Stabilization of the speckle pattern of a multimode fiber undergoing bending

The propagation of light in a multimode optical fiber waveguide results in speckle, a complicated mapping of the input field onto the output field. The speckle pattern changes as the fiber undergoes twists and bends. We show theoretically and demonstrate experimentally that changes in the mapping caused by bends in one region of the fiber can be compensated with bends applied along a fixed region of the fiber. In this way the output speckle pattern of the fiber can be stabilized. In this method it is supposed that the modes evolve adiabatically without intermixing and that the analytical dependence of perturbed propagation eigenvalues of the modes follows R(-2) behavior, where R is the local value of bend radius. (C) 1996 Optical Society of America