Multimode instability in ring fibre lasers. Inhomogeneous broadening and modal structure

Summary form only given. The interest in the analysis of the multimode instability of ring fibre lasers has increased in the recent years because of the identification of such instability in Er/sup 3+/-doped fibre lasers as the classical Risken-Nummedal instability. Two factors not considered up to now play a major role on the lasing to instability thresholds ratio, r: (i) the transverse profile of pump and lasing fields due to their guided nature, and the extension of the doped region within the fibre core; and (ii) the inhomogeneous broadening of the Er/sup 3+/ gain induced by the fibre host.