Long-period grating Michelson refractometric sensor

This paper presents a single-probe Michelson interferometer that uses mode coupling in a long-period grating to establish the two optical paths in a single optical fibre. The interferometer phase shift depends on the refractive index of the material that surrounds the fibre probe, with the phase sensitivity directly proportional to the probe length. A simple phenomenological model explains the experimental results obtained with a liquid level sensor and a refractive index sensor. Its temperature sensitivity depends on the type of fibre that constitutes the probe. With a 45 mm long fibre probe, it is -2.5 and 12.8 degrees degreesC(-1) for normal single mode fibre (SMF28) and germanium-boron co-doped fibre (PS1500), respectively.