Design and crosstalk suppression of deep subwavelength waveguides

To manipulate on-chip mid-IR signals, it is pivotal to construct a waveguide with subwavelength energy confinement. However, a deep subwavelength optical waveguide always suffers from high signal crosstalk, resulting in an inevitable coupling loss of multi-channel communication. To solve this problem, in this paper, a mid-IR hybrid waveguide which is composed of a graphene/hexagonal boron nitride (hBN) structure and a dielectric waveguide, is designed to realize a strongly enhanced light-matter interaction, accompanied by a low crosstalk transmission. The surface-phonon-plasmon-polariton mode generated by the graphene-hBN is coupled to a nanowire dielectric mode to form a hybrid guiding mode. Benefiting from this hybrid mode, the results show that it is possible to minimize the crosstalk of two parallel waveguides by reducing the width of the graphene-hexagonal hBN structure even if the waveguide separation length is at the nanoscale, thereby enabling low crosstalk optical transmission. Our designed approach opens the door for possible uses in nanophotonic devices such as amplitude equalizers, mode multiplexers, and wavelength-selective switches in optical communication systems.