Tailoring the soliton and supercontinuum dynamics by engineering the profile of tapered fibers.

We demonstrate by means of numerical simulations of the generalized Nonlinear Schrödinger Equation that the variation of the diameter of a tapered fiber along the fiber axis can be used as a new degree of freedom to tailor the spectrum generated by ultrashort laser pulses.We show that, apart from the cross-section geometry of the fiber and the materials used for the core, cladding, and surrounding medium, the diameter profile along the fiber axis crucially influences the soliton dynamics, the temporal and spectral evolution as well as the generation of a supercontinuum. As an example, we have investigated a few centimeters long conical waists, which reveal large differences of the output spectra depending on the incoupling direction. For a decreasing fiber diameter, we find that, keeping the pulse energy constant, a lower input peak power may generate a broader supercontinuum. We attribute this result to the dynamics of higher-order solitons. A comparison of the simulated spectra to experimentally measured ones shows excellent agreement.