Optical fiber twist sensor with two orthogonally oriented mechanically induced long-period grating sections

We propose and demonstrate, for the first time, an optical fiber twist sensor consisting of two mechanically induced long-period grating sections, whose birefringent axes are mutually orthogonal. The twist sensor, whose temperature stability is supposedly high and sensitivity is tunable by pressure, is based on the change in the loss peak separation due to the twist-induced polarization rotation.