Theoretical And Technical Research About Multi-Mode Transmission Based On Mode Multiplexing

As transmission techniques develop and many high speed applications occur, the need for increase of network capacity becomes urgent. In the past few years, people took great effort on single mode fiber for the purpose of capacity growth, for example, simple modulation replaced by high-order modulation, PDM, DWDM, OFDM, etc. Recently the capacity of single mode fiber has nearly reached the Shannon limit. Letting the multiple mode take signals separately and making full use of fiber bandwidth could bring another leap to fiber communication. As a result, research on mode division multiplexing is key technology and trend for the future.In our dissertation, we performed theoretical and numerical research on mode multiplexing on step-index multi-mode fiber, based on which we analyzed some discipline and got some conclusion. At the same time, some key relevant devices are also discussed. The core study of this dissertation is the study of important parameters during mode multiplexing process, coupling coefficiency and the intensity patterns. The combination of degenerate modes is also discussed. Main results achieved are:1) Study of mode conversion and mode multiplexing By calculating multiplexing efficiency in single mode tilted fiber, we find that: in x-tilted fiber, LP11ccan only be coupled into LP01mode, similarly in y-tilted fiber, only LP11scan be coupled into LP01mode. In double-tilted fiber, LP11c can be coupled intoLP11s first through coupling into LP01and vise versa. At the same’ time, we discovered that the angle between x and y gratings can cause a big difference to coupled mode field and light intensity. TE10、TM01、HE21、LP11with different polarization directions can be generated during the mode conversion process.2) Study of mode equalized amplificationMeanwhile, study of mode equalized amplification is also made, which plays very important role in long-haul fiber transmission. MM-EDFA simulation module is set up. By adjusting the power and incidence angle, dynamic range of mode dependent gain is researched. In the end, we performed study about the influence inexact excitation, mode coupling and macro-bending caused to mode dependent gain.3) Study of mode nonlinear effectsBi-mode fiber is used to set up the simplified model of WDM-PDM-QPSK transmission system. The importance of DGD (differential group delay) and differential dispersion in the transmission process are also been calculated. Tolerance of nonlinear effects in200Gb/s system is relatively small over1200km. Mode division multiplexing technique could be a promising way to increase the fiber total capacity.