Fig. 1. Curves of wavelength scanning range of DFB laser driven by different currents as function of modulation frequency

Fig. 2. Demodulation process of amplitude modulated laser interferometer underwater sound

Fig. 3. Time-frequency diagram of interference measurement under silent source condition. (a) Simulation result; (b) spectrum curve

Fig. 4. Time-frequency diagram of interference measurement with sound source of 200 Hz frequency. (a) Simulation result; (b) spectrum curve

Fig. 5. Interference signal spectrum of different methods with sound source of 200 Hz frequency. (a) Traditional laser interferometry method; (b) amplitude modulated laser interferometry method

Fig. 6. Schematic of experimental system

Fig. 7. Measurement results natural fluctuations on surface of calm water. (a) Simulation result; (b) spectrum curve

Fig. 8. Interferometric spectra measured by different methods under different underwater sound source frequencies. (a) Laser interferometry method; (b) amplitude modulated laser interferometry method

Fig. 9. Interferometric spectra obtained by different methods under different sound pressure conditions. (a) Laser interferometry method; (b) amplitude modulated laser interferometry method

Fig. 10. Spectrum diagrams of different light intensity ratios. (a) 10∶1; (b) 1∶1

Fig. 11. Amplitude measurement results of water surface waves under different sound pressure conditions

Fig. 12. Measurement results of different methods under noise interference. (a) Measurement results without optical noise interference; (b) measurement results with optical noise interference