Wavelength demultiplexing waveguide couplers have important applications in integrated nanophotonic devices.Two of the most important indicators of the quality of a wavelength demultiplexing coupler are coupling efficiency and splitting ratio.In this study,we utilize two asymmetric high-index dielectric nanoantennas directly positioned on top of a silicon-on insulator waveguide to realize a compact wavelength demultiplexing coupler in a communication band,which is based on the interference of the waveguide modes coupled by the two nanoantennas.We add a Au substrate for further increasing the coupling efficiency.This has constructive and destructive influences on the antennas in-coupling efficiency owing to the Fabry-Perot(FP)resonance in the SiO2 layer.Therefore,we can realize a wavelength demultiplexing coupler with compact size and high coupling efficiency.This coupler has widespread applications in the areas of wavelength filters,on-chip signal processing,and integrated nanophotonic circuits.