Localized states in an anisotropic single GaAs quantum ring were investigated in terms of polarization dependence of micro-photoluminescence spectrum at 5K. Given four Stokes parameters measured with a pair of linear polarizers and waveplates, the elliptical polarization states of two different vertical confinement states (k=1 and k=2) were compared with phase, rotation, and ellipticity angles. While the polarized emission intensity of the k=2 states becomes enhanced along [1,1,0] compared to that along [1,1¯,0], the polarization asymmetry of the k=1 states shows the opposite result. We conclude the polarization state is determined by the shape of the lateral wavefunctions. In the k=2 state, crescent-like wavefunctions are strongly localized, but the k=1 state consists of two crescent-like wavefunctions, which are connected weakly through quantum tunneling.

The optical modal gain of Cd0.6Zn0.4Te/ZnTe double quantum dots was measured using a variable stripe length method, where large and small quantum dots are separated with a ZnTe layer. With a large (~18 nm) separation layer thickness of ZnTe, two gain spectra were observed, which correspond to the confined exciton levels of the large and small quantum dots, respectively. With a small (~6 nm) separation layer thickness of ZnTe, a merged single gain spectrum was observed. This can be attributed to a coupled state between large and small quantum dots. Because the density of large quantum dots (4 × 1010 cm−2) is twice the density of small quantum dots (2 × 1010 cm−2), the density of the coupled quantum dots is determined by that of small quantum dots. As a result, we found that the peak gain (123.9 ± 9.2 cm−1) with the 6 nm separation layer is comparable to that (125.2 ± 29.2 cm−1) of the small quantum dots with the 18 nm separation layer.

We have studied optical modal gain in two-dimensional perovskite nanostructures in terms of gain saturation and mode confinement, where CsPbBr3 nanosheets of large lateral size (80 ∼ 300 nm) and thin thickness (5 ∼ 8 nm) were stacked in a patterned waveguide of polyurethane-acrylate. Concerned with the uncertainties and pitfalls in retrieving gain coefficient from the variable stripe length method, we have obtained a gain contour g(ℏω, x), whereby gain saturation was analyzed in terms of both spectrum energy (ℏω) and stripe length (x). For increasing excitation and temperature, an average gain was also obtained from g(ℏω, x), where the two dimensional excitons and the localized states are involved. We found the waveguide enhances both modal gain and thermal stability due to the increased mode confinement and heat conduction.