Strain-induced phase-matching and tunability of acoustic gratings in fibers

We study the effect of strain on the properties of a one-dimensional acoust ic grating: a tapered optical fiber with a periodically varying diameter. I ts spectral response has a strong frequency stop band for flexural waves. C hanging the tension of the fiber changes the wave velocity, and so modifies the acoustic response of the grating. The resulting tunability of the stop band over a wide frequency range is demonstrated experimentally. Furthermo re, the stop band can almost disappear completely due to a strain-induced p hase-matching phenomenon. Such structures are suitable as frequency-selecti ve acoustic mirrors in acousto-optic fiber devices. (C) 2001 American Insti tute of Physics.