Why is multimode fibre used for Temperature sensing?
Since multimode fibre has a larger core (and a larger numerical aperture) you are able to launch more power into the fibre than for single mode fibre. The larger core size also results in a higher threshold for nonlinearities, which can cause errors in the measurement of temperature of the fibre. Distributed temperature sensing measures the backscattered light along the fibre. However, the amount of backscattered light is a very tiny proportion of the initial laser pulse and so in order to get enough backscattered signal to make a temperature measurement it is very important to have as much power as possible in the initial laser pulse. Given its larger core size and higher threshold for nonlinearities, multimode fibre provides a large improvement in backscatter signal power over singlemode fibre.
