Switchable and tunable multi-wavelength erbium-doped fiber ring laser based on single STS filter

A novel switchable and tunable multi-wavelength erbium-doped fiber ring laser (EDFL) is proposed and experimentally demonstrated by using a single SMF-TMF-SMF (STS) structure filter. The STS filter, based on mode interference, is fabricated by sandwiching a section of two-mode fiber (TMF) between single mode fibers (SMF) through core-offset splicing, which has a comb spectrum with obvious envelope and uniform fluctuation. The transmission characteristics of the STS filter can be changed by adjusting the polarization controller (PC) wrapped on the TMF. Based on the cooperation of the STS filter and polarization dependent loss (PDL), the fiber laser can be individually switchable and widely tunable. By adjusting the PC, the outputs can be switched from single-wavelength to adjacent eight-wavelength and can be tuned in the range of 1528 similar to 1561 nm. Furthermore, non-adjacent dual-, three- and four-wavelength with different intervals can also be achieved by appropriately adjusting the PC. With the assistance of four wave mixing (FWM) effect, the fiber laser has a stable output. The tuning and switching of the proposed multi-wavelength EDFL is simple and flexible.