Bimodal grating coupler design on SOI technology for mode division multiplexing at 1550 nm

In this paper, we evaluate by means of simulation and experimentally the simultaneous coupling of the LP_01x-LP_11ax fiber modes and the TE₀-TE₁ nanophotonic SOI waveguide modes using a grating coupler for a two-mode fiber at 1550 nm. Both the grating width (ranging from 10 µm to 15 µm) and the grating vertical profile have been considered in the design procedure. The optimum design (14 µm width and 609 nm grating period) has been selected in terms of coupling efficiency (both LP_01x-TE₀ and LP_11ax-TE₁), compactness and tolerance to lateral misalignments between fiber and coupler. The LP_01x-TE₀ and LP_11ax-TE₁ modes achieved coupling efficiencies of 49% and 45%, respectively.