A singular perturbation method is used to analyze the effect of sliding-frequency guiding filters on an optical soliton, which has been proposed to be used as a bit carrier in fiber-optics communication systems. We find that there is a broad range of physical parameters, only inside of which would the sliding-frequency filter scheme operate stably. The lower limit (in soliton energy) of this parameter regime was found earlier by Mollenauer et al. [Opt. Lett. 17, 1575 (1992)] and by Kodama et al. [Opt. Lett. 18, 1311 (1993)] and is determined by whether the soliton will continue to stay in synchronization with the array of filters. The upper limit is determined when the comoving dispersive waves that are continually being generated by the filtering are no longer decaying and instead start to grow and generate, finally, a secondary soliton. This upper limit was discovered recently in both experiments and numerical simulations by Mamyshev and Mollenauer [Opt. Lett. 15, 2083 (1994)]. We have found a simple analytical estimate of this upper limit by the use of a singular perturbation method. Our analytical results agree well with the numerical and experimental findings of Mamyshev and Mollenauer.
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