Fig. 1. Schematic structure of the transverse mode-switchable few-mode ring fiber laser

Fig. 2. Principle of mode MUX/DEMUX. (a) Schematic of the MSC; (b) mode effective index matching graph for the LP₀₁ in the SMF and the desired modes in the designed FMF; (c) schematic of all-fiber mode MUX/EDMUX

Fig. 3. Mode intensity profiles of the few-mode laser. (a) LP₀₁ mode; (b) LP₁₁ mode; (c) LP₂₁ mode; (d) hybrid mode

Fig. 4. Relation between output power and pump power

Fig. 5. Spectral feature of lasing output for the LP₀₁ mode, the LP₁₁ mode, the LP₂₁ mode, and the hybrid mode. (a) LP₀₁ mode; (b)LP₁₁ mode; (c)LP₂₁ mode; (d) hybrid mode