Abstract

Guided-light sources with electronically tunable frequency shift or offset are needed as local oscillators in heterodyne integrated-and fiber-optic communication and sensor systems [1], [2]. A number of schemes for producing such frequency-shifted light sources have been reported [3-16]. One of the attractive schemes utilizes guided-wave acoustooptic (AO) Bragg diffraction [9] in which the frequency of the diffracted light is shifted from that of the incident light by the acoustic frequency. One of the unique features of this AO scheme is its inherent single-sideband property. We had earlier performed AO frequency shifting experiments using the surface acoustic waves (SAW) in planar-, crossed channel-, and spherical-waveguides in LiNbO₃ [9-11, 15, 16]. However, the specific device structures utilized all suffer from an undesirable characteristic in that the propagation direction of the frequency-shifted light varies with the frequency of the acoustic wave. This undesirable characteristic will be especially acute in a single-mode fiber optic system in which the very small cross-section of the fiber core is fixed in space, as it will severely limit the useful bandwidth of frequency shift.

© 1989 Optical Society of America