UBC Theses and Dissertations
Modeling of the transistor vertical cavity surface emitting laser Faraji, Behnam
The direct modulation of semiconductor lasers has many applications in data transmission. However, due to the frequency response it has been challenging to use directly modulated lasers for high speed digital transmission at bit-rates above 10 Gbps. With this in mind, designing a laser with a large modulation bandwidth to be used in high data-rate optical links is very important. Transistor lasers (TLs) are a potential candidate for this purpose. Based on these motivations, the main focus of this PhD research is on understanding the physics of the TL and predicting its performance. A detailed model that correctly incorporates the transistor effects on laser dynamics did not exist. The previous models do not differentiate between the bulk carriers and the quantum well (QW) carriers in the rate equations, do not include the effects of the capture and escape lifetimes in the QW, and significantly overestimate the bandwidth. To account for these phenomena, a model has been developed to study the dynamics of the TL. The model is based on the continuity equation in the separate confinement hetero-structure region of the conventional laser and the base region of the TL. It uses the quantum mechanical escape and capture of carriers in the quantum well region and the laser rate equations to model the laser operation. The model has been used to gain insight into the conventional separate confinement hetero-structure lasers, and the results of the model have been compared with the experimental results obtained for 850 nm vertical cavity surface emitting lasers(VCSELs). Analytical expressions have been derived for DC and AC parameters of the TL operating in common-base and common-emitter configurations. It has been shown that the TL operating in the common-emitter configuration has a similar modulation bandwidth as a conventional laser (~ 20 GHz). The common-base configuration, on the other hand, has a very large small-signal modulation bandwidth (> 40 GHz) due to bandwidth equalization in the TL. The large-signal performance of the TL has been studied. Finally, it has been shown that the common-emitter configuration with feedback has improved bandwidth by a factor of 1.5 in high bias currents.
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