Relative Humidity Sensor Based on Double Sagnac Interferometers and Vernier Effect

A double Sagnac interferometer (DSI) and vernier effect sensor for relative humidity (RH) is proposed experimentally implemented, in which two single interferometers (SI1 SI2) cascaded parallel to construct the structure of sensor. Owing approximate free spectral range (FSR) SI1 SI2, can produce fundamental harmonic effect. Theoretical analysis shows that RH sensitivity only related lengths polarization-maintaining fibers (PMFs). The experimental results show 30∼80%RH, sensitivities envelope reach −0.48 nm/%RH, 60 times higher than measured by (8 pm/%RH). are consistent with theoretical analysis. has superiorities high sensitivity, good repeatability, simple fabrication, compact size, it potential applications areas biopharmaceuticals, environmental monitoring, food processing, microbial sensing.