Parametric study of optical transmission through plasmonic hole arrays modulated by the phase transition of vanadium dioxide

We have performed comprehensive electromagnetic simulations and preliminary experiments to explore the effects of geometrical and material parameters on the extraordinary optical transmission (EOT) through periodic arrays of subwavelength holes in a bilayer stack consisting of a gold or silver film atop a vanadium dioxide film (Au/Ag + VO2), where the latter undergoes a semiconductor-to-metal phase transition. Using the finite-difference time-domain (FDTD) and finite-element methods (FEM), we vary iteratively the array periodicity, VO2 film thickness and hole diameters, as well as the refractive index inside the VO2-layer holes and the VO2 optical constants. For each variation, we compare the metallic-to-semiconducting ratios of the zero-order transmission (T00) peaks and find sharp maxima in these ratios within narrow parameter ranges. The maxima arise from Fabry-Perot and Fano-type resonances that minimize T00 in the semiconducting phase of the perforated bilayers. At a fixed array period, the primary factors controlling the VO2-enabled EOT modulation are the VO2 thickness, diameter of the VO2-layer holes, and absorption in the two VO2 phases. Besides uncovering the origins of the higher metallic-phase T00, this study provides a protocol for optimizing the performance of the bilayer hole arrays for potential uses as dynamically tunable nano-optical devices

Dynamic Optical Gratings Accessed by Reversible Shape Memory

Shape memory polymers (SMPs) have been shown to accurately replicate photonic structures that produce tunable optical responses, but in practice, these responses are limited by the irreversibility of conventional shape memory processes. Here, we report the intensity modulation of a diffraction grating utilizing two-way reversible shape changes. Reversible shifting of the grating height was accomplished through partial melting and recrystallization of semicrystalline poly­(octylene adipate). The concurrent variations of the grating shape and diffraction intensity were monitored via atomic force microscopy and first order diffraction measurements, respectively. A maximum reversibility of the diffraction intensity of 36% was repeatable over multiple cycles. To that end, the reversible shape memory process is shown to broaden the functionality of SMP-based optical devices