Research On A High Speed Fiber Bragg Grating Demodulation System Based On USB Bus

In sense field,fiber Bragg grating (FBG) becomes a research hot spot because of its superiority.The FBG wavelength demodulation is one of the most important technology which extends the application of FBG sensor.Although some FBG demodulation products already appears in commercial market,their sampling speed is only from several Hz to several hundred Hz.These demodulation products only can demodulate static parameters and quasi-static parameters,but can't demodulate high speed dynamic parameters,like oscillation and geological monitoring.In order to adapt to dynamic measurement,and to improve the sampling and transmission speed of the demodulation system,a high speed FBG demodulation system based on USB bus and edge filters is introduced in this article.This project implements the design of interface card based on USB bus.It utilizes fully the characteristics of USB bus,for example,plug and play, hot plug and so on.The system can realize real-time acquisition,processing and displaying of data on PC.The main work of this thesis are as follows:1. The demodulation system is based on passive proportion demodulation method.Coase Wavelength Division Mulitiplexing (CWDM) based on dielectric thin films technology,whose splitting ratio is very high,is used as linear filter.The performance test about CWDM splitting ratio is done,the experiment result shows that CWDM can achieve from 1539.5nm to 1543nm wavelength measurement,and the splitting ratio of CWDM is arrived at 15dB/nm,which makes the response speed and wavelength differentiating rate of the demodulation system very high.2. Data acquisition and data transmission hardware system of the high speed FBG demodulation system based on USB bus,including conversion circuit of A/D and interface control circuit of USB,is designed according to specific requirement of the project.3. The firmware program of special interface chip CY7C68013 is designed;GPIF waveforms is compiled by GPIF Designer utility;Then bulk data transfer from data acquisition and transmission card to PC via USB interface is completed.4. Application software based on multi-threading technology is programmed under the utility of VC++ 6.0,by which data acquisition and storing could be carried out simultaneously. 5. In order to adapt to the high splitting ratio of CWDM,and to improve measurement range of the demodulation system,optical signal inspecting and demodulation circuit of the system is improved.6. Built a experiment system.Then done several experiments to research on sampling speed,transmission performance,demodulation range and wavelength differentiating rate of the demodulation system.The experiment results show that sampling speed of the system is 6.53kHz,this high speed makes the system could demodulate dynamic signals whose frequency is less than 400Hz.If the optical power in CWDM is above 4μw ,wavelength demodulation range is from 1539.5nm to 1543nm.When the optical power in CWDM is 6.2μw ,the wavelength differentiating rate arrives at 9pm in wavelength demodulation range.