Frequency tunable perfect absorber in visible and near-infrared regimes based on VO2 phase transition using planar layered thin films

We show a frequency tunable perfect absorber in visible and near-infrared regimes based on the vanadium dioxide (VO2) phase transition with a wide tuning capability typical of asymmetric Fabry-Perot (FP) cavities, comprising only an unpatterned, ultrathin (similar to lambda/15) film of VO2 deposited on a metal-reflecting substrate. VO2 undergoes a structural transition from an insulating phase (i - VO2) to a metallic phase (m - VO2) at 68 degrees C. A perfect absorption wavelength can be dynamically tuned over a wide wavelength range over 175 nm (from 905 to 730 nm in the measured spectrum) in visible and near-infrared regimes by controlling the temperature. More importantly, its absorption peaks become even stronger during the process of increasing temperature (from 96.8% at 905 nm to 98.4% at 730 nm). The frequency tunable absorption peaks were explained because both indices of i - VO2 and m - VO2 are very close to the maximum absorption point in n - k parameter space. (C) 2016 Optical Society of America.