Temperature-controlled photonic nanojet via VO2 coating

摘要

In this work, a numerical investigation of how temperature can tune the FWHM and working distance (WD) of a photonic nanojet (PNJ) is conducted. Vanadium oxide (VO2), a phase change material, is coated onto the top half-surface of a glass microsphere and illuminated with incident light at a wavelength of 800 nm. As VO2 changes from semiconducting to metallic phase, the refractive index of the VO2 layer changes at its transition temperature of 68 degrees C. It is found that a coating of 75 nm on a 5.0 mu m diameter microsphere with a refractive index of 1.50 is the most optimal, as it tunes the FWHM the greatest while remaining thin enough to have a high transmission. When temperature is raised from 20 degrees C to 90 degrees C, the FWHM varies from 0.43 to 0.37 mu m, corresponding to a 14.0% change. The WD varies from 0.29 to 0.20 mu m, corresponding to a 31.0% change. Tunable PNJs have potential applications in tunable nanolithography and imaging. (C) 2016 Optical Society of America