- 學位論文
設計與研製雷射加工用光纖次波長圓環結構
Design and Fabrication of Sub-wavelength Annular Aperture on Fiber for Laser Machining
摘要
傳統光學因受限於透鏡的大小，不能無限提高透鏡的數值孔徑來增加空間解析度。但自從貝索光束的次波長聚焦能力被發現後，我們開始有機會突破焦點大小以及焦深長短交互影響的各種限制。為了突破光學的繞射極限，近場光學方法雖然可以達到超越繞射極限的聚焦點，但是其焦深短以及近場高度控制上都有一些問題。本研究團隊曾提出以次波長圓環孔徑結構製作在金屬薄膜上，可具有次波長尺度的貝索光束，並且可以應用在曝光微影製程以及雷射加工上，製作出高深寬比的結構。 另外，本研究團隊近年以研究具有次波長聚焦能力之光學頭為目標，對錐狀中空微管與次波長圓環孔徑結構進行研究，因此本論文的目標為將研究團隊所研究之次波長圓環孔徑與光纖作結合，先討論將次波長圓環孔徑製作在單模光纖光學頭上，再利用633nm波長的氦氖雷射去進行光強實驗，同時利用時域有限差分法電磁模擬軟體，對次波長圓環孔徑的各種尺寸進行模擬，探討不同尺寸下，次波長圓環孔徑對光學頭出光特性的影響。研究結果發現次波長圓環孔徑的大小確實會影響貝索光束的產生，而且會影響貝索光束的焦點位置和焦深長度，接著實驗光纖偏極態的特性，討論當線性偏極態的雷射光耦合進光纖後，出光是否仍維持同一種模態。
並列摘要
In traditional optical system, the size limit of lens prevents us from improving the spatial resolution by raising the numerical aperture of lens unlimitedly. It may break free the strong interactions between the focal spot size and depth of the focus after the Bessel beam’s sub-wavelength focal spot was discovered. To overcome the diffraction limit, near-field optical methods was identified to be one potential approach. But the extremely short depth of focus associated with the near-field system makes the distance control between the tip and the sample difficult. Our research group proposed a sub-wavelength annular aperture (SAA) on metallic film that produces Bessel beam before, which could maintain a sub-wavelength focusing capability. Some potential applications of this SAA approach include using lithography process or material processing technique to make high aspect ratio microstructures. Continue our team’s past goal of making long depth of focus sub-wavelength focal spot, the fabrication and usage of tapered hollow micro-tube and sub-wavelength annular aperture were explored in this thesis. Started from examining the approaches for making sub-wavelength annular aperture on the optical fiber head, 633nm He-Ne laser was used as the light source for the optical fiber head so as to examine the intensity profile of the light beam emitted. FDTD simulation was used to verify the effect of the geometric parameters of SAA fabricated on top of the optical fiber head on the emitted light beam properties. The results showed the size of SAA on the optical fiber head was an important factor for generating sub-wavelength Bessel beam with vastly different focal length and depth of focus. The polarization of the optical fiber head emitted light beam was also studied.