High-Speed DPP-BOTDA Based on Differential Group Delay of Polarization - Maintaining Fiber

Distributed optical fiber sensing technology based on Brillouin scattering is widely used to monitor the health of infrastructures such as oil and gas pipelines, smart grids, highways and bridges. However, long measurement time limits the application in many cases. In this paper, we propose a balanced detection polarization-independent Brillouin optical time domain analysis technology that reduces the measurement time from the order of minutes to the order of milliseconds. Polarization-independence is achieved by modulating the polarization states of the high-frequency and low-frequency probe light into orthogonality by using a 17.4-meter-long polarization- maintaining fiber , which is spliced at 45-degree to the pigtail of the electro-optical modulator. We use the balanced detection technology to acquire gain and loss spectra concurrently, which improves the signal-to-noise ratio of a single measurement, eliminates the effects of pump attenuation and nonlocal effects effectively, and removes polarization random noise and common mode noise. According to theoretical calculations, this method can achieve 500 Hz dynamic measurements along a sensing distance of 30 kilometers. Finally, we achieved a spatial resolution of 30 cm and 20 Hz vibration along a sensing distance of 4.1 km, which provides a practical solution for long-distance dynamic sensing.