High speed InP-based lasers: quantum well vs. bulk

The author reviews the basic factors governing high-speed lasers, focusing on those factors which are affected by the use of quantum well (QW) vs. bulk material, and summarizes results on recent high-speed lasers at 1.3 and 1.55 mu m. It is found that the present bandwidth results for InP-based lasers do not support the conclusion that QW lasers are faster than bulk lasers. At 1.3 mu m the 24 GHz record is held by a bulk laser, and at 1.5 mu m the 17-GHz record is a tie between bulk and unstrained quantum well lasers. The situation is quite different for GaAs-based lasers, where the record bandwidth is 28 GHz for a strained 4-well InGaAs/GaAs laser. Here, the improvement in differential gain from using strained QW lasers is much more dramatic, as high as 80*10/sup -16/ cm/sup 2/. It is noted that many earlier predictions of superior performance from QW lasers overlooked factors which offset the enhanced differential gain, such as the smaller optical confinement factor and internal loss, and reduction of differential gain by gain saturation and carriers in the barriers.<>