High-sensitivity cryogenic fibre-Bragg-grating temperature sensors using Teflon substrates

Low-temperature sensing was studied using a fibre Bragg grating fixed on Te flon substrate that has a large thermal expansion coefficient. The waveleng ths of reflected light from 1.55 mum fibre Bragg gratin gs were measured in the temperature range from 77 to 300 K. By bonding the fibre Bragg grating in between two Teflon substrates, the temperature sensitivity of 39 pm K-1 was obtained at 77 K, which is 1.5 times higher than that of the sensor us ing a poly(methyl methacrylate) substrate. At room temperature, the sensiti vity increased to 150 pm K-1. For a more compact structure using one substr ate only, the temperature sensitivity decreased by 5% compared with the sen sor using two Teflon substrates. Comparisons with theoretical values are al so discussed.