Measurement of the linear electro-optic effect in chiral nonlinear optical crystal

The Bi₁₂SiO₂₀(BSO) single crystal possesses the second and third order nonlinear optical properties, and is widely adopted for the applications such as dynamic holography, phase conjugation, fiber-optic sensor, and photorefractivity. Differently from the other second-order anisotropic nonlinear optical crystals, the BSO crystal is isotropic optically, but still gives rise to the electro-optic effect, one of the second-order nonlinear optical effects. The inherent optical isotropy is important in the device applications, because the electro-optic coefficients do not vary much in R wide range of the operating temperature. The point group symmetry of the BSO crystal is 23, one of the cubic symmetry classes; it shows natural optical activity and has three nonzero electro-optic coefficients, r41 r 52 r= 6 3 . The presence of the natural optical activity complicates the determination of the electro-optic coefficients, the reason for a confusion in the reported literature values. In this paper, we propose a polarization interferometry technique to measure the electro-optic coefficient in an optically active system. The technique makes use of the interference of two polarization states of the incident beam after experiencing both the electro-optic phase modulation and the optical rotation in the BSO crystal. The modulated light intensity is analyzed for a measurement system consisting of a polarizer, a half wave plate, the BSO crystal, a Soleil-Babinet compensator, and an analyzer arranged as shown in Fig.1 The crystal is positioned in a longitudinal electro-optic configuration with the light propagating along (100) direction and the electric field applied along (loo] direction. The sample dimension is 5mm[100] x 5mm(010] x 7mm[001]. The (100) faces are sputtered with transparent conductive electrodes indium-thin- oxide(IT0). Wires are then bounded to a corner of each electrode with a silver paste.