A Novel Coupled Quantum Well Structure with Low-Driving Voltage, Low Absorption Loss and Large Field-Induced Refractive Index Change

Based on a two-energy-level system, we analyse the changing ground eigenenergies of symmetric CaAs/Alx Ca1-x As coupled quantum wells in the presence of an applied electric field. From the theoretical analysis for symmetric coupled quantum well, we find the advantages and disadvantages when it is applied to travelling wave modulator.Hence the conception of quasi-symmetric coupled quantum wells is put forward. Based on the demands of travelling wave modulator for quantum well materials, the configuration of quasi-symmetric coupled quantum well is further optimized. Consequently, in the case of low applied electric field (F=20 kV/cm) and low absorption loss (α≤100cm^-1), a large field-induced refractive change △n (for TE mode, △n = 0.021; for TM mode, △n=0.0121) is attained in the optimized coupled quantum well.