Fig. 1. (a) Schematic diagram of DBA-BOTDA with pump bandwidth modulation. (b) Pump bandwidth (Δν) distribution with exponential variation (blue) and proposed design with multiple bandwidths modulation (red). In (a), the position of the dotted line denotes the frequency of the optical source.

Fig. 2. Measured (squared) and fitted (solid) pump-to-pulse gain coefficient as a function of pump bandwidth.

Fig. 3. Experimental setup of DBA-BOTDA using pump modulation. DFB-LD, distributed feedback laser diode; EOM, electro-optic modulator; EDFA, erbium-doped fiber amplifier; PS, polarization scrambler; VOA, variable optical attenuator; FUT, fiber under test; AOM, acoustic-optic modulator; AOFS, acoustic-optic frequency shifter; AWG, arbitrary waveform generator; MWS, microwave source; TBPF, tunable bandpass filter; PD, photodetector; DAQ, data acquisition; OSA, optical spectrum analyzer; OSC, oscilloscope.

Fig. 4. Instantaneous frequency offset of FM applied to generate the multiple bandwidths pump modulation.

Fig. 5. (a) BGS of conventional DBA-BOTDA. (b) BGS of proposed DBA-BOTDA. (c) Comparison of Brillouin responses at 10,845 MHz. (d) Comparison of extracted BFS distributions. In (c) and (d), blue and red lines correspond to pump modulation with constant bandwidth and multiple bandwidths, respectively.

Fig. 6. STD of BFS for conventional DBA-BOTDA (blue) and multiple bandwidths pump modulation (red).

Fig. 7. (a), (b) Recorded pulse waveforms after transmission without (red) and with (blue) DBA for different pulse peak powers. (c) BFS distributions for various pulse peak powers. (d) The detail of BFS for the far end. Measurement is executed for the proposed multiple bandwidths pulse modulation.

Fig. 8. Recorded pulse waveforms after transmission without (red) and with (blue) DBA for different pulse peak powers. Conventional constant bandwidth pumping is used.

Fig. 9. (a) BFS of the hot spot as a function of temperature. (b) Extracted temperature distribution around the hot spot (∼55.8°C). Multiple bandwidths modulation is used.

Fig. 10. Brillouin traces for different combinations of LAB and LCD.