RESONANCE-ENHANCED REFRACTIVE-INDEX AND ITS DYNAMICS IN RARE-EARTH-DOPED FIBERS

We present a theory that enables us to account for the pump-induced ch ange of refractive index in a rare-earth-doped fiber. Experimental res ults carried out on an erbium-doped fiber with cw pump and cw signal o peration confirm the accuracy of this theory at the steady state. Both theoretical and experimental results show that significant index chan ges can be obtained for the order of 1-2 mW of cw optical pump or sign al power. In addition we studied the transient dynamics of the resonan ce-enhanced refractive index in a wide range of pulse widths from mill isecond to tens of femtoseconds. The result shows that a fast response of refractive-index changes is achievable since the effects of sponta neous emission and nonradiative decay are negligible in the short-puls e case.