Numerical analysis of a dual polarization mode-locked laser with a quarter wave plate

Abstract

Dynamical behaviors and frequency characteristics of an active mode-locked laser with a quarter wave plate (QWP) are numerically studied by using a set of vectorial laser equation. Like a polarization self-modulated laser, a frequency shift of half the cavity mode spacing exists between the eigen-modes in the two neutral axes of QWP. Within the active medium, the symmetric gain and cavity structure maintain the pulse's circular polarization with left-hand and righthand in turn for each round trip. Once the left-hand or right-hand circularly polarized pulse passes through QWP, its polarization is linear and the polarized direction is in one of the directions of AE45°with respect to the neutral axes of QWP. The output components in the directions of AE45°from the mirror close to QWP are all linearly polarized with a period of twice the round-trip time.