Imaging exciton–polariton transport in MoSe2 waveguides

The exciton polariton (EP), a half-light and half-matter quasiparticle, is potentially an important element for future photonic and quantum technologies. It provides both strong light-matter interactions and long-distance propagation that is necessary for applications associated with energy or information transfer. Recently, strongly-coupled cavity EPs at room temperature have been demonstrated in van der Waals (vdW) materials due to their strongly-bound excitons. Here we report a nano-optical imaging study of waveguide EPs in MoSe2, a prototypical vdW semiconductor. The measured propagation length of the EPs is sensitive to the excitation photon energy and reaches over 12 {\mu}m. The polariton wavelength can be conveniently altered from 600 nm down to 300 nm by controlling the waveguide thickness. Furthermore, we found an intriguing mode back-bending dispersion close to the exciton resonance. The observed EPs in vdW semiconductors could be useful in future nanophotonic circuits operating in the near-infrared to visible spectral regions.