| Driven by the rapid developments of emerging services and applications such as high-definition video,cloud computing and the internet of things,the network capacity has increased 100-fold in the past decade.It has been a huge challenge for the existing transmission technology to accommodate the explosive growth of network capacity.The related research shows that,based on Shannon theory,the capacity limit of single-mode optical fiber communication is 100 Tb/s,which has been verified by transmission experiment.Under this trend,there will be a capacity crisis for the single mode optical fiber transmission system around 2020.To break through the Shannon limit of optical fiber nonlinearity,a new multiplexing scheme?multi-dimensional multiplexing?is generally considered as an effective way.Space division multiplexing?SDM?has become a promising research direction in optical communication.Therefore,this paper focuses on the key technologies of weakly-coupled mode-division multiplexing transmission and few-mode Raman amplifier.The main innovative work is summarized as follows:?1?The characteristics of polarization maintaining few-mode fiber and the polarization/mode-group multiplexing transmission without multiple-input-multiple-output?MIMO?equalization are investigated.Based on the fiber mode theory and the physical mechanism of stress birefringence,we manufactured a Panda-type of polarization-maintaining few-mode fiber to break the degeneracies in polarization in a mode group.Polarization-and mode group-multiplexed transmission without MIMO precessing for short distance was experimentally demonstrated using this fiber.The polarization crosstalk of less than-22.0 dB and a power penalty of less than 3 dB were achieved.?2?The characteristics of polarization/space maintaining few-mode fiber and the MIMO-free polarization/mode multiplexing transmission are investigated.Combined with non-circular symmetric optical waveguide and stress birefringence,the polarization/space-maintaining few-mode fiber and multi-core/few-mode fiber are designed,respectively.The effective index difference(?35?ne ff?29?7?10-4)between adjacent modes is achieved over the entire C-band.This fiber simultaneously breaks the degeneracies in space and polarization in a mode group.6?10 Gbit/s polarization-and mode-multiplexed transmission(HG0x 0&HGy00,HG0x 1&HGy01,HG1x 0&HGy10)without MIMO equalization for short distance was experimentally demonstrated to reduce the complexity of transmission system.?3?The mode/wavelength gain equalization and noise in few-mode fiber Raman amplifiers are studied.Firstly,the Raman propagation equation is established based on the Raman scattering effect in a few-mode fiber.The mode/wavelength gain equalization is achieved using non-negative least-square method and genetic algorithm.The residual mode dependent gain and wavelength dependent gain are less than 0.334dB and 0.5 dB,respectively.We then take into account the amplified spontaneous emission?ASE?noise and Rayleigh noise in the few-mode fiber Raman amplifier.It is demonstrated that by equalizing the multiple mode signals,the mode-dependent gain of ASE noise and Rayleigh noise is also equalized,which realizes the equalization of optical signal to noise ratio?OSNR?. |
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