Multiplexed Fiber Bragg Gratings as a Substance Sensor

We demonstrate the application of polymer-coated fiber Bragg gratings (FBGs) as a substance sensor, in which different polymers are used to achieve simultaneous measurement of the substance and temperature. As an example of polyimide-coated grating for detecting soluble substances, the sensitivities of the grating on the sugar and potassium chloride concentrations are 0.0012 nm/°Bx and 0.0126 nm/M, respectively. The temperature sensitivities of the acrylate and polyimide-coated FBGs are 0.0102 and 0.0094 nm/°C, respectively. The technique provides an approach to detect different water-soluble substances without prior knowledge once a calibration curve is developed.