Fiber optic Bragg grating sensor based on hydrogels for measuring salinity

We report a new type of optical salinity sensor with a fiber Bragg grating (FBG) coated with hydrogels. The sensing mechanism in this device is based on mechanical stress that is induced in the chemically sensitive water swellable polymers (hydrogels) coating when the water escapes from it. The stress in the hydrogels coating stretches and shifts the Bragg wavelength of the FBG. Varying the composition of the gel, the sensor can be used to response to different trigger stimulus. Here the sensors for measuring salinity are demonstrated.