Strong coupling of metamaterial resonances to intersubband transitions of quantum dots for enhanced second-harmonic generation.

Recently, quantum confined structures have been widely studied for their nonlinear properties and applications in harmonic generation. However, because of lower orders of susceptibility, the generated harmonic power is low. In this paper, we present coupling of metamaterial resonance to intersubband transitions of quantum dots (QDs) for enhanced second-harmonic generation efficiency. To do so, first the QDs are designed so as to exhibit three electronic energy levels with identical energy spacing. The values of energy levels and the wave functions are calculated by solving the Schrödinger equation using modified effective mass approximation. The second-order nonlinear susceptibility of QD layers is then calculated, and the results are used in finite-difference time domain (FDTD) simulation of structure. Metamaterial structure is also designed to resonate in response to the frequency of QDs. The results show that for a pump input with 24 THz fundamental frequency, a harmonic with the 48 THz frequency appears in the output, with conversion efficiency of about 5×10.