Fig. 1. Characterization of confined-doped fiber and experimental setup. (a) Refractive index distribution of fiber core; (b) cross-section photograph of fiber; (c) experimental diagram of confined-doped fiber laser amplifier

Fig. 2. Measurement results of confined-doped fiber laser amplifier. (a) Output powers and optical-to-optical efficiencies at different pump powers (inset: power meter reading data at the highest output power); (b) output spectra under different output powers; (c)output beam quality and spot profile under the maximum output power; (d) 3D view of light intensity distribution