Research On Fiber Grating Demodulation System Based On F-P Filter

With the constant improvement of fiber bragg grating (FBG) manufacturing technology, FBG has become one of the most promising and the most representative optical fiber passive components. The sensing information of FBG was encoded based on wavelength, the key issue which fiber Bragg grating sensor's practical application faced is that identify the location of the grating of distributed sensor, detect the movement of Bragg wavelength, increase the multiplexing number of FBG sensor of the system, namely achieve fast and accurately demodulation. To solve these problems, the demodulation system based on F-P filter is put forward in this paper, and research its reusability, measurement accuracy.Firstly, in order to improve the system's multiplexing capability, we established a reflection spectrum's reconstruction model, and developed the fitness function of genetic algorithm for the reconstruction model, and processed the fitness function by the roulette method of genetic algorithm, and obtained the center wavelength of reconstructed reflection spectrum. Then we simulate the reflection spectrum's Gaussian model via matlab software. We found that multiplexing capacity of the system is greatly improved, even for two completely overlapped reflection spectrum, we still could distinguish their center wavelengths out, and made the error in a lower range from 1.2pm?4.3pm.Secondly, we designed the demodulation system based on F-P filter and the spectrometer; we also designed the portable demodulation system based on F-P filter and optical signal receiving circuit. We used the C8051F020 microcontroller to provide sawtooth voltage for F-P. In the portable demodulation system, the C8051F020 microcontroller is used as a data acquisition card, together with the photoelectric detector and the differential amplifier circuit constituted the optical signal receiving circuit.Finally, we used VB software to achieve the waveform display interface, during the F-P operating voltage range of 0?5v, we had data collection of a thousand times, through the voltage value that the center wavelength corresponded and the liner fitting relationship between F-P center wavelength and the signal voltage, we could get the center wavelength of measured FBG sensor. Taking FBG sensor that its strain was measured for example, compared with the result of the spectrometer, the mean difference of portable demodulation system was 3.8??. Because the demodulation system used the F-P filter, so the speed would be faster than the other demodulation systems.After the above studies, we not only improved the reusability of the demodulation system, also made the portable demodulation system based on F-P have the advantages of small size, low cost, easy to carry and fast measurement speed. But compared with the spectrometer, the precision had a big gap, we needed to be further improved.