Improvement of Electro-Optical Properties of HPDLC Gratings by in situ Shearing During Holographic Recording

Abstract

We report the results of the recording of holographic polymer-dispersed liquid crystal (HPDLC) reflection gratings while applying a shear stress parallel to the film plane. The shear is transmitted through the film by moving one glass window with respect to a fixed glass window during the holographic recording in a single beam, total internal reflection geometry. The optical properties of the resulting Bragg grating are related to timing and magnitude of the stress. High diffraction efficiency for light polarized in a direction parallel to the stress is obtained with nearly zero diffraction efficiency (DE) for the perpendicular polarization. Contrary to post-recording stress-induced polarization sensitization, the in situ process results in permanently polarized gratings. The polarization sensitivity is related to stress-induced morphology changes of liquid crystal droplets that are frozen at gelation of the thio-ene polymerization process.