Propagation of circularly polarised radiation along a twisted path

An analysis is made of the influence of a slight twist on the parameters of the field of a mode in a fibre waveguide. Rotation of the speckle pattern by an angle equal to the geometric Berry phase is predicted for a helicoidal twisted multimode fibre. The geometric optics approximation is used to show that the presence of a twist leads to additional bending of the optical path, which depends on the sign of the circular polarisation. It therefore follows that in the case of an elliptically polarised ray we can expect splitting of this ray into two components with the left- and right-handed circular polarisations.