基于频域-时域变换的高精度微波光子滤波解调技术

High-Precision Microwave Photonic Filtering Interrogation Technique Based on Frequency-Time Transform

针对传统基于频域-时域变换的微波光子滤波解调技术应用于多点或准分布式传感系统时解调精度受限于射频(RF)响应测量带宽的问题,借助频谱细化算法选带快速傅里叶变换(Zoom-FFT)的思想,推导出时域细化表达式,有效解决了RF响应测量带宽、解调速率和解调精度三者之间相互制约的问题。相比于直接和补零离散傅里叶逆变换,在相同时域分辨率下,所提算法能大大降低对RF响应测量带宽的要求和频域-时域转换时的计算量,同时可有效提升解调速率。在验证性实验中,构建了包含5个光纤布拉格光栅(FBG)的多点传感系统,测试结果表明:在相同时域分辨率下,所提算法所需的计算点数减少为补零算法的1/200,运算时间降低为补零算法的10/145;对于给定的5 GHz扫频带宽,当采样点数大于1000点时即可实现亚皮秒级的时域分辨率,对应的FBG的波长解调精度为皮米量级。

The demodulation accuracy of the traditional microwave photonic filtering interrogation technique based on the frequency-time transform is limited by the radio frequency(RF)response measurement bandwidth when it is applied to multi-points or quasi-distributed sensing systems.By the idea of the zoom fast Fourier transform(Zoom-FFT)of the spectrum refinement algorithm,the expression of time-domain refinement is derived,which effectively solves the problem of mutual restriction between RF response measurement bandwidth,demodulation rate,and demodulation accuracy.Compared with the direct and zero-padding inverse discrete Fourier transforms,the proposed algorithm can greatly reduce the requirements for the RF response measurement bandwidth and the computation load of frequency-time transform under the same time-domain resolution,and the demodulation rate is effectively improved.In the verification experiment,a multi-point sensing system containing five fiber Bragg gratings(FBGs)is constructed.The test results reveal that under the same time-domain resolution,the calculated sampling points and time consumption of the proposed algorithm are reduced to 1/200 and 10/145 of the results of the zero-padding algorithm,respectively;for a given 5 GHz sweep-frequency bandwidth,the time-domain resolution in sub-picosecond level can be achieved when the number of sampling points is greater than 1000,which corresponds to the picometer-level wavelength demodulation precision of FBGs.