Research On High-speed Demodulation Technique Of Fiber Bragg Grating

The fiber grating is one of the important fiber devices and has been widely used in fiber communication systems and fiber sensor technology.Soon after the invention of fiber,people tried to fabricate gratings on the fiber to create desired spectral features to be used in important applications such as wavelength division multiplex technology.Fiber Bragg grating(FBG)sensing technique is used to measure physical parameters by monitoring wavelength-shift.To achieve a fast and real-time demodulation of wavelength-shift of the FBG sensor,a high-speed process method is required.The key to the high speed demodulation of FBG sensor signal is how to extract the central wavelength of FBG reflection wave quickly.In this paper,five parts of the main content are studied: first of all,the research status about FBG high-speed demodulation technique is reviewed.secondly,the fundamental of FBG sensing is introduced.After comparing different methods of high-speed demodulation,a high-speed demodulation technique is established using tunable narrowband laser interrogation.And then,DBR tunable lasers are chosen considering their wide spectrum and few moving parts.Besides,the circuit scheme and software program are designed.The next,the control principle of wavelength is investigated,and a high-speed laser control board including FPGA,secondary power supply,current source,temperature control,serial port and filter are designed.The fast output of laser wavelength is realized.Finally,The laser is statically calibrated.On the basis of measurement,a high-speed dynamic calibration scheme is designed.The simulation and experiment are carried out.The relationship between wavelength and control current is accurately obtained.The objective of FBG high-speed demodulation system is to improve demodulation speed by optimizing scheme and improving algorithm on the basis of existing demodulation.In this paper,the high-speed demodulation system is examined through FBG fundamental and practical applications.In addition,the laser demodulation algorithm is optimized on the host computer,and the central wavelength of the fiber Bragg grating is calculated with higher speed.According to experimental results,the demodulation frequency of the laser is larger than 8 kHz.