Investigation on Switching Characteristics of Multiple Pulse States in a Dual-Wavelength Bismuth-Doped Fiber Laser

We demonstrate four switchable pulse states at 1.3 μm in a dual-wavelength bismuth-doped fiber laser based on nonlinear polarization rotation. By adjusting the pump power and polarization, we achieve four switchable pulse states: mode-locking, breathing, Q-switching, and Q-switched mode-locking. All states are dual-wavelength, operating at 1362 nm and 1426–1431 nm with a separation of 63–69 nm. The laser delivers a fundamental repetition rate of 1.71 MHz. At the breathing-pulse state, the pulse envelope undergoes periodic modulation with a characteristic period of 50 μs, whereas the Q-switching state operates at a repetition rate of 21.0 kHz. The Q-switched mode-locked envelope amplitude is continuously tunable via polarization.