Femtosecond laser inscribed Bragg grating arrays in long lengths of polymer optical fibres; a route to practical sensing with POF
The first practical demonstration of readily useable fibre Bragg gratings in long lengths >20 m) of polymer optical fibres (POFs) is reported; this is an increase in fibre length that exceeds two orders of magnitude for use in the C band. A low loss perfluorinated fibre and a femtosecond laser, direct write method to inscribe gratings at two different wavelengths are used. Gratings are fabricated to operate at ~800 nm, where the optical loss is minimal, and in the C band, commonly used with traditional optical fibres for the majority of telecommunication applications. The development of POF Bragg gratings inscribed in long fibre lengths is the first important step for the integration of practical sensing devices and could promote the use of multiplexed POF sensors. The sensors were tested and characterised and demonstrate their compatibility with a commercial Bragg grating demodulator.