Metasurface‐Based Fiber‐to‐Chip Multiplexing Coupler

Abstract Here, a metasurface‐based fiber‐to‐chip multiplexing coupler is presented that can realize flexible mode conversion and multiplexing coupling between few‐mode fibers and on‐chip single‐mode waveguides. The proposed approach makes use of the symmetrical characteristics of fiber eigenmodes and high freedom of light phase manipulation to obtain the functional phase distribution of metasurfaces. The use of cylindrical nanopillar as metasurface nanostructures ensures its polarization independent optical response. Several fiber‐to‐chip multiplexing couplers are demonstrated by using the angular spectrum methods and the finite‐difference time‐domain (FDTD) simulations. It is found that the two or three modes can be flexibly demultiplexed and then be coupled into the corresponding on‐chip waveguides with low crosstalk. Further, two possible fabrication schemes for multiplexing couplers are proposed and then the related fabrication tolerances and misalignment effects are evaluated and discussed. Compared with traditional on‐chip couplers, metasurface‐based couplers have advantages of ultracompact footprint and low crosstalk. Such study explores the application of metasurfaces in multiplexing coupling between few‐mode fiber and on‐chip single‐mode waveguides, which is expected to break through the bottleneck of current mode‐division multiplexing technologies in optical interconnection and meet the ever‐increasing demand for large data throughput of the photonic integrated chips.