Multiple strain state measurements using conventional and absolute optical fiber-based extrinsic Fabry-Perot interferometric strain sensors

A modified design of the extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor to allow complete characterization of multicomponent strain fields is proposed, The novel EFPI includes a sensor head with two input fibers such that the respective interference pattern from the end face of the output multimode fiber are in quadrature. Any strain field possessing a component along the line joining the axes of the two fibers causes the initial phase difference to be modulated. The measured change in phase difference is employed to determine this transverse component of the strain field. Absolute, rather than differential measurements of strain are possible using the absolute EFPI sensing system. Applications of the modified sensor-head to smart materials and structures are discussed.