Switchable multi-wavelength erbium-doped fiber laser based on core-offset structure and four-wave-mixing effect

A switchable multi-wavelength erbium-doped fiber laser (EDFL) based on the two-mode fiber (TMF) with core-offset structures and the four-wave-mixing effect (FWM) is experimentally demonstrated in this paper. The proposed filter is constructed by splicing a section of TMF with two segments of single-mode fiber (SMF) and the insertion loss is similar to 0.4 dB, which is smaller than the most of offset structures. The filter is based on the interference of the LP01 mode and the LP11 mode, which are excited by the core-offset structure. Due to the characteristics of the filter spectra and wavelength competition, the output wavelengths can be single-, dual-, and triple-wavelength by adjusting polarization controller (PC). In order to mitigate the intense gain competition, the FWM is introduced by using highly nonlinear fiber (HNLF) and SMF, respectively. Benefiting from the intensity-dependent gain caused by FWM, the number of output lasers increases and outputs are more flexible, which can be quadruple-, quintuple-, septuple- and decuple-wavelength by adjusting PC. The flatness of the wavelengths is also studied.