Fig. 1. The principle diagram of the OWTDR technology

Fig. 2. The variation of the reflected spectra in the dense grating array

Fig. 3. The variation of the induced index change of the Bragg grating along the fiber axis

Fig. 4. The intensity distribution curves and simulated reflection spectra with different G

Fig. 5. The reflected spectra of single grating and time domain reflection signal of the whole array

Fig. 6. Schematic diagram of the AFBGs array in the temperature experiment

Fig. 7. Variation of the center wavelength in the array when AFBGs were heated