The features of light modulation in cubic gyrotropic crystals by varyi
ng both the magnitude and direction of the external electric field are
analyzed. An explicit form of all possible types of modulation charac
teristics for plane-polarized and circularly polarized incident light
is obtained for an arbitrary propagation direction in a gyrotropic cub
ic crystal, taking into account the magnitude and direction of the mod
ulating field. The optimum geometries of the electrooptic interaction,
in which 100% modulation depth of the optical radiation is achieved,
are found for a [110] cut of a Bi12GeO20 crystal. (C) 1998 The Optical
Society of America.