SCALAR OFF-RESONANT MODULATION INSTABILITY IN RARE-EARTH-DOPED FIBER AMPLIFIERS

This letter presents an analytical model which describes the dynamics of the modulation instability in a nonlinear, dispersive, homogeneousl y broadened and nonsaturable fiber amplifiers. The general case of arb itrary detuning between the laser frequency and the resonance frequenc y and arbitrary bandwidth of the amplifying transition is treated. The model accounts both for the gain dispersion and for the gain-induced, near resonant refractive index dispersion. Simple closed form express ions for the combined gain coefficients of the Stokes and anti-Stokes frequencies are obtained.