Fiber-optic Sagnac interferometer for the observation of Berry's topological phase

Abstract

Few experiments have been reported for the observation of Berry’s phase for the photon. This may be due to the difficulty of configuring suitable experiments. We start by repeating previous work on the observation of the optical activity of a helically wound fiber coil in the transmissive mode, but then we go on to demonstrate that when the light is reflected back through the same coil from a mirrored surface, it cancels this optical activity. We also report on a new experimental configuration in which a helical fiber coil is built into the loop of a Sagnac interferometer. The changes in Berry’s phase acquired by the two counterpropagating beams can be varied by stretching the coil with the result that fringes are produced at the output. One of the major benefits of this experimental setup is that it enables observations of Berry’s phase to be made for light in any state of polarization.