Research On Interferometric Fiber-Optic Bragg Grating Demodulation

With the improving technic and the emergence of more and more advance research production , fiber Bragg grating(FBG) had become one of the most successful optic passive device. Nowadays, As a worldwide research hotspot ,FBG sensor has been attracting many research teams. All their efforts is to develop a kind of FBG sensor simply and effectively. In this article, with the analyzing of advantage and disadvantage of all kinds of FBG demodulation scheme and the mechanism of FBG reflection, a new scheme named correlated sampling is advanced base on so called unbalanced M-Z interferometric demodulation technique. The main aim of this scheme is to eliminate the interferometer bias which is unavoidable in the M-Z interferometric demodulation technique and make it available in the field of static measure.To do so, a piezoelectric ceramics (PZT) be used to modulate the phase of the interferometer and when the interferometer is in quardrature condition the optic signal reflected by the FBG transmit into the interferometer for demodulating. The conversion of the states need some times, but if the time of conversion is short enough , we can believe that those two kinds of state is highly correlated, and the noise of the demodulation can be got rid of. To realize and test the method mentioned-above , the control circuit is designed by CPLD (Complicated Programmable Logic Device) and other unit circuit such as bias circuit of photodetector, preamplifier , sampling –holding circuit and low-pass filter are also designed in this article. In the end of this article the precision,the scope of measure,and the sensitivity of the experiment system are given.