P5F-2 Improved Fiber Optic Hydrophone Sensors

Broadband fiber optic hydrophones are an attractive solution for characterization and measurement of high intensity acoustic fields which are encountered in clinical ultrasound applications upto 100 MHz. A small sensing area avoids spatial acoustic field averaging and provides sub-millimeter resolution required for enhanced imaging in diagnostic applications. In this paper we present analytical and experimental performance results of broadband down-tapered fiber optical hydrophone sensors based on reflection type sensing and intensity detection scheme. Both uncoated as well as gold coated down-tapered fibers have been fabricated. Experimental results employing these fiber sensors for a 1.6 MHz acoustic signal, at 1 MPa pressure have corroborated the analytical predictions that thin metal coating can improve the sensitivity by almost 15 dB over that of uncoated tapered fiber. Such improvement in sensitivity is due to enhanced reflectance from the thin metal layer that senses the incident acoustic pressure.