Research Of Optical Fiber Modes Separation Based On Spatial Phase Modulation

With the development of multiplexing technology,the transmission capacity of single-mode fiber is approaching the Shannon limit.Multi-mode fiber is increasing used in short distance communication networks with low cost and high coupling.Optical fiber mode can be regarded as a new dimension,and each mode is an independent channel for loading signal.When a variety of optical fiber modes are transmited and received at the same time,the system transmission capacity and spectrum efficiency are improved.We call it mode division multiplexing technology.This thesis starts from the demand of optical fiber mode demultiplexing.We theoretically analyzed the optical fiber mode spatial separation based on optical phase modulation,and used the G-S algorithm and tilted phase factor method to calculate the required phase modulation information.By the way of simulation and experiment,we verified the feasibility of optical fiber mode spatial separation.The main contents of the thesis include the following aspects:1.The physical properties of optical fiber mode was analyzed theoretically,and the energy spatial distribution of different optical modes are studied.Based on the theory of scalar diffraction,we studied the propagation of light in free space.Then,we established an optical fiber mode spatial separation calculation model based on optical phase modulation.2.We introduced the basic principle of phase plate design based on G-S algorithm.Firstly,the modulation phase information and phase modulation results ofLP₀₁andLP₁₁were obtained by using G-S algorithm.And then we combined the two modulation phase information in a certain way.When theLP₀₁andLP₁₁were modulated by the new optical phase,the optical fiber mode spatial seperation was realized.Besides,we discussed how the spatial separation result influenced by the optical fiber mode separation position and the different phase combination methods,and we analyzed the energy loss and inter-mode crosstalk.3.We introduced the basic principle of tilted phase factor method.This method is much simpler and easier to understand.We studied two kind of factors?separation position and different phase combination?how to influence the numerical simulation result.The spatial separation results of optical fiber modes based on two different methods were compared and analyzed.4.The experimental platform was established,and the Fresnel diffraction phenomenon of lens occurred in the experimental process was analyzed theoretically.TheLP₀₁andLP₁₁separated relatively in space based on the G-S algorithm and the tilted phase factor was realized.The experimental results and numerical simulation results of optical mode spatial separation were compared and analyzed.