以金屬與多層介電質組態實現可運用於矽基奈米光路之波導90度轉折結構

A 90-degree Waveguide Bend in Metal/Multi-Insulator Configuration for Silicon-Based Optical Nanocircuitry

劉侑昌(You-Chang Liu)

指導教授 ： 張殷榮

國立中央大學/理學院/光電科學研究所/碩士(2011年)

摘要

本論文藉助表面電漿波可強力侷限電磁波於垂直金屬-介電材料介面之特性，設計出幾不受極化影響「金屬-多層介電質」組態之90度波導轉折結構。文中闡述波導結構設計之概念，並對波導結構參數依序由輸入端至輸出端逐步進行最佳化設計。模擬時以內建有限時域差分法之Rsoft商用軟體進行，網格大小不大於5 nm，並以採用有限元素分析法之商用軟體COMSOL Multiphysics相互驗證。此二維波導轉折結構透過歸一化後發現橫向電場與橫向磁場模態於轉折處之轉折效率皆可達近0.99，表示波導結構之損耗主要是由光波通過模態轉換器後能量散失至空氣所造成。又橫向電場與橫向磁場模態之插入損耗分別為-0.0846與-0.2287 dB。整體波導轉折結構所佔面積僅有3.773 μm2。轉折處長度透過最佳化設計可縮減至450 nm，小於三分之ㄧ操作波長(1550 nm)，尺寸在次波長範圍下。不同極化模態之傳輸效率在波長1414 nm 到 1605 nm 間皆可達0.90以上。
在決定最佳化之參數後再對能量於波導結構內轉移情況進行分析，細部探討在不同極化下波導結構幾何形狀改變對於能量轉移之影響，描繪最佳化波導轉折結構傳輸效率對波長之變化。最終將此金屬-多層介電質組態之90度波導轉折結構與目前文獻結果比較，分析此轉折波導之優劣。對比他人文獻結果，本論文所描述之「金屬-多層介電質」組態之90度波導轉折結構具有幾不受極化影響與狹小轉折區域之優點，期望可對奈米積體光路帶來相當助益。

關鍵字

波導轉折 ； 表面電漿波

並列摘要

With the aid of surface plasmon polaritons featuring strong lateral confinement of electromagnetic energy in the direction perpendicular to the metal-insulator interface, a polarization-insensitive 90o waveguide bend in the metal/multi-insulator configuration is described in this thesis. The design and optimizations are conducted using Finite-Difference-Time-Domain-based software package, RSOFT Design Group, with the grid size no larger than 5 nm and are cross-checked by COMSOL Multiphysics, a software based on Finite Element Method. The bending efficiency associated with the metal/multi-insulator structure, excluding the input/output tapers, can achieve approximately 0.99 for transverse electric (TE) and transverse magnetic (TM) polarizations, indicating the loss primarily results from the input/output tapers. The insertion losses for modes are -0.0846 and -0.2287 dB, respectively. The area occupied by the plasmonics-assisted region is only 3.773 μm2 and the length of waveguide bending section is shorter than one-third of the operating wavelength at 1550 nm. The transmission is above 0.90 in the wavelength window ranging from 1414 nm to 1605 nm for both polarizations.
In addition to the design optimizations, power transfer between silicon and silica regions along the bend and the transmission spectra are presented for both polarizations. Comparing with other literature, the present 90o waveguide bend in metal/multi-insulator configuration is polarization-insensitive and has an ultra-small footprint. This research may thus be of real value in integrated photonics.

並列關鍵字

SPP ； plasmonics ； waveguide bend

參考文獻

[1] W. L. Barnes, A. Dereux, and T. W. Ebbesen, “Surface plasmon subwavelength optics,” Nature, vol. 424, no.14, pp. 824-830, Aug. 2003.

[2] E. Ozbay, “Plasmonics: Merging photonics and electronics at nanoscale dimensions,” Science, vol. 311, no. 5758, pp. 189-193, Jan. 2006.

[3] R. Zia, J. A. Schuller, A. Chandran, and M. L. Brongersma, ”Plasmonics: The next chip-scale technology,” Mater. Today, vol. 9, no. 7, pp. 20-27, Jul. 2006.

[4] R. W. Wood, “On a remarkable case of uneven distribution of light in a diffraction grating spectrum,” Proc. Physical Soc., vol.18, pp. 269-275, Jun. 1902.

[5] R. H. Ritchie, “Plasma losses by fast electrons in thin films,” Phys. Review, vol. 106, no. 5, pp. 874-881, Jun. 1957.