High-Efficiency Orbital Angular Momentum Beams Multiplexing System With Compact Shaper and Transformation Optics

In recent years, mode-division multiplexing (MDM) has been intensively proposed to cope with the information capacity crisis. However, how to multiplex a large number of OAM modes efficiently with low insertion loss and broad bandwidth is still a crucial issue. To solve this problem, we design a multiplexing system in which we make two functional blocks including a compactable shaper and a pair of free-form refractive optical elements. In one block, a self-designed compactable shaper is used to turn the Gaussian beam output from a single mode fiber into the elongated beams with tilted plane wave so that it can meet the phase requirement for the subsequently transformation. In the other block, a pair of free-form refractive optical elements is reversely used to multiplex multi modes based on coordinate transformations. Based on these structures, OAM multiple modes multiplexing experiment has been successfully performed in C+L band and the insertion losses of all modes are less than 1.6 dB . Furthermore, in the limited number of modes, the energy insertion loss does not increase with the increase of the number of OAM modes. The scheme offers a great potential for the integration in the next platform of MDM.