Numerical study on an optimum Q-switching profile for complete multipeak suppression in an actively Q-switched Ytterbium fibre laser

Abstract

We propose an optimum Q-switching profile for complete suppression of the multi-peak phenomenon (MPP) without loss of pulse energy in an actively Q-switched ytterbium (Yb)-doped fibre laser. Most of the previously demonstrated approaches to suppress MPP have been based on adjusting of the rise time, and these rely on the assumption that the switching profile of the Q-switch has a trapezoidal temporal shape with a linear leading edge. These approaches leave one fundamental question as to whether or not there exists an optimum leading edge profile other than a simple linear one for complete suppression of MPP without loss of pulse energy. Through comparison among four different leading edge profiles. i.e. linear shape, sinusoidal function shape (increasing slope), sinusoidal function shape (decreasing slope), and composite function shape profiles, the proposed leading edge shape of a sinusoidal function (increasing slope) is shown to be capable of achieving complete suppression of MPP without loss of pulse energy under particular rise time conditions. It is shown that the use of a sinusoidal function (increasing slope) with a rise time of approximately 11 times the cavity round-trip time allows for the complete suppression of MPP without pulse energy loss in an exemplary, Q-switched, Yb-doped fibre Fabry–Perot laser.