Triple-wavelength EDF laser based on phase-shifted fiber grating and 50 μm MMF

We propose and experimentally demonstrate a novel switchable triple-wavelength erbium-doped fiber laser using linear cavity structure. It is composed of two Sagnac loops that act as cavity mirrors in the resonant cavity. The left loop consists of a 3 dB fiber coupler (FC), a three-ring polarization controller (PC), and a phase-shifted fiber grating. The right loop consists of a same 3 dB FC, a same PC and a length of multimode fiber with 50 µm core diameter. The two loops based on different operation principles become two comb filters to jointly excite the multiwavelength output. On the role of the polarization hole burning effect, after adjusting the two PCs, the laser can switch flexibly to output three kinds of different modes from single-wavelength to the triple-wavelength. All lasing lines with a narrow linewidth less than 0.4 nm have the optical signal-to-noise ratio of more than 28 dB. (paper)