Microwave photonic filtering for fibre optic interferometer sensors

Microwave photonic filtering has been used to explore new potential directions in sensing technology. In this work a microwave photonic filter (MPF) has been proposed to transfer the optical response of a fibre optic interferometer into the microwave frequency domain and thus to overcome some of the potential limitations imposed by optical measurement. The MPF used consists of a fibre optic Fabry-Perot interferometer (FPI) as the sensing element as well as a spectrum slicer, and a dispersive fibre link as a frequency down-conversion factor. The shift of the central frequency of the MPF passband was modulated by the change of the effective cavity length which can be monitored to demodulate the sensing parameters. FPIs with different cavity lengths were used with different lengths of the fibre link to test the performance and the feasibility of the sensing system. By using the MPF, measurements of temperature and refractive index were successfully demonstrated with adjustable sensitivity and operational frequency.