Optical orbital angular momentum shift-keying communication based on coherent demodulation

Rapidly detecting orbital angular momentum (OAM) modes is crucial for optical OAM shift-keying (OAM-SK) communication. Here, we propose and investigate a novel coherent detection method for demodulating optical OAM-SK signals. A reference light beam with desired OAM modes and weights is well-designed and employed to interfere with the light beam which carries OAM-SK signals. Then the OAM-SK signals representing as the rapid switching of OAM modes are converted to intensity changes for demodulation. In the numerical simulation, a pseudo-random sequence is mapped and encoded to different OAM modes (+1, +2, +3, +4) to produce OAM-SK signals, and the demodulated bit-error-rate (BER) of 9.7656×10−4 is obtained at the signal-noise ratio (SNR) of 12-dB. By modulating the OAM modes and phase of the optical carrier synchronously, a multi-dimensional modulation format (16-ary OAM-Phase modulation) is constructed, and the demodulated BER is less than 4.8828×10−4 at the SNR of 14-dB. These results demonstrate that the coherent detection method provides an effective way to demodulate OAM-SK signals, and may shows great potential in high-speed optical OAM communications.