Combined effects due to phase, intensity, and contrast in electrooptic modulation: Application to ferroelectric materials

The combination of phase, intensity, and contrast effects during electroopt ic modulation is theoretically and experimentally investigated. One consequ ence of this combination is the modification of the amplitude of the single -frequency signals which are commonly used as working points for electroopt ic modulators and for the measurements of the electrooptic coefficients. An other consequence of direct intensity modulation is to shift the double-fre quency points of the transfer function from the positions they normally occ upy at the intensity extrema. They can even make them disappear if the dire ct intensity modulation is stronger than the phase modulation. Such phenome na are expected with any ferroelectric material in which a significant part of the incident light is deflected or scattered by domain walls or grain b oundaries. They can lead to considerable mistakes in the determination of t he electrooptic coefficients. Appropriate procedures to extract the differe nt contributions are explained. Experimental results in rubidium hydrogen s elenate are given, and consequences of the working of electrooptic modulato rs are discussed.