本文主要利用電子束微影系統等半導體奈米製程技術，在氧化鋁基板上製作氮化鎵奈米圓柱設計基於可見光範圍中，具有與入射光偏振無關以及寬頻特性的超穎光學(metaoptics)元件。奈米圓柱中所產生的波導模態以及導模共振，利用改變奈米圓柱之直徑，使在設計波長中達成360度之相位變化並同時所有直徑之奈米圓柱保有相當高的穿透率。透過對所設計之奈米結構尺寸的優化，將達成360度相位變化並保有高穿透率的性質拓展到接近全部可見光範圍。在本文中主要展示了三種不同的光學元件，分別是光束偏折超穎表面(beam deflection metasurface)、超穎聚焦透鏡與集成以上兩者的斜聚焦超穎透鏡，上述光學元件在可見光波長範圍中皆擁有偏振無關與寬頻之特性。在數值模擬結果中，超穎聚焦透鏡與斜聚焦透鏡在可見光範圍中皆有良好的聚焦效果，光束偏轉超穎表面在設計波長532奈米中擁有高達94%之偏轉效果，並在波長480奈米到680奈米的波長範圍中皆擁有高於50%的偏轉效果。

關鍵字：氮化鎵、介電質超穎表面、超穎透鏡、斜聚焦透鏡、可見光寬頻、偏振無關

Recently, metasurfaces have gained a great attention due to their achievements of wavefront engineering. However, metasurfaces usually suffer from low working efficiency and narrow operating bandwidth. Although the Pancharatnam–Berry phase-based metasurface is able to expand the working bandwidth, this approach is limited to circularly polarized light. Here, we design dielectric nanocylinders to address the issue. By controlling the diameter of nanocylinder, these structures possess strong resonance out of the central wavelength and still cover full 2π phase modulation at target wavelengths. Thus, we optimize the physical dimensions of nanocylinders to generate appropriate transmission and phase response in the visible, expanding the working wavelength into nearly whole visible window. In this letter, we demonstrate three different optical elements, including on-axis focusing metalens, off-axis focusing metalens, and gradient metasurfaces. All these elements have broadband and polarization-insensitive properties in the visible. According to the simulation results, both on-axis and off-axis focusing metalenses have great focusing efficiency across the entire visible spectrum. The gradient metasurface shows ~94% deflection efficiency at a wavelength of 532nm and over 50% efficiency for 200 nm bandwidth in average.

Key words: Gallium nitride, Dielectric metasurfaces, Metalens, Off-axis focusing metalens, broadband response, polarization independent.

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