Optical signal inversion phenomenon for 1.53 mu m laser in an erbium-dopedlithium niobate

Modulation characteristics of a negative nonlinear absorption effect were i nvestigated in 3 wt % erbium-doped lithium niobate using a 1530 nm laser di ode. With a decreasing incident modulation degree, a reversed-phase wavefor m was obtained in the transmitted laser at modulation degrees smaller than 85% for a sample length of 14 mm. The reversed-phase transmitted waveforms were observed at modulation frequencies from 1 kHz to 10 GHz. The negative nonlinear absorption effect for 1.5 mu m can be explained by considering an enhanced absorption model for a four-level system of the Er3+ ion. (C) 199 9 American Institute of Physics. [S0003-6951(99)04352-1].