於平面波導上製作次波長光柵耦合結構之研究

The research of fabricating sub-wavelength grating structure on planar waveguide

張佑誠(You-cheng Jhang)

指導教授 ： 陳昇暉

國立中央大學/理學院/光電科學與工程學系/碩士(2015年)

摘要

本論文研究主要以雷射雙光束干涉微影法，製作波導耦合元件於玻璃基板上，目的在於縮小元件體積與增強光耦合效率，並且對於光柵週期、薄膜厚度、不同光柵結構影響耦合角度與耦合效率及薄膜粗糙度影響傳遞損耗作探討，文中所使用的模擬方法為有限時域差分法(Finite Difference Time Domain, FDTD)，模擬結果顯示當雷射光源為532 nm時，光柵結構週期在300 nm，五氧化二鉭(Ta2O5)的波導厚度在100 nm時的耦合效率最高而耦合角度也較小。

在實驗製程上，利用雙電子槍蒸鍍系統外加離子源助鍍系統鍍製二氧化矽(SiO2)與五氧化二鉭(Ta2O5)作為底部包覆層(bottom cladding)與波導層(guiding layer)，並利用干涉微影技術(Interference lithography)在波導層上製作300 nm的光柵。由於光阻的光柵已經有初步的耦合效果，所以會對其量測光耦合效率；此外由於波導層的折射率係數與薄膜表面粗糙度，影響光耦合效率與傳遞損耗尤為重要，本文中也會探討雙電子槍蒸鍍系統環境參數，如何影響上述兩種因子，試圖找出最佳的參數提昇元件的品質與效率，在製程最後本文提出了中空形光柵的概念與製程方法，根據FDTD模擬的結果顯示其可有效地提高光耦合效率。

最後在量測上，除了觀察到光耦合進波導外，也成功量測到元件耦合進波導的效率與耦合角度，經計算後光阻光柵的波導耦合元件在TE波的耦合效率最高為3.63%；而中空形光柵的波導耦合元件在TE波的耦合效率可達16.14%，傳遞損耗為 5.1 dB/cm，耦合角度為6.5度，TM波的耦合效率為4.93%，傳遞損耗為6.0 dB/cm，耦合角度為 -7.0度，本研究所使用的製程方法，在製作上簡單方便、節省成本並可量產，未來可以應用於生醫感測元件、光檢測器、光通訊元件。

關鍵字

干涉微影 ； 次波長光柵 ； 平面波導 ； 耦合器

並列摘要

In this study, a laser interference lithography is used to fabricate the sub-wavelength grating as a coupling device on a glass substrate. The purpose of this research is to reduce the device size and to enhance the coupling efficiency. The coupling device was designed using the finite-difference time-domain (FDTD) method. The grating period, depth, fill factor, film thickness and different grating structure were analyzed to enhance the coupling efficiency and reduce the coupling angle. According to the simulation results, when the working wavelength, the grating period and the Ta2O5 film are 532 nm,300 nm and 100 nm, there are optimum coupling efficiency and relatively smaller coupling angle than large period.

We used dual E-beam evaporation system with ion-beam-assisted deposition system to fabricate the bottom cladding (SiO2) and the guiding layer (Ta2O5) on glass. Then laser interference lithography was used to fabricate the grating with the period of 300 nm as a guiding layer. In this part, the best process parameters was studied to deposit the film and the precise exposure time and development time was also developed to fabricate the grating with good quality. Finally, the air hole grating was proposed to enhance the coupling efficiency. According to the FDTD simulation results, the structure can improve the coupling efficiency more effectively.

After the device fabrication, the photonic properties were measured. The results show the TE wave coupling efficiency of the photoresist grating coupling device is 3.63% and the coupling angle is 2.5 degree. And the TE wave coupling efficiency of the air hole grating device is 16.14%, the coupling angle is 6.5 degree and propagation loss is 5.1 dB/cm. The TM wave coupling efficiency is 4.93%, the coupling angle is -7 degree and propagation loss is 6.0 dB/cm.

並列關鍵字

Interference lithography ； Sub-wavelength grating ； Planar waveguide ； Coupler

參考文獻

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