Wavelength switchable erbium doped fiber laser based on hybrid filter composed of Sagnac loop and Mach-Zehnder filter using tunable delay line

In this study, a switchable and tunable erbium-doped fiber laser (EDFL) based on a tunable Mach-Zehnder (MZ) and Sagnac hybrid filter was proposed. An optical delay line (ODL) was inserted into one arm of the MZ interferometer (MZI) to control the comb spacing, forming a hybrid filtering system with the Sagnac loop. The erbium-doped fiber (EDF) serves as the gain medium for the fiber laser, with a lasing threshold of 43 mW. When the EDFL was set to single-wavelength output, a tuning range from 1556.1 to 1567.4 nm was achieved by adjusting the polarization controller (PC). In the dual-wavelength output, the wavelength spacing could be tuned within the range of 0.84 to 6.62 nm, with side-mode suppression ratio (SMSR) exceeding 33.44 dB. Wavelength drift and power fluctuations were controlled to be less than 0.112 nm and 2.73 dB, respectively. Stable three-wavelength and four-wavelength laser outputs were also achieved, each with SMSR values exceeding 31.04 dB. The proposed hybrid filter EDFL exhibited flexible tuning capabilities and simple structure, indicating potential applications in fiber sensing and optical communication.