液晶光波導之研製與應用

Study of Liquid Crystal Waveguides and Its Applications

莊棋凱(Chi-Kai Chaung)

指導教授 ： 王子建

國立臺北科技大學/電資學院/光電工程系研究所/碩士(2012年)

摘要

本研究提出兩種新型液晶光波導結構，所設計製作的元件具有：製程簡單、製作成本低，且不會受基板晶格結構所限制，可製作任意波導方向等優點。在蝕刻通道的製作上，論文中提出使用超音波輔助蝕刻與新型金屬光阻複合層作為蝕刻遮罩兩種方法，可有效提升蝕刻結構品質，降低蝕刻後的表面粗糙度。
所設計的液晶核心波導，其核心層折射率分布會隨外加電壓產生變化，可應用於調變光波導中傳輸的模態數或傳輸光功率值。B270基板上之液晶光波導為一TM單極化可調光波導，當外加電壓大於4.5V時，開始可以導單模光場，當電壓超過7V時，開始變成多模傳輸，隨著電壓持續增加，傳導模態數增加，且光功率也會持續增強，直到電壓達到10V時，輸出光功率趨近於飽和，其傳輸損耗最低為1.31dB/cm，其消光比可以達27.3dB。
石英基板上之液晶光波導為一TM和TE雙極化可調光波導，在未施加電壓時，TE與TM模態都能導光但傳輸損失較大。對於TM 極化，在電壓4.5V前為單模傳輸，直到電壓超過5V時轉變為多模傳輸。兩極化的輸出光當外加電壓達4.5V時光強度開始增強，隨著電壓持續增加，傳輸損耗會逐漸變小，直到電壓達到10V時趨近於飽和。TM模態傳輸損耗最低為0.94 dB/cm，TE模態傳輸損耗最低為7.9dB/cm。
在元件應用上，兩液晶光波導元件具有結構簡單、模態數可調等特點，藉由調整外加電壓改變輸出模態數，也可用於調變輸出光強度，作為光強度調變器。

關鍵字

液晶 ； 光波導 ； 氧化銦錫 ； 熔融石英

並列摘要

We present two new structure of liquid crystal waveguide, its advantage is simple fabrication, low cost and without restrict lattice structure of substrate. Waveguide can be fabricated in any direction. In etching process, we provide ultrasonic etch method and a novel metal-photoresister etching mask, which can efficiency improvements in the quality of etched structure and reduce the surface roughness after the etching.
In our result, we observe refractive index distribution be changed with applied voltage, It can be applied to modulate transition modes and output intensity in waveguide. In B270 substrate liquid crystal waveguide (LCWG), that is TE mode tunable optical waveguide. At 4.5V will turn waveguide on in single-mode and over 7V will be turn to multi-mode. The output intensity and transition mode increases with more electric field. Output intensity is saturation in voltage over 10V. The propagation loss can decreases with higher voltage, and it achieved 1.31dB/cm at 10 V. A maximum extinction ratio is 27.3 dB when the applied voltage was reversed.
In quartz substrate LCWG is TM and TE mode tunable optical waveguide, without applied voltage it can propagate two modes light but the propagation loss is higher. For TM mode is single mode at 4.5V and voltage over 5V will be turn to multi mode. The TM and TE mode output intensity and transition mode increases with more electric field. Output intensity is saturation in voltage over 10V. The TM mode propagation loss is 0.94dB/cm and TE mode propagation loss is 7.9dB/cm when voltage is 10V. In future, it can be an important component in integrated optical circuits.

並列關鍵字

liquid crystal ； optical waveguide ； indium tin oxide ； fused quartz

參考文獻

[1] W. D. Cort, J. Beeckman, R. James, F. A. Fernandez, R. Baets and K. Neyts, “Tuning of silicon-on-insulator ring resonators with liquid crystal cladding using the longitudinal field component,” Opt. Lett., vol. 34, pp. 2054-2056, 2009.

[2] T. Cai, Q. Liu, Y. Shi, P. Chen, and S. He, “An efficiently tunable microring resonator using a liquid crystal-cladded polymer waveguide,” Appl. Phys. Lett. 97, 121109, 2010.

[3] T. T. Larsen, A. Bjarklev, D. S. Hermann, J. Broeng, “Optical devices based on liquid crystal photonic bandgap fibres,” Opt. Express., vol.11, pp. 2589-2596, 2003.

[4] F. Du, Y. Q. Lu, and S. T. Wu, “Electrically tunable liquid-crystal photonic crystal fiber,” App. Phys. Lett. vol.85, 2004, pp.2181-2183.

[6] K. S. Hsiao, and C. Y. Ko, "Light-controllable photoresponsive liquid-crystal photonic crystal fiber," Opt. Express. , vol.16, pp.12670-12676, 2008.