Polarization independent fast BOTDA based on pump frequency modulation and cyclic coding

We propose and experimentally demonstrate a scheme of polarization independent fast Brillouin optical time domain analysis (F-BOTDA) based on pump frequency modulation and cyclic coding. The Brillouin gain spectrum (BGS) is reconstructed by fast scanning frequency of the pump using an arbitrary waveform generator (AWG). To realize long range distributed dynamic strain sensing, polarization diversity technique and cyclic coding are employed to eliminate polarization fading and enhance the signal-to-noise ratio (SNR). Based on this configuration, the need of trace averaging is avoided, sensing speed of 440 Hz is achieved over ~2 km single mode fiber with 50 scanning frequencies and a spatial resolution of 1.5 m. Vibration events up to 40 Hz are successfully identified.