Reflectance tuned at infrared wavelengths based on aluminum metasurfaces

Infrared reflectance tuning or controlling based on functioned nanostructure has become a research hotspot. Via designing particular surface nanostructure, special infrared optical devices can be devised. However, once these functioned structures are fabricated, their optical characteristics are also determined, so as to limit their application. Here, we theoretically and experimentally demonstrated a signal voltage tunability of a dynamic infrared reflectance device by using an aluminum 2-dimension grating with a birefringence nematic liquid-crystal (LC). The hybrid microstructure allows electrically controlled reflectance at infrared wavelength by only applying a voltage signal with relatively low RMS amplitude. Besides the rubbed polyimide film fabricated for shaping initial LC direction contacted directly with nanostructures, the aluminum 2-dimension grating itself serves as an alignment layer to form a twisted LC cell. And the nanostructured aluminum also serves as an electrode. The working principle of our device is based on the fact that LC is polarization tunability. When applied a small electric field on the aluminum electrode and another electrode, the LC molecule can be reoriented and thus lead to a remarkable change of the dielectric constant surrounding the metallic nanostructure, and also excite relatively strong surface plasmon polaritons (SPP) modes on the LC-metal interface so as to provide a possibility of adjusting the reflectance. The aluminum metasurfaces is prepared by electron-beam lithography (EBL). The Fourier Transform Infrared Spectrometer (FT-IR) is used to observe the reflectance of the device at infrared wavelengths. A significant spectral tunability at 3μm to 4μm of such a device has been demonstrated by applying the voltage from 0 to 20 V_rms.