinear propagation of femtosecond pulses in double core square lattice PCF made of multicomponent glass was investigated experimentally at excitation wavelength 1250 nm in the anomalous dispersion region. The obtained results expressed soliton fission and self frequency shift in the anomalous region, inspected by IR registration, with increasing complexity by increasing excitation energy. The visible registration, inspecting the normal dispersion region, exhibited soliton induced dispersive wave generation with blue shifting feature suggesting nonlinear phase change effect on the phase matching condition. The width of the overall spectral feature approached two octaves at approximately 10 nJ excitation energy in 6 cm long fiber sample. The knowledge about the evolving processes was extended by numerical simulation of the nonlinear propagation in the near IR region in reasonable correspondence with the experimental results. Furthermore, separate registration of the visible spectral features originating from the two fiber cores was ensured exhibiting significant differences between the multipeak spectra. The two core spectral content differences was possible to further alternate by rotation of the excitation polarization direction with application potential for polarization switched directional coupler accompanied by frequency conversion. Finally, single versus double core excitation conditions were compared. The double core excitation resulted in smoother spectral features, both in the case of IR and visible registration, at requirement at expense higher excitation energies needed for broadband supercontinuum generation.