Investigations On The Fundamental Theory And Key Techniques Of Multicore Fiber Based Spatial Division Multiplexing Optical Transmission System

With the popularization of Internet services like cloud computing,HD video and virtual reality,current optical fiber communication system is suffering from severe constraint of capacity sharp increasment.The space division multiplexing(SDM),which multiplexes the information in the signal spatial degree,is able to increase the transmission capacity greatly.Among the SDM techniques,the multicore fiber(MCF)based SDM transmission system has broken the record of current transmission.It shows great potentials in various transmission scenarios from long-haul,access,fronthaul and data center due to its parallel transmission and flexible deployment.Thus,it is viewed as one of the most promising techniques to upgrade current optical transmission system in the near future.Although the investigations of the MCF based long haul transmission experiments have developed very fast,the MCF used for short reach interconnection is still few.MCF has the merits of not only increasing the capacity,but also providing more flexibities and services for either access network or mobile fronthaul systems.In term of theoretical investigation,few reports can be found for the wavelength dependent intercore crosstalk and the effect of crosstalk on the MCF nonlinear transmission.In this thesis,in terms of fundamental theory,we investigate the relationship between the wavelength dependent intercore crosstalk and MCF structure,due to the fact of enhanced crosstalk at the longer operation wavelength.Then we propose a solution to suppress the wavelength sevsitivity of crosstalk.Considering the MCF based long-haul transmission,we establish the model of MCF nonlinear transmission,and explore the impacts of the crosstalk on the signals during the transmission.In the aspect of key techniques,we design,fabricate and characterize several kinds of MCFs.After breaking through the technique bottelneck,we fabricate the MCF and the fan-in/fan-out devices with high quality.Based on these two key components,we build up the MCF based space-wavelength division multiplexing system with ultra-large capacity.We also investigate the applications of MCF in the access network and mobile fronthaul systems.The main research outputs are summarized as follows:Firstly,based on the coupled mode theory and coupled power theory,we investigate the fundamental principle of intercore crosstalk.We analyze the wavelength dependent intercore crosstalk and propose a method to suppress its wavelength sensitivity with the help of core pitch reduction.It is experimentally confirmed that the crosstalk wavelength sensitivity of MCF with 35?m core pitch is 0.05dB/nm smaller than that of MCF with 42?m core pitch.Secondly,we establish the MCF's nonlinear transmission model based on the intercore crosstalk's statistical properties.We demonstrate that the crosstalk can be treated as an additive white Gaussian noise during long-haul MCF transmission.We relate this with the MCF design and propose a method which can not only increase the effective area for the purpose of mitigating nonlinear transmission impairment,but also avoid degrading the crosstalk.Eventually it can reach a balance between them for optimal system performance.Thirdly,we illustrate the MCF structure design and investigate the structural parameters' impacts on the optical property.In addition to using COMSOL commercial software,we also develop analytical calculation method to investigate the structural parameters' impacts on the crosstalk to reduce the computation complexity.The fabricated MCF's attenuation is less than 0.25 dB/km,meanwhile the crosstalk is lower than-40 dB/100km.Fourthly,by using chemical etching fiber bundles and fiber cold-forming connection methods,we prepare the fiber bundles with the same layout as MCF,and align them with individual MCF cores under free space manner.Using this method,we successfully fabricate fan-in/fan-out device with low crosstalk(less than-50 dB),low insertion loss(lessthan 1 dB per core)and high reflection loss(more than 50 dB),which approaches the world class level.Based on these key components,we successfully demonstrate the SDM-WDM transmission system with a capacity of 33.6 Tb/s and a SE of 44.8 bit/s/Hz,and experimentally verify the super performance of the MCF and fan-in/fan-out devices.Fifthly,we demonstate the SDM-WDM optical access network.We further explore the MCF's great potentials in capacity enhancement,providing various services in a flexible way.Via the MCF's parallel channels in the spatial dimension,we experimentally demonstrate the bidirectional optical access network with low cost,large capacity(300 Gb/s),and multiple users(60 ONUs),together with mobile backhaul services.Sixthly,we investigate the MCF's application in the mobile fronthaul system and demonstrate the 2 × 2 MIMO wireless signal bidirectional transmission over 20 km MCF.We investigate the tolerance of MCF crosstalk and design a 64-core fiber whose intercore crosstalk is below-10 dB/20km,for the purpose of implementation of 5G key technique--massive MIMO,indicating the great potentials of MCF in 5G mobile communication system.Optical fiber is a typical artificial channel,especially for the MCF employed in the SDM transmission system.Therefore,the identification of channel distortion source,the optimization of channels and the study of the MCF's potentials in enhancing the capacity are the key scientific problems.We carry out great theoretical investigations of the MCF design and structure optimization,the crosstalk's impacts on the signal and MCF nonlinear transmission model.With the self-developed MCF and fan-in/fan-out device as enabler,we can successfully realize the MCF based ultra-large space-wavelength multiplexing optical transmission system,MCF based optical access network with large capacity and mobile fronthaul applications,leading to the great advantage of MCF in terms of large capacity and flexible implementation.