Parallel Coded Optical Vortex Beam Free-Space Communication Based on Single-Photon Detection

A free-space communication scheme is proposed based on orbital angular momentum (OAM) states and pulse position modulation (PPM). It can not only improve the channel capacity, but also be suitable for single-photon detection to realize the communication in the case of ultra-weak light. A parallel coding method is proposed to realize high-capacity and low bit error rate (BER) communication under high background. Theoretical simulation and experimental results show that the scheme can effectively suppress the background noise. The BER is as low as 1.27 × 10$^{-5}$ under the condition of 16 OAM states, 16 single-photon detectors (SPDs) coincidence, and the background noise of 10$^{7}$ counts per second. The BER performance is an order of magnitude better than the traditional PPM, and the channel capacity is increased by 12 times. This work provides an effective solution for deep space high-speed and low BER communication.