Convertible all polarization-maintaining fiber laser in low threshold mode-locked state

An all polarization-maintaining figure-nine cavity fiber laser, which could be self-starting in low threshold state was reported. A phase shifter was used in the resonator structure to reduce the mode-locking threshold. When the pump power reached 120 mW, a self-starting conventional soliton mode-locking could be realized, with the central wavelength of 1530 nm and the pulse width of 614.6 fs. Then the pump power gradually increased to 470 mW, which realized the conversion from soliton pulse to noise-like pulse. In this mode-locking state, the laser output power is 63.2 mW, and the corresponding noise-like pulse energy is 5.69 nJ. The constructed laser has the advantages of low mode-locking threshold, self-starting, and can realize the conversion between ultrafast pulses and high-energy pulses only by adjusting the pump power, which has extensive application values.