Erbium-doped fiber laser enabled by combination of comb filter and thermal control

We demonstrate a tunable erbium-doped fiber laser (EDFL), which employs a comb filter consisting of a polarization-maintaining fiber-based Sagnac interferometer (PMF-SI) and a Mach–Zehnder interferometer with multimode fiber-thin core fiber-multimode fiber structure (MTM-MZI). By exploiting the synergistic spectral response of PMF-SI and MTM-MZI and their spectral temperature-dependent properties, the comb filter achieves high-resolution wavelength selection with single-wavelength tuning in the range of 1529.65 to 1533.78 nm and a maximum side-mode suppression ratio (SMSR) of more than 55 dB. The proposed EDFL is highly stable with a wavelength drift of <0.03 nm and peak power fluctuation of less than 0.15 dB over 65 min. Moreover, the polarization controller can be adjusted to achieve a dual-wavelength output and shows wavelength shifts of 0.04 and 0.05 nm and power fluctuations of 0.69 and 0.67 dB, respectively. The proposed EDFL combines high SMSR, good tunability, high stability, and single- and dual-wavelength flexibility, which makes it suitable for applications in optical communications, optical sensing, and microwave photonics.