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 PSPBOTDA 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.