在伽瑪射線照射鈮酸鋰基板上研製脊形方向耦合器

Abstract

本論文探討伽瑪射線照射鈮酸鋰基板製作脊形光波導，藉以改善脊形外觀結構，並研究其對光場及電光調變特性的影響。 在脊形結構製作方面，使用純苯甲酸及含有已二酸之混合酸兩種不同質子酸源，在相同條件下利用氫氟酸與硝酸之混合酸進行溼式蝕刻，以完成脊形結構。同時，亦在相同的伽瑪射線照射劑量下，比較不同質子酸對脊形結構所造成的影響，以及比較不同的伽瑪射線照射劑量對脊形外觀的變化。實驗數據顯示採用伽瑪射線照射162.5krad且以純苯甲酸作為質子酸源之組合，在蝕刻8小時後，可獲得脊形的深度為4.472μm，深寬比為1.3。 在元件應用上，以製作脊形結構方向耦合器為例，實驗結果顯示經伽瑪射線照射過之元件可縮短耦合長度8.2%，表示耦合效應因伽瑪射線照射而增強。在電光調變部份顯示其半波電壓降低37.94%，訊熄比提高46.54%。證實伽瑪射線可有助於鈮酸鋰積體光學元件之改善。

In this thesis, ridge waveguides are fabricated by using proton exchange and wet etching in gamma-ray irradiated lithium niobate(LiNbO3). Experimental results show the depths and aspect ratios of ridge structures are all improved, which gives rise to optical fields of higher aspect ratios and electro-optic modulators with better characteristics. The ridge structures are obtained by proton exchange for 8 hr with various acid sources and etched for 8 hr with a mixture of hydrofluoric acid and nitric acid. The deepest depth and the aspect ratio of ridge structure are 4.472μm and 1.3 when the dosage of gamma-ray irradiation is 162.5krad. Moreover, the coupling length is shortened by 8.2% when a ridge-type directional coupler is fabricated with gamma-ray irradiated lithium niobate, which indicates that coupling effect is enhanced due to gamma-ray irradiation. And the half-wave voltage is decreased by 37.94%, and the extinction ratio is increased by 46.54%. Thus, it shows that gamma-ray irradiation is advantageous for the improvement of lithium niobate integrated optical waveguides.