  Waves entering a spatially uniform lossy medium typically undergo exponential
decay, arising from either the energy loss of the Beer-Lambert-Bouguer
transmission law or the evanescent penetration during reflection. Recently,
exceptional point singularities in non-Hermitian systems have been linked to
unconventional wave propagation, such as the predicted extremely spatially
broad constant-intensity guided modes. Despite such promises, the possibility
of decay-free wave propagation in a purely lossy medium has been neither
theoretically suggested nor experimentally realized until now. Here we discover
and experimentally demonstrate decay-free wave propagation accompanied by a
striking uniformly distributed energy loss across arbitrary thicknesses of a
homogeneous periodically nanostructured waveguiding medium with exceptional
points. Predicted by coupled-mode theory and supported by fully vectorial
electromagnetic simulations, hundreds-of-waves deep penetration manifesting
spatially constant radiation losses are experimentally observed in photonic
slab waveguides. The uniform, decay-free radiative energy loss is measured
across the entire structured waveguide region, regardless of its length. While
the demonstrated constant-intensity radiation finds an immediate application
for generating large, uniform and surface-normal free-space plane waves
directly from the photonic chip surface, the uncovered decay-free wave
phenomenon is universal and holds true across all domains supporting physical
waves, opening new horizons for dispersion-engineered materials empowered by
exceptional point physics.
