A Hybrid Single-End-Access BOTDA and COTDR Sensing System Using Heterodyne Detection

A hybrid single-end-access BOTDA and COTDR sensing system is proposed and demonstrated experimentally. In our configuration, the heterodyne detection techniques are applied to improve the SNR of the single-end-access BOTDA. Without adding extra instruments, our system could easily switch between BOTDA and COTDR modes by changing the intermediate frequency of the detected heterodyne signals. We performed the distributed temperature measurement when the sensor works as BOTDA, and a 24 km sensing range with 5m resolution together with a temperature uncertainty of 1.0°C are achieved. When it operates as COTDR, a peak dynamic range of 12 dB is obtained by using 50 ns probe pulse and the loss coefficient of fiber under test (FUT) is accurately measured. The hybrid system not only offers an excellent solution for the requisite of two-end-access in conventional BOTDA and obtains a longer measurement range than that of the existed one-end BOTDA, but also can be used to measure the attenuation of a fiber link or locate the discrete defects on optical fiber systems.