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  • 學位論文

可見光氮化鎵超穎介面產生高拓樸電荷數完美渦漩光

Generating perfect vortex beams with high topological numbers at visible wavelengths by GaN metasurfaces

指導教授 : 管傑雄 蘇文生
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摘要


渦漩的現象在生活中隨處可見,像是熱帶性低氣壓引起的颱風、水流造成的漩渦等,同樣的,在光場中也存在著類似的概念。和一般雷射光束不同,因渦漩光束夾帶著軌道角動量(Orbital Angular Momentum, OAM)的資訊,且其具有e^ilθ的方位角項,傳遞時會隨著拓樸電荷(Topological Charge, TC)進行扭轉,並且不同拓樸電荷數l的渦漩光束之間彼此正交,行進時不會互相影響。 這篇論文利用氮化鎵奈米天線柱搭配Pancharatnam-Berry(PB) phase設計原理,在藍寶石基板上使用六角形基底進行幾何排列,並針對450nm的雷射光進行模擬,成功製作出l=16、l=32兩種不同拓樸電荷的超穎介面,其直徑為100μm、焦距150μm、數值孔徑(Numerical Aperture, NA值)為0.3。為確保成品與設計相符,為長160nm、寬90nm的長方形奈米柱,在製作完成後也使用掃描式電子顯微鏡(Scanning electron microscope, SEM)檢測氮化鎵奈米天線柱的尺寸與垂直度。 在最後,我們使用圓偏振的雷射光束作為輸入,經過超穎介面後,在輸出端成功觀察到兩種不同TC數的渦漩光束,且以聚焦平面為對稱平面進行變化。並期許具備完整性與高解析度的渦漩光束在未來能應用在許多場合,像是光纖傳輸、光學顯微鏡、粒子操縱等。

並列摘要


The phenomenon of vortex is common in our daily lives everywhere. For instance, the typhoon is caused by the Tropical Depression and the vortex is generated by flowing water, etc. Simultaneously, the similar concept also occurs in the light field. Different from the common laser, because vortex beams provide information of Orbital Angular Momentum equipped with spatial phase dependence factor exp(ilθ) and twists with Topological Charge while transmitting. Moreover, vortex beams of different topological charge l are orthogonal, which will not have impact on each other while transmitting. This paper uses gallium nitride (GaN) nano-resonators with Pancharatnam-Berry(PB) phase design principle. The nano-resonators are arranged on sapphire substrate by hexagonal base, and simulated for 450nm laser. Two different topological charges(l=16、l=32) of OAM metasurfaces are designed with the diameter of 100μm, the focal length of 150μm and the numerical aperture of 0.3. To ensure that the products match the design (W=90nm, L=160nm), we also inspect the size and verticality of the GaN nano-resonators using scanning electron microscope(SEM). In the end, we successfully measured vortex beams with two topological charges after the circularly polarized incident light go through the metasurface. In the future, the vortex beams with integrity and high resolution can be applied to fiber transmission, optical microscope and particle manipulation.

參考文獻


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