Finite Element Analysis And Design Of Few Mode Fiber With Low Differential Mode Delay

People’s demand for bandwidth is much greater than the increase in the bandwidth of a single mode fiber transmission system. The ever growing demand for higher data rate is rapidly exhausting the capacity available for single-mode fibers. In order to resolve the enormous pressure to the optical transport network caused by the emerging bandwidth consumption business, Space division multiplexed transmission based on few mode fiber has been proposed to promote the capacity of optical network. Space division multiplexed transmission in few mode fibers has the highest spatial density among various schemes of spatial multiplexing to increase the transmission capacity of a single fiber. So, space division multiplexing over few mode fibers is emerging as an attractive solution in the field of optical communication. It is necessary to note that excitation of high-order modes will bring differential mode delay (DMD) which is an important factor for space division multiplexing system. So, few mode fiber with low DMD is emerging as a significant issue.Two different types of few mode fiber have been considered:a graded-core with a cladding few mode fiber and a multi-step-index few mode fiber. The characteristics of mode field distribution, the effective index are analyzed based on Comsol software. Then DMD is analyzed. The structure and profiles parameters are optimized in order to achieve the lowest possible DMD. Under the condition of supporting four modes, a graded-core with a cladding few mode fiber is designed. The DMD’s absolute value of LP11, LP21, LP02is below0.015ps/m over C band. Under the condition of supporting two modes, a multi-step-index few mode fiber is designed. The DMD of LP11is0.185ps/m over C band.The designed fibers have low DMD, which is suitable for mode division multiplexing.This paper consists of three main parts:The first part is the research on the mode characters of mode. The mode characters are analyzed by solving the derivation of helmholtz equations. Then simulate the field distribution of the LP01, LP11,LP21,LP02mode in few-mode fiber. And as the most fundamental theoretical basis of space multiplexing, the orthogonality of fiber modes is derived in this paper.The second part is the research on existing models to solve space division multiplexing transmission system. We put them into two major groups according to the use of different devices:space division multiplexing based on fiber structure; space division multiplexing based on optics. Then, the paper summarizes the key attributes of few mode fiber for space division multiplexing. Finally, optical networking involving space division multiplexing is researched in the paper.The third part is research on two approaches to reduce the DMD. The first one is the design of few-mode fibers guiding few linearly polarized(LP)modes with low DMD over the C-band, suitable for space division multiplexing system. Two different types of refractive index profile have been considered:a graded-core with a cladding trench profile and a multi-step-index profile. We analyze the effect of structures and parameters on DMD. Make use of Comsol and Matlab software to investigate the propagation properties of guided modes providing highly reliable estimates on modal characteristics such as effective refractive index, field distribution. Choose suitable structure and parameter of few mode fiber. The second one is is using DMD-compensated fiber. In a DMD-compensated fiber link, fiber whose DMD is positive and fiber whose DMD is negative are spliced together...