  The transport distance of excitons in exciton-polariton systems has
previously been assumed to be very small ($\lesssim 1~\mu$m). The sharp spatial
profiles observed when generating polaritons by non-resonant optical excitation
show that this assumption is generally true. In this paper, however, we show
that the transport distances of excitons in two-dimensional planar cavity
structures with even a slightly polaritonic character are much longer than
expected ($\approx 20~\mu$m). Although this population of slightly polaritonic
excitons is normally small compared to the total population of excitons, they
can substantially outnumber the population of the polaritons at lower energies,
leading to important implications for the tailoring of potential landscapes and
the measurement of interactions between polaritons.
