  We report on III-nitride waveguides with c-plane GaN/AlGaN quantum wells in
the strong light-matter coupling regime supporting propagating polaritons. They
feature a normal mode splitting as large as 60 meV at low temperatures thanks
to the large overlap between the optical mode and the active region, a
polariton decay length up to 100 $\mu$m for photon-like polaritons and lifetime
of 1-2 ps; with the latter values being essentially limited by residual
absorption occurring in the waveguide. The fully lattice-matched nature of the
structure allows for very low disorder and high in-plane homogeneity; an
important asset for the realization of polaritonic integrated circuits that
could support nonlinear polariton wavepackets up to room temperature thanks to
the large exciton binding energy of 40 meV.
