| 摘要: | 本次研究首先會介紹鈮酸鋰這種特殊材料，接著是講解有關於非線性現象以及準相位匹配的部分，還有介紹應用。比較傳統的塊狀鈮酸鋰和鈮酸鋰薄膜兩者之間的差別並了解二次諧波產生。接著將模擬鈮酸鋰薄膜的單模條件、極化週期變化和相位匹配波長，還有計算轉換效率跟製程容忍度，最後還有電極模擬。
模擬結束後就可以開始製程，黃光使用TSRI的儀器來製造極化反轉電極和波導黃光，蝕刻鍍膜使用台大的儀器，觀察極化反轉的結果使用清大PFM，極化反轉的部分利用設計的電路控制電流和電壓，LabVIEW用於控制極化反轉的脈衝訊號和量測極化反轉時的電流訊號，還有使用MATLAB來計算占空比，為了得知極化反轉深度，使用清大FIB進行切割後濕蝕刻來觀察反轉深度。極化反轉確認可行後下一步將進行波導製程，使用化學性乾蝕刻的方式來製造波導，最後鍍上一層SiO2來保護波導，下一步就可進行拋光，確認端面沒問題後才進入量測，但量測結果不太理想，因此後續將進行改善，重新量測損耗，最後的TE損耗為9.46 dB/cm，TM損耗為11.27 dB/cm，改善後的晶片成功量測到SHG現象，歸一化轉換效率計算出來的結果為281 %∙W^(-1)∙〖cm〗^(-2)。未來期望能有更好的製程結果，將有利於量測到更好的歸一化轉換效率，期望可以應用到壓縮態的量測。
;This research begins with an introduction to lithium niobate, a unique material, followed by an explanation of nonlinear optical phenomena and quasi-phase matching, as well as relevant applications. It compares traditional bulk lithium niobate and thin-film lithium niobate, highlighting their differences and relevance to second-harmonic generation (SHG). Subsequently, simulations are conducted to determine the single-mode conditions of thin-film lithium niobate, variations in poling periods and phase-matching wavelengths, as well as conversion efficiency and fabrication tolerance. Electrode design simulations are also included.
After simulations, the fabrication process begins. Photolithography is performed using equipment at TSRI to define the poling electrodes and waveguide patterns. Etching and film deposition are carried out with instruments at NTU. The poling results are examined using Piezoresponse Force Microscopy (PFM) at NTHU. The domain inversion process is controlled by a custom-designed circuit that regulates current and voltage. LabVIEW is used to manage the poling pulse signals and record the current during domain inversion, while MATLAB is employed to compute the duty cycle. To determine the inversion depth, the sample is sliced using Focused Ion Beam (FIB) at NTHU, followed by wet etching for visualization.
Upon confirming successful poling, waveguide fabrication proceeds using chemical dry etching. A protective SiO₂ layer is deposited, and the sample is polished. After verifying the end faces are suitable, optical measurements are performed. The initial measurement results were suboptimal, prompting further improvement. After re-measuring, the final transverse electric (TE) mode propagation loss was 9.46 dB/cm and the transverse magnetic (TM) mode loss was 11.27 dB/cm. The improved chip successfully demonstrated SHG, achieving a normalized conversion efficiency of 281 %·W⁻¹·cm⁻². Future work aims to enhance further the fabrication quality, which will be beneficial for achieving even higher normalized conversion efficiencies, with potential applications in squeezed-state measurements. |
