Hydrogel‐Scalable Nanoslide for Switchable Optical Spatial‐Frequency Processing

Abstract Spatial frequency processing is an essential technology for extracting morphological information from an optical image. Although various Fourier‐based flat optical elements have been proposed as spatial‐frequency filters to realize image processing, their transfer functions are statically fixed once fabricated, thus limiting the versatile, dynamic functionalities and practical applications. Here, a novel practical tuning strategy is demonstrated to realize switchable spatial‐frequency processing for edge‐enhanced and bright‐field imaging by employing a tunable hydrogel‐scalable nanoslide. By utilizing multilayered metallic and hydrogel stacks construction, the nanoslide directly manipulates the optical spatial frequency in the wavevector domain and exhibits opposite image processing at different wavelength channels due to the cavity‐induced wavelength‐sensitivity. More intriguingly, via controlling the ambient humidity, the angular‐dependent optical response of the nanoslide can be effectively tuned for dynamic edge‐enhanced imaging due to the hydrogel's inflation from moisture. In addition, the nanoslide is readily fabricated at a large scale and integrated into compact imaging systems, such as a biomicroscope. With the advantages of a high numerical aperture ≈0.8, polarization‐insensitive, microscopy‐compatible, and facile architecture, the proposed hydrogel‐based nanoslide can find potential applications in machine vision, real‐time image processing, biological imaging, and analog computing.