RESUMEN
Dynamic control of circular dichroism in photonic structures is critically important for compact spectrometers, stereoscopic displays, and information processing exploiting multiple degrees of freedom. Metasurfaces can help miniaturize chiral devices but only produce static and limited chiral responses. While external stimuli can tune resonances, their modulations are often weak, and reversing continuously the sign of circular dichroism is extremely challenging. Here, we demonstrate the dynamically tunable chiral response of resonant metasurfaces supporting chiral bound states in the continuum combining them with phase-change materials. Phase transition between amorphous and crystalline phases allows for control of chiral response and varies chirality rapidly from -0.947 to +0.958 backward and forward via the chirality continuum. Our demonstrations underpin the rapid development of chiral photonics and its applications.
RESUMEN
Meta-lenses composed of artificial meta-atoms have stimulated substantial interest due to their compact and flexible wavefront shaping capabilities, outperforming bulk optical devices. The operating bandwidth is a critical factor determining the meta-lens' performance across various wavelengths. Meta-lenses that operate in a narrowband manner relying on nonlocal effects can effectively reduce disturbance and crosstalk from non-resonant wavelengths, making them well-suitable for specialized applications such as nonlinear generation and augmented reality/virtual reality display. However, nonlocal meta-lenses require striking a balance between local phase manipulation and nonlocal resonance excitation, which involves trade-offs among factors like quality-factor, efficiency, manipulation dimensions, and footprint. In this work, we experimentally demonstrate the nonlocal meta-lens featuring Huygens' bound states in the continuum (BICs) and its near-infrared imaging application. All-dielectric integrated-resonant unit is particularly optimized to efficiently induce both the quasi-BIC and generalized Kerker effect, while ensuring the rotation-angle robustness for generating geometric phase. The experimental results show that the single-layer nonlocal Huygens' meta-lens possesses a high quality-factor of 104 and achieves a transmission polarization conversion efficiency of 55%, exceeding the theoretical limit of 25%. The wavelength-selective two-dimensional focusing and imaging are demonstrated as well. This work will pave the way for efficient nonlocal wavefront shaping and meta-devices.
RESUMEN
Metasurfaces have shown their unprecedented ability in wavefront shaping and triggered various applications with state-of-the-art performances, e.g., color nanoprinting and metaholograms. Recently, these two functions have been combined into a single metasurface to further expand its capabilities. Despite the progress, the current dual-mode metasurfaces are mostly static and strongly hinder their practical applications. Herein, the realization of dynamic bifunctional metasurfaces is reported. Five metaholograms at two different wavelengths are multiplexed with structural colors by controlling the spectral and phase response of metasurface. Owing to the destructive interference and the resonance on external environment, the light diffraction at particular wavelengths can be switched between "ON" and "OFF" states, or remain unchanged with the change of surrounding refractive index. Consequently, the encoded metaholograms are selectively turned on and off, making the overall holographic image dynamically switchable. This concept paves a solid step toward practical applications of all-dielectric metasurfaces.