Ultracompact wavelength and polarization directional coupler based on nanowire waveguides

In this paper, we numerically study and propose a wavelength and polarization selective directional coupler based on nanowire waveguides. The plane wave expansion method is used to design the structures and the finite-difference time–domain method is used to evaluate the device performance, which agrees well with each other. The results show that the proposed directional coupler can realize functions of the wavelength and polarization splitters simultaneously without changing the structure parameters. The crosstalks for both wavelength and polarization splitters are lower than ?17 dB at telecommunication wavelengths. The proposed structure has the advantages of small foot print, fabrication without complex nanostructures and complementary metal-oxide-semiconductor compatibility, which is promising for highly dense photonic integration.