Dynamic Strain Measurements Based on High-Speed Single-End-Access Brillouin Optical Correlation Domain Analysis

We propose and demonstrate a high-speed single-end-access Brillouin optical correlation-domain sensor based on a lock-in-amplifier (LIA)-free detection scheme. In the system, the pump and the probe are injected into the same end of a polarization-maintaining fiber with orthogonal polarization states, and a state-of-polarization-selective reflection configuration installed at the other end of the PMF is used to reflect the probe but block the pump. Therefore, the forward pump interacts with the backward probe, and this situation is similar to the process in the conventional double-end-access Brillouin optical correlation domain analysis system. In order to implement high-speed measurement, a voltage-controlled oscillator, rather than a microwave synthesizer, is used to sweep the pump-probe frequency interval rapidly. By using an LIA-free detection scheme, an ultrahigh sampling rate of up to 200 kS/s at an arbitrary position is first achieved. As a proof of concept, dynamic strains with frequencies up to 10 000 Hz are measured at an arbitrary position with a centimeter-level spatial resolution. When distributed measurements are performed with 400 points, a repetition rate of 250 Hz with a measurement accuracy of 1.5 MHz (the sampling rate is set to be 100 kS/s) is verified by measuring dynamic strains with frequencies up to 40 Hz in a fully distributed manner.