Fig. 1. Underwater single-photon communication system

Fig. 2. Data demodulation process based on photon counting in time slot

Fig. 3. Diagram of photon trajectory

Fig. 4. Photon statistical distributions in different distance planes. (a) Transmitter lens plane; (b) channel entry plane; (c) plane at 2 m of underwater channel;(d) plane at 5 m of underwater channel; (e) plane at 10 m of underwater channel; (f) receiver lens plane

Fig. 5. Received intensity versus distance. (a) Different water types; (b) different launching angles and different water types; (c) different received apertures and different water types; (d) different FOV and different water types

Fig. 6. Channel impulse response under different channel parameters.（a）Different launching angles in clear water；（b）different received apertures in clear water

Fig. 7. Relationship between channel parameters and BER. (a) Influence of distance on BER; (b) influence of received aperture on BER; (c) influence of launching angle on BER

Fig. 8. Relationship between distance and BER under different noise factors