Fiber optic sagnac interferometer for characterizing ultrasound biomicroscopy transducers

There is a lack of hydrophones with sufficient spatial resolution and bandwidth for accurate measurements of ultrasound biomicroscopy transducers. Optical techniques achieve extremely fine spatial resolution and broad detection bandwidth. Furthermore, fiber optic technology can significantly improve portability and ease of use. We demonstrate a fiber optic Sagnac interferometer with an immersible probe head for characterizing high frequency ultrasound transducers. The fiber-coupled probe head contains optical components as well as the acoustic sensing surface, which is made from polydimethylsiloxane (PDMS). The entire probe head is encapsulated with PDMS for immersion applications. The fiber optic hydrophone is used to characterize a 100 MHz f/1 zinc oxide transducer (2 mm focal length). The Sagnac measurements show the transducer transmits a peak frequency of 105 MHz and a -6 dB bandwidth of 55 MHz. The detection bandwidth of the hydrophone is 350 MHz, limited by the photodetector bandwidth. The focal pattern is mapped by laterally scanning the transducer over a 50 × 50 pixel grid in 2 ¿m increments. The -3 dB transmit beam width is 14 ¿m along both x and y axes. These results demonstrate that a fiber optic Sagnac interferometer with an immersible probe head is well suited for characterizing ultrasound biomicroscopy transducers.