Fig. 1. Schematic diagram of TGD-OFDR system

Fig. 2. Beat signals received by BPD and equivalent reference signal

Fig. 3. Flow chart of PID algorithm

Fig. 4. Pre-distortion system and calculation process

Fig. 5. Results of predistortion experiments of DFB laser. (a) Original time-frequency curve (10 GHz sweep frequency range within 25 μs); (b) time-frequency curve after pre-distortion; (c) residual error curves before and after pre-distortion

Fig. 6. Schematic diagram of TGD-OFDR system based on internally modulated DFB

Fig. 7. Effect of different sweep linearities on spatial resolution of correlation operation. (a) Time-frequency curves of sweep signals with different linearity; (b) spatial resolution corresponding to sweep signals with different linearity

Fig. 8. Influence of spectrum correlation on demodulation results

Fig. 9. Experimental results of TGD-OFDR system based on DFB laser. (a) Rayleigh intensity curve over 74 km FUT; (b) spatial resolution at near end of FUT; (c) spatial resolution at far end of FUT