Very low-refractive-index optical thin films consisting of an array of SiO_2 nanorods

Abstract

The refractive-index contrast in dielectric multilayer structures, optical resonators, and photonic crystals is an important figure of merit that creates a strong demand for high-quality thin films with a low refractive index. A $\mathrm{Si}{\mathrm{O}}_2$ nanorod layer with low refractive index of $n=1.08$, to our knowledge the lowest ever reported in thin-film materials, is grown by oblique-angle electron-beam deposition of $\mathrm{Si}{\mathrm{O}}_2$. A single-pair distributed Bragg reflector employing a $\mathrm{Si}{\mathrm{O}}_2$ nanorod layer is demonstrated to have enhanced reflectivity, showing the great potential of low-refractive-index films for applications in photonic structures and devices.