Fig. 1. Schematic diagram of echo pulse train

Fig. 2. Diagrams of detecting different reflection points of body target. (a) Optical path; (b) pulse response

Fig. 3. Response of a detection system to echo signal

Fig. 4. Circuit diagram

Fig. 5. Simulation results of source voltage waveform with input pulse width of 4-12 ns

Fig. 6. Test system

Fig. 7. Output light pulse waveforms of input signal with pulse width of 8-18 ns displayed by oscilloscope and waveforms obtained based on derived data. (a)-(f) Waveforms displayed by oscilloscope; (g) waveforms obtained based on derived data

Fig. 8. Relative amplitude of output light pulse varying with input pulse width

Fig. 9. System principle diagram