By using a 520-m-long highly nonlinear fiber (HNLF) pumped by a 20 W CW Yb-doped fiber laser, four Raman Stokes emissions are demonstrated in a simple cavity-free configuration. The Stokes wavelengths are 1121 nm, 1178 nm, 1247 nm and 1319 nm respectively with a total frequency shift of 53 THz, and the maximum output power is 3.2 W. The evolution of the multiple Raman Stokes emission is presented and analyzed. The generation of the multiple Stokes from the cavity-free configuration is attributed to the random distributed feedback based on Rayleigh scattering. It is also demonstrated that the fiber length of the cavity-free Raman fiber laser can be largely shortened by using a HNLF as the Raman gain medium.
R. Vallée, E. Bélanger, B. Déry, M. Bernier and D. Faucher. Highly efficient and high-power Raman fiber laser based on broadband chirped fiber Bragg gratings. Journal of Light Wave Technology, 2006, 24(12): 5039-5043.
J. W. Nicholson, M. F. Yan, P. Wisk, J. Fleming, F. DiMarcello, E. Monberg, T. Taunay, C. Headley and D. J. DiGiovanni. Raman fiber laser with 81 W output power at 1480 nm. Optics Letters, 2010, 35(18): 3069-3071.
S. K. Turitsyn, S. A. Babin, A. E. El-Taher, P. Harper, D. V. Churkin, S. I. Kablukov, J. D. Ania Castanon, V. Karalekas and E. V. Podivilov. Random distributed feedback fibre laser. Nature Photon-ics, 2010, 4(4): 231-235.
D. Churkin, S. Babin, A. E. El-Taher, P. Harper, S. Kablukov, V. Karalekas, J. D. Ania-Casta？ón, E. Podivilov and S. K. Turitsyn. Raman fiber lasers with a random distributed feed-back based on Rayleigh scattering. Physical Review A, 2010, 82(3): 033828.