可形變鏡子的設計與製作

Abstract

在這篇論文裡，我們介紹了可形變的鏡子用在小型的光學系統上。這種鏡子是透過兩個平行板電容相吸的原理來達成形變而造成曲律半徑的不同，而使焦距也因此改變，便能達到自動對焦與變焦的目的。首先我們介紹了可形變鏡子的製程改進，主要是在上下電極間加了一個光阻高度以確保最後兩電極之間的距離是我們能夠確切掌握的，這對於模擬的精準度會有一定程度的提升；並且修改了製程的流程，使得在透過感應耦合電漿離子蝕刻系統蝕刻矽的時候並不會有金屬層存在。接著我們介紹自動對焦的光學系統，在這個系統裡需要可形變的鏡子在切線方向和法線方向有不同的焦距，因此我們需要在鏡子上設計一個橢圓的開孔去達到該需求。經過計算之後我們算出橢圓的長軸和短軸，接著模擬並在實驗中驗證模擬結果。基於光學系統影像品質的需求，必須在鏡子加電壓之後會成為自由曲面。我們根據光學系統的形狀模擬鏡子在加電壓之後的形狀與中央形變量。 在變焦系統裡，所需要的形變量大於目前我們所能夠製作的限制。所以我們選了一個楊氏模數和波森比較低的材料來做為彈性形變層，並用ANSYS模擬。從模擬結果，我們發現新材料能夠在同樣的電壓下達到更大的形變量。此外，我們將下電極透過ITO來導電以達到透明的效果，如此一來我們能將曲率由本來正的變成負的，滿足變焦系統裡的需要。

We compare the conventional and improved processes of deformable mirror(DM). The main difference between the conventional process and the new process is changing the order of the conventional process in order to etch silicon by ICP without any metal and putting a spacer between the top membrane and the bottom electrode to precisely control the gap between two electrodes which can ensure the accuracy of simulation of the relation between applied voltage and the displacement of the center of deformable mirror. The auto-focus(AF) optical system and zoom system which consist of deformable mirrors are the optical system without any moving elements that can fold the optical path to reduce the thickness of DM. We design the parameters of the major axis and minor axis of ellipse on the back side of the top membrane to address the need of AF optical designed by Wei-Ling Chang. Then we use ANSYS to simulate the design of DM which was used in AF system. We verify the simulation result by experiment. In the end of this part, we simulate the free form deformable mirror which can improve the preference of optical properties of auto focus system. Zoom system consisting of DM with bifocal type is introduced. The DM in zoom system needs negative optical power and large central displacement of DM. Changing the material to transparent can solve the problem of negative optical power. We use ITO as a conductive layer on glass and other parts are the same as conventional DM. The problem with large displacement we try to change is the material from PI-2610 to PDMS which has lower young’s module and Poisson ratio and simulate the displacement to compare it with the displacement of DM made by PI-2610 under the same power supplied. The displacement will increase by about 95% after changing the material of flexible layer. Then we design a process to produce the DM made by PDMS. To complete the DM and compare it with a the result of simulation is our future work.