Enhanced Refractive Index Sensing with Direction-Selective Three-Dimensional Infrared Metamaterials

Three-dimensional (3D) geometries ensure large surface area interaction of photonic devices with the surrounding medium. Here, we demonstrate that metamaterials composed of 3D metallic Split Cube Resonator (SCR) elements assembled in various arrangements enable resonantly enhanced refractive index sensing. The proper arrangement of the SCR elements results in almost perfect narrow-band direction-selective absorption, which is highly sensitive to the refractive index of the surrounding environment. The experimental sensitivity achieved exceeds 5.5 μm per Refractive Index Unit (RIU) with theoretical predictions showing that this can reach 11 μm/RIU. The structures allow easy fabrication via direct laser writing and highly selective electroless metal plating. Thus, the proposed metadevices are ideal candidates for assisting cost-effective infrared polarization-resolved sensing and direction-selective spectral filtering in and out of the infrared atmospheric transparency window.