利用非均質結構產生之介電泳力操控聚苯乙烯微球作為可調式光學共振腔

Tunable Optical Resonators by Manipulating Polystyrene Microspheres through Dielectrophoretic Force at Inhomogeneous Structures

廖則幀(Liao, T.J.)

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(2014年)

摘要

本研究目的為利用非均質結構產生之介電泳力去調控聚苯乙烯微球(共振腔)與脊狀波導間的垂直耦合距離，首先利用投影機投影圖形在光導材料(a-Si)上，利用其產生的不均勻電場誘發介電泳力去操控微米球共振腔至波導附近，此時微米球會受到非均質結構(脊狀波導)的吸引力而停在波導的正中心，接著利用改變外加電壓去調整微米球共振腔與單模脊狀波導之間的垂直耦合距離。
在我們的元件中滴入混有聚苯乙烯球(n=1.571)的蔗糖水溶液(n=1.34)，並以SU-8負光阻(n=1.569)製作脊狀波導(非均質結構)於晶片上，經由實驗量測微米球共振腔與光波導間的穿透頻譜，透過分析頻譜上峰值的深度以及透過頻譜擬合計算得到的品質因子，可將在不同操作電壓下聚苯乙烯球與光波導間的耦合情形分別歸類在過耦合(over-coupling)，近臨界耦合(near critical-coupling)，和弱耦合(under-coupling condition)等三種情況。

關鍵字

微米球共振腔 ； 介電泳力 ； 耦合間距

並列摘要

The main theme of this research is to implement a tunable microsphere resonator platform with an ability of manipulating the coupling distance between a polystyrene microsphere (resonant cavity) and a rib waveguide through a controllable dielectrophoretic (DEP) force on an inhomogeneous structure. The microsphere is suspended in liquid sealed in between two transparent conductive plates. One is coated with amorphous Si and the other is with an SU-8 waveguide structure. First, we use the image-controlled dielectrophoresis for moving the microsphere near the rib waveguide; then, the microsphere will be attracted by the rib and stop in the center of the rib waveguide by a localized DEP on the inhomogeneous structure (rib edge). By changing the applied voltage, the coupling distance between the microsphere and the single-mode rib waveguide is continuously adjustable. Through measuring the waveguide transmittance spectra at different biased voltages across the top and bottom plate, the PSB microsphere is able to be operated either at the over-coupling, near critical-coupling or under-coupling condition. The intrinsic quality factor is estimated to be 26707.

參考文獻

[25] “Light-induced Dielectrophoresis for the Applications on Dynamic and Passive

[1] S. M. Spillane, T. J. Kippenberg, and K. J. Vahala, "Ultralow-threshold Raman laser using a spherical dielectric microcavity," Nature, vol. 415, pp. 621-623, Feb 2002.

[2] K.J. Vahala, “Optical microcavities,” Nature,vol.424,pp.839-846,Aug2003.

[3] M. Hossein-Zadeh and K. J. Vahala, "Free ultra-high-Q microtoroid: a tool for designing photonic devices," Optics Express, vol. 15, pp. 166-175, Jan 2007.

[4] V. S. Ilchenko, A. A. Savchenkov, A. B. Matsko, and L. Maleki, "Nonlinear optics and crystalline whispering gallery mode cavities," Physical Review Letters, vol. 92, Jan 2004.