Study On Wavelength Demodulation For The Multichannel Distributed FBG Sensing Network

Fiber Bragg grating has the characteristics of small dimension, light in weight, approval of integration, resisting of electromagnetic interference, being capable of realizing wavelength encoding, and so on. The performance of FBG excels the fiber sensor of light intensity encoding or phase encoding. For a great deal of FBG might be written in a fiber and be encoded by multiplexing technique, FBG sensor has the capability of distributed sensing measure and a multichannel distributed fiber Bragg grating sensing system network may have hundreds of FBG sensors. But how to measure the pm-level resonance wavelength displacement of hundreds of FBG sensors accurately, which is the key techniques to make fiber Bragg grating sensing technique utilized and industrialized.In this paper, wavelength demodulation technology of multichannel distributed FBG sensing network is researched deeply and a kind of an original and parallel demodulation system for multichannel and distributed FBG sensing network, which can demodulate accurately, stably and rapidly multichannel sensing network, is designed. The paper includes: analyzing the sensing theoretical model and sensing theory of FBG;introducing the common methods of manufacture;studying the common method of FBG wavelength demodulation and wavelength demodulation technology of multiplexing network;designing a kind of original and parallel demodulation system which is based on a tunable F-P filter for multichannel and distributed FBG sensing network;designing concretely its hardware system including light path and circuit;studying deeply four schemes to calibrate wave length of FBG,viz. calibrating wavelength of FBG according to corresponding relation of voltage-signal peak position and wavelength , calibrating wavelength according to corresponding relation of scanning voltageand wavelength of transmitted light of the F-P filter;calibrating wavelength according to the corresponding relation of center position of rectangular pulse voltage signal and wavelength and calibrating FBG center wavelength based on fiber comb filter;doing an experiment in calibrating FBG center wavelength by three methods of piecewise linear interpolation, Lagrangeinterpolation and cubic spline interpolation, the two latter methods of which have very high precision of ± 1 pm~ ± 3 pm and stability.At present, sensing technique of FBG is the hot research field both here and abroad. Wavelength demodulation technology of FBG develops remarkably. In order to exploit multichannel and distributed wavelength demodulation instrument with high precision, good stability and low cost, there are a lot of jobs to be done, which is the key to make fiber Bragg grating sensing technique utilized and industrialized.