Analysis and design of surface-normal Fabry-Perot electrooptic modulators

Design equations relating the refractive index shift, absorption change, cavity length, and grating properties of Fabry-Perot modulators are derived. Experimental results of reflection modulators with GaAs/AlGaAs multiple-quantum-well active regions are given. The design equations are applied by investigating the optimization of the reflectivity modulation and the sensitivity of the performance on the operating conditions. The modulation is found to be determined mainly by the index shift and is less sensitive to the accompanying absorption change for a chirp greater than one where the chirp is defined as the ratio of the real part of index change to the imaginary part. Modulation can also be obtained via absorption modulation when the chirp is small. However, the residual loss in the cavity with multiple quantum wells should be kept lower than 500 cm^-1