Error analysis of dual wavelength quadrature phase demodulation for low-finesse Fabry-Pérot cavity based fibre optic sensor

An analysis of the errors in the dual wavelength quadrature phase demodulation technique for low-finesse Fabry-Pérot cavity based fibre optic sensor is presented. A simple numeric model for calculating the error is established. For sensors that experience only small cavity length changes during measurement, a simplified analytical expression of relative error is also derived. Errors for various sets of interrogation wavelengths are calculated and analyzed. The results show that two wavelengths with very slight difference should be chosen to avoid significant errors.