Amplification of femtosecond optical solitons in Er-doped fibers with smooth and strong varying dispersion

The main goal is to investigate the femtosecond optical solitons dynamics in amplifying optical fibers with smooth and strong group velocity dispersion inhomogeneities. It is well known that the Raman self-frequency shift effect shifts the spectrum of a soliton pulse from under the gain line profile and is one of the main factors that limits the maximum energy and minimum duration of the output pulses. We analyze the possibility of using dispersion inhomogeneities to weaken this undesirable effect. As follow from our computer simulations it is possible to capture the femtosecond soliton by a dispersion trap formed in an amplifying optical fiber. This process makes it possible to accumulate an additional energy in the soliton dispersion trap and reduce significantly the soliton pulse duration. The main objective of our work is the analysis and presentation of the physics of a new nonlinear effect, femtosecond soliton tunnelling and trapping in the amplifying optical fibers, which occurs when solitons pass through localized inhomogeneities of the fibers medium group velocity dispersion