Subdivision of Brillouin gain spectrum to improve the spatial resolution of a BOTDA system

A pulse subdivision analysis method was developed to improve the spatial resolution of a conventional long pump pulse Brillouin optical time domain analysis (BOTDA) system. An exclusive photodetector was used to obtain the accurate energy distribution along the long pulse, based on which the long pulse was subdivided into several sub-pulses with certain energy weights. With these energy weights, the Brillouin spectrum generated by the long pulse was subdivided into equal numbers of sub-spectra. Each sub-spectrum could provide detailed sensing information about a fiber sub-segment related to a sub-pulse. Thus, the actual spatial resolution of the BOTDA system was determined by the sub-pulse instead of the long pulse. As a result, spatial resolution was increased by several times, depending on the subdivision multiples. The method was theoretically simulated and experimentally demonstrated. For experimental demonstration, the recognization capability of the melting point of two different fiber sections and the discrete strain distribution on a sensing fiber were respectively tested. For melting point recognization, thanks to five-multiple subdivision, a 1 m spatial resolution over 31 km sensing fiber was realized using a 50 ns pump pulse. For the strain sensing test, ten-multiple subdivision was performed to distinguish two 0.5 m stretched fiber sections with a 0.2 m interval using a 20 ns pump pulse. The spatial resolution is 0.2 m, which is a ten times' improvement compared with that before subdivision analysis. Due to its simplicity and cost-effectiveness, the method is believed to have extensive application prospects in distributed fiber sensing fields.