基于空间干涉成像的七芯光纤芯间群延时差测量

Inter-core Differential Group Delay Measurement of Seven Core FiberBased on Spatial Interference Imaging

提出了基于空间干涉成像的多芯光纤芯间群延时差的测量方法。用CCD记录不同波长下的空间干涉图,利用干涉图中所有像素点的干涉信息构建三维空间干涉光谱,并通过光谱分析可得芯间群延时差。搭建了基于空间干涉成像的多芯光纤芯间群延时差测量实验装置,测量了沟槽辅助型弱耦合七芯光纤芯间群延时差。该方法的测量装置简单,测量精度可达10~(-4)ps/m,不仅可测量两芯间的延时差还可同时测量任意相邻的多个芯的芯间延时差。测量时使用三维调节台加CCD的组合使得待测纤芯的选择激发更加简单。此外,还研究了多芯光纤芯间延时差的弯曲依赖性,结果显示,随着弯曲半径的增大,多芯光纤芯间群延时差不断减小。

Using different cores of a Multi-Core Fiber(MCF)as independent parallel spatial paths to transmit different information simultaneously offers cost,space and energy savings.The inter-core Differential Group Delay(DGD)is a key parameter of the multi-core fibers,and its accurate measurement is of great importance.In the multi-core fibers,errors in the preparation process or bending of the fiber caused by external forces can result in inter-core differential group delay in various cores.When light is transmitted in a multi-core fiber,the outgoing light from different cores will interfere with coherent superposition in space due to different group delays.According to this character,this paper proposes a spatial interferometric imaging-based method for measuring the inter-core differential group delay of multi-core fibers,and building an experimental measurement device.At the input of the multi-core fiber,the laser is shifted and injected by adjusting the three-dimensional adjustment table to excite different cores,and the output light of the excited cores will interfere in space.The computer controls the CCD to scan the wavelength of the input light in one dimension and records the spatial interferogram at different wavelengths in real time.The interferometric information of all pixels in the interferogram is used to construct a three-dimensional spatial interferometric spectrum,and the inter-core differential group delay of the multi-core fiber can be obtained by spectral analysis of the interferometric spectrum.The inter-core differential group delay of the weakly linked trench assisted seven core fiber is measured in this paper.We measured the inter-core differential group delay between the central and six outer cores respectively.When two cores are excited at the same time,a peak will appear at the delay difference between the two cores through the Fourier transform of the interference information.Subtracting the-inter core differential group delay between the central core and two adjacent outer cores yields the inter-core differential group delay between the two outer cores,which is only 10-4 dissimilar from the actually measured inter-core differential group delay of two adjacent outer cores.When three spikes are excited simultaneously,two adjacent spikes will interfere with each other.By Fourier transforming the interference information obtained by CCD containing the differential group delay,a plot of differential group delay versus interference intensity containing three spikes can be constructed.The values of the horizontal coordinates of the three spikes in the plot are the differential group delay between the three cores,and they correspond to the measurement results when only any two of the three cores are excited,respectively.Simultaneously,the bending dependence of the inter-core DGD of the multi-core iber is measured and researched.The inter-core differential group delay was measured for three bending radii of 5 mm,75 mm,and 110 mm.The results reveal that the inter-core DGD decreases as the bending radius increases,which is consistent with the theory.This method′s measurement instrument is simple,and the measuring precision can reach 10-4.It can measure the delay difference not only between two cores,but also between any nearby cores at the same time.In addition,the outgoing light from the end face of the multi-core fiber to be measured is focused through the objective lens and connected to the CCD and adjust the three-dimensional adjustment table,the excitation state of the cores in the multi-core fiber and the degree of coupling of optical energy can be observed on the CCD,which makes the selection and excitation of the cores to be measured easier.The spatial interference imaging approach suggested in this study has the characteristics of simple,fast,high accuracy.It can be widely used to measure inter-core DGD of the multi-core fiber in SDM systems,MWP signal processing and other application circumstances.