This project investigates novel semiconductor saturable absorber structures based on III-V and Si/Ge- semiconductors for controlling the dynamics of mode-locked solid-state lasers. The novelty lies in an additional broadband absorber layer that is integrated into the saturable absorber and which allows for an independent external loss modulation by optical carrier-injection or quantum well saturation. The devices, which shall be designed, fabricated and tested in advanced laser systems, and are an extension of the semiconductor saturable Bragg mirror. This extension is necessary to suppress undesired laser instabilities like mode-locked Q-switching. Thus it should significantly increase the system lifetime and might bring mode-locked solid-state lasers in a specification range where they can be considered as a source for future optical communication systems. In addition it gives the possibility to achieve exceptionally high amplitude stability and to fully exploit the nonlinear optical response of the saturable absorber. The Si/Ge-technology offers the possibility for very broadband or short pulse mode-locked laser operation due to the high index contrast Si/SiO2-Bragg mirrors available in this technology.
With these absorbers a laser system can be operated in the continuous wave mode-locked regime independent of its other laser parameters such as pump power, repetition rate, output power, mode volume, upper-state lifetime, etc. For some applications intentional mode-locked Q-switched operation is desirable. This mode of operation can be enhanced to extract high-peak power ultrashort pulses. In this project, the device will be applied to mode locking of high-repetition rate lasers.
The project is a close cooperation between researchers in material science for semiconductor growth and device fabrication and investigators characterizing and testing the devices in advanced laser systems.
