A switchable multi-wavelength EDFL using cascaded Sagnac fiber loops with mode differential delay line

We propose and experimentally demonstrate a switchable multi-wavelength Erbium-doped fiber laser that employs cascaded weakly-coupled few-mode fiber (FMF) Sagnac fiber loops with mode differential delay line. A comb filter of multiple specific wavelengths is performed by incorporating a weakly-coupled FMF in cascaded Sagnac fiber loops. The incorporation of the weakly-coupled FMF is realized with all-fiber mode multiplexer/demultiplexer (MUX/DEMUX), which can simultaneously generate transversal LP01 and LP11 modes. The comb filter characteristics of cascaded Sagnac fiber loops are simulated and analyzed by Jones matrix. By adjusting the polarization controllers (PCs), the fiber laser can operate in single-, dual-, and triple-wavelength laser states around C band. The side mode suppression ratio is larger than 30.0 dB. Moreover, the laser output stabilities for single-, dual-, and triple-wavelength lasing are investigated in a range of over 30 min at room temperature. Experimental results indicate that this work has potential applications in WDM systems, sensing, and instrument testing. © 2021 Elsevier GmbH