Erbium-doped fiber laser with switchable wavelength generation based on tunable filter and dual-pass mach-zehnder filter incorporated with fiber delay line

A wavelength switchable erbium-doped fiber laser incorporated with a tunable filter and dual-pass Mach-Zehnder interferometer (MZI) was designed and experimentally demonstrated. The erbium-doped fiber was used as the gain medium for the fiber laser and the laser working threshold was 92 mW. The dual-pass MZI was fabricated using three optical couplers (OCs) and the variable fiber delay line. A tunable filter was used for laser tuning and it was combined with two OCs to construct a subsidiary cavity. A tunable and stable single- and dual-wavelength laser output was obtained in the experiment. In the case of single-wavelength laser output, the tuning span was in the range of 1527.6-1562.4 nm with an interval of 1.2 nm. Additionally, the side-mode suppression ratio (SMSR) was greater than 37.45 dB. In the case of dual-wavelength laser emission, the lasers were tuned from 1540.7 and 1541.6 nm to 1560.8 and 1561.2 nm, respectively. The stability of the single-, dual-and triple-wavelength laser output was evaluated and the power fluctuation was less than 1.36, 1.34, and 1.37 dB, respectively. Finally, quadruple- and quintuple-wavelength laser outputs were achieved by adjusting the loss of the intra-cavity.