Fig. 1. Experimental setup of Q-switched erbium-doped fiber laser with switchable mode

Fig. 2. Measurement of reflection peak of FM-FBG. (a) Setup used to test reflection peaks of FM-FBG. Dashed box indicates diagram of MSC; (b) measured reflection spectrum of incident broadband light with highly purified LP₁₁ mode

Fig. 3. Laser outputs at 1530.5 nm. (a) Q-switched pulse trains under different pump powers; (b) output spectrum and pulse duration under pump power of 60 mW; (c) output power as a function of pump power. Inset is laser mode monitored from SMF-FBG port; (d) repetition rate and pulse duration as functions of pump power

Fig. 4. Laser outputs at 1532.15 nm. (a) Q-switched pulse trains under different pump powers; (b) Q-switched pulse output spectrum at 60 mW pump power and pulse duration; (c) output power versus pump power; (d) repetition rate and pulse duration as functions of pump power; (e) donut-shaped intensity distributions of radially polarized beam after passing through polarizer and corresponding polarization states

Fig. 5. Laser dual-wavelength outputs at 1530.5 nm and 1532.15 nm. (a) Dual-wavelength Q-switched output and LP₀₁ and LP₁₁ modes; (b) repetition rate and pulse duration as functions of pump power; (c) Q-switched pulse trains under different pump powers