Research On Quasi-distributed FBG Multiplexing Technology Based On FMCW

Fiber Bragg grating (FBG) sensor with the unique characteristics of wavelengthcoding and ease of composing sensing network enables multi-point measurements.This paper proposed and implemented a quasi-distributed FBG multiplexing andsensing system taking advantage of FBG multiplexing technology based onFrequency Modulated Continuous Wave (FMCW) that can ensure the wider tuningran`ge and obtain higher signal to noise ratio (SNR). Meanwhile, the sensingnetwork by combining the different strings of FBG sensors can achieve thetwo-dimensional or even three-dimensional distributed sensing.This paper establishes the simulation model of quasi-distributed FBGmultiplexing technology based on FMCW by LabVIEW. When the FBGmultiplexing distance is an integer multiple of the minimum system resolution,addressing relying on the size of difference frequency is achieved; when the FBGmultiplexing distance is a non-integer multiple of the minimum system resolution,the curve rule of the magnitude of difference frequency changing with themultiplexing distance is found, and addressing relying on the amplitude value ofdifference frequency is achieved; and the theory of the FBG addressing for ultralong-range that realizes the addressing for million meters and above is perfected andvalidated in the simulation of multiplexing distance and the frequency sweep cycle.On the basis of the theory and simulation, the experimental platform ofquasi-distributed FBG multiplexing technology based on FMCW is established. Withthis experimental platform, first, we verify that addressing relying on the size ofdifference frequency can be achieved by the experiment of the FBG multiplexingdistance being an integer multiple of the minimum system resolution; then, the sizeand number of difference frequency obtained by the experiment of the FBGmultiplexing distance being a non-integer multiple of minimum system resolution isconsistent with the simulation results; additionally, the variation range of frequency sweep of the system is studied, which verifies that the size of difference frequency isproportional to the variation range of frequency sweep and the minimum distanceresolution is inversely proportional to the variation range of frequency sweep, whenthe variation range of frequency sweep of the signal generator is80MHz, theminimum distance resolution is1.25m; at last, the quasi-distributed FBG sensingsystem is studied experimentally, which realizes the FBG sensing and multiplexingtechnology based on FMCW, and the system sensitivity is0.59℃/mV, which hasreached the standard of practical engineering application.