Tunable random Raman fiber laser at 1.7 µm region with high spectral purity.

We demonstrate a tunable, high order cascaded random Raman fiber laser (RRFL) with high purity at 1.7 µm band by using a high power amplified spontaneous emission source (ASE) with both wavelength and linewidth tunability as pump source. The influence of the spectral bandwidth of the ASE source on the spectral purity of the output at 1.7 µm band is investigated. By adjusting the spectral bandwidth of the ASE source to the optimized 20 nm, output power >14 W with spectral purity up to 98.29% at 1715 nm is achieved. As far as we know, this is the highest spectral purity ever reported for a RRFL at 1.7 µm region. Furthermore, by adjusting the central wavelength of ASE source, the output of the RRFL can be tuned from 1695 to 1725 nm with >10 W output power. What's more, the spectral purity is above 92% over a tuning range from 1705 to 1725 nm.