All-optical loop stores 1.25-kilobit packet at 10-gigabit rates for minutes
Data packets of 1.25 kbit traveling at rates of 10 Gbit/s can be stored in an all-optical storage loop, report researchers at MIT`s Lincoln Laboratory (Lexington, MA) in collaboration with the MIT Department of Electrical Engineering (Cambridge, MA). A 980-nm master oscillator/ power amplifier pumps an erbium-doped fiber to generate a signal at 1532 nm. Optical amplitude modulation preserves data spacing by cross-gain saturation of a semiconductor diode-laser amplifier; it is periodically saturated by an external 1480-nm control laser modulated at 10.6 GHz with a lithium niobate electro-optic modulator. This output is coupled into the loop by a polarizing beamsplitter. The resulting variations in amplifier transmission maintain pulse spacing for the data bits in the loop. A 10% output coupler pulls the stored packet for display and analysis. The ring successfully preserved packets on the order of minutes, far in excess of the estimated millisecond durations required for time-division multiplexing (TDM) networks.
The group has demonstrated storage loops with a capacity of 1.75 kbit at up to 20 Gbit/s transmission rate, but that configuration required an electro-optic modulator in the loop. While the all-optical loop contains an out-of-loop electro-optic modulator at present, researchers expect to replace the control source with an optically modulated alternative. The approach thus has the potential to achieve the 100-Gbit/s rate necessary for the high-speed TDM networks of the future.