Resonant hydrophones based on coated fiber Bragg gratings. Part II: Experimental Analysis

Here, we report on recent experimental results obtained with Fiber Bragg Grating (FBG) hydrophones for underwater sound pressure detection. Investigated optical hydrophones consist of FBGs coated with ring shaped polymers of different size. Coating material has been selected to provide mechanical amplification through a low elastic modulus combined with acoustic impedance matching. Underwater acoustic measurements carried out in the range 4-35KHz reveal a resonant behaviour depending on the coating size. This behaviour is consistent with numerical analysis performed using finite element method and presented in part I. In addition, good linearity was observed versus local sound pressure demonstrating a minimum detectable sound pressure of few Pascal