在光纖通訊發展中，已經有許多利用波導與光柵來當作濾波器的研究，且根據不同的光柵週期參數便可以選擇特定訊號，以達成濾波效果。而相較於短週期的傳統布拉格光柵 (bragg grating)，長週期光柵在製程上更為簡單，且為了達到更佳的雜訊抑制效果，長週期光纖光柵 (long-period fiber grating，LPFG)進而被廣泛研究且應用於光纖通訊領域中。然而，長週期光纖光柵卻有材料方面以及幾何形狀上的限制，光纖本身不能做太小之外，成本也相對高，很難達成微縮與量產，而為了滿足元件積體化的需求，長週期波導光柵 (long-period waveguide grating，LPWG)濾波器被提出，利用波導材料設計與選擇上的靈活性，提供了更多光學方面的應用。
在本論文實驗中，我們於z-cut的鈮酸鋰 (z-cut Lithium Niobate，LiNbO3)基板上，使用硬脂酸，且溫度280℃，分別交換4小時製作批覆層以及交換2小時製作波導層。並在完成兩次質子交換 (two-step proton-exchange)後，利用稜鏡耦合技術測得兩層折射率，再透過MATLAB程式求解超越波導方程式 (transcendental waveguide equations)並設計出光柵週期 Λ=50μm 的長度。接著利用三種不同的製作方式來完成光柵，其一同樣利用質子交換方式，以280℃交換0.5小時來完成相位光柵；其二是利用S1813光阻，經由標準黃光微影完成光阻波紋光柵；最後則是利用蒸鍍沉積銀金屬來完成銀波紋光柵。
此三種元件，在透過近場 (near-field)光纖對準量測後，結果顯示相位光柵抑制頻帶對比度 (dip contrast)最大可到達31.188dB，半高全寬 (FWHM)約為0.77nm；光阻波紋光柵抑制頻帶對比度最大可到達28.44dB，半高全寬約為1.18nm；銀波紋光柵抑制頻帶對比度最大可到達8.15dB，半高全寬約為0.6nm。
接著利用相位光柵探討溫度對於抑制頻帶的影響，在元件底部置入升溫器並施加溫度，且從室溫提高至40°C、50°C與60°C，並從頻譜分析儀中觀察到當溫度升高時，最大的抑制頻帶對比度會漸漸偏移至短波長地方，形成藍移 (blue shift)的現象。而三者光柵皆出現複數的抑制頻帶，我們判斷可能是MMI (multi mode interference)現象。

Steric acid respectively maintained at 280°C for 4 and 2 hours on different occasions is used as processing parameters to fabricate cladding and waveguide layers on z-cut lithium niobate (LiNbO3) substrate. After completing the two-step proton exchange (PE), the refractive index of the two layers is ascertained by using the prism coupling technique, and with this information at hand, the grating period Λ of 50μm was deduced by solving a system of transcendental waveguide equations with MATLAB. There are three methods adopted to fabricate the grating. One of them is to utilize the proton-exchange method by directly diffusing ions into LiNbO3 to realize phase grating while keeping the solution melt at 280°C for 0.5 hours. Another one is relied on using a Shipley S1813 photoresist to complete the corrugation grating by standard lithography. The third approach is to deposit and subsequently pattern silver metal as corrugation grating.

After measuring these three devices with the near-field optical alignment, the results show that the maximum dip contrast of the phase grating could reach up to 31.188 dB, and the corresponding full width at half maximum (FWHM) is about 0.77 nm. In comparison, the maximum dip contrast of the photoresist corrugation grating attains up to 28.44 dB with the FWHM of approximately 1.18nm. On the other hand, the maximum dip contrast ratio of the silver corrugation grating is determined to be around 8.15 dB with an FWHM of about 0.6nm. The thermal dependency of the phase grating is also probed by increasing the temperature from 40 to 60C and the corresponding dips have appeared to be blue-shifted. All of these devices have managed to demonstrate the multi-rejection bands, which is believably due to the multimode interference (MMI) phenomenon.

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