Exceptional Absorption in a Deep-Subwavelength Plasmonic Film

In the realm of photonic integrated circuit design, on-chip absorbers are imperative for preventing signal degradation caused by unintended stray photons, which induce signal crosstalk and operational errors. An ideal on-chip optical absorber is expected to have a superior absorption capability across a wide range of frequencies while maintaining a minimal footprint. However, widely employed optical thin-film absorbers suffer from limited absorption due to inherent refractive index mismatches and short light-matter interaction lengths. Here a ≈45-nm thin metalayer is demonstrated that exhibits uniformly high absorption over a broad wavelength range from 350 nm to 4.5 µm in a wide range of incident angles up to over 60 degrees. The metalayer's performance notably exceeds the absorption predicted by standard plane-wave optics theories, potentially attributing to the Anderson localization effect. Integration of such a deep-subwavelength metalayer absorber into photonic circuits will facilitate the creation of highly efficient photonic chips, propelling the advancement of optical communication and computing.