High-speed (/spl ges/1 GHz) electrical and optical adding, mixing, and processing of square-wave signals with a transistor laser

This letter reports the common-emitter operation (gain beta=DeltaI_C/DeltaI_B>1, 20degC, I_B =36 mA, lambda=970 nm) of a dual-input transistor laser, arranged with a separate base contact on either side of a single emitter, that adds, mixes, and processes high-speed square-wave electrical inputs and delivers separate electrical and optical outputs. Applying a square-wave electrical input X₁(t) to one base contact and X₂(t) at a second base input, we obtain, with the pulsewidth modulated because of mixing, an electrical output proportional to betatimes[X₁(t)+X₂(t)] and a laser output tracking the electrical output (hnutimesf[X₁(t)+X₂(t)]) and exceeding it in bandwidth (pulse sharpness)