電控膽固醇液晶相位光柵

Abstract

在適當的條件下，垂直配向的膽固醇液晶可以排成指紋結構，此種結構可以應用在相位光柵。我們觀察了液晶盒厚度與螺距比，對膽固醇液晶排列的關係。實驗上我們也發現外加電場的大小會改變條紋排列的方式，並討論了可能的原因。此外，並利用條紋排列方向的改變，製作出可以電場控制方向之相位光柵。最後並觀察繞射點角度上之變化，討論電場對膽固醇液晶螺距之變化。

Our previous experimental evidence has shown that the plane-parallel aligned cholesteric liquid crystal (CLC) cell has no more than two possible directions of stripe in fingerprint state. The direction of stripe is affected by the alignment direction and thickness-to-natural-pitch ratio, d/po, where d and po are cell gap and natural pitch of the cholesteric liquid crystal, respectively1. In suitable condition, homeotropic aligned CLC cell can also be in fingerprint state when abruptly switching off the applied external field. We found that the stripe direction depends not only on the boundary condition, but also on the profile of the driving voltage. Here we show that the angle between the stripe direction and the rubbing direction was tunable by the applied voltage. The theta modulation in the optical information processing can be realized in this type of CLC phase grating.