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

We report the improvement, from $10.5to22GHz$⁠, 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 $3dB$ bandwidth $(f3dB=1∕2πτ)$⁠.