Photosensitive polymer optical fibres and gratings

Abstract

This paper reports the development of photosensitive polymer optical fibres for gratings. These fibres, processed by the preform drawing technique, are composed of polymethylmethacrylate cladding and methyl methacrylate copolymer cores. Three core systems with enhanced UV sensitivity are proposed, including benzyl methacrylate (with strong UV absorption) co-monomer contained, benzophenone (photo-initiator)-doped, and trans-4-stilbenemethanol (a molecule which undergoes photo-isomerization)-doped cores, respectively. These cores display significant absorption at wavelength longer than ∼250 nm in which the cladding PMMA is basically transparent. Irradiation tests disclosed the occurrence of photo-induced change in absorption upon exposure to UV at wavelength longer than 250 nm for these cores, ie, at 260 and 280 nm for benzyl methacrylate contained, at around 320 nm for both benzophenone-doped and trans-4-stilbenemethanol-doped. The photo-induced change in refractive index was detected on trans-4-stilbenemethanol-doped core polymer by the Prism Coupler. The photosensitivity of this doped system was demonstrated by Bragg gratings in the core of the fibre fabricated by use of a pulse laser at 325 nm with a low photo-energy and comparatively short exposure time.