The split-cavity cross-coupled extrinsic fiber interferometer

Abstract

Fiber optic interferometric sensors have been used to measure a number of physical measurands like strain and temperature. Among the different interferometric sensor configurations in use today, the Fabry-Perot interferometer has been shown to have a high sensitivity. The extrinsic Fabry-Perot sensor (EFPI) is a very good candidate for smart structure applications. In this thesis, a new configuration of the extrinsic Fabry-Perot interferometer is developed and demonstrated. This new configuration, based on four-beam interference, utilizes two EFPI sensor heads on a single directional coupler in a Split-cavity Cross-coupled Extrinsic Fiber Interferometer (SCEFI) arrangement. This sensor configuration eliminates the need for biasing the phase difference at the quadrature point. The spectrum analysis scheme, devised for signal demodulation of the SCEFI output allows a linear readout of the phase shift. Both dynamic and static phase shifts are considered. The spectrum analysis scheme developed in this thesis, also allows independent measurements of the phase shift in the two sensor heads. This leads to the multiplexing of two sensors, using a single source and a single coupler. The application of the SCEFI to two-sensor multiplexing is demonstrated experimentally in this thesis. Other significant applications of this new sensor configuration are also discussed.