Design And Performance Analysis On Bragg Few-mode Fiber

With the rapid development of optical fiber communication network,the capacity of the existing single mode optical fiber communication is close to the shannon limit,the problem is that the capacity of the single mode optical fiber cannot meet the today's gradually growing needs of information.Mode division multiplexing technology is a good way to solve this problem,while few mode optical fiber is the key device of mode division multiplexing system.Few mode fiber can support a certain number modes transmitting in the fiber core.Compared with the single mode fiber,a big advantage of few mode fibers is that mode division multiplexing technology can be used to increase the transmission capacity of few mode fiber.At the same time,the number of modes supported could be controlled by changing the parameters of the few mode fiber in a reasonable range,these changes can reduce mode dispersion and crosstalk between modes effectively.In addition,few mode fiber can also be applied to fiber Bragg grating and optical fiber sensing.This paper puts forward a kind of Bragg few mode fiber which is working at 1550 nm wavelength.Through the analysis of the loss sources of Bragg fiber and material properties,we select SiO2 and Si as Bragg fiber cladding materials,and determine its cladding lattice period is 4?m.Using COMSOL Multiphysics simulation tool through the finite element method(FEM)from two aspects of transmission capacity and mode loss to optimize the structure parameters of the hollow-core Bragg few mode fiber.The parameters of the Bragg fiber structure are as follows: the radius of the hollow-core is 9.3?m,the period lattice is 4?m and the thickness of first period is 4.15?m,high and low refractive index material thickness are respectively 2.9?m and 1.1?m,the periods of the cladding is 13,the Bragg fiber can be implemented large capacity and low loss transmission at 1550 nm,while there are 7 linear polarization modes can be transmitted in the fiber and the loss of six of these linear polarization modes are less than 0.1dB/m,especially the LP31 mode can be reduced to 1.8E-4dB/m,far better than the performance of current few mode fiber.Considering the imperfect of fabrication process,the errors may occur during the fabrication of the Bragg fiber are analyzed in this paper,such as the change of the shape or size of Bragg fiber core,and the deviation of the center between the core and cladding.The simulation results show that the above fabrication errors will reduce Bragg fiber transmission capacity,and increase the loss of Bragg fiber.Therefore,in the process of fabricating fiber should try to avoid the introduction of the structure of the larger error to protect the existing large capacity and low loss characteristics of Bragg fiber.The research results is of great significance to guide the fabrication process of the Bragg fiber,reducing the negative effect introducing by the fabrication errors.Besides,these results can also speed up the practical application process of the Bragg fiber in the mode division multiplexing system,further improving the optical fiber communication capacity.