Self-Similar Multiresonant Nanoantenna Arrays for Sensing from Near- to Mid-Infrared

Tailoring nanoscale light concentration and electromagnetic near-field enhancement over a broad spectral range is crucial for many photonics applications such as infrared spectroscopy, photodetection, and light harvesting. So far, broadband light enhancement has faced significant challenges due to the difficulty of efficiently exciting resonances at spectrally separated wavelengths and the inability of current devices to individually tune each specific resonance. Here, we introduce a multiresonant structure based on the non-overlapping combination of plasmonic nanoantenna arrays with multiple periodicities. The self-similarity of the multiperiodic array, obtained by a fractal-like generation procedure, enables the excitation of a high number of resonances without compromising their excitation efficiency. We experimentally demonstrate devices with up to four independent resonances covering an unprecedentedly wide spectral range from 10 to 1.5 μm. Significantly, the reflectance signal is uniformly strong fo...