單石化平面光波光路之導波模態共振濾波器

Monolithic Integration of GMR Filter and Rib Waveguide on SOI-based Platform

張家齊(Chia-chi Chang)

指導教授 ： 伍茂仁

國立中央大學/理學院/光電科學研究所/碩士(2008年)

摘要

在既有PLC上的濾波器架構中，我們可以發現具「單石積體化」的濾波器結構已成為研究主流，早期由NTT等所提出之利用薄膜濾波器的外插法，用混成構裝技術封裝至PLC機板上，在特性及成本上皆不具量產之可行性；也因此，目前尚無該架構的商品化應用。而具單石積體化的PLC架構中，為了能實現高密度堆積，布拉格式波導光柵或凹面型光柵由於作用區會高達數毫米，無法善盡PLC之微型化的優勢，在研究上或商品化上較不受青睞。而與波導光柵相近的Fabry-Perot共振腔濾波器則是目前相當受到矚目的結構，主因在於該種濾波器，可以經由適當的設計，就達到帶通、帶拒等濾波特性，但若要達到一定程度的消光比、或夠窄的頻帶寬度等濾波需求，則需要增加前/後的反射鏡組；然而，其中所引入的散射損耗和繞射損耗則相當可觀。
在此論文中將提出利用具導波模態共振特性的次波長光柵作為PLC上之波導光學濾波器，成為可實際應用之WDM系統之濾波元件。引入GMR光柵成為一種在PLC基板上的新式濾波器將將具有下述特點：工作區域距離甚小、具單石積體化特性以及具彈性的多種濾波特性。然而設計使用的GMR結構僅有光柵部分並無波導的部分，在此光柵將同時扮演著光柵與波導的角色。對於1310 和1550 nm波長做分波作用，並利用FDTD的模擬運算，可以得到1550 nm波長有著高穿透特性，其穿透效率高達94 %。而1310 nm波長而有高反射的現象，其反射效率高達96 %。
在我們所設計使用的光柵濾波器其波長頻譜圖可以得知在1310 和1550 nm區域中能量衰減0.5 dB的波長帶寬各有 60 nm 和40 nm的帶阻以及帶通頻寬對於應用在光通訊上有很大的好處。
材料方面選用 SOI晶圓來做為系統的材料基板，因為其二氧化矽層之絕緣性佳，目前大都應用在製作互補性金氧半導體元件，而矽與二氧化矽的光學折射率各為3.4811與1.450，所以SOI 的上層矽包夾在兩個低折射率介質中，因此SOI本身就形成平板波導的條件。選用SOI 來製作光學元件有機會與CMOS積體電路做通訊元件的相關整合。最後藉由半導體製程可以實際製作出GMR光柵濾波器與波導的整合元件可行性。

關鍵字

平面光波光路 ； 導波模態共振濾波器 ； 波導

並列摘要

Wavelength-division multiplexer (WDM) is one of the most important technologies in the lightwave network systems, such as Fiber-to-the-home (FTTH) application [2-5]. Thin film filter (TFF) has been widely used in the passive optical network (PON) architecture, and its optical sub-assembly (OSA) is generally adopted as the TO-CAN [2-3] and planar lightwave circuits (PLC) type [4-5]. TFF based on TO-CAN OSA is the con-ventional type. However, it suffers from hard packaging tasks, whose alignment tolerance between LD, TFF, SMF, or ball lens should be achieved micro-scaled precision within such macro-sized device [2-3]. PLC-typed OSA can be further miniaturized and straightly become a platform of assembling drive IC, opto-electronic devices [4-5]. Suntae Jung et al. have developed hybrid integration technology via inserting a TFF in the trench with an adhesive . However, for reducing coupling efficiency between waveguide facets, the width of trench is only 20 μm. It is still a big task to insert such tiny film within this small trench.
In this paper, a monolithic integrated-WDM via sub-wavelength si grating filter, which is replaced the hybrid-integrated TFF, is proposed on SOI-based PLCs. As shown in Fig. 1-7, this Si-grating filter structure can be monolithically fabricated on the integrated PLC, and the separated length between waveguide facets can also be narrowed to sub-wavelength scaled by e-beam lithography process, which maintains the waveguide coupling efficiency.
In design consideration, this sub-wavelength si grating is formed as a guided-mode resonance (GMR) filter [16]. As satisfying the phase-matched condition, lightwave of the resonant wavelength would be extremely reflective, and the others would be trans-mitted. This sub-wavelength Si grating is very different from conventional free-space GMR filter because the incident lightwave emitted from rib waveguide is of finite-size and Gaussian-like profile, which is away from the free-space condition [16]. Fortunately,not only the sub-wavelength-scaled distance between waveguide facets maintains a finite-sized, however, planar wave-front of the waveguide field, but also the large dielectric constants of silicon, both of which make the resonant mode indeed locally exist in this si grating.
In this work, the 1310/1550 nm WDM filter via this monolithically integrated device is demonstrated numerically and experimentally. The stop- and pass-band of 1310 and 1550 nm, respectively, are broad of 60 and 40 nm within 0.5 dB variations. The fabrication process is also dis-cussed.

並列關鍵字

guided-mode resonance (GMR) ； waveguide ； planar lightwave circuits ； SOI

參考文獻

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