3 W average-power high-order mode pulse in dissipative soliton resonance mode-locked fiber laser

Recently high-order modes (HOMs) lasers have been extensively investigated due to their potential applications in mode-division multiplexing. In this paper, we present two schemes of generating HOMs from the mode-locked fiber lasers (MLFLs) in the dissipative soliton resonance (DSR) regime. Watt-level HOM outputs are implemented through intra-cavity mode conversion. 3 W average-power HOMs with an efficiency slope of 25% can be obtained based on an MLFL in the DSR regime, which is achieved by incorporating a long-period fiber grating (LPFG) and a dual-resonant acoustically induced fiber grating (AIFG), respectively. Their different spectrum responses enable flexible mode conversion in the MLFLs. Both fiber mode converters are exploited to show their robust capability of efficient mode manipulation. The MLFL with an LPFG inserted in the cavity can achieve wide-bandwidth intra-cavity optical vortex beams (OVBs) near the dispersion turning around point because of the pulses of the fundamental mode and high-order vortex eigenmodes oscillating in the cavity with the same group velocity to form spatiotemporal mode locking. The MLFL based on a dual-resonant AIFG can perform the function of fast switching (∼0.3 ms) in LP01, LP11a, and LP11b modes with a high modal purity of 96%. These different modes with high-energy pulses can be flexibly switched with programmable radio frequency modulation. Furthermore, a quarter-wave plate and a polarizer are employed at the output of fiber laser to realize the controllability of the mode field, which is possible to generate a controllable mode field of OVBs based on the first-order Poincaré sphere. This control method can be integrated with the MLFLs to extend the flexibility of high-power HOMs generation.