  The boundary-value problem of the reflection and transmission of a plane wave
due to a slab of an electro-optic structurally chiral material (SCM) is
formulated in terms of a 4x4 matrix ordinary differential equation. The SCM
slab can be locally endowed with one of 20 classes of point group symmetry, and
is subjected to a dc voltage across its thickness. The enhancement (and, in
some cases, the production) of the circular Bragg phenomenon (CBP) by the
application of the dc voltage has either switching or
circular-polarization-rejection applications in optics. The twin possibilities
of thinner filters and electrical manipulation of the CBP, depending on the
local crystallographic class as well as the constitutive parameters of the SCM,
emerge.
