| In optical fiber transmission system, because of the advantages of the single fiber, such as the wide available spectrum and Dense Wavelength Division Multiplexing (DWDM), Time Division Multiplexing (TDM), erbium-doped optical fiber amplifier technology (EDFA) based on the single fiber has bring the revolutionary development of the current information society and greatly accelerate the system channel capacity of ascension. Following with the polarization multiplexing, optical coherent detection and optical linearly loss compensating based on digital signal processing technology, have also push the mature of high speed large capacity optical transmission system. However, in recent years, with the evolution of the communication technologies and the rapid growth of the large capacity data business in the broadband network, the need of the transmission capacity around the world is in the form of exponential growth every year. But, take the demand of the optical signal-to-noise ratio and the inherent nonlinear effect of the single mode fiber into account, Channel spacing cannot reduce indefinitely in DWDM system, the single mode fiber may reach the foreseen bandwidth exhaust. Therefore, it is important to explore a new multiplexing technology to break through the current choke point to satisfy the request of the growth network. The mode division multiplexing based on few-mode fiber come into being developed in this background. The limited and stable modes have been used to be independent channels to transfer signals for mode division multiplexing technology, which can proportional increase the system capacity. In this paper, paper work arrangement is as follows:Firstly, we study on the basic characteristic of the few-mode fiber and then analyze the mode characters in few-mode fiber by solving the derivation of Maxwell’s equations. Analysis the different patterns of light field intensity distribution and the important structural parameters of the fiber which determine the mode characters.Secondly, the mode division system model has been analyzed in details. Research the key technologies need to be solved and the key components required in the mode division multiplexing system. Compare the advantages and disadvantages of the different components. Introduce the few-mode fiber design in topic, which providing a reliable theoretical basis and technical background for proposing a new few-mode fiber in future.Thirdly, according to the coupling-mode theory, deduce the coupling-mode equation under the different mode parameters. We use the optical fiber segmental and axial offset structure to simulate the mode coupling and mode dispersion effects in few-mode fiber, and according the matrix propagation theory to setup the transmission model.Finally, as the key technology in the mode division multiplexing system, a new multi-step index few-mode fiber is designed in this paper. The new fiber can be fabricated with both negative and positive DGD and by combining fibers with opposite sign for the DGD, the total accumulated DGD can be minimized. A mode division multiplexing system with three modes in this new fiber is built by using the optical fiber segmental and axial offset structure. And the system performance is analyzed under the mode-coupling and the mode dispersion. |
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