Lightguiding in ion-exchanged photochromic glass layers is reported. The guides were formed by ion exchange of Ag+ for Na+ or by outdiffusion of F. Guide attenuation was less than 0.2 dB/cm in many cases. The attenuation in the guide was varied over a range of Δα = 30 dB/cm by illuminating the guide with (1) uv radiation to darken the guide or order of seconds. (2) visible radiation to bleach the guide. Switching times were in the order of seconds.
J. D. Crow, N. F. Borrelli, T. P. Seward III, and J. Chodak, "Lightguiding in Photochromic Glasses," Appl. Opt. 14, 580-585 (1975)