Polarization-dependent Bragg gratings formed by shearing of polymer-dispersed liquid crystals \textit{in situ} during holographic recording

We report the recording of holographic polymer-dispersed liquid crystal 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 timing and magnitude of the stress are related to optical properties of the resulting Bragg grating. High diffraction efficiency for light polarized in a direction parallel to the stress is obtained with nearly zero diffraction efficiency for the perpendicular polarization. Contrary to post-recording stress-induced polarization sensitization, the \textit{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 during the cure process.