RESONANT TRANSMISSION OF A CHIRPED SOLITON IN A LONG OPTICAL-FIBER WITH PERIODIC AMPLIFICATION

Using narrow solitons is a natural way to increase the data-transmissi on rate in soliton-based optical communications lines. However, in the present work it is demonstrated that it does not make sense to employ ultrashort solitons whose dispersion lengths Z(0) are much smaller th an the amplification spacing Z(a): In this case, the interaction betwe en the solitons gives rise to stable bound states in which the tempora l separation between the solitons only increases with a decrease of th e soliton width. This is the reason why, when Z(0) and Z(a) are close, the case is potentially the most promising. Also in this case; howeve r, resonance effects are possible. In the present work, resonance exci tation of the internal vibrations of a fundamental soliton by the peri odic amplification is considered analytically. Both the fundamental an d the second resonances are analyzed in detail by means of a variation al approximation. The most salient feature of the resonant propagation of the soliton is that it is bistable. Interaction between vibrating solitons is also considered, and it is shown that this interaction can be suppressed by vibrations with fairly small amplitudes, preventing formation of bound states. These resonant features are beneficial for use in communication lines. Emission of radiation by the vibrating sol iton, which is a detrimental effect, is considered too, and it is demo nstrated that it can be suppressed in two different ways: by the strai ghtforward use of notch filters, or, in a smarter way, by the vibratio ns being switched into a range in which the first vibrational harmonic does not radiate. (C) 1996 Optical Society of America