Widely Wavelength-Swept Single-Longitudinal-Mode Fiber Laser With Ultra-Narrow Linewidth in C+L-Band

This study proposes and demonstrates a widely wavelength-swept single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) enabled by a dual-coupler-ring based compound-cavity (DCR-CC) filter, a fiber Fabry-Pérot tunable filter (FFP-TF) and a C+L-band erbium-doped fiber amplifier (EDFA). Moreover, it develops a novel methodology utilizing the signal-flow graph combined with the matrix algebra to analyze the DCR-CC filter and obtain its essential design parameters for SLM selection of the EDFL. The C+L-band EDFA is constructed to provide a gain range >90 nm. On the other hand, it demonstrates that, under a sweep-rate ≤100 Hz, a lasing wavelength-swept range >87 nm is obtained, the SLM operation is permanently guaranteed for every instantaneous lasing wavelength. Furthermore, the instantaneous lasing parameters of an optical signal-to-noise ratio ≥66 dB, a relative intensity noise ≤−153.33 dB/Hz@≥3 MHz, a linewidth ≤625 Hz and a power fluctuation ≤0.704 dB are achieved. The distinguished performance of the proposed fiber laser enables it to have a significant potential for application in optical frequency domain reflectometry, spectroscopy and Lidar system.