Self-calibrated interferometric-intensity-based optical fiber sensors

This paper presents self-calibrated interferometric-intensity-based optical fiber sensors, which combine for the first time fiber interferometry and i ntensity-based devices into a single sensor system. The sensor involves an extrinsic Fabry-Perot (FP) interferometric cavity. The broadband light retu rned from the FP cavity is split into two channels in such a way that one c hannel has a coherence length much longer than the doubled air-gap separati on in the sensor so the Fl? generates effective interference, while the coh erence length in the other channel is so short that no effective interferen ce takes place. As a result, the optical signal in the channel with a long coherence length yields information about the Fl? cavity length while the s ignal in the other channel is proportional only to the source power, fiber attenuation, and other optical loss factors in the optical path. To elimina te fringe direction ambiguity and relative measurement limitations associat ed with interferometric sensors, the sensor is designed such that it is ope rated over the linear range between a valley and a peak of one interference fringe in the first channel. Moreover, the ratiometric signal-processing m ethod is applied for the signals in the two channels, to obtain self-calibr ating measurement to compensate for all unwanted factors, including source power variations and fiber bending losses. Various pressure and temperature sensors based on the self-calibrated interferometric/intensity-based schem e are designed, fabricated, and tested. Experimental results show that a re solution as high as 0.02% of full scale can be obtained for both the pressu re and temperature measurements.