Two-path self-interference in PTCDA active waveguides maps the dispersion and refraction of a single waveguide mode

Bound waveguide modes propagating along nanostructures are of high importance since they offer low-loss energy-/signal transport for future integrated photonic circuits. Particularly, the dispersion relation of these modes is of fundamental interest for the understanding of light propagation in waveguides as well as of light-matter interactions. However, for a bound waveguide mode, it is experimentally very challenging to determine the dispersion relation. Here, we apply a two-path interference experiment on microstructured single-mode active organic waveguides that is able to directly visualize the dispersion of the waveguide mode in energy-momentum space. Furthermore, we are able to observe the refraction of this mode at a structure edge by detecting directional interference patterns in the back-focal plane.