Eccentric Design of Fabry-Perot Interferometer for High Sensitivity and Broadband Ultrasound Sensing

Ultrasound sensing with broadband and high sensitivity enables high resolution and large penetration in ultrasound imaging such as photoacoustic imaging and nondestructive testing. Traditional piezoelectric ultrasound transducers suffer from limited bandwidth and sensitivity. On the contrary, fiber-based Fabry-Perot (F-P) interferometer exhibited very high sensitivity on vibrations, which potentially acted as a high sensitivity ultrasound sensor. However, due to the high quality factor of silica in fibers, its reverberation lasts a long time, leading to a narrow bandwidth and a high noise level. In this research, we designed a multi-core fiber sensor with the eccentric cores. The diameter of the fiber was investigated while the distance between the core and the fiber surface remained 40 μm for optical signal integrity. Finite element modeling demonstrated that a 500 μm fiber provides reasonable signal to noise ratio. At eccentric positions, the actual sensing signal is almost identical as that at the center, whereas the reverberating noise decreased from -1 dB to -28 dB. The proposed F-P sensor based on thick optical fiber with eccentric cores exhibited high sensitivity and broadband response compared to either piezoelectric sensors or conventional fiber sensors, pioneering a promising future of ultrasound sensing.