Electron beam induced structural changes in Ge-doped silica fabricated by planar-FHD and tube-deposited MCVD

Abstract

Since the discovery of the photosensitivity in silica by Hill [1], a great deal of research has been carried out to understand the mechanisms associated with the UV-induced refractive index changes that allow the direct-writing of gratings and optical waveguides in glass [2]. Potential advantages include the formation of buried waveguides with smooth sidewalls and a reduction in the number of fabrication steps. Electron-beam (e-beam), irradiation of silica has also received significant attention [3] because a large refractive index change, >7×10−3 [4], can be induced in the material without the need for pre-sensitization techniques, such as hydrogen-loading. Structural rearrangements leading to the formation of colour-centres and densification of the material [5] have been reported as the origin for the refractive index change. The depth distribution of the e-beam effect inside the material is very important since it determines the refractive index profile, a key parameter in the design of optical devices.