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High-speed modulation of quantum-dot lasers

The formation of nanostructures through the Stranski-Krastanow growth mode has proven to be an excellent method of forming damage-free quantum dots and has demonstrated laser operation and some improved characteristics expected for quantum dots. However, due to the complex nature of the bandstructure, quantum dot array formation, and carrier interactions in the dots, the understanding of self-assembled quantum dot lasers is still in the early stages. In order to meet a wide range of applications, the dynamic properties of the lasers have to be characterized, understood and, if necessary, improved. These properties impact small- and large-signal modulation phenomena and associated gain switching and chirp. We present our observations on the dynamic properties of self-assembled quantum dot lasers. In addition to improving laser performance, the discrete energy levels in quantum dots provide for unique laser applications. The lasing in self-assembled quantum dot devices has been shown to exist for ground and excited state transitions, depending on the gain in the active region. Through use of a cavity-coupled saturable absorber region, the gain may be altered to provide lasing in either the ground or excited state in a quantum dot laser, providing controlled wavelength switching, useful for optoelectronic integrated circuit applications and wavelength division multiplexing. Laser heterostructures with self-assembled In/sub 0.4/Ga/sub 0.6/As quantum dots as the gain medium were grown by molecular beam epitaxy (MBE).