Surface vertical alignment effect on performance of holographic polymer dispersed liquid crystal gratings

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.