Bit error rate performance analysis for the orbital angular momentum of a multiplexed optical communication system based on multistaircase spiral phase plates

Multistaircase spiral phase plates (MSSPPs), which are alternatives to ideal continuous surface SPPs, are commonly applied to passively generate optical vortices (OVs). In addition, one of the universal applications of OVs is in orbital angular momentum (OAM)-multiplexed quadrature amplitude modulation (QAM) optical communication systems. In this paper, the relationship between bit error rate (BER) performance and the key parameters of the MSSPPs, e.g. the number of staircases M and the topological charge l, is researched, and four OAM-multiplexed QAM systems with different modulation orders (16 QAM, 32 QAM, 64 QAM and 256 QAM) are qualitatively and quantitatively evaluated. Theoretical analysis and the simulation results show that OAM multiplexing leads to negative impacts on BER performance. The impacts include a decrease in the power of the useful signal and possible crosstalk between OAM-multiplexed paths. In addition, appropriately setting M, l and the modulation order can help reduce the impact of the power decrease and avoid crosstalk. This work provides a reference for practical OAM-multiplexed QAM systems based on MSSPPs.