Optical Signal Inverter Derived from Negative Nonlinear Absorption Effects

Abstract
Using a modulated laser diode, dependence of a negative nonlinear absorption effect on both the wavelength and the sample length was observed in an erbium doped yttrium aluminum garnet crystal which has a four-level energy structure. The effect was seen at wavelengths of 787.4 to 788.6 nm in excited state absorption spectra which showed a peak corresponding to the transition from 4 I 13/2 to 2 H 11/2 in Er3+ for sample lengths greater than 2.0 mm. An optical signal inverter which had a negative input-output characteristic was realized using the negative nonlinear absorption effect.