Fig. 1. Diagram of sensing system. (a) Diagram of fiber ring laser based on SOA; (b) reflection spectrum of FBG; (c) transmission spectrum of FFP filter

Fig. 2. Simulation results. (a) Transmission spectrum of FFP filter; (b) relationship between output optical power and wavelength difference δλ

Fig. 3. Relationship between detection sensitivity and wavelength difference δλ

Fig. 4. Diagram of demodulation principle. (a) Transmission spectrum of FFP filter and reflection spectrum of FBG; (b) demodulation range of 0.2-nm bandwidth FBG corresponding to FFP filter with 100-GHz channel interval

Fig. 5. Spectra of FBG and FFP filter

Fig. 6. Demodulation results of dynamic strain signals (3 με) at different frequencies. (a) 5 kHz; (b) 10 kHz; (c) 60 kHz; (d) 200 kHz

Fig. 7. Demodulation results of different dynamic signals and Fourier transform spectra. (a) 18 MHz and 20 MHz demodulation signals; (b) fast Fourier transform of 18 MHz and 20 MHz demodulation signals

Fig. 8. Demodulation results of ultrasound signals. (a) Demodulation results of 33 kHz transient ultrasound signal; (b) demodulation results of 33 kHz continuous ultrasound signal

Fig. 9. Spectra of FBG and FFP filter for multiplex demodulation

Fig. 10. Multiplexed demodulation signal of the system