Research On Multi-granularity Flexible-grid Optical Switching Technology

In recent years,with the development of information technologies such as big data,cloud computing and artificial intelligence,the current global network traffic has seen explosive growth.The communication system based on single mode fiber（SMF）has reached shannon limit due to its nonlinear effect and can not meet the demand of service development.Researchers proposed to use few mode fiber（FMF）as communication transmission medium.Using a few but stable orthogonal modes in the FMF as independent channels can not only reduce the dispersion between modes,but also greatly increase the transmission capacity.It greatly improves the transmission capacity and provides a solution to the problems faced by the current communication transmission.With the increase of network service,the burden on nodes become heavier.Both the telecommunication and data communications industries are now considering the data transfer rate towards 400 Gb/s and 1Tb/s.However,the spectrum widths occupied by 400 Gb/s and 1 Tb/s in standard modulation formats are too wide to fit into the traditional 50 GHz ITU fixed grid,overlapping at least one 50GHz grid boundary.Therefore,optical networks need a switching node that can switch flexible spectrum from input port to output port.According to the above requirements,a multi-granularity flexible-grid switching optical-node architecture is designed in this paper.Firstly,the different types of multi-granularity switching optical-node structures are discussed,and the blocking probability of networks based on multi-granularity switching optical-nodes is analyzed.One kind of granularity is mode-level,so the mode division multiplexing（MDM）technology and flexible grid multi-granularity switching structure based on mode division multiplexing are analyzed.This paper also discusses an OXC structure based on few-mode fiber gratings and few-mode fiber circulators.The loss of the structure comes mainly from crosstalk,so the crosstalk and the signal-to-crosstalk beating interference（SCBI）are analyzed.Based on the above theoretical analysis,a multi-granularity flexible grid switched optical node system is built,and the experimental test data and corresponding analysis are given.In the experiment,the photonic lanterns are used as mode division multiplexing/demultiplexing（MD-Mux/MD-Demux）for selecting modes.The wavelength division multiplexer/demultiplexer（WD-Mux/WD-Demux）and the fiber bragg gratings（FBG）are used to select wavelength channels with different grids.The value of the transmission loss（Loss）,transmission crosstalk（Crosstalk）and bit error rate（BER）of the experimental system are measured.The experimental results show that the average transmission loss of the system is-15.5 d B,the average crosstalk is-30.5 d B,and the BER is less than 10^-4.It shows that the node structure has good performance.Secondly,we demonstrate all the functions of the node including flexible-grid switching,flexible-grid service convergence,multi-granularity service convergence and performance monitoring.The optical signal transmission quality is monitored by the eye diagram test unit.The obtained eye diagram and spectrum diagram of the signal before and after switching can verify that the system has good communication quality.