Stable and switchable single-longitudinal-mode dual-wavelength erbium-doped fiber laser based on a fiber ring filter

A switchable dual-wavelength and single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) based on a fiber ring filter (FRF) is proposed and demonstrated through a detailed experimental verification. In the design, the simple linear-cavity EDFL is composed of one 976-nm laser diode (LD), one fiber loop mirror (FLM), two cascaded fiber Bragg gratings (FBGs), and an EDF. To improve the laser stability, the FRF is spliced into a specially designed EDFL, which is fabricated from an EDF and two couplers with splitting ratios of 50:50 and 30:70, respectively. Both single- and dual-wavelength lasers can be realized by adjusting the variable attenuator (VA) between the two FBGs. In the proposed EDFL, the 1540-nm laser and the 1545-nm laser, respectively, incur laser-frequency shifts at room temperature of less than 3 pm and 2 pm over a period of 60 min. The single-wavelength 1540- and 1545-nm lasers show single-longitudinal-mode (SLM) operation within the frequency range of 0–500 MHz, as measured by the delayed self-heterodyne method using a 50-km single-mode fiber, and the 3-dB linewidths of the output of two lasers are about 2.8 kHz and 2.5 kHz, respectively.