Source of instability in fibre soliton lasers

To describe the propagation of a soliton in a medium where it experiences a periodic gain or loss, the concept of the guiding centre or average soliton has proven invaluable. It has been shown that stable pulse propagation can be achieved provided that z₀≫z_a , where z_a is the amplification period and z₀ is the characteristic soliton period. By extending the average soliton concept to regions where z₀ is comparable to z_a, theoretical and experimental results are presented which propose a mechanism for the instability of short pulse fibre soliton lasers, distinct from modulational instability, which clearly can be ruled out as the instability mechanism, due to the nature of the power scaling of the generated spectral modulations. A good agreement has been shown between theory and experiment for the proposed model of this instability process