Brillouin Optical Correlation Domain Analysis at MHz Sampling Rates Using Lock-in-Free Orthogonally Polarized Probe Sidebands

1 An extremely high-speed Brillouin optical correlation domain analysis (BOCDA) system is demonstrated through the utilization of lock-in-free balanced detection of orthogonally-polarized probe sidebands. The proposed system achieves a sampling rate exceeding 106 Sa/s (1 MSa/s) with a centimeter-level spatial resolution, surpassing the capabilities of former correlation-domain Brillouin sensors. In test experiments, we demonstrate the polarization-independent measurement of the local Brillouin gain spectrum at a sampling rate of 2 MSa/s with a spatial resolution of 5 cm. In distributed measurements we acquire the full distribution map of Brillouin frequency along a 5.2 m standard single-mode fiber at a 10 kHz repetition rate for 144 points, equivalent to the effective sampling rate of 1.44 MSa/s. This high-speed system allows us to analyze the occurrence and propagation of the axial strain waves in a stretched optical fiber, induced by the popping noise of a powered speaker.