Fig. 1. The schematic diagram of the PCL-BOCDA principle. (a) The power sequence and phase sequence of the PCL. (b) Distribution map of beat spectra along the fiber. (c) Construction of the SBS gain along the fiber. (d) Gain accumulation of Stokes at a frequency of νB and the measured BGS by sweeping frequency.

Fig. 2. Simulation of temporal-spatial distribution of the acoustic field in different conditions. (a) Only phase term correlated. (b) Only amplitude term correlated.

Fig. 3. Intensity distribution in the phase chaos and original chaos schemes. (a) Acoustic field. (b) Gain variation of the Stokes wave.

Fig. 4. The BGSs after single scanning and averaging 15 times in the (a1) original scheme and (b1) PCL-BOCDA scheme. The BGSs after averaging 15 times and their Lorentz-fitted curves in the (a2) original scheme and (b2) PCL-BOCDA scheme. The BGSs, after averaging 50 times, at different positions in the 100-km system at the (c) front and (d) end of the fiber.

Fig. 5. Experimental setup of the proposed PCL-BOCDA. Chaos-LD, chaos laser diode; DFB-LD, distributed feedback-laser diode; PC, polarization controller; VOA, variable attenuator; OC, optical circulator; EOM, electro-optic modulator; MWG, microwave signal generator; PODG, programmable optical delay generator; C-EDFA, continuous-wave erbium-doped fiber amplifier; PS, polarization scrambler; ISO, isolator; SOA, semiconductor optical amplifier; P-EDFA, pulse erbium-doped fiber amplifier; BPF, optical bandpass filter; PD, photodetector; LIA, lock-in amplifier.

Fig. 6. Characteristics of the (1) original chaos and (2) PCL. (a) Optical spectrum. (b) Phase sequence. (c) Power sequence. (d) Probability density distribution of the power. (e) Autocorrelation curve of power sequence.

Fig. 7. Measured (a) BGSs and (b) BFS errors in the 1 km-long FUT in different schemes.

Fig. 8. (a) Structure of the FUT. The measured BGSs at the (b) front and (c) tail of the FUT in different schemes.