Spectral Dynamics of Actively Q-Switched Erbium-Doped Fiber Lasers

We report the spectral dynamics of actively Q-switched erbium-doped fiber lasers implemented in two common laser configurations: linear Fabry-Pérot cavity with a pair of fiber Bragg gratings as reflectors and one-directional ring cavity without spectrally selective elements. In both geometries, the spectral width of sub-pulses, forming a Q-switch pulse, depends on the sub-pulse number, the spectrum of the most powerful sub-pulse is much broader than those of the rest, less powerful, ones. In the case of the ring laser, the optical spectra of sub-pulses shift to the Stokes side with increasing a sub-pulse's number. Possible reasons for such laser spectral dynamics are discussed. We also reveal the details of supercontinuum generation in a 100-m-long telecom fiber when such Q-switch pulses are employed as pump.