Design of on-fiber diffractive microrelief for efficient graded-index fiber mode excitation

The problem of energy-efficient excitation of high-order fiber modes is under discussion. Some examples of mode excitation using diffractive optical elements (DOEs) and on-fiber microreliefs are given. For the graded-index fiber modes an approach is proposed and a numerical procedure is described that allows calculating a microrelief height function that provides a phase incursion necessary for the energy-efficient excitation of the high-order modes. The results of numerical and optical experiments are presented that prove the appropriateness of the approach.