光通訊中低電壓微機電式二維光切換器之特性分析及改良

Abstract

隨著頻寬需求的成長，光通訊變的日趨重要，全光學式(O-O-O)的微機電(MEMS)式光切換器因有相對優良的特性，可以廣泛的運用在光通訊上分波多工(WDM)系統的波長加減(add/drop)模組中。

本文中介紹一個小巧且由電磁力致動的低電壓微機電式光切換器，它的核心是一個垂直光行進路徑移動的微小鏡子，為了避免沾黏(stiction)的問題，透過彈簧來連接擺動的部分，但是這麼做會產生擺動幅度過大的不良影響，根據分析和模擬的結果，我們使用了一些技巧來克服這個困難，首先，我們模擬磁場的分布狀況，並且找到一個適當的位置來放置晶片，接著我們將本來使用的collimator換成lensed fiber，藉此來縮小光聚焦的範圍，最後我們根據傅立業(Fourier)轉換函數，發展出一套快速找尋特殊波形的方法，這個方法可以提升切換的速度，並且可以容忍因為製程所引起的些微誤差。

最後的實驗結果顯示，致動電壓僅需0.5V，切換時間大約是3ms，因為鏡面所引起的插入損耗(insertion loss)大約為0.45dB，WDL為0.05dB，TDL少於0.05dB，PDL 少於0.1dB. 整個元件的體積很小，適合和其他元件整合在同一個光通訊系統中。

Optical communications become more and more important due to the growth of bandwidth requirement. Transparent (O-O-O) MEMS optical switches are applied in add/drop switch modules in WDM systems with relative good performance.

A compact MEMS optical switch with low actuation voltage is demonstrated in this thesis. It is actuated by electromagnetic force. The kernel is a moving micromirror which is perpendicular to the light propagation. The flap is connected by serpentine springs to prevent the stiction problem. The trade-off for stiction-free (or no stopper) is large vibrations. To overcome this difficulty, several techniques are discussed in this thesis. We start from the simulation of magnetic field intensity and find the best position for the magnetic flap. Secondly, we analyze the optical property. To reduce the vibration, the collimator is replaced by a lens fiber with small beam size. Finally, we develop a fast method for finding a special driving waveform to achieve fast switching time based on Fourier transform function. This method also can tolerate the variation in fabrication processes.

Our experimental results show the actuated voltage is 0.5 volts. The switching time is about 3ms. The insertion loss caused by the micromirrors is 0.45 dB, WDL is 0.05 dB. TDL is less then 0.05 dB. PDL is less than 0.1 dB. The size is compact for the integration in optical communications.