Liquid Crystal Based Electro-Optic Diffractive Spectacle Lenses and Low Operating Voltage Nematic Liquid Crystals

Abstract

Diffractive optical elements in which discrete phase levels are used to approximate a continuous blaze profile offer the advantage over conventional refractive optics in that they are essentially planar structures and thus consume very little space. Furthermore, it has been shown that switchable diffractive elements can be fabricated using electro-optic materials such as inorganic electro-optic crystals and liquid crystals. In this work, liquid crystal diffractive lenses are investigated for their possible use as switchable spectacle lenses, an alternative to current bifocal and progressive lens technologies. In these lenses, discrete, rotationally symmetric electrodes are used to generate the stepped phase levels of a diffractive lens in a 5 micrometer layer of nematic liquid crystal. Near theoretical diffraction efficiencies are reported for both 2 and 4 phase level lenses and it is shown that the inter-electrode gap is a critical design parameter for achieving these values. For the 4 level lenses the near theoretical values are achieved by implementing a novel, multi-level electrode structure that eliminates the inter-electrode gap while maintaining electrical isolation between adjacent electrodes. Additionally, the results of a study aimed at reducing the operating voltages of nematic liquid crystal are also included. In this study, colorless molecular dopants with high dipole moments are added to commercial nematic liquid crystal mixtures for the purpose of increasing dielectric anisotropy, upon which the threshold voltage is inversely dependent. While a reduction in threshold voltage is observed it is determined that a reduction in order parameter is the cause. Quantum-chemical analysis of the dopant molecules indicate that the structures are too rigid for introduction into a liquid crystal host and a new, less rigid structure is proposed.