Abstract

A number of acousto-optic fiber devices have been described previously.^1,2,3 Here we report a new acousto-optic device based on tapered single-mode fiber (Fig. 1). In the taper, the fundamental mode spreads out from the core to fill the narrow uniform waist, which also guides many higher-order cladding modes. A unidirectional flexural acoustic wave is excited in the taper by using a piezoelectric-transducer (PZT) disk and concentrator horn fixed to the fiber near the taper. Its frequency f is adjusted to match the acoustic wavelength to the beat length between fundamental and second modes in the waist, causing light to couple between them. The taper transition acts as an additional acoustic concentrator. In the present form, light coupled to the second mode by the acoustic wave remains in the cladding downstream of the taper and is absorbed by the fiber coating, whereas light left in the fundamental mode is recaptured by the fiber core. The device therefore functions as an amplitude modulator or tunable filter.

© 1994 Optical Society of America