Highly efficient free running cascaded Raman fiber laser that uses broadband pumping

A 3^rd-order cascaded Raman fiber laser has been demonstrated without using fiber Bragg gratings at all in the entire laser system. More than 2 W output power at the 3^rd Stokes emission wavelength of 1307 nm, a bandwidth of 4.2 nm and a slope efficiency of ∼46% was measured when a 500 m long moderately Ge-doped silica fiber was pumped by a free running broadband Yb³⁺-dopcd fiber laser. This method is simple, versatile and cheap when compared with conventional methods employing narrow band pumping and fiber Bragg gratings to resonate the Stokes wavelengths. A slope efficiency of ∼72% and an output power of over 4 W was also achieved at the 1^st order Stokes wavelength of 1168 nm when a 130 m long Ge-dopcd silica fiber was used.