Fig. 1. Phase extraction in coherent ϕ-OTDR based on the single frequency light. (a) Process of phase extraction; (b) phase change of one pulse under a small perturbation; (c) phase change of one pulse under a large perturbation

Fig. 2. Analysis of two frequency lights. (a) Pulse train with the original probe light and the auxiliary light; (b) distribution of differential phase under ideal state; (c)(d) distribution of differential phase under wrong unwrapping condition; (e) distribution of differential phase under correct unwrapping condition

Fig. 3. Phase extraction in coherent ϕ-OTDR with auxiliary light. (a) New process of phase extraction; (b) phase change of one pulse under a large perturbation

Fig. 4. Experimental setup and its schematic for coherent ϕ-OTDR with/without the auxiliary light

Fig. 5. Superposition of retrieved results when the amplitude of driving signal is 2.5 V in ϕ-OTDR only using the original probe light. (a) Intensity of Rayleigh scattering signal; (b) phase change

Fig. 6. Superposition of retrieved results when the amplitude of driving signal is 5.0 V in ϕ-OTDR only using the original probe light. (a) Intensity of Rayleigh scattering signal; (b) phase change

Fig. 7. Retrieved results from the original probe light when auxiliary probe light is used in ϕ-OTDR. (a) Superposition of phase changes; (b) phase signal

Fig. 8. Maximum phase jump values under different parameters. (a) Frequency; (b) amplitude