Mode demultiplexer based on cascaded vertical waveguide directional coupler

The invention provides a mode demultiplexer based on a cascade vertical waveguide directional coupler, which takes a silicon wafer as a substrate and is composed of three waveguides Core1, Core2 and Core3, and the three waveguides are of polymer structures from bottom to top; the Core1 is a multi-mode waveguide, is positioned in the middle of the three-dimensional mode multiplexer, and supports E11, E12 and E21 modes; and the Core2 and the Core3 are few-mode waveguides and support an E11 mode and an E21 mode. The few-mode waveguides Core2 and Core3 are placed in the positive direction of the Y axis of the cross section of the multi-mode waveguide Core1, and the few-mode waveguides Core2 and Core3 and the multi-mode waveguide Core1 form an asymmetric directional coupler in the vertical direction. When E11, E12 and E21 modes are input from the Core1 input end and pass through the coupling area along the straight waveguide, the modes are respectively transmitted in the few-mode waveguide in a fundamental mode th