Theoretical And Experimental Analysis Of Mode Control Based On Few Mode Fibers

With the development of fiber techonology,various optical fibers that can realize special functions have been introduced,which not only expands the application areas of fibers,but also promotes the development of scientific research and production.This paper focuses on the mode control of few-mode fibers.In this paper,a mode analysis method based on high-order Jones vectors is proposed for the key problem of mode control in few-mode fibers.Then,the author proposed two applications:generation of continuous tunable OAM and generation of the first-order scalar Poincare Sphere(PS)mode.In this paper,by analogy with the traditional Jones matrix,the higher-order Jones vectors based on four linear polarized modes are proposed,and the representations of some typical high-order Jones vectors are introduced.Then we analyze the principle of the two-mode fiber polarization mode controller and propose higher-order Jones matrix.We use three matrices to describe the process that a mode passes through a polarization mode controller:rotation matrix,delay matrix and rotation matrix.The derivation of the rotation matrix is introduced in detail.Finally,we introduce the representation of the first-order mode Poincare Sphere by analogy with the representation of the polarized Poincare Sphere.It is noteworthy that the first-order modes of Poincare Sphere introduced in this paper correspond to scalar modes.Based on the proposed high-order Jones matrix analysis method,the principle of generation of continuous tunable OAM is introduced in detail in this paper.When the transmission matrix of the polarization mode controller satisfies a certain angle and phase relationship,the average OAM of the x-polarization component of the output changes with the direction of the input linear polarization.We calculate the energy of left chiral and right chiral OAM modes and their weighted averages by representing the output modes with these two chiral OAM modes.We find that the average OAM of the output mode varies with the input polarization angle according to the sin2(?)law.In this paper,the experimental results are analyzed,including experimental patterns,experimental interference patterns and experimental average OAM.The trend of experimental results are similar to that of simulation results,but the maximum average OAM of the experiment results is lower than that of the simulation results.In addition,the insertion loss of the experimental system is measured and the high-speed quality of the system is analyzed.Similarly,based on the proposed higher-order Jones matrix analysis method,the principle of the generation of the first-order mode Poincare Sphere mode is introduced in this paper.In this paper,three special circles(equator,meridian,the circle lying at 45° with equator plane)on the Poincare Sphere are selected for simulation and experiment.The experimental results are analyzed in detail,including simulation and experimental output modes,and the corresponding positions on the Poincare Sphere,the similarity between simulation modes and experimental modes.In general,the positions on the Poincare Sphere of the experimental results are consistent with that of simulation results.But the positions of some specific points are different.There are several points of experiment results deviating obviously from that of simulation results.The reasons are analyzed carefully in this paper.