Ethanol sensing properties of PMMA-coated fiber Bragg grating

In this paper are reported some preliminary results about the sensing properties of a single-mode silica fiber Bragg grating (FBG) coated with a poly(methyl methacrylate) (PMMA) thin layer are reported. The PMMA coating on the fiber grating was deposited by using a micro-pipette bulb as mechanical vessel filled with polymer solutions in acetone. For ethanol sensing tests, the FBG sensor was placed in a measurement chamber equipped with a controlled gas system, then the output response was acquired using an optical spectrum analyzer which also provided laser illumination. Absorption of ethanol from the gas phase onto the PMMA layer causes swelling which can be recorded as an extension/compression of the fiber grating. As a consequence of this transduction effect, the peak shift response can be related to the ethanol concentration. Based on this simple principle, detection of low alcohol concentrations can be easily obtained.