Research On A New Directional Coupled Mode Division Multiplexer

The demand for all kinds of communication services is increasing rapidly with the development of society,which leads to the severe nonlinear tolerance challenge of the single-mode optical fiber communication system.Mode division multiplexing based on few-mode fiber can make the capacity of the transmission system multiply according to the number of modes,thus it has become the frontier of optical communications.As the core component of the mode division multiplexing transmission system based on few-mode fiber,mode division multiplexer has received extensive attention and research.Aiming at the problems of various multiplexers,such as high insertion loss,large crosstalk,high nonlinearity,narrow working band,large differential mode group delay,difficult interconnection with fiber,complex structure and difficult integration,two new mode division multiplexers are proposed in this paper.The main innovative work is as follows:Firstly,a mode division multiplexer with large effective area and graded-index refractive is proposed.The performance of mode division multiplexer is studied by beam propagation method and full vector finite element method.The research shows that the multiplexer achieves graded index distribution,large effective mode area,low nonlinearity coefficient,high coupling efficiency and wide operation band 6 mode multiplexing/demultiplexing operation.The coupling efficiency of the multiplexer is better than that of-0.449 dB and presents a flat characteristic from 1450 nm to 1650 nm.The multiplexer scheme is an effective method to realize low nonlinear coefficient,high coupling efficiency and wide working band.Secondly,a graded-index mode division multiplexer with low loss and low crosstalk is proposed.The transmission channel uses pure silicon core with large effective area to achieve low attenuation,which can effectively reduce the fusion loss with pure silicon core few-mode fiber.The low differential mode group delay is realized by the graded-index distribution.And making the effective index difference of the core and cladding greater than 0.5x10~-33 to guarantee low crosstalk between modes.The performance of the transmission channel is studied and mode division multiplexer structure is determined by beam propagation method and the full vector finite element method.The results show that the coupling efficiency of the multiplexer is better than that of-0.479 dB and the extinction ratio is higher than 31.2 dB from 1400 nm to 1700 nm.In the C band,the average coupling efficiency of all mode channels of the multiplexer is better than that of-0.140 dB and show flatness.The multiplexer scheme is an effective method to achieve low crosstalk,low loss and low fusion loss,high coupling efficiency,high extinction ratio and wide operation band.