Abstract

Bismuth silicon oxide (Bi₁₂SiO₂₀) crystals can be utilized in the transverse electro-optic configuration for several optical device applications, including spatial light modulation and holographic optical interconnections. In many such applications, a uniform electric field profile within the bulk crystal under conditions of holographic recording is desirable. However, even under conditions of uniform illumination, it has been shown by the technique of transverse electro-optic imaging¹ that significant charge accumulation near the negative electrode results in a large, local field buildup that in turn lowers the bulk field. This technique has been extended to examine the field profile during the process of photorefractive grating formation by simultaneously measuring both the time-dependent internal electric field and the diffraction efficiency. Local field reductions of up to 90% have been observed.² Two methods in particular are utilized to reduce the magnitude of the field collapse. In the first method, illumination at a highly absorbed wavelength is made incident on the crystal through a transparent negative electrode. The second method involves application of an opposite polarity voltage across the crystal to alter the region near the negative electrode. Both of these methods reduce the resistivity near the electrode, lowering the field at the electrode and significantly increasing the bulk electric field. This results in an increase of a factor of two in the measured saturation diffraction efficiency for both cases. Other methods will be discussed such as the utilization of various contact materials in conjuction with thermal indiffusion.

© 1992 Optical Society of America