High-efficiency optical switching using an electrochromic nanoplasmonic device

Abstract

We demonstrate high-contrast, high-speed switching of light transmission through nanoplasmonic devices using electrochromic films, at optical frequencies, by switching them between their reduced and partially oxidized states. Electrochromic polymers such as Polyaniline and PolyProDOT are two of the most studied conducting polymers with numerous applications including sensors [1], energy storage [2] and as the active component in smart-display devices [3]. In this work we study the electro-optical performance of electrochromic polymers deposited on deep subwavelength metallic slits and achieve high-contrast fast-switching optical response over a broad spectral range. The configuration of the electrochromic polymer deposited along the slit-sidewalls allows for orthogonalization of light and current paths; as well as the utilization of surface-bound electromagnetic waves, referred to as surface plasmon polaritons (SPPs) [4], to achieve significantly enhanced interaction of light-propagating inside the slits with the slit-sidewall coated polymer films (Fig. 1(a)). Furthermore, placement of the polymers on the slit-sidewalls enable use of thinner films of polymers to achieve the same contrast as thicker films in a conventional device along with a faster switching speed (Fig. 1(b) and (c)). We further demonstrate that by controlling the pitch of the nanoslit arrays, it is possible to achieve a full-color response with high contrast and fast switching speeds, while relying on just one electrochromic polymer. This enhanced electrochromic switching performance is enabled by the orthogonalization between the directions of light propagation, and that of charge transport from the electrolyte to ultra-thin active material inside the nanoslit and offers significant promise for the realization of full-color fast-switching smartdisplay devices. The approach presented here can be further translated to any optically sensitive material with thickness-dependent properties such as the charge diffusion length, with applications ranging from catalysis to photovoltaics.