Semiconductor Mirrors for Ultrafast Fiber Technology

This thesis studies the design of Semiconductor Saturable Absorber Mirrors (SESAMs) and their properties in mode-locked fiber lasers. The recovery times of SESAMs were controlled by ion bombardment and metamophoric growth. Quantum-dot structures enabled fast absorber recovery. In resonant saturable absorbers the modulation depth is enhanced, while the saturation fluence is decreased. The strong self-starting mechanism of high-modulation-depth and low-saturation-energy absorbers was used to achieve reliable mode locking without the need for dispersion compensation, while maintaining stability against Q-switched mode locking. It was shown that the two-photon absorption can become the dominant nonlinear mechanism in resonant SESAMs. Two-photon absorbtion in resonant absorbers can improve the stability against Q-switching instabilities; however, excessive two-photon absorption can decrease the modulation depth of a saturable absorber and, therefore, prevent mode locking.

The influence of the SESAM recovery time on the pulse quality was investigated. A fast absorber is preferable in order to avoid instabilities in the pulse shapes and to generate highly compressible pulses. We studied the effect of the recovery time on the self-starting operation of a mode-locked fiber laser. It was shown that amplified spontaneous emission can saturate a slow absorber and, therefore, degrade the modulation depth and prevent self-starting operation. Finally, we demonstrated synchronized operation of a mode-locked µm erbium fiber laser to a mode-locked 1.05 µm ytterbium fiber laser using a semiconductor mirror as an optically driven modulator.