微機電技術應用於光開關之研製

Development of Optical Switches Using MEMS-based Technology

廖柏亭(Bo-Ting Liao)

指導教授 ： 楊燿州

國立臺灣大學/工學院/機械工程學研究所/博士(2009年)

https://doi.org/10.6342/NTU.2009.01954

摘要

本研究係運用以微機電為基礎之技術，研製新型光開關元件，包括2×2光開關，及較高埠數之N×N複合式光開關等元件，進而改善傳統光開關所存在的缺點。在2×2光開關方面，本文提出一種新型的設計，謂之「分裂十字型光開關」。傳統的十字型光開關，存在因鏡面厚度影響所導致的光路偏移問題，及為降低此種光路偏移所造成的光損耗，需一厚度極薄之雙面反射鏡。分裂十字型光開關，則可避免此種因鏡面厚度所造成的光路偏移問題，且無鏡面厚度之限制。另外，相較於傳統的2×2鏡面陣列型光開關，分裂十字型光開關又有需較少致動器數量的優勢，故可增加製程與組裝的良率。
分裂十字型光開關，係由2個可動式鏡面、與2個固定式鏡面所組成，本研究並分別運用二種微致動器，控制可動式鏡面。這二種微致動器包括「靜電式梳狀致動器」，及「電熱式V型樑致動器」搭配「雙穩態機構」。其中，電熱式V型樑致動器搭配雙穩態機構，不僅可以控制微鏡面之運動，更能使得微鏡面停留於二個穩定狀態，進而減少光開關元件之耗能。分裂十字型光開關，可利用深式反應離子蝕刻技術於SOI晶圓上製造而得。實驗結果顯示，靜電式梳狀致動器與V型樑致動器的驅動電壓皆約40伏特，便能使得可動式鏡面產生60 m之位移量。分裂十字型光開關之平均插入損失約-1.1 ~ -1.4dB，而光開關元件之切換時間則可小於10 ms。
分裂十字型光開關，雖能解決傳統2×2光開關之缺點，但因受光路設計上的限制，故無法將此光路設計擴展至較高埠數之N×N光開關。因此，在較高埠數之N×N光開關方面，本研究將採用鏡面陣列式的光路設計，並結合微機電技術與傳統精密機械技術，以實現一擁有高精密度、高生產良率、低成本與低耗能的新型複合式N×N光開關，包含4×4及8×8複合式光開關。該複合式光開關，係由高精密度之微鏡面陣列，與擁有雙穩態特性之小型致動器陣列所組合而成。微鏡面陣列，包含垂直鏡面、懸臂樑、與光路凹槽等微結構，都可利用本研究所提出之單一步驟濕式非等向性蝕刻製程，便能同時蝕刻製造出來，故能有效地降低生產成本，及提高生產製造良率，而且微鏡面陣列更具有自我對準之能力，所以，可進一步地降低後續光開關組裝之困難度。小型致動器陣列，於4×4複合式光開關中，則使用市售之雙穩態致動器與L型推桿所組成；於8×8複合式光開關中，由於考量到需要使用更小體積之致動器驅動微鏡面陣列，故致動器陣列，遂由本研究自行開發之螺線管式雙穩態致動器與推桿所組成。
此外，本研究亦針對複合式光開關之驅動電路與電腦端控制程式進行研發，使得使用者可以透過電腦，輕易地控制該複合式光開關。實驗結果顯示，小型致動器陣列之驅動電壓約為5 ~ 6伏特，利用濕式非等向性蝕刻技術所製造之微鏡面，其表面粗糙度約為78nm。4×4複合式光開關之平均插入損失約為-1.6dB ~ -2.3dB；切換時間則可小於13ms；8×8複合式光開關之平均插入損失約為-2.2dB ~ -3.3dB；切換時間則可小於12ms。

關鍵字

光開關 ； 光通訊 ； 微機電技術 ； 濕式非等向性蝕刻 ； 雙穩態致動器

並列摘要

In this work, novel MEMS-based optical switches, which include 2×2 optical switch and N×N hybrid optical switches, are presented. The proposed novel optical switches possess advantages over traditional optical switches.
A novel 2×2 MEMS optical switch using the proposed split cross-bar (SCB) design is demonstrated. When compared with the cross-bar switches, the SCB switch does not have the constraint on mirror thickness which affects fiber alignment significantly. When compared with the mirror-array switches, the SCB switch requires less movable mirrors and thus potentially gives better fabrication yield. The SCB switch consists of two fixed mirrors, two movable mirrors, and two actuators. Two types of actuators, including electrostatic comb-drive actuators and electrothermal V-beam actuators, are utilized. Furthermore, the electrothermal V-beam actuators are integrated with the bi-stable mechanism to move and latch the movable mirrors. Thus, the power consumption of the SCB switch can be greatly reduced.
The SCB device is easily realized by using inductively-coupled-plasma (ICP) etching on a silicon-on-insulator (SOI) wafer with one photo-mask. The comb-drive actuators and electrothermal V-beam actuators can move the movable mirrors with a displacement of 60 m under a driving voltage of 40V. The optical performance and the dynamic response of the SCB switch are also investigated. The measured insertion losses are between -1.1dB and -1.4dB and the measured switching time is less than 10 ms.
Although the SCB design can eliminate the drawbacks of traditional designs for 2×2 optical switches, it is not suitable to be utilized in N×N optical switch designs. Thus, the novel N×N hybrid optical switches, which include 4×4 and 8×8 hybrid switches, are presented in this work. The proposed hybrid switches comprising a MEMS-based micro-mirror array and a mini-actuator array possess the advantages of high precision, high yield, low cost, and low power-consumption. The micro-mirror array, which includes vertical mirrors, cantilevers, and light-path trenches, can be monolithically realized by using single-step KOH anisotropic etching process. The micro-mirrors can be naturally self-aligned and thus reduces the complexity of the packaging process. For 4×4 hybrid switch, commercially-available bi-stable actuators integrated with L-shape arms are used in the mini-actuator array. For 8×8 hybrid switch, smaller-footprint solenoid-based bi-stable actuators integrated with pushing arms are used in the mini-actuator array. Each micro-mirror of the mirror array can be individually actuated by the bi-stable actuator, and thus the power consumption of the system can be greatly reduced.
We also develop a driving circuit and a Window-based program for controlling the hybrid switches. Device characterizations and optical performance are also investigated. The driving voltage of the mini-actuator array is about 5 ~ 6 volt. The typical surface roughness of the fabricated mirrors is about 78nm. For 4×4 hybrid switch, the measured insertion losses are between -1.6dB and -2.3dB and the measured switching time is less than 13 ms. For 8×8 hybrid switch, the measured insertion losses are between -2.2dB and -3.3dB and the measured switching time is less than 12 ms.

並列關鍵字

Optical switch ； optical communication ； MEMS ； wet anisotropic etching ； bi-stable actuator

參考文獻

[116] 施順智，“雙穩態電磁致動式光開關系統之開發”，國立台灣大學機械工程研究所碩士論文，2008。

[95] 郭文正，“高深寬比懸浮微結構之製程開發及在微機電式光開關的應用”，國立台灣大學機械工程研究所博士論文，2006。

[6] 林穎毅，“2006全球光通訊市場綜覽”，光連雙月刊，67期，第39-43頁，2007。

[5] 鍾沛璟，“2005台灣光通訊產業回顧”，光連雙月刊，61期，第37-39頁，2006。

[8] 鍾沛璟，“光通訊市場走出陰霾 台灣廠商看準FTTH”，光連雙月刊，55期，第38-42頁，2005。