Integrated optoacoustic transducer

Optical methods for detection and generation of ultrasound have unique features attractive for high resolution imaging. Very small receiver elements in the order of 10 μm can be formed without compromising signal to noise ratio. Advances made during the recent years boosted the sensitivity of resonant optics devices for ultrasound detection. The detection limit of these devices outperforms that of a piezoelectric detector of similar size. Transmitter elements, utilizing thermoelastic effect, allow realization of nearly a point source for a wide bandwidth exceeding 100 MHz. These features could promote the development of very small 2D imaging arrays (less than 0.5 mm) with element spacing of 10 μm, operating at a bandwidth exceeding 50 MHz. Such a miniaturized ultrasound camera, providing real-time 3D images, would revolutionize interventional medical procedures such as angioplasty, and biopsy by providing real time guiding. However, there are still major challenges that have to be resolved, concerning the integration of ultrasound generation, ultrasound detection and signal delivery by optical methods, before a complete device operation could be demonstrated. In this work we describe our approach to device integration that addresses both issues of transmit/receive integration and optical signal delivery for arrays. An etalon resonator device for high frequency ultrasound detection was integrated with a thermoelastic film for optical generation of ultrasound. The integrated device forms a complete ultrasound transducer array. Basic pulse-echo characterization is demonstrated. A plastic graded index (GRIN) imaging fiber is suggested to deliver high density of optical signals between the device base and a remote imaging probe. A fiber of 1 mm diameter containing more than 6000 individual optical channels is used to connect the optical scanning setup and the etalon detector. Remote detection of acoustic test signals of a 50 MHz transducer is presented.