Optimization of single-mode fiber lengths for enhanced performance of Sagnac-based multiwavelength random fiber laser

This work investigates the effect of single-mode fiber (SMF) length on the performance of a multiwavelength random fiber laser (MWRFL) based on a Sagnac loop mirror (SLM) interferometer. The incorporation of highly nonlinear fiber (HNLF) effectively suppresses mode competition at high pump powers, enabling stable multiwavelength operation. Different SMF lengths were examined, with the optimum performance obtained using 10 km of standard SMF, yielding a broad bandwidth with an extinction ratio of 20 dB. In contrast, replacing 0.3 km of Rayleigh enhancement fiber (REF) with SMF reduced the output to 58 channels due to the lower Rayleigh backscattering coefficient. Polarization-maintaining fiber (PMF) length was also found to be critical. A 42 m PMF produced 84 lasing lines within a wide bandwidth, while shortening it to 8 m severely degraded performance to only 7 lasing lines within a 7 nm wavelength bandwidth. Additionally, the half-wave plate angle influenced spectral flatness, and stability testing confirmed minimal power fluctuations below 0.7 dB. These results demonstrate the potential of the proposed MWRFL for practical applications in optical communications and sensing.