A random fiber laser with multiple bidirectional Rayleigh scattering provided by dual-ring sub-cavity structure

• The proposed laser incorporates enhanced Rayleigh-distributed feedback (R-DFB) and filtering functions, providing excellent laser output. • The designed dual-ring sub-cavity structure provides sufficient R-DFB, which is cost-effective, easy to fabricate and compact in structure. • The proposed Rayleigh scatterings (RS) enhancement method can be applied to any random fiber laser (RFL) to improve laser output performance. • The designed dual-ring sub-cavity RFL can serve as an alternative light source for biomedical imaging, lidar, and optical communication. In this study, a simple and effective method for enhancing Rayleigh scattering (RS) intensity is proposed and experimentally validated, enabling stable output with exceptionally low-frequency noise across each wavelength channel of random fiber lasers (RFLs). The design employs two segments of single-mode fibers (SMFs) symmetrically arranged in dual-ring sub-cavity. This unique structural configuration facilitates multiple bidirectional RS interactions, providing sufficient random distributed feedback (R-DFB) for the laser system. Initially, random laser (RL) outputs at 1560 nm were achieved using both ring-cavity and single-ring sub-cavity structures. These systems exhibited frequency noise exceeding 1.21 Hz/√Hz and wavelength and output power fluctuations of 0.79 nm and 1.52 dB, respectively. Subsequently, the laser system was upgraded to a dual-ring sub-cavity configuration, and its output performance was re-evaluated. The experimental results show that the wavelength and output power fluctuations are reduced to 0.28 nm and 0.26 dB, respectively. Benefiting from the enhanced R-DFB and superior filtering properties of the dual-ring sub-cavity, the frequency noise of the lasing output decreased significantly to 0.03 Hz/√Hz, the lowest value reported to date. In addition, the importance of sufficient R-DFB for RFL is demonstrated by measuring frequency amplitude, output linewidth, and slope efficiency.