Simultaneous displacement and temperature sensing using a white light interrogated low finesse cavity in line with a fiber Bragg grating

A fiber optic sensing system for simultaneous measurement of displacement and temperature is presented. It is based on the use of a low finesse extrinsic Fabry-Perot cavity and a fiber Bragg grating for temperature compensation. A white light tandem interferometric technique is used to recover the signal from the low finesse cavity, providing both fringe visibility and phase measurements. These, together with the fiber grating signal, give two equations that can be used to simultaneously determine temperature and displacement. Theoretical analysis of the sensing scheme is performed. Experimental results are presented which validate theoretical predictions and also demonstrate the feasibility of this sensing system in practical applications.