Fiber-Optic Fabry-Perot Phase Shifted Interferometer Using Modal Demultiplexing

A fiber-optic phase-shifted Fabry-Perot interferometer (PS-FPI) using a modal phase shifter (MPS) and modal demultiplexing is demonstrated. The PS-FPI is used as a temperature sensor to obtain two output fringe sets as a result of a 6°C rise in temperature. A controllable phase shift between the fringe sets is obtained using the MPS and is beneficial in quadrature demodulation of measurand induced sensor signals which can extend the unambiguous range beyond half a fringe. Located before the sensing cavity, the MPS introduces a phase shift between the LP01 and LP11 modes. These modes travel to the FP cavity to produce interference fringes. This results in a few-mode sensor system having 2 orders of magnitude higher sensitivity than conventional few-mode systems, with a worst case voltage signal to noise ratio of 16.9 dB for a 0.5°C rise in temperature.