Generating vortex beams by transforming near-field coordinates of coherent beam combining system.

In this study, we introduce a method of generating vortex beams based on coherent beam combining (CBC) configuration. By utilizing a pair of static optical elements with specific phase distributions, the near-field of array beams is transformed from Cartesian to polar coordinate. After the converted light field is focused, the focal point is associated with the wavefront. With the aid of CBC configuration and active phase control, it is easy to switch orbital angular momentum (OAM) modes by controlling the position of focal point. Hence, the OAM modes can be measured and generated simultaneously. The performance of the method has been numerically explored, and different OAM modes including integer and fraction topological charge have been generated efficiently.