Frequency shifting in optical fiber using a SAW horn

The authors present an in-fiber frequency shifter for optical fiber which uses flexural acoustic waves to induce mode coupling between the two optical modes of a dual-mode, elliptical-core fiber. A sharply tapered surface-acoustic-wave horn is used to excite these waves in the fiber, providing a robust, efficient acoustic source. Optical mode filters at the input and output ensure spectral purity of the frequency-shifted light. A 6.3-MHz frequency upshift in 1.3-μm light with 400-mW input power, with a 35-dB sideband suppression, was demonstrated. Recently studied methods for improving the sideband suppression through mode-filtering techniques are also discussed