Enhanced Photorefractive Lithium Niobate for Passive Agile Filters

Single crystals of lithium niobate can be used to construct a very simple passive agile filter, in which an incoming beam interferes with its own back-reflection to set up a diffraction grating that results in energy transfer and depletion of the transmitted power. The virtue of such an approach is that it can respond to incident coherent radiation of any wavelength within its range of sensitivity. Although considerable efforts in the past have been directed toward understanding and controlling the photorefractive properties of LiNbO3, nearly all of these studies have focused on so-called "congruent" material - crystals with a Li/Nb ratio of around 0.94, and grown from a melt of composition identical to that of the crystal. Recently, a new composition of LiNbO3 has been developed, the so-called stoichiometric (or near-stoichiometric) composition, in which Li/Nb ratios very close to 1.0 are obtained. These crystals appear to have electro-optic and other properties that are superior to those of congruent LiNbO3, thus improving their usefulness in a number of device applications. In this SBIR Phase I program, Nova Phase proposes to produce a suite of crystals of Fe-doped LiNbO3 with varying Fe concentration, oxidation state, and Li/Nb ratio, and to study their optical, electrical, and photorefractive properties.