Low bend loss in tightly-bent fibers through adiabatic bend transitions

We demonstrate low bend loss for tightly bent optical fibers by winding the fiber around a mandrel designed to follow an adiabatic transition path into the bend. Light in the fundamental core-guided mode is smoothly transferred to a single cladding mode of the bent fiber, and back to the core mode as it leaves the bent region again. Design of the transition is based on modeling of the propagation and coupling characteristics of the core and cladding modes, which clearly illustrate the physical processes involved.