A thiol-ene-based HPDLC grating with <i>s</i>-polarization-dominated diffraction

Holographic Polymer-Dispersed Liquid Crystal (HPDLC) gratings exhibit excellent electro-optical performances due to their unique optical characteristics and tunability. However, the previously reported HPDLC gratings where the<i>p</i>-polarization response dominates in their diffraction, i.e., the diffraction efficiency of HPDLC gratings in <i>p</i>-polarization is much larger than that in <i>s</i>-polarization. This Letter reports a thiol-ene monomer-based HPDLC grating, which exhibits a high <i>s</i>-polarization diffraction efficiency rather than <i>p</i>-polarization. The dependence of refractive index modulation (Δ<i>n</i>) on recording intensity and liquid crystal (LC) doping concentration is experimentally investigated. The results show that Δ<i>n</i> is able to reach as high as 1.93 × 10^-2 in <i>s</i>-polarization and 1.21 × 10^-2 in <i>p</i>-polarization with an optimum recording condition. Combining with the morphology examinations, the results imply that the Δ<i>n</i> strongly depends on the ratio of LC-rich and polymer-rich phases in the grating. Moreover, we confirm that a lower recording intensity leads to a larger LC droplet size formed by holographic recording and thereby results in a decrease in threshold driving voltage of HPDLC gratings. We believe that the finding of <i>s</i>-polarization-dominated diffraction in the proposed thiol-ene photopolymer provides a new direction for HPDLC grating design.