Phase-sensitive optical time domain reflectometry (Ф-OTDR) is an effective way to detect vibrations and acoustic waves with high sensitivity, by interrogating coherent Rayleigh backscattering light in sensing fiber. In particular, fiber-optic distributed acoustic sensing (DAS) based on the Ф-OTDR with phase demodulation has been extensively studied and widely used in intrusion detection, borehole seismic acquisition, structure health monitoring, etc., in recent years, with superior advantages such as long sensing range, fast response speed, wide sensing bandwidth, low operation cost and long service lifetime. Significant advances in research and development (R&D) of Ф-OTDR have been made since 2014. In this review, we present a historical review of Ф-OTDR and then summarize the recent progress of Ф-OTDR in the Fiber Optics Research Center (FORC) at University of Electronic Science and Technology of China (UESTC), which is the first group to carry out R&D of Ф-OTDR and invent ultra-sensitive DAS (uDAS) seismometer in China which is elected as one of the ten most significant technology advances of PetroChina in 2019. It can be seen that the Ф-OTDR/DAS technology is currently under its rapid development stage and would reach its climax in the next 5 years.

In this paper, a novel birefringence measurement method through the Rayleigh backscattered lightwave within single-mode fiber is proposed, using a single chirped-pulse with arbitrary state of polarization. Numerical analysis is carried out in detail, then pulse-compression phase-sensitive optical time domain reflectometry (PC-Φ-OTDR) with polarization-diverse coherent detection is employed to verify this method. A 2 km spun single-mode fiber is tested with 8.6 cm spatial resolution, and the average birefringence of the fiber under test is measured as 0.234 rad/m, which is consistent with previous literatures about single-mode fiber. Moreover, the relationship between the measured birefringence and the spatial resolution is also studied for the first time, and the results show that spatial resolution is crucial for fiber birefringence measurement.

The effects of gamma ray (γ-ray) radiation and electron beam (e-beam) radiation on Rayleigh scattering coefficient in single-mode fiber are experimentally investigated. Utilizing an optical time domain reflectometry (OTDR), the power distribution curves of the irradiated fibers are obtained to retrieve the corresponding radiation-induced attenuation (RIA). Based on the backscattering power levels and the measured RIAs, the Rayleigh scattering coefficients can be characterized quantitatively for each fiber sample. Under the given radiation conditions, Rayleigh scattering coefficients have been changed very little while RIAs have been changed significantly. Furthermore, simulations have been implemented to verify the validity of the measured Rayleigh scattering coefficient, including the splicing points.

In this paper, a cladding-pumped erbium-ytterbium co-doped random fiber laser (EYRFL) operating at 1550nm with high power laser diode (LD) is proposed and experimentally demonstrated for the first time. The laser cavity includes a 5-m-long erbium-ytterbium co-doped fiber that serves as the gain medium, as well as a 2-km-long single-mode fiber (SMF) to provide random distributed feedback. As a result, stable 2.14W of 1550nm random lasing at 9.80W of 976nm LD pump power and a linear output with the slope efficiency as 22.7% are generated. This simple and novel random fiber laser could provide a promising way to develop high power 1.5 µm light sources.