Fig. 1. Schematic diagrams of experimental system. (a) Dynamic range extended distributed optical-fiber sensing experimental device; (b) Schematic diagram of LFM sideband modulation pulse

Fig. 2. Discrete theoretical model of LFM pulse DAS

Fig. 3. Coherent time domain signal and envelope simulation results. (a) 40 MHz frequency-modulated bandwidth overall display; (b) 40 MHz frequency-modulated bandwidth local display; (c) 200 MHz frequency-modulated bandwidth overall display; (d) 200 MHz frequency-modulated bandwidth local display,(b) and (d) correspond to dotted ellipse parts in (a) and (c), respectively

Fig. 4. Experimental results of coherent time domain signals and envelopes under different LFM bandwidths. (a) 40 MHz; (b) 120 MHz; (c) 200 MHz; (d) 400 MHz

Fig. 5. Experimental results with frequency-modulated bandwidth of 40 MHz

Fig. 6. Experimental results with frequency-modulated bandwidth of 200 MHz