ULTRASONIC HYDROPHONE BASED ON SHORT IN-FIBER BRAGG GRATINGS

We investigate the feasibility of using in-fiber Bragg gratings for me asuring acoustic fields in the megahertz range. We found that the acou stic coupling from the ultrasonic field to the grating leads to the fo rmation of standing waves in the fiber. Because of these standing wave s, the system response is complex and, as we show, the grating does no t act as an effective probe. However, significant improvement in its p erformance can be gained by use of short gratings coupled with an appr opriate desensitization of the fiber. A noise-limited pressure resolut ion of approximate to 4.5 x 10(-3) atm/root Hz was found. (C) 1998 Opt ical Society of America.