Phase Shift Pulse Brillouin Optical Time Domain Analysis (PSP-BOTDA) employing Dual Golay Codes

This paper proposes and analyzes the employment of Dual Golay Codes in the PSP-BOTDA system for the application of fiber optics distributed strain sensor. In the previous research, Golay codes generated through the complementary sequences method were used in PSP-BOTDA in order to improve its signal to noise ratio (SNR). There were four optical signals involved in order to analyze the typical Golay code based PSP-BOTDA system. In this research, the employment of Dual Golay Codes is introduced for the improvement of the Brillouin optical power amplification detection. A typical PSP-BOTDA system consists of two types of optical pump called 0-pump and π-pump; each pump produces positive and negative Brillouin gain respectively. Since Golay codes generated in PSP-BOTDA system are in bipolar forms (+1 and -1), these codes can be applied to the 0-pump which corresponds to +1 and π-pump that corresponds to -1 code. Compared to the previous research results, as the numbers of optical signal used for the Dual Golay Code PSP-BOTDA are doubled to eight, the Brillouin optical power detected and correlated is also doubled. The unique feature of Dual Golay Code PSP-BOTDA is that the Brillouin optical power detected at the stressed part of the optical fiber is increased and the signal-to-noise ratio increases considerably compared to the previous ones because the total length of Golay codes used in a given time period is increased. Furthermore, the side-lobes from the correlation process were completely cancelled, producing a noiseless correlated code. For this paper, the research was carried out by evaluating the power detection at the stressed fiber for 2ⁿ × 2^m Dual Golay code length.