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The possibility of tailoring III-V GaAs/Al0.3Ga0.7As concentric double quantum rings (CDQRs) by tuning the central barrier, width, and height of the rings brings out carrier confinement in different regimes, which make them suitable for specific applications. Using variational ansatz, Coulomb interaction and carrier localization in the rings are investigated through calculation of diamagnetism and binding energy of donor for different ring dimensions (both axial and radial). Conspicuous changes occur in the behavior of both binding energy and diamagnetism for different dimensions of the inner and outer rings. Tuning the central barrier below a critical limit favors coupling of the two rings and promotes tunneling. The effect of these modifications on the carrier localization has been investigated, which gives a good insight into selective design of CDQRs for specific applications.

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We propose a realistic numerical model based on cascaded self-similar pulse compression to generate low pedestal ultrashort pulses at 2.5 µm. Self-similarity in photonic crystal fibers (PCFs) has been attained by modelling exponentially dispersion decreasing and exponentially nonlinearity increasing chalcogenide PCFs. The tapered PCF (TPCF) model is theoretically designed using the fully vectorial effective index method (FVEIM) to obtain accurate effective refractive index, group velocity dispersion (GVD), and Kerr nonlinearity values with low computation time. Initially, fundamental soliton compression in As2S3 tapered PCF is being investigated for the pedestal-free reduction of the pulse width. Subsequently, the compression factor is further enhanced in the As2Se3 PCF-based nonlinear optical loop mirror. The numerical outcomes reveal a compression of 1 ps pulse down to a pulse width of 16.6 fs with a peak power of 116 W in a total fiber length of L = 61 cm.

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