Fig. 1. Characterization of Nd∶YAG crystal-derived fiber. (a) SEM scanning image(inset) and composition concentration distribution diagram; (b) optical fiber refractive index distribution diagram; (c) optical fiber absorption spectrum and emission spectrum; (d) tested optical fiber transmission at 1550 nm by the cut-back method loss

Fig. 2. Gain coefficients of Nd∶YAG crystal-derived fiber and CorActive ND-103 fiber at 915 nm were measured by small signal amplification device. (a) Gain test optical path; (b) gain coefficient change with the pump power

Fig. 3. Single-frequency DBR laser setup

Fig. 4. Laser longitudinal mode characteristic of optical fibers with different gain lengths. (a) Test results of the wavemeter when the gain fiber is 10 mm; (b) test results of the wavemeter when the gain fiber is 8 mm; (c) test results of the wavemeter when the gain fiber is 6 mm; (d) stability test results of the wavemeter when the gain fiber is 6 mm

Fig. 5. Output power characteristics of 915 nm ultra-short cavity DBR single-frequency fiber laser. (a) 800--1200 nm output spectra; (b) 914.5--916.5 nm output spectra; (c) diagram of pump power and output power