Electrically tunable two-dimensional holographic photonic crystal fabricated by a single diffractive element

An electrically tunable two-dimensional holographic photonic crystal was fabricated in polymer-dispersed liquid crystal using a single diffraction element, which was a specially designed photomask consisting of three diffraction gratings, which had a period of 4μm, oriented 120° relative to one another. With the photomask subjected to a collimated Ar+ laser beam operating at 514.5nm, a two-dimensional spatial light intensity pattern was created by interference of the three first order diffracted beams produced by the mask. The spatial light intensity pattern was then recorded inside a cell filled with the liquid crystal/prepolymer mixture to create a photonic crystal. The photonic crystal structures were observed under an optical microscope. It showed triangular structures with a lattice constant of about 2.50μm. The diffraction properties and electro-optic tunability were also presented.