Research On Mode Excitation And Testing Technique In Mode Division Multiplexing Optical Communications

In the background of information and communication technology rapid development, global data traffic burst growth, single-mode optical fiber communication system capacity has become increasingly close to its nonlinear Shannon limit. The optical fiber communication system capacity can be doubled by mode division multiplexing technology through the mining mode of this new degree of freedom, is considered as able to break through the traditional single-mode optical fiber communication system transmission capacity bottlenecks effective technical means. At present, the mode division multiplexing system based on the few-mode fiber has become a global research hot spot. As transmission medium, mode excitation and testing the mode characteristics for few-mode fibers are also becoming increasingly important. The method of model excitation based on the free-space optical path has the advantages of high flexibility, accurate transformation and simple experimental device. Spatially and Spectrally resolved imaging method, S~2 method, based on spatial and spectral resolution measurement of the principle of optical fiber measurement method to measure the characteristics of fiber measuring, is the recently preferred method to analyze modal properties of fibers. In this paper, an experimental measurement system based on the S~2 method is built, and the experimental results show that the mode dispersion and mode coupling of the few mode fiber and the effective refractive index difference of the few-mode polarization maintaining fiber are obtained respectively. The main attributions and innovations of this dissertation are as the following three aspects:1. Methods of mode excitation based on the free-space optical pathThis paper analyzes the few-mode fiber and the propagating mode characteristics commonly used in the mode division multiplexing transmission system, and explains the solving process of the mode. We set up the testing system based on the free-space optical path and realise the excitation of high-order modes in the few-mode fiber.2. Measurement of the characteristics for the few mode fiber based on S~2 imaging methodWe set up the few-mode fiber testing system based on S~2 method to measure the two-mode fiber and four-mode fiber respectively and obtain the data of mode group delay difference of few-mode fibers. We process data to obtain the intensity distribution and phase image of each mode in few-mode fibers and the characteristic of mode coupling.3. Measurement of the characteristics for the few mode polarization maintaining fiber based on S~2 imaging method for the first timeWe set up the few-mode polarization maintaining fiber testing system based on S~2 method for the first time. We measure the Panda style few-mode polarization maintaining fibers and obtain the data of group delay difference of each mode propagating through fibers. We process data to obtain the intensity distribution and phase image of modes propagating through the few-mode polarization maintaining fiber, we also obtain the effective refractive index difference.