Highly dispersive liquid crystal diffraction gratings with continuously varying periodicity

By using well-designed anchoring patterns in a liquid crystal (LC) device, novel electro-optic components with enhanced functionality can be designed. We present two types of nematic LC diffraction gratings with varying periodicity, manufactured with patterned photoalignment at the confining substrates. By varying the surface anchoring periodicity, the incident light can be redirected into many different diffraction orders, giving rise to a scattering appearance of the grating. In Type I gratings the anchoring patterns at the top and bottom substrates are aligned in the same direction, whereas in the Type II grating the anchoring patterns at the top and bottom substrates have a relative rotation of 90°. The structural and optical properties of the gratings can be tuned by applying an external voltage. The director configuration in the bulk is revealed with the use of polarizing optical microscopy images and numerical simulations. Experimental results of the diffraction spectra and intensities of different diffraction orders are supported by finite difference time domain (FDTD) simulations. The results specifically aim at tunable LC diffraction gratings which are highly dispersive and have weak zeroth order diffraction. In general, this work is a contribution to the field of LC flat optical components with electric tunability.