Polarization-independent quantum-confined Stark effect in an InGaAs/InP tensile-strained quantum well

We present a theoretical analysis and experimental studies on the control of the polarization-dependent characteristics of the refractive index change and the absorption change due to the quantum-confined Stark effect in an InGaAs/InP quantum-well structure. The polarization dependency which arises from the energy level splitting of heavy-hole and light-hole states in the quantum well can be controlled by inducing an appropriate amount of tensile strain in the quantum well. Measurements were carried out on the polarization dependency of the refractive index change and the absorption change in unstrained, 0.15, 0.3, and 0.45% tensile-strained 11.5-nm-thick InGaAs quantum-well structures through the whole spectral range, i.e., near and below the transition energy. We found that by inducing a 0.3% tensile strain in the 11.5-nm quantum well, the spectral profiles for the transverse electric and the transverse magnetic modes are brought closer to each other, with the peaks of the negative index changes corresponding to both modes occurring at the same wavelength with a slight difference in their absolute values. Moreover, in the long wavelength region, the refractive index change for both modes coincides in the wavelength as well as the absolute value. Based on these results, we have fabricated an absorption modulator and controlled the modulation characteristics with respect to the incident light polarization