Ultrasensitive Fiber Optic Ethanol Gas Sensor Based on Anisotropic Nematic Liquid Crystal Film-Embedded Cascade Sagnac Interferometers

In this study, we investigated a novel ethanol gas sensor based on anisotropic nematic liquid crystal (NLC) film-embedded cascade Sagnac interferometers (SIs). NLC film was employed as both the sensing material of ethanol gas and the generator of birefringence in an SI, which acted as the sensing arm. A section of polarization-maintaining fiber (PMF) was utilized to construct another SI, which worked as the reference arm. The sensing arm and reference arm were cascaded together to achieve the amplification of measurement sensitivity in the patterns of parallel and tandem, respectively. Experimental results demonstrated that the parallelly cascade SIs showed a sensitivity of 12.512 pm/ppm with a magnification factor of 5.779, while the tandemly cascade SIs showed a sensitivity of 11.748 pm/ppm with a magnification factor of 5.445. The proposed ethanol gas sensor exhibited the advantages of compact structure, high sensitivity, small size, and low cost could present a secure and advantageous approach for the leakage detection of ethanol gas.