  One of the greatest challenges in utilizing multimode optical fibers is
mode-mixing and inter-modal interference, which scramble the information
delivered by the fiber. A common approach for canceling these effects is to
tailor the optical field at the input of the fiber to obtain a desired field at
its output. In this work, we present a new approach which relies on modulating
the transmission matrix of the fiber rather than the incident light. We apply
computer-controlled mechanical perturbations to the fiber to obtain a desired
intensity pattern at its output. Using an all-fiber apparatus, we demonstrate
focusing light at the distal end of the fiber and conversion between fiber
modes. Since in this approach the number of degrees of control can be larger
than the number of fiber modes, it allows simultaneous control over multiple
inputs and multiple wavelengths.
