Fig. 1. Schematic of four-quadrant detector

Fig. 2. Schematic of space four-quadrant active positioning technology

Fig. 3. Space four-quadrant active positioning system (high-speed modulation and demodulation of information)

Fig. 4. Schematic of spot center position detection. (a) Receiver center coincides with space four-quadrant center; (b) receiver center offset relative space four-quadrant center

Fig. 5. Equivalent calculation diagram of Monte Carlo method

Fig. 6. Schematic of center position detection with h<2R

Fig. 7. Position simulation curves under different scanning spot intervals

Fig. 8. Relative error curves under different scanning spot intervals

Fig. 9. Relative error curves for different spot radii

Fig. 10. Schematic of spot position detection experimental system

Fig. 11. Experimental platform for verifying positioning function of space four-quadrant system

Fig. 12. Schematic of APD defocus

Fig. 13. Detection results of spot position

Fig. 14. Relative error curve of spot position detection

Fig. 15. Transmitter modulation signal

Fig. 16. Communication rate test result chart at receiving end

Fig. 17. Test principle of detection sensitivity of APD receiver