Optical bandwidth enhancement of heterojunction bipolar transistor laser operation with an auxiliary base signal

We report the improvement, from 10.5 to 22 GHz, in the optical modulation bandwidth of a quantum-well (QW) heterojunction bipolar transistor laser (TL) by the use of an ac auxiliary base signal. Because of the three-terminal form of the TL, an auxiliary signal can be used to peak the photon output, e.g., stimulated recombination which simultaneously reduces the operating current gain, Β (= ICO IBO), and increases the laser differential gain. A shorter effective base carrier lifetime, τ, owing to the increased QW recombination rate (stimulated recombination), enhanced carrier transport to the "faster" QW collector (reduced Β) and differential gain, result in a higher 3 dB bandwidth (f3 dB =12π τ).