All fibre hydrogen sensing through palladium coated long period and tilted gratings

All optical hydrogen detection techniques are required to provide a safe compact monitoring system within existing and future hydrogen technologies. The well documented chemochromic changes induced in palladium through hydrogen absorption provide a mechanism for an optical detection of hydrogen. Long period gratings [LPGs], with absorption bands sensitive to cladding – free space refractive index contrast, provide a means for monitoring this absorption. A thin (~30nm) coatings of palladium deposited onto the fibre has been demonstrated to provide a measurable wavelength shift in the position of the LPG lossband when exposed to low (~1%) concentrations of hydrogen. The dependency of hydrogen concentration, coating thickness, temperature and the presence of pollutant chemicals will be explored. An alternative method of monitoring the chemochromic hydrogen absorption through the use of tilted fibre Bragg gratings will also be addressed with particular reference to the resultant polarisation dependencies.