Fig. 1. Architecture of UWOC system based on LED or LED array and FPGA

Fig. 2. Modelsim simulation diagram of NRZ-OOK pulse shaping signal

Fig. 3. System diagram of UWOC RS-16QAM modulation signal

Fig. 4. 16QAM partial differential encoding modulation. (a) Differential coding modulation process; (b) π/2 rotation invariant mapping constellation

Fig. 5. Performance parameters of optical transmitter. (a) Volt-ampere characteristics curve; (b) spectrum measurement using optical transmitter sphere integration method

Fig. 6. Physical photo of miniaturized optical transmitter based on FPGA and high-power LED array. (a) Picture of optical transmitter circuit; (b) picture of optical transmitter working after waterproof packaging

Fig. 7. Curve of irradiance distribution with divergence angle

Fig. 8. Spatial irradiance curve

Fig. 9. Amplitude frequency response curve of optical transeiver

Fig. 10. Physical photo of optical receiver. (a) OOK signal and its eye diagram on oscilloscope received by optical receiver; (b) picture of optical receiver circuit

Fig. 11. Printed circuit board+assembly (PCBA) of automatic gain control optical communication receiver

Fig. 12. Experimental diagrams of miniaturized underwater optical communication terminal prototype

Fig. 13. Change curve of BER with data rate for OOK and 16QAM modulation modes

Fig. 14. Spectrum of 30 Mbps rate signal. (a) Spectrum of OOK signal; (b) spectrum of 16QAM signal

Fig. 15. Curve of BER with degree of deviation from main optical axis

Fig. 16. BER at different rates with/without optical collimation antenna

Fig. 17. Curve of OOK signal BER versus transmission distance in water-air cross media link optical communication