High-performance mid-infrared plasmonic bispectral routers by inverse design

In modern imaging systems, the application of multispectral imaging technologies is pervasive, furnishing an enhanced spectrum of information. Multispectral methods typically employ arrays of filters to selectively exclude light from undesired spectral bands, thus facilitating the capture of discrete narrowband data. However, the inherent multi-channel filtering process limits their energy utilization efficiency, a constraint that is magnified by the current trend of miniaturization in imaging devices. In this work, we have developed a pixel-level, metal-based, mid-infrared router by employing an inverse design method. This design achieved peak spectral efficiencies of 58.61% and 67.35% within the operational bands of 3.5–4.2 and 4.4–5 μm, respectively, and an average energy utilization efficiency across the entire operational range of 3.5–5 μm was elevated to 72%, which is 1.44 times higher than that of conventional filter-based systems. The designed routers were realized by standard nanofabrication processes that transfer the designed patterns into a gold film on a ZnS substrate. The spectral measurements show that the fabricated routers have a routing performance close to the simulation results.