Flexible Dual-Wavelength Mode-Locked Fiber Laser Using Spun Fiber Filter

We propose and demonstrate a novel and flexible dual-wavelength mode-locked scheme based on spun fiber (SPF) filter. Benefiting from the special polarization dispersion effect, connecting a polarizer after the SPF can form a comb-like filter that allowed the propagated laser to be linearly polarized. The transmission curve of the filter can be shifted by changing the angle between the SPF and the polarizer, while the period of the curve is inversely proportional to the SPF length. By changing the SPF length, periods ranging from 30 nm to 2 nm have been demonstrated. This filter is implemented in a mode-locked fiber laser to achieve flexible dual-wavelength mode-locking. While maintaining a repetition-rate difference of similar to 1.5 kHz, the repetition rate was varied from 30 MHz to 20 MHz by increasing the cavity length. Similarly, with repetition rate of 20 MHz, the difference in repetition rates changes from 0.5 kHz to 1.4 kHz by decreasing SPF length. This method provides a simple and effective approach for the flexible design of the DMFL.