Fig. 1. Frequency division multiplexing FBG sensing system based on the dual-loop OEO

Fig. 2. Overall oscillation frequency. (a) Response of the sensor in initial state; (b) oscillation frequency f_beat; (c) oscillation frequency f_{dual Ⅰ}, insert is oscillation frequency f_{single Ⅰ}; (d) oscillation frequency f_{dual Ⅱ}, insert is oscillation frequency f_{single Ⅱ}

Fig. 3. Response of the dual-loop OEO at different strains and temperatures. (a) Microwave spectrum of the signal generated by dual-loop OEO under different strains; (b) relationship between frequency and strain variation; (c) microwave spectrum of signals generated by dual-loop OEO at different temperatures; (d) relationship between frequency and temperature variation

Fig. 4. Stability of OEO oscillation frequency. (a) Stability of the single-loop OEO oscillation frequency; (b) stability of the dual-loop OEO oscillation frequency