Sharp Fano Resonance and Spectral Collapse in Stimuli‐Responsive Photonic Structures

Abstract Stimuli‐responsive materials can sense environmental conditions and respond in predesigned ways. Such intelligent materials have a wide range of potential applications; however, they are usually limited to rather simple geometries. 3D printing is suitable for complex 3D objects with fine details. In particular, four‐dimensional (4D) printing of smart materials can be ideal for various stimuli‐responsive structures with highly enhanced functionalities. However, no studies on active, reconfigurable photonic structures in which external stimuli can induce a drastic response change have been reported. The 4D printing of stimuli‐responsive, Fano‐resonant structures that can exhibit sharp spectral resonances in an optimized lattice structure is demonstrated here. Specifically, shape memory polymers are employed and resonant microwave structures that undergo structural reconfiguration upon heating are demonstrated. When heated above the glass‐transition temperature, disordered lattices are transformed into a permanent, ordered lattice, resulting in a drastic change in their transmission spectrum. The origin of the sharp Fano resonance and spectral collapse is further elucidated using angle‐dependent transmission spectra. 4D printing could be a very interesting route for microwave active photonics. It can enable active reconfiguration without an electric power supply. It could therefore be useful in remote sensing applications such as long‐distance environmental monitoring.