Abstract: A refractive index variable element includes a structure including quantum dots having discrete energy levels and a dielectric matrix surrounding the quantum dots, and an electron injector injecting an electron into the quantum dots through the dielectric matrix.

Abstract: Refractive index changing apparatus includes quantum dots each having discrete energy levels including ground level and excited level, the excited level being higher than the ground level even if energy due to ambient temperature is provided on the quantum dots, barrier structure unit formed of dielectric which surrounds the quantum dots, injection unit configured to inject an electron into position of the ground level in each quantum dot via the barrier structure unit, utilizing tunneling effect, or to prevent injection of an electron into the position, injecting the electron or preventing injection of the electron controlled by changing an energy level of the injection unit, source which emits, to the quantum dots, first light beam having first energy for exciting electrons from the ground level to the excited level, and source which emits, to the quantum dots, second light beam having second energy different from the first energy.