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 X 1 (t) to one base contact and X 2 (t) at a second base input, we obtain, with the pulsewidth modulated because of mixing, an electrical output proportional to betatimes[X 1 (t)+X 2 (t)] and a laser output tracking the electrical output (hnutimesf[X 1 (t)+X 2 (t)]) and exceeding it in bandwidth (pulse sharpness)