Research On The Method Of Precise Control And Accurate Selection For Optical Mode Using Spatial Light Modulator

In high-speed optical fiber communication system Space division multiplexing (SDM) is a new fiber channel multiplexing method. Research on space division multiplexing is to solve the single mode optical fiber channel capacity shortage, multiplexing method which is used in multi core or less mode/multimode fiber by using the fiber in the space of freedom to multiplex channel capacity. Among them, Mode division multiplexing (MDM) is a method for realizing space division multiplexing, refers to the few mode/multimode, spatial pattern by using mutually orthogonal channel so as to realize the method of Space division multiplexing.Mode conversion method is the core technology of mode division multiplexing method, research on accurate control and selection method of optical model is the foundation of mode division multiplexing technology further promotion. In recent years, the optical fiber communication system in die research on key technology of multiplexing results we can conclude that, at present, for the design of die mode conversion method in reuse can be classified into two kinds, namely optical waveguide type and spatial light way. Mode conversion is the key research point in the optical fiber communication system module division multiplexing technique, this thesis proposes the conversion method of solution space optical mode control and the choice of the mode of implementation based on spatial light modulator, the method has low requirement to the device, without the need for each scheme special custom specific optical components, more easy to realize.This paper first analyzes the domestic and international research progress about the mode multiplexing, analysis the research background of the thesis. Then it introduces the basic theory of knowledge involved in the subject, including the two-dimensional Fourier transform theory, spatial frequency spectrum, transfer function and the transformation properties of Fourier lens, spatial light modulator. This paper combines the characteristics of field distribution pattern structure and optical Fourier system, proposes the use of a spatial light modulator and the simulated annealing optimization technique to model accurately control and selection method, and the simulation results are given. Finally, research on the effect of mode conversion scheme and model for execution efficiency do horizontal analysis, and put forward the local annealing, Graphic Processing Unit(GPU) for further optimization scheme, perfect simulation scheme model. The results show that the proposed method can accurately complete, efficient and fast mode conversion.The research content and innovation points of this paper:1、This paper put forward based on the Fourier optics system and spatial light modulator to achieve light patterns between free conversion of simulation program, and record in detail the scheme of MATLAB simulation process.First using laguerre-gaussian function can derive the initial model and target model field distribution of the expression. On this basis, based on Fourier transform properties of the lens is able to calculate the initial model after lens1arrived at the left side of the spatial light modulator of field distribution and the target mode after lens2to spatial light modulator on the right side of the field distribution, convenient to calculate the next loaded into the transfer function between modes on the spatial light modulator. The ideal transfer function between the mode of expression is the spatial light modulator at the right and the left side of the light field distribution division, which can know the ideal mode between the transfer function is due to the different transition model and target model, but its calculation method are the same, thus free conversion between theoretical model can be verified is feasible.2、This paper proposes a method to achieve precise control of the modes and options based on simulated annealing algorithm.As the simulation model corresponding protocol selected is loaded only change the phase of the reflection type spatial light modulator, and between the ideal model of the transfer function expression is a complex matrix carrying the amplitude and phase information, if the amplitude is simply removed information, and the remaining portion as an inter-phase transfer function model is loaded onto the spatial light modulator, will cause a lot of missing information, mode conversion between a low degree of precision. So how to adjust in order to achieve a more accurate phase information to any mode conversion is a key issue of this paper. This paper presents a computer simulation based optimization algorithm-simulated annealing algorithm for inter-phase mode only information transfer function phase change random point by point, and each time after the changes are in accordance with the simulated annealing algorithm to accept or discard the changes the probability of selecting action, this can inter-loaded into the spatial light modulator mode transfer function to achieve real-time control, real-time changes after this beam mode conversion program models, using global simulated annealing algorithm to optimize performance, can get target mode which is the closest to the ideal target mode after annealing eventually achieve accurate conversion modes. 3、the scheme to realize the effect made the multi analysis on the precise mode conversion, through local annealing, change the termination condition, joined GPU and other ways to enhance the efficiency and accuracy of the conversion program.1) with local annealing instead of global annealing:according to the ideal spot size, the calculation range is narrow for small area to the spot center starting, avoid no practical significance of regional operation consumption, transfer function phase diagram change scope also make corresponding amendments, can effectively shorten the operation time.2) annealing termination condition:termination of adaptive annealing conditions according to the model and the annealing effect do adaptive processing, when many iterations and the degree of correlation is not ascending, even if did not reach the end temperature should also be the end of the iteration, to avoid repeated calculation of no significance.3) using GPU:using special image processing core processor, the implementation of parallel processing.Through the above algorithm to optimize the processing, the accuracy of the algorithm and the computational efficiency is greatly increased, further optimization of the model of accurate control and selection scheme.