Extending the Detection Range of Optical Vortices by Dense Phase Stitching Algorithm

With the development of optical communication technology based on orbital angular momentum (OAM), more and more OAM modes are employed in communication systems, which puts forward higher requirements for the capacity of OAM state detection at the receiving end. In this work, we reported a scheme to measure and demultiplex OAM beams with topological charges from -32 to +32 by using a specially engineered two-dimensional 64-focus vortex demultiplexing array. The phase mask for generating this array was calculated by dense phase stitching algorithm which integrates four candidate phase masks that can generate four 16-focus arrays respectively. The first step of the algorithm is to extract sector phase areas from the four phase masks successively by using rotationally symmetric sector apertures whose total angular aperture is pi/2. The second step of the algorithm is to form a stitched phase mask with the extracted sector phase areas. Consequently, the 64-focus vortex array can be generated by using the stitched phase mask, which is almost equivalent to generating four 16-focus arrays by four candidate phase masks simultaneously. Furthermore, by adjusting the number of sector apertures, the modal crosstalk in the OAM detection range can be greatly reduced. With the help of this scheme, both single OAM mode and multiplexing OAM modes in the range from -32 to +32 can be effectively measured. According to this scheme, simple devices can be arranged to achieve both low modal crosstalk and wide detection range of vortex beams, which can support the advanced high-capacity OAM-based optical communication systems.