Abstract Circular polarization shift-keying (CPolSK) modulation is crucial for optical communication in free space optical communication. In this paper, we propose a new optical communication system with multiple orbital angular momentum (OAM) modes for division multiplexing CPolSK modulation signals. A well-designed reference beam is employed to interfere with the CPolSK-OAM-division multiplexing (CPolSK-OAM-DM) signals for coherent detection. Then, the complex modulation signal is converted into intensity change directly detected by photo-detector. The communication performance can be further improved by subtracting the two interference beams detected. In numerical simulation, the demodulated bit error rate (BER) is 2.25 × 10−4 with the signal noise ratio (SNR) of 12-dB, and it can be reduced to 1.25 × 10−4 after difference operation. Through mapping the signals to both the initial phases and circular polarization states of the multiplexing channels, we construct the phase-CPolSK-OAM-DM system, the demodulated BER is 1.07 × 10−4 with the SNR of 15-dB. The results demonstrate that the CPolSK-OAM-DM modulation can effectively expand the communication capacity of the CPolSK system. The CPolSK-OAM-DM system has great potential in the field of high-speed broadband optical communications.

中文翻译：

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自由空间光通信中基于轨道角动量分复用的圆偏振移键控调制

摘要 圆偏振移键控（CPolSK）调制对于自由空间光通信中的光通信至关重要。在本文中，我们提出了一种具有多轨道角动量 (OAM) 模式的新光通信系统，用于分路复用 CPolSK 调制信号。设计良好的参考光束被用来干扰 CPolSK-OAM 分复用 (CPolSK-OAM-DM) 信号以进行相干检测。然后，复合调制信号被转换为光检测器直接检测到的强度变化。通过减去检测到的两个干扰波束，可以进一步提高通信性能。在数值模拟中，解调误码率(BER)为2.25×10-4，信噪比(SNR)为12-dB，经差分运算后可降至1.25×10-4。通过将信号映射到复用信道的初始相位和圆偏振态，我们构建了phase-CPolSK-OAM-DM系统，解调BER为1.07×10−4，SNR为15-dB。结果表明，CPolSK-OAM-DM调制可以有效扩展CPolSK系统的通信容量。CPolSK-OAM-DM系统在高速宽带光通信领域具有巨大的潜力。