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 Δnsat 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 Δnsat scales proportional to the rear earth doping concentration and may be increased to about 10-4.
© 1993 Optical Society of America
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