Fig. 1

Concept and principle of the FMF-chip-FMF mode/polarization switching system with fs-laser inscribed (de)multiplexer and silicon switch array. a The FMF-chip-FMF mode/polarization switching system with three basic functions, i.e. mode/polarization demultiplexing, multi-port switching/routing, and mode/polarization multiplexing. b, d The 1 × 2N mode/polarization (de)multiplexer consisting of a mode (de)multiplexer on the 3D silica chip and N PBSs. The inset in (d) shows the cross section of multimode port in the (de)multiplexer. c The topology-optimized 2N × 2N non-blocking switch on 2D silicon chip consisting of fewer 2 × 2 element switches and crossings. MUX: multiplexer; DEMUX: demultiplexer; MZI: Mach-Zehnder interferometer, PBS: polarization beam splitter