157-nm Photosensitivity in Germanosilicate Waveguides

In standard optical communication fiber, low Ge-dopant levels (~3%-GeO2) preclude strong photosensitivity responses, restricting index-of-refraction changes to 1-4 × 10-4 [1,2]. Type II index changes that rely on high laser fluence are less attractive because of material damage [3,4]. Therefore, sensitization techniques such as hydrogen loading [5], high germanium concentration [6], and flame brushing [7] are frequently employed to provide commercially attractive index-of-refraction changes of >10-3. However, this improved sensitivity trades against poor coupling efficiency and inconvenience when exposed fibers are connected into ordinary telecommunication networks.