Optical fibre interferometric sensors using buffer guided light

A novel type of interferometric fibre optic sensor is described, based on a curved section of a buffered single-mode optical fibre. Interference occurs between the core-guided mode and the 'whispering gallery' mode guided within the fibre buffer. The fibre buffer coating thus serves as the sensing element. The technique is illustrated by its application to temperature measurement. A linear output is produced by using a two-wavelength phase-stepping technique.