Fiber-optic frequency shifter

Abstract

A new type of fiber-optic frequency shifter was studied theoretically and experimentally. It consists of a birefringent optical fiber embedded in an aluminum acoustic waveguide. Light with a wavelength of 1.3 μm enters the input fiber polarized along one of its principal axes and is coupled to the orthogonal axis by the induced birefringence produced by a traveling ultrasound wave. This acousto-optic interaction shifts the frequency of the light by the frequency of the acoustic wave, in the vicinity of 1 MHz. Different prototypes were fabricated, and sideband suppression of 30 dB and carrier suppression of 26 dB were measured, using 500 mW of electrical driving power. The fabrication of this frequency shifter was made possible by the development of a process that allowed for the first time the embedding of optical fibers in aluminum. The resulting device is very sturdy and easy to fabricate, in contrast to alternative types of fiber-optic frequency shifters.