Complex photosensitivity observed in germanosilica planar waveguides

Photosensitive effects distinguished as type I and type IIA photosensitivity within optical fibers were observed in a much more pronounced form within germanosilica waveguides deposited by hollow-cathode plasma-enhanced chemical-vapor deposition. With increasing exposure to 193-nm UV light, positive index changes greater than $2\times {10}^{-3}$ were observed, followed by negative index changes greater than $-5\times {10}^{-3}$. These behaviors are attributed to an increase in macroscopic polarizability and a reduction in material density, respectively. The negative index change is more temperature resistant and is fully annealed only at 900 °C, whereas the positive one is annealed at 500 °C.