週期與閃耀角可調變光柵元件之設計研發

本研究目的在於透過微機電技術發展週期與閃耀角均可調變的光柵元件。光柵是一結構簡單卻用途廣泛的光學元件，它的主要功用在於將入射光依波長繞射至不同角度形成光譜。在第一個結構可調變光柵GLVTM發表以來，可調變光柵已為光學系統開啟了全新的發展方向，因為它的設計是如此多變，光學系統的設計可以更彈性更簡化。週期可調變光柵及閃耀角可調變光柵已分別被發展出來，但同時俱有這兩個調變功能的光柵元件至目前為止卻仍未曾面世。因此，我們發展可同時調變這兩個結構參數的調變光柵，希望它可以比目前的光柵更有效率且用途更廣泛。根據光柵方程式，建設性干涉波長和光柵週期在同一繞射角條件下成正比。因此，在光譜儀應用時，我們可以透過調整光柵週期旋轉光譜，再以便宜的單一光感測元件依續讀取各波長訊號，進而組合獲得完整的光譜。此外，閃耀角調變功能使我們可以任意調整光譜強弱分佈，將大部份光能量反射到所需的角度，進而達到增強光柵光效率的目的。在我們的光柵中，週期調變功能是由體型結構熱致動器驅動控制，而閃耀角調變功能則是由平行板靜電致動器達成。為了增加光柵的週期調變範圍，我們設計了全新的熱致動器。根據量測結果，這個致動器可以在5.48瓦內達到316微米的輸出位移。因為這樣的消耗功率仍大，我們另外提出了數個方法以降低所需消耗功率並透過實驗驗證其中幾個方法的可行性。在反射面部份，因為製程設備造成材料性質與結構尺寸上的不均勻，導致在驅動時所有反射面無法控制在同一角度，目前僅能操作在全開(on)和全關(off)兩狀態。雖然閃耀角是由非線性的靜電力所驅動，但根據理論，在靜電吸附(pull-in)現象產生前閃耀角是可以穩定控制在任意角度的。因此，若製程設備的均勻度可以改善，隨意控制閃耀角是可以達到的。雖然這個可調變光柵目前因為一些製程設備能力限制還不能作用得很好，但實驗結果已驗證這確實是一個可行的設計。製程方面若有更良好的機台，相信這個可調變光柵元件將可以很快被實現並帶來更多的應用。

關鍵字

微機電；可調變光柵；週期可調變；閃耀角可調變

並列摘要

This study aims at developing a novel pitch and blaze angle tunable grating device via Micro-Electro Mechanical Systems (MEMS) technologies. Grating is a powerful optical component for dispersing incident ray into specific angular direction corresponding to individual optical wavelength. After the first tunable grating device GLVTM was reported, tunable grating devices initiated a new region of optics since device design is variable, enabling easy construction of a flexible optical system. Pitch tunable gratings and blaze angle tunable gratings have been developed individually, but grating with these two tuning functions simultaneously has never been presented so far. In our group, we have been developing such gratings to bring more applications. According to the grating equation, the constructively interfered wavelength is in proportion to the grating pitch for the same diffraction angle. Thus we can tune the grating pitch and then detect all spectral lines sequentially by a photodetector. Besides, blaze angle tuning could adjust the intensity of the spectrum and enhance the grating performance. In our device, the pitch tuning function is carried out by bulk-micromachined thermal actuators, and the blaze angle tuning function is realized by electrostatic actuators. In order to enlarge the pitch tuning range, a novel thermal actuator is designed for our grating device. The experimental results show that the maximum output displacement of this actuator is over 316m within 5.48W. The non-uniform stiffness results from non-uniform pre-strain on the slats, which comes from the quality control of our fabrication facility available. Thus the blaze angle of our grating device presently could only work with on-off two modes. Although the blaze angle is tuned by electrostatic force via non-linear pull-in phenomenon, it is theoretically possible to tune the blaze angle stably before the pull-in happens if the quality of the fabrication facility is good to achieve good structure pre-strain uniformity. Although this tunable grating device does not function well due to some fabrication limits of available facilities, experimental results verify that this is a workable tunable grating design with feasible fabrication process. If better fabrication facilities are available, the full features of the high-performance grating device could be realized soon and bring more applications.

並列關鍵字

MEMS ； tunable grating ； pitch tunable ； blaze angle tunable

參考文獻

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