STRUCTURAL-CHANGES OF GEGAS BULK GLASSES INDUCED BY UV EXPOSURE

Glasses in the GeGaS system are promising hosts for Pr3+-ions and are thus interesting matrices for a planar optical amplifier at wavelength 1.3 mu m. For such an application a technique to induce patterned cha nges in the index of refraction for generating strip waveguides must b e developed. We have found that the index of refraction of Ge25Ga5S70 and Ge25Ga10S65 glasses can be reduced by more than 0.1 through a defi ned band gap exposure. Atomic force microscope measurements have demon strated an expansion of the exposed areas of the sample surface. Also. a different H2O2 etching rate for exposed areas has been observed. In connection with the experimentally proved reversibility of the photos tructural changes, a microscopic model in which heteropolar bonds are broken by absorption of high energy photons and new homopolar bonds ar e formed simultaneously has been developed to describe the effect. (C) 1998 Elsevier Science B.V. All rights reserved.