利用矽基光學平台應用於板上光學連接之研究

Research on On-Board Optical Interconnect Based on Silicon Optical Bench

蕭旭良(Hsu-Liang Hsiao)

指導教授 ： 伍茂仁

國立中央大學/理學院/光電科學研究所/博士(2012年)

摘要

在本論文中，主要研究在利用矽基光學平台的技術應用於高速、短距離、且多通道的光學引擎。近年來的發展，雲端電腦及相關的高速連接之可攜帶的周邊元件，如何運用光學連接技術，以更高速、多通道、微型化，甚至於低成本應於市場的大量生產，已經成為了日漸重要的研究領域，其中，矽基光學平台技術已於日前完成光電、電光的轉換模組，成功應用於市場的產品。利用矽微機電技術，引入可達微米等級之高結構精度的封裝技術，將是導入高精度整合於光電元件的關鍵，如面射型雷射、光檢測器、光纖陣列等主被動元件。使得在大量生產時更具備有低成本的優勢。
首先，在第一個研究討論中，發展出一具有四通道 × 10 Gbps之光連接模組。此模組中，光學平台具有一45度微反射面，且同時具有多通道之V型凹槽陣列積體化至一微小的光學平台中，此凹槽提供了後續光纖陣列之被動封裝。此矽基光學平台利用金錫的共晶材料及覆晶封裝的方式將面射型雷射(VCSEL)及光檢測器(PD)封裝至光學平台上形成一矽基雙通道之光學次模組(BOSA)。BOSA體積僅只有4 mm × 3.75 mm × 0.6 mm 的大小，且四通道的發射模組及四通道的接收模組將可完全的置放於此BOSA中，光纖陣列置放於此模組中達到微型化的優點。此外，在光路的結構上，不添加任何額外的光學系統，即可將光從面射型雷射高度耦合至光纖陣列中，耦合效率達到-5.2 dB；同時，光於光纖陣列發射至光檢測器，耦合效率高達-2 dB。平均1 dB的光功率變化，不論在發射端，亦或是接收端，均可達到15 ?m的容忍度。在高頻的檢測下，發射端搭載10 Gbps的傳輸速度，BER可通過10-12的量測規範；於接收端的檢測，靈敏度也可達到-12 dBm的等級，且此量測的架設，通道的串音影響已經考慮進來。本研究中，從開始的晶片製程、光電元件封裝、PCB的設計、元件封裝、光纖對準製程及高頻測試均有一一介紹。此光電模組也通過了工業上的可靠度驗證。此結果表示矽基光學平台是具有一個多功能、整合性高的系統平台，可應用於光電、電光的轉換模組。
本論文的另一部分，是成功的將以聚合物的波導結構應用於矽基光學平台上。此應用將大幅的提供光路佈局、設計的靈活性。以目前不易設計之25 Gbps的光路應用，在光學耦合上，即面臨到感光區較小的光檢測器，亦或是大數值孔徑的面射型雷射的問題。因此，聚合物的波導結構將可伴演一重要的角色去克服目前所面臨到的問題。四通道的光電、電光轉換模組利用聚合物波導的結構已成功的實現，並且可以搭載光學傳輸訊號。聚合物之波導結構是利用標準的黃光微影製程所製作，其波導的纖核為40 ?m等級的大小，這和實用上的多模光纖之纖核的尺寸是吻合的。因此我們相信此結構可以成為未來光連接應用之轉換模組，且更具有微型化適合的尺寸。

關鍵字

光學連接 ； 矽基光學平台 ； 45度反射面

並列摘要

In this dissertation, the researches focus on the high-speed multi-channel short-reach (SR) optical engine platform development based on the silicon optical bench (SiOB) technologies. As the rapid development of cloud computing and upcoming high-speed link expectation for portable devices, how to drive the optical interconnect technology to higher speed, multi-channels, miniaturization, and even low costs in mass production has become the research hot zone, where the SiOB technology has been received with great attentions on completing the OE/EO converter. SiOB-based optical engine can be conducted via silicon Micro Electro Mechanical Systems (MEMS) process, leading to high structural accuracy up to few micron-meters, precisely packaging among micro-optical elements, such as VCSEL/PD and MMFs, and cost competitive advantages in mass batch production.
In first research topic, a 4-channel x 10-Gbps optical interconnect module based on a SiOB with a 45 degree reflector as well as monolithic V-groove array for fiber alignment is developed. The 4-channel VCSEL and PD arrays are flip-chip assembled onto the pedestal of SiOB using Au/Sn eutectic solder bumps to form a SiOB-based bi-directional optical sub-assembly (BOSA) configuration. In a 4 mm × 3.75 mm × 0.6 mm small size, 4-Tx and 4-Rx channels can be completed, bringing into physical size advantage for portable cables with optical link. The optical coupling of VCSEL-to-MMF and MMF-to-PD without adding coupled optics is -5.2 and -2 dB, respectively. The widely alignment tolerances of 1-dB power variation for the transmitting and receiver parts are 15-?m are achieved. The clearly open 10-Gbps eye patterns of Tx part as well as BER of 10-12 . The Rx sensitivity can reach to as low as -12 dBm as input optical power with channel cross-talk enabled. The research study starts from wafer process, chip-level packaging, PCB circuit and chip-on-board assembly, fiber mounting, to highs-speed testing, and also industrial reliability testing applied. The results indicate this SiOB optical engine can be a fundamental platform for versatile optical interconnect applications with high-speed and compact OE/EO module.
In the last part of this dissertation, a polymer waveguide technology has been to apply into this SiOB platform. To providing more optical layout flexibility and also, the upcoming 25-Gbps optical link with tougher optical coupling requirement due to the smaller sensing area of PD or larger NA of VCSEL, polymer waveguide can play an important role to overcome these issues. A multi-channels OE/EO module with polymer waveguide on SiOB has been successfully realized with optical link by fiber coupled. The polymer waveguide can be fabricated onto the SiOB with standard lithography process, whose core size is approx. up to 40-?m scale with compatible size of MMF’s core. We believe this configuration can be a basis for future more compact size OE module or higher speed optical interconnects applications.

並列關鍵字

Optical Interconnect ； 45 Degree Reflector ； SiOB

參考文獻

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