  We theoretically study the propagation and storage of a classical field in a
$\Lambda$-type atomic medium using coherent population oscillations (CPOs). We
show that the propagation eigenmodes strongly relate to the different CPO modes
of the system. Light storage in such modes is discussed by introducing a
"populariton" quantity, a mixture of populations and field, by analogy to the
dark state polariton used in the context of electromagnetically induced
transparency light storage protocol. As experimentally shown, this memory
relies on populations and is then - by contrast with usual Raman coherence
optical storage protocols - robust to dephasing effects.
