Wide-band operation of horns for excitation of acoustic modes in optical fibers

Acousto-optic interaction in fibers between optical modes and acoustic waves has been investigated recently by several groups. Coupling has been demonstrated between spatial modes in two-mode fibers as well as between polarization modes of high birefringence fibers. Most publications have reported results for a single acoustic frequency without discussing the frequency response of such devices. This paper reports an experimental investigation on the frequency behavior of horns, in particular aimed at wide band operation of devices coupling optical spatial modes by acoustic flexural waves in the fiber. This is provided by longitudinal waves impinging on the horn tip. Results for fused silica horns as well as aluminum horns are reported.