Active tuning of the Fano resonance from a Si nanosphere dimer by the substrate effect.

Abstract

All-dielectric materials have aroused great interest for their unique light scattering and lower losses compared with plasmonics. Generally, optical properties made by all-dielectric materials can be passively controlled by varying the geometry, size and refractive index at the design stage. Therefore, the realization of active tuning in the field of nanophotonics is important to improve the practicality and achieve light-on-chip technology in the future. Herein, we combine the high refractive index of Si and the phase transition of VO2 to form an active tuning hybrid nanostructure with higher quality factor by depositing Si nanospheres on the VO2 layer with an Al2O3 substrate. As the temperature goes up, the refractive index of the VO2 layer switches from high to low. The scattering intensity of the magnetic dipole resonance of Si nanospheres decreases differently depending on their size, while the intensity of the electric dipole resonance remains almost unchanged. Meanwhile, Fano resonances are observed in the Si nanosphere dimers with a continuous variable Fano lineshape when adjusting the temperature. Mie theory and substrate-induced resonant magneto-electric effects are used to analyze and explain these phenomena. Tuning of the Fano resonance is attributed to the substrate effect from the interaction between Si nanospheres and phase transition of the VO2 layer with temperature. These light scattering properties of such a hybrid nanostructure make it promising for temperature sensing or as a light source at the nanometer scale.