Self-organization in germanium silicate fibers and its role in second harmonic generation

Based on Raman and hyper-Raman experiments and on direct green-light absorp tion measurements, excitations of a new type-charge transfer excitons-are f ound to exist in silicate fibers with addition of GeO2, whose self-organiza tion (orientational ordering of dipole moments) leads to positive feedback on a static electric field. The strong electric field of 10(5) V/cm that re sults breaks the initial inversion symmetry and allows the second harmonic to be generated, which exists only at the medium preparation stage and swit ches off when a transition to the stationary state takes place.