In the study, we demonstrate an erbium-doped fiber (EDF) laser system by integrating the Mach-Zehnder interferometer (MZI) and triple-fiber-ring structures to generate the single-longitudinal-mode (SLM) output in L-band bandwidth. Here, a sub-ring with a 5.5 m unpumped EDF based saturable absorber (SA) is also applied to induce the narrowband auto-tracking filter behavior. Based on the proposed fiber cavity induced mode-filter effect, the EDF laser can achieve the stable, narrow and wavelength-tunable output characteristics over an effective tuning range of 1568.0 to 1613.0 nm. Furthermore, the output stability, optical signal to noise ratio (OSNR), output power and laser linewidth of the laser are also performed and discussed.

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