Repetition frequency difference and SNR well-controlled dual- and triple-frequency pulses based on multimodal interference effect

We experimental demonstrate dual- and triple-frequency pulses with controlled repetition frequency difference and signal to noise ratio in a carbon nanotube-based fiber laser. A short segment of multimode fiber is added to the resonant cavity to adjust the total cavity dispersion. Based on the principal modes in multimode fiber, the wavelength multiplexing dual-frequency pulses obtain with the repetition frequency difference variation from 32 Hz to 1 kHz. Linear and nonlinear mechanism enables tuned repetition frequency difference in this case. By carefully tailoring linear birefringence in multimode fiber, trip-frequency pulses emit. The tuning range for repetition frequency difference is 60 Hz to 110 Hz, and for signal to noise is 26.5 dB in the two polarization multiplexing pulses. This laser will provide a potential technical approach for applications such as versatile dual-comb ranging.