  Cascaded Raman fiber lasers have offered a convenient method to obtain
scalable, high-power sources at various wavelength regions inaccessible with
rare-earth doped fiber lasers. A limitation previously was the reduced
efficiency of these lasers. Recently, new architectures have been proposed to
enhance efficiency, but this came at the cost of enhanced complexity, requiring
an additional low-power, cascaded Raman laser. In this work, we overcome this
with a new, all-passive architecture for high-efficiency cascaded Raman
conversion. We demonstrate our architecture with a fifth-order cascaded Raman
converter from 1117nm to 1480nm with output power of ~64W and efficiency of
60%.
