High Resolution Ultrasonic Images by Miniaturized Fiber-Optic Probe

A new Micro-Opto-Mechanical System (MOMS) probe on optical fiber is presented. High miniaturization levels are reached in the MOMS devices (fiber-optic emitters and detectors with minimum diameter around 350 and 250 mu m respectively). The transmitting element consists of an optical fiber with a graphite-compound absorbent layer on the tip. The receiving element is an extrinsic fiber hydrophone based on a Fabry-Perot interferometer, the thickness of which is modulated by ultrasonic signals. The possibility to use optoacoustic sources in conjunction with the fiber-optic acousto-optical detectors within a minimally invasive probe is demonstrated by successfully measuring the ultrasonic echo reflected from a fingerprint made of cornstarch flour and from a silicon substrate with micrometric machining. The ultra-wide bandwidth and the high frequencies allowed by photoacoustic generation, in conjunction with the extreme miniaturization derived from the MOMS technology, can generate images at very high resolution and permits to obtain different "ultrasonic views" of the investigated object.