Real-time optical fiber sensing system for multi-point temperature measurement based on beat frequency signals

Abstract

A fiber optic quasi-distributed temperature sensing system based on multi-longitudinal mode beat frequency signals (BFS) for multi-point monitoring is proposed. To the best of the authors’ knowledge, this is the first multiplexed fiber laser BFS sensing system without any power coupler utilized for multiple fiber laser sensors’ power division. By simple connecting multiple fiber laser sensors with different resonance wavelengths, the relatively wideband output laser from pump laser transmits into different narrowband laser resonators and corresponding BFS are generated related to different sensing resonators. In comparison with the common multi-point sensing system with couplers for power division, the multiple sensing resonators are connected in series so that a relatively low power laser can be used without affecting the performances of the sensing system. By utilizing corresponding fiber Bragg gratings (FBGs) of the fiber laser resonators for temperature sensing, a high sensitivity can be achieved without mutual interference. A five-points temperature sensing system is achieved as an example and are discussed. Measurement results demonstrated the five-points temperature sensing system’s simple structure and accurate five points temperature sensing capability without mutual interference.