Few-mode Fiber Testing Technique Based On Spatially-and Spectrally-resolved Imaging(S~2)

Optical communication systems based on single-mode fibers are approaching their transmission capacity limit.Utilizing the new dimension in space,space-division multiplexing(SDM)based on few-mode fibers has been proposed to provide multiplicative growth in transmission capacity.As few-mode fibers find important for practical applications,the measurement of their properties becomes more and more important.In this thesis,we set up a spatially-and spectrally-resolved imaging(S~2)testing system to characterize few-mode fibers,including intermodal dispersion and mode coupling.Improvements over existing experimental configuration are proposed.The theoretical and experimental research performed include the following:1.The properties of modes in few-mode fibers was introduced and the procedure of mode solving was discussed.Based on the data of practical few-mode fibers,we solved the parameters of each mode,including the propagation constant,dispersion and modal field distribution.2.We introduced the theory of S~2 testing technique and simulated the results of S~2 few-mode fiber testing according to the data of two mode fiber.The value of intermodal dispersion was successfully extracted from the simulation result.3.We set up the S~2 few-mode fiber testing system and defined the parameters of each component.Two-mode fiber and four-mode fiber were tested and the values of intermodal dispersion were acquired,which were in good agreement with the simulation results.Through the study of data processing algorithm,we wrote program to obtain the intensity distribution of each mode in few-mode fibers and the value of mode coupling.The discrete mode coupling and distributed mode coupling made up the total mode coupling.4.The electromagnetic interference(EMI)in the S~2 few-mode fiber testing system was analyzed and measures were taken to mitigate the EMI.We compared the results between results with and without EMI and discussed the effect of EMI on the testing results.5.According to the pixel-to-pixel correlation of the images collected by the S~2 few-mode fiber testing system,we utilized the principal component analysis to do further data processing.The interference data of four-mode fiber was obtained,including the beat profile as well as respective spectra of each mode pair.