Waveguide-polaritons differ from microcavity-polaritons by substituting the mirrors with a waveguide that confines light by total internal reflection, thus with a linear dispersion (as opposed to parabolic, or massive, in a cavity). This allows for higher group velocities (e.g., 20-60 μm/ps) and longer propagation distances (hundreds of microns to millimeters).
They have recently regained much attention, although they have been studied in the early days of the field.[1]