RESUMO
Utilizing an automated optimization method, we propose a perfectly vertical grating coupler (PVGC) characterized by random structure, superior performance, simplified fabrication process, and increased minimum feature size (MFS). Within the range of MFS from 60 to 180â nm, the optimized PVGC exhibited a simulated coupling efficiency of approximately -2.0â dB at 1550â nm with a 34â nm 1-dB bandwidth. Experimental results for the PVGCs fabricated by electron beam lithography (EBL) demonstrated coupling efficiencies ranging from -2.5 to -2.8â dB with a 32â nm 1-dB bandwidth while maintaining high manufacturing tolerances. This represents the most outstanding experimental outcome to date regarding the coupling performance of a PVGC fabricated on a 220â nm silicon on insulator (SOI), without requiring any complex processes as reported in the existing literature.
RESUMO
Manipulation of the electromagnetic signature in multiple wavebands is necessary and effective in civil and industrial applications. However, the integration of multispectral requirements, particularly for the bands with comparable wavelengths, challenges the design and fabrication of current compatible metamaterials. Here, a bioinspired bilevel metamaterial is proposed for multispectral manipulation involving visible, multi-wavelength detection lasers and mid-infrared (MIR), along with radiative cooling. The metamaterial, consisting of dual-deck Pt disks and a SiO2 intermediate layer, is inspired by the broadband reflection splitting effect found in butterfly scales and achieves ultralow specular reflectance (average of 0.013) over the entire 0.8-1.6 µm with large scattering angles. Meanwhile, tunable visible reflection and selective dual absorption peaks in MIR can be simultaneously realized, providing structural color, effective radiative thermal dissipation at 5-8 µm and 10.6 µm laser absorption. The metamaterial is fabricated by a low-cost colloidal lithography method combined with two patterning processes. Multispectral manipulation performances are experimentally demonstrated and a significant apparent temperature drop (maximum of 15.7 °C) compared to the reference is observed under a thermal imager. This work achieves optical response in multiple wavebands and provides a valuable way to effectively design multifunctional metamaterials inspired by nature.