We designed and experimentally reported modified potential InGaAs/InAlAs coupled quantum wells. In this structure, a large blue shift of the absorption edge of more than 35 meV is obtained at a reverse bias of -4 V. This predicts that a large negative electrorefractive index change can be achieved at longer wavelength region of the absorption edge.
The formation of the ground states in a GaAs/AlGaAs asymmetric coupled
quantum-well is analyzed with the use of coupled-mode theory. Based on perfect
work condition of traveling-wave modulators, the GaAs/AlGaAs coupled
quantum-well is optimized and the optimal coupled quantum well has a large
electro-refractive index change at low absorption loss.
By analyzing the ground eigenstates of an InGaAs/InAlAs symmetric coupled quantum well for zero applied electric field and their changes along with an applied electric field, we find its advantages and disadvantages when it is applied to optical switching device. Hence a novel coupled quantum well structure is put forward. To obtain polarization independence, a tensile strain is applied to the quantum well layer. In the case of low applied electric field (F=15 kV/cm) and low absorption loss (for TE mode, α=55.56cm<sup>-1</sup>; for TM mode, α=75.58cm<sup>-1</sup>), a polarization-independent large electric-field-induced refractive index change (for TE mode, Δn=0.0108; for TM mode, Δn=0.0107) is obtained in the optimized InGaAs/InAlAs coupled quantum well structure at operating wavelength (λ1550nm). The large refractive index change obtained with the optimized InGaAs/InAlAs coupled quantum well under so low absorption loss and applied electric field is very attractive for the semiconductor optical switch device. This manifests the optimized coupled quantum well structure has a great potential for application to ultra-fast and low-voltage optical switches and traveling wave modulators.
From the theoretical analysis for symmetric coupled quantum well, a novel coupled quantum well structure with low driving electric-field, low absorption loss and large field-induced refractive index change at 1.55 μm is put forward.