  Recently the general linear transformation for point rotation coordinate
frames was considered. A distinguishing feature of the frame, in contrast to
the Cartesian one, is the existence of the rotation axis at every point. The
frame coordinates are an angle and time, the frequency of rotation is a
parameter. The concept of the frame originated from the optical indicatrix
(index ellipsoid). Rotation of the optical indicatrix arises in three-fold
electrooptical crystals under the action of the rotating electric field applied
perpendicular to the optical axis \cite% {pat}. Such a rotation is possible as
in the Pockels as Kerr crystals and also in the isotropic Kerr medium. The
rotation is used in single-sideband modulators. The single-sideband modulation
has very interesting features from the theoretical viewpoint. In applications
it may be used for the frequency modulation and frequency shifting. In contrast
to usual modulation such a shifting is "100 persent transformation" of the
initial into output frequency. However at present the modulation practically is
not in use. It is connected with the high controlling voltage of bulk
modulators; creating waveguide single-sideband modulators calls for
considerable technological efforts.
