Enhancement of excitonic optical nonlinearity in a quantum dot array

We propose a quantum dot array for enhancing excitonic optical nonlinearity, especially its figures of merit. The most important aspect of the quantum dot array for enhancing optical nonlinearity is the enlarged exciton coherence length due to the exciton transfer among quantum dots via dipole-dipole interaction. The important requisites for the material of the quantum dot array to enhance the figures of merit of the optical nonlinearity are shown to be the large oscillator strength of the excitonic transition and the small exciton Bohr radius. The optical nonlinearity of the quantum dot array is estimated for typical semiconductor materials, and an enhancement factor of the figures of merit is predicted to be several orders of magnitude over the previously known values. The tolerance limits are also discussed for the fluctuation of the quantum dot size and of the lattice constant of the quantum dot array, which would be unavoidable in actual samples.