Soliton propagation and soliton collision in double-doped fibers with a non-Kerr-like nonlinear refractive-index change.

A physical mechanism for a non-Kerr-like nonlinear refractive-index change in double-doped fibers is proposed, which shows for realistic material parameters a bistable (or two-valued) soliton regime with a large bistability range. The collision of two bistable solitons with a frequency difference in such materials is investigated. Solitons of the lower solution branch retain their shape after the collision. In contrast, two solitons of the upper solution branch with a low-frequency difference fuse to a single high-energy soliton after the collision. The possible applications of this effect for nonlinear photonic switching are discussed.