ANALYSIS OF MODULATIONAL INSTABILITY IN MONOMODE OPTICAL FIBERS WITH HIGH-ORDER NONLINEARITY

The modulational instability (MI) in monomode optical fibres with fift h-order nonlinearity, fibre loss, higher-order dispersion, and the tem poral variation of third-order nonlinearity is studied theoretically. The conditions for the existence of the MI and the maximal modulationa l growth are given and discussed in detail. The results obtained show that the key factor dominating the producing condition of the MI is th e power P of the continuous wave initially launched into the optical f ibres. If P falls into 3/1 0 < P/P0 < 1/2 where P0 is defined as chara cteristic power, the MI can be produced in the range of not only anoma lous group velocity dispersion but also the normal in which the final evolution state of the modulated wave is dark soliton.