Widely and Continuously Tunable Continuum Generation From CW-Pumped Cascaded Fibers

A tunable continuum with multiwatt output power is demonstrated for the first time through the pumping of cascaded fibers by using a continuous-wave (CW) ytterbium fiber laser. The central wavelength of the output continuum can be tuned continuously and monotonically by varying input pump power, with a wide wavelength-tunable range from 1.2 to 1.4 $\mu{\rm m} $ and a 3-dB bandwidth of tens of nanometers. Two configurations of the cascaded fibers both display the power-dependent wavelength tunability. The output spectral characteristics are presented, and the generation of the CW-pumped tunable continuum is tentatively attributed to the seed-dependent Raman amplification.