高效率低深寬比幾何相位超穎介面;High efficiency and low aspect ratio of geometric metasurface

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题名:	高效率低深寬比幾何相位超穎介面;High efficiency and low aspect ratio of geometric metasurface
作者:	賴澔霆;Lai, Hao-Ting
贡献者:	光電科學與工程學系
关键词:	深寬比;超穎介面;aspect ratio;metasurface
日期:	2022-08-25
上传时间:	2022-10-04 11:14:05 (UTC+8)
出版者:	國立中央大學
摘要:	幾何相位超穎表面可以通過增加結構的深寬比來實現高效率。然而，高深寬比的結構不利於製造。在本論文中，我們提出了一種解決方案，通過在GaN和Nb2O5 Nano-fin結構中添加高折射率材料層(a-Si)來降低深寬比要求。我們數值研究了三層Nano-fin結構的光學特性和提高總偏振轉換率(OPCE)。與GaN Nanofin結構相比，三層Nano-fin結構(a-Si=30nm)的深寬比要求從6下降到4 (下降33%)。在Nb2O5的情況下，深寬比(a-Si=35nm)要求從6下降到4(下降33%)。由於a-Si在633nm處有損耗，當共振節點位於a-Si層時，觀察到高穿透率。然而，具有高折射率的a-Si提供了好的相位調制能力。因此，當共振波腹位於a-Si層時，觀察到高偏振轉換率(PCE)。考慮到Nanofin結構製造的挑戰，我們專注於研究深寬比等於5的Nanofin結構來使OPCE增強。在此條件下，a-Si層的最佳位置是在基板上方300nm處。GaN三層Nanofin的OPCE比GaN Nanofin高7.3%。另一方面，Nb2O5三層Nanofin的OPCE增強為62.5%。三層Nanofin結構不僅可以降低深寬比的要求，還可以提高效率。;Geometric phase metasurface can achieve high efficiency by increasing the aspect ratio of structure. However, the structure with high aspect ratio is unfavorable for fabrication. In this thesis, we proposed a solution to reduce the aspect ratio requirement by adding a high refractive index material (a-Si) layer in GaN and Nb2O5 Nanofin structure. We numerically investigated the optical property and overall polarization conversion efficiency (OPCE) enhancement of three-layer Nanofin (GaN/a-Si/GaN and Nb2O5/a-Si/ Nb2O5). In comparison with GaN Nanofin, the aspect ratio requirement of three-layer Nano-fin (a-Si =30nm) dropped from 6 to 4 (about 33%). In the case of Nb2O5, the aspect ratio requirement (a-Si=35nm) dropped from 6 to 4 (about 33%). Due to the a-Si is lossy at 633 nm, higher transmittance was observed when a-Si layer located at the node of resonance. However, a-Si with high refractive index which provided better phase modulation capability. Therefore, higher PCE was observed when a-Si layer located at the anti-node of resonance. Consider the challenge of the Nanofin fabrication, we focused on investigating the OPCE enhancement of the Nanofin with aspect ratio equal to 5. Under this condition, the best location of a-Si layer is 300 nm above the substrate. The OPCE of the three-layer Nanofin was 19% higher than the GaN Nanofin. On the other hands, the OPCE enhancement of Nb2O5 three-layer Nanofin is 62.5%. Nanofin with three-layer can not only reduce the aspect ratio requirement but also enhance the efficiency.
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