Abstract

There has been considerable interest in all-optical devices for achieving the high-speed and parallel processing. Up to the present the amount of absorption in any absorption process has been considered to be proportional to the incident light intensity until in some cases saturation occurs [1]. Recently we observed experimentally negative nonlinear absorption (NNA) phenomena which cause transmission to decrease as the laser intensity increase and confirmed that the transmitted laser intensity with the variation of incident laser showed negative nonlinear (i. e. Maeda's effect) [2, 3]. In this report we demonstrate that the net quantity of light absorbed in an erbium doped yttrium aluminum garnet crystal can be a negative function of the incident laser intensity. The absorbing material has a four-level energy structure: absorption can occur between a ground level and an excited level and between two other excited levels. The input-output characteristic has a negative region due to the absorption between excited states.

© 1996 IEEE