Highly sensitive fiber laser ultrasound hydrophones for sensing and imaging applications

We have developed highly sensitive photonic ultrasound hydrophones based on polymer-packaged dual-polarization-mode fiber lasers. The incident ultrasound wave is scattered by the polymer cylinder due to the difference in elastic property. The scattered wave can drive harmonic vibration of the cylinder and result in optical response in terms of beat-frequency variation of the laser output. Experimental results exhibit a broadband ultrasound response at frequencies below 1 MHz. The individual vibration modes are excited by the ultrasound waves with different efficiencies, yielding a frequency-dependent response. A hydrophone with a diameter of 5 mm presents a detection limit of 2  mPa/Hz^1/2 at 200 kHz. We further demonstrate its capability of ultrasound imaging for applications in underwater acoustics and sonar systems.