利用光學天線結構達成光頻譜與偏振態之解析

Analysis of Optical Spectrum and Polarization by Plasmonic Optical Antenna

謝翊群(HSIEH, I CHUN)

指導教授 ： 黃承彬

國立清華大學/電機資訊學院/光電工程研究所/碩士(2012年)

https://doi.org/10.6843/NTHU.2012.00646

摘要

摘要
本論文利用經過設計的光學天線結構，以不同的天線尺寸以及光學天線排列方式分別達到解析不同入射光源頻率及偏振態之目的，為了得到較佳的解析能力，使用有限差分時域法模擬單一長條天線與長條天線對的光譜響應與近場能量分布，藉由調整長條狀天線排列方式（例如天線長軸方位角、長條對天線間間隔長度）與天線大小（包括天線長度、寬度及厚度）得到較佳的頻譜響應。若以相同光源激發不同幾何參數的天線陣列，當入射光源的頻率對應到該結構頻率響應峰值時，在結構附近將得到較強的近場光學訊號並藉由空間上近場訊號分布分辨入射光之波長；若考慮入射光偏振態，相同長條結構天線來說，電場方向平行於天線長軸相較於電場垂直天線長軸擁有較大的響應能力，因此亦可藉由不同的天線排列區分激發光源的偏振態。
實驗樣品以金作為結構材質配合電子束微影在玻璃基板上製作奈米天線陣列，量測上採用收集式近場掃描光學顯微鏡，以近紅外光波段光源經全反射光路產生之漸逝波做為遠場激發光源，再利用剪力回饋的方式量測天線陣列結構之近場光學訊號分布並與數值模擬結果比對。

關鍵字

電漿子 ； 偏振態解析 ； 可調變光場控制

並列摘要

Abstract
In this work, we use a designed optical antenna structure to analyze the frequency and polarization with varied antenna size and arrangement, respectively. First, we simulate the spectral response and near-field intensity distribution of single- and two-wire antenna using finite-difference time domain method. By modifying the antenna arrangement, such as the azimuth of long axis of the antenna, the gap width of two-wire antenna and the size of optical antenna, then we can have a better response to distinguish the different light. We illuminate the antenna array with different geometric condition at the same time. There is more powerful near-field optical signal nearby the structure when the frequency of incident light is corresponding to the resonance peak of spectrum. Considering the polarization of incident, when polarization is parallel to antenna’s long axis, the enhancement will be larger than the polarization perpendicular to antenna’s long axis, and then we can tell the difference of the wavelength and polarization of incoming light.
We use electron beam lithography to design and fabricate gold nano-antenna array on the glass substrate. In the aspect of measurement, we utilize the collection mode near-field scanning optical microscope with total internal refection set-up to obtain the real near-field intensity distribution around the optical antenna by shearing force feedback.

並列關鍵字

Plasmonics ； Polarization analysis ； Adaptive optical field control

參考文獻

15. P. Muhlschlegel, H. J. Eisler, O. J. F. Martin, B. Hecht, and D. W. Pohl, "Resonant optical antennas," Science 308, 1607-1609 (2005).

1. R. W. Wood, "On a remarkable case of uneven distribution of light in a diffraction grating spectrum," Philosophical Magazine 4, 396-402 (1902).

2. U. Fano, "Some theoretical considerations on anomalous diffraction gratings," Physical Review 50, 573-573 (1936).

3. U. Fano, "On the anomalous diffraction gratings II," Physical Review 51, 288-288 (1937).

5. U. Fano, "The theory of anomalous diffraction gratings and of quasi-stationary waves on metallic surfaces (Sommerfeld's waves)," Journal of the Optical Society of America 31, 213-222 (1941).