A Transparent All-Dielectric Multifunctional Nanoantenna Emitter Compatible With Thermal Infrared and Cooling Scenarios

In modern thermal infrared applications, multi-spectral camouflage scenarios should be developed to mitigate the thermal signature of an object. In general, camouflage needs to be satisfied in two main optical ranges: visible, and infrared (IR). In the IR range, two main camera modes are deployed to detect the IR signature of an object: i) short-wave IR (SWIR) cameras that detect the solar photons reflected off a surface, ii) mid-wave IR (MWIR) and long-wave IR (LWIR) cameras that directly collect the blackbody photons emitted from a hot object. Therefore, in an ideal scheme to acquire a multi-spectral camouflage function with self-cooling capability, the object should have: i) perfect absorption in the SWIR range, ii) perfect reflection in the MWIR and LWIR ranges, iii) perfect absorption and one-way transmission in non-transmissive IR (NTIR) window (to radiatively cool itself), and iv) visible transparency (to keep background visual appearance intact and to minimize the heat build-up due to solar absorption). In this paper, an all-dielectric nanoantenna emitter design is developed to comply with all the above-mentioned requirements. The approach relies on the indium tin oxide (ITO) grating structures coated on a flexible and transparent substrate (polystyrene). The spectral behaviors of the proposed structure are obtained using both analytical and numerical approaches. The design has an absorption peak with 0.8 amplitude in the SWIR mode (for the backward and forward illuminations), while it shows average reflections similar or equal to 0.7 in the MWIR and LWIR ranges for the forward illumination. The peak values of transmission and absorption within the NTIR window for the forward illumination are around 0.6 and 0.9, respectively. Meanwhile, the use of lossless materials within the visible range provides visible light transmission and minimizes the heat build-up due to solar absorption. In addition, the radiated power calculation model is utilized to demonstrate the low power detection on the IR cameras.