All-optical signal inverter derived from negative nonlinear absorption effect

A model of the negative nonlinear absorption effect (NNA effect) with the laser wavelength of about 1.5 μm is proposed. When the intensity of the incident laser irradiated on Er doped materials varied in Er:yttrium aluminum garnet (YAG), the NNA effect was observed, i.e. the transmitted laser intensity shows opposite phase of the incident laser at the wavelength of about 780 nm. The wavelength of the laser is related to the both of the 4I15/2–4I9/2 and the 4I13/2–2H11/2 transitions of Er3+ ion. In addition, the NNA effect is found in erbium-doped materials of another wavelength (about 1.5 μm) of the laser, which is related to the both of the 4I15/2–4I13/2 and the 4I9/2–2H11/2 transitions of Er3+ ion. In the model we have pursued the energy-level system of the Er3+ ion for the former wavelength. In this study, we analyzed the mechanism of the NNA effect at the wavelength of about 1.5 μm.