光纤光栅马赫-曾德干涉仪条纹信号的傅里叶分析

Fourier Analyses for Fringe Signals of Fiber Grating Based on Mach-Zehnder Interferometer

基于长周期光纤光栅马赫-曾德干涉仪的频分复用技术是实现光纤多参量传感的重要途径.研究了频分复用中复合条纹信号的傅里叶处理方法,分析了傅里叶频谱中和频与差频信号的幅值与单个干涉条纹信号的关系,提出了抑制和频与差频信号的有效方法,即改变光栅结构参量适当降低中心波长处的条纹对比度以提高频谱信号的信噪比,增加特征频谱滤波的有效性.结果表明:经过优化调整的傅里叶频谱信噪比可以提高至原来的2倍以上;对比频谱调整后恢复相位的余弦曲线与原条纹信号发现,频谱信噪比提高的同时保留了反映各单个原条纹特征的足够相位信息.该光谱优化方法可为基于光纤光栅马赫-曾德干涉仪和频分复用的光纤多参量传感技术提供理论与技术指导.

Frequency division multiplexing based on long-period fiber grating Mach-Zehnder Interferometer（MZI）is an important way to implement fiber multiparameter sensing.The Fourier method for the composite fringes in freqency division multiplexing was investigated,with emphasis on the relationship between the value of different frequency and sum frequency in the Fourier frequency spectra and the structral parameters of the single grating in fiber MZI and then,an effect method for depressing the different and sum frequencies was proposed.The results show that the singal to noice ratio can be effectively improved by properly selecting the grating structual parameters to reduce the fringe contrast at central wavelength to a certain extend,which improves the effectiveness of filtering in freqency domain.After adjustment and optimization,the singal noice ratio of the frequency spectrum is doubled comparing to the original value.A comparison between the cosine curves of recovered phases and the orignal fringes confirms that the tuned frequency spectra remain sufficient phase information that characterize the original fringes.The spectrum optimization method developed in this paper can provide theoretical and technical guidance for multiparameter sensing based on fiber grating MZI and freqency division multiplexing.