Wavelength-spacing-controllable multi-wavelength fiber laser based on a Lyot-Sagnac filter.

A wavelength-spacing-controllable multi-wavelength polarization-maintaining erbium-doped fiber laser (MW-PM-EDFL) in a linear cavity configuration is presented based on a Lyot-Sagnac filter and a nonlinear optical loop mirror (NOLM). Using a Lyot-Sagnac filter as the wavelength selective filter makes the wavelength spacing controllable by adjusting the effective length of polarization-maintained fiber (PMF) segments. An NOLM inducing wavelength-dependent cavity loss can be used as an amplitude equalizer, which is employed to suppress the mode competition resulting from the homogeneous line broadening effect of the erbium-doped fiber in the cavity. Thus, a stable wavelength-spacing-controllable MW-PM-EDFL is realized. In this experiment, 20 stable lasing wavelengths are obtained with a pump power of 170 mW at 980 nm when the length of the PMF is 13 m. When the length of the PMF is 8 m, 10 stable lasing wavelengths are obtained at 185 mW pump power. The power fluctuations and wavelength shifts are less than 2 dB and 0.02 nm in 1 h at room temperature. The demonstrated multi-wavelength fiber laser has great potential for applications in optical communications and optical sensing systems.