Dual parameter fiber optic sensor combining a Fabry-Perot and a Mach-Zehnder interferometer

A new concept for dual parameter fiber optic sensor has been developed and characterized, both in a two-fiber and single-fiber configuration. The liquid sensor measures ethanol concentration with a stimuli responsive hydrogel which constitutes a low finesse Fabry-Perot cavity, and refractive index with a Mach-Zehnder type fiber optic interferometer. The two-fiber configuration utilize a fiber optic 1310/1550 nm wavelength division multiplexer to separate the two parameters, while a versatile filtering algorithm extracts and separates the two parameters in the single-fiber configuration. No cross talk were observed for the measured parameters of free spectral range and refractive index for the two-fiber configurations, while for the single fiber configuration cross-talk were observed. The two configurations prove to be versatile dual parametric fiber optic sensor concepts for accurate detection of specific parameters, based on stimuli responsive hydrogels.