Research on Mode-Locked Erbium-Doped Fiber Laser Based on the Lyot Filter

We reported a wavelength-tunable mode-locked fiber laser, in which an asynchronous dual-wavelength phenomenon was observed during laser operation. The laser was based on a mode-locked technique of carbon nanotubes (CNTs). A wavelength-tunable Lyot fiber filter was designed using a segment of polarization-maintaining fiber, along with a three-ring and a squeeze-type polarization controller. The filter exhibited a tunable wavelength range from 1554.37 nm to 1562.27 nm. At a pump power of 45 mW, a repetition frequency of 26.07 MHz and a pulse width of 837 fs were achieved. At the same time, asynchronous dual-wavelength mode-locked pulse output with central wavelengths of 1557.6 nm and 1563.2 nm and a frequency interval of 359.5 Hz was obtained by adjusting the polarization controller. The Lyot filter, consisting of a polarization-maintaining fiber and two cascaded polarization controllers, has been shown to support both continuous wavelength tuning and controllable asynchronous dual-wavelength mode-locking. Such a design offers a compact route to dual-function pulse generation in fiber cavities.