Random fiber laser

In this paper, a dual-ring sub-cavity erbium-doped random fiber laser (RFL) with strong random feedback distribution is proposed and experimentally investigated, utilizing erbium-doped fiber (EDF) for gain amplification and two segments of 10 km single-mode optical fibers (SMFs) for random feedback. SMFs are symmetrically inserted into the two sub-cavities, where photons undergo multiple bidirectional Rayleigh scattering (RS) after gain amplification by EDF, thereby enhancing the interaction between photons and the gain medium and consequently increasing the intensity of random feedback. In the experiment, 1560 nm random laser (RL) outputs were initially achieved through ring-cavity and single-ring sub-cavity structures with a 10 km SMF, respectively. The frequency noise was 1.46 and 1.21 Hz/√Hz, respectively, and the stability of the single-ring sub-cavity was monitored, its wavelength and output power fluctuations of 0.79 nm and 1.52 dBm, respectively. On this basis, dual-wavelength RL outputs at 1533.74 nm and 1557.62 nm were achieved by constructing a dual-ring sub-cavity RFL with two segments of 10 km SMFs. Benefiting from the strong random feedback, significant suppression of frequency jitter and residual random modes caused by mode competition was achieved. The designed RFL achieves output power and wavelength fluctuations of less than 0.56 dBm and 0.85 nm respectively, with frequency noise reduced to 0.03 Hz/√Hz, achieving stable low-frequency noise RL output. The slope efficiency is 4.1%, with a linearity greater than 99%. The proposed method of random feedback enhancement based on multiple bidirectional RS makes a step forward in developing robust and reliable RFLs. Such a stabilized RL source with low cost and low noise will find wide applications in optical communication, sensing, and biomedical imaging.