微機電有機光學薄膜應用於可調式光衰減器

Abstract

可調式光衰減器在分波多工的光通訊系統中是一個非常重要的元件。它可以用來調整光的能量使增益平坦、遮擋光訊號與防止接收端訊號的飽和。在本篇論文中我們將介紹一個新的反射式光衰減器的設計。此設計不僅有反射式光衰減器的低偏極相關損耗(PDL)的優點，而且相較於一般的反射式光衰減器其製作上非常簡單。我們的光衰減器是由光纖準直器與可形變的光學薄膜所組成，而光能量的衰減是藉由改變面鏡的曲率進而改變聚焦點的位置所達成。 我們根據材料選擇圖選擇了一個低薄膜殘餘應力的有機材料來製造此可形變的面鏡。透過微機電的製程6 mm X 6mm開孔的可形變面鏡已被成功的製造出來並且無任何的破損。量測結果顯示其薄膜殘餘應力與楊氏係數均非常低，各為3.5 Mpa 與 15 Gpa，也由於這些好的機械性質我們才可以用氣壓的方式使面鏡達到20 mm的曲率。 實驗上我們量測到的光衰減約為8 dB，此與理論計算的質非常吻合，另外我們還量測了偏極相關損耗(PDL)與波長相關損耗(WDL)，由於光傳輸過程都是沿軸心對稱的，所以他們都跟預期的一樣低。根據以上的結果，我們成功的設計、製造和測試了一微機電製造的可調式光衰減器。

The variable optical attenuator is a critical optical component in WDM fiber-optic communication system. It can be used to equalize the optical gain, block the optical signal, and prevent the saturation of the receiver. In this thesis, we design a novel reflection type variable optical attenuator. It not only includes the characteristic of low PDL, but also can be easily fabricated compared to the common reflection type VOA. The VOA is made by an optical fiber collimator and a deformable mirror. Due to the defocus effect, the optical power could be adjusted by controlling the curvature of the deformable mirror. According to the material selection chart, the low stress organic material is applied to compose the deformable mirror. By micromachining fabrication, the 6 mm X 6 mm deformable mirror was successfully fabricated and tested without crack. The residual stress and Young’s modulus are measured as low as 3.5 Mpa and 15 Gpa, respectively. Due to these mechanical properties of organic thin films, the curvature of the deformable mirror as large as 20 mm is achieved by pneumatic force. The 8 dB optical attenuation is experimentally measured and agreed well with theoretical simulation. The PDL and WDL are both as low as expectation because of the center symmetric optical design. As a result, the novel MEMS VOA has been successfully designed, fabricated, and tested.