Echelle grating based mode demultipexer for vertical mode-division multiplexing.

We have proposed a mode multi/demultiplexer based on the echelle grating suitable for vertical multimode bus waveguide. Compared with the lateral multimode waveguide, the vertical scheme has much smaller bending radius which leads to compact system size. The guided modes in the multimode waveguide are able to be separated simultaneously by the echelle grating since they experiences different propagation constants in the free propagation region. Due to the high performance of the grating itself, the theoretical modal crosstalk can be as low as around -40dB. Moreover, we demonstrate the possibility to integrate WDM together with MDM by using only one echelle grating, which is favorable in real applications considering the compact system setup and simple design rules.