Demodulation for multi vortex beams based on composite diffraction hologram

While projecting a Gaussian beam onto the spatial light modulator (SLM) which has loaded a composite hologram, several vortex beams can be generated at one time. On the contrary, while projecting the corresponding vortex beam onto the hologram, the Gaussian beam can be restored, realizing the demodulation of vortex beam. In traditional optical communication systems, a hologram can only demodulate one incident vortex beam. In this paper, a vortex beam demodulation method based on composite diffraction hologram is proposed, which can demodulate several incident vortex beams with only one hologram. An experimental system is set up in this paper which achieves the generation, transmission and demodulation experiments of vortex beams with 64QAM-OFDM signals. After a series of offline processing on the demodulated Gaussian beam, constellation and bit error rates (BER) of each subcarrier for OFDM signals are acquired. The experimental results show that good system performance can be achieved with this method as the BERs of all subcarriers are under the FEC threshold.