Soliton amplification and reshaping in optical fibers with variable dispersion

We look for a setup providing optimum amplification and reshaping of short solitons in a lossy optical fiber. We consider a reshaper model. combining a pointlike amplifier and a segment of a variable-dispersion fiber whose length is comparable with the soliton's dispersion length. The objective is to find reshaping configurations with a minimum length providing for release of a chirpless duly amplified soliton into the bulk fiber. In most cases the input pulse is taken as a soliton with no chirp, but chirped input pulses are tested as well. Two particular types of variable dispersion (dispersion management) are considered: piecewise constant and linear. The main part of the analysis is done semianalytically by means of the variational approximation. Direct numerical simulations are also performed at some values of the parameters to permit us to examine the accuracy of the approximation (which proves to be good). It is found that the amplifier placed at the input edge of the reshaper always gives better results than the one at the output. The minimum necessary length of the variable-dispersion segment proves to be a decreasing function of the amplification factor. It is found that the performance characteristics are only weakly sensitive to a particular choice of the configuration within a given type of variable dispersion, so the actual choice can be determined by convenience of fabrication. The obtained results can be applied as well to optimize compression of solitons (without amplification) by variable-dispersion fibers. (C) 1996 Optical Society of America