Variable optical attenuators based on SOI with 3 μm top silicon layer.

In this paper, electro-absorption variable optical attenuators (VOAs) have been designed and fabricated on silicon-on-insulator material with a 3 μm thick top silicon layer. We have simulated the impact of doping distance, doping width, doping depth, doping concentration, and doping length on VOA's power consumption at 20 dB attenuation. We have found that the power consumption of VOA at 20 dB attenuation will decrease as the doping distance and doping width get smaller, while the doping depth and doping concentration get larger. We have further demonstrated that the power consumption can also be reduced by increasing the doping length and by taking a series structure theoretically. In this paper, VOAs with different doping structures, doping distances, doping widths, and doping lengths have been fabricated, and the tested results have verified our theoretical analysis. With doping distance of 8 μm, doping width of 15 μm, doping length of 1 cm, doping concentration of 1×1019  cm-3, and doping depth of 0.9 μm, the power consumption of the series VOA at 20 dB attenuation is 470 mW, and the rising/falling time is 54 ns/49.5 ns.