The Modulation Optimization Technique Of Mode Division Multiplexing Transmission Over Few-mode Fiber

With the rapid development of large data, cloud computing and artificial intelligence technology, the high-speed and large-capacity data traffic is booming in optical fiber transmission system and broadband network. So the demand for transmission capacity has been exponentially increasing year by year. However, the development of multiplexing techniques such as time, frequency, polarization, and M-ary coding is far from enough to meet the capacity growth. The traditional system capacity will reach the Shannon limit. Therefore, Finding new multiplexing dimension and seeking a practical high-performance large-capacity mode reuse technology has become a hotspot. As a new optical multi-input and multi-output transmission scheme, the mode-multiplexing technology based on the few-mode fiber is developed under such a large background.In this paper, we studied the application characteristic of mode multiplexing in few-mode fiber from the basic theory. Then, an optical transmission experiment platform is built to realize the mode-excitation and multiplex transmission of two different modes. Finally, An iterative water injection algorithm based on power allocation and adaptive modulation optimization techniques to improve the performance of modular multiplexing system. The specific work of the paper is divided into the following three points:First, the basic properties of the SMF fiber are studied. From the Maxwell equations, the optical transmission characteristics of the SMF are deduced. The distribution of the optical field intensity in different modes is analyzed. The mode coupling in the SMF is simply introduced. Effect and inter-mode dispersion effect, which provides a theoretical basis for pattern reuse.Second, the coupling theory of mode-division-multiplexing system is analyzed, and the mode-coupled transfer matrix is modeled and simulated.Then, by studying the existing model excitation mechanism and implementation method, we designed and built a small-mode optical fiber transmission optical experiment platform based on spatial light modulator,successfully realized the transformation from base mode to LP11a and LP11b mode , As well as two different modes 2.5Gbit/s signal in the system of low-loss multiplexing / transmission / demultiplexing.Third, in this paper, we study and learn the classical power allocation and modulation optimization algorithms in traditional MIMO (Multiple Input Multiple Output) systems, and propose a modulation optimization algorithm based on Iterative Water Injection Algorithm. By comparing and validating, the optical power and modulation format of the allocation of resources has been optimized, the system performance has been improved.