Dynamic reconfigurable metasurfaces represent an advancing frontier in optical and materials science, enabling the modulation of optical properties for applications ranging from smart displays to optical sensing. Traditional methods, however, are predominantly restricted to single mode (reflection or transmission) displays and exhibit significant loss. This paper presents a novel all-dielectric metasurface incorporating low-loss phase change material (PCM) Sb₂S₃, designed to achieve concurrent high-efficiency reflective and transmissive structural color display in the visible spectrum. The research demonstrates dynamic optical control through reversible phase transitions of Sb₂S₃, and investigates the applications of such metasurfaces in multifunctional optical devices.

The metasurface architecture comprises TiO₂ nanopillars integrated with a Sb₂S₃ PCM layer at the base, positioned on a transparent quartz substrate. The configuration utilizes Mie resonance effects in dielectric nanostructures to achieve robust light-matter interaction with minimal loss. Critical structural parameters include nanopillar diameter (D), gap between nanopillars (G), and thicknesses of the Sb₂S₃ layer (t_PCM), upper TiO₂ layer (tTiO2), and bottom TiO₂ reflector (t_sub). Through switching Sb₂S₃ between amorphous (low extinction coefficient) and crystalline (high extinction coefficient) states, the effective refractive index and loss of the metasurface are dynamically modulated, enabling regulation of electric dipole (ED) and magnetic dipole (MD) resonances. Time-domain finite-difference (FDTD) simulations were performed to examine the optical responses, including reflectance, transmittance, and CIE chromaticity coordinates, under varying structural parameters and PCM states.

The metasurface structure, incorporating TiO₂ nanopillars with a Sb₂S₃ PCM layer at the base (Fig. 1), employs Mie resonance to achieve independent tuning of ED modes through layer thickness adjustment. Increasing t_PCM amplifies optical loss in the crystalline state, suppressing ED resonance (positioned at the nanopillar base) more substantially than MD resonance (distributed internally), resulting in stronger attenuation of the ED-related reflection peak (up to 70% intensity decrease) compared to the MD peak during phase transition [Figs. 3(a)?(b)]. Modification of D and G enables full visible spectrum coverage in reflective mode, with reflection peaks redshifting as nanopillar volume increases due to enhanced effective refractive index, and a broad CIE chromaticity gamut (exceeding 70% of CIE 1931 space) in the amorphous state that contracts upon ED suppression in the crystalline state (Fig. 5). In transmissive mode, the metasurface exhibits notch patterns corresponding to reflection peaks with high transmittance (>60%) due to low-loss materials, with minimal PCM impact as the transmission path primarily traverses the nanopillar and substrate, avoiding the PCM base [Fig. 2(d)?(f)]. The PCM’s volume directly affects tuning efficiency: larger t_PCM enhances extinction coefficient in the crystalline state, promoting ED suppression and peak redshifting [Figs. 3(a)?(b)]. Furthermore, the metasurface demonstrates high sensitivity to environmental refractive index, with reflection peaks redshifting and colors changing from green to magenta as the refractive index increases from 1.0 to 1.44, enabling visual refractive index sensing (Fig. 6). The low extinction coefficient of amorphous Sb₂S₃ ensures high energy efficiency (reflectance >70%, transmittance >80%), with crystalline-state absorption primarily affecting ED modes while preserving MD functionality, demonstrating independent resonance control through PCM phase transitions.

This investigation presents a reconfigurable transflective structural color metasurface utilizing low-loss PCM Sb₂S₃, engineered for full-color reflective and transmissive display applications. Through optimization of structural parameters and film thicknesses, the metasurface achieves comprehensive visible spectrum coverage and dynamic optical tuning via independent control of ED resonances through Sb₂S₃ phase transitions. The architecture incorporates polarization-insensitive cylindrical TiO₂ nanopillars with a Sb₂S₃ PCM layer embedded at the base, adjacent to a TiO₂ reflector on a quartz substrate. This configuration optimizes energy efficiency by reducing polarization dependence and utilizing low-loss materials, facilitating simultaneous high reflectance (>70%) and transmittance (>80%) across the visible spectrum. PCM’s strategic positioning at the ED resonance region enables selective suppression of ED modes during crystallization, while MD resonance remains largely unaffected due to internal nanopillar distribution. Computational analyses demonstrate that the upper TiO₂ layer primarily modulates MD resonance wavelengths, while the bottom TiO₂ layer affects ED resonances. In the amorphous state, pronounced Mie resonances produce vibrant structural colors, whereas crystallization disrupts ED resonances through increased extinction, diminishing reflectance and constraining the color gamut. The tuning efficiency increases with PCM volume, as thicker Sb₂S₃ layers enhance loss-induced ED suppression. Furthermore, the metasurface exhibits significant sensitivity to environmental refractive index variations, with reflection peaks redshifting and colors changing noticeably across different media, indicating its potential for optical sensing applications. This research introduces an adaptable metasurface design that integrates dual-mode color display, dynamic tunability, and low-loss operation, providing novel perspectives for reconfigurable optical devices in smart displays, optical communications, and adaptive sensing systems.