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(Color online) (i) Collector I-V characteristics of a single QW transistor laser (1 μm width, cavity length L = 300 μm) displaying current gain reduction, BVCE improvement, and decreased laser threshold (ITH = 18 to 14 mA), as temperature is reduced from 15 °C to 0 °C. (ii) Transistor laser optical output LI-V characteristics, showing the enhanced optical output power and wider VCE range of laser operation, as temperature is reduced from 15 °C to 0 °C. The open circles represent the transition from ground state to first-excited state laser operation.
(Color online) Measured and fitted optical frequency response of a single-QW TL at various base currents: T = 15 °C and VCE = 1 V; and T = 0 °C and VCE = 1.25 V. The reduced carrier-photon resonance (< 4 dB) is owing to the “fast” base recombination lifetime τB,eff (54 ps at 15 °C and 44 ps at 0 °C, including all the parasitic charging delay).
(Color online) Simultaneous electrical and optical channel eye diagrams at 20 Gb/s and 40 Gb/s data rates for a 300 μm cavity length TL: (i) 20 Gb/s eye diagram at T = 15 °C, IB = 60 mA, and VCE = 1 V; (ii) 20 Gb/s; and (iii) 40 Gb/s eye diagram at T = 0 °C, IB = 90 mA, and VCE = 1.25 V. For comparison, the optical channel eye diagrams are shifted to overlap with the reference collector electrical channel output.
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