Fig. 1. Schematic diagram of nutation convergence process. (a) First stage; (b) second stage; (c) third stage; (d) fourth stage

Fig. 2. Spatial location of nutation coupling

Fig. 3. Principle of nutation coupling

Fig. 4. Flow chart of our algorithm

Fig. 5. Experimental setup. (a) Schematic diagram; (b) physical diagram

Fig. 6. Optical power change during nutation convergence

Fig. 7. Coupling range under system tracking state

Fig. 8. Received optical power of the photodetector under different disturbances. (a) Disturbance1; (b) disturbance2

Fig. 9. Coupling efficiency under different angle errors

Fig. 10. Test results when the signal-to-noise ratio is 13.1 dB. (a) Power received by the detector; (b) average coupling efficiency of the system

Fig. 11. Test results when the signal-to-noise ratio is 7.9 dB. (a) Power received by the detector; (b) average coupling efficiency of the system

Fig. 12. Test results when the signal-to-noise ratio is 4.6 dB. (a) Power received by the detector; (b) average coupling efficiency of the system