Photonic crystals made of nematic liquid crystal intercalated into the void space of close-packed silica spheres (synthetic porous opal) exhibit significant electric-field-induced shift of the optical Bragg reflection peak when the liquid crystal has the long molecular axis oriented parallel to the sphere surfaces. No such effect is observed for comparable fields when the long-axis orientation is normal to the sphere surfaces.

A mixture of two polyamic acids, one having an alkyl side chain and ordinarily used for vertical liquid crystal alignment, and the other without a side chanin and ordinarily used for planar alignment, is deposited on two substrates and baked at high temperatures. When the resulting cell is filled with the liquid crystal pentyl cyanobiphenyl, it is found that the pretilt angle θ 0 is a function of the baking temperature, and can be controlled continuously over the range 0 • ≤ θ 0. 90 • .

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