Research on narrow-linewidth erbium-doped fiber lasers based on composite double-ring structures

This work presents an innovative erbium-doped fiber laser with ultra-narrow linewidth and single longitudinal mode operation. In this paper, a composite double-ring cavity composed of double couplers combined with a uniform fiber Bragg grating with a reflection bandwidth of only 0.25 nm is used to achieve good performance of single longitudinal mode laser and narrow linewidth output. The experimental results clearly show that under room temperature conditions, the output central wavelength of this laser is 1558.31 nm, the optical signal-to-noise ratio is as high as 61.71 dB, and the slope efficiency is 1.34 %. After a continuous measurement process of 60 min, the fluctuation amplitude of the output wavelength is only 0.05 nm, and the fluctuation amplitude of power is 0.008 dB, fully confirming that the designed laser has good wavelength stability and power stability. The delay self-heterodyne method is used to measure its linewidth, and the results show that the linewidth of the laser is as low as 352 Hz. Such lasers have broad application prospects in cutting-edge fields such as lidar and space optical communication systems.