Suppression of cladding mode coupling in Bragg grating using Ge2O-B2O3 codoped photosensitive cladding optical fibre

Abstract
A new type of photosensitive optical fibre codoped with Ge2O-B2O3 in both the core and cladding has been fabricated for applications in Bragg gratings. Coupling of the fundamental core mode into the cladding modes was suppressed with a narrow 3 dB bandwidth in the Bragg grating. An increase in photosensitivity was also achieved by using high reflectivity Bragg gratings imprinted without the need for any hydrogen treatment.