Polaritons in 2D-crystals and localized modes in narrow waveguides

We study 2D-polaritons in an atomically thin dipole-active layer (2D-crystal) placed inside a parallel-plate wavegude, and investigate the possibility to obtain the localized wavegude modes associated with atomic defects. Considering the wavegude width, $l,$ as an adjustable parameter, we show that in the waveguide with $l\sim 10^{4} a,$ where $a$ is the lattice parameter, the localized mode can be provided by a single impurity or a local structural defect.