Abstract
AbstractEffective dynamic modulation of visible light properties has been significantly desired for advanced imaging and sensing technologies. In particular, phase-change materials have attracted much attention as active material platforms owing to their broadband tunability of optical dielectric functions induced by the temperature-dependent phase-changes. However, their uses for visible light modulators are still limited to meet multi-objective high performance owing to the low material quality factor and active tunability in the visible regime. Here, a design strategy of phase-change metafilm absorber is demonstrated by making the use of the material drawbacks and extending design degree of freedom. By engineering tunability of effective anisotropic permittivity tensor of VO2-Ag metafilm around near-unity absorption conditions, strong dynamic modulation of reflection wave is achieved with near-unity modulation depth at desired wavelength regions without sacrificing bandwidth and efficiency. By leveraging effective medium theory of metamaterial and coupled mode theory, the intuitive design rules and theoretical backgrounds are suggested. It is also noteworthy that the dynamic optical applications of intensity modulation, coloring, and polarization rotation are enabled in a single device. By virtue of ultrathin flat configuration of a metafilm absorber, design extensibility of reflection spectrum is also verified. It is envisioned that our simple and powerful strategy would play a robust role in development of miniaturized light modulating pixels and a variety of photonic and optoelectronic applications.
Highlights
The field of dynamic nanophotonics [1,2,3] suggests the ultimate goal of high performance integrated optical modulation with compact volume and improved functionality via combination of active optical materials and advanced metamaterial technologies [1,2,3]
We start from investigating tunable complex refractive index of a baer 40 nm-thick VO2 film via the reconfigurable gradual insulator-metal transition (IMT) phenomenon
For systematic design of VO2 metafilm layer in phase-change metafilm absorber (PCMA) configuration, we propose the design rule based on anisotropic counter-intuitive properties of the Wiener’s bounds of effective medium approximation visualized in a complex (n, k) plane [52,53,54]
Summary
The field of dynamic nanophotonics [1,2,3] suggests the ultimate goal of high performance integrated optical modulation with compact volume and improved functionality via combination of active optical materials and advanced metamaterial technologies [1,2,3]. The main obstacle originates from the large extinction coefficients and moderate tunability of dielectric functions of PCMs in the visible spectrum (Figure S1 of Supplementary Materials) compared to those in the infrared regime Since these properties limit efficient oscillation of guided photonic mode and quality factor of PCMs, modulation depth and efficiency are hardly increased, simultaneously. Lee et al [38] proposed impressive demonstrations of reconfigurable switching of visible color using ultrathin GiresTournois absorber configurations that consist of indium tin oxide-capped GST thin film on metallic mirrors, respectively Their devices exhibit switching between two differently encoded visible spectra for certain fixed thicknesses of absorbing PCMs. it is hard to integrate those PCM based Gires-Tournois absorber pixels with different thicknesses for multiple spectral operations on a single substrate. Design extensibility of dynamic PCMA is studied numerically
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