Abstract

The writing of fiber Bragg gratings through the coating has important implications for the mass production of these devices. For instance, the time-consuming steps of stripping and recoating of the grating (potentially leading to fiber strength degradation), can be completely eliminated resulting in a simpler, more efficient and lower cost fabrication process. In the first demonstration of writing Bragg gratings through the coating, up to ~3 dB Bragg gratings were written through a UV-transparent acrylate-based 25 μm thick coating at 257 nm [1]. Subsequently, other researchers demonstrated a ~1 dB fiber Bragg grating written through a standard coating using 334 nm light [2]. Because the absorption band at 334 nm is much weaker than at 244 nm, these gratings required a very high germanium concentration (~20 mol%) and the addition of boron as a codopant to increase the photosensitivity of the fiber. The high level of germanium makes it difficult to achieve low-loss splices to standard communications grade fiber. Here we report for the first time highly reflective (99.99% Reflectivity, -40 dB transmission) Bragg gratings written through a novel polymer coating using a photosensitive germanium-doped fiber with 5 mole% germania.

© 1997 Optical Society of America