Mitigating Crosstalk of Vortex Beam Within an OAM-Mode Group Over an OAM Fiber by Reversing Transmission Matrix

For enhancing channel capacity and spectrum efficiency, vortex beam carrying orbital angular momentum (OAM) has been ardently investigated in optical communication. However, the crosstalk among OAM modes induced by mode coupling has seriously hindered the development of vortex beam communication (OBC). A novel concept of mitigating crosstalk within an OAM-mode group for a short-haul optical fiber communication (OFC) is proposed by reversing the transmission matrix. To support more OAM modes propagation, a step-index OAM fiber with ring-shaped profile is also designed and fabricated, which can support 6 vector/OAM modes propagation. A proof-of-concept experiment is performed for verifying the feasibility of the proposed concept, where a quadrature-phase-shift-keying (QPSK) signal is utilized as an excitation signal. Bit-error-ratio (BER) and constellation diagram (CD) are employed to evaluate the performance of the proposed system. The captured intensity profiles and interference diagrams demonstrate that the propagated four OAM beams within the 2rd OAM-mode group are successfully received. The measured BER and CD illustrate that the crosstalk within the mode group can be significantly mitigated. Further, although the data speed or fiber length is increased, the system performance using the proposed concept is still superior to the case without increasing fiber length or data speed when the proposed concept is missed. Therefore, the proposed concept is effective for mitigating the crosstalk and can be then used for a short-haul OAM-based OFC.