All-fiber passively mode-locked ytterbium fiber laser with a rectangular spectrum profile

Abstract

We have demonstrated an all-fiber passively mode-locked ytterbium fiber laser operating with a rectangular spectrum profile. Mode-locking is achieved by adopting nonlinear polarization rotation (NPR) in an all fiber ring cavity with normal dispersion. The 3 dB bandwidth of the spectrum is 8.6 nm, the signal-to-noise ratio (SNR) is more than 40 dB, and the rising and falling band edges are very steep. The mode-locking pulse train is stable and has a repetition of 13.4 MHz. We believe that the laser is operating in the gain-guided soliton state, which means soliton formation is induced purely by the existence of gain and gain dispersion. This kind of mode-locked fiber laser with the rectangular spectrum has potential applications in optical-based ultra-high-speed signal collection system, optical frequency combs generation and supercontinuum light source.