Bandwidth extension by trade-off of electrical and optical gain in a transistor laser: Three-terminal control

We present data and describe analytically the “trade-off” between collector current gain and the differential optical gain of a heterojunction bipolar transistor laser (TL). The electrical-optical gain relationship shows that a reduction in the transistor current gain is accompanied by an increase in the differential optical gain of the TL and, as a consequence, results in a larger optical modulation bandwidth. Third-terminal electrical control can be used to enhance the optical bandwidth of a TL beyond the “gain-clamped” cutoff limitation of the carrier-photon (population) resonance characteristic of a diode laser.