Influence of the length of the absorber section on the mode locking behaviour of a 1064nm DBR laser determined on a single device

Easy-to-use and miniaturized laser systems emitting short infrared light pulses with high pulse energiesare more and more requested for applications in medicine, fluorescence spectroscopy, metrology, LIDAR, material processing and display technology. Mode locking in lasers is a well known technique to generate short and intense optical pulses. Passively mode-locked semiconductor lasers, monolithically integrating a forward biased gain section with a reverse biased saturable absorber (SA) section, have been identified as promising optical pulse sources. The shortest pulses are obtained with Fabry-Perot type of cavities due to the large number of longitudinal modes which can built-up the pulse. However, some applications require a fixed and stable center wavelength for which a grating has to be introduced in the cavity, either in an external cavity configuration or monolithically integrated as distributed Bragg reflector (DBR). One of the major challenges for passively mode locked DBR lasers is to increase the stability of the generated optical pulse train with respect to variations in the operation conditions. For this purpose it is important to optimize the lengths of the SA and gain sections carefully. Other parameters for stable mode locking are the reverse bias applied to the SA and the input current to the gain section. It is the aim of this paper to present detailed experimental investigations of the mode-locking behavior in dependence of these parameters.