Active near-field plasmonic switches based on Sierpinski-fractal nanoantennas on VO2 films

We propose active near-field plasmonic switches based on a Sierpinski-fractal contour-bowtie plasmonic nanoantenna on top of a VO2 (vanadium-dioxide) thin film. The near-field intensity of the proposed fractal plasmonic nanoantenna can be switched by the application of heat, voltage, or optical energy to the underlying VO2 layer, which leads to a phase change of VO2 from the semiconductor state to the metallic state. This phase transition of the underlying VO2 film leads to an overall change in the optical properties of the nanoantenna system, hence driving the switch from an OFF state (with low near-field intensity) to an ON state (with high near-field intensity). The near-field switching ability of the proposed switch is quantified by the intensity switching ratio (ISR), i.e. the ratio of the intensity between the two arms of plasmonic nanoantenna in its ON state to its OFF state (I (ON)/I (OFF)). Finite difference time domain simulations were employed to calculate the ISR of the proposed near-field plasmonic switches. As the fractal order of the Sierpinski-fractal contour-bowtie nanoantenna is increased, the intensity in the 'ON' state of the switch is enhanced along with a reduction of intensity in the 'OFF' state of the switch. Thus, higher fractal orders of the Sierpinski-fractal contour-bowtie plasmonic nanoantenna lead to very high values of the ISR for the proposed near-field switch. We demonstrate an ISR of similar to 900 with a fractal order of 2 for the proposed switch which is the highest value of near-field ISR reported thus far for a near-field plasmonic switch. Further, we also demonstrate that the ISR and the spectral response of the proposed near-field switch can be controlled by changing its structural parameters such as the length of the nanoantenna arm, the contour thickness, and the thickness of VO2 layer.