Effect of surface rubbing alignment on electro-optical properties of holographic polymer dispersed liquid-crystal gratings

Abstract

In order to obtain holographic polymer dispersed liquid crystal( HPDLC) grating with high diffraction efficiency and low threshold, the effect of parallel rubbing alignment on electro-optical properties of HPDLC grating is investigated. According to the theoretical analysis, the improvement of phase separation structure and the lower order difference of the liquid crystal droplets are essential for perfect electro-optical properties of the grating. The phase separation is significantly improved due to the diffusion match between monomers and liquid crystals in the case of parallel alignment treatment. So the diffraction capability is enhanced while the driven voltage is reduced obviously. Moreover, the order difference of liquid crystal droplets is reduced because of the uniform liquid crystal alignments and consequently the scattering loss is reduced greatly. Experimental results indicate that the diffraction efficiency of grating with rubbing alignment increases from 75.6% (traditional HPDLC grating) to 98.1% and the driving voltage is lowered from 9.2 V/μm to 4.8 V/μm. And also, only in the case of certain surface rubbing strength, the HPDLC with high diffraction efficiency and low threshold will be realized.