Tunable multi-wavelength EDF laser based on Sagnac interferometer with weakly-coupled FMF delay line

A simply manufactured and broadly tunable multi-wavelength Erbium-doped fiber (EDF) ring laser based on Sagnac interferometer with weakly-coupled few-mode fiber (FMF) delay line is proposed and experimentally demonstrated. The incorporation of FMF is realized with all-fiber mode multiplexer/demultiplexer (MUX/DEMUX) consisted of mode-selective couplers (MSC). The FMF and the mode MUX can simultaneously generate higher-order modes and fundamental mode. Single-, dual- and triple-wavelength lasing are obtained with broad tuning over 30-nm and smallest tuning step of 0.52-nm by adjusting polarization controller (PC) in the Sagnac interferometer. Optical signal-to-noise ratio (OSNR) higher than 30-dB and stability in 30-min are also measured.