The On-Chip Solutions to Mode Separation and Crossing of Vertical Multi-Modes in Silicon Waveguide

Solutions to mode separation and crossing of vertically distributed multi-modes inside silicon nanophotonic integrated devices are investigated. Mode demultiplexers based on both echelle gratings and asymmetric directional couplers are demonstrated. A device with curved reflectors which allows multi-modes to cross simultaneously is also designed. The simulation results based on the 3D Finite-Difference Time-Domain methods show that the echelle grating allows altogether 9 channels of different modes and wavelengths to be separated with crosstalks no more than -30 dB. The curved reflectors works properly for crossings of three modes, and the crosstalks are merely around -40 dB.