A Wavelength-Multiplexed Dual-Frequency Mode-Locked Fiber Laser with Tunable Repetition Frequency Difference

We present a wavelength-multiplexed dual-frequency mode-locked fiber laser capable of generating asynchronous dual-frequency pulses with a widely tunable repetition frequency difference. The laser achieves the center wavelength separation adjustable from 1.02 to 26.7 nm, while the repetition frequency difference can be tuned from 147 Hz to ~3 kHz. Such wide tunability is realized within a compact cavity by leveraging the low-threshold saturable absorption of carbon nanotubes (CNTs) and the wavelength selectivity introduced by nonlinear polarization rotation (NPR). The tunability of repetition frequency difference not only broadens the scope of wavelength-multiplexed asynchronous mode-locking but also provides a versatile and practical dual-frequency source.