Abstract

Among photorefractive materials, BSO has the peculiarity of showing strong optical activity (about 45°/mm). Previous investigations demonstrated that such a regime denies soliton formation in this material because of a not complete nonlinear compensation of the diffraction in both the polarisation components [1-2], nevertheless we have observed and characterised, at really low signal intensity and at zero background, really efficient 1-D and 2-D selfocusing These transient conditions survive for a few seconds. In this case, contrarily to the steady- state case, no background is present Particular selfocusing regimes behave as quasi-steady state solitons for which the transversal shapes remain almost constant along 1-2 diffraction lengths Peculiarity of this selfocusing is the unavoidably soliton destruction induced by any background presence The soliton formation in this case is much faster than in the steady-state case and occurs at much lower external bias fields, going from 25-30 kV/cm in the case of 1-D steady state soliton [3] to 5-10 kV/cm in the quasi-steady-state case

© 2000 IEEE