Light propagation in a helical medium with a large-scale periodicity

The propagation of light in helical media whose pitch greatly exceeds the radiation wavelength has been investigated. It is shown that such a system includes forbidden zones corresponding to the effect of ray turning. The propagation of an extraordinary ray corresponding to a very narrow forbidden zone has been analyzed in detail. The radiation wave field has been obtained both far from a turning point and in the close vicinity of such a point. It is shown that, in the vicinity of a turning point, mode transformation takes place and the wave acquires an elliptical polarization. The parameters of the ellipticity and the relations between the amplitudes of the waves passed through the forbidden zone and “reflected” from it are calculated.