基于色散效应的光纤光栅高速高精度解调方法研究

利用普通单模光纤(SMF)与色散补偿光纤(DCF)分别具有正色散和负色散系数特性,实现光纤光栅阵列的高速高精度解调.系统采用全光纤结构,仅需发出单一高速光脉冲,即可根据反射光脉冲时延差同时获取各个光栅的波长与位置信息,大幅提高了光纤光栅解调速度;通过建立DCF-SMF双通道和色散差矫正模型,削弱了温度变化及色散值误差对系统解调精度的影响.实验表明,本方法解调速率可达1 MHz,解调过程受传感网络光纤及双通道温变影响较小,具有良好稳定性及高精度;5—75?C温度扰动实验中,传感网络传输光纤温变时系统解调均方差16.8 pm,DCF-SMF双通道受温度扰动时系统解调均方差为11.9 pm,恒温下系统长时间解调时均方差为6.4 pm;应力实验中,解调线性度可达0.9998,解调精度约为8.5 pm.

High speed and high precision demodulation method of fiber grating based on dispersion effect

Fiber Bragg grating sensor is widely used in military, construction, transportation, aviation and other fields due to its advantages in high sensitivity, high precision, high multiplexing and small volume. However, in some special fields such as ultrasonic flaw detection, high-speed vibration and aeroengine monitoring, the signals are rapidly changing, thus requiring high speed sampling. But the demodulation speed of traditional fiber Bragg grating demodulation techniques is hardly to satisfy the requirements, which seriously limits the application of fiber Bragg grating sensor in these fields. To solve this problem, in this paper we propose a dispersion compensation fiber(DCF)-single mode fiber(SMF) dual-channel demodulation method. Based on the SMF and the DCF with the characteristics of positive and negative dispersion coefficients in the anomalous dispersion region respectively, and combining with the optical time domain reflection technology, high speed and high precision demodulation of fiber grating can be realized. This system adopts the whole fiber structure without wavelength scanning, and the grating wavelength and position information can be obtained according to the pulse delay difference under a single optical pulse. There are three factors that quite influence the system accuracy and need to be solved: the grating space disturbance which is caused by the temperature change of the sensor network fiber; the dual-channel length disturbance caused by the DCF-SMF dual-channel temperature change; the dispersion disturbance caused by the inaccurate dispersion difference of the DCF-SMF. By constructing the DCF-SMF dual-channel, adopting the reference grating and introducing the dispersion difference correction model, these influence factors are solved. The case of temperature disturbance elimination is tested by the 5-75℃ temperature experiments. And the results are as follows: when the temperature of the sensor network fiber changes, the standard deviation of this dual-channel demodulation system is 16.8 pm, while only using the DCF single-channel to form the demodulation system, the standard deviation is 3614 pm. And when the DCF-SMF dual-channel is disturbed by temperature, the standard deviation is 11.9 pm. For a long time demodulation under constant temperature, the standard deviation of this system is 6.4 pm. Thus the influences of the sensor network fiber temperature change and the dual-channel temperature change on the system demodulation accuracy are effectively reduced. The feasibility and accuracy of this method are also verified by the strain experiment. Experimental results show that the highest demodulation rate of this method is 1 MHz, while the linearity can be up to 0.9998, and the accuracy is about 8.5 pm. So the system with the dispersion difference correction model has a high precision. Therefore, this novel demodulation method has advantages of high speed and high precision, good stability and large dynamic range, and it is very applicable to quasi-distributed fiber Bragg grating sensing system.