Grating assisted mode selective optical waveguide coupler

Currently, mode division multiplexing (MDM) based on different modes or mode groups of a multi-mode (MM) waveguide are explored as individual transmission channels in order to keep up with the increasing data traffic demand in backbone single-mode (SM) fiber optic telecommunication applications. For the implementation of MDM transmission networks one key challenge is the development of appropriate waveguide couplers. Therefore, in this work we discuss a grating assisted optical waveguide coupler to multiplex and demultiplex individual modes of MM waveguides. The proposed optical waveguide coupler is based on a SM waveguide with a grating structure and an adjacent unmodified MM waveguide. Simulations verify that by using evanescent field coupling and an appropriate grating structure light from the SM waveguide can be coupled selectively into an arbitrary mode of the MM waveguide with high efficiency and low crosstalk. Consequently, the proposed optical waveguide coupler may allow in the future MDM implementation with a large number of mode channels with low insertion loss, mode dependent loss and also modal selectivity.