Fig. 1. Schematic of the proposed fiber laser and detection devices.

Fig. 2. Reflection spectrum of the four-mode FBG with hybrid mode injection.

Fig. 3. (a) Autocorrelation trace of single pulse and (b) RF spectrum of the mode locking laser.

Fig. 4. Pulse train of the passively mode-locked laser in (a) large time range and (b) short time range.

Fig. 5. Optical spectrum of the mode-locked laser (blue solid line), CW operation (red solid line), and the four mode reflection (black dashed line).

Fig. 6. Intensity distribution of the (a) RPB output; (b)–(e) show the intensity distributions of the output beam after passing through a linear polarizer. Arrow indicates the orientation of the linear polarizer.

Fig. 7. Function fitting of the output beam intensity distribution. Black circles represents the measured intensity, red line represents the function fitting.