Radiation loss of dispersion-managed solitons in optical fibers

A nonlinear optical fiber with a periodic group-velocity dispersion variation, called a dispersion-map, allows transmission of breathing soliton-like pulses. These pulses, commonly referred to as dispersion-managed solitons (even though they are not true solitons), experience substantial distortion within each map period but recover their shapes after each complete cycle. Since linear dispersive waves composed of particular frequencies can oscillate with the same period as the dispersion-managed soliton, the two can couple together in a nonlinear resonance. As a result, dispersion-managed solitons tend to radiate. Here we calculate the radiation intensity by analyzing the nonlinear Schrِdinger equation with a periodic dispersion coefficient. When the dispersion-map period is shorter than the average dispersion length, the radiation intensity is found to be exponentially small and can be determined by the techniques of asymptotics beyond all orders. It is shown that the resonant radiation generally has nonzero intensity and thus drains energy from dispersion-managed solitons, so that they are thus not truly periodic. We also show that there are low-radiation windows for particular parameter values where the dispersive radiation shed is greatly diminished.