Surface vertical alignment effect on performance of holographic polymer dispersed liquid crystal gratings
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摘要: 为了提高聚合物/液晶（HPDLC）光栅的衍射效率并改善光栅的表面形貌，研究了表面垂直取向处理对HPDLC光栅的影响。首先，研究了表面垂直处理对液晶分子的取向作用，发现垂直取向层对液晶的锚定作用随着盒厚的增加而逐渐减弱，取向层的作用范围大概在3 m ~5 m之间；其次，对相分离程度进行了实验表征，结果表明，随着液晶盒厚度的增加，相分离开始的时间越来越快，并且分离程度也越来越彻底。最后，讨论了表面垂直取向对HPDLC光栅衍射效率的影响，随着盒厚的增加，相分离出来的液晶微滴形成连续的区域，光栅的衍射效率逐渐升高，当盒厚增加到一定程度，其衍射效率和无取向处理的光栅接近。当盒厚过大时，垂直取向处理对HPDLC光栅散射损失并没有太大的改善，只有当盒厚适中（12 m）时，光栅的衍射效率最高，散射损失最小。Abstract: In order to get the holographic polymer dispersed liquid crystal (HPDLC) grating with high diffraction efficiency and perfect morphology, the effect of surface vertical alignment on the properties of HPDLC grating was investigated. Firstly, the effect of the vertical surface treatment on the orientation of liquid crystal molecules was studied. It is found that the vertical anchor effect of liquid crystal decreases with the increase of cell gap and the orientation depth is about 3 m ~ 5 m. Secondary, the characterization experiment of separation was done.And results show that as the cell gap increases, the surface effect on the bulk LC droplets reduces due to the longer distance. For the thinner cell, almost all the LC droplets are confined on the inner surfaces of the substrates which cannot flow and coalesce with the neighboring droplets, so the phase separate is not good. However, if the cell is too thick, the effect of vertical alignment on the LC droplets in the middle of the cell is very small and the bulk droplets are less ordered so that the morphology is similar to those of conventional (without vertical alignment) HPDLC cells. Experimental results indicate that only in the condition of certain surface vertical alignment strength(cell gap is 12 m), the HPDLC with high diffraction efficiency and low scattering loss can be realized.
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Keywords:
- surface vertical alignment /
- HPDLC /
- diffraction efficiency /
- scattering loss
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