Cascaded Raman fiber lasers are agile and scalable offering high optical powers at various wavelength bands inaccessible with rare-earth doped fiber lasers. Although several architectures for building cascaded Raman lasers exist, only the use of cascaded Raman resonators (CRRs) provide a high degree of power-independent wavelength conversion. A cascaded Raman resonator comprises of nested cavities built with two sets of high reflectivity fiber Bragg gratings at fixed Stokes wavelengths and thus can be used only for a fixed input wavelength; thereby restricting its use to a specific Ytterbium-doped fiber laser. The need for fabricating separate grating sets for each input wavelength compromises the simplicity and cost-effectiveness of this technique. Here, we demonstrate through experiment and simulations that the simple inclusion of a distributed broadband reflector at the first-order Stokes component along with the grating sets makes the CRR module very flexible to the input wavelengths, with remarkable improvement in efficiency over a widerange of inputs. In our experiment, a 17W Ytterbium-doped fiber laser tunable from 1055nm to 1080nm is used to pump a CRR module designed for an input wavelength of 1117nm and output wavelength of 1480nm. In conventional operation, for a non-resonant pump input into the CRR, nearly all the output was still unconverted pump. However, with the addition of the broadband distributed feedback reflector for the first-order Stokes component we achieved the 6thorder Stokes at 1480nm over the entire tuning range with a significant improvement in conversion ranging from ~33% to 86% of output at 1480nm.
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