BOCDA sensor measurement system for 1 mm spatial resolution at distances over 200 m

Abstract

Both bit and sub-bit delays were simultaneously applied to twin pseudo random bit sequence (PRBS) codes to establish a correlation between the probe and pump in the Brillouin optical correlation domain analysis (BOCDA) system to generate the stimulated Brillouin scattering (SBS) gain. The bit delay made the BOCDA measurement system simpler and more efficient by eliminating the need for a delay line to determine the measurement position, while the sub-bit delay improve the precision of the measurement point selection. The distorted probe and pump pulses were correlated in a region smaller than one bit by adjusting the bandwidth of the RF amplifier. A dramatic improvement in the spatial resolution of the BOCDA measurement system was achieved through the combination of sub-bit delays and pulse waveform distortion. It has been demonstrated that when a 20 Gbps modulation corresponding to a 5 mm resolution in the conventional method is applied, it is possible to achieve a five-fold improvement, enabling measurements with a 1 mm resolution. This allowed experiments to be performed to achieve a measurement effect equivalent to using a modulation rate above 100 Gbps, which would otherwise incur significant costs or would be difficult to implement in hardware. The BOCDA systems using bit waveform distortion and sub-bit delay technologies was applied to sensing fibers over 200 m. This finest resolution measurement was achieved with less than half the pump power of previous methods, which used a powerful pump power of 1–2 W to achieve a resolution of a few millimeters.