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

  • 摘要: 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。

     

    Abstract: In order to get low scattering and polarization-independent holographic polymer dispersed 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 fabricating temperature on the HPDLC grating was investigated, and it is found that the highly anisotropic 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 demonstrated. 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.

     

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