Fresnoite-type Ba2TiGe2O8 glass-ceramics toward electro-optic device: Crystallization structure and Pockels effect

Abstract

Optical modulation based on second-order optical nonlinearity is required to control a light-wave for telecommunication with optical-fiber network, and its controlling device is basically constructed using a single crystal material. To fabricate an optical device material having the connectivity to glass fiber, glass-ceramic (GC) processing is effective. In this study, a bulk-like GC material with a polar fresnoite-type Ba2TiGe2O8 were successfully fabricated. The obtained GCs were formed by densely-aggregated structure of two phase, fresnoite-type (major phase) and tetragermanate (minor phase). The fresnoite-type Ba2TiGe2O8 domains with submillimeter-sized were oriented with the polar c-axis perpendicular to sample plane. The GC sample exhibited the optical modulation driven by Pockels effect, and the Pockels coefficients could be quantitatively estimated, i.e., r13 = 2.3 ± 0.1 pm/V and r33 = 2.5 ± 0.1 pm/V. The experimental results demonstrate the potential of higher Pockels coefficients by microscopic structural studies, because of good controllability of the polar orientation and suppression of secondary phase.