Fig. 3: Sketches of two possibilities to boost the SPPS response via polaritonic dispersion engineering.

a A ring topology for the SPPS-active element side-coupled to a bus waveguide increases the gain dramatically, but requires the Stokes shift Ω to align with a multiple of the free spectral range (FSR) of the ring, significantly restricting any tunability. b A corrugation at 1/4 the pump wavelength in the waveguide introduces a "slow-light'' regime with the corresponding Purcell enhancement for the polariton mode (solid blue lines compared with dashed for the uncorrugated waveguide). As the enhancement appears at a fixed wave number, the polaritonic Purcell enhancement is controlled by the pump frequency and can be achieved virtually irrespective of the actual Stokes shift Ω, which remains tunable, e.g., via the Fermi level.