Impact of optical noises on unipolar-coded Brillouin optical time-domain analyzers

Abstract

Noise models for both single-pulse and coded Brillouin optical time-domain analyzers (BOTDA) are established to quantify the actual signal-to-noise ratio (SNR) enhancement provided by pulse coding at any fiber position and in any operating condition. Simulation and experimental results show that the polarization noise and spontaneous Brillouin scattering (SpBS) to signal beating noise could highly penalize the performance of coded-BOTDA, depending on the code type and the interrogated fiber position. The models also serve as a useful tool to optimize the SNR improvement by trading off the accumulated Brillouin gain and optical noises.

High-performance distributed Brillouin sensing: from fundamentals to latest developments

“…However, this approach might be considered suboptimal, as lowering the probe power leads to a reduction in SNR, which contradicts the primary objective of utilizing pulse coding. On the other hand, the performance of coded-BOTDA faces additional limitations beyond those previously mentioned, resulting from the increase of Brillouin-gain-dependent noises [32,33]. While these noises are typically negligible in longrange single-pulse BOTDA, they can become relevant, even dominant, in unipolar coded-BOTDA due to the substantial cumulated Brillouin gain.…”

“…In a single-pulse BOTDA system, photo-detection noise and signal-ASE beating noise typically dominate [12]. However, in coded-BOTDA sensors, polarization noise and signal-SpBS noise become dominant [32,33]. This shift occurs because the use of several coded pulses increases the cumulated Brillouin gain, making the system more sensitive to polarization fluctuations.…”

Analytical Signal-to-Noise Ratio Model on Frequency-Scanned Brillouin Optical Time-Domain Reflectometry

“…The trivial latter can practically be removed in actual measurement by subtracting the measured data by the mean value of its direct current part. On the other hand, Table I indicates that the power detection process makes the measurement affected by three types of noises: I) the polarization noise, i.e., the randomly varying polarization fading effect resulting from the beating between the OLO light and the PSc-induced randomly polarized SpBS light (the mechanism is similar to the polarization noise in the BOTDA sensors based on PSc [18]), II) the signal-amplified detection noise, and III) the squared detection noise, with STDs denoted by Eqs. ( 6), ( 8) and (10), respectively.…”

“…This highlights the significance on the establishment of SNR models for both techniques. For standard BOTDA a mature SNR model has been established [17], which has even been recently extended for advanced BOTDA techniques [18], [19]; however, till now the models dealing with the SNR of FS-BOTDR present in literature remain incomplete. They are originally established to analyze a specific technical detail such as the impact of number of wavelength used [20]- [22] or the pulse extinction ratio [23], [24], but have not yet precisely taken into account either the signal-amplified detection noise originating from the envelope detection process, or the polarization fading noise caused by the use of polarization scrambler (PSc).…”