Fig. 1. Structure of single-end pumped all-fiber laser oscillator

Fig. 2. Relationship between output power and pump power of single-end pumped laser oscillator

Fig. 3. Temperature characteristic of CLS with and without TMI. (a) Pump power of 1.845 kW without TMI; (b) pump power of 1.85 kW with TMI

Fig. 4. Output spectrum characteristic of single-end pumped laser oscillator with and without TMI

Fig. 5. Output power characteristic of single-end pumped laser oscillator with different fiber lengths

Fig. 6. Power and spectrum after reducing active fiber lengths. (a) Power with active fiber length of 37.5 m; (b) power with active fiber length of 27 m; (c) spectrum with active fiber length of 27 m

Fig. 7. Scheme of double-side pumped all-fiber laser oscillator with core/inner cladding diameter of 25 μm/400 μm

Fig. 8. Experimental results of double-side pumped all-fiber laser oscillator. (a) Spectra of the laser before shortening the fiber length; (b) time and frequency domain of the laser before shortening the fiber length; (c) spectra of the laser after shortening the fiber length; (d) time and frequency domain of the laser after shortening the fiber length

Table 1. TMI pump threshold with different passive fiber lengths