Tunable and switchable multi-wavelength actively Q-switched random fiber laser based on an electro-optic modulator and Sagnac loop filter

In this article, an actively Q-switched multi-wavelength random fiber laser based on a Sagnac loop filter and electro-optic modulator is proposed and demonstrated experimentally. The random distributed feedback media is a section of a 25 km long single-mode fiber. When the pump power is 350 mW, the polarization angle of the Sagnac loop filter can be adjusted by polarization controller to achieve the switching of a single, double, triple, and quadruple channels laser output. In the case of a single laser channel, dual laser channels, and three laser channels output, multiple laser channels can be tuned simultaneously with a fixed wavelength interval. In addition, by changing the waveform of the external signal source, the light and dark pulses can be switched. Owing to the half-open cavity structure and the high gain of the erbium-doped fiber, the laser threshold was reduced to 25 mW, and the light conversion efficiency was 0.67%. The laser is an ideal light source for medical imaging and long-distance sensing.