Electro-Optic Coefficients of Ferroelectric Strontium Barium Niobate

Abstract

Linear electro-optic coefficients as large as r ~ 4 X 10-5 cm/statvolt have been measured in the system of ferroelectric strontium barium niobates, Sr ... Bal_ ... NbtOs. In the first crystals x varies from 0.75 to 0.25, with Curie temperatures ranging from -600C to 25()OC. At 15 Me, the respective half-wave field distance products range from 48 to 1236 V.The ferroelectric strontium barium niobates, Sr xBal-xNb20s, synthesized recently as well-formed crystals by A. A. Ballman,1 are optically negative, uniaxial cry.stals belonging to the tetragonal point group 4mm. 2 In this series of crystals, x varies from 0.75 to 0.25 with Curie temperatures ranging from -60°C to -250°C. The crystal growth, chemical properties, and ferroelectric characteristics are reported separately. I At room temperature, in poled single crystals we have observed and measured a transverse linear electro-optic effect between one and two orders of magnitude larger than those reported previously in the literature. The crystals are of the tungsten-bronze type with niobium ions octahedrally coordinated with the oxygen ions. 2 Various cation substitutions then allow control of the Curie temperature and other dielectric and optical properties.For a crystal of point group 4mm, the electrooptic matrix has three independent nonzero moduli (r13 = r23, r42 = r51> r33)' In SrxBal-xNb20s the large electro-optic effect was observed for the electric field parallel to the single tetrad symmetry axis (X3), which is also the polar axis, and light propagation normal to the X3 direction.The optical phase retardation in radians, f, is given by f=(21TI/Ao)(n'2-n'3), where n'2 and n'3 are the principal indices of refraction normal to the direction of propagation (XI), Ao is the wavelength of light in vacuum, and I is the optical path length. For point group 4mm, n'2 = no -no3,rI3E/2 and n'3 = ne -ne3r33E/2, where E is the field strength and no and ne are the ordinary and extraordinary indices of refraction respectively. For light parallel to X3 and electric field parallel to XI (a axis), and n'2 = no.Crystals in the series SrxBal-xNb20s which have been investigated are those for which X = 0.25, x = 0.50, and X = 0.75. Measurements were made of the half-wave field distance product [E . l] 11. /2 and the relative dielectric constant, E3' along the X3 or optic axis. The [E . I] 11. /2 at 6328 A with polarization of the incident light at 45° with respect to the principal axes are tabulated in Table I. In Sro.75Bao.25Nb20s for a 1: 1 aspect ratio of electric field path to optical path length the half-wave field distance product [E . I] 11./2 is 48 V at 15 Me. This value is comparable to the value of 28 V (ref.3) for the quadratic effect in potassium tantalate niobate at dc bias fields of 2000 V. The 48 V required is also 60 times smaller than the -2800 V figure given previously for LiTaO:! (ref. 4) and LiNb0 3 . 5The lithium tantalate modulator which was described 4 used a 10 mm light path and a 0.5 mm electric field path and resulted in a reduction of the half-wave re...

Strontium Barium Niobate Thin Films for Dielectric and Electro-Optic Applications

“…The domain of transparency is 0.35μm -6 μm. Ferroelectric, dielectric and non linear optic properties of SBN crystals are very sensitive to the Sr/Ba ratio consistently with the impact of this ratio on Curie temperature (Glass, 1969;Lenzo, 1967). Increasing the Sr content reduces the interval between room and Curie temperatures, thus inducing a drastic enhancement of the dielectric permittivity, pyroelectric coefficient and non linear optic properties.…”

“…Increasing the Sr content reduces the interval between room and Curie temperatures, thus inducing a drastic enhancement of the dielectric permittivity, pyroelectric coefficient and non linear optic properties. Exceptionally large values of the linear electro-optic coefficient have been obtained (r 33 =1340 pm/V at λ=633 nm) with a 75% Sr content (Lenzo et al, 1967).…”

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