Fig. 1. Influence of delay time of delayed fiber on power spectral profile of beat signal

Fig. 2. Schematic of experimental setup of laser linewidth measurement based on recirculating self-heterodyne method with short fiber

Fig. 3. Influence of coupling coefficient on peak intensity of beat signal. (a) Output beat signal from interferometer when α=0.9; (b) output beat signal from interferometer when α=0.1

Fig. 4. Different beat signals and their fitted curves. (a) 2nd order beat signal; (b) 3rd order beat signal; (c) 4th order beat signal

Fig. 5. Laser linewidth measured by traditional beat frequency method