【正文】 6我們可以看出。當(dāng)輸入兩術(shù)光的時候，兩術(shù)光在波導(dǎo)內(nèi)發(fā)生相互的干涉，干涉現(xiàn)象與圖1相比，沒有圖1明顯，那么我們可以考慮將兩個短波導(dǎo)的寬度進行縮小，縮小至1時，我們得到圖17：圖17 兩個輸入端寬度均變窄的光場干涉將圖17與圖16相比較，圖17的干涉現(xiàn)象沒有圖16的明顯，我們考慮將兩個段波導(dǎo)的寬度進行增加，增加至，我們將得到圖18：圖18 兩個輸入端均變寬的光場干涉圖18的干涉現(xiàn)象與之前都明顯，我們可以通過調(diào)整前面輸入光的兩個波導(dǎo)的寬度來使第三個寬波導(dǎo)內(nèi)的干涉達到最大，同時我們還可以通過調(diào)整折射率及第三個寬波導(dǎo)的長度，從而實現(xiàn)我們需要的光束。，，波導(dǎo)在z軸的偏移量設(shè)置為5300布局寬度設(shè)置為60，后面的寬波導(dǎo)的寬度設(shè)置為48，前面兩個輸入光場的波導(dǎo)的垂直偏移量設(shè)置為，我們將得到圖19圖19 中間輸出的兩個波導(dǎo)寬度變化的光場干涉與圖17相比較，我們可以看出，當(dāng)前面兩個輸入光的波導(dǎo)都設(shè)置的比較小時，很明顯，當(dāng)guide和cladding的折射率相差不大時（即圖19的參數(shù)），此時輸入光場的波導(dǎo)看起來比guide折射率和cladding的折射率相差大時（即圖17的參數(shù)）要寬。且干涉現(xiàn)象更明顯，所以，當(dāng)我們需要寬波導(dǎo)內(nèi)的光場干涉更明顯時，我們需要guide的折射率和cladding的折射率相差不大，而且，當(dāng)我們繼續(xù)縮小輸入光場的波導(dǎo)的寬度時，我們應(yīng)該會得到更加明顯的光場干涉，我們得到圖20：圖20 從右側(cè)調(diào)色板的值及圖20中峰值的顏色可以看出，圖20寬波導(dǎo)內(nèi)的光場比圖17寬波導(dǎo)內(nèi)的光場干涉更明顯。所以當(dāng)兩個輸入端均有光輸入時，將輸入光場的波導(dǎo)變窄比變細更容易得到明顯的干涉現(xiàn)象（與圖17相比較）。致謝這篇論文是在時堅老師的悉心指導(dǎo)下完成的，時堅老師為人隨和、幽默。從畢業(yè)設(shè)計選題到設(shè)計完成，時堅老師給予了我耐心指導(dǎo)與細心關(guān)懷。在我無助的時候他給予我?guī)椭谖颐悦５臅r候他給予我方向，每次和老師的討論我都會獲益匪淺，老師的性格也給了我很大的影響，時堅老師嚴謹治學(xué)的態(tài)度和精益求精的工作精神讓我獲益匪淺。這篇論文的寫作過程也是我的科研方法和工作能力提高的過程，很感謝時堅老師給予了我這樣一個學(xué)習(xí)機會。其次感謝我們一組的同學(xué)的幫助，正是有了我們的相互幫助和相互鼓勵，我們才圓滿的完成了本次的畢業(yè)設(shè)計。參考文獻【1】朱京平 光電子技術(shù)基礎(chǔ)（第二版）北京 科學(xué)出版社 2009 277~279【2】宋豐華 現(xiàn)代光電器件技術(shù)及應(yīng)用 北京 國防工業(yè)出版社 ， 39~40【3】石順祥 物理光學(xué)與應(yīng)用光學(xué) 西安 西安電子科技大學(xué)出版社【4】Gerd keiser 光纖通信 北京 電子工業(yè)出版社【5】萬助軍，吳亞明 基于多模干涉耦合器的集成熱光開關(guān)實驗研究 光學(xué)學(xué)報, 2006【6】馬慧蓮 多模干涉型集成光學(xué)器件研究進展 光電子 激光, 2003【7】黃耐容，王謙基于多模干涉耦合器的陣列波導(dǎo)光柵設(shè)計研究 光子學(xué)報, 2003【8】蔡純，張夕飛，朱建彬，張明德，肖金標多功能 2 2GaAs/GaAlAs 多模干涉型光開關(guān)分析電子學(xué)報, 2003【9】孫一翎, 李善祥, 李景鎮(zhèn)，多模干涉耦合器中光傳輸特性的分析與模擬，光電子激光，2001年3月 第3期 第12卷【10】孫一翎, 江曉清，王明華，多模干涉耦合器一般成像位置分析，光學(xué)學(xué)報，2004年6月，第6期24卷【11】孫一翎, 江曉清，王明華，多模干涉耦合器及其在光通信系統(tǒng)中的應(yīng)用，光通信研究，2004年，第2期，總第122期譯文Operation Principles for Optical Switches Based on Two Multimode Interference CouplersJunhe Zhou and Philippe Gallion ,Senior Member,IEEEAbstract—In this paper, the operation principles for optical switches based on two multimode interference (MMI) coupler are discussed in detail. Based on the analytical expressions of transfer matrix of the MMI couplers, the control mechanism and principles of the twostage MMI coupler based switch are derived. The device can be controlled by proportionally adjusting the interstage variable phase shifter array. N different switching states can be realized on this device. Index Terms—MMI coupler, optical switch. I. I NTRODUCTION OPTICAL munication networks have evolved into the era of all optical switching and various approaches to realize all optical switches have been proposed. The MEMS switch[1],the liquid crystal based switch[2],the directional coupler based switch[3],the thin ?lm based switch[4]and the MMI coupler based switch[5]–[7]have been either ercially available or realized in laboratories. In parison with other optical switches, the MMI coupler based switch has the advantages of smaller size, greater feasibility for integration, and the capability of thermaloptical and electrooptical tuning. More attentions have been placed on this novel switching technology and recently there have been signi?cant progresses in this ?eld .In[5],F. Wang etal. proposed a optical switch based a MMI coupler and realized it experimentally .L Cahill proposed the generalized structure for a cascadedMMIcoupler based switch in[6],[7].N different states of the switch were discussed in detail when N equals [8],aMMI coupler based switch was experimentally fabricated and demonstrated.Despite these pioneering works, the development of MMI coupler based switch still requires a prehensive theoretical model in order to characterize its operation principles. With such a model, we will know how to operate the device in an optimal manner.In this paper, based on the theory of the transfer matrix of the MMI couplers [9]–[12], the operation principles of MMI coupler based switches will be provided with the assistance of the analytical expressions. Totally N different states of the switch can be realized by proportionally tuning the variable phase shifter array in the middle of two MMI couplers. Simulations are performed to verify these operation principles. It is worth mentioning that the number of the states can be increased if the switches are operated in a cascaded manner, as is indicated by[7]. Detailed numerical simulation will be provided to verify our proposals. II. T HEORY A. MMI Coupler Transfer Matrix Theory [9]–[12] MMI coupler works as a selfimaging device and can be characterized by the transfer matrix theory [9]–[12]. With this theory, the analytical relationship between the input vector and the output vector can be obtained.To achieve the required transfer matrix, the positions of the input and output ports of the MMI coupler should be set carefully, so are the length and the width of the MMI coupler. Like [9], [10], the center of the input / output waveguides are placed at the position of (1)where is the effective width of the MMI coupler, is the number of input / output. The length of the MMI is set to be [10] (2)Where is the effective index of the MMI coupler, the free space wavelength. With the above configuration, the transfer matrix, which indicates the relationship between the input vector and the output vector, can be derived as [9] , [12] (3)where stands for the entry of the transfer matrix .The validity of the transfer matrix theory can be proved by the parison with the results obtained by [12],which gives the accurate information of the phase difference between the input and output signals and only differs from (3)by a few constant phase terms. B. MMI Coupler Based Switch Optical Schematic The optical schematic of the cascaded MMI coupler based switch has been introduced in [6], [7].The basic structure poses of two cascaded MMI couplers with phase shifters embedded in the middle of them. The phase shifters can be tuned either thermally or electronically and the tuning mechanism is dependent on the materials of the phase shifters.However, according to (3), the a