An etched two-mode fiber modal coupling element

When a fiber with topological structures built directly on the cladding is compressed longitudinally, lateral bends are induced. The lateral bends lead to mode coupling. We have built several etched two-mode fiber modal coupling elements to take advantage of this effect of bending. The resulting modal coupling elements are compact. More importantly, the percentage of power converting from one mode to another is variable by varying the axial compression. In this paper, we present a theoretical model describing the mode conversion in the etched fiber elements. Also discussed are the fabrication and testing of the modal coupling elements and the experimental confirmation of the theoretical model.