Frequency dependent electro-optic property of SBN single crystal

Abstract

In electro-optic (EO) modulator devices ferroelectric crystals of strontium barium niobate (SBN) are attractive due to exceptional high EO coefficients and low half wave voltage. SBN single crystals grown by laser heated pedestal growth are investigated to explore frequency dependent EO property at low frequency and near resonant frequency range. The mechanism of its frequency dependence is discussed briefly. IntroductionA number of investigators have studied optical properties of strontium niobium oxide series crystals because they possess large electro-optic coefficients and low normalized half-wave voltages. Their room temperature linear electro-optic coefficients increase with increasing Sr concentration across the solid solution range as a result of decreasing phase transition temperature. Several attempts to measure the electro-optic coefficients for pure or doped SBN were reported since Lenzo's work [1][2][3][4][5][6] , but there has been limited agreement among reported results [3,7,8] . The inconsistencies, to a large extent, may be attributed to the poling conditions and measurement boundary conditions, in addition to the temperature dependence of the optical birefringence, space charges effects, and crystal quality, among others.Frequency dependence of electro-optic coefficients on modulating field is one aspect scarcely reported in literature; however is of significant importance for using the crystals as electro-optic modulators in optical engineering at different frequencies.Common assumptions are that EO coefficients are frequency independent based on the frequency independency of electronic polarizability of the material. Yet the EO coefficient measured by conventional technique contains without exception both primary and secondary effects arising from electronic and ionic polarizations which contain dispersive components (such as reorientation and electromechanical coupling of ions).This paper reports the electro-optic property of SBN crystal fiber as function of electric field frequencies (at low frequency and at near resonant frequencies) studied via both direct EO modulating method and a microwave waveguide method.