Charge transfer states in GeO2-doped silicate fiber-optic waveguides and their role in second-harmonic generation

The concentration dependence of the broad-band luminescence arising in GeO2 -doped silicate fiber-optic waveguides is measured and interpreted. The sp ectra obtained show that electronic excitations of a new type that are abse nt in pure silicate glass - charge transfer excitons arise in the doped sys tem. Under the action of light an electron can be transferred both from a G e center into the host and between Ge centers. Self-organization of these e xcitations in the field of a light wave (orientational ordering of their di pole moments) results in the appearance of a macroscopic electric field tha t destroys the initial centrosymmetry of the system and allows second-harmo nic generation. (C) 1998 American Institute of Physics. [S0021-3640(98)0042 2-8].