Abstract

Experiments have shown the presence of a spatially periodic gain/loss and/or dispersion, as experienced by a soliton pulse propagating in the distributed environment of a fibre laser (or for that matter any other equivalent system) can act as a source of instability, see [1] and references therein. In rare earth doped fibre lasers this is paricularly evident with the generation of femtosecond soliton pulses, [2,3]. A characteristic signature of this instability is the appearance of a series of well defined spectral resonances(sidebands) in the spectral wings of the pulse. These components act as an energy sink, introduce destabilising effects and also preclude full use of the gain linewidth. Theoretical studies have indicated the magnitude [4] and position [5] of these resonances scales as $\approx \sqrt{\frac{Z_o}{Z_a}}$ where Z_o is the soliton period which is inversly proportional to the (net)second order dispersion and Z_a is the fundamental period associated with the perturbation, typically the fibre (cavity)length. In principle therefore, using fibres of shorter length and/or lower dispersion should permit the generation of shorter pulses and hence more efficient use of the gain linewidth, [1,3]. With the former there is a practical limit on how short a fibre can become whereas in the latter a point is ultimately reached where higher order dispersion, in particular third order dispersion, becomes important.

© 1993 Optical Society of America