Figure-eight mode-locked fiber lasers based on a nonlinear symmetrical optical loop mirror

In this work we investigate a figure-eight passive mode-locked fiber laser which is formed by a Nonlinear Optical Loop Mirrror (NOLM) using a symmetrical coupler and a Quarter-Wave Retarder (QWR) in the loop. The NOLM has the-function of a saturable absorber, which is a non-lineal element. Thus, the response for an optic signal of entrance is dependent of the intensity, so the NOLM output pulse is narrower than the NOLM input pulse. The advantage of this configuration is that we need to adjust only one element to get the mode-locked pulses when the pump power is up to 70 mW, this element is the QWR angle. The laser generated pulses around 30 ps by a fundamental repetition frequency approximately of 0.8 MHz.