TDM Interrogation of Identical Weak FBGs Network Based on Delayed Laser Pulses Differential Detection
We report a time- and wavelength multiplexing sensing network based on nearly identical ultraweak fiber Bragg gratings (FBGs). In the multiplexing scheme of the network, each wavelength channel is distinguished by time delays of the two probe laser lines, and every channel works as an optical time domain reflectometry, and the response of each FBG is represented by two delay pulses corresponding to the two laser lines. The Bragg wavelengths of the FBGs are interrogated by calculating the ratio of two peak power of returned laser lines. Compared with a conventional wavelength scanning system, the proposed system can achieve relatively high interrogation speed. A proof of concept experiment with nine FBGs, at three wavelength channels was demonstrated, and fast measurements for static strain were achieved, with the sensitivity around <inline-formula><tex-math notation="LaTeX">$ - 0.0023\;{\text {dB}}/{{\mu \varepsilon }}$</tex-math></inline-formula> and dynamic range over <inline-formula><tex-math notation="LaTeX">$2500\;{ {\mu \varepsilon }}$</tex-math></inline-formula> for three channels.