本論文對電光效應造成 非對稱之週期性反轉鈮酸鋰波導元件的光頻譜調變做詳細的探討。首先，我們推導了一個方便的公式可以用來對波導元件產生之二倍頻波的光頻譜調變做估計。而考慮到回火式質子交換波導製程會造成鈮酸鋰晶體本身電光係數的損失，此一損失對 非對稱之週期性反轉鈮酸鋰波導元件之光頻譜調變能力的影響也同時做了討論。從導波型式之準相位匹配二倍頻波產生的理論分析中，我們更進一步研究 非對稱之週期性反轉鈮酸鋰波導元件之非線性轉換效率與光頻譜調變能力兩者之間的關係。這些理論上的分析同時也提供了元件上的設計準則。針對不同的應用領域，可以搭配出適合的轉換效率與光頻譜調變能力。

在實驗中，我們首先驗證了 非對稱之週期性反轉鈮酸鋰波導元件 可經由電光效應，在外加一直流電壓的情況下觀察到輸出光頻譜的調變。頻譜調變量跟外加直流電壓的確是成正比的。不過我們也從實驗中發現，此種波導元件的頻譜調變能力居然跟打入波導的光功率有關係。當光功率比較強時，我們量測到的頻譜調變量會大於理論的估計值。此種現象從未在塊狀(非波導形式) 非對稱之週期性反轉鈮酸鋰晶體 上被發現，似乎是一種波導型元件才有的獨特現象。這表示有某些機制存在於我們的波導元件中，當光功率比較強時會加強頻譜調變的能力。在本論文中，我們也嘗試著去找出合理的機制來解釋此一現象。

降低光功率到一定程度後(在2mW以下)，頻譜調變能力跟波導中的光功率就比較無關了。所以在此狀況下量測到的頻譜調變可以與理論值來做比較。從比較中我們得知，鈮酸鋰經過回火式質子交換波導製程後，其電光係數約剩下原來的八成左右。而增加在波導中的光功率(超過25mW)可以讓頻譜調變能力提高成理論值的四倍。當波導中的光功率超過超過25mW，我們在電極間距為200um的通道波導上量到1.44nm/KV的頻譜調變率。此一數值也是我們在實驗中所量測到的最大值。使用一隨時間逐漸上升的高壓脈衝訊號(三角脈衝)取代原本的直流高壓加在我們的波導元件上，脈衝形式的二倍頻波便因此而產生。(此時打入波導的基頻波波長是固定的) 因為電荷累積的原故，使我們的波導元件不能產生高功率且短脈衝形式的二倍頻波。這些電荷累積可能存在於波導內部與緩衝層內。因此我們以降低波導內光功率的方式來得到較短脈衝的二倍頻波。實驗中，我們可以得到的最短脈衝約50us。

Electro-optic spectral tuning of asymmetric duty-cycle PPLN APE channel waveguide is investigated in this thesis. Firstly, we derived a useful formula for estimating spectral tuning of SHG process and figured out the influence of the decrease of electro-optic coefficient for wavelength tuning ability. From the theory of guided-wave QPM SHG, we further discussed the compromise between wavelength tuning rate and normalized conversion efficiency. Those analyses provide principles for designing such waveguide device with suitable ability of nonlinear conversion and spectral tuning.

In the experiment, we demonstrated the spectral tuning for SHG process by applying a DC voltage on waveguide chip. The wavelength tuning is linearly proportional to the applied DC voltage. A strange discovery is that normalized tuning rate is power dependent. When the power of guided-wave inside APE channel waveguide is high, the normalized tuning rate we measured is larger than theoretical value. Such a phenomenon seems to be never founded in bulked asymmetric duty-cycle PPLN case. Certain mechanisms may exist in our waveguide and assists the wavelength tuning when the power of guided-wave is high. Moreover, those mechanisms seem to be a threshold at 2mW fundamental power. When fundamental power exceeds the threshold, the normalized tuning rate increases linearly with fundamental power first and tends to saturate. We have tried to find the reasonable mechanism for interpreting the phenomenon in this thesis.

From the comparison between theoretical calculation and the normalized tuning rate we measured with 2mW fundamental wave at the waveguide input, we deduce the electro-optic coefficient could remain 80% of bulked LiNbO3 value after we performed the APE process. The normalized tuning rate can be increased by a factor four when the power of fundamental wave exceeds 25mW. On the channel waveguide with 200um spacing of electrodes and above 25mW fundamental wave at the waveguide input, we measured the largest wavelength tuning rate which is about 1.44nm/KV for fundamental wave. Second harmonic pulses are generated by applying voltage ramps on waveguide chip when the wavelength of fundamental wave is fixed. Charge accumulation may exist in channel waveguide and SiO2 buffer layer. By reducing the power of fundamental and second harmonic wave inside channel waveguide, 50us second harmonic pulse was produced in our experiment.

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