Comparison of the limits in performance of multiple quantum well and Franz-Keldysh InGaAs/InP electroabsorption modulators

The use of InGaAs/InP for electro-optical intensity modulation is discussed. In multiple quantum well (MQW) materials the peak excitonic absorption α_p imposes a limit on the maximum change in intensity due to electroabsorption. For InGaAs (100 Å)/InP(100 Å), α_p is only 25% of that for GaAs/AlGaAs. This accounts for the observed modulation limit of 1.4 dB/μm, which is significantly lower than the 3.9 dB/μm for GaAs based MQWs. For comparison, the authors calculated the maximum contrast possible in bulk InGaAs and found it to be 0.7 dB/μm. It is concluded that the major benefit of using InGaAs/InP MQWs is associated with their insertion loss and not their contrast ratio