All-fiber acousto-optic frequency shifter excited by focused surface acoustic waves

A fiber-optic frequency shifter that couples light between two spatial modes is discussed. The acoustic flexural wave that provides the coupling is excited in the fiber by pressing it against the surface of a LiNbO(3) substrate at a location where a surface acoustic wave is focused by a curved interdigital transducer. This results in an excitation arrangement that is not destructive and provides high efficiency.