Abstract

The intensity dependent refractive index and absorption coefficient are third order optically nonlinear effects which offer the possibility to realise all-optical switching devices. The refractive index change Δn due to the applied field E is expressed as Δn = n₂ · |E|². Important material parameters are the value and relaxation time of the nonlinear coefficient n₂, the maximum achievable refractive index change Δn_sat and the linear absorption α₀ [1]. Rare earth-doped materials are well known for their use in optical amplification but may also be of importance for all-optical switching. By implantation of the rare earth atoms in a (poly)crystalline material it is possible to obtain sharp absorption peaks which are accompanied by a relatively broad dispersive change of the refractive index. This property may be used in a device where a pump beam tuned at the absorption peak changes the refractive index which influences the behaviour of a signal beam tuned just outside the absorption region. The n₂ relaxation time of this type of materials is in the order of ms but can be drastically reduced by injection of a short turn off pulse [2]. The Δn_sat scales proportional to the rear earth doping concentration and may be increased to about 10-₄.

© 1993 Optical Society of America