Control of orbital angular momentum of light with optical fibers

We present a fiber-based method for generating vortex beams with a tunable value of orbital angular momentum from -1 (h) over bar to + 1 (h) over bar per photon. We propose a new (to our knowledge) method to determine the modal content of the fiber and demonstrate high purity of the desired vortex state (97% after 20 m, even after bends and twists). This method has immediate utility for the multitude of applications in science and technology that exploit vortex light states. (C) 2012 Optical Society of America