Fig. 1. Schematic of fabrication process of the EFPI optical fiber microphone

Fig. 2. Acoustic demodulation system based on FMQC-PSI method. (a) Schematic of the proposed FMQC-PSI system; (b) generated quasi-continuous quadrature phase shifting signals using four operating frequencies with π/2 phase bias; (c) timing diagram of the frequency tunning and phase retrieval

Fig. 3. Demodulation results of the EFPI optical fiber microphone with a cavity length of 279.502 μm. (a) Interference frequency spectrum obtained by linear frequency scanning and the four selected operating frequencies; (b)--(e) time-domain waveforms corresponding to the four operating frequencies and the retrieved phase signals under different acoustic pressures

Fig. 4. Output power spectrum of the sensor under 2.43 Pa acoustic pressure and 3 kHz frequency

Fig. 5. Sensor response. (a) Sound pressure response curve; (b) frequency response characteristic curve

Fig. 6. Demodulated results of EFPI acoustic sensor with different cavity lengths. (a) 1 kHz phase waveform demodulated by sensor with cavity length of 33.518 μm; (b) 15 kHz phase waveform demodulated by sensor with cavity length of 136.534 μm; (c) 9 kHz phase waveform demodulated by sensor with cavity length of 494.833 μm; (d) 12 kHz phase waveform demodulated by sensor with cavity length of 745.504 μm

Fig. 7. Schematic of the four-sensor sound source localization system

Fig. 8. Typical time-domain waveforms detected by the four sensor systems when the point sound source is placed at (30 cm, -15 cm)

Fig. 9. Six repeated measurements at 25 different positions