Lensless focusing with an array of phase-adjusted optical fibers

A bundle of monomode fibers can be used for transmission of coherent radiation at power levels beyond the damage threshold of an individual fiber. The coherence at the bundle output can be reestablished by proper correction of the phases at the individual fiber ends. For a phase adjustment that leads to a convergent wave the focusing efficiencies are calculated for various geometric parameters of the fiber bundle. For practical situations concentration of almost 40% of the power into the focal spot seems realistic.