Chirp mechanisms in soliton-dragging logic gates.

We theoretically and experimentally study the chirping mechanism responsible for the time shifts in soliton-dragging logic gates. Cross-phase modulation during the first one or two walk-off lengths in a birefringent optical fiber causes most of the frequency shift that translates into a time shift after propagation in a soliton dispersive delay line. Introducing gain or loss during the pulse interaction asymmetrizes the pulse walk-off and, consequently, increases the temporal window over which soliton dragging can result in a time shift. Analytic formulas for the time shift provide the scaling laws as a function of various fiber parameters.