| In recent years,with the rapid development of the Internet,a series of new mobile communication business being appeared,the current social demand for communication capacity is growing,the new communication technology is urgent need.At present,in the field of optical communication,multiplexing technology is mainly time division multiplexing,wavelength division multiplexing,polarization multiplexing and orthogonal frequency division multiplexing.Although these technologies greatly improve the optical communication capacity to a certain extent,but they are limited by the capacity of electromagnetic communication and wouldn't meet today's growing demand for communication capacity.To this end,a new degree of multiplexing is proposed and extensively studied-orbital angular momentum(OAM).Mode carrying orbital angular momentum can be called OAM mode.Due to the orthogonality between the OAM modes,the OAM mode can be used for mode multiplexing.OAM mode can be achieved infinity order in theory,we can use it for optical communication multiplexing and achieve a substantial increase in communication capacity.To this end,the OAM mode generation and detection techniques for optical communication system are the subjects concerned.At the same time,OAM mode generation and detection technology is also constantly updated and developed.So,it is important that using new methods to optimize and enhance the existing OAM mode generation and detection technology to achieve less power loss,higher signal to noise ratio,performance more stable OAM optical communication applications.We put forward a new technique for directly generating OAM mode in few mode fiber and an efficient technique for the detection of OAM mode using graded periodic phase grating by studying the existing generation and detection techniques of OAM modes.Specific work as follows:1.We introduce the basic characteristics of OAM beam and the research status of optical communication using OAM mode at home and abroad.We also summarize and analyze some basic techniques for the generation and detection of OAM modes at home and abroad.2.We propose a theory of generating OAM mode by using multiple linear polarization modes with small phase difference based on the existing OAM mode generation technique and the technique of generating OAM mode by using the superposition of two LP mode with p/ 2 phase difference.The corresponding formula is deduced and demonstrated,and the feasibility of the theoretical model is verified by MATLAB simulation.Finally,thetheoretical model is reconstructed in the few-mode fiber by twisting the few-mode longperiod grating,and the purity of the generated OAM mode is 99%3.We proposed a new technology for the detection of high order OAM mode by using the gradient period phase grating,which is more sensitive than the existing detection technology of OAM mode by using the gradient period amplitude grating.The simulation results show that the OAM mode will have three diffraction orders by using the gradient periodic amplitude grating,While the simulation results of the gradient phase grating has only one diffraction order.What's more,10-order OAM mode passes through the phase grating will produces a clearly visible Hermite-Gaussian pattern which is used to detect the incident OAM mode.At the same time,we carried out the corresponding experiment.The experimental results show that our new method is better than the existing method even though in the case of 10-order OAM... |
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