Demodulation techniques for two-mode elliptical-core fibre sensors

Demodulation methods are presented that allow measurement of the amplitude and the direction of dynamically varying environmental parameters with two-mode, elliptical-core fibre sensors. The wavelength dependence of the differential phase-shift between the and the LP₀₁ and the LP₁₁^even modes is used to obtain quadrature-phase-shifted signals at the sensor output. It is also shown that a two-fibre coupler attached to the output of the sensing fibre enables stable demodulation.