1×2、1×4與2×2微/奈米機械式光開關之研製

Abstract

本論文之研究目的在於設計製造出小尺寸、結構簡單與具高可靠度之微/奈米機械式光開關，包含了1×2、1×4與2×2三種重要型式之光開關元件。本研究採用了精密定位技術與微機電製程技術相結合，應用了微機電技術高精度之優點，製作出精密的光纖夾持器與超薄反射鏡，並且節省了高昂的全微機電(all MEMS-based)式製程開發費用與設備成本。此外，利用幾何縮小定位誤差原理來達到微/奈米定位精度等級，以完成光開關元件之製作。 在1×2光開關方面，以『光纖直接對位』為光路傳輸架構，以微機電製程製作出光纖夾持器來精確地夾持兩根輸出端光纖。運用了兩階段幾何縮小定位誤差原理，將輸入端光纖的切換定位誤差縮小至0.18μm以下。經實驗結果證明，光開關最佳插入損耗為ch1:0.8dB、ch2:1.4dB，串音≦80dB，切換時間為5ms，經切換10,000次後其插入損耗之變化值為ch1: 0.04dB、ch2: 0.02dB，再持續切換1,000,000次後取值100次之插入損耗的變化值為ch1: 0.024dB、ch2: 0.006dB。元件外觀尺寸為7.5×16×20mm 。 在1×4光關關方面，藉由已研發成功之1×2光開關製程技術與光路傳輸架構，應用兩繼電致動器來組成兩切換方向相互垂直之撥切機構，以邏輯電路控制來驅動兩繼電致動器作動以達到1×4光路切換之目的。首先，以微機電製程製作出光纖夾持器來精確地夾持四根輸出端光纖，並運用了兩階段幾何縮小定位誤差原理，將輸入端光纖的切換定位誤差縮小至0.27μm以下。經實驗結果證明，最佳插入損耗為：ch1: 0.68dB、ch2: 1.49dB、ch3: 0.71dB、ch4: 0.97dB，最快切換時間為5ms，為測試長時間穩定度，再撥切10,000次後之插入損耗值分別為ch1: 1.67dB、ch2: 1.63dB、ch3: 0.75 dB、ch4: 0.98dB，元件外觀尺寸為20×20×25mm 。 在2×2光開關方面，設計上採四根光準直器呈90°相互垂直排列在同一平面上，以微機電技術製作出超薄雙面反射鏡當作光訊號反射元件，厚度: 1.8μm，表面粗糙度: 5.721nm。應用了微機電技術的高精度優點，並克服在組裝上須使用透鏡光纖之高成本、高錯位敏感度之缺點。相較於傳統2×2稜鏡反射式光開關，將減少對光困難度及使結構簡單化。經實驗結果證明，最佳插入損耗為: ch3: 0.281dB、ch4: 0.547dB(光路直行狀態時)。ch3: 0.545dB、ch4: 0.571dB(光路反射狀態時)，最快切換時間: 5ms，串音≦80dB，長時間撥切10,000次後，其插入損耗值分別為ch3: 0.31dB、ch4: 0.52dB(光路直行狀態時)，ch3: 0.61dB、ch4: 0.62dB(光路反射狀態時)。 另外，為突破光開關元件自動化量產之產業發展瓶頸，本論文提出一套整合了CCD影像處理模組，壓電平台微動模組及光損耗檢測模組，以LabVIEW軟體自行撰寫之『自動尋光對位程式』來進行輸出埠間之尋光對位，應用於我們設計之1×2光開關上。首先，以CCD影像處理技術分析計算出輸入端光纖與輸出端ch1光纖之錯位量，並以壓電微動平台驅動輸入端光纖移動此錯位量來初步對準輸出端光纖(ch1)。運用了二次估計法與爬坡演算法分別將兩輸出埠尋光對位至＜1dB以下。接下來，利用了『動態切換對位』與『平衡切換對位』步驟將兩輸出埠之插入損耗及其差值，同時尋光對位至＜1dB與＜0.1dB以下。經實驗結果證明，可在383秒內將一1×2光開關之兩輸出埠尋光對位完成，插入損耗值分別為0.47dB與0.51dB，差值為0.04dB，順利完成研究目標，該技術可成功克服目前仍大量使用人工尋光對位之窘境與突破光通訊“最後一哩”之產業發展瓶頸。

This research is to develop micro/nano mechanical optical switches including 1×2, 1×4 and 2×2 switches which features small size, simple structure and high reliability. We have adopted precision positioning and MEMS technologies to accomplish the development of those switches. These switches assume the advantages of MEMS technology while omitting the disadvantage of high manufacturing cost. The fiber holder and ultra thin mirror are fabricated by MEMS technology; they functions as an output fibers holder and optical signal reflector. By applying the two stages geometry error reduction principle, the switching position error of the input fiber can be reduced and the position resolution can reach micro/nano degree. For the 1×2 optical switch, we adopt fiber-to-fiber configuration and use a fiber holder to hold the two output fibers. Using two stages geometry error reduction principle, the precision of the input fiber switching position can be adjusted to reach 0.18μm. Experimental results showed the insertion loss can be controlled to ch1: 0.8dB, ch2: 1.4dB with switching time 5ms, and crosstalk≦80dB. The reliability tests demonstrated the variation of the insertion losses are ch1: 0.04dB, ch2: 0.02dB after 10,000 cycle times, and ch1: 0.024dB, ch2: 0.006dB throughout 100 switch times after 1,000,000 cycle times. The switch size is only 7.5×16×20mm . For the 1×4 optical switch, we apply the previously successfully developed 1×2 opical switch technology. This switch uses two relays as the two actuators whose switching direction is perpendicular to each other by orthogonal arrangement. Due to the use of a fiber holder, the fiber position errors could be reduced to less than 0.27μm. The experimental test results show that after an initial 100 cycles test run the insertion losses of the four channels are ch1: 0.68dB, ch2: 1.49dB, ch3: 0.71dB, ch4: 0.97dB. The reliability tests of the insertion losses of the four channels after 10,000 cycles are ch1: 1.67dB, ch2: 1.63dB, ch3: 0.75dB, ch4: 0.98dB. The switch size is only 20×20×25mm . This 2×2 switch utilizes four collimators arranged 90° to each other on a common plane, and use an ultra thin mirror as the reflector whose thickness is less than 1.8μm and roughness 5.721nm to allow double-sided reflection. We apply the advantage of high precision of MEMS process, and omit the disadvantage of all MEMS-based type switches which is high in cost and dramatically increase the insertion loss when the lens-fiber lateral misalignment occurs. In addition, compared to the traditional prism type 2×2 optical switch, our switch will reduce alignment steps leading to a simpler switch structure. Experimental results show that the best insertion loss of two output channels at transmission state are: ch3: 0.281dB, ch4: 0.547dB and at reflection state: ch3: 0.545dB, ch4: 0.571dB, respectively. In order to test for the long-term reliability we continue to switch 10,000 cycle times. The best insertion loss of two output channels at transmission state are found to be: ch3: 0.31dB, ch4: 0.52dB and at reflection state: ch3: 0.61dB, ch4: 0.62dB respectively. To overcome the bottleneck of mass production of optical switches, we have successfully developed an automatic light tracing alignment technology (ALTA), which comprise of CCD image processing module, PZT motion control module and the light detection module, and is edited in the LabVIEW environment and applied to our 1×2 optical switch. With the aid of the CCD module the ALTA program calculates the initial position of the input fiber, which is then moved by the PZT module close to the ch1 output fiber. The program will carry out quadratic estimation algorithm and hill-climbing algorithm for ch1 and ch2, and terminate when the insertion losses are below 1dB individually. The program will run the DSA and BSA process until the ch1 and ch2 insertion losses and difference are below 1dB and 0.1dB, simultaneously. The results show the best insertion loss of ch1, ch2 are 0.47dB, 0.51dB, respectively and the total alignment took only 383 seconds. The difference between the ch1 and ch2’s insertion loss is 0.04dB. This technology could be save manual assembly and alignment time, and overcome the bottleneck of the so called 'last-mile' in fiber-optics communication development.