Influence of the helical shape of a fibre waveguide on the propagation of light

A study is reported of the influence of twisting a fibre waveguide into a helix on the speckle pattern of light transmitted by the fibre when the pitch of the helix was altered. Rotation of the speckle pattern was discovered. This rotation was numerically equal to the change in the solid angle formed on a unit sphere in the space of the tangents to the fibre.