Parameter design of signal processing for transmission/reflection-type hybrid extrinsicFabry–Perot interferometric optical fiber sensors

Abstract

A transmission/reflection-type hybrid extrinsic Fabry–Perot interferometric (TRHEFPI)optical fiber sensor presents transmission-type and reflection-type sensor signalssimultaneously, and measurement directions can be robustly distinguished withthe phase lead or lag of the linear combination signal from the original sensorsignal. This sensor principle compensates for the ambiguous distinction of themeasurement directions and direction changes of conventional interferometric optical fibersensors, including extrinsic Fabry–Perot interferometric optical fiber sensors, dueto the exclusive use of fringe counting in signal processing. Designing a sensorcoefficient in the linear combination signal is one of the most important works insignal processing for the TRHEFPI optical fiber sensor because the magnitudeof the phase shifts depends on the sensor coefficient. A design method of thesensor coefficient is presented in this research. The method was verified withexperimental sensor signals and applied to strain measurement experiments. A method ofabsolute measurement using the TRHEFPI optical fiber sensor is also presented.