Figure 8: Generation of non-zero-order modes.
From: Exploiting multimode waveguides for pure fibre-based imaging
(a) Any optical field (within the accessible field of view and range of spatial frequencies supported by the optical fibre) can be expressed as a superposition of the output modes. For the specific case of optical vortices, we distribute a series of output modes along a circle of an appropriate diameter and offset their phases accordingly to the required topological shape of the final wavefront. (b) Experimentally generated optical vortices with varying topological charge. (c,d) Interferograms of l=±1 vortices with a plane wave for six different phase shifts of the plane wave covering an interval of 
0,2π
. Rotation of the phase singularity (dark spot) along the vortex circumference reveals its helical wavefront together with its handedness.
