Multiple pulse gain switched operation of surface-emitting semiconductor lasers

Surface-emitting semiconductor lasers are attractive for applications in optical computing, coherent communications, high-power two dimensional arrays, and integrated optoelectronics. For applications involving information processing, high speed pulsed operation of these lasers is necessary. The very short cavity length (~2–5 μm) results in a very short transit time; however, the required high-Q resonator substantially lengthens the cavity lifetime, and hence the gain-switched pulsewidth. Recent optical pumping experiments have demonstrated ultrafast gain-switched operation with pulse widths as short as 3.9 ps. In this report, we present the first results on optically pumped double-pulse excitation with pulse delays as short as 10 ps. Independently switched high-bit-rate multiple pulse trains are required for transmitting information. For pumping with a pair of time delayed pulses, we observe output pulse separations shorter than the input pulse separation. This suggests the use of SELs for optical multiplexing and signal processing. Output pulse separation and pulse width as a function of the input pulse separation at a constant pump power show good agreement with the theoretical simulation. For large pulse separations, the input and output pulse separations are identical. The shortest output pulse separation having a 7:1 peak to background ratio, for a BER of <10−9, was about 35 ps for an input pulse separation of 50 ps. This is readily extendable to smaller pulse separations for higher speed pulses by using lower-Q resonator structures.