Research On A Novel Few Mode Fiber With Low Loss And Low Crosstalk And Optical Transmission

With the continuous and substantial growth of the global data traffic,the demand for communication capacity is also increasing.Because of nonlinear effects in optical fibers,the maximum transmission capacity of traditional single mode fiber transmission systems is gradually approaching the theoretical Shannon limit.In order to support the surge of data traffic in the network,the mode division multiplexing overcomes the current single mode fiber transmission capacity limitation,reduces the loss and crosstalk in the transmission process,and realizes long distance and high speed communication in the mode division multiplexing transmission based on the few mode fiber.In this thesis,we optimize the design of few mode fiber,proposed a novel few mode fiber,and built an experimental platform of mode division multiplexing system to test the performance of all-fiber mode multiplexer and demultiplexer based on photonic lanterns.The main innovative work is as follows:（1）A novel few mode fiber with low loss and low crosstalk is proposed,which integrates the advantages of pure silica core fiber,ring core fiber and supermode fiber,and realizes the supermode operation of four linear polarization modes(LP₀₁,LP₁₁,LP₂₁ and LP₃₁).The results show that the adoption of supermode fiber can realize the characteristics of large effective mode field area,large effective refractive index difference,low loss and low nonlinear coefficient and so on.Pure silica core can effectively reduce the intrinsic loss of the fiber.The sag refractive index is used in the fiber cladding,which achieves low bending loss compared with the equivalent single core few mode fiber,and the whole fiber core is arranged in a ring,which supports a large effective refractive index difference and single-order radial modes,which effectively reduces the mode crosstalks of the fiber.In summary,the good performance of the novel low-loss and low crosstalk six-core fiber provides a good transmission channel for the mode division multiplexing transmission of long distance few mode fiber.（2）An experimental platform of the mode division multiplexing optical transmission system is built.The system uses photonic lanterns all-fiber multiplexer and demultiplexer to test the performance of all-fiber multiplexer of photonic lantern.The changes of constellation,error vector magnitude,Q factor,bit erroe rate and spectral peak power of 28GBaud and PM-4QAM signals transmitted in an all-fiber multiplexer based on photonic lanterns are discussed.When the input optical power is given,the constellation diagrams of back to back,LP₀₁ to LP₀₁,LP_11b to LP_11band LP_11a to LP_11a are relatively tight and do not have serious distortion.With the increase of input power,EVM gradually decreases and tends to be flat,which is less affected by nonlinearity;The Q factor increases with the increase of incident optical power and tends to be flat.When the input power is larger than-26 d Bm,the Q-factor is larger than 10 d Bm.The spectral peak increases linearly with the increase of input optical power,and the nonlinear effect is small,so it has good transmission characteristics.