在矽-氮化矽複合波導實現可調式慢光

Implementation of Tunable Slow-Light on Si-Si3N4 Composite Waveguide

張芝翠(Chih-Tsui Chang)

指導教授 ： 李明昌

國立清華大學/電機資訊學院/光電工程研究所/碩士(2021年)

摘要

本論文主要是利用矽-氮化矽複合波導結構，結合一維光子晶體慢光波導，透過加熱改變元件整體等效折射率，實現可調式慢光波導。
氮化矽材料本身折射率較小，作為波導結構時與包覆層材料二氧化矽的相對折射率較小，因模態侷限在波導中傳遞時分布較大，受到波導邊緣粗糙度的影響較小而降低了傳播損耗，結合矽材料本身與現今半導體製程相容、可作為高速元件材料等特性，作為矽 -氮化矽複合波導結構，可以實現高速元件、被動元件、電晶片製程上整合的最大優勢 。
慢光波導設計首先利用平面波展開法計算能帶結構，設計慢光波導結構參數調整操作區域，再利用有限時域差分法模擬慢光波導穿透頻譜，估算損耗，最後利用干涉架構推出波導群折射率。
在量測結果中我們成功量測到相同溫度下，慢光群折射率可以從2.73調變至 9.57 隨溫度變化於30˚C至 50˚C之間群折射率從8.4調變至14.54，而穿透率隨溫度變化從 58%損耗至10%；若穿透率固定在41%，群折射率從7.69調變至 12.16。

關鍵字

矽光子 ； 光子晶體 ； 氮化矽 ； 慢光 ； 波導

並列摘要

This study designs an one-dimensional photonic crystal slow-light structure based on the Si-Si3N4 composite waveguide and tunes the effective refractive index of slow-light waveguide by heating to achieve a tunable slow-light waveguide.
Compare with silicon, the refractive index of silicon nitride is smaller, when being used as waveguide material, the refractive index difference beteween core and cladding is relatively small. Since the mode extends to out of the core, it is less affected by the roughness of sidewall of the waveguide, resulting in lower propagation loss. Combined with the silicon, which is compatible with semiconductor process technology, and with the high thermal-optic effect, it is mostly used as the material of high-speed device. As a silicon-silicon nitride composite waveguide structure, it can realize lossless integration with high-speed device, passive device, and electronic integration circuit.
For the design of slow-light waveguide, the operation wavelength is first adjusted according to band structure, which is obtained by plane wave expansion method calculation. Then, the finite time domain difference method is implemented to simulate the slow-light waveguide transmission spectrum and estimate the loss. Finally, unbalanced Mach-Zehnder Interferometer is used to calculate the waveguide group refractive index.
This study experimentally demonstrate a tunable slow-light waveguide, and the group index is tuned from 2.73 to 9.57 by scan wavelength. Heating result in the group index is tuned from 8.4 to 14.54, while the transmittance varies from 58% to 10%. If the transmittance is fixed at 41%, the group refractive index is tuned from 7.69 to 12.16.

並列關鍵字

Silicon Photonics ； Photonics crystals ； Si3N4 ； Slow-light ； waveguide

參考文獻

1. Jafari, O., et al., Mode-conversion-based silicon photonic modulator loaded by a combination of lateral and interleaved p-n junctions. Photonics Research, 2021. 9(4): p. 471-476.

2. Kondo, K., et al., Fan-beam steering device using a photonic crystal slow-light waveguide with surface diffraction grating. Optics Letters, 2017. 42(23): p. 4990-4993.

3. Yablonovitch, E., Inhibited Spontaneous Emission in Solid-State Physics and Electronics. Physical Review Letters, 1987. 58(20): p. 2059-2062.

4. John, S., Strong localization of photons in certain disordered dielectric superlattices. Physical Review Letters, 1987. 58(23): p. 2486-2489.

5. Notomi, M., et al., Extremely large group-velocity dispersion of line-defect waveguides in photonic crystal slabs. Physical Review Letters, 2001. 87(25): p. 4.