Accurate estimation of modulation amplitude in Brillouin optical correlation-domain reflectometry based on Rayleigh noise spectrum

Abstract

In Brillouin optical correlation-domain reflectometry (BOCDR), spatial resolution relies on the modulation amplitude of the light. We propose a Rayleigh-based method that utilizes the spectral width of Rayleigh-induced noise to measure this amplitude without altering the setup or requiring an optical spectrum analyzer. With high frequency resolution and ease of implementation, our approach enhances the convenience and accuracy of spatial resolution evaluation in BOCDR.

Noise mechanism clarification in external-modulation Brillouin optical correlation-domain reflectometry with double-sideband modulator

“…Figure 4 schematically represents the obtained electrical spectrum, which comprises four main components: (a) the noise attributed to Rayleigh scattering, (b) the BGS signal from the correlation peak, (c) the BGS noise from the entire length of the FUT, and (d) the noise of interest discussed in this paper. While components (a) and (b) are also observed in direct-modulation BOCDR, with the generation mechanism of (a) previously elucidated, 15,17,26) components (c) and (d) are unique to the external modulation approach. The generation of (c) is straightforward, resulting from the observation of the BGS along the entire FUT due to an unmodulated residual carrier.…”

“…However, noise (a) limits Δf to half the BFS 070904-2 © 2024 The Japan Society of Applied Physics in direct-modulation BOCDR. 15,17,26) Given the relatively high intensity of Rayleigh scattering, surpassing this limit poses a challenge. In external-modulation BOCDR, it is crucial to avoid further reducing this limit, necessitating f VCO to satisfy either…”