低散射非偏振依赖的聚合物/液晶光栅

Low scattering and polarization-independent polymer/liquid crystal grating

为了降低聚合物/液晶光栅的散射损失,并消除光栅的偏振依赖性,选取了低官能度的光敏单体作为反应体系,并逐步提高光栅的制备温度。首先选用五官能度的DPHPA(dipentaerythritol hydroxyl pentaacrylate)、双官能度的PDDA(phthalic diglycol diacrylate)以及单官能度的NVP(N-vinylpyrrolidone)作为反应体系;其次,在制备过程中在光栅的后面放置加热台,逐步提升制备温度。实验结果表明:当制备温度上升到62℃以上,光栅有更多(36%)的液晶析出,相分离比常温下制备时要更完全一些,而且高温下制备的光栅其平整度更高,从而使光栅的散射损失比常温下减小了66.7%,器件的SEM图片也进一步证明了这个结论。同时高温制备也消除了液晶光栅的偏振依赖特性。

In order to get low scattering and polarization-independent holographic polymer dis-persed liquid crystal(HPDLC)grating ,low functionality acrylate monomers were adopted and the fabricating temperature was increased gradually .First ,two kinds of acrylate monomers were selected ,one was penta-functional dipentaerythritol hydroxyl pentaacrylate (DPHPA ) , the other was difunctional phthalic diglycol diacrylate (PDDA ) .Besides N-vinylpyrrolidone (NVP) which served as solvent and chain extender was adopted .Then ,the effects of fabrica-ting temperature on the HPDLC grating was investigated ,and it is found that the highly aniso-tropic grating fabricated at room temperature becomes polarization-independent by its clearing point(62 ℃) .Also a more complete phase separation of liquid crystal from polymer is demon-strated .Besides ,optical measurement carried at the Bragg angle shows a 66 .7% scattering loss decrease ,this result is further conformed by scanning electron microscopy (SEM ) analyses .And also this high-temperature fabricated grating shows a polarization independent behavior .