Effect of chaotic time delay signature on Brillouin gain spectrum in the slope-assisted chaotic BOCDA.

In the chaotic Brillouin optical correlation domain analysis (CBOCDA) system, the broadband chaotic laser naturally widens the Brillouin gain spectrum (BGS), which provides an enhanced range for dynamic strain measurement via slope-assisted technology. However, inherent off-peak amplification at the time delay signature (TDS) position results in a deteriorated gain envelope. The mechanism behind the sub-peak of chaotic BGS is first analyzed and the negative correlated relationship between the value of main-sub-peak ratio (MSPR) and magnitude of TDS has been experimentally demonstrated. The limitation of sub-peak on the dynamic range is investigated, where the range is not greater than 400 µε at MSPR < 0 dB, and 600 µε at MSPR > 0 dB. Meanwhile, by eliminating the TDS, the BGS without sub-peak is obtained and a dynamic strain of 1200 µε is successfully identified. Moreover, the application of optimized chaotic BGS in a multi-slope assisted system to realize the enlargement of dynamic strain range is also discussed.