Multiplexing Sensing Based on Spectrum-Sliced Microwave Photonic Filter Utilizing Optical Path Difference Matching

A multiplexing fiber-optic interferometer (FOI) sensing system interrogated by microwave photonic filter (MPF) technique is proposed and experimentally demonstrated. Four single mode fibers with different lengths act as the sensing heads. The optical path differences (OPDs) between any two of these fibers are longer than the coherence length of the light source, resulting that there is no interference pattern generated in the optical domain. However, with the help of a tunable Mach-Zehnder interferometer (MZI), two or more fibers can be selected to form Michelson interferometers (MI) since the OPDs can be adjusted by the MZI. The selected MI is affected by the parameters to be measured, causing the free spectrum range (FSR) or the visibility change of the interference pattern, which are mapped into the central frequency shift or the peak power varies of the generated MPF. Hence, the measurements can be recovered by recording the change of the MPF. The experimental results exhibit that a single MI formed by two fibers can be selected freely to measure temperature, axial strain and curvature, respectively. Moreover, two MPFs can be observed meanwhile to achieve dual parameters sensing simultaneously.