Coding Gain Analysis of Coded Brillouin Optical Time-Domain Reflectometry

Coding technique is a widely adopted approach to improve single-to-noise ratio in systems based on the principle of optical time-domain reflectometry. The performance enhancement is characterized by the coding gain which is directly associated to the coding length of the optical pulse train. In this work, we find out that the coding gain in coded Brillouin optical time-domain reflectrometry (BOTDR) based on spontaneous Brillouin scattering is very different from the conventional definition, and it needs to be corrected due to the spectral measurement nature of the coded BOTDR. The physical principle of this phenomenon is different from that in coded Brillouin optical time-domain analysis which is based on stimulated Brillouin scattering. Moreover, we investigate in details the coding gain dependence on the duty cycle of the pulse train. We conduct experiments using both the Simplex code and Golay code to confirm our analysis and conclusions, indicating that the performance enhancement of the coded BOTDR should be adjusted from the conventional expectation.