高效率光波導為積體光學重要的基本元件，利用簡單的蝕刻在Silicon-on-insulator(SOI)晶圓上製作出脊狀型線波導，此脊狀線波導量測到傳播損耗及耦合損耗分別為15.52dB/cm、17.37dB/Coupler.。以脊狀型線波導為基本元件，利用多模干涉耦合器所具有的光分離與結合特性、寬操作頻譜與對於極化輸入光場不敏感的優點，並且在製程上有較大的可接受誤差範圍，將光比例分成50：50後，加上一偏壓進行單邊光傳遞上折射系數的改變，使兩邊光傳遞後產生π相位差後，再經由一多模干涉耦合器結合，使出口端造成一相減性干涉後輸出光，得到有如開關般的效果。初步實驗結果顯示，整體元件的損耗徧高（約為64dB），主要原因在於製造過程中離子佈植濃度沒有得到適當控制。在訊號調變方面，嘗試以逆向偏壓機制得到折射系數改變的結果，在單邊脊狀型波導上輸入一頻率100MHz方波訊號後，成功地在輸出端量測到一同週期性的訊號，經過結果分析後得到訊號的上升和下降生命週期時間分別 2及3奈秒。

This research includes simulation, fabrication and measurement for silicon-based modulators through free-carrier plasma dispersion effect. By taking advantage of this plasma dispersion effect, a Mach-Zehnder-Interferometer (MZI) structure was employed and successfully demonstrated signal modulation with speed more than 100 MHz, which is only limited by the experimental instrument. Regarding the research work, a rib silicon waveguide was fabricated by standard CMOS process on silicon-on-insulator(SOI) wafer. The propagation loss and the coupling loss of rib waveguides were measured to be 15.52dB/cm and 17.37dB per Coupler, respectively. Multimode interference(MMI) couplers were used to split and combine light in the MZI configuration. To introduce a significant phase shift, a 5V bias was applied on one arm of the MZI branch, which was realized by incorporating a p-n junction on the rib waveguide. Experimental results show that the operational speed can exceed 100 MHz while the insertion loss was relatively high (about 64 dB). The extra loss is due to unintentional high dose of impurity on the waveguide region. A future work includes a better control on the doping level and reduction of surface roughness on the rib waveguide.

[1] Bahram Jalali, Mario Paniccia, and Graham Reed, "Silicon photonics," IEEE microwave magazine, 7(3):58-68, 2006.
[2] Jalali, B. and S. Fathpour, "Silicon photonics," Journal of Lightwave Technology, 24(12): 4600-4615, 2006.
[3] Lipson, M., "Guiding, modulating, and emitting light on silicon - Challenges and opportunities," Journal of Lightwave Technology, 23(12): 4222-4238,2005.
[4] H. Y. Ng, M. R. Wang, D. Q. Li, X. Wang, J. Martinez, R. R. Panepucci, and K. Pathak, "4X4 wavelength-reconfigurable photonic switch based on thermally tuned silicon microring resonators," Optical Engineering, vol. 47, 2008.
[5] R. V. Schmidt and R. C. Alferness, "DIRECTIONAL COUPLER SWITCHES, MODULATORS, AND FILTERS USING ALTERNATING DELTA-BETA TECHNIQUES," Ieee Transactions on Circuits and Systems, vol. 26, pp. 1099-1108, 1979.
[6] Q. F. Xu, B. Schmidt, S. Pradhan, and M. Lipson, "Micrometre-scale silicon electro-optic modulator," Nature, vol. 435, pp. 325-327, 2005.
[7] C. A. Barrios, "Electrooptic modulation of multisilicon-on-insulator photonic wires," Journal of Lightwave Technology, vol. 24, pp. 2146-2155, 2006.
[8] R. A. Soref and B. R. Bennett, "ELECTROOPTICAL EFFECTS IN SILICON," Ieee Journal of Quantum Electronics, vol. 23, pp. 123-129, 1987.
[9] C. E. Png, S. P. Chan, S. T. Lim, and G. T. Reed, "Optical phase modulators for MHz and GHz modulation in silicon-on-insulator (SOI)," Journal of Lightwave Technology, vol. 22, pp. 1573-1582, 2004.
[10] R. Halir, I. Molina-Fernandez, A. Ortega-Monux, J. G. Wanguemert-Perez, D. X. Xu, P. Cheben, and S. Janz, "A Design Procedure for High-Performance, Rib-Waveguide-Based Multimode Interference Couplers in Silicon-on-Insulator," Journal of Lightwave Technology, vol. 26, pp. 2928-2936, 2008.
[11] L.B. Soldano and E. C. M. Pennings, "OPTICAL MULTIMODE INTERFERENCE DEVICES BASED ON SELF-IMAGING - PRINCIPLES AND APPLICATIONS", Journal of Lightwave Technology, vol. 13, pp. 615-627, Apr 1995.
[12] H. F. Talbot, "Facts relating to optical science No. IV," London, Edinburgh Philosophical Mag., J. Sci., vol. 9, pp. 401407, Dec. 1836.
[13] D. Marcuse, "Light Transmission Optics," New York: Van Nostrand Reinhold, 1972.
[14] 0. Bryngdahl, "Image formation using self-imaging techniques," J. Opt. Soc. Amer., vol. 63, no. 4, pp. 41-19, 1973.
[15] R. Ulrich, "Image formation by phase coincidences in optical waveguides," Optics Commun., vol. 13, no. 3, pp. 259-264, 1975.
[16] M. Bachmann, P. A. Besse, and H. Melchior, "General self-imaging properties in N x N multi-mode interference couplers including phase relations," Appl. Opt., vol.
[17] M.-K. Chin, C.-L. Xu, and W.-P. Huang, "Theoretical approach to a polarization-insensitive single-mode microring resonator," Opt. Exp., vol.12, pp. 3245–3250, 2004.
[18] R. Hanfoug, L. M. Augustin, Y. Barabarin, J.J.G.M. van der Tol, E.A.J. M. Bente, F. Karouta, D. Rogers, S. Cole, Y. S. Oei, X.J.M. Leijtens and M. K. Smit, "Reduced reflections from multimode interference couplers," Electron. Lett. 42, 465-466, 2006.
[19] D.-X. Xu, S. Janz and P. Cheben, "Design of polarization-insensitive ring resonators in SOI using cladding stress engineering and MMI Couplers," Photon. Technol. Lett. 18, 343-345, 2006.
[20] Dan-Xia Xu, Adam Densmore, Philip Waldron, Jean Lapointe, Edith Post, André Delâge, Siegfried Janz, Pavel Cheben, Jens H. Schmid, and Boris Lamontagne, "High bandwidth SOI photonic wire ring resonators using MMI couplers," Optics Express, Vol. 15, Issue 6, pp. 3149-3155, 2007.