Torsion sensor based on a figure-of-eight cavity fibre laser

A figure-of-eight based fibre laser cavity is proposed for the measurement of torsion.In one of the loops a section of photonic crystal fibre is inserted, acting both as an optical filter and the sensing head.The laser emission depends on the optical filter polarization and length.A single lasing band is achieved with a full width at half maximum of ∼1.72 nm.The proposed sensor presents sensitivity to torsion of 7.13 pm/degree over a range of 180 • .This configuration can also be used to measure optical power variations.Besides, due to the properties of the optical filter this sensor presents low sensitivity to temperature.