ABSTRACT
Quantum-dot-based semiconductor saturable absorber mirrors (SESAMs) with fast response times were developed by molecular beam epitaxy (MBE). Using quantum dots (QDs) in the absorber region of the SESAMs instead of quantum wells, enables additional degrees of freedom in the design, the control of saturation parameters and the recovery dynamics. However, if one wants to integrate such a SESAM element into semiconductor surface emitting lasers such as a mode-locked integrated external-cavity surface-emitting laser (MIXSEL), the saturable absorber layers have to withstand a longer high-temperature growth procedure for the epitaxial formation of distributed Bragg reflectors (DBR). Typically defect related SESAMs will be annealed at those growth temperatures and lose their high-speed performance. Here we present a systematic study on the growth parameters and post-growth annealing of SESAMs based on high-quality InxGa1-xAs/GaAs quantum dots (QDs) grown by MBE at growth temperatures of 450 °C or higher. The good quality enables the QDs to survive the long DBR overgrowth at 600 °C with only minimal shifts in the designed operation wavelength of 1030 nm required for growth of MIXSEL devices. The introduction of recombination centers with p-type modulation doping and additional post-growth annealing improves the absorption of the high-quality QDs. Hence, low saturation fluences < 10 µJ/cm2 and a reduction of the τ1/e recovery time to values < 2 ps can be achieved.
ABSTRACT
We report on high quality InAs/InP quantum dot optical amplifiers for the 1550 nm wavelength range operating over a wide temperature range of 25 to 100 °C. A temperature dependent shift of the peak gain wavelength at a rate of 0.78 nm/K is observed. Consequently, two possible modes of operation are performed for a systematic device characterization over the entire temperature range. In the first mode, the signal wavelength is tuned to always match the peak gain wavelength while in the second mode, the signal wavelength is kept constant as the gain spectrum shifts with the temperature. Static characteristics, such as gain spectra and saturation levels, as well as dynamical properties, are presented. Distortion-less amplification of a single 28 Gbit/s signal and cross-talk free amplification of two channels, detuned by 2 nm, were demonstrated over the entire temperature range.
ABSTRACT
Quantum decoherence times in semiconductors are extremely short, particularly at room temperature where the quantum phase is completely erased in a fraction of a picosecond. However, they are still of finite duration during which the quantum phase is well defined and can be tailored. Recently, we demonstrated that quantum coherent phenomena can be easily accessed by examining the phase and amplitude of an optical pulse following propagation along a room temperature semiconductor optical amplifier. Taking the form of Rabi oscillations, these recent observations enabled to decipher the time evolution of the ensemble states. Here we demonstrate the Ramsey analogous experiment known as coherent control. Remarkably, coherent control occurs even under room temperature conditions and enables to directly resolve the dephasing times. These results may open a new way for the realization of room temperature semiconductor-based ultra-high speed quantum processors with all the advantages of upscaling and low-cost manufacturing.
