以液晶為夾層之光纖耦合器中液晶層厚度對開關時間的影響

Abstract

實驗中使用不同介電異向差（Δε＞0及Δε＜0）的低折射係數液晶，作為研磨式光纖耦合器的夾層。對不同的液晶材料，分別採用平行排列和垂直排列二種方式。以632.8ｎｍ雷射為光源，藉由外加電壓改變液晶的有效折射係數，來控制耦合比例。 我們成功的做出比以前薄的液晶夾層，在不同的外加電壓下，比較不同液晶層厚度對於耦合率及耦合器開關時間的影響。實驗結果顯示液晶夾層較薄的耦合器比過去較厚的耦合率大且開關時間短。

We use 632.8nm He-Ne Laser as light source and low-refractive index liquid crystals with positive and negative dielectric anisotropy(Δε＞0 andΔε＜0), respectively, as intermediate layer of the optical fiber coupler. By applying voltage, we can change the effective refractive index of the liquid crystal to tune the light coupling ratio. We successfully reduce the thickness of the liquid crystal intermediate layer by using thinner mylar spacer. We measure the coupled and uncoupled fiber output power when varying the applied voltage under different layer thickness. We also study the response time of our fiber couplers. The results show that both coupling ratio and response time performance are better for couplers with thinner liquid crystal layer.