Abstract
We report the extraordinary result of rapid fibre Bragg grating inscription in doped polymer optical fibres based on polymethyl methacrylate in only 7 ms, which is two orders of magnitude faster than the inscription times previously reported. This was achieved using a new dopant material, diphenyl disulphide, which was found to enable a fast, positive refractive index change using a low ultraviolet dose. These changes were investigated and found to arise from photodissociation of the diphenyl disulphide molecule and subsequent molecular reorganization. We demonstrate that gratings inscribed in these fibres can exhibit at least a 15 times higher sensitivity than silica glass fibre, despite their quick inscription times. As a demonstration of the sensitivity, we selected a highly stringent situation, namely, the monitoring of a human heartbeat and respiratory functions. These findings could permit the inscription of fibre Bragg gratings during the fibre drawing process for mass production, allowing cost-effective, single-use, in vivo sensors among other potential uses.
Highlights
Fibre Bragg gratings (FBGs) can be inscribed in silica optical fibres in o1 min, but the grating inscription time in polymethyl methacrylate (PMMA) optical fibres is much longer, and in some polymer optical fibres (POFs), this process takes 41 h1,2
We demonstrate the fabrication of a single-mode POF using a unique core dopant, diphenyl disulphide (DPDS), which is responsible for both the increase in the core refractive index and the photosensitivity
We record the fabrication of FBGs that are UV-inscribed in 7 ms, which is over 140 times faster than previous results reported for PMMA fibres[3,4], and we report the experimental results of a direct comparison of silica and polymer FBGs for monitoring vital signs
Summary
Fibre Bragg gratings (FBGs) can be inscribed in silica optical fibres in o1 min, but the grating inscription time in polymethyl methacrylate (PMMA) optical fibres is much longer, and in some polymer optical fibres (POFs), this process takes 41 h1,2. The shortest reported inscription time using a 325 nm He-Cd laser is 1 s3,4, while a much faster grating inscription of 15 ns (1 pulse) was recently reported using an expensive high peak-power 248 nm excimer laser[5]. These times are too slow for the grating inscription to be carried out during the fibre-drawing process at a reasonable cost. We record the fabrication of FBGs that are UV-inscribed in 7 ms, which is over 140 times faster than previous results reported for PMMA fibres[3,4], and we report the experimental results of a direct comparison of silica and polymer FBGs for monitoring vital signs.
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