Film-coupled Log-periodic Optical Antennas For Near-intrared Light Absorption

In recent years, the absorption properties of metallic nanostructures obtained from THz to visible light have been widely studied and obtained some good absorption results, but the adaptability of the incident light polarization and angle conditions are not perfect. Log-periodic optical antennas have also been demonstrated to have not only the great performance in radiation properties but the new potential applications such as sensing, etc. Based on the versatile and commercially available finite element method (FEM), the paper numerically investigates the absorption properties of film-coupled log-periodic optical antennas in the near-infrared region, which have the potential absorption performance and corresponding application value.According to simulated data, the maximum absorption for TE and TM polarizations at normal incidence reach to 95% and 93%, respectively, and the optimal absorption of around 90% can be simultaneously obtained for both cases. Moreover, the main absorption peak remains more than 60% when the angle of the incident light changes ranging from ±85°.It is shown that the absorber represents the great absorption performance, including perfect absorption efficiency, light polarizations independence at normal incidence and the wide-angle feature, which reflects the resilience of external abilities and superiorities compared with other absorbers that have been studied.Besides, the distribution of electromagnetic physical fields and the benchmark have been used to explore and specify the reasons why film-coupled log-periodic optical antennas could have the perfect absorption in near-infrared region. The first reason is the electric field enhancement effect caused by the charge agglomeration on the antennas, which determines the absorption efficiency. The second reason is the magnetic resonance effect between the metal antennas and the metal patch, which contributes the location of the absorption peaks.What’s more, the log-periodic antenna-assisted absorption represents distinct polarization selectivity at high-order resonances. For oblique incidence, only the incident light of specific wavelengths within a narrow incidence angle can be almost entirely trapped inside the absorber, indicating special direction and wavelength selectivity of the absorber.Therefore, I fill up the gap that film-coupled log-periodic optical antennas can have the perfect absorption properties, including high absorption rate, light polarization independence and wide-angle feature. And all these features would lead to potential applications in photothermal generation, infrared detection technology, etc.