[OPTICAL REVIEW Vol. 6, No. 4 (1999) 284-287]
Negative Nonlinear Absorption Effect for 1.5 μm Laser in an Erbium Chloride Solution
Department of Information and Control Engineering, Toyota Technological Institute, 2-12-1, Hisakata, Tempaku, Nagoya, 468-8511 Japan
(Received November 25, 1998; Accepted February 25, 1999)
The dependence of the negative nonlinear absorption effect on both modulation degree and frequency of the incident laser was investigated in an erbium chloride solution using a 1.5 μm laser diode. The reversed-phase waveform was observed at modulation degrees smaller than 71%. As modulation frequency increased, the transmitted waveforms became asymmetrical and the effect was suppressed. The effect was obtained at wavelengths of 1510.3 to 1510.8 nm. The negative nonlinear absorption effect for 1.5 μm can be explained by considering an enhanced absorption model for a four-level system of the Er3+ ion.
Key words : negative nonlinear absorption effect, optical inverter, erbium chloride, excited state absorption, enhanced absorption, up-conversion, energy transfer