Theoretical Study of Operational Limits of High-Speed Quantum Dot Lasers
Final rept. 1 Oct 2008 - 30 Jun 2012
VIRGINIA POLYTECHNIC INST AND STATE UNIV BLACKSBURG
Pagination or Media Count:
A comprehensive theory of the modulation response of quantum dot QD lasers is developed. The factors limiting the modulation bandwidth are identified and the highest possible bandwidth is calculated. The highest bandwidth increases directly with overlap integral of the electron and hole wave functions in a QD, number of QD-layers, and surface density of QDs in a layer, and is inversely proportional to the inhomogeneous line broadening caused by the QD-size dispersion. At 10 dispersion and 100 overlap, the upper limit for the modulation bandwidth in a single QD-layer laser is as high as 60 GHz. The carrier capture from the waveguide region into QDs strongly limits the modulation bandwidth. As a function of the capture cross-section, the modulation bandwidth asymptotically approaches its highest value when the cross-section increases infinitely the case of instantaneous capture. With reducing the capture cross-section, the modulation bandwidth decreases and becomes zero at a certain nonvanishing value of the cross-section. The use of multiple-layers with QDs significantly enhances the modulation bandwidth. The internal optical loss, which increases with carrier density in the waveguide region, considerably reduces the modulation bandwidth. With internal loss cross-section increasing and approaching its maximum tolerable value, the modulation bandwidth decreases and becomes zero.
- Lasers and Masers
- Quantum Theory and Relativity