Analysis and improvement of SNR in FBG sensing system

Abstract

The improvement of the signal to noise ratio (SNR) has significant meaning to the fiber Bragg grating (FBG) sensing system. The source of the noise as well as the signal attenuation of the FBG sensing system is analyzed. It is found that optical noise caused by the optical return loss (ORL) is the main source of noises in the system, and the coupler is the main source of attenuation of the signal. The cause of the ORL in fiber-optic elements (such as jumper cables connector and fiber end) is presented. In addition, suggestions to optimize the fiber optical sensing network in order to improve the SNR are presented. Methods to suppress noises caused by the fiber end interfaces of FBGs, including using index-matching fluid, bending fiber pigtails in the way mentioned in this paper and cleaving the slant angle of the fiber interfaces to be 8°, all contribute to the optimized SNR. Besides, the thermo-weld method is suggested to be used for both parallel and serial FBG setups to provide a low insertion loss. The results would be a useful engineering tool to design the high SNR optical sensing system.

Keywords

SNR / return noise / return loss / fiber Bragg grating / reflection of fiber end interface / bending loss

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