Double gap surface plasmons enabled ultra-thin meta-F–P cavity for light filtering in the near-infrared

Over the past years, metasurfaces have demonstrated remarkable and diverse capabilities in advanced control over light properties. Embedding metasurfaces into the Fabry–Pérot (meta-F–P) cavity reduces the required cavity length and provides new degrees of freedom for tuning. Most meta-F–P cavities exhibit excellent color filtering effects within the visible spectrum. However, achieving single mode-F–P resonance across the entire near-infrared range remains challenging due to the phase condition limitations of the metasurfaces. Here, we explore the integration of silver metasurfaces into an F–P cavity with a cavity length of only 150 nm. The very short cavity length allows for the existence of gap surface plasmons between the silver metasurfaces and both the top and bottom silver mirrors of the F–P cavity. This setup achieves narrowband filtering in an ultra-wide spectral range from 626.6 to 2548.3 nm while consistently maintaining single-mode resonance. Furthermore, we analyze the filtering effects of embedding anisotropic structures into the F–P cavity under x- and y-polarized incident light, revealing polarization-dependent filtering capabilities. Embedding the metasurface within the F–P cavity also allows for stable responses to different angles of incident light. This study underscores the potential of meta-F–P cavities in advancing optical filter technology for diverse applications in spectroscopy, telecommunications, and sensing.